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Polynuclear Metallocene Complexes Incorporating Ansa-Chromocene

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Polynuclear Metallocene Complexes Incorporating Ansa-Chromocene Polynuclear Metallocene Complexes incorporating Ansa -Chromocene and Ferrocene Units Dissertation to receive the Degree of a Doctor in Natural S ciences Presented by Dipl. -Chem. Ralph Zehnder from Bergneustadt Handed in at Fachbereich 8 of the Universität -Gesamthochschule Siegen Siegen 2002 urn:nbn:de: hbz:467 -296 Day of oral examination: 04.02.2003 Examiners: Prof. Dr. Wenclawiak Prof. Dr. Shapiro Prof. Dr. Deiseroth Abstract Novel bimetallic and trimetallic complexes containing ansa -chromocene units have been synthesized by a ligand substitution approach. The carbonyl ligands of the corresponding ansa -chromocene carbonyl complexes were substituted by the mono - and diisocyanide species ferrocenylisocyanide, ferrocenyldiisocyanide, and 1,4 - phenylene diisocyanide in order to form polymetallic complexes that might exhibit mixed valence behavior. The heteronuclear complexes containing a ferrocene unit show a remarkable stability against thermolysis and photolysis. Crystallographic data show that the C -N-C bond angles and Cr -C bond distances of these species follow the trend of other ansa -chromocene isocyanides that show a moderate dependence of the Cr 2+/3+ redox potential on the substituents of the isocyanide groups. In contrast, the heteron uclear complexes do not follow such a trend in respect to their electronic properties. Interestingly, these complexes can modulate the electron density at the Cr metal centers, which enables them to keep their redox potentials constant. Neuartige ansa -Chr omocenk omplexe mit zwei bzw. drei Metallzentren wurden mittels Ligandensubstitut ion synthetisiert. Die Carbonyl -Liganden der entsprechenden ansa - Chromocenca rbonylk omplexe wurden von den Isocyanid derivaten Ferrocenisocyanid, Ferrocendiisocyanid und 1,4 -Phen yldiisocyanid substituiert, um mehrkernige Komplexe zu e rhalten, die eventuell gemischt valente Eigenschaften aufweisen könnten. Die heteronuklearen ansa -Chromocenk omplexe mit einer Ferroceneinheit zeigen eine beachtliche Stabilität in Bezug auf Photolyse u nd Thermolyse. Kristallografische D aten zeigen, dass die C -N-C Bindungswinkel und Cr -C Bindungslängen dem Trend anderer Isocyanide folgen, die eine gewisse Abhängigkeit des Cr 2+/3+ Redoxpotentials von der Art der Substituenten an den Isocyanidgruppen aufwe isen. I m Kontrast dazu folgen die heteronuklearen Komplexe nicht solch einem Trend in Bezug auf ihre elektronischen Eigenschaften. Interessanterweise können diese Komplexe die Elektronendichte an den Cr Metallzentren regulieren , was es ihnen ermöglicht, ih re Redoxpotentiale konstant zu halten. 1able of Contents I able of Contents 1. Introduction .....................................................................................................................1 1.1. The Historical Development of Metallocene Complexes of t he Early Transition Metals ....................... 1 1.2. The Goal of this Work ................................ ................................ ................................ ........................... 13 1.2.1. Ansa -Chromocene(III) Complexes ................................ ................................ ................................ ... 13 1.2.2. Polynuclear Ansa -Chromocene(II) isocyanide Complexes ................................ .............................. 13 2. Analytical Methods ........................................................................................................ 15 2.1. NMR -Spect roscopy ................................ ................................ ................................ ............................... 15 2.2. IR -Spectroscopy ................................ ................................ ................................ ................................ .... 18 2.3. UV -VIS -NIR Spectroscopy ................................ ................................ ................................ .................... 22 2.4 . Cyclic Voltammetry ................................ ................................ ................................ ............................... 25 2.5. Magnetic Susceptibility ................................ ................................ ................................ ......................... 29 2.5.1. Association of Magnetic Susceptibility and Magnetic Moment ................................ ....................... 29 2.5.2. The Johnson Matthey Magnetic Susceptibility Balance ................................ ................................ ... 32 2.5.3. The Evans NMR Method ................................ ................................ ................................ ................. 35 3. Experimentals ............................................................................................................... 36 3.1. General Considerations ................................ ................................ ................................ ........................ 36 3.2. Preparation of the Starting Materials ................................ ................................ ................................ ... 38 3.3. Preparation of all new Polynuclear