oth and 1st Generation Organometallic Nanostars from Ferrocenylamine and Ferrocenylaniline by Cynthia L. Perrine Submitted in Partial Fulfillment ofthe Requirements for the Degree of Master ofScience in the Chemistry Program YOUNGSTOWN STATE UNIVERSITY August, 2004 oth and 1st Generation Organometallic Nanostars from Ferrocenylamine and Ferrocenylaniline by Cynthia L. Perrine I hereby release this thesis to the public. I understand this thesis will be made available from the Ohio Link ETD Center and the Maag Library Circulation Desk for public access. I also authorize the University or other individuals to make copies ofthis thesis as needed for scholarly research. Signature: 7 Approvals: r. Allen D. Hunter, ?sAdVlsor L/ Z~ /15f?~~ Curti11)01IUl1ittee Member ate iii Abstract Covalently bonded organometallic oligomers and polymers have been designed to have rigid and thermally and chemically stable organometallic repeating units such as [trans-Mo(phJ>CH2CH2Ph2h(j.t-CN-l,4-C6f4-NC)]. In the first step towards such materials, the chemical and electronic properties ofmodel compounds with only one or a few metal centers will be investigated. Putting electrochemical "sensors" (e.g., ferrocenyl isocyanide or para-isocyanoferrocenylbenzene) at one or more ends of the oligomers, will give information pertaining to the electronic communication via the metal centers. Ferrocenylamine is the essential starting material for the synthesis offerrocenyl isocyanide. The main drawback for the synthesis of ferrocenylamine is its multistage preparation. Ithas been found that the conventional methods ofelectrophilic substitution, which were appropriate for benzene analogues, resulted in the oxidation ofthe ferrocene to the ferricenium cation. A procedure using ferrocenylphthalimide as the precursor proved to be most successful. Bromo- or iodoferrocene were prepared as a precursor of N-ferrocenylphthalimide; the amine is then liberated using the Gabriel method. The electronic properties of the CN-R function can be altered by the nature of the various alkyl and aryl substituents. Using cyclic voltammetry, the oxidation potentials of the molybdenum or nickel centers having ferrocenylisonitrile ends will be determined depending on other substituents on the molecules. These substituents, in addition to chelating phosphines, include other isonitriles such as p-isocyanotetramethylbenzene, p anisole, p-nitrobenzene, p-ferrocenylbenzene, and ferrocene. IV Acknowledgements I would like to thank Dr. Allen D. Hunter for his guidance, leadership and friendship throughout my studies. I would like to thank Matthiaz Zeller for his knowledge, guidance and expertise in lab technique. I would like to also thank the members of my group, whose friendships I will never forget. I would like to especially thank Jim Updegraff for his everlasting support and camaraderie throughout our studies. I would like to extend a special thanks to my family and friends for their continued support in my thirst for knowledge. Table ofContents Page Abstract iii Acknowledgements IV Table ofcontents V List ofequations IX List offigures XlI List oftables XlV List ofabbreviations xv Chapter 1. Introduction Section 1. Organometallic structure and bonding 1 Section 2. Organometallic polymers and dendrimers 12 Section 3. Organometallic nanomaterials 1.3. 1. Introduction 17 1.3.2. Requisite organic and organometallic reagents 19 1.3.3. Characterization ofthe organometallic building blocks 25 Section 4. Ferrocene chemistry 1.4.1. Introduction 27 1.4.2. Synthesis ofaminoferrocene 28 1.4.3. Synthesis ofmonoisocyanoferrocene 30 1.4.4. Synthesis ofisocyanoferrocenylbenzene 32 1.4.5. Nanorod building blocks 34 1.4.6. Electrochemistry 35 1.4.7. Conclusion 41 Section 5. Nickel chemistry 1.5.1. Introduction 42 1.5.2. Nickel (0) complexes 42 1.5.3. Peroxo complexes 43 1.5.4. Transition-metal alkynyl complexes 44 1.5.5. Related analogues 47 v 1.5.6. Tetrakis nickel (0) complexes 49 1.5.7. Conclusion 50 Fteferences 51 Cha?&2. Experimem~ 2.1. Fteagents 55 2.2. Instrumentation 55 2.3. Syntheses 2.3.1. Para-methoxyisocyanobenzene 56 2.3.2. 1,4-Bis(n-formylamino)-2,3,5,6-tetramethylbenzene 57 2.3.3. 1,4-Diisocyano-2,3,5,6-tetramethyl benzene 58 2.3.4. Para-nitroisocyanobenzene 59 2.3.5. Tris(p-anisyl)phosphine 60 2.3.6. 1,2-Bis[di(p-anisyl)phosphino]ethane 62 2.3.7. 1,2-Bis[bis(p-ethylphenyl)phosphino]ethane 63 2.3.8. Trans-bis[bis{di(p-anisyl)phosphino}ethane] 64 bis(dinitrogen)molybdenum(0) 2.3.9 Trans-bis[bis{di(p-ethylphenyl)phosphino}ethane] 65 bis(dinitrogen)molybdenum(0) 2.3.10. o-Benzylhydroxylamine 66 2.3.11. a-Azidostyrene 67 2.3.12. Ferrocenylamine 68 2.3.13. Lithioferrocene 69 2.3.14. Iodoferrocene 70 2.3.15. N-ferrocenylphth~de 71 2.3.16. Ferrocenylamine 72 2.3.17. Formylferrocenylamine 73 2.3.18. Isocyanoferrocene 75 2.3.19. Para-nitrophenylferrocene 76 2.3.20. Para-ferrocenylaniline 77 2.3.21. N-formylferrocenylaniline 78 2.3.22. Para-isocyanoferrocenylbenzene 79 VI 2.3 .23. Tetrakis(para-methoxyisocyanobenzene)nickel(0) 80 2.3.24. Tetrakis(ferrocenylisocyanide)nickel(O) 81 2.3.25. Tetrakis(para-isocyanoferrocenylbenzene)nickel(O) 82 2.3.26. Tetrakis(para-nitro-isocyanobenzene)nickel(0) 83 2.3.27. Bis[bis{di(p-ethylphenyl)phosphino}benzene] 84 bis(ferrocenylisocyano)molybdenum(0) 2.3.28. Bis[bis{di(p-ethylphenyl)phosphino}benzene] 85 bis(isocyanoferrocenylbenzene)molybdenum(O) Fleferences 87 Chapter 3. Flesults and Discussion 3.1. Isonitriles 3.1.1. Para-methoxyisocyanobenzene 88 3.1.2. 1,4-Diisocyano-2,3,5,6-tetramethylbenzene 89 3.1.3. X-Flay structural analysis of1,4-diisocyano-2,3,5,6- 90 tetramethylbenzene 3.1.4. Para-nitroisocyanobenzene 91 3.2. Phosphines 3.2.1. Tris(p-anisole)phosphine 93 3.2.2. 1,2-bis(di(P-anisyl)phosphino)ethane 95 3.2.3. 1,2-bis[di(p-ethylphenyl)phosphino]ethane 96 3.3. Dinitrogen complexes 3.3.1. trans-bis[bis{di(p-anisyl)phosphino}ethane] 97 bis(dinitrogen)molybdenum(O) 3.3.2. trans-bis[bis{di(p-ethylphenyl)phosphino}ethane] 99 bis(dinitrogen)molybdenum(O) 3.4. Ferrocene chemistry 3.4.1. o-Benzylhydroxylamine 100 3.4.2. Ferrocenylamine 102 3.4.3. Ferrocenylamine (Gabriel method) 103 3.4.4. X-Flay structural analysis offerrocenylamine 105 3.4.5. Isocyanoferrocene 108 vii 3.4.6. 4-Ferrocenylaniline 111 3.4.7. 4-Ferrocenylaniline 112 3.5. Nickel complexes 3.5.1. Tetrakis(para-methoxyisocyanobenzene)nickel(O) 113 3.5.2. X-Ray structural analysis oftetrakis 114 (para-methoxyisocyanobenzene)nickel(0) 3.5.3. Tetrakis(ferrocenylisocyanide)nicke1(0) 116 3.5.4. Tetrakis(para-isocyanoferrocenylbenzene)nickel(0) 117 3.5.5. Tetrakis(para-nitroisocyanobenzene)nickel(O) 118 3.6. Nanorod building blocks 3.6.1. Bis[bis{di(p-ethylphenyl)phosphino}benzene]bis 119 (ferrocenylisocyanide)molybdenum(O) 3.6.2. Bis[bis{di(p-ethylphenyl)phosphino}benzene]bis 120 (isocyanoferrocenylbenzene)molybdenum(0) References 123 Chapter 4. Tricarbonyl chromium complexes Section 1. Introduction 124 Section 2. Experimental 4.2.1. Tricarbonyl(rl-fluorobenzene)chromium(O) 128 4.2.2. Tricarbonyl(rl-trifluoromethylbenzene)chromium(O) 132 References 136 Chapter 5. Conclusion 139 Appendix 1 140 Appendix 2 142 Appendix 3 146 viii List ofEquations Equation Page 1. 1. 1 Displacement ofdinitrogen ligands. 11 1.2.1, 1.2.2 Methods to prepare polymers by step growth polymerization. 13 1.3.2a, 1.3.2b Common methods to synthesize isonitriles. 20 1.3.2c Synthesis ofdiisocyanides utilizing diphosgene. 20 1.3.2d Synthesis ofchelating phosphines. 21 1.3.2e Synthesis ofmolybdenum(O)dinitrogen complexes. 22 1.3.2f Synthesis ofnanorod building blocks. 23 1.3.2g Synthesis ofmonometallic complexes. 23 1.3.2h Synthesis oforganometallic caps. 24 1.3.2i, 1.3.2j Synthesis ofmetal-isocyanide complexes. 24 1.4.2a Synthesis of ferrocenylamine. 29 1.4.2b Synthesis of ferrocenylamine via the Gabriel method. 31 1.4.3a Synthesis ofisocyanoferrocene. 30 1.4.3b Equilibrium mixture offerrocenylformamide. 32 1.4.4a Synthesis ofpara-ferrocenylaniline. 33 1.4.4b Synthesis ofisocyanoferrocenylbenzene. 34 1.4.5a Synthesis ofbis[bis{di(p-ethylphenyl)phosphino}benzene]bis 35 (isocyanoferrocenylbenzene)molybdenum(O). 1.5.2a Nickelocene reaction. 43 1.5.2b 1,5-cyclooctadiene reaction. 43 1.5.4a Cis and trans dialkynylplatinum complexex. 44 1.5.4b Dehydrohalogenation reaction. 45 1.5.4c Hay's coupling reaction. 46 1.5.4d Copper-catalyzed alkynylligand exchange. 47 2.3.1 Synthesis ofpara-methoxyisocyanobenzene. 56 2.3.2 Synthesis of1,4-bis(N-formylamino)-2,3,5,6-tetramethylbenzene. 57 ix x 2.3.3 Synthesis of1,4-diisocyano-2,3,5,6-tetramethy1benzene. 58 2.3.4 Synthesis ofpara-nitroisocyanobenzene. 59 2.3.5 Synthesis oftris(p-anisyl)phosphine. 60 2.3.6 Synthesis of1,2-bis[di(p-anisyl)phosphino]ethane. 62 2.3.7 Synthesis of1,2-bis[bis(p-ethylphenyl)phosphino]ethane. 63 2.3.8 Attempted synthesis oftrans-bis[bis{di(p-anisyl)phosphino} 64 ethane]bis(dinitrogen)molybdenum(0). 2.3.9 Attempted synthesis oftrans-bis[bis{di(p-ethylphenyl) 65 phosphino}ethane]bis(dinitrogen)molybdenum(0). 2.3.10 Synthesis ofo-benzylhydroxy1amine. 66 2.3.11 Synthesis ofa-azidostyrene. 67 2.3.12 Synthesis offerrocenylamine. 68 2.3.13 Synthesis oflithioferrocene. 69 2.3.14 Synthesis ofiodoferrocene. 70 2.3.15 Synthesis ofN-ferrocenylphthalimide. 71 2.3.16 Synthesis ofaminoferrocene. 72 2.3.17 Synthesis offormylferrocenylamine. 73 2.3.18 Synthesis ofisocyanoferrocene. 75 2.3.19 Synthesis of4-nitrophenylferrocene. 76 2.3.20 Synthesis of4-ferrocenylaniline. 77 2.3.21 Synthesis ofN - formylferrocenylaniline. 78 2.3.22 Synthesis ofpara-isocyanoferrocenylbenzene. 79 2.3.23 Synthesis oftetrakis(para-methoxyisocyanobenzene)nickel(0). 80 2.3.24 Synthesis oftetrakis(ferrocenylisocyano)nickel(0). 81 2.3.25 Synthesis oftetrakis(para-isocyanoferrocenylbenzene)nickel(0). 82 2.3.26 Synthesis oftetrakis(para-nitroisocyanobenzene)nickel(0). 83 2.3.27 Synthesis ofbis[bis{di(p-ethylphenyl)phosphino} 84 benzene]bis(ferrocenylisocyano)molybdenum(0). 2.3.28 Synthesis ofbis[bis{di(p-ethylphenyl)phosphino} 85 benzene]bis(isocyanoferrocenylbenzene)molybdenum(O). 3.1.1 Synthesis ofpara-methoxyisocyanobenzene. 88 xi 3.1.2 Synthesis of1,4-diisocyano-2,3,5,6-tetramethylbenzene. 89 3.1.4 Synthesis ofpara-nitroisocyanobenzene. 92 3.2.1 Synthesis oftris(p-anisyl)phosphine. 94 3.2.2 Synthesis of1,2-bis(di(p-anisyl)phosphino)ethane. 95 3.2.3 Synthesis of1,2-bis[di(p-ethylphenyl)phosphino]ethane. 96 3.3.1 Synthesis oftrans-bis[bis{di(p-anisyl)phosphino}ethane] 96 bis(dinitrogen)molybdenum(0). 3.3.2 Synthesis oftrans-bis[bis{di(p-ethylphenyl)phosphino}ethane] 99 bis(dinitrogen)molybdenum(O). 3.4.1 Synthesis ofo-benzylhydroxylamine. 101 3.4.2 Synthesis offerrocenylamine. 102 3.4.3 Synthesis offerrocenylamine. 104 3.4.5 Synthesis ofisocyanoferrocene. 111 3.4.6 Synthesis of4-ferrocenylaniline. III 3.4.7 Synthesis ofpara-isocyanoferrocenylbenzene. 112 3.5.1 Synthesis oftetrakis(para-methoxyisocyanobenzene)nickel(0). 113 3.5.3 Synthesis oftetrakis(ferrocenylisocyano)nickel(0). 116 3.5.4 Synthesis oftetrakis(para-isocyanoferrocenylbenzene)nickel(0). 117 3.5.5 Synthesis oftetrakis(para-nitroisocyanobenzene)nickel(0). 118 3.6.1 Synthesis ofbis[bis{di(p-ethylphenyl)phosphino}benzene]bis 119 (ferrocenylisocyano)molybdenum(0). 3.6.2 Synthesis ofbis[bis{di(p-ethylphenyl)phosphino}benzene]bis 121 (isocyanoferrocenylbenzene)molybdenum(O). List ofFigures XlI Figure Page 1.1.1 Metal "acting" as a Lewis acid. 1 1.1.2 A "Dewar-Chatt-Duncanson" representation ofthe bonding ofa 5 carbonyl ligand to a transition metal. 1.1.3 Valence Bond Theory representation ofthe bonding ofa carbonyl ligand. 5 1.1.4 A Dewar-Chatt-Duncanson model representation ofthe bonding ofan 7 isocyanide ligand to a transition metal. 1.1.5 Valence Bond Theory model for an isocyanide ligand. 7 1.1.6 A Dewar-Chatt-Duncanson model representation for the bonding ofan 8 alkene ligand to a transition metal. 1.1.7 Valence Bond Theory representation ofthe bonding ofa metal-olefin 9 and metallocyclopropane. 1.1.8 A Dewar-Chatt-Duncanson representation for the bonding ofthe 10 bidentate dppe ligand to a transition metal. 1.1.9 A Dewar-Chatt-Duncanson model representation for the bonding ofa 11 dinitrogen ligand to a transition metal. 1.1.10 Valence bond theory representation ofthe bonding ofa dinitrogen ligand 11 to a transition metal. 1.2.1 Structures ofa polyphosphazene, polysiloxane, and polysilane. 12 1.2.2 Transition metal based polymers containing ferrocene with 14 organosiloxane spacers. 1.2.3 An example ofa rigid-rod metal polyyne. 14 1.2.4 Some examples ofmain-chain organometallic polymers. 15 1.2.5 A first-generation organometallic dendrimer. 16 1.3.1 An example ofan organometallic polymer containing aromatic 17 isocyanides. 1.3.2 Free isonitriles bridging molecular wire junctions. 18 1.3.3 Metal phosphine center bridging aromatic isonitriles. 18 1.3.4 Possible geometries ofhomoleptic metal complexes. 19 XlII 1.3.5 An examples ofsome chelating phosphines. 21 1.4.1 Isocyanoferrocene. 27 1.4.2 An example ofa bridging ferrocene. 36 1.4.3 An example ofa ferrocenic polymer (PVFc). 37 1.4.4 Ferrocene units with a n-conjugated system. 37 1.4.5 Ferrocene-containing dendrimers. 39 1.4.6 An example ofa tunable complex. 40 1.5.1 Star shaped tetraferrocene. 48 1.5.2 Examples oftetrakis isocyanide nickel(O) complexes. 49 3.1 Molecular structure showing 30% probability displacement ellipsoids. 91 3.2 ORTEP representation ofellipsoids are drawn at 50% probability. 106 3.3 Representation ofthe helical chain formed by the hydrogen bridges. 107 3.4 ORTEP plot oftetrakis(para-methoxyisocyanobenzene)nickel(0). 115 4.1.1 Three-dimensional tripod of(116-CJl6)Cr(CO)3. 124 4.1.2 n-Symmetry interactions ofsubstituted (116-arene)Cr(CO)3 complexes 125 (where D = a n-donor substituent, e.g. NMe, and A = a n acceptor substituent, e.g. NOz). 4.1.3 n-Donor interactions, D = a n-donor, e.g. NMez, OMe, or F. 126 4.1.4 n-Acceptor interactions, A = a n-acceptor, e.g. COzMe, C(O)Me, 127 or CF3. 4.2.1 ORTEP plot oftricarbonyl(rl-fluorobenzene)chromium(O). 130 4.2.2 ORTEP plot oftricarbonyl(rl-trifluoromethylbenzene)chromium(O). 134 1.1 ORTEP plot of1,4-diisocyano-2,3,5,6-tetramethyl- benzene. 141 2.1 ORTEP plot offerrocenylamine. 143 2.2 Representation ofthe helical chain formed by the hydrogen bridges. 144 3.1 ORTEP plot oftetrakis(para-methoxyisocyanobenzene)nickel(O). 147 xiv List ofTables 129 129 130 131 134 135 140 140 141 141 Table 1.1.1 3.1 3.2 Page Structure and bonding properties ofsome commonly encountered ligands. 2 Selected bond lengths (A) of1,4-diisocyano-2,3,5,6-tetramethylbenzene. 91 Selected bond angles e) of tetrakis(para-methoxyisocyanobenzene) 115 nickel(O). 4.2.1a X-Ray crystal data oftricarbonyl(rl-fluorobenzene)chromium(O). 4.2.1b X-Ray data collection oftricarbonyl(rl-fluorobenzene)chromium(O). 4.2.1c X-Ray refinement oftricarbonyl(rl-fluorobenzene)chromium(O). 4.2.1d X-Ray geometric parameters oftricarbonyl(ll-fluorobenzene) chromium(O). 4.2.2a X-Ray crystal data oftricarbonyl(ll-trifluoromethylbenzene)chromium(O). 133 4.2.2b X-Ray data collection oftricarbonyl(ll-trifluoromethylbenzene) 133 chromium(O). 4.2.2c X-Ray refinement oftricarbonyl(rl-trifluoromethylbenzene) chromium(O). 4.2.2d X-Ray geometric parameters oftricarbonyl(rl-trifluoromethylbenzene) chromium(O). X-Ray crystal data of1,4-diisocyano-2,3,5,6-tetramethyl-benzene. X-Ray data collection of1,4-diisocyano-2,3,5,6-tetramethyl-benzene. X-Ray refinement of1,4-diisocyano-2,3,5,6-tetramethyl-benzene. X-Ray geometric parameters of1,4-diisocyano-2,3,5,6-tetramethyl benzene. 1.1 1.2 1.3 1.4 2.1 X-Ray crystal data offerrocenylamine. 142 2.2 X-Ray data collection offerrocenylamine. 142 2.3 X-Ray refinement offerrocenylamine. 143 2.4 X-Ray geometric parameters offerrocenylamine. 143 3.1 X-Ray crystal data oftetrakis(para-methoxyisocyanobenzene)nickel(O). 146 3.2 X-Ray data collection oftetrakis(para-methoxyisocyanobenzene)nickel(O). 146 xv 3.3 X-Ray refinement oftetrakis(para-methoxyisocyanobenzene)nickel(O). 147 3.4 X-Ray geometric parameters oftetrakis(para-methoxyisocyanobenzene). 148 nickel(O). a A Ar b 13 n-Bu t-Bu e CO "CN' CN-R Cp CV d 8 !1 dd dppe Dx Eq Et EtOH F Fc Fe Fo List ofAbbreviations Length ofunit cell axis (as in X-ray diffraction) Angstrom Substituted aryl group Length ofa unit cell axis (as in X-ray diffraction) Beta angle (as in X-ray diffraction) between a and e axis n-Butyl tert-Butyl Length ofa unit cell axis (as in X-ray diffraction) Deuterochloroform Dichloromethane Reciprocal centimeters, wave numbers Carbonyl ligand Coordination number Substituted isocyanide ligand Cyclopentadienyl (115_C5H5) Cyclic voltammogram Doublet (as in NMR spectroscopy) Chemical shift (as in NMR spectroscopy) Heat (thermal reaction) Doublet ofdoublet (as in NMR spectroscopy) 1,2-Bis(diphenylphosphino)ethane Density (as in X-ray diffraction) Equivalents Ethyl Ethanol Structure factor refinement (as in X-ray diffraction) Ferrocene Calculated structure factor (as in X-ray diffraction) Observed structure factor (as in X-ray diffraction) XVi xvii FTIR Fourier transform infrared g Grams h Hour, Miller indices (as in X-ray diffraction) Hz Hertz HOMO Highest occupied molecular orbital IR Infrared (as in spectroscopy) J Coupling constant (as in NMR spectroscopy) k Miller indices (as in X-ray diffraction) I Miller indices (as in X-ray diffraction) L Ligand LUMO Lowest unoccupied molecular orbital J1. Mu m multiplet (as in NMR) Me Methyl MHz Megahertz mL Milliliters MoKa. Molybdenum K alpha (as in X-ray diffraction) mol Mole romol Millimole rom Millimeter MO Molecular Orbital Mr Molecular weight (as in X-ray diffraction) Mw Molecular weight 11 Eta NLO Non-linear optical NMR Nuclear Magnetic Resonance 0 Ortho OMe Methoxy 1t Bonding pi orbital 1t* Anti-bonding pi orbital p Para ph ppm PR3 R R cr S s T Tmin Tmax OJ o Omax t THF UVvis V v Vas Vsy in vacuo wR X Z xviii Phenyl Parts per million (as in NMR) Phosphine or Phosphite Alkyl or aryl group Discrepancy index (as in X-ray diffraction) Bonding sigma orbital Goodness offit (as in X-ray diffraction) Singlet (as in NMR spectroscopy) Temperature Minimum transmission (as in X-ray diffraction) Maximum transmission (as in X-ray diffraction) Omega (e.g, measurement angle used in X-ray diffraction) Theta (e.g., Angle between the incident and the diffracted beams in X-ray diffraction) Theta (e.g., maximum Bragg angle as in X-ray diffraction) Triplet (as in NMR spectroscopy) Tetrahydrofuran Ultraviolet-visible (as in spectroscopy) Cell volume (as in X-ray diffraction) Stretching frequency (as in IR spectroscopy) Asymmetric stretching frequency (as in IR spectroscopy) Symmetric stretching frequency (as in IR spectroscopy) Under high vacuum Weighted discrepancy index (as in X-ray diffraction) CI, Br, or I ligand Number ofmolecules in unit cell (as in X-ray diffraction) 1 Chapter One - Introduction Section One Organometallic Structure and Bonding Organometallic chemistry combines features of inorganic and organic chemistry. Approximately fifty years ago, research in this area went through a renaissance driven by breakthroughs in both synthetic methods and bonding theories leading to its current growth phase. Much ofthe interest in organometallic compounds has been due to their efficiency as catalysts for organic and polymer syntheses.1 In turn, this efficacy stems from the seemingly infinite number of derivatives which can be obtained by varying the ligands and metals of organometallic complexes. A transition metal organometallic compound is composed of one or more metal centers surrounded by a set ofligands. In the most basic terms, the ligands may be thought of as Lewis bases that donate pairs of electrons to the central metal atom(s), which acts as a Lewis acid(s). L " ~ L: ? MI+ ... :L1\ "L L Figure 1.1.1 Metal "acting" as a Lewis acid. The relative stability of each complex is related to the valence electron count of the metal. Thus, the IS-electron rule predicts that a complex will be relatively stable ifit has eighteen valence electrons associated with each metal center (i. e., in the non-bonding orbitals of the metal and in the metal-ligand bonds). There are some exceptions to the rule, but metals in the middle of the transition series in low formal oxidation states 2 generally obey the rule (e.g., the complexes that will be discussed in this thesis which contain chromium and molybdenum).1,2 Organometallic ligands may vary in the manner in which their valence electrons interact with the metal. For n-complexes in which unsaturated organic ligands are bonded "side on" to the metal (e.g., olefins and aromatics), one or more n-bonds on the ligand may donate electrons to one or more metal atoms. The hapticity ofthe ligand (i.e., its if number) is defined as the number ofatoms that are within bonding distance ofthe metal atom. The total number and the nature of the ligands that are coordinated to a metal center determine its coordination number, eN. The number of coordination positions that a ligand occupies typically is equal to the number ofelectron pairs donated to the metal. While metal oxidation states and formal charges assigned to ligands do not accurately reflect the net electron charges in the complexes, they are useful bookkeeping tools and so are still widely used. Different ligands may vary in formal charge, the number of electrons that may be donated to the metal atom, and the number of coordination positions around the metal as shown in Table 1.1.2 Table 1.1.1 Structure and bonding properties of some commonly encountered ligands Ligand Formal Electrons Coordination Charge(s) Donated Positions Acyl -1 2 1 r1-alkene 0 2 1 Alkyl -1 2 1 Alkylidene -2 4 1 Alkylidyne -3 6 1 rl-allyl -1 2 1 3 r/-allyl -1 4 2 rI-alkyne 0 2to 4 1 Amine 0 2 1 rI-arene 0 2 1 rl-arene 0 6 3 Carbene 0 2 1 Carbine 0 3 1 Carbonyl 0 2 1 rl-cyclopentadienyl -1 2 1 r/-cyclopentadienyl -1 4 2 r{-cyclopentadienyl -1 6 3 Dinitrogen 0 2 1 Halide (e.g., Cl") -1 2 1 Hydride -1 2 1 Isocyanide (isonitrile) 0 2 1 Nitrile 0 2 1 Nitrosyl (linear) +1 2 1 Nitrosyl (bent) -1 2 1 4 Ligand Formal Electrons Coordination Charge(s) Donated Positions Phosphate 0 2 1 Phosphine 0 2 1 Pyridine 0 2 1 The carbonyl ligand is perhaps the most common ligand in transition metal organometallic chemistry. Its bonding in the linear terminal geometry is typical of other linear 1t-acidic ligands such as N2, NO+, and CN-R. In linear carbonyl complexes, the carbonyl is attached to the metal via the carbon atom, and the metal-carbon-oxygen angle is approximately 180?. According to the Dewar-Chatt-Duncanson model,2 a-bonding occurs when a lone pair of electrons is donated from a filled a-symmetry orbital on carbon (i.e., the approximately sp hybrid orbital) to an empty a-symmetry orbital on the metal (i.e., the approximately d2sp3 hybrid orbital in an octahedral complex). There are also two 1t-backbonding interactions, which are perpendicular to one another. In each of the two back bonds, there is a filled 1t-symmetry orbital on the metal (e.g., the approximately dxy, dxz, or dyz in an octahedral complex), which donates a pair ofelectrons into an empty 1t-symmetry orbital on carbon monoxide (i.e., the approximately CO 1t* antibonding orbital). These a-bonding and 1t-backbonding components are synergic and the overall metal-carbonyl bond is thus stronger than the linear sum of the two components. 5 The electron transfer back to the ligand via the 1t-backbonding effectively neutralizes the Figure 1.1.2 A "Dewar-Chatt-Duncanson" representation of the bonding of a carbonyl ligand to a transition metal.3 electron transfer of the a-bonding interaction to the metal. Thus, the overall metal carbonyl bond is not polarized very much and there is only a small net electron transfer to the carbonyl ligand. An alternate and complementary explanation for the bonding of metal carbonyls e (&M-C=O: ........ !------,.~ "metal carbonyl" M=C=O: "metalla ketone" Figure 1.1.3 Valence Bond Theory representation ofthe bonding ofa carbonyl ligand. is provided by Valence Bond Theory.2 Valence Bond Theory represents the bonding as contributions from two resonance forms. The first resonance form has metal-carbon single and carbon-oxygen triple bonds, with a formal charge of +1 on an sp hybridized oxygen. The second resonance form has both metal-carbon and carbon-oxygen interactions as double bonds, has no formal charges on carbon monoxide, and has oxygen 6 sp2 hybridized. In this interpretation, increased backbonding to the carbonyl is reflected in an increased contribution from the second "metallo-ketone" resonance form. Spectroscopy and X-ray diffraction may be used to provide experimental evidence ofthe nature and extent ofthe metal-carbonyl interaction. Infrared spectroscopy may be used to measure the amount ofbackhonding ofthe metal to the ligand. The IR stretching frequencies of carbonyls decrease from 2120cm-1 to below 1850cm-1 as the metal becomes more electron rich and, consequently, as the amount ofbackbonding increases. In turn, as the amount of backbonding increases, the CO bond order decreases and the carbon-metal bond order increases. Various studies have shown that carbonyl ligands are poor a-donors and strong n-acceptors. Thus, carbonyls act as net electron withdrawing ligands. Nuclear magnetic resonance spectroscopy may also be used to examine the electron richness ofthe complex. As the amount ofbackbonding increases, the chemical shift of the carbonyl carbon correlates with the electron richness of the complex (i.e., shifting either downfield or up-field for a series ofrelated complexes). X-ray diffraction may also be used to examine metal-ligand interactions. Thus, as the bond order ofthe carbon-metal bond increases the corresponding bond length decreases and as the carbon oxygen bond order decreases its bond length increases.4 Isonitrile ligands are isoelectronic with carbonyl ligands and their bonding is therefore closely related. However, isonitriles are less electronegative than carbon monoxide and the lobes ofthe n*-antibonding orbitals on CN are less polarized towards carbon. Thus, isonitriles are generally better net electron donors than carbonyls. In terms ofthe Dewar-Chatt-Duncanson model, there is a-donation from the lone pair ofelectrons on the carbon (i.e., the approximately sp hybrid orbital) to an empty a-symmetry orbital of the metal (i.e., approximately d2sp3 in octahedral complexes). There is also n-back donation from a pair offilled orbitals ofn-symmetry on the metal (i.e., the approximately dxy, dxz, or dyz orbitals in octahedral metals) to a pair ofempty n-symmetry orbitals on the isocyanide ligand (i.e., the approximately n*-orbitals localized on CN).3,4 7 Figure 1.1.4 A Dewar-Chatt-Duncanson model representation of the bonding of an isocyanide ligand to a transition metal. Valence Bond Theory provides an alternative and complementary explanations of the bonding that occurs during the coordination of an isonitrile to a transition metal. In Valence Bond terms, the coordination is explained via resonance. Thus, greater backbonding results in an increased contribution from the second resonance form and - 1 + 1M-C=N-R ....---..... /RM=C=N Figure 1.1.5 Valence Bond Theory model for an isocyanide ligand. hence a decreased CN-R bond angle due to the Sp2 hybridization ofthe nitrogen atom on the latter.5 Both the Dewar-Chatt-Duncanson and Valence Bond Theory explanation can be used to rationalize the same experimental observations. The electron richness of the metal center affects the bond orders for the metal-carbon and carbon-nitrogen bonds as well as the CN-R bond angles. Ifthe electron richness ofthe metal is increased, there is more backbonding and the second resonance form is favored. The metal-carbon bond 8 order therefore increases and the carbon-nitrogen bond order decreases while the CN-R angle decreases. As with carbonyls, the electron richness ofisonitrile complexes may be measured through infrared spectroscopy. The CN stretching frequency for isonitrile complexes is 250-350 wavenumbers lower than the stretching frequency for the free isonitrile reflecting both the weakening of the net CN 0'- and 1t-bonds upon coordination.3,4 Olefins and related unsaturated organics are also common ligands. In the Dewar Chatt-Duncanson model, the bonding ofolefins involves a forward donation of1t-electron density from the occupied 1t-bonding orbitals ofthe alkene (i.e., O'-symmetry with respect to the metal) to empty O'-symmetry valence orbitals on the metal atom (e.g., approximately d2sp3 on an octahedral complex). Back donation occurs from filled 1t symmetry orbitals on the metal (e.g., approximately dxz, dyz, and dxy on an octahedral metal center) into an empty 1t* molecular orbital on the ligand, (i.e., which have 1t symmetry with respect to the metal). ,,~ .(j D ~ ~ Q . ~~ . CH2V'" ,() \) Figure 1.1.6 A Dewar-Chatt-Duncanson model representation for the bonding of an alkene ligand to a transition metal. In Valence Bond terms, the two resonance forms of olefins are referred to as the metal-olefin and metallo-cyclopropane forms, which differ in both their metal-carbon and carbon-carbon bond orders and in the hybridizations ofthe carbon atoms. Thus, increased 9 backbonding increases the contribution ofthe second resonance form which increases the metal-carbon bond order, decreases the carbon-carbon bond order, and 9hanges the carbon hybridization from Sp2 towards Sp3. .. = Figure 1.1.7 Valence Bond Theory representation of the bonding of a metal-olefin and metallocyclopropane. As with carbon monoxide and CN-R, the electron richness ofthe metal containing olefin and related complexes may be measured through spectroscopy and X-ray diffraction. Increasing the electron richness on the metal produces increased backbonding and, therefore, the net bond order ofthe carbon-carbon bond decreases. X ray diffraction has shown that increased electron richness on the metal and the subsequent backbonding, decreases the metal to ligand bond distance, increases the carbon-carbon bond length, and decreases the H-C-H bond angles from 1200 towards 1090 . The 1t-bonded hydrocarbons such as olefins and 7]6-arenes generally increase the net electron density on the metal in contrast to 1t-acidic ligands such as carbonyls and isocyanates, which typically decrease the net electron density on the metal. The PR3 ligand is widely used in metal coordination chemistry because it is a soft ligand and can be incorporated into metal complexes having central atoms in low oxidation states. The stability of complexes with PR3 ligands results from the soft acceptor nature of the metal in low oxidation states and the stability of soft-donor/soft acceptor combinations.6 It is generally accepted that the bonding ofphosphines to metals is almost entirely a-donor in nature for alkyl phosphines. However, for aryl phosphines, phosphites, and fluorinated phosphines 1t-backbonding into phosphorus orbitals that have 10 phosphorus-carbon 0'* orbital character become increasingly important in the order given. The 1,2-bis-diphenylphosphinoethane ligand (dppe) is typically a bidentate ligand in most complexes, meaning that both phosphorus atoms coordinate to the metal. Each phosphorus atom has a lone pair ofelectrons from an Sp3 hybrid orbital that is donated to an empty O'-symmetry orbital on the metal (e.g., approximately d2sp3 orbital on an octahedral metal center). For the phosphine ligands used in this research, backbonding plays little or no role because the aryl substituents are relatively electron rich.7 Figure 1.1.8 A Dewar-Chatt-Duncanson representation for the bonding ofthe bidentate dppe ligand to a transition metal. The dinitrogen ligand is usually a linear monodentate ligand because only one pair ofelectrons from the dinitrogen molecule coordinates to the metal. As with carbon monoxide and CN-R, 2,7 one can describe M-N2 bonding in both Dewar-Chatt-Duncanson (i.e., a-donation and n-back donation) and Valence Bond (i.e., two resonance contributions) terms. Free dinitrogen is IR inactive due to its lack of a dipole moment, but it is Raman active. The polarization that results from its synergic bonding to metal atoms leads to the observation ofa N-N stretching vibration between 1920-2150cm-1 and to chemical activation ofthe dinitrogen ligand. 11 Figure 1.1.9 A Dewar-Chatt-Duncanson model representation for the bonding ofa dinitrogen ligand to a transition metal. e ~ ~ e M-N:=N: ......f----i~ .. M=N=N: Figure 1.1.10 Valence Bond Theory representation ofthe bonding ofa dinitrogen ligand to a transition metal. However, for a terminal N2 ligand net a and 1t interactions are weaker than for other 1t acid ligands such as carbonyls and isocyanides. Therefore, dinitrogen ligands often may be readily displaced from the complex by them, e.g., as in equation 1.1.1 8 2 C=::N-D-R + THF -2Nz Equation 1.1.1 Displacement ofdinitrogen ligands. 12 Section Two Organometallic Polymers and Dendrimers Metal-ligand complexes may be incorporated into polymers to produce new classes of organometallic polymers that are at least formally related to conventional organic and/or inorganic polymers. Most transition elements have a higher coordination number than carbon. This allows inorganic atoms incorporated into polymers to have more side groups. In addition, metal-ligand bonds are typically longer than conventional organic bonds (e.g., carbon-carbon, carbon-nitrogen, and carbon-oxygen bonds). These differences in bonding and valences between carbon and metals produce different bond angles, internuclear distances, and backbone rigidities.7 Because oftheir variable bonding characteristics, organometallic polymers may also possess intriguing electrical, conductivity, magnetic, optical, liquid crystalline, and redox properties. Polymers with inorganic fragments in their repeating unit have many actual and/or potential advantages compared to conventional organic polymers. In particular, inorganic elements are expected to induce properties in polymers that cannot easily be induced using conventional organic fragments.9,l0 Organometallic polymers of most relevance to this research are polymers having transition elements that possess M-C cr or 1t bonds in the backbone. Polyphosphazenes, polysiloxanes, and polysilanes are some inorganic polymers that have been produced commercially because oftheir novel properties.7 Figure 1.2.1 Structures ofa polyphosphazene, polysiloxane, and polysilane. 13 To facilitate practical applications, a main goal of organometallic polymer researchers is to synthesize organometallic polymers with favorable materials processing characteristics (e.g., melting point, solubility, and high or controllable molecular weights (Mn > 10,000?. Since the early 1950s, many organometallic polymers have been synthesized; however, these polymers typically had low molecular weights. They were also often insoluble or could not be melted without decomposing. In order to overcome these obstacles, researchers have attempted various synthetic approaches. Step growth polycondensation reactions involving the reaction of bifunctional monomers were used because addition polymerization reactions could not usually be employed for main-chain organometallic polymers.11 There are two approaches for preparing polymers using step growth polymerization.12 n A-R-B - -tR-xtn n A-R-A + nB-R'-B Equations 1.2.1 and 1.2.2 Methods to prepare polymers by step growth polymerization. The first method uses a molecule that has two functional groups and the second method uses two different difunctional monomers. The first soluble, well-characterized transition metal based polymers of appreciable molecular weight were ferrocene-containing materials with organosiloxane spacers, which were reported in 1974 by Pittman and co-workers.13 - - 14 - n Figure 1.2.2 Transition metal based polymers containing ferrocene with organosiloxane spacers. In 1977, the first high molecular weight rigid-rod metal polyyne materials were described by Hagihara et al. 14 Figure 1.2.3 An example ofa rigid-rod metal polyyne. These are prototypical examples of main chain organometallic polymers: Poly(metallocenes) and rigid-rod acetylide polymers. 15 Me CJI13 n Figure 1.2.4 Some examples ofmain-chain organometallic polymers. Many ofthe polymers shown in Figure 2.4 are soluble in common organic solvents such as benzene, toluene, tetrahydrofuran, and dichloromethane. They also have good electrical, optical, and nonlinear optical properties.9 Another type of organometallic compounds of interest are dendrimers (Greek: dendron = tree). Dendrimers are hyper-branched nanoscale materials that have potential applications as sequestration agents, micro-catalyst chambers, viscosity modifiers, analogues ofproteins and enzymes, etc. Dendrimers are also being used in analytical and NLO applications. The generation number of a dendrimer is essentially the number of branching points along each arm. 16 Figure 1.2.5 A first-generation organometallic dendrimer. As the size of a dendrimer increases, steric crowding increases in the outermost layers. Thus, a typical high generation number dendrimer is sterically crowded on its surface layers, but has significant free space near its central core. This crowding gradient sets the maximum dendrimer generation number at about seven and is responsible for many of their useful properties.15,16 Many rigid-rod organometallic main chain oligomers and polymers are 0.5 to 1.0 nm in diameter and several hundreds of nanometers in length and are thus classified as nanomaterials. These materials may have potential uses for their electronic and nonlinear (NLO) properties.17 Nonlinear optical properties arise from interactions of the electromagnetic fields of light with those of matter. Materials possessing nonlinear optical properties are able to change the nature oflight as it propagates through them and also to charge their electronic and other properties as a function of the incident light. This allows different frequencies, amplitudes, polarization, or propagation characteristics to be produced and may also produce coupled changes in electrical and optical properties. Materials with NLO properties are oftechnological importance in areas that use optical devices such as optical data storage, optical communication, optical switching, image processing, and optical computing.12,18 17 Section Three Organometallic Nanomaterials 1.3.1 Introduction Aromatic isocyanides are of interest in the synthesis of organometallic nanomaterials because they are relatively stable, non-toxic, non-volatile and because they form strong complexes with rationally tunable bonding characteristics. - - n Figure 1.3.1 An example ofan organometallic polymer containing aromatic isocyanides. In addition, free aromatic diisocyanide ligands are also of interest because they are effective molecular-level conductors.19 These ligands are capable of bridging transition metal centers while mediating communication between the centers through a conjugated d1t-p1t-d1t network.20 Thus, aromatic diisocyanide ligands could be deposited on a gold surface (Figure 1.3.2) and thus enhance the surface's electrochemical properties. 18 Au c c c c CIII III III III III????? N N N N NIII III III III III C C C C C Au Figure 1.3.2 Free isonitriles bridging molecular wire junctions.19 If one uses metal phosphine centers, the steric and electronic properties ofthe resultant nanomaterials should also be tunable by varying the metal and PR3 groups. There is a wide variety of structural data available from previous work on monometallic metal isonitriles and metal phosphines that should enable the prediction ofthe metal geometries ofthese complexes. Figure 1.3.3 Metal phosphine center bridging aromatic isonitriles. 19 Inorganic materials having from three to seven ligands bound to a central metal atom or ion are expected to have star like shapes: ? Two coordinate: Au+ ? ? ? ? ? Three coordinate: Ag+ F d" N"o A + C + Rh+ N"+z Pd+z C +z, etc. F" di FOR 0 C + C +z, etc. . d' Coo ...,0 C + Mn+ C +Z F +zSIX coor mate: r, Mo , vv, r, , r , e , etc. Seven coordinate: Mo+z, W Z, W 3, etc. -(1,4-C~ Y)2 where Y = OMe, Me, Et, etc.) will be used to systematically change the electron richness at Mo and the materials' steric bulk. y~ ~y ~/\N ,?'yp p~ N ~y y Y = OMe, Et, CH3 Figure 1.3.5 Examples ofsome chelating phosphines. The typical synthetic route for preparing the phosphines is shown below?3 Mg/THF~_----i.... 4 Br-Mg~R 22 R~ r?YR ~I\AJ P p0" l?) R/V ~R R = OMe, Et, CH3 Equation 1.3.2d Synthesis ofchelating phosphines. In this reaction, commercially available bis(dichlorophosphino)ethane is used as the starting material. Reaction ofthis compound with a Grignard or organolithium reagent in THF generally produces the desired dppe derivatives. The precursors used for the synthesis of our organometallic materials are molybdenum and tungsten dinitrogen complexes of the type M(N2h(PR3)4. They are generally well known compounds for the phenyl derivatives and have been extensively investigated as possible catalysts for chemical low-pressure nitrogen fixation.24 In our new chemistry, the dinitrogen ligands will be exchanged with diisonitrile molecules to get the first generation-metal-diisonitrile building blocks. Bis-isonitrile complexes ofthe molybdenum phosphine complex (e.g., Mo(PR3)4(C=N-CJI5)2) have previously been prepared by displacement ofa weak ligand such as N2 from the phosphine center. These starting materials (e.g., Mo(PR3)4(N2)2 and Mo(PR3)4(N2)(NCMe)) can be made by several routes, most commonly by the reduction of a molybdenum halide under an atmosphere of dinitrogen using a variety of reducing agents, or by analogous multistep procedures involving the isolation ofintermediate products ofthis process.25 Moets + 2 dppe + exc. Mg THFIN2------;..~ Mo(dppe)2(N2h 23 Equation 1.3.2e Synthesis ofmolybdenum dinitrogen complex. In the next step, the first new nanorod building blocks will be synthesized. To avoid the uncontrollable formation of polymers, an excess ofthe isonitrile ligand will be used: --- Mo(dppeh(CN-CJi4-NCh Equation 1.3.2f Synthesis ofnanorod building blocks. Similar monometallic complexes with only one isonitrile ligand per molybdenum center have been reported using a slightly different approach starting with Shiff-bases instead of diisonitriles.26 MeO-< f-N, + \\ II 'C-Ph IH Equation 1.3.2g Synthesis ofmonometallic complexes. 24 Longer oligomers will then be synthesized by combining the dinitrogen terminated first generation nanorods, the isonitrile terminated first generation nanorods, the bifunctional isonitriles, and/or the bis-dinitrogen complexes in appropriate proportions. When oligomers of the final desired chain length are made, they will be capped with terminal organometallic groups, including: M(CO)5 (M = Cr, Mo, W), CpFe(CO)2+, CpMn(CO)2, Mo(dppe'hCO, or Mo(dppe')2(CN-R). The organometallic 'caps' will be prepared via published routes (equation 1.3.2h).27 + toluene/reflux 3h .. Equation 1.3.2h Synthesis oforganometallic caps. However, the syntheses will require careful exploration of the reaction conditions to optimize conditions and prevent mixtures of non-capped, mono-capped, and di-capped species from forming. When more electron poor caps such as MO(CO)5 are used, it is expected that they will tend to polarize the organometallic isocyanide backbone and will also influence the degree ofconjugation between the backbones and the caps. The most electron rich caps are expected to display the best conjugation. These 'capped' complexes will then be used to form organometallic nanostars. Many metal-isocyanide complexes of transition metals are known. They are typically prepared in excellent yields, either by reacting isocyanides with a metal salt or reducing the metal salt in the presence ofisocyanides.25 MClx(solventh + z CN-arene-X ----I~ M(CN-arene-X)zx+ 25 MClisolvent)k + reducing agent + z CN-arene-X ---l.~ M(CN-arene-X)z Equation 1.3.2i and 1.3.2j Synthesis ofmetal-isocyanide complexes. Each nanostar will be prepared by using the specific reaction conditions used for the metal and conventional aryl isocyanides. It is expected that high yields will be obtained, but a major synthetic challenge will be the purification of the nanostars. Possible methods for purification are fractional crystallization and chromatography. Fractional crystallization works remarkably well ifthe synthesis is designed so that any byproducts are different from the desired material. Chromatography is very effective at removing byproducts that have different end-groups. However, column chromatography is quite tedious and often unsuccessful if there is a mixture of oligomers varying only in the number ofrepeating units. The proposed organometallic nanostars are expected to have varying degrees of electronic conjugation down their arms and across their central vertices. They are likely to have fascinating electrical, conductive/semiconductive (i.e., when doped/partially oxidized, and NLO behavior when attached to surfaces. In molecular orbital terms, the maximum degree of electronic communication of the nanostars is expected when the metal fragment's highest occupied molecular orbitals, HOMOs (ofpredominately metal d character), are of relatively high energy and the isonitrile's lowest unoccupied molecular orbitals, LUMOs (of 1t* character), are ofrelatively low energy. It is also expected that increasing the electron richness at the molybdenum centers and decreasing it at the isonitriles should result in increased HOMO-LUMO overlap and hence conjugation. 1.3.3 Characterization ofthe Organometallic Building Blocks It is expected that the new organometallic materials will be relatively air and thermally stable. Elemental analysis, IR, and IH, 13C, and 31p NMR spectroscopy will be used to characterize the physical and spectroscopic properties and for information on 26 purity and identity. X-ray diffraction will be used to determine the solid-state crystal structures of these building blocks. This will provide detailed structural information including: the degree of linearity down their oligomer backbones, the three dimensional geometries at the central metal cores, and the extent of steric interactions. Intermetallic interactions can be quantitatively evaluated by cyclic voltammetric studies and qualitatively inferred from IR spectroscopy. 27 Section Four Ferrocene Chemistry 1.4.1 Introduction Ferrocene is one ofthe most important compounds in the fields oforganometallic chemistry and electrochemistry. The accidental synthesis offerrocene28,29 in 1951 caused an explosion in the organometallic field that still continues. It is a prototypical metallocene that consists of two cyclopentadienyl rings bound on opposite sides of a central iron atom to form an organometallic "sandwich complex." Ferrocene's novel structure and chemistry are credited with the rapid acceleration of modern organotransition metal chemistry. Because of ferrocene's unique properties, its derivatives are the most frequently used molecules for applications in molecular electronic devices. For example, when two ferrocenyl units are incorporated into a conjugated system, the intramolecular electronic interactions between them, so-called electrochemical communication, are readily observed. Thus, if one ofthe two ferrocenyl groups is oxidized to the monocation, the delocalization of the cationic charge between ferrocene and the ferrocenium ion may occur to give a mixed valence state?O Ferrocene is oxidized at a potential of approximately 0.35 with respect to SeE and the relative potential between free ferrocene and its complexes as measured by cyclic voltammetry acts as a sensitive probe ofmetal ligand interactions. A specific ferrocene derivative, isocyanoferrocene (115-e5H5)Fe(115-e5~-N=e:), is a redox-active ligand that was developed in the late 1980'S.31 Figure 1.4.1 Isocyanoferrocene. 28 The chemical and physical properties ofisocyanoferrocene promise to be very intriguing from both fundamental and practical points of view. It is a redox-active ligand that is compatible with highly electron rich fragments. Isocyanoferrocene also has remarkable thermal stability due to the partial delocalization ofback-donated electron density into the rings' 1t* system.32 Finally, one ofthe most important aspects ofits properties is that the iron atom ferrocenyl unit of isocyanoferrocene complexes should be in strong electron communication with the central metal unit in an oligomer or polyme?3 via the extended 1t system in the isonitrile bridge. The incorporation of isocyanoferrocene into our systems is not only because of ferrocenes unique properties, but also due to the distinctive properties ofthe isocyanide complex. Continuous interest in isocyanide complexes of transition metals has been associated, in part, with their similarity to metal carbonyls. It has been found that certain CNR (R = aryl) ligands, e.g., isocyanoferrocene, are far more versatile compared to CO not only sterically but also electronically. Isocyanides are commonly synthesized by the dehydration reaction of formamides. This method was first developed by Ugi et al.34 in the early 1960's, which allows the synthesis ofa wide range ofsubstituted aryl and alkyl isocyanides. The Ugi dehydration method can also be used for the synthesis of organometallic isocyanides including isocyanoferrocene. The chemistry of isocyanoferrocene has remained practically undeveloped since its discovery in the late 1980's. This is undoubtedly, due to the tedious synthesis of the starting material aminoferrocene which involves one ofseveral multiple step procedures. In our research, isocyanoferrocene will be used as an electronic sensor. It will be placed at one or more sides ofother metal centers to supply information pertaining to the electronic communication within and between the centers. 1.4.2 Synthesis ofAminoferrocene The first successful methods for the synthesis ofthe aminoferocene were based on the reaction ofthe ferrocenyl anion with an amine reagent ofreversed polarity.35,31 29 ~NH2CH 2 III 2. HCl/H 20 Fe o-C'N3 .. ~ 1. 0- ~Li IFe ~ ~NH2NH2'oV I 1. 10- 2. HCl/H20 Fe... ~ Equation 1.4.2a Synthesis of ferrocenylamine. These methods utilizing either alpha-azido styrene36 or benzylhydroxylamine31 were not very reliable and the purity of the isolated amine was not acceptable. Among other problems, the in situ formation and reaction ofthe ferrocenyl anion seems to be critical. This anion is only moderately stable even at low temperatures and dilithiation is a common side reaction. The choice of solvent and the correct temperature were discovered to be important factors. For the selective monolithiation of ferrocene, THF below -20?C was found to be the best solvent and tBuLi slowly added to the solution (over a period of 1 h) was found to be the preferable base. To overcome these problems, Bildstein et al.,37 developed an alternative multi gram synthesis offerrocenylamine based on using phthalimide as the protecting group for the synthesis.38,39 a) t-BuLi I THF 10?CFe-H .. b) n-hexane I -80?C Fe-Li (s) IIITHF/-80 ?C .. Fe-I 30 phthalimide CU20 I pyridine I !!. 48h .. ?~-FC ? ~ I Fe= Fe ~ H1N-NH2 1EtOH I !!. 2h----------l.. ~ Fe-NH2 Equation 1.4.2b Synthesis of ferrocenylamine via the Gabriel synthesis. In the first step, ferrocene is selectively monolithiated and isolated as a solid. In the next step, it is reacted with iodine to form iodoferrocene following which iodoferrocene is then converted via a copper catalyzed coupling reaction into the phthalimide. In the last step, deprotection with hydrazine using the Gabriel reaction gives high yields of analytically pure ferrocenylamine, the precursor ofisocyanoferrocene. 1.4.3 Synthesis ofmonoisocyanoferrocene As stated previously, isocyanoferrocene40 is an attractive synthetic target due to its ability to act both as a cap for the organometallic oligomers as well as an electrochemical sensor for these compounds. It can be synthesized in a way similar to other aryl isocyanides and bisisocyanides by the dehydration ofthe corresponding formamide. The formamide is made from ferrocenyl amine by the reaction with a formylating agent such as ethyl formate. OEtI Fe H~O IFe-NH 2 --------I~... HI(N.?H A,18h ? ~ I Fe= Fe ~ Cl Cl+0V Cl Cl II ?--------.........~ Fe-N=C CH2Cl2 / NEt3 / 2 h 40?C 31 Equation 1.4.3a Synthetic route for the synthesis ofisocyanoferrocene. Ferrocenyl formamide is the first intermediate in this sequence and exists in solution as a mixture of several isomers as shown in Equation 1.4.3b. It was characterized by Knox et al.,31 via analytical techniques such as mass spectrometry and IH and l3e NMR and IR spectroscopies. The IR spectra are in agreement with the formamide structure and in the mass spectra only monomeric ferrocenyl formamide and its fragments were found. In contrast to this finding, the NMR spectra contain multiple sets of signals and thus in solution it appears to be an equilibrium of the cis and trans isomers ofthe monomer and at least one dimeric or oligomeric aggregate. 32 .. H)=O----H ffSlFe'!O-N, 'N-{jrFe?fi'V.I H----O={ 'VI Ig H Equation 1.4.3b Equilibrium mixture offerrocenyl formamide. The formamide was found by Knox et al., to be a microcrystalline solid which could not be analyzed by single crystal X-ray diffraction. Knox also states that the resulting isocyanoferrocene compound was obtained in various non-reproducible yields (25-90%) and that the results may be effected by the numerous isomeric forms ofthe formamide. 1.4.4 Synthesis of1,4-isocyanoferrocenylbenzene A phenyl derivative of isocyanoferrocene (e.g., 1,4-isocyanoferrocenylbenzene)40 can also be prepared. Para-ferrocenylaniline is used as the starting point for the synthesis ofisocyanoferrocenylbenzene. The starting material for this compound is para nitrophenylferrocene. Para-nitrophenylferrocene is synthesized by the arylation of ferrocene with a diazonium salt under phase transfer conditions following which the nitro compound is then reduced with tin under acidic conditions to produce the ferrocenylaniline.41 Fc-H phase transfer catalyst FC-oNOZ ~ I Fc= Fe ~ 33 Equation 1.4.4a Synthesis ofpara-ferrocenylaniline. Ferrocenylaniline will then be converted into isocyanoferrocenylbenzene by the same method as described in the previous literature as shown in Equation 1.4.4b. FC-o-NHZ D,18h ClCl+0 V ClCl \I ? ~ I Fc= Fe ~ 34 FC-o-N::C Equation 1.4.4b Synthesis ofisocyanoferrocenylbenzene. The solubility and electronic properties ofthe aniline derivative will be compared to the parent isocyanoferrocene. The electronic properties of the two complexes are expected to be similar. When comparing their solubility properties, the insertion of the aromatic ring between the ferrocene unit and the isocyanide should allow for an increased solubility in organic solvents. In the next phase ofour research, the ferrocene derivatives will be integrated as ligands in our metal complexes to produce the first nanorod building blocks with a ferrocene moiety. Based on the literature, it appears that the syntheses ofthe parent ferrocenylamine will be substantially more challenging than that of the 1,4-ferrocenylphenylanaline. However, the subsequent formylations and then dehydrations of these species are expected to be of similar difficulties and to be generally less challenging than the amine preparations. 1.4.5 Nanorod building blocks The ferrocene units (e.g., isocyanoferrocene and isocyanoferrocenylbenzene) on an oligomer will serve as electrochemical "sensors." Thus they will give information reguarding the electronic communication between the metal center and the ferrocene 35 components and between sets ofintermediary metal-ligand-metal chains. A route for the synthesis of the molybdenum-monoisocyanide oligomers will start with Mo('dppe')2 (dinitrogenh complexes. The dinitrogen molecules ofthese complexes are only loosely bonded to the metal center and can be easily exchanged by other ligands such as isocyanoferrocene. 2 C=N-Q-FC Ar=~ ~ I Fc= Fe ~ Equation 1.4.5a Synthesis ofbis[bis{di(p-ethylbenzene)phosphino}benzene] bis (isocyanoferrocenylbenzene) molybdenum(O). The isocyanide is able to displace the dinitrogen ligand due to the terminal N2 ligands' net 0' and n interactions being weaker than those for n-acid ligands such as isocyanides. With the ferrocenyl electrochemical sensors now incorporated into the metal chains and stars, the delocalization of charge between the two or more ferrocene units will be observed by electrochemistry. 1.4.6 Electrochemistry With the importance of ferrocene in the field of material science, there has currently been great interest in the chemistry offerrocene-based oligomers and ferrocenyl 36 containing conjugated compounds. The electrochemical properties of ferrocene and its derivatives have been extensively exploited in a large number of electronic applications including molecular switches, metal probes, molecular magnets, and non-linear optics. Complexes with ferrocene units can, upon oxidation, form mixed valence states and charge transfer complexes. The ferrocene / ferrocenium (Fe(II) / Fe(III? couple is stable, is largely independent of solvent in terms ofits redox behavior, and the redox processes are electrochemically generally totally reversible.42 It has been found that a combination of factors influence the electrochemical interactions between connected ferrocene moieties including the type of connection, the length ofconnector, and the orientation ofthe ferrocene unitS.43 A few examples will be presented here to illustrate the different types ofinteractions between ferrocene units with various connectors (e.g alkyl groups or 1t-conjugated units) in their main or side chain. The first example, in Figure 1.4.2, shows two ferrocene units that are connected by the covalent bonds of a pair of bridging alkynes. The compound displays an interesting redox activity which can be accounted for by the very fast electron exchange between the ferrocene centers.44 ~c=c~ I IFe Fe -d?r-c=c~ Figure 1.4.2 Example ofa bridging ferrocene. In the next example, Figure 1.4.3, it has been discovered that polymers with an undetermined number of ferrocene units give only "one" sharp redox couple in their cyclic voltammograms. This result indicated that each ferrocene unit is oxidized at the 'al 45same potent! . 37 Figure 1.4.3 An example ofa ferrocenic polymer (PVFc). Finally, conjugated bridging ligands are advantageous as they allow the metal atoms to interact through the adjoining 11" segment, thus influencing the metal-metal electronic interaction between the 1,1'-ferrocenylene units.46 n ~C=C-Ar-C=C IFe OQ la Ib Figure 1.4.4 Ferrocene units with a 1t-conjugated system. Cyclic voltammetry was performed on these 1t-conjugated systems in a 1: I mixture of CH3CN and CH2Ch containing 0.1 M [n-Bu4N]BF4 under nitrogen and with the concentration of the ferrocene unit being 1.0 x 10-3 M. A Ag+!Ag quasi-reference electrode was used in the determination of the redox potentials. The polymers were 38 shown to be redox active and showed a higher oxidation potential than that offerrocene presumably due to the electron withdrawing nature ofthe ethynylene units attached to the ferrocenes. In the cyclic voltamograms, a broadened peak is observed indicating an electron exchange between the ferrocene units. Furthermore, the delocalization and intermolecular exchange of electrons were considered to be the origin of the bulk electrical conductivity in partially oxidized polymers.46 The type of compounds in Figure 1.4.4 have been found to exhibit unique redox behavior and have the potential to lead to 47 al 48 d h ?althe development of new redox systems. Yamamoto et . propose t at sequentt super exchanges between the neighboring redox sites in these compounds would occur. The cyclic votamograms of these compounds have demonstrated one couple of Fe(II)/Fe(III) redox peaks and the CV's showed excellent reversibility.46 In addition to the investigation of these specific conjugated systems, attention has recently been given to new highly branched systems (metallodendrimers) containing a regular three-dimensional monodisperse macromolecule which has branches occurring from each monomer unit. Examples ofvarious ferrocene dendrimers are shown in Figure 1.4.5.49 2 IFe ~ 1 IFe ~ ~ I ~ Fe 39 IFe ~ IFe ~ IFe ~ I Fe ~ 3 I ~ IFe ~ Figure 1.4.5 Ferrocene-containing dendrimers. CV in CH2Ch revealed a chemically reversible ferrocene/ferrocenium couple indicating electron delocalization along the conjugated systems. It was also discovered that systems which contained a greater degree of delocalization were oxidized at lower potentials. Interestingly, a single reversible wave (i.e. having the same peak. to peak separation of ferrocene but three times as intense) was found to occur for 1 and 2 which indicated that the iron centers are not interacting. Two reversible, three-electron oxidations were observed for 3 which probably arise from substituent effects. In an interesting note, investigation into the redox behavior of compounds 1-3 has yielded a correlation in the 40 nature ofthe redox behavior with solubility and the oxidation states ofthe compounds.50 It was also found that the intensity of the cathodic peak is to some extent higher and sharper than the anodic one, which is due to precipitation onto the electrode surface.49 The investigation into the electrochemistry ofthese complexes has generated interest into specific canidates that would be eligible for size tunable complexes. It has been discovered that compound 3 is a size tunable complex in which the radius can be electrochemically switched as observed in Figure 1.4.6.49 6+ Figure 1.4.6 An example ofa tunable complex. When compound 3 is fully oxidized it shows a structural rearrangement to give a fully expanded form. This effect occurs to minimize the electrostatic repulsion between the six iron centers. The rearrangement could also be partially due to the stabilization produced by an intramolecular 1t-stacking ofthe ancillary ligands.49 The complexes in Figure 1.4.6 possess redox centers which have been incorporated into the molecule to give the supramolecular species interesting electrochemical properties. The electrochemical studies do not demonstrate any significant through bond interactions between the iron centers ofdifferent branches ofthe complexes. 41 1.4.7 Conclusion Because of ferrocene's unique properties, its derivatives will be integrated into our metal complexes to produce the first nanorod building blocks with ferrocene caps. In the first step of our research, the chemical and electrochemical properties of model compounds with only one or two metal centers will be investigated. Putting electrochemical "sensors" such as isocyanoferrocene at one or two sides ofthe complexes will give information about the electronic communication via the metal centers. Using cyclic voltammetry, the oxidation potentials ofthe iron and molybdenum centers will be determined as functions ofthe other substituents ofthe molecule. 42 Section Five Nickel Chemistry 1.5.1 Introduction With a steadily growing interest in organometallic complexes, newly developed compounds continue to broaden the scope of possible chemical and electrochemical applications from the research to the industrial level. Tetrakis nickel(O) complexes have been recently investigated due to their chemical and electrochemical properties. One of the most important properties ofthe complexes is their tetrahedral star shape which are expected to have degrees ofconjugation down its arms and across its central vertices with appropriate arms. These complexes are also expected to display electrical conductivity and semiconductivity when they are doped or partially oxidized. Last and foremost, the association of electronically delocalized stars with surfaces is expected to influence the electrochemical properties ofthe surfaces. 1.5.2 Nickel (0) complexes Nickel(O) complexes have been chosen for this specific research because they can induce oxidative addition5! and are also catalytically active.52 Numerous complexes of nickel exist which contain a variety of ligands. As an example, unsaturated molecules (e.g., alkenes and alkynes) are frequently used as substituents on nickel complexes along with group V donors (e.g., As, P, and Sb). Bis(1,5-cyclooctadiene)nickel(O) is a common starting material for the NiL4, N~, and N~(UN) class of compounds (e.g., L = phosphine, arsine, stibine, nitrogen base, or isocyanide, and UN = olefin, acetylene, or azide complex).53 Bis(1,5-cyclooctadiene)nickel(O) has been found to be an exceptionally good starting material for the less x-accepting homoleptic isocyanide nickel(O) complexes. The complex [Ni(M~Si-NC)4] was the first homoleptic isocyanosilane complex reported and was prepared from bis(1,5-cyclooctadiene)nickel(O) and trimethylcyanosilane.54 This reaction represents a successful isomerization of a nitrile to 43 an isocyanide. The homoleptic isocyanide complexes can also be prepared in reasonable yields by the reaction ofnickelocene with an excess ofan alkyl or aryl isocyanide. [Ni(CsHshl +CNR (excess) Equation 1.5.2a Nickelocene reaction. --..... [Ni(CNR)4l + 2 CsHs Otsuka et al.55 investigated the synthesis of nickel isocyanide complexes. They discovered that treatment ofthe aliphatic isocyanide ligands (e.g., t-BuNC) with bis(1,5 cyclooctadiene)nickel(O) gave the tetrakis nickel isocyanide complexes Ni(RNC)4 (R = t butyl or cyclohexyl). [Ni(CgHd2l + CNR (excess) Equation 1.5.2b 1,5-cyclooctadiene reaction. 1.5.3 Peroxo complexes Nearly all Nio complexes are moderately to very air sensitive and give intractable oxidation products in the presents of oxygen.56 Tetrakis nickel isocyanide complexes have been found to be air sensitive in organic solvents. In aromatic hydrocarbons, ether, or THF solutions below _200 C, a peroxo complex results when the nickel isocyanide compound is exposed to pure gaseous oxygen or air. In a preliminary study, a pale green peroxo complex (e.g., Ni(02)(RNCk R = t-butyl or cyclohexyl) resulted when oxygen was introduced into solutions of the nickel isocyanide complex Ni(RNC)4. It has also been observed that an oxygen molecule introduced into an etheral solution of at-butyl isocyanide nickel complex results in the quantitative formation of the equivalent peroxo complex.55 44 The peroxo complexes discussed above are sensitive towards air in the solid state and in solution. It has been discovered that a dried sample of the peroxo complex on exposure to air, even without shock, can explode. In a CHCh solution at 0 ?C, the peroxo complexes have also been found to slowly decompose.55 1.5.4 Transition-metal alkynyl complexes Transition-metal alkynyl complexes are isoelectronic with CN, CO, CNAr, and Nz. The color, magnetic properties, and stoichiometry of the transition-metal alkynyl complexes are also very similar to the isocyanide complexes. Based on these findings, Hagihara57 developed a method to synthesize cr-alkynyl derivatives oftransition metals. It involved the direct dehydrohalogenation reaction between the Group 10 metal halides and terminal alkynes with electron withdrawing substituents. A few years later, a copper (I}-catalyzed reaction was developed for the dehydrohalogenation of a wider range of metal halides (Ni, Pt, and Pd) in an amine solvents.58 In this reaction, the use ofspecific amines (e.g., diethylamine, diisopropylamine, or piperidine) resulted in mono- or dialkynyl compounds which have square planar metal centers with a trans- orientation of the ligands.59,6o After extensive research, the cis isomer was prepared using N,N,N',N'? tetramethylethylenediamine.61 Equation 1.5.4a Cis and trans dialkynylplatinum complexes. To prevent further reactions in compounds with a second terminal alkynyl group, a large excess of the alkyne needs to be used. This prevents the formation of oligomers or polymers. Slow isomerization was observed between the cis and trans forms in amine solutions under reflux. In addition, the addition of the cuprous halide was found to accelerate the isomerization process.58 45 Following the work ofHagihara,57 three general copper catalyzed reactions can be employed to synthesize various rigid-rod a-bonded alk.ynyl polymers with molecular weights (Mw) greater than 106. In the first reaction, diterminal alkynes and transition metal halides react with an amine to induce dehydrohalogenation. Equation 1.5.4b shows the result ofthe dehydrohalogenation reaction. Y = none or aromatic spacer=lR~ PR3t?-c::c-tY}-c::c1; PR3 Equation 1.5.4b Dehydrohalogenation reaction. Hence the amine acts as both an acid acceptor and as the solvent for this reaction. Polymerization was found to occur both at room temperature and under reflux.62,63 In the second copper catalyzed oxidative coupling reaction, transition-metal species with two terminal alkynyl groups are coupled by oxygen. 46 PR3I HC=C-Y-C=C-M-C=C-Y-C=CH IPR 3 M=Pd, Pt Y = none or aromatic spacer PR31? -C=C-Y-C=C--c=C-Y-C=C~ PR3 Equation 1.5.4c Hay's coupling reaction. The degree of polymerization is usually very high in the reaction and there IS no stoichiometric restrictions on a reactant bearing different functional groups. The dehydrohalogenation and the oxidative coupling reactions work well for Platinum (Mw of approximately 100,000 units) and fairly well for palladium (Mw ofapproximately 20,000) but neither ofthese methods work for Nickel. Nickel complexes are not well suited for the dehydrohalogenation or oxidative methods due to reactions ofthe nickel centers with the oxidative-coupling reagents and the decomposition ofthe nickel complexes in amine solvents. To solve this problem, a third copper catalyzed route involving an alkynyl-ligand exchange process in amine solvents is used. Equation1.5.4d represents the result of the alkynyl-ligand exchange process.64 47 Equation 1.5.4d Result ofcopper-catalyzed alkynylligand exchange. To prevent decomposition of the polymer, a small amount of free PR3 is added to the reaction. The PR3 presumably works by suppression ofphosphine dissociation from the metal center. These three methods have been developed to add various end groups on the polymers and to vary their electronic properties. In addition, the degree of polymerization can be easily controlled by the amount ofthe alkynyl group added to the reaction. Along with the rigid-rod a-bonded alkynyl polymers, polythiophenes are considered an important class ofcompounds in material science. 1.5.5 Related analogues Polythiophenes have been found to exhibit excellent electronic conducting properties and are used in the construction of opto-electronic devices.65 Figure 1.5.1 shows an example offour ferrocene units that are attached by triple bond to a thiophene core. 48 &/ Fe!1 Spacer = none, Figure 1.5.1 Star shaped tetraferrocene. The tetra-ferrocenyl thiophene complex was synthesized by the palladium-catalyzed cross coupling reaction of ferrocenyl alkynes and 2,3,4,5-tetrabromothiophene. An excess ofthe terminal alkyne was used in the synthesis to ensure complete conversion. It was discovered that the air-stable compounds were soluble in common chlorinated solvents. It was also found that the solubility of the complexes decreased with increasing chain lengths. The UV-vis data of the complex exhibited a 1t-1t* absorption band with a high absorption coefficient. A d-d transition was responsible for the weak, low energy band from the ferrocene complex. Subsequently, cyclic voltammetry demonstrated the electronic properties ofthe complexes. A lack of interactions between the ferrocene units was observed in the cyclic voltammetry (CV) data.66 As noted above, the communication between the ferrocene units depends upon the chain length and the specific components in the chain. Along 49 with thiophene complexes, the electronic properties of other transition metal complexes are currently being investigated. 1.5.6 Tetrakis nickel (0) complexes Ittel et al.53 describes the synthesis ofnickel (0) complexes such as tetrakis (tert butyl isocyanide)nickel(O), tetrakis(triphenylphosphine)nickel(O), and tetrakis (triethyllphosphite)nickel(O) via bis(l,5-cyclooctadiene)nickel(0). A similar method to that of Ittel will be used to synthesize nickel complexes of isocyanides containing vanous substituents, including: para-methoxyisocyanobenzene, para-nitro isocyanobenzene, isocyanoferrocene, and para-isocyanoferrocenylbenzene. ATI NIII CI \,Ni-C=N- AT ,\\ \~C'\' Ar/ N " C N ~ ~ I Fe ~ ,~ Fe ~ ,{rNOz Figure 1.5.2 Examples oftetrakis isocyanide nickel(O) complexes. The materials properties ofthese complexes will also be explored and contrasted to the properties ofconventional organic and organometallic rigid rod analogues. As discussed in the introduction, the nickel complexes are expected to have measurable amounts of conjugation down their arms and across their central vertices due to metal d-ligand 7t* overlap. The incorporation of a ferrocene moiety into a nickel complex will allow the electrical conjugation down the arms to be investigated. The interaction between the 50 terminal subunits will be ofgreat interest and will allow the modulation ofthe electronic properties ofthe material. 1.5.7 Conclusion Cyclic voltammetry will be used to investigate the red/ox properties offerrocene containing nanostars. The redox potentials ofthe complexes will be determined to assess their prospective use as electron reservoir complexes for stoichiometric redox reactions. The electronic properties ofthe tetrahedral nickel(O) complexes will be compared to the properties of conventional organic and organometallic analogues. The successful synthesis ofthese complexes will further our understanding oftheir potential in chemical and electrochemical applications. 51 References 1. P. R. Jenkins, Organometallic Reagents in Synthesis; Oxford University Press: NewYork, 1992. 2. (a) B. Douglas, D. McDaniel, 1. Alexander, Concepts andModels ofInorganic Chemistry; John Wiley and Sons Inc.: New York, 1994. (b) 1. 1. 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Kataoka, S. Takahashi, N. Hagahara, 1. Organomet. Chem., 1978, 160,319. 63. S. Takahashi, H. Morimoto, E. Murata, S. Kataoka, K. Sonogashira, N. Hagihara, 1. Polym. Sci. Polym. Chem. Ed. 1982,20,565. 64. K. Sonogashira, K. Ohga, S. Takahashi, N. Hagahara, 1. Organomet. Chem., 1980, 188,237. 65. K. 1. Thomas, 1. T. Lin, J. Organomet. Chem., 2001,637-639, 139-144. 66. H. Fink, N. 1. Long, A. 1. Martin, G. Opromolla, A. 1. P. White, D. 1. Williams, P. Zanello, Organometallics, 1997, 16, 2646. (b) T. Nakashima, T. Kunitake, Bull. Chem. Soc. Jpn., 1972, 45, 2892. 55 Chapter 2 - Experimental The reactions were perfonned under an atmosphere ofultra high purity dinitrogen (Praxair 99.9999%) using standard Schlenk techniques for the manipulation of air- ., d nl d h . 12senSItIve compoun suess state ot erwlse. ' 2.1 Reagents Unless otherwise stated, the reagents used were purchased from commercial suppliers and were ofreagent grade or comparable purity. They were not further purified before use. The solvents used were dried and deaerated by standard procedures3 and stored under purified N2. Thus, THF, diethylether, and toluene were distilled from benzophenone ketyl radical using Na-K alloy for THF and diethylether and using sodium for toluene. Methylene chloride was distilled from calcium hydride. 2.2 Instrumentation Infrared spectra were recorded on a JASCO FTIIR-410 infrared spectrophotometer. IH (400 MHz), l3C (100 MHz), and 31p (161.88 MHz) NMR spectra were recorded on a 400 MHz Varian Gemini-2000 spectrometer. IH and l3C NMR chemical shifts are reported in parts per million (ppm) downfield from external Me4Si (0 = 0). The 31p NMR chemical shifts are reported in parts per million (ppm) downfield from external 85% H3P04 (0 = 0). Single Crystal X-ray analysis was completed via Broker AXS Smart Apex CCD Diffractometer. 56 2.3 Syntheses 2.3.1 Para-methoxyisocyanobenzene4 ? H'N)lH CIII N? Cl CHzCl zI NEt3 ?+ 1 Cl+OyCl2 ? 2 Cl A,2h,40?C ?? O'CH 33 Equation 2.3.1 Synthesis ofpara-methoxyisocyanobenzene. Para-formamidoanisole (10.0 g, 66.15 mmol), previously prepared by Matthias Zeller using the method as described by Hanack et al.4, CH2Ch (200 mL), and triethylamine (45.85 mL, 33.29 g, 0.329 mol) were combined in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. Diphosgene (3.9 mL, 6.54 g, 33.0 mmol) was placed into a dropping funnel containing CH2Ch (46 mL). The diphosgene solution was added drop wise to the solution over a 15 minute period and then the solution was refluxed for an additional 2 h. The solution was allowed to cool to ambient temperature and washed under nitrogen with a 10% solution ofNa2C03 (3 x 100 mL) and with H20 (1 x 100 mL). The organic layer was dried over anhydrous MgS04. The MgS04 was filtered off, washed with CH2Ch (3 x 20 mL), and all volatile materials were removed in vacuo from the combined filtrates (e.g., high vacuum manifold at room temperature). Crystallization ofthe resulting light brown solid from pentane at 4 ?C gave white-yellow needles. The crystals were dissolved in a 2:1 hexane / CH2Ch mixture (- 40 mL). The solution was filtered through a neutral aluminum column (0.50 m) using a 2:1 hexane / CH2Ch mixture (- 150 mL) and all volatile materials were removed from the filtrate in vacuo. The solid was again crystallized from pentane at 4?C to give a 21% yield (1.84, 13.8 mmol) of the product as white-yellow needles exhibiting a pronounced isonitrile 57 smell. The crystals start to melt at room temperature and have to be stored under nitrogen at -19 ?e to avoid rapid decomposition. No spectroscopic properties were recorded due to the thermal sensitivity of the compound. The identity ofthe compound was verified by its conversion into the Ni(O) tetraisocyanide complex, see below. 2.3.2 1,4-Bis(n-formylamino)-2,3,5,6-tetramethylbenzene 4 o H'N)lH H3 C*CH 3I~ H3C CH3 HI(N'H o Equation 2.3.2 Synthesis of1,4-bis(n-formylamino)-2,3,5,6-tetramethylbenzene. The 2,3,5,6-tetramethylphenylene-1,4-diamine (10.09 g, 61.4 mmol) was combined with formic acid (150 mL) in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. The stirred solution was heated to reflux for 2 h. It was then cooled to room temperature, water (100 mL) was added, and the resulting suspension was stirred at ambient temperature for approximately 12 h. The beige solid was collected by filtration and was rinsed with H20 until the filtrate was neutral (pH-paper). The solid was dried in vacuo to give an 80% yield (10.9g, 0.0493 mol) ofthe product as a white solid. No spectroscopic properties were recorded due to the insolubility ofthe product in common organic solvents. The identity ofthe compound was verified by its dehydration to form 1,4-diisocyano-2,3,5,6-tetramethylbenzene. MP: 350 ?e. 58 2.3.3 1,4-Diisocyano-2,3,5,6-tetramethylbenzene 4 + Cl Cl+OVCl Cl II ? Equation 2.3.3 Synthesis of1,4-diisocyano-2,3,5,6-tetramethylbenzene. 1,4-Bis(n-formylamino)-2,3,5,6-tetramethylbenzene (10.87 g, 49.32 mol) was combined with CH2Ch (150 mL) and triethylamine (34.2 mL, 24.83g, 0.245mol) in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. Diphosgene (6.1 mL, 10.0 g, 50.6 romol) was placed into a dropping funnel containing CH2Ch (34 mL). The diphosgene solution was added drop wise to the refluxing suspension over a 15 minute period and then the solution was refluxed for an additional 3 h. The solution was cooled to ambient temperature and washed under nitrogen with a 10% solution of Na2C03 (3 x 100 mL) and with H20 (1 x 100 mL). The organic layer was dried over anhydrous MgS04for 1 h. The MgS04was filtered off, washed with CH2Ch(3 x 20 mL), and all volatile materials were removed from the combined filtrates in vacuo. The brownish solid that resulted was sublimed at 75?C under oil pump vacuum to give a 34% yield (2.19 g, 17.0 romol) ofthe product as a white crystalline solid. It is stable in air for a short time and can be stored at 4 ?C under nitrogen for extended periods without signs ofdecomposition. 59 Spectroscopic Properties: l3C eH} NMR (CDCh): 0 = 168.870 (s, C::N), 131.550 (s, C-CH3), 126.724 (t, IJ(l3C/'*N) = 11.4 Hz, C-N), 16.366 (s, CH3). IH NMR (399.905 MHZ, CDCh): 0 =2.357 (s, 12 H, elL). IR (emulsion in paraffin oil, NaCl plates): 2115 em-I (s, v C::N). MP: 112?C. X-Ray structure analysis: see Results and Discussion and Appendix 1. 2.3.4 Para-nitro-isocyanobenzene 4 H o~-o-~ N02 + H - CI 1/2 a+oVCI CI II ? CH2CI2 ! NEt] ! A. 2 h, 40 ?C.. C=N-< >-N~ Equation 2.3.4 Synthesis ofpara-nitroisocyanobenzene. Para-nitro-formamide (4.050 g, 0.02438 mol), previously prepared by Matthias Zeller using the method as described by Hanack et al.4, was combined with CH2Ch (50 mL) and triethylamine (50 mL, 36.3 g, 0.359 mol) in a nitrogen purged 250 mL three necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. Diphosgene (2.1 mL, 3.36 g, 17.0 mmol) was placed into a dropping funnel containing CH2Ch (10.0 mL). The diphosgene solution was added drop wise to the refluxing suspension over a 15 minute period and then the solution was refluxed for an additional 3 h. The solution was cooled to ambient temperature and washed under nitrogen with a 10% solution ofNa2C03 (3 x 100 mL) and with H20 (1 x 100 mL). The CH2Ch solution was dried over anhydrous MgS04 for 1 h. The MgS04 was filtered off, washed with CH2Ch (3 x 20 mL), and all volatile materials were removed from the combined filtrates in vacuo. The brownish solid was sublimed at 75 60 ?C under oil pump vacuum to give a 21% yield (0.750 g, 50.6 mmol) ofthe product as a white solid. Spectroscopic Properties: l3C CH} NMR (CDCh): 8 = 169.3 (s, C=N), 147.3 (s, C-N02), 131.0 (t, IJ(13Cl~ = 16.0 Hz, C=NC), 127.4 (s, C Ph-C), 124.9 (s,C Ph-C). IH NMR (399.905 MHZ, CDCh): 8 = 8.230 (d, 3JeH1H) = 9.00 Hz, 2H), 7.508 (d,3J eH1H) = 9.00 Hz, 2H, Ph-H). IR (toluene, CaF2): 2121 cm-1(s, v C=N), 1520 cm-1(s, VasN02), 1345 cm-1(s, vsy N02). IR (KBr): 2130 cm-1(br, v C=N), 1541 cm-1(hr, Vas N02), 1349 cm-1(br, vsy N02). MP: 81?C. 2.3.5 Tris(p-anisyl)phosphine5 Equation 2.3.5 Synthesis oftris(p-anisyl)phosphine. Magnesium turnings (9.707 g, 0.399 mol) were combined with a few crystals of iodine and THF (50.0 mL) in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. The mixture was warmed with a heat gun until the color of the iodine disappeared. The 4-Bromoanisole (14.94 g, 0.0798 mol, 99% Aldrich) in THF (50 mL) was added drop wise to this solution and a heat gun was used to initiate the reaction. After the addition was complete the solution was stirred an additional 0.5 h at 40?C, 61 filtered under nitrogen to remove the excess magnesium and then the solid was washed with THF (3 x 20 mL). A second round bottom flask (500 mL) was equipped with a nitrogen adapter, Schlenk filter, and a magnetic stirring bar. The Grignard suspension was transferred into the Schenk filter via transfer tube. Phosphorus trichloride (3.54 g, 25.8 mmol, 2.25 mL) dissolved in THF (30.0 mL) was placed into the 500 mL flask and the mixture was cooled to 0 0c. The Grignard suspension was then filtered into the phosphoros trichloride solution over a period of 0.5 h, the solid washed with THF (3 x 20 mL), and the solution was stirred for approximately 12 h at ambient temperature. The resulting suspension was hydrolyzed with a degassed 10% aqueous Nl4CI solution and extracted with diethylether (3 x 100 mL). The organic extracts were dried over anhydrous MgS04 for 1 h. The MgS04 was filtered off under nitrogen, washed with diethylether (3 x 20 mL), and all volatile materials were removed from the filtrate in vacuo. The resulting solid was crystallized from diethylether to give a 39% yield (3.50 g, 99.4 mmol) ofthe product as white needles. Spectroscopic Properties: l3C eH} NMR (CDCh): 8 = 159.780 (s, C-OCH3), 134.740 (d, J(l3C/1p) = 20.51 Hz, Ph-C), 114.009 (d, J(l3C,31p) =7.64 Hz, Ph-C), 113.895 (d, J(13C/1p) = 7.64 Hz, Ph C), 55.196 (s, CH3). 1H NMR (CDCh): 8 = 7.220 (dd, 3JeH/H) = 8.70 Hz, JeH,31p) = 7.40 Hz, 6H, Ph-H), 6.870 (d, 3JeH,1H) = 8.70 Hz, 6H, Ph-H), 3.795 (s, 9H, Clli). 31p NMR (161.884 MHZ, CDCh, 25?C): 8 = -10.83 (s). 62 2.3.6 1,2-Bis[di(p-anisyl)phosphino]ethane 5 Mg/THF ~ H3CO-{ }-MgBr THF/rt Arn Ar'p p- Ar/ 'AI Ar= H > Equation 2.3.6 Synthesis of1,2-bis[di(p-anisyl)phosphino]ethane. Magnesium turnings (7.32 g, 0.301 mol) were combined with a few crystals of iodine and THF (50.0 mL) in a nitrogen purged 500 mL three-necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. The mixture was warmed with a heat gun until the color of the iodine disappeared. p-Bromoanisole (0.043 mol, 8.04 g, 31.0 mL, 99% Aldrich) in THF (50 mL) was added drop wise to this solution and a heat gun was used to initiate the reaction. After the addition was complete the solution was stirred an additional 12 h at ambient temperature, filtered under nitrogen to remove the excess magnesium, and the solid was then washed with THF (3 x 20 mL). Bis(dichlorophosphino)ethane (6.5 mL, 9.97 g, 0.043 mol) dissolved in THF (35.0 mL) was placed into a dropping funnel and added to the Grignard suspension over a 15 minute period at 0 ?C. The solution was then allowed to stir for approximately 12 h at ambient temperature. The resulting solution was hydrolyzed with a degassed 10% aqueous NlLtCI solution (120 mL) and the organic layer removed via cannula. The organic extracts were dried over anhydrous MgS04 for 1 h and then the MgS04 was filtered off under nitrogen, washed with toluene (3 x 20 mL), and all volatile materials were removed from the filtrate in vacuo. The resulting solid was crystallized from toluene (- 30 mL) at -19?C to give a 40% yield (8.33 g, 17.0 mmol) ofthe product as a white crystalline powder. 63 Spectroscopic Properties: IH NMR (CDCh): B= 7.280-7.241 (m, Ph-H), 6.84 (d, 3JCH,1H) = 8.80 Hz, 8H, Ph-ill, 2.000 (pt, JCH,31p) = 4.00 Hz, 4H, Clli), 3.788 (s, 12H, Cfu). 31p NMR (161.884 MHZ, CDCh): B= -16.621 (s). 2.3.71,2-Bisfbis(p-ethylphenyl)phosphinojethane 5 Et--O-Br + Mg/THF/ A .. nClzP PCl z TIIF/rt Ar= Et-{ > Equation 2.3.7 Synthesis of1,2-bis[bis(p-ethylphenyl)phosphino]ethane. Magnesium turnings (7.86 g, 0.323 mol) were combined with THF (60.0 mL) in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, reflux condenser, dropping funnel, and magnetic stirring bar. 1-Bromo-4-ethyl benzene (0.290 mol, 53.72 g, 40.0 mL) in THF (70 mL) was added drop wise to this suspension and a heat gun was used to initiate the reaction. After the addition was complete the solution was stirred an additional 2 h at ambient temperature, filtered under nitrogen to remove the excess magnesium, and the solid was then washed with THF (3 x 20 mL). Bis(dichlorophosphino)ethane (9.8 mL, 14.99 g, 0.065 mol) dissolved in THF (40.0 mL) was placed into a dropping funnel and added to the Grignard suspension over a 15 minute period at 0 ?C following which the solution was allowed to stir for approximately 12 h at ambient temperature. The resulting solution was then hydrolyzed with a degassed 10% aqueous ~CI solution (120 mL) and the THF removed via cannula. The organic extract was dried over anhydrous MgS04 for 1 h and then the 64 MgS04 was filtered offunder nitrogen, washed with toluene (3 x 20 rnL), and all volatile materials were removed from the filtrate in vacuo. The resulting solid was crystallized from toluene (- 40 rnL) at -19?C to give an 82% yield (18.6 g, 0.163 mmol) of the product as a white crystalline solid. Spectroscopic Properties: IH NMR (CDCh): 8 =7.271-7.233 (m, Ph-H), 7.146 (d, 3JeH,tH) =8.80 Hz, 8H, Ph-H), 2.623 (q, 3JeH,IH) = 7.60 Hz, 3JeH,IH) = 15.20 Hz, 8H, C!k), 2.062 (pt, JCH/IP) = 4.00 Hz, 4H, Clli), 1.218 (t, 3JCH,IH) = 8.00, 12H, Clli). 31p NMR (161.884 MHZ, CDCh, 25?C): 8 = -14.774 (s). 2.3.8Attemptedsynthesis oftrans- bisfbis{di(p-anisyl)phosphino}ethane} bis(dinitrogen)molybdenum(Oi NaHg+MoCls Ar=H3CO-{ ) Equation 2.3.8 Attempted synthesis oftrans- bis[bis{di(p-anisyl)phosphino}ethane] bis(dinitrogen)molybdenum(O). The 1,2-Bis(di(P-anisyl)phosphino)ethane (8.33g, 0.0170 mol) was combined with THF (20.0 rnL) and added to liquid NaHg (2% by weight Na, 3.811g Na, 0.00829 mol Na; 15.6 g Hg, 0.0778 mol Hg, 12.0 rnL Hg)6 in a nitrogen purged 500 rnL Schlenk flask equipped with a magnetic stirring bar. THF (80 rnL) and MoCls (2.26g, 0.00829 mol) were then added to the solution and the mixture was stirred vigorously with a large stirring bar for 60 h at ambient temperature with a constant pressure of nitrogen. The suspension was filtered through celite under nitrogen, the celite rinsed with toluene (3 x 20 rnL), and all volatile materials were removed from the combined filtrates in vacuo. 65 The resulting solid was dissolved in toluene (100 mL) and anhydrous methyl alcohol (150 mL) was then added to precipitate the product. The solution was removed by filtration and the solid rinsed with methyl alcohol (3 x 20 mL). All volatile materials were removed from the solid in vacuo to give a 39% yield (3.63 g, 3.20 mmol) of the product as an orange-yellow powder. This powder, as determined by NMR, contains approximately 20% tetrahydride (e.g., (C30H160J>Z)Z~o) which formed as side product and was not successfully removed via crystallization. Spectroscopic Properties: 13C {lH} NMR (Benzene): 8 = 160.523 (s, Ph-C-O), 130.306 (d, JClp,13C) = 7.44 Hz, Ph-C), 134.513 (d, J(13C/lp) = 11.46 Hz, Ph-C), 114.558 (d, J(13C/lp) = 21.12 Hz, Ph-C), 54.787 (s, CH3), 25.787 (s, CHz). lHNMR(399.905 MHZ, CDCh): 8 = 7.283-7.244 (m, Ph-H), 6.71 (d, 3JeH,lH) = 8.80 Hz, 16H, Ph-H), 3.234 (s, 24H, Clli), 2.323 (pt, JeH,31p) = 4.00 Hz, 8H, CHz). 3lp NMR (161.884 MHZ, CDCh, 25?C): 8 = 39.347 (s). IR(toluene, CaF2): 2359 cm-l (s, Vas N=N), 2336 cm-l (s, vsy N=N). MP: 74?C. 2.3.9 Attemptedsynthesis oftrans-bis[bis{di(p-ethylphenyl)phosphino} ethane]bis(dinitrogen)molybdenum(O)s Mg/THF ;;:P+MoCls AI= Et-{ > Equation 2.3.9 Attempted synthesis oftrans-bis[bis{di(p-ethylphenyl) phosphino}ethane]bis(dinitrogen)molybdenum(0). 66 Mg turnings (7.42 g, 0.305 mol, Aldrich 99.9%) and 1,2-bis(di(p-ethylphenyl) phosphino)ethane (2 eq, 10.0 g, 20.7 mmol) were placed into a nitrogen purged 500 mL Schlenk flask equipped with a stirring bar. THF (500 mL) and MoCls (1 eq, 2.841 g, 0.0104 mol, Aldrich 98%) were added to the mixture and the mixture was stirred vigorously at ambient temperature for 48 h. The solution was filtered over celite under nitrogen, the celite rinsed with THF (3 x 20 mL), and the combined filtrates reduced in vacuo to approximately 100 mL. Methyl alcohol (200 mL) was added at 0 ?C to precipitate a yellow solid. The resulting solid was filtered off under nitrogen, washed with methyl alcohol (3 x 20 mL), and all volatile materials were removed from the solid in vacuo. The yellow solid was dissolved in toluene (- 100 mL) and methyl alcohol (100 mL) was added to precipitate the product. Crystallization at 4 ?C gave a yellow solid which was determined by NMR to be the starting material, 1,2-bis(di(p ethylphenyl)phosphino)ethane. Spectroscopic Properties: IH NMR (Benzene): 0 = 7.370-7.332 (m, Ph-H), 7.113 (s, 8H, Ph-H), 2.318 (q, 3JeH,tH) = 7.60 Hz, 3JeH,1H) = 15.20 Hz, 8H, Cfu), 0.969 (t, 3JeH,1H) = 8.00, 12H, Clh). 31p NMR (161.884 MHZ, CDCh, 25?C): 0 =-14.774 (s). 2.3.10 O-Benzylhydroxylamine 7 Equation 2.3.10 Synthesis ofo-benzylhydroxylamine. O-benzylhydroxylamine hydrochloride (25 g, 0.157 mol, Aldrich 99%) was combined with Na2C03 (15.5 g, 0.157 mol) in 100 mL ofH20 in a nitrogen purged 250 67 mL three-necked round bottom flask equipped with a nitrogen adapter and magnetic stirring bar. The resulting aqueous suspension was stirred for approximately 15 minutes until it was converted into an oil. This biphasic liquid was saturated with NaCI and the resulting suspension was extracted with diethylether (5 x 100 mL). The etheral extracts were combined and all volatile materials were removed from them in vacuo. The light yellow oil produced was purified by distillation under oil pump vacuum to give an 83% yield (16.0 g, 0.130 mol) ofthe product as a light yellow oil. Spectroscopic Properties: BC eH} NMR (CDC!)): 0 = 136.941 (s, C-CH2), 127.700 (s, Ph-C), 127.647 (s, Ph-C), 127.146 (Ph-C), 77.088 (s, CH2). IH NMR (CDC!)): 0 =7.45-7.28 (m, 5H, Ph-H), 5.390 (s, 2H, NIh), 4.676 (s, 2H, Cfu). 2.3.11 a-Azidostyrene 8 H2C-Br I(5' H2C-Br0' K-t-BuO .. Hexanes Equation 2.3.11 Synthesis ofa-azidostyrene. 1,2-Dibromo-l-phenyl ethane (74.60 g, 0.283 mol, 99% Aldrich), sodium azide (18.37 g, 0.283 mol, 99% Aldrich), and dimethyIformamide (404 g, 5.52 mol, 430 mL, 99.8% Aldrich) were combined in a 1,000 mL round bottom flask equipped with a stirring bar and the solution was stirred at ambient temperature for approximately 12 h. Water (400 mL) and hexanes (200 mL) were then added to the solution, the organic layer was separated, and the aqueous layer was extracted with hexanes (3 x 100 mL). The combined organic extracts were dried over anhydrous Na2S04 for 1 h. The Na2S04 was 68 filtered off under nitrogen, washed with hexanes (3 x 20 mL), and all volatile materials were removed from the combined organic solutions in vacuo. The resulting solid was dissolved in toluene (- 200 mL). Potassium tert-butoxide (45.21 g, 0.403 mol, 95% Aldrich) was added to the solution and the solution was stirred for approximately 12 h. The solution was diluted with hexanes (1,000 mL) and washed with H20 (3 x 700 mL). The combined hexane solutions were dried over anhydrous Na2S04 for 1 h. The Na2S04 was filtered off under nitrogen, washed with hexanes (3 x 20 mL), and all volatile materials were removed in vacuo. The resulting solid was dissolved in hexanes (- 50 mL), filtered through a neutral Al203 column (50 cm), and the column was then eluted with hexanes (- 300 mL) until the filtrate became clear. All volatile materials were removed from the combined hexanes filtrate in vacuo to give a 74% yield (30.3 g, 0.208 mol) ofthe product as a yellow solid. Spectroscopic Properties: IH NMR (CDCh): 8 = 8.90 -7.20 (m, 5, Ph-H), 5.553 (s, IH, =Cfu), 5.076 (s, IH, =Cfu). 2.3.12 Ferrocenylamine9 Fc-H t-BuO/THF? t-BuLi Fc-Li ~ I Fc= Fe ~ Fc-NHz Equation 2.3.12 Synthesis offerrocenylamine. 69 Ferrocene (8.0 g, 0.043 mol, Aldrich 98%) and potassium tert-butoxide (0.6 g, 5.35 mmol) were combined with THF (450 mL) in a nitrogen purged 1,000 mL three necked round bottom flask equipped with a nitrogen adapter and magnetic stirring bar. Tert-butyllithium (1.7 M, 32.99 g, 0.515 mol, 50.6 mL) was added to the solution at -80 ?C over a 15 minute period and the solution was stirred for Ih at -80?C. The a azidostyrene (6.200g, 0.0375 mol) was added to the solution following which the solution was slowly allowed to warm to -10?C over 1 h and then was allowed to warm to ambient temperature. A solution of 3N HCI (~ 10.0 mL) was added drop wise over a 30 minute period to the solution. H20 (50 mL) was then added to the solution and the resulting suspension was extracted with diethylether (3 x 100 mL). The combined organic extracts were dried over anhydrous MgS04for 1 h and the MgS04 was then filtered off under nitrogen and washed with diethylether (3 x 20 mL). The ether extracts were combined and all volatile materials were removed in vacuo. The red oil which resulted was sublimed at 120?C under oil pump vacuum to give a 9% yield (0.780 g, 0.386 mmol) of the product as a crude dark red oil. Spectroscopic Properties: IH NMR (CDCh): mixture ofcis and trans: B=4.150 (s, Cp-H), 3.983 (s, Cp-H), 3.915 (s, Cp-ID, 3.831 (s, Cp-ID, 3.740 (s, Cp-ID, 2.612 (s, NIh), 2.331 (s, NIh). 2.3.13 LithioferrocenelO Fc-H a) t-BuLi I TIIF 10?C ~b) n-hexane I -80?C ~ I Fe= Fe ~ Fe-Li (5) Equation 2.3.13 Synthesis oflithioferrocene. 70 Ferrocene (40.0 g, 0.215 mol, Aldrich 98%) was combined with dry / degassed THF (250.0 mL) in a nitrogen purged 1,000 mL three necked flask equipped with a magnetic stirring bar and a nitrogen adapter. Tert-butyl-lithium (146.0 mL, 95.15 g, 0.248 mol, Aldrich 1.7 M) was added to the solution via cannula over a 15 minute period at 0 ?C. The solution was then cooled to -80?C and n-hexanes (300 mL) were added to precipitate the product. The suspension was allowed to warm to ambient temperature, filtered offunder nitrogen, and the solid was then washed with hexanes (5 x 20 mL). All volatile materials were removed from the combined organic solutions in vacuo to give a 92% yield (38.2 g, 0.198 mol) ofthe product as a yellowish pyrophoric powder. No spectroscopic properties were collected due to the pyrophoric nature of the material. Fe-Li(8) ~ I Fe= Fe ~ Fe-I Equation 2.3.14 Synthesis ofiodoferrocene. THF (200 mL, Aldrich 99.9%) was combined with lithioferrocene (24.93 g , 0.130 mol) in a nitrogen purged 1,000 mL three necked flask equipped with a magnetic stirring bar and a nitrogen adapter. The solution was cooled to -80?C following which iodine (33.06 g, 0.130 mol, Aldrich 98%) was added to the solution and the solution was then allowed to warm to ambient temperature and was stirred for a further 12 h. Diethylether (600 mL) was then added to the mixture and the solution was washed with a 10 % aqueous solution ofNa2S203 (3 x 100 mL) and H20 (3 x 100 mL). The solution was dried over anhydrous Na2S04 for 1 h and then the Na2S04 was filtered off and 71 washed with diethylether (3 x 20 mL). All volatile materials were removed from the combined organic extracts in vacuo. A 70% yield (28.5 g, 91.0 nunol) ofthe product was produced as an orange-brown oil. The oil solidified upon standing at 4 0c. Spectroscopic Properties: IHNMR (CDCh): 0 =4.412 (dd, 3JCH,l H) =2.40 Hz, 3JCH/H) =2.40 Hz, 2H, Cp-H), 4.192 (s, 5H, Cp-H), 4.154 (dd, 3JCH,1H) = 1.60 Hz, 3JCH,1H) = 1.60 Hz, 2H, Cp-ID? 2.3.15 N-fe"ocenylphthalimidelO Fc-I phtbalimide ? CU20 / pyridine / A, 48h ~ I Fe= Feo ?C-N=C ~Ar= Fe ~ ~ I Fc=Fe ~ ArI NIII CI "Ni-C=N-Ar", \ C'" Ar..... N~ C\\\ NAx Equation 2.3.25 Synthesis oftetrakis(para-isocyanoferrocenylbenzene)nickel(O). THF ( 15 mL) was combined with bis(I,5-cyclooctadiene)nickel(0) (0.386 g, 1.4 mmol, Strem 98+%) in a nitrogen purged 250mL three-necked round bottom flask equipped with a nitrogen adapter, dropping funnel, and a magnetic stirring bar. Para- 83 isocyanoferrocenylbenzene (0.160 g, 0.00701 mol) was then dissolved in dry / degassed THF ( 25.0 mL) and cooled to 0 ?C following which it was added drop wise to the solution over a 15 minute period. The solution was allowed to stir for 3 h at ambient temperature, concentrated in vacuo to approximately 20 mL, and layered with hexanes (50 mL). Recrystallization attempts at -19?C are still ongoing. 2.3.26 Tetrakis(para-nitro-isocyanobenzene)nickel(O)12 AII NIII C EtzO/O?C .. I\\Ni-C=N-AI ~C\\\\\\ \ AI..... N .... C NAt- AI= OzN{ ) Equation 2.3.26 Synthesis oftetrakis(para-nitro-isocyanobenzene)nickel(O). Diethylether (12 mL) was combined with bis(1,5-cyc100ctadiene)nickel(0) (0.279 g, 1.01 mmol, Strem 98+%) in a nitrogen purged 250mL three-necked round bottom flask equipped with a nitrogen adapter, dropping funnel, and a magnetic stirring bar. Para nitro-isocyanobenzene (0.75 g, 0.00506 mol) was then dissolved in diethylether (25 mL) and cooled to 0 ?C following which it was added drop wise to the solution over a 15 minute period. The suspension was allowed to stir for 3 h at ambient temperature producing a dark red precipitate. This solid was removed by filtration, and rinsed with hexanes (3 x 10 mL). All the volatile materials were removed from the solid in vacuo. The crude dark red product was dissolved in dry / degassed THF (Aldrich 99.9%) and the solution layered with hexanes. Recrystallization attempts at -19?C are still ongoing. 84 2.3.27 Bis[bis{di(P-ethylphenyl)phosphino}benzenejbis(isocyanoferrocene) molybdenum(O) 2 C=N-Fe + ~ I Fe= Fe ~ Equation 2.3.27 Synthesis ofbis[bis{di(p-ethylphenyl)phosphino} benzene]bis(isocyanoferrocene)molybdenum(0). THF (20 mL) was combined with isocyanoferrocene (0.10 g, 0.472 mmol) in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, dropping funnel, and a magnetic stirring bar. The dinitrogen complex13 (0.260 g, 0.214 mmol) was then dissolved in THF (75 mL) and added drop wise to the solution over a 15 minute period. After the addition ofthe dinitrogen complex, the solution was allowed to stir for 30 minutes and the precipitate was then collected by filtration and washed with hexanes (3 x 20 mL). The resulting solid was dissolved in THF (~ 20 mL) and the solution was layered with hexanes (~ 50 mL). Cooling to -19?C produced a 20% yield (0.150 g, 0.0949 mmol) ofthe product as dark orange fibrous crystals. 85 Spectroscopic Properties: IH NMR (CDCh): 7.799 (br, 8H, Ph-H), 7.304 (d, 3 IH) = 7.20 Hz, 16H, Ph H), 6.987 (d, 3JeH;H) = 8.00 Hz, l6H, Ph-H), 4.065 (br, 4H, Cp-H), 3.921 (br, lOll, Cp H), 3.774 (br, 4H, Cp-H), 2.500 (q, 3JeH;H) = 7.60 Hz, 3JeH;H) = 15.00 Hz, 16H, CHz), 1.154 (t, 3JeH;H) = 7.60 Hz, 24H, ClL). IR (benzene, CaF2): 1883 cm-l (s, v isonitrile). MP: 104?C. 2.3.28 Bis[bis{di(P-ethylphenyl)phosphino}benzene]bis(isocyanoferrocenylbenzene) molybdenum(O) ~ I Fe= Feo Equation 2.3.28 Synthesis ofbis[bis{di(p-ethylphenyl)phosphino} benzene]bis(isocyanoferrocenylbenzene)molybdenum(O). THF (20 mL) was combined with isocyanoferrocenylbenzene (0.100 g, 0.472 mmol) in a nitrogen purged 250 mL three-necked round bottom flask equipped with a nitrogen adapter, dropping funnel, and a magnetic stirring bar. The dinitrogen complex13 86 (0.260 g, 0.214 mmol) was then dissolved in THF (75 mL) and added drop wise to the to the solution over a 15 minute period. After the addition ofthe dinitrogen complex, the solution was allowed to stir for 30 minutes and the precipitate was collected by filtration and washed with hexanes (3 x 20 mL). The resulting solid was dissolved in THF (~ 20 mL) and the solution layered with hexanes (~ 50 mL). Crystallization at -19?C gave a dark purple solution. All the volatiles were then removed in vacuo and the remaining solid was dissolved in toluene, filtered under nitrogen, and layered with hexanes. Recrystallization at -19?C produced an 81% yield (0.300 g, 17.3 mmol) ofthe product as a dark purple crystalline material. Spectroscopic Properties: IH NMR (CDCh): 7.802 (br, 8H, Ph-H), 7.371 (d,3JeH,lH) = 7.60 Hz, 16H, Ph H), 6.881(d, 3JeH,tH) = 8.00 Hz, 16H, Ph-H), 6.079 (br, 8H, Ph-H), 4.405(br, 4H, Cp H), 4.078 (br, 10H, Cp-H), 3.3.905 (br, 4H, Cp-H), 2.446(q, 3JeH,l H) = 7.60 Hz, 3JeH,tH) = 15.20 Hz, 16H, Cfu), 1.093 (t, 3 eH,IH) =7.20 Hz, 24H, Cfu). IR (benzene, CaF2): 1877 cm-1 (s, v C:=:N). MP: 225?C. 87 References 1. W. Chasar, J. Org. Chem. 1985,50,545. 2. D. F. Shriver, M.A. Drezdzon, The Manipulation ofAir Sensitive compounds; 2nd ed.; Wiley & Sons: New York, 1986. 3. W. L. F. Armarego, D.D. Perrin, Purifiation ofLaboratory Chemicals; 400 ed.; BH: NewYork, 1996. 4. M. Hanack, S. Kamenzin, C. Kamenzin, L. R. Subramonian, Synthetic Metals 2000, 110,93-103. 5. G. 1. Kubas, C. 1. Bums, J. Eckert, S. W. Johnson, A. C. Larson, P. 1. Vergamini, C. 1. Unkefer, G. R. K. Khalsa, S. A. Jackson, o. Eisenstein, J. Am. Chem. Soc. 1993, 115, 569-581. 6. ADH Chemistry Experiment Papers: Hunter, A. D.: "Solid Sodium Amalgam," in Inorganic Experiments, 2nd ed.; 1. D. Woollins Ed.; VCH: New York, 2003; pp 211. 7. G. R. Knox, P. L. Pauson, D. Willison, Organometallics 1990,9,301-306. 8. G. Smolinsky, J. Am. Chem. Soc. 1962,27,3557. 9. D. Van Leusen, B. Hessen, Organometallics 2001,20,224-226. 10. B. Bildstein, M. Malaun, H. Kopacka, K. Wurst, M. Mitterbock, K. H. Ongania, G. Opromolla, P. Zanello, Organometallics 1999, 18,4323-4336. 11. P. Hu, K. Quing Zhao, H. Bo Xu, Molecules 2001, 6, M249. 12. S. D. Ittel, "Complexes ofNickel (0)," in Inorg. Synth., R.. 1. Angelici, Ed.; Wiley: New York, 1990; Vol. 28, pp 98-99. 13.1. B. UpdegraffIII, The Synthesis ofOrganometallic Nanorods from Molybdenum and Tungsten diisonitrile complexes and a New Method to Synthesize Air Stable Sodium Cyclopentadienide, Master of Science, Youngstown State University, August 2004. 88 Chapter Three - Results and Discussion 3.1 Isonitriles 3.1.1 Synthesis ofpara-methoxyisocyanobenzene In the isonitriles, the nature ofthe various alkyl and aryl substituents can be used to alter the electronic properties ofthe CN-R function. The p-anisyl group was used as a substituent on NC to enhance the solubility of the complexes and make it a more electronic rich NC. The synthesis ofpara-methoxyisocyanobenzene was done using a procedure similar to the literature method described by Hanack et al.l ?H'N)lH CIII N? Cl ? 2 + 1 CI+OyCI CHzClz/ NEt3 ? 2CI A, 2 h, 40 ?C? ? O'CH3CH3 Equation 3.1.1 Synthesis ofpara-methoxyisocyanobenzene. Under reflux conditions, para-formamidoanisole was reacted with diphosgene in the presence of triethylamine, which was used as the base, in a methylene chloride solution. Diphosgene was used as the dehydrating reagent to avoid the use ofphosgene which is a highly toxic gas that has to be synthesized each time before the reaction. With diphosgene, the reaction conditions are not as mild as with phosgene itself Thus, slightly lower yields or more forcing conditions have to be expected. Crystallization from pentane produced a 21% yield of the product as white-yellow needles exhibiting a pronounced isonitrile smell. The crystals start to melt at room temperature and have to be stored under nitrogen at -19?C to avoid rapid decomposition. Even under Nz, it decomposes at room temperature within less than an hour to leave a brown tar. 89 Recrystallization could have probably removed small amounts ofimpurities in the isolated product. Due to the loss ofvaluable material in recrystallization, however, it was decided to use the compound as is. No spectroscopic properties were recorded due to thermal sensitivity ofthe compound and the identity ofthe compound was verified by its conversion into the tetraisocyanonickel(O) (Chapter 3.1.2). 3.1.2 Synthesis of1,4-diisocyano-2,3,5,6-tetramethylbenzene To enhance the solubility ofthe isonitriles, we decided to use the tetrametylated isonitrile, 1,4-diisocyano-2,3,5,6-tetramethylbenzene, that was prepared by a method similar to the one in previous subchapter (3.1.1). H*HH H OH~ 88%H 0100?C,2h H*0=\ - ,Hl~!I)=o Equation 3.1.2 Synthesis of1,4-diisocyano-2,3,5,6-tetramethyl benzene. In the first step of its formation, the commercially available 2,3,5,6-tetramethyl phenylenediamine was reacted under reflux in a condensation reaction with formic acid and the product was precipitated with water to give 1,4-bis(N,N'-formylamido)-2,3,5,6 tetramethylbenzene as an air stable white powder in 82% yield. The compound proved to be insoluble in organic solvents and its NMR spectra were not recorded. To obtain the isonitrile, the formamide was dehydrated with diphosgene as described for the methoxy derivative (3.1.1). Initial attempts to purify the compound by 90 column chromatography and by crystallization by the layering of a methylene chloride solution with hexanes produced fairly clean material, but the workup was not very efficient. Sublimation proved to be the method ofchoice and, in this way, the compound was produced as a white crystalline material in a 34% yield. The solid is stable in air at room temperature, however, a solution ofthe compound should be kept under nitrogen to avoid decomposition. Over longer periods of time, the solid should be stored under nitrogen at 4 ?C to avoid decomposition. In the l3C NMR, a signal is observed at 168.870 ppm attributable to the carbonyl carbon atoms. The signal at 131.550 ppm is due to the carbon atoms ofthe phenyl ring that have a methyl substituent. A signal is observed at 126.724 ppm which is due to the phenyl carbon atoms attached to the isonitrile group. The signal of the methyl carbon atoms is observed at 16.366 ppm. In the lH NMR, a signal from the methyl protons is observed at 2.357 ppm. In the IR spectrum, a vibration is observed at 2115 cm-l attributable to the stretching vibration ofthe isonitrile group. The melting point of the compound was observed at 112?C. 3.1.3 X-Ray structural analysis of1,4-diisocyano-2,3,5,6-tetramethylbenzene In the course of this work, we had been able to isolate X-ray quality crystals of 1,4-diisocyano-2,3,5,6-tetramethylbenzene and, thus, we determined its solid state structure. It crystallizes in the space group C2/c with 4 molecules in the unit cell. The crystal data are summarized in Appendix 1. The bisisocyanide is located on a crystallographical inversion centre with only half the molecule being crystallographically independent. Both crystallographically independent methyl groups show a disorder ofthe H atoms which have been refined as idealized disordered methyl groups with the two positions rotated from each other by 60?. The site distributions have been refined to be approximately 0.90/0.10 and 0.72/0.28 for the two types ofmethyls. Bond length and angles are in the expected range for aromatic isonitriles. (Figure 3.1) In particular, the most important distances are shown in Table 3.1. 91 Table 3.1 Selected bond lengths (A) of1,4-diisocyano-2,3,5,6-tetramethylbenzene. NI-Cl 1.1628 (14) C3-C4 1.4008 (13) NI-C2 1.4045 (12) C3-C2 1.4070 (13) These distances are expected to vary upon coordination to a metal. In particular, it would be expected that coordination would lengthen NI-Cl and C3-C2 and shorten NI-C2 and C3-C4 due to metal ligand backbonding and the quinoidal character that it would induce to the isonitrile bridge. Figure 3.1 Molecular structure showing 30 % probability displacement ellipsoids. The disorder ofthe hydrohen atoms is shown. 3.1.4 Synthesis ofpara-nitroisocyanobenzene In order to build a library of isonitrile ligands with different electronic and solubility properties, a nitro derivative was also prepared. Para-nitroisocyanobenzene was synthesized in a similar manor to the isonitriles described in the previous subchapters (3.1.1. and 3.1.2). H o~-o-~ N02 + H - o 1/2 CI+OVO CI II ? 92 Equation 3.1.4 Synthesis ofpara-nitroisocyanobenzene. The crude product was purified by sublimation to give a 21% yield of the isonitrile as a white solid. Itwas necessary to sublime the crude product several times for complete purity. Unlike its more volatile analogues in the previous subchapters, the compound in virtually odor free. The solid is air stable but solutions should be kept under nitrogen to avoid slow decomposition. In the BC NMR, a signal that is due to the isonitrile carbon atom is observed at 169.3 ppm. The phenyl carbon atom with the nitro substituent has a signal observed at 147.3 ppm. A signal from the phenyl carbon atom attached to the isonitrile is observed at 131.0 ppm that is a triplet with a I~ coupling constant of 16.0 Hz. Two singlets are observed at 127.4 and 124.9 ppm attributable to the signals ofthe unsubstituted phenyl carbon atoms. In the IH NMR, two doublets are observed at 8.230 and 7.508 ppm with coupling constants of2 x 9.0 Hz that are due to the proton signals ofthe phenyl ring. In the IR spectrum, two separate sets ofsignals are observed. The first set using CaF2 had a strong vibration at 2121 em-I due to the isonitrile group. Two strong signals are also observed from the nitro group with an asymmetric and symmetric stretching frequency at 1520 and 1345 cm-I repectively. Using a KBr pellet, a broad absorption is observed at 2130 cm-I attributable to the isontrile. Two signals are due to the asymmetric and symmetric stretching frequencies of the nitro group respectively at 1541 and 1349 cm-I . The melting point ofthe compound was observed to be 81?C. At this point, a few comments concerning the synthesis and workup of the isonitriles should be made. To begin with, the synthesis and isolation of the crude 93 products were all very similar but the workup ofthe three isonitriles varied slightly. The thermal sensitivity ofthe methoxy derivative made it necessary to obtain a clean product by crystallization while the nitro derivative had to be sublimed several times for complete purity. The tetramethyldiisonitrile seemed to be the easiest to purify by either crystallization or sublimation. Sublimation will be used as the purification method in all subsequent reactions due to the time consuming procedure involved in the crystallization technique. The tetramethyldiisonitrile was prepared to enhance the solubility of our complexes and because it can bridge two metal centers and was selected as the main isonitrile used in our work. 3.2 Phospbines 3.2.1 Synthesis oftris(p-anisyl)phosphine The two most common types ofphosphines are alkyl and aryl substituted ones. In general, alkyl phosphines and their complexes are very soluble and more electron donating, and, thus, for many applications they would be the ligands of choice. On the other hand, they are typically very sensitive towards oxidation and are generally not easy to handle. Aryl phosphines are much less air sensitive, however, most lack the solubility of their alkyl counterparts and their complexes, especially the larger oligomers, will not be soluble enough for easy chemical manipulation. To overcome this disadvantage while keeping their enhanced stability, we introduced alkyl or ether substituents on the aryl rings. Depending on the type ofsubstituent on the aryl ligands, their net ability to transfer electron density to the aryl moiety was varied as well. Thus, a small library of aryl phosphines with different electronic as well as solubility properties was established. The first member of this library is a phosphine of the PR3 type which has the ability to be incorporated into metal complexes containing central atoms in low oxidation states. The stability of the PR3 complexes results from the combination of soft donor/soft-acceptor ligands with the soft acceptor nature of metals in low oxidation states. In the context of this research, the phosphine will be used to synthesize a dinitrogen complex ofthe type M(Nz)z(PR3)4 which will be the starting materials for the synthesis ofthe organometallic oligomers. 94 Tris(p-anisyl)phosphine was prepared using a procedure similar to the literature method described by Kubas et al.2 Equation 3.2.1 Synthesis oftris(p-anisyl)phosphine. The first step in the synthesis is the formation of the Grignard reagent by the addition ofp-bromoanisole to an iodine activated magnesium suspension. The Grignard reagent was then reacted with phosphorus trichloride in a nucleophilic substitution reaction and hydrolyzed with a 10% aqueous ~el solution to remove the unreacted Grignard reagent. After workup, crystallization from diethylether produced a 39% yield of the product as white needles. The solid is stable in air at room temperature but solutions ofthe ligand should be kept under nitrogen to avoid decomposition. In the l3e NMR, a signal is observed at 159.780 ppm attributable to the phenyl carbon atoms with the methoxy substituent. Three doublets are observed at 134.740, 114.009, and 113.895 ppm that are due to the other three phenyl carbon atoms with 31p coupling constants of 20.51, and 2 x 7.64, respectively. A singlet is observed at 55.196 ppm due to the methyl carbon atoms. In the IH NMR, a doublet of a doublet is observed from the phenyl protons at 7.220 ppm with IH and 31p coupling constants of 8.70 and 7.40 Hz respectively. A signal from the remaining phenyl protons is observed at 6.870 ppm with a coupling constant of 8.70 Hz. The singlet at 3.795 ppm is due to the methyl proton signal. The 31p NMR also has a signal observed at -10.83 ppm. 95 3.2.2 Synthesis of1,2-Bis(di(p-anisyl)phosphino)ethane In a related study, chealating phosphines that are para substituted dppe derivatives were used because they were expected to give more soluble complexes than does the parent dppe ligand. The bidentate ligands generally give complexes that are more stable than their monodentate analogues because both phosphorus atoms coordinate to the metal acid on entropic barriers to their simultaneous release being present. A library of chelating phosphines was established to allow a wide range of net electron transfer abilities to the metal center as discussed in the previous subchapter (3.2.1). 1,2-Bis(di(P-anisyl)phosphino)ethane was prepared according to the procedure in the previous subchapter (3.2.1). nClzP PCl z 1HF/rt Equation 3.2.2 Synthesis of1,2-bis(di(P-anisyl)phosphino)ethane. A Grignard reagent was prepared by combining p-bromoanisole with iodine activated magnesium in a THF solution. The Grignard reagent was then reacted with bis(dichlorophosphino)ethane in a nucleophilic substitution reaction and the mixture was hydrolyzed with a 10 % aqueous NlttCI solution to remove the unreacted Grignard reagent. After workup, the phosphine was isolated by crystallization from toluene in 40% yield as a white crystalline powder. In the IH NMR, a multiplet is observed between 7.280 and 7.241 ppm assigned to the signals ofthe phenyl protons. A doublet is observed at 6.84 ppm with a coupling constant of8.80 Hz that is due to the signal ofthe remaining phenyl protons. A pseudo triplet is observed at 2.000 ppm which is due to the 96 signal ofthe CH2 protons. A singlet is observed at 3.788 ppm attributable to the signal of the methyl protons. The 3lp NMR has a signal observed at -16.621 ppm. 3.2.3 Synthesis of1,2-Bis[di(P-ethylphenyl)phosphinojethane The next member in the library of chealating phosphines is an ethyl substituted dppe derivative. This dppe derivative should have solubility properties similar to its anisyl analogue but the ethyl substituent being a-electron donating while the methoxy group has a-electron withdrawing and 1t-electron donating effects. The electronic properties of the two derivatives will be systematically different and should prove interesting. 1,2-Bis[di(p-ethylphenyl)phosphino]ethane was prepared usmg a procedure similar to the method described in the previous subchapters (3.2.1 and 3;2.2). Et-Q-Br + Mg/THF/ A .. Et-Q-MgBr THF/rt .. Ar= Et-\ > Equation 3.2.3 Synthesis of1,2-bis[di(p-ethylphenyl)phosphino]ethane. After workup, the solid was crystallized from a toluene / hexane solution to give an 82% yield ofthe product as a white crystalline solid. The solid is stable in air at room temperature but solutions of the compound should be kept under nitrogen to avoid decomposition. In the IH NMR, a multiplet between 7.271 and 7.233 ppm is observed that is due to the protons from the phenyl ring. The remaining proton signals are observed as a doublet at 7.146 ppm with a coupling constant of 8.80 Hz. A quartet at 97 2.626 ppm is attributable to the signal ofthe CH2 protons with coupling constants of7.60 and 15.20 Hz. At 2.062 ppm, a pseudo doublet with a 31p coupling constant of4.00 Hz. The signal ofthe methyl protons is observed at 1.218 ppm that is a triplet with a coupling constant of8.00 Hz. The 31p NMR has a signal observed at -14.774 ppm. Since this reaction was completed, studies in our group have shown that the purity of the compound in Equation 3.2.3 could be significantly improved ifthe crystallization is initiatied with methanol instead of hexanes. Also, the reaction in Equation 3.2.3 was carried out using Aldrich 99.9% high purity magnesium and as a result gave a higher yield and a cleaner product in comparison to the reactions in Equations 3.2.1 and 3.2.2 that were completed in reagent grade magnesium and thus gave lower yields. The reagent grade magnesium apparently either did not allow complete reduction to occur on the surface ofthe metal, or it resulted in its partial decomposition due to the impurities as MgO or Mg(OH)z. The high purity magnesium will be therefore be used in all subsequent reactions. 3.3 Dinitrogen complexes 3.3.1 Synthesis oftrans-bis[bis{di(p-anisyl)phosphino}ethane}bis(dinitrogen) molybdenum(O) The metal-diisonitrile building blocks needed for the generation of the nano-rod complexes were synthesized using Mo and W dinitrogen complexes as the precursors. The dinitrogen complexes were synthesized by two different synthetic methods. The first method utilizes liquid sodium amalgam3 with the phosphine and MoCh in THF. The mercury contained in the sodium amalgam mixture is not only highly toxic, but its disposal is also very tedious and expensive. The second method uses high purity (99.9 %) magnesium as discussed in the previous subchapter (3.2.3) in place of the sodium amalgam. Giving comparable yields, the latter method was determined to be the method of choice because the use of a toxic reagent is eliminated, as the clean up procedure is easier, and the disposal ofthe mercury is eliminated. A series ofdinitrogen complex with various substituted phosphine ligands will be discussed. The first member in this series, trans-bis[bis{di(p-anisole) 98 phosphino}ethane]bis(dinitrogen)molybdenum(O), was synthesized by the sodium amalgam method which is a method similar to that described by Kubas et al.2 MoC15 + Equation 3.3.1 Synthesis oftrans-bis[bis{di(p-anisyl)phosphino}ethane]bis(dinitrogen) molybdenum(O). A THF solution of I,2-bis(di(p-anisyl)phosphino)ethane was combined with NaHg and MoCl5 was added to the suspension. The suspension was then stirred vigorously for 60 h under a constant pressure of nitrogen to ensure that a complete reaction occurs. After the removal ofthe NaHg by filtration, the solvent was removed in vacuo and the resulting solid was dissolved in toluene following which methanol was used to precipitate the product. A 39% yield ofthe product was produced as a yellow orange powder. This powder was determined by NMR to contain approximately 20% tetrahydride (e.g., (C30H160.J>2)2~0) which formed as side product and could not be removed via crystallization. In the 13C NMR, a signal is observed at 160.523 ppm that is due to the signal of the methoxy aryl carbon atoms. Three doublets are observed at 130.306, 134.513, and 114.558 ppm with 31p coupling constants of7.44, 11.46, and 21.12 Hz repectively. Two singlets are observed at 54.787 and 25.787 ppm that are due to the signals of the methyl and CH2 carbon atoms. In the IH NMR, a multiplet is observed between 7.283 and 7.244 ppm attributable to the phenyl proton signals. A doublet is observed at 6.71 ppm with a coupling constant of8.80 Hz that is due to the signal ofthe remaining phenyl protons. A singlet at 3.234 is observed for the signal of the methyl protons and the signal of the CH2 protons with a 31p coupling constant of 4.00 Hz is observed at 2.323 ppm. The 31p NMR has a signal observed at 39.347 ppm. In the IR 99 spectrum, an asymmetric and symmetric vibration was observed at 2359 and 2336 cm Idue to the dinitrogen group. The melting point was observed to be 74?C. The tetrahydride can be recognized by its characteristic quintet at ~ -5 ppm that is due to the proton signals ofthe hydrides. 3.3.2 AttemptedSynthesis oftrans-bis[bis{di(p-ethylphenyl)phosphino} ethane]bis(dinitrogen) molybdenum(Ol The second dinitrogen complex in this senes, trans-bis[bis{di(p-ethylphenyl) phosphino}ethane]bis(dinitrogen)molybdenum(O), was prepared by a method similar to the one in the previous subchapter (3.3.1) using the magnesium method. MoCls + ArI\Ar2 'p p-Ar/ 'AT Ar= Et-{ > Mg/nIF ~ Equation 3.3.2 Synthesis oftrans-bis[bis{di(p-ethylphenyl)phosphino}ethane] bis(dinitrogen)molybdenum(0). High purity magnesium was combined with 1,2-bis(di(p-ethylphenyl) phosphino)ethane in THF and MoCls was added to the suspension. The suspension was stirred for 48 h and then after workup, it was crystallized from a toluene / methanol mixture which produced a yellow solid that was determined by IH NMR to be the starting material 1,2-bis(di(p-ethylphenyl)phosphino)ethane. The reaction was repeated using new reagents and freshly degassed solvents and similar results were achieved. Since this reaction was completed, studies in our group have shown that using pure phosphine crystallized from methanol usually gave the desired product. In summary, as stated in subchapter 3.3.1, the high purity magnesium method is the method ofchoice to synthesize the dinitrogen complexes due to the comparable yields 100 and the elimination of hazardous materials. It has also been detennined by other members of our group that using pure phosphine crystallized from methanol is necessary to prepare the ethyl substituted dinitrogen complex. Furthermore, the methoxy substituted dinitrogen complex was found to be very soluble in solution, impeding its purification, but looking well for the usability ofits eventual oligomer products. In addition to the properties ofthe complexes already discussed, an explanation of the origins oftheir color should be given. The low intensity color (yellow-orange) of a dinitrogen complex can be attributed to the d-d transitions in the complex which are Laporte forbidden due to its center of inversion. The Laporte selection rule can be by passed by distortion of the complex from its precise octahedral symmetry with an asymmetrical vibration. Such a distortion can allow a Laporte forbidden d-d transition to occur which would promote an electron into an e orbital to create an environment in which two electrons have opposite spins. The electronic transition allows the absorbtion oflight to occur resulting in a rather intense Laporte-forbidden d-d band to be detected. 3.4 Ferrocene chemistry 3.4.1 Synthesis ofo-ben1J11hydroxylamine The central intermediate for the synthesis of ferrocenyl isocyanide is ferrocenyl amine. As explained in the introduction, several different approaches for its synthesis have been reported in the literature. The method ofKnox et al.4 describes the synthesis of ferrocenylamine usmg O-benzylhydroxylamine as the precursor. 0 benzylhydroxylamine hydrochloride is the starting material in the synthesis of 0 benzylhydroxylamine. A literature method4 describes the synthesis of 0 benzylhydroxylamine hydrochloride using O-benzylacetoxime as the precursor. The method involves the hydrolysis of O-benzylacetoxime with concentrated hydrochloric acid to produce the product, O-benzylhydroxylamine hydrochloride. 0 benzylhydroxylamine hydrochloride is commercially available and was used m this procedure to avoid the multiple step synthesis ofthe desired starting material. 101 2 Equation 3.4.1 Synthesis ofo-benzylhydroxylamine. O-benzylhydroxylamine hydrochloride was deprotonated with NaZC03 in an aqueous solution. After workup, the light yellow oil produced was purified by distillation to give an 83% yield ofthe product as a light yellow oil. A solution ofthe compound should be kept under nitrogen to avoid decomposition. Impurities are observed in the IHNMR which were removed by distillation. In the l3C NMR, a signal is observed at 136.941 ppm that is due to the signal ofthe carbon atom with the CHz substituent. The signals at 127.700, 127.647, and 127.146 ppm are attributable to the remaining phenyl carbon atoms, while a signal at 177.088 ppm is observed for the carbon atom ofthe CH2 group. In the IH NMR, a multiplet is observed between 7.45 and 7.28 ppm that is due to the signals ofthe phenyl carbon atoms. The amine proton signals are observed at 5.390 ppm and the signal from the CH2protons is observed at 4.676 ppm. The synthesis of ferrocenylamine as described by Knox et al.4 combines 0 benzylhydroxylamine with lithiated ferrocene. The mixture is acidified followed by a basic extraction. The method gives only a 12-13% yield as reported in the literature. The synthesis of ferrocenylamine using o-benzylhydroxylamine as the starting material was attempted and a no yield was obtained. 102 3.4.2 Synthesis offen-ocenylamine The alternative method described by Knox et al.4 was the most convenient method found to synthesize ferrocenylamine until a new method described by Leusen et al.5 using a-azidostyrene6 as the starting material proved to be more successful. H2C-Br6' DMF H2C-Br2) N 3 K-t-BuO ... Hexanes Fe-H t-BuO/THF t-BuLi Fe-Li CH21/o-C'N 3 1. ... 2. HCIIH20.., ~ I Fe"" Fe ~ Fe-NH2 Equation 3.4.2 Synthesis offerrocenylamine. Changes to the procedure in our hands included the use of toluene in place of benzene to avoid the use of this carcinogen. In the first step, 1,2-dibromo-l-phenyl ethane and sodium azide were reacted in dimethylformamide. Extraction with hexanes followed by the addition oftoluene and potassium tert-butoxide produced a-azidostyrene as a crude product. Purification by column chromatography produced a 74% yield ofthe vinyl azide product as a yellow solid. In the IH NMR, a multiplet is observed between 8.90 and 7.20 ppm attributable to the proton signals ofthe phenyl ring. Two CH2 proton signals are observed at 5.553 and 5.076 ppm. 103 In the synthesis offerrocenylamine using the method described by Leusen et al. 5, lithiated ferrocene was reacted with cx.-azidostyrene. Acidification of the mixture with HCI followed by hydrolysis and the precipitation with a base afforded a red oil which was purified by sublimation to give a 9% yield (0.780 g, 0.386 mmol) ofthe product as a dark red oil. The literature describes the compound as a red solid. The compound could not be purified by sublimation. Further purification techniques were not attempted due to the low yield. Column chromatography could possibly be used in future reactions to remove the impurities in the compound. In the IH NMR, a mixture ofthe cis and trans isomers are present. The signals observed at 4.150, 3.983, 3.915, 3.831, and 3.740 ppm are attributable to the proton signals ofthe Cp ring. Two signals are observed at 2.216 and 2.331 ppm that are due to the protons ofthe amine group. 3.4.3 Synthesis offerrocenylamine (Gabriel method) The most reliable route for the synthesis offerrocenylamine (Equation 3.4.3) was the Gabriel synthesis as described by Bildstein et al.7 Fe-H a) t-BuLi I THF 10?C ..b) n-hexane I -80?C Fe-Li (s) IziTHF/-80 ?C Fe-I 104 phthalimide . CuzO I pyridine I A , 48h ?~N-FC o ~ I Fe= Fe4 HzN-NHzIEtOH/A2h----==-------'=------..- Fe-NH z Equation 3.4.3 Synthesis offerrocenylarnine. In the first step, ferrocene was metallated with tert-butyllithium in THF. The main advantage of this procedure is the selective monometalation of the ferrocene. A 92% yield of the product was produced as a yellowish pyrophoric powder. Due to the pyrophoric nature ofthe material, no spectroscopic data were recorded. Lithioferrocene is a very sensitive material and was thus never stored but was always directly converted into iodoferrocene by reaction with iodine in THF. The iodo product was isolated as orange-brown oil in 70% yield. The oil solidified upon standing at 4?C. In the IH NMR, a singlet is observed at 4.192 ppm attributable to the signal of the hydrogen atoms at the unsubstituted Cp ring. The substituted Cp ring exhibits two doublets ofdoublets with coupling constants of2.40 and 1.60 Hz at 4.412 and 4.154 ppm, respectively. Starting from iodoferrocene, N-ferrocenylphthalimide was then synthesized by a copper (I) oxide catalyzed coupling reaction with phthalimide in refluxing pyridine. After workup, the product was isolated as dark red crystals in a 28% yield. In the BC NMR spectrum ofN-ferrocenyl phthalimide a peak is observed at 166.806 ppm attributable to the carbonyl carbon atoms. Two singlets are observed at 134.016 and 123.079 ppm which 105 are due to two phenyl carbon atoms. The signals observed at 88.570, 69.508, 65.537, and 62.935 ppm are attributable to the Cp carbon atoms. The IH NMR ofthe N-ferrocenyl phthalimide exhibits two multiplets at 7.897 and 7.760 ppm caused by the phenyl protons. Three proton signals are observed for the Cp rings. One ofthe signals at 4.226 ppm is a singlet that is due to the protons ofthe unsubstituted Cp ring. The other two proton signals are observed as doublets ofdoublets at 5.009 and 4.208 ppm and are due to the protons ofthe substituted Cp ring with coupling constants of2 x 2.00 Hz. Finally, ferrocenylamine was synthesized by treatment of N-ferrocenyl phthalimide with hydrazine in a Gabriel type reaction. The product was isolated in a 97 % yield as a yellow solid. The product was stable in air for short periods of time, but solutions should be kept under nitrogen to avoid decomposition. The IH NMR of ferrocenylamine exhibits a singlet at 4.099 ppm due to the proton signal of the unsubstituted Cp ring. The signals observed at 3.994 and 3.842 ppm are due to the proton signals ofthe substituted Cp ring. The amine hydrogen atoms cause the singlet at 2.588 ppm. The overall yield of ferrocenylamine is very high and consistant at approximately 90 % as compared to the 9 % yield obtained from the azide reaction. 3.4.4X-Ray structural analysis offen'ocenylamine Despite the general interest ferrocenylamine has attracted as a versatile starting material for a manifold of organometallic compounds, its solid-state structure has not been reported previously. Thus, attempts were made to grow single crystals of this important organometallic building block. By slowly cooling a saturated etheral solution down to 4?C, X-ray quality crystals were produced and the structure was determined by single crystal X-ray structural analysis at 90 K. It was found to crystallize in the tetragonal space group 141/a with a = 23.5540(15), b = 5.8964(8) A and Z = 16. A molecular representation ofthe structure is shown in Figure 3.2. 106 rr ~ H12 rr rr .. F., r ~r rr rH'25r r l.""_ifi~.242--=2: ~ H23 C23 C22 Figure 3.2 ORTEP representation offerrocenylamine. Ellipsoids are drawn at 50% probability. The ferrocenyl part of the molecule is unexceptional displaying the expected sandwich structure. Thus, the 115-cydopentadienyl rings show no significant deviation from planarity, conventional iron to ring centroid distances of 1.6564(11) and 1.6564(11) A are observed, and the two cyclopentadienyl rings deviate by only 10.5(2.9)? from an ideal staggered conformation. The average angle around the nitrogen atom is 112(2)? making the geometry slightly distorted from the ideal Sp3 geometry with the amine hydrogen atoms pointing below the plane ofthe cydopentadienyl ring. Thus, the lone pair on the nitrogen atom is in an orientation to allow interaction with the 1t-electron density ofthe adjacent aromatic ring. Consequently, an influence on the C-C bond distances due to delocalization ofthe free electron pair into the 1t* orbital might be expected. However, the average C-C bond distances of the two cydopentadienyl rings, which are 1.415(3) A for the amine substituted and 1.423(4) Afor the unsubstituted rings, do not differ significantly. One ofthe two amine hydrogen atoms is hydrogen bonded to the nitrogen atom of a neighboring molecule, forming a N-H?..N hydrogen bridge. The hydrogen acceptor 107 amine group then itself acts as a hydrogen bond donor, thus extending the hydrogen bridges to give infinite chains. (Figure 3.3) ' .. "'.:~,..e' ,,\ Figure 3.3 Representation ofthe helical chain formed by the hydrogen bridges. The ferrocenyl hydrogen atoms are omitted for clarity. Due to the uncertainty ofthe hydrogen positions, the values for the N-H and H???N distances, which are 0.85(3) and 2.414(35) A, respectively, will not be discussed in detail. The more reliable N(donor)-N(acceptor) distance of3.249(3) A is consistent with a weak to moderate interaction.8 Thus, the bond energy associated with the N-H???N can be roughly estimated to be less than 5 kcal morl . As expected for hydrogen bonds, the H-bonding interactions in ferrocenyl amine are directionally significant. Thus, the angle of the two hydrogen bonds originating at each nitrogen atom is near to 90? and by cooperation of the individual hydrogen bonds a helical chain with four-fold sYmmetry results. A hydrogen-bonded spiral is propagating along the crystallographic four fold screw axis in the direction ofthe c-axis ofthe unit cell. 108 Only four other cyclopentadienyl amme compounds have been structurally characterized to date,9 and, of those, only 1,1'-bisferrocenylamine exhibits N-H???N hydrogen bridges. This molecule is electronically and sterically very similar to ferrocenyl amine, but both of its amine groups can act as donors for hydrogen bonding and the two ferrocenylamine rings can be rotated with regard to each other. A multitude of different N-H???N interactions thus becomes possible and no cooperation of the individual hydrogen bonds to form a regular network such as is observed for ferrocenyl amine might be expected. Instead, 1,1'-bisferrocenylamine forms a complicated irregular network of hydrogen bonds ranging from 2.325 up to 2.619 A in length. Two independent molecules are found in its unit cell and the amine groups seem to be oriented in such a way as to allow for the maximum number of hydrogen bonds possible in the solid state. The carbon atoms in the Cp rings of both molecules are basically eclipsed. The amine groups in one ofthe molecules are located on eclipsed carbon atoms, those in the other molecules are rotated by one fifths ofthe Cp ring. The hydrogen atoms ofthree of the four amine groups are pointing below the planes of the cyclopentadienyl rings, while those of the forth one are located atop the Cp ring. All of the crystal data are summarized in Appendix 2. 3.4.5 Synthesis ofIsocyanoferrocene Several synthetic methods have been reported for the synthesis of isocyanides as discussed in the introduction. The method for the synthesis of isocyanoferrocene is similar to the method described in Chapter 3.1 109 OEt I Fe H~O I Fe-NH2 -------... HI(N'H A,18h ? Cl Cl+OVCl Cl II ?----------1.... Fe-N=C CH2C12 / NEt3 /2 11, 40?C ~ I Fe= Fe ~ Equation 3.4.5 Synthesis ofisocyanoferrocene. In the first step, the condensation reaction offerrocenylamine with ethyl formate produced a 76% yield offerrocenylformamide as a dark orange solid. The solid is stable in air and solution. As discussed in the introduction, due to the cis-trans isomerism and a monomer-dimer equilibrium three isomers are present in toluene solutions of formylferrocenylamine. In the IH NMR, only two singlets ofequal intensity are observed in the aldehyde and N-H region at 8.309 and 7.817 ppm, respectively. Thus, it has to be assumed that some ofthe signals are broadened out by exchange processes. In the Cp-H region three sets ofproton signals are observed with an intensity ratio ofapproximately 1: 0.9: 2. The Cp-H proton signals with an intensity ratio of 1 consist ofa singlet at 4.061 ppm and two doublets of doublets at 4.575 and 3.789 ppm with coupling constants of 4.00 Hz, are attributable to the unsubstituted and substituted Cp rings, respectively. The set with an intensity ratio of0.9 shows one singlet at 4.002 ppm for the unsubstituted Cp ring and two doublets of doublets at 3.906 and 3.695 ppm for the substituted rings with coupling constants of 4.00 Hz, respectively. The final set with the intensity ratio of 2 no exhibits a singlet at 3.985 ppm which is due to the unsubstituted Cp-H proton signal. Two doublets ofdoublets from the substituted Cp ring are found at 3.731 and 3.712 ppm with coupling constants of 3.60 Hz. The literature values reported by Knox et al.4 differ slightly from those observed here. This can be attributed to the use ofdifferent solvents and different concentrations which would be expected to affect the equilibria between the three isomers. Some impurities observable in the NMR spectra could not be removed by recrystallization. The melting point of the compound was observed at 62?C which is about 10?C degrees lower than that reported in the literature. The temperature difference seen between the literature value and the experimental value is consistent with the impurities that are seen in the NMR spectra. The formamide was then converted into the isocyanide as shown in Equation 3.4.5. The crude solid was purified by sublimation to give a 77% yield ofthe product as a dark orange solid. The product was stable in air for short periods oftime but solutions should be kept under nitrogen to avoid decomposition. In the l3C NMR, a triplet is observed at 167.04 and 7.95 ppm with l~ coupling constants of 5.23 and 15.29 Hz, respectively. Additional singlets are observed at 70.938, 70.764 and 66.860 ppm attributable to Cp carbon atoms. In the IH NMR, two doublets ofa doublet are observed at 4.089 and 3.545 ppm, with coupling constants of2 x 2.00 Hz. A singlet is observed at 3.900 ppm, is due to the proton signal ofthe unsubstituted Cp ring. In the IR spectrum, a vibration was observed at 2122 cm-I due to the isonitrile group. The melting point ofthe compound was observed to be 48?C which is in agreement with the value reported by Knox et al. IO III 3.4.6 Synthesis ofpara-fen-ocenylaniline Para-nitrophenylferrocene is the starting material for the synthesis of para ferrocenylaniline. The synthesis is similar to a method described by Hu et al. 11 eID-O-~ClNz NOz Fc-H phase transfer catalyst Sn/HO ~ I Fe= Fe ~ FC-o-NHZ Equation 3.4.6 Synthesis ofpara-ferrocenylaniline. In the first step of the reaction, ferrocene was arylated with the appropriate diazonium salt under phase transfer conditions. After workup, crystallization :from hexanes, and then further purification by sublimation, a 55% yield of the nitro complex was produced as dark purple crystals. This solid is stable in air and solution. In the IH NMR spectrum ofpara-nitrophenylferrocene, two doublets are observed at 8.513 and 7.668 ppm attributable to the phenyl proton signals. The observed coupling constant is 8.80 Hz. The substituted Cp ring exhibits two signals, which are doublets ofdoublets at 4.472 and 4.475 ppm with coupling constants of2 x 5.20 and 2 x 4.40 Hz, respectively. The proton signal ofthe unsubstituted Cp ring appears as a singlet at 4.068 ppm. In the second step ofthe reaction, para-nitrophenylferrocene was reduced to the amine with tin under acidic conditions. A solution of NaOH was then added to the suspension to give a pH of 14. After workup, a 93% yield ofthe product was produced as a dark orange solid. The solid is stable in air and solution. The IH NMR spectrum of 112 para-nitrophenylferrocene reveals the phenyl proton signals as doublets at 7.303 and 6.651 ppm with a coupling constant of8.40 Hz. Two multiplets are observed at 4.552 and 4.249 ppm that are due to the signals ofthe substituted Cp ring. The unsubstituted ring exhibits a singlet at 4.405 ppm. The amine signal is observed at as a broad singlet at 3.620 ppm. 3.4.7Synthesis ofpara-isocyanofe"ocenylbenzene The para-ferrocenylaniline was then converted into the isocyanide by the same method described in subchapter 3.4.5. Cl Cl+OVCl Cl II ? ~ I Fe= Fe ~ FC-o-N:=C Equation 3.4.7 Synthesis ofPara-isocyanoferrocenylbenzene. The final para-isocyanoferrocenylbenzene product was isolated as a dark orange solid in a 28 % yield from n-formylferrocenylaniline. The solid is air stable at room 113 temperature for short periods oftime, however, the product should be kept under nitrogen in solution to avoid decomposition. In the lH NMR spectrum, two doublets are found at 6.939 and 6.806 ppm, that are due to the phenyl proton signals with coupling constants of 8.40 Hz. The substituted Cp ring results in two proton signals at 4.282 and 4.085 ppm that are doublets of doublets with coupling constants of 2 x 2.00 and 2 x 1.60 Hz, respectively. A singlet is observed at 3.801 ppm that is due to the proton signals ofthe unsubstituted Cp ring. Inthe IR spectrum, a vibration is observed at 2120 cm-l due to the isonitrile stretching mode. The melting point was observed at 84?C. 3.5 Nickel complexes 3.5.1 Synthesis oftetrakis(para-mdhoxyisocyanobenzene)nickel(O) Ni(O) complexes are important for our project because they are expected to have tetrahedral geometries. We decided to use substituded isonitrile ligands for our research for the reasons discussed in the introduction. This will allow a library of the nickel(O) complexes to be made with a range ofproperties. The first complex in this library is tetrakis(para-methoxyisocyanobenzene) nickel(O) which was synthesized by a method similar to that reported by Ittell et al. l2 Ar=\ }-~ Ni(CODh + 4 C=N-< >-~ Et20/0?C .. Equation 3.5.1 Synthesis oftetrakis(para-methoxyisocyanobenzene)nickel(0). 114 Bis(l,5-cyclooctadiene)nickel(0) was combined with para- methoxyisocyanobenzene in an ether solution and the mixture was stirred for 2 h. An 87% yield ofthe product was collected by filtration as a crude yellow solid and purified by crystallization from THF. Inthe BeNMR, a signal is observed at 165.373 ppm which is due to the isonitrile carbons with a 1~ coupling constant of 4.73 Hz. The signals at 157.770, 126.653, 123.371, and 114.146 ppm are attributable to the carbon atoms of the phenyl rings. A signal is also observed at 55.473 ppm which is due to the carbon atoms of the methyl groups. In the IH NMR, two doublets are observed at 6.982 and 6.337 ppm with coupling constants of 8.40 Hz. A singlet is observed at 3.034 ppm that is due to the protons ofthe methyl groups. In the IR spectrum, a vibration was observed at 2017 cm-1 due to the isonitrile group. The melting point ofthe compound was observed to be 98 ?e. 3.5.2 X-Ray structure analysis ofTetrakis(para-methoxyisocyanobenzene)nickel(O) In the course ofthis work, the first tetrahedral nickel (0) complex isoelectronic to Ni04 was structurally characterized. The complex crystallizes in the orthorhombic space group P212121 with 4 molecules in the unit cell. The aromatic hydrogen atoms were taken from a difference Fourier calculation and the methyl hydrogen atoms were placed at calculated positions. All hydrogen atoms were isotropically refined. The crystal data are summarized in Appendix 3. What is interesting about this complex is that the environment around the nickel center varies from the standard tetrahedral angles of 109.5? (Figure 3.4). Table 3.2 lists the angles which are of immense interest in the complex. Table 3.2 Selected bond lengths (A) and angles e) of tetrakis(para-methoxy isocyanobenzene)nickel(0). C41-Ni1-e31 103.28 (10) C41-Ni1-ell 114.3728 (10) C31-Nil-Cl1 109.66 (9) C41-Ni1-C21 114.25 (10) C31-Ni1-e21 112.24 (10) C11-Ni1-e21 103.26 (10) Ni1-Cx 1.846 (2) (Avg.) Cx-Nx 1.174 (3) (Avg.) NX-C(aryl) 1.394 (3) (Avg.) 115 I( J~\ '~~ \" , l..-i.'4.' Figure 3.4 ORTEP plot oftetrakis(para-methoxyisocyanobenzene)nickel(O). 116 3.5.3 Synthesis oftetrakis(isocyanoferrocene)nickel(O) The next two complexes in this library contain ferrocene units that were linked to the nickel center. The synthesis oftetrakis(isocyanoferrocene)nickel(O) was attempted by a method similar to that described in the previous subchapter (3.5.1). Ni(CODh + ~N=C I4 Fe ~ ~ I Fe = Feo Equation 3.5.3 Synthesis oftetrakis(isocyanoferrocene)nickel(O). An 81% yield ofthe penta metallic product was produced as a crude dark orange powder. Attempts to recrystallize the solid from a CH2Ch / hexanes solution at -19?C proved to be unsuccessful. A dark blue solution resulted when the product was stored at 19?C for approximately 24 h. It is presumed that oxidation ofthe product occurred by 02 when it was dissolved in CH2Ch; CH2Clz was the only solvent that would dissolve the product. Attempts to dissolve the product in other organic solvents (e.g., THF and toluene) were unsuccessful. The product has not been isolated at this time. Further attempts to recrystallize the product are under way. In the IR spectra of the crude product, a vibration was observed at 2122 cm-\ attributable to the stretching vibration of the isonitrile group. 117 3.5.4 Synthesis oftetrakis(para-isocyanoferrocenylbenzene)nickel(O) This specific compound was prepared to increase the solubility of the previous nickel complex (subchapter 3.5.2) in organic solvents via the addition ofthe phenyl ring. Tetrakis(para-isocyanoferrocenylbenzene)nickel(O) was prepared by the same method as the other nickel complexes described in Chapter 3.5. Ni(CODh + 4 FC-<" ';;-N=C ~AI= Fe ~ ~ I FC=Fe ~ Equation 3.5.4 Synthesis oftetrakis(para-isocyanoferrocenylbenzene)nickel(0). The product did not precipitate out of solution. Therefore, the dark orange solution was concentrated in vacuo, layered with hexanes, and was placed at -19?C for crystallization. The product has not been isolated at this time. Recrystallization with other organic solvents are currently under way. 118 3.5.5 Synthesis oftetrakis(para-nitro-isocyanobenzene)nickel(O) To add to the various nickel complexes used in this series, an attempt was made to synthesize tetrakis(para-nitro-isocyanobenzene)nickel(O). The synthetic method was thus duplicated from Chapter 3.5. Ni(COD)z + 4 02N-Q-N::C Ar=02N <) Equation 3.5.5 Synthesis oftetrakis(para-nitro-isocyanobenzene)nickel(0). Attempts to crystallize the crude dark red solid from a THF / hexanes solution at 19?C were not successful. Recrystallization attempts are currently under way with other organic solvents. In reference to the nickel complexes, the crystallization ofthe methoxy derivative proved to be the most successful. Recrystallization attempts ofthe remaining compounds are currently in progress in varied solvents. It is hoped that the correct solvent mixtures will thus be established. 119 3.6 Nanorod building blocks 3.6.1 Synthesis ofbis[bis{di(P-ethylphenyl)phosphino}benzene}bis(ferrocenyl isocyanide)molybdenum(O) A molybdenum dinitrogen complex13 combined with two equivalents of isocyanoferrocene gave the first complex in the library of capped nanorod building blocks. The reaction scheme of bis[bis{di(p-ethylphenyl)phosphino}benzene]bis (isocyanoferrocene)molybdenum is shown in Equation 3.6.1. 2 C=N-Fe + 1HF/O?C ~ I Fe= Fe ~ Equation 3.6.1 Synthesis ofbis[bis{di(p-ethylbenzene)phosphino}benzene]bis (isocyanoferrocene)molybdenum(0). Two equivalents of isocyanoferrocene were combined with the dinitrogen complex in a THF solution and the suspension was stirred for 30 minutes. The resulting solid was crystallized at -19?C from a THF / hexanes solution to give a crude dark orange solid. The dark orange solid was then recrystallized from a toluene / hexanes solution at 19?C to produce a 20% yield of the trimetallic product as dark orange fibrous crystals. The crystals are fairly stable in air at room temperature. 120 In the IH NMR, a broad signal is observed at 7.799 which is due to the eight protons of the phenyl rings bridging the phosphorus atoms. The signals at 7.304 and 6.987 with coupling constants of7.20 and 8.00 Hz are attributable to the protons from the remaining phenyl rings. Two broad signals are observed at 4.065 and 3.774 ppm that are due to the protons from the substituted Cp ring. The broad signal observed at 3.921 ppm is due to the protons from the unsubstituted Cp ring. A quartet is observed due to the protons ofthe CH2 groups at 2.500 ppm with coupling constants of7.60 and 15.00 Hz. A signal is observed at 1.154 ppm that is a triplet with a coupling constant of 7.60 Hz attributable to the protons of the methyl group. In the IR spectrum, a vibration was observed at 2122 em-I due to the isonitrile group. The melting point ofthe compound was observed to be 104?C. An X-ray structure ofthe product was not successful due to the fibrous morphology ofthe crystal. 3.6.2 Synthesis ofBis[bis{di(P-ethylphenyl)phosphino}benzene}bis(isocyano fe"ocenylbenzene)molybdenum(O) Bis[bis{di(p-ethylphenyl)phosphino}benzene]bis(isocyanoferrocenylbenzene) molybdenum(O) was prepared as a benzene derivative of the complex in the previous subchapter 3.6.1. The reaction scheme is thus shown below (Equation 4.6.2) 121 2 C:::N-Q-Fe ~ I Fe= Fe ~ Equation 3.6.2 Synthesis ofbis[bis{di{p-ethylphenyl)phosphino}benzene]bis (isocyanoferrocenylbenzene)molybdenum(O). Recrystallization from a toluene / hexane mixture at -19?C produced an 81% yield ofthe product as a dark purple crystalline material. The solid seems stable in air at room temperature for short periods oftime. In the IH NMR, a broad signal is observed at 7.802 ppm that is due to eight protons ofthe phenyl ring bridging the phosphorus atoms. The remaining phenyl rings attached to the phosphorous atoms have signals observed at 7.371, and 6.881 ppm which are doublets with couplings constants of 7.60 Hz, and 8.00 Hz respectively. The phenyl ring attached to the ferrocene has a broad signal at 6.079 ppm. A broad signal is observed for the protons ofthe unsubstituted Cp ring at 4.078 ppm. The substituted Cp rings have two broad proton signals at 4.405 and 3.905 ppm. A quartet is observed for the protons ofthe CH2 group at 2.446 ppm with coupling constants of7.60 and 15.20 Hz. The methyl group has a signal at 1.093 which is a triplet with a coupling constant of7.20 Hz. In the IR spectrum, a vibration was observed at 1877cm-1 due to the isonitrile group. 122 The melting point ofthe compound was observed to be 225 DC. An X-ray structure of the product was not successful due to the thin crystal morphology. These complexes (Chapter 4.6) not only possess the Laporte forbidden d-d transitions as discussed in Chapter 3.3, but also a metal-to-ligand charge-transfer transition (MLCT transition) where an electron makes a transition from a d orbital ofthe central metal atom (e.g., Mo) into a 1t* orbital of the isonitrile ligand. The MLCT transitions occur with ligands that have low lying 1t* orbitals, including aromatic ligands, and are responsible for color changes in these type ofcomplexes. 123 References 1. M. Hanack, S. Kamenzin, C. Kamenzin, L. R Subramonian, Synthetic Metals 2000, 110,93-103. 2. G. 1. Kubas, C. 1. Bums, 1. Eckert, S. W. Johnson, A. C. Larson, P. 1. Vergamini, C. 1. Unkefer, G. R K. Khalsa, S. A. Jackson, O. Eisenstein, J. Am. Chem. Soc. 1993, 115, 569-581. 3. ADH Chemistry Experiment Papers: Hunter, A. D.: "Solid Sodium Amalgam," in Inorganic Experiments, 2nd Edition, 1. D. Woollins Ed., VCH: New York, 2003; pp 211. 4. G. R Knox, P. L. Pauson, D. Willison, Organometallics 1990,9,301-306. 5. D. Van Loosen, B. Hessen, Organometallics 2001,20,224-226. 6. G. Smolinsky, J. Am. Chem. Soc. 1962,27,3557. 7. B. Bildstein, M. Malaun, H. Kopacka, K. Wurst, M. Mitterbock, K. H. Ongania, G. Opromolla, P. Zanello, Organometallics 1999, 18,4323-4336. 8. G. A. Jeffrey An Introduction to Hydrogen Bonding, Oxford University Press: Oxford, 1997. 9. a) Y Takaki,; Y Sasada, J. Nitta Phys. Soc. Jpn 1959, 14, 771. b) RD. Rogers, R Shakir, 1. L. Atwood, D. W. Macomber, Y-P. Wang, M. D. Rausch, J. Chrystal/ogr. Spectrosc. Res. 1988, 18, 767. c) K. Sunkel, U. Birk, S. Soheili, C. Stramm, R 1. Teuber, Organomet. Chem. 2000, 599, 247. d) A. Shafir, M. P. Power, G. D. Whitener, 1. Arnold, Organometallics 2000, 19, 3978. 10. G. R Knox, P. L. Pauson, D. Willison, Organometallics 1990,9,301-306. 11. P. Hu, K. Quing Zhao, H. Bo Xu, Molecules 2001, 6, M249. 12. S. D. Ittel, "Complexes ofNickel (0)," in Inorg. Synth., R1. Angelici, Ed., Wiley: New York, 1990; Vol 28, pp 98-99. 13.1. B. UpdegraffIII, The Synthesis ofOrganometallic Nanorods from Molybdenum and Tungsten Diisonitrile Complexes and a New Method to Synthesize Air Stable Sodium Cyclopentadienide, Master of Science, Youngstown State University, August 2004. 124 Chapter Four-Tricarbonyl Chromium Complexes Section One Introduction The chemistry of ll-benzenechromiumtricarbonyl, (116-C6H6)Cr(COh, and its derivatives continues to be of immense interest. In our research, we are trying to synthesize low molecular weight complexes with structures similar to repeating units of organometallic polymers.1 A series of complexes were prepared with varied substituents, e.g. (116-CsHs)Fe(CO)2' Fp, groups a-bonded to arene rings, and Cr(CO)3 centers 1t bonded to these ringS. 1a,2 The structural, spectroscopic, and electrochemical data ofthese complexes will be compared to the conventional (116-arene)Cr(CO)3 complexes with main group substituents. The properties of the (116-C6H6)Cr(CO)3 complex will be measured and used as a standard for the substituted arenes. The structural and electrochemical data of the standard (116-C6H6)Cr(CO)3 complex was studied and the results were thus reported. Through X-ray characterization, it was established that the benzene ring is planar and the chromium tricarbonyl center is 1t-bonded to the benzene ring to give a 3-D tripod? ~ Cr., /1 "'coco co Figure 4.1.1 Three-dimensional tripod of(116-C6H6)Cr(CO)3. It has been reported that the chromium atom in the center of the complex contains a partial positive charge because ofthe carbonyl groups electron withdrawing effect. It has also been determined that the standard complex has a dipole moment from the benzene ring to the tripod.4 In the substituted arene complexes, the significance of 1t- 125 symmetry interactions has been proven to provide diverse alterations in the reactivityS, spectroscopic properties6, bonding7, and structures8 ofthese species that can be utilized to identify and enumerate these interactions.3c Figure 4.1.2 1t-Symmetry interactions ofsubstituted (116-arene)Cr(CO)J complexes (where D = a 1t-donor substituent, e.g. NMe, and A = a 1t acceptor substituent, e.g. NOz). The interaction between an arene and a substituent has been a vital subject matter in physical organic chemistry. As an example, it has been observed that an arene in a substituted (116-arene)Cr(CO)3 complex, e.g. (116.1,3,5-C6H3Fp3)Cr(COh, Fp = (116 CsHs)Fe(CO)l, is very nonplanar. The arene was also found to exhibit a crown like geometry where the Fp groups and the carbon atoms to which they are attached being bent significantly away from the Cr(CO)J fragment.9,1a,2a The geometry ofthe chromium complex was first thought to be due to the Fe-Cr interaction, but was later determined to be an expression ofthe 1t-donor character ofthe Fe-aryl bond.1a,lb,lc,1d,2a,Zb,9,lO In order to have a more complete understanding ofthe communication between the substituents and the rest ofthe molecule, the electrochemical data ofthe complex was evaluated. It has been determined via cyclic voltammety that the addition of a Fp group to the benzene ring of a standard Cr(CO)3 complex increases its electron richness. It was observed that the incremental effects of the electron richness were dependent upon the character of other substiuents on the benzene ring and, the relative positions of the substituents with respect to the Fp groUp?b,9 It was determined that the more electron rich the initial complex the smaller the incremental effect of each additional Fp group upon the oxidation potential. It was established that the addition ofthe first Fp group to the 126 chromium complex caused a 230-mV decrease in EO' and the third caused a l70-mV decrease in EO'.Zb A model was thus developed to test this hypothesis. A universal model was prepared to test the electronic communications between the substituents on the arene rings and the Cr(CO)3 center.14 The model was established to "predict and explain the electron richness of the chromium centers in these substituted (,,6-arene)Cr(CO)3 complexes as a function ofthe 1t-donor and / or 1t-acceptor character of the substituents.,,3c The predicted structure of the 1t-donor substituent was first recognized. 1t-donation ? Figure 4.1.3 1t-Donor interactions, D = a 1t-donor, e.g. NMez, OMe, or F. In Figure 4.3, 1t-donation contributes to the electronic structure ofthe complex via a resonance form having an exocyclic double bond, a positive charge localized on D, and a negative charge localized on the Cr(CO)3. The Cr(CO}3 center in the charge separated zwitterionic ion has an 18--electron configuration and is anticipated to repel the electron density ofthe exocyclic double bond. The 1t-donor substituent is therefore predicted to bend away from the Cr(CO)3 center. The consequence ofthis action is the loss of arene planarity and the complete nonbonding of D is expected in extreme cases.11 Similar studies were completed on complexes with 1t-acceptor substituents. ~A x-acceptance... 127 Figure 4.1.4 x-Acceptor interactions, A =a x-acceptor, e.g. C02Me, C(O)Me, or CF3. The x-acceptor substituents are also expected to have x-symmetry interactions. First, the exocyclic double bond is predicted to bend toward, and bond with, the 16 electron cationic Cr(CO)3 to complete its 18 valence electron count. The total electronic contribution from the resulting resonance form to the overall bonding ofthe complex is anticipated to be comparatively small compared to the x-donor case due to both steric reasons and also because this contribution would result in a decreased electron density on the electron deficient Cr(CO)3 center. Very little structural distortion of the complex is anticipated under these conditions for x_acceptors.3b,3C The characterization by X-ray crystallography of substituted (116-arene)Cr(CO)3 complexes such as tricarbonyl(1l-trifluoromethylbenzene)chromium(O)12 and tricarbonyl(1lfluorobenzene) chromium(O)13 have been completed. The structural data are compared with that ofrelated (1]6-arene)Cr(COicomplexes reported in the literature. 128 Section Two Experimental 4.2.1 Tricarbonyl(rl-fluorobenzene)chromium(0) Comment The compound crystallizes in the monoclinic space group nIle, with Z = 4 (Fig. 4.2.1 and Table 4.2.1a). The fluoro functional group is displaced out ofthe least-squares plane defined by the atoms C1, C2, C3, C4, C5, and C6. The F atom and its ipso C atom, C1 are bent by 0.0082 (17) and 0.0100 (8) A, respectively, away from the Cr atom. This distortion is consistent with the earlier structure-property relationship study of (rl arene)chromium(tricarbonyl)complexes3c, which revealed that 1t-donor groups on the arene bend away from the chromium fragments. The degree ofbending was shown to be strongly correlated with the 1t-donor I 1t-acceptor strength of the substituents?b It is therefore not surprising that the observed structural distortion for this F substituent is similar to that reported for the OMe group, another moderately strong 1t-donor3b, in (anisole)Cr(CO)3.3c The title compound was prepared from chromium(O) hexacarbonyl and fluorobenzene in a tetrahydrofuran/dibutyl ether mixture.14 Pale-yellow crystals were grown by the slow diffusion ofa layer ofhexane into a methylene chloride solution. 129 Table 4.2.1a Crystal data Table 4.2.1b Data colledion Cr(CJfsF)(CO)3 Broker P4 diffractometer Mr=232.13 diffractometer Monoclinic, P2I /c OJ scans a = 6.4048 (8) A Absorption correction: multi-scan(SADABS b = 11.0668 (5) A in SAINT-Plus; Broker, 1997-1999) c = 12.7124 (16) A Tmin =0.542, Tmax = 0.743 ~ = 102.940 (2) ? 8984 measured reflections V= 878.18 (19) A3 2190 independent reflections Z=4 2067 reflections with I > 20(1) Dx = 1. 756 Mg m-3 Rint = 0.023 Mo Ka radiation Bmax = 28.3? Cell parameters from 7097 reflections h=-8 ~ 8 B= 2.5?28.3? k= -14 ~ 14 J.l = 1.29 mm-I 1=-16~16 T= 100 (2) K Block, yellow 0.46 x 0.28 x 0.23 mm Table 4.2.1c Refinement Refinement on R[F > 2o(F)] = 0.025 wR(F) = 0.070 S= 1.08 2190 reflections 147 parameters All H-atom parameters refined w= 1/[ 20(1) Dx = 1.756 Mg m-3 Rint = 0.023 Mo Ka radiation ()max = 28.30 Cell parameters from 7097 reflections h= -8 ~ 8 ()= 2.5?28.3? k=-14 ~ 14 II. = 1.29 mm-I 1=-16~16 T= 100 (2) K Block, yellow 0.46 x 0.28 x 0.23 mm Table 4.2.2c Refinement Refinement on R[F > 2o(F)] =0.025 wR(F) = 0.070 S= 1.08 2190 reflections 147 parameters All H-atom parameters refined w = l/[if(Fo2) + (0.042Pi + 0.2388P] where P = (Fo2 + 2F/)/3 (l!Jcr'kax = < 0.001 ..1Pmax = 0.43 exA-3 ..1Pmin = -0.32 exA-3 134 Figure 4.2.2 ORTEP plot of title compound. Ellipsoids are at the 50% probability level. 13S Table 4.2.2d Selected geometric parameters (A, 0). Cr-Cll 1.8441 (12) 011-C11 1. 149S (IS) Cr-CI2 1.8442 (12) 012-C12 1.1S34 (1S) Cr-C13 1.8493 (12) 013-C13 1.1S21 (IS) Cr-Cl 2.21S1 (12) CI-C2 1.3908 (18) Cr-C6-2.2221 (12) CI-C6 1.406 (2) Cr-C4-2.2292 (12) C2-C3 1.4191 (17) Cr-C2-2.2343 (12) C3-C4 1.4015 (17) F-CI 1.3442 (14) C4-CS 1.4154 (16) CII-Cr-C12 90.44 (6) CS-C6 1.4047 (17) CII-Cr-C13 88.44 (5) C4-C3-C2 120.69 (11) C12-Cr-C13 87.S1 (6) C3-C4-CS 119.73 (10) F-CI-C2 118.55 (11) C6-e5-C4 120.42 (11) F-CI-C6 118.51 (11) CS-C6-el 118.24 (10) C2-CI-C6122.92 (11) 011-C11-Cr 177.82 (12) CI-C2-C3 117.97 (11) 012-C12-Cr 179.12 (11) 013-C13-Cr 179.07 (10) 136 References 1. (a) A. D. Hunter, Organometallics 1989, 8, 1118-1120. (b) A. D. Hunter, A. B. Szigety, Organometallics 1989,8,2670-2679. (c) R. Chukwu, A. D. Hunter, B. D. Santarsiero, Organometallics 1991,10,2141- 2152. (d) R. Chukwu, A. D. Hunter, B. D. Santarsiero, S. G. Bott, 1. L. Atwood, 1. Chassaignac, Organometallics 1992, 11,589-596. (e) R. Mcdonald, K. C. Sturge, A. D. Hunter, L. Shilliday, Organometallics 1992, 11, 893-899. 2. (a) A. D. Hunter, 1. L. McLernon, Organometallics 1989, 8, 2679-2688. (b) G. B. Richter-Addo, A. D. Hunter, Inorg. Chem. 1989,28,4063-4065. (c) G. B. Richter-Addo, A. D. Hunter, D. Ristic-Petrovic, 1. L. McLemon, Organometallics 1992, 11, 864-870. 3. (a) A. Solladie-Cavallo, Polyhedron 1985, 4, 901-927. (b) A. D. Hunter, V. Mozol, S. D. Tsai, Organometallics 1992, 11,2251-2262. (c) A. D. Hunter, L. Shilladay, W. S. Furey, M. J. Zaworotko, Organometallics 1992, 11, 1550-1560. (d) E. L. Muetterties, 1. R. Bleeke, E. 1. Wucherer, T. Albright, Chem. Rev. 1982, 82 (5), 499-525. 4. (a) C. M. Lukehart, Fundamental Transition Organometallic Chemistry; Brooks / Cole: Monterey, 1985, pp 1-140. (b) H. Lumbroso, C. Segard, B. Roques, Journal of Organometallic Chemistry 1973, 61, 249-260. (c) R. W. Neuse, Journal of Organometallic Chemistry 1975,99,287-295. 5. (a) 1. March, AdvancedOrganic Chemistry, Reactions, Mechanisms, andStructure, 3rd ed.; Wiley and sons: New York, 1985, pp 453-462. (b) F. A. Carey, R. 1. Sundberg, AdvancedOrganic Chemistry, PartA: Structure andMechanisms, 3rd ed.; Plenum: New York, 1990, pp 196-209. 6. G. C. Levy, R. L. Lichter, G. L. Nelson, Carbon -13 Nuclear Magnetic Resonance Spectroscopy; Wiley and Sons: New York, 1980. (b) 1. B. Stothers, Carbon -13 NMR Spectroscopy; Academic:New York, 1972. (c) 1. D. Memory, N. K. Wilson, NMR ofAromatic Compounds; Wiley and Sons: New York, 1982. (d) G. L. Nelson, G. C. Levy, 1. D. Cargioli, 1. Am. Chem. Soc. 1972,94,3089-3094. (e) D. 137 F. Ewing, Org. Magn. Reson. 1979, 12,499-524. (t) A. R. Katritzky, R. D. Topsom, Angew. Chem., Int. Ed. Eng!. 1970,9,87-100. (g) G. L. Nelson, E. A. Williams, Prog. Phys. Org. Chem. 1976,12,229-342. (h) 1. Brornilow, R. T. C. Brownlee, D. 1. Craik, M Sadek, R. W. Taft, J. Org. Chem. 1980, 45,2429-2440. (i) H. M. Hugel, D. P. Kelly, R. 1. Spear, 1. Brornilow, R. T. C. Brownlee, D. 1. Craik, Aust. J. Chem. 1979,32, 1511-1519. G) R. T. C. Brownlee, M. Sadek, Aust. J. Chem. 1981,34, 1593-1602. (k) 1. Brornilow, R. T. C. Brownlee, R. D. Topsom, R. W. Taft, JAm. Chem. Soc. 1976, 98, 2020-2022. (I) G. E. Maciel, J. 1. Natterstad, J. Chem. Phys. 1965, 42, 2427-2435. 7. (a) G. W. Dillow, P. Kebarle, 1. Am. Chern. Soc. 1989, Ill, 5592-5596. (b) S. Chowdhury, H. Kishi, G. W. Dillow, P. Kebarle, Can. J. Chem, 1989, 67, 603 61O. (c) I. R. Gould, D. Ege, 1. E. Moser, S. Farid, J. Am. Chem. Soc. 1990, 112, 4290-4301. (d) G. Ferguson 1. M. Robertson, Adv. Phys. Org. Chem. 1963, 1, 203-281. (e) W. 1. Hehre, R. W. Taft, R. D. Topsom, Prog. Phys. Org. Chem. 1966,4,31-71. (g)K. Jug, A. M. Koster, JAm. Chem. SOC. 1990, 112,6772 6777. 8. F. H. Allen, O. Kennard, R. Taylor, Acc. Chem. Res. 1983, 16, 146-153. (b) A. Domenicano, A. Vaciago, C. A. Coulson, Acta Crystal/ogr., Sect. B 1975, 31, 221-234. (c) A. Skancke, In Flouroine-ContainingMolecules; J. F. Liebman A. Greenberg, W. R. Dolbier Jr., Eds.; VCHPublishers: New York, 1988, pp 43-64. 9. G. B. Richter-Addo, A. D. Hunter, N. Wichrowska, Can. J. Chem. 1989,68,41-48. 10. (a) 1. L~ A. D. Hunter, B. D. Santarsiero, S. G. Bott, J. L. Atwood, Unpublished observations. (b) R. P. Stewart, P. M. Treichel, J. Am. Chem. Soc. 1970,92,2710-2718. 11. M. Lacoste, H. Rabao, D. Astruc, N. Ardion, E. Varet, 1. Y. Saillard, A. Le Beuze, J. Am. Chem. Soc. 1990, 112, 9548-9557. (b) L. S. Crocker, B. M. Mattson, D. M. Heinekey, Organometallics 1990,9, 1011-1016. (c) L. S. Crocker, D. M. Heinekey, J. Am. Chem. Soc. 1989, 111,405-406. (d) A. Ceccon, A. Gambaro, A. Venzo, J. Chem. Soc., Chem. Commun. 1985, 540-542. (e) A. Ceccon, A. Gambaro, A. Venzo, J. Organomet. Chem. 1984,275,209-222. (t) A. Ceccon, A. 138 Gambaro, A. M. RomaninA. Venzo, J. Organomet. Chem. 1983,254, 199-205. (g) M. Lacoste, F. Varret, L. Toupet, D. Astruc. J. Chem . Soc. 1987, 109,6504 6506. (h) R. D. Rieke, W. P. Henry, 1. S. Arney, Inorg. Chem. 1987, 26, 420-427. (i) S. N. Milligan, R. D. Rieke, Organometallics 1983, 2,171-173. 12. M. Zeller, A. D. Hunter, C. L. Perrine, 1. Payton, Acta Crystallogr., Sect. E 2004, 60, 668-669. 13. M. Zeller, A. D. Hunter, C. L. Perrine, 1. Payton, Acta Crystallogr. Sect. E 2004,60, 650-651. 14. A. D. Hunter, L. Shilliday, W. S. Furey, M. Zaworotko, J. Chem. Educ. 1998, 75, 891-893. 139 Chapter 5 Conclusion The tetramethyl bisisonitrile was selected as the main isonitrile used in our work because it can enhance the solubility ofour complexes and bridge two metal centers. The synthesis of isocyanoferrocene and para-isocyanoferrocenylbenzene were successful, but the yields need to be improved. In the synthesis ofisocyanoferrocene, a procedure using ferrocenylphthalimide as the precursor proved to be most successful. Using this method, ferrocene was first monolithated and reacted with iodine. Iodoferrocene was then converted into N-ferrocenylpthalimide and the amine was liberated using the Gabriel method. Ferrocenylformamide and N-formylferrocenylaniline, used as the precursor in the synthesis of isocyanoferrocene and para-isocyanoferrocenylbenzene, respectively, were both synthesized by a formylation reaction of the respective amine with ethyl formate. In future projects, using cyclic voltammetry, the oxidation potentials of the molybdenum or nickel centers having isocyanoferrocene or para isocyanoferrocenylbenzene ends will be determined depending on other substituents on the molecules. The work completed in this thesis is very valuable and will contribute to the success ofpolymer synthesis in our group. 140 Appendix 1: Crystallographic Data Tables for 1,4-Diisocyano-2,3,5,6 tetramethylbenzene Table 1.1 Crystal data Table 1.2 Data collection CSH12N2 Broker SMART CCD area-detector Mr = 184.24 diffractometer Monoclinic, C2/c OJ scans a = 17. 1518 (17) A Absorption correction: none b=5.1324(5)A 4935 measured reflections c = 12.3670 (12) A 1257 independent reflections (3 = 112.010 (2) 0 1181 reflections with 1> 20'(1) V= 100.32.02 (17) A3 Riot = 0.080 2=4 omax = 28.30 Dx = 1.221 Mg m-3 h=-22 ~21 Mo Ka radiation k=-6 ~6 Cell parameters from 4202 reflections 1=-16~16 0= 2.6?28.3? f.J = 0.07 mm-1 T= 100 (2) K Block, colorless 0.50 x 0.35 x 0.35 mm Table 1.3 Refinement Refinement on R[P > 2o(P)] = 0.046 wR(P) = 0.131 S = 1.05 1257 reflections 69 parameters H-atom parameters constrained w = 1/[if(Fo2) + (0.0698Pi + 0.449P] where P = (Fo2 + 2F/)/3 (Ncr)max = 0.016 8pmax = 0.32 exA-3 8Pmin = -0.27 exA-3 141 Figure 1.1 ORTEP plot oftitle compound. Ellipsoids are at the 50% probability level. Table 1.4 Selected geometric parameters (A, 0). Nl-el 1.1628 (14) C3-eS 1.5106 (13) Nl-e2 1.4045 (12) C4-e6 1.5105 (13) C3-e4 1.4008 (13) C2-e4 1.4065 (13) C3-C2 1.4070 (13) C3-e4-C6 121.39 (8) CI-Nl-e2 178.30 (10) C2i-C4-C6 120.69 (9) C4-C3-e2 117.65 (9) Nl-e2-e4i 117.59 (8) C4-e3-e5 121.14 (8) N1-e2-e3 117.99 (8) C2-e3-e5 121.20 (9) C4i-C2-e3 124.42 (9) C3-e4-C2 117.92 (9) Appendix 2: Crystallographic Data Tables for Ferrocenylamine 142 Table 2.1 Crystal data Table 2.2 Data coUection ClOHllN:zFeI Broker SMART CCD area-detector Mr= 201.05 diffractometer tetragonal,14I/a OJ scans a = b =23.5540 (15) A Absorption correction: semiempiracle from c = 5.8964 (8) A multi scans V= 3271.3 (5) A3 15654 measured reflections Z= 16 2037 independent reflections Dx = 1.633 .g cm3 2001 reflections with 1> 20(1) Mo Ka radiation Rint = 0.0240 Cell parameters from 5819 reflections (J max = 28.290 (J= 1.73?28.29? h = -31 ~ 31 f.L = 0.07 mm-I k = -31 ~ 31 T=90(2)K 1= -7 ~ 7 needle, yellow-orange 0.60 x 0.11 x 0.06 mm Table 1.3 Refinement Refinement on R[P > 2o(P)] = 2001 wR(P) =0.0822 S= 1.343 2037 reflections 153 parameters H atoms treated by a mixture of independent and constrained refinement w = 1/[d(Fo2) +(0.0698Pi + 0.6662P] where P = (Fo2 + 2F/)/3 (Ncrbx =0.001 ~Pmax: =0.493 exA-3 ~Pmin = -0.254 exA-3 Figure 1.1 ORTEP plot oftitle compound. Ellipsoids are at the 50% probability level. H14 "~~..:.:;;;.;;.:~ .....- 143 Figure 2.2 Representation of the helical chain formed by the hydrogen bridges. The ferrocenyl hydrogen atoms are omitted for clarity. 144 145 Table 2.4 Selected geometric parameters (A, 0). Fel-en 2.025 (2) Cll-Nl-RlB 112 (2) Fel-C14 2.031 (2) Cll-Nl-RlA 113 (2) Fel-e24 2.042 (2) RlB-Nl-RlA 111 (3) Fel-e25 2.044 (2) N1-e11-e15 125.2 (2) Fel-e23 2.046 (2) Nl-ell-e12 125.6 (2) Fel-e12 2.050 (2) CII-CIS-e14 108.0 (2) Fel-e22 2.051 (2) C23-e24-e2S 107.8 (2) Fel-e2l 2.055 (2) C22-e2l-e25 107.6 (2) Fel-ell 2.097 (2) C2l-e2S-e24 108.4 (2) Cl5-ell 1.420 (3) Cl4-e13-e12 108.1 (2) C15-e14 1.427 (3) Cn-e14-e15 107.9 (2) Nl-ell 1.406 (3) C2l-e22-e23 108.0 (2) Nl-RIB 0.85 (4) CIS-ell-e12 108.1 (2) NI-RIA 0.85 (3) C24-e23-e22 108.2 (2) C24-e23 1.408 (4) Cll-e12-e13 107.8 (2) C24-e25 1.416 (4) C2l-e22 1.414 (4) C21-e25 1.416 (4) Cn-e14 1.418 (4) C13-eI2 1.428 (4) C22-e23 1.420 (4) C11-e12 1.422 (4) Appendix 3: Crystallographic Data Tables for Tetrakis (para-methoxyisocyanobenzene)nickel(O) 146 Table 3.1 Crystal data Table 3.2 Data collection C32H28N4Ni04 Bruker SMART CCD area-detector Mr= 591.21 diffractometer Orthorhombic, P2I2I2I OJ scans a = 9.6709 (8) A Absorption correction: multi-scan b = 15.2324 (13) A (SADABS in SAINT+; Bruker,1997-1999) c = 19.0955 (16) A Tmin = 0.74297, Tmax = 0.86 V= 2813.0 (4) A3 28954 measured reflections Z=4 6979 independent reflections Dx = 1.396 Mg m-3 6048 reflections with I > 20(1) Mo Ka radiation Rint = 0.0474 A= 0.71073 A emax = 28.28? Cell parameters from 7213 reflections h=-12~21 e = 2.3605-28.2675? k= -20 ~20 J..l = 0.734 rom-I 1= -24 ~ 25 T= 100 (2)K Block, yellow 0.4 x 0.4 x 0.2 rom 147 Table 3.3 Refmement Figure 3.1 ORTEP plot oftitle compound. Ellipsoids are at the 50% probability level. Refinement on R[P > 2o(P)] = 0.0382 wR(P) = 0.0824 S= 1.049 6979 reflections 374 parameters H-atom parameters constrained w =1/[ci'(Fo2) + (0.0418Pi + O.OOOP] where P = (Fo2 + 2Fc2)/3 (Ma)max =0.001 dPmax = 0.733 exA"3 dPmin =-0.236 exA-3 N3 t.1. N ..~}1~ l 148 Table 3.4 Selected geometric parameters (A, 0). Nil-e41 1.840 (2) C24-e23-H23 119.8 Ni1-e31 1.846 (2) C22-e23-H23119.8 Ni1-e11 1.847 (2) C45-e46-C47 119.3 (2) Nil-e21 1.852 (2) C45-e46-H46 120.4 C31-N3 1.171 (3) C47-e46-H46 120.4 N3-e32 1.392 (3) C15-01-e18 117.5 (2) 02-e25 1.367 (3) C47-e42-C43 120.0 (2) 02-e28 1.427 (3) C47-e42-N4 121.3 (2) Cll-N1 1.169 (3) C43-e42-N4118.7 (2) C41-N4 1.181 (3) C36-e37-e32 120.4 (2) C21-N2 1.173 (3) C36-e37-H37119.8 N2-e22 1.395 (3) C32-e37-H37 119.8 N4-e42 1.398 (3) C37-e36-e35 119.6 (2) 04-e45 1.374 (3) C37-e36-H36 120.2 04-e48 1.425 (3) C35-e36-H36 120.2 N1-e12 1.392 (3) C44-e43-e42 120.1 (2) 03-e35 1.362 (3) C44-C43-H43120.0 03-e38 1.435 (3) C42-e43-H43 120.0 C23-e24 1.377 (3) 04-e45-e44 114.9 (2) C23-e22 1.390 (3) 04-e45-e46 124.5 (2) C23-H230.9500 C44-e45-e46 120.6 (2) C46-e45 1.389 (3) C27-e22-e23 119.8 (2) C46-e47 1.394 (3) C27-e22-N2 121.0 (2) C46-H46 0.9500 C23-e22-N2 119.1 (2) 01-e15 1.373 (3) C23-e24-e25 119.9 (2) 01-e18 1.429 (3) C23-C24-H24 120.0 y 1'+:::- j C4Z-C47 1.386 (3) CZS-CZ4-H241Z0.0 j C42-C43 1.398 (3) 02-eZ8-H28A 109.5 j C37-C36 1.380 (3) 02-eZ8-H28B 109.5 j C37-C32 1.389 (3) H28A-CZ8-H28B 109.5 j C37-H370.9500 02-C28-H28C 109.5 j C36-C35 1.392 (3) H28A-C28-H28C 109.5 C36-H36 0.9500 H28B-C28-H28C 109.5 j C43-C44 1.371 (3) C43-C44-e45 lZ0.0 (2) j C43-e43 0.9500 C43-C44-H44120.0 j C45-C44 1.388 (3) C45-C44-H44 120.0 j C2Z-e27 1.386 (3) CI7-C12-N1 120.3 (2) j j CZ4-e25 1.399 (3) CI7-C12-C13 120.0 (2) j C24-H240.9500 NI-C12-C13 119.7 (2) j C28-H28A 0.9800 C37-C32-N3 120.0 (2) j C28-H28B 0.9800 C37-C32-C33 120.3 (2) j C28-H28C 0.9800 N3-e32-e33 119.6 (2) j j C44-H44 0.9500 C22-C27-e26 120.3 (2) j CIZ-e17 1.391 (3) CZ2-e27-H27 119.9 j CI2-C13 1.396 (3) C26-C27-H26119.9 j C32-C33 1.395 (3) C34-C33-e32 119.3 (2) j C27-C26 1.392 (3) C34-e33-H33 120.3 j CZ7-H270.9500 C32-C33-H33 120.3 j j C33-C34 1.383 (3) 03-e35-C36 lZ4.8 (2) j C33-H33 0.9500 03-C35-C34 115.0 (Z) j C35-C34 1.397 (3) C36-C35-C34 120.1 (2) j Cl4-e13 1.379 (3) C13-C14-e15 119.7 (2) j Cl4-e15 1.389 (3) C13-C14-H14 120.2 j j CI4-H14 0.9500 CI5-C14-HI4 120.2 j C34-H34 0.9500 C33-C34-C35 120.Z (Z) j Cl6-C17 1.374 (3) C33-C34-e34119.9 j Cl6-C15 1.394 (3) C35-C34-H34 119.9 j j j j j j j j j Cl6-H16 0.9500 C48-H48A 0.9800 C48-H48B 0.9800 C48-H48C 0.9800 C47-H47 0.9500 C17-H17 0.9500 C26-C25 1.391 (3) C26-H260.9500 C38-H38A 0.9800 C38-H38B 0.9800 C38-H38C 0.9800 C13-H13 0.9500 C18-H18A 0.9800 C18-H18B 0.9800 C18-H18C 0.9800 C41-Ni1-e31 103.28 (10) C41-Ni1-e11 114.3728 (10) C31-Nil-e11 109.66 (9) C41-Nil-e21 114.25 (10) C31-Ni1-e21 112.24 (10) C11-Nil-e21 103.26 (10) N3-C31-Nil176.41(19) C31-Ni3-e32 176.9 (2) C25-G2-e28 117.31 (17) N1-e11-Nil 177.7 (17) N4-C41-Ni1 173.6 (2) N2-e21-Nil 174.3 (2) C21-N2-e22 163.4 (2) C41-N4-C42 160.0 (2) C45-G4-C48 117.36 (18) Cll-N1-e12 170.0 (2) C17-e16-C15 120.1 (2) C17-e16-H16 120.0 C15-e16-C16120.0 04-C48-H48A 109.5 04-C48-H48B 109.5 H48A-e48-H48B 109.5 04-C48-H48C 109.5 H48A-C48-H48C 109.5 H48B-e48-H48C 109.5 C42-e47-C46 120.0 (0) C42-e47-H47 120.0 C46-C47-H47120.0 Cl6-C17-e12 119.9 (2) Cl6-C17-H17120.1 C12-e17-H17120.1 C25-e26-C27 119.6 (2) C25-e26-H26120.2 C27-e26-H26 120.2 02-e25-e26 124.9 (2) 02-e25-e24 115.2 (2) C26-C25-C24 119.9 (2) 03-C38-H38A 109.5 03-e38-H38B 109.5 H38A-e38-H38B 109.5 03-e38-H38C 109.5 H38A-e38-H38C 109.5 H38B-e38-H38C 109.5 01-e15-e14 124.5 (2) 01-e15-e16 115.2 (2) Cl4-C15-e16 120.2 (2) C14-e13-e12 120.0 (2) 150 C3S-03-e38 116.63 (19) C24-C23-e22 120.4 (2) C24-C23-H23 119.8 C22-e23-H23119.8 C4S-e46-C47 119.3 (2) Cll-N1-e12 170.0 (2) C3S-03-e38 116.63 (19) C24-e23-e22 120.4 (2) Cl4-C13-H13 120.0 C12-e13-H13 120.0 01-e18-H18A 109.S 01-e18-H18B 109.5 H18-e18-H18B 109.5 OI-e18-H18C 109.5 H18A-e18-H18C 109.5 H18B-C18-HI8C 109.5 lSI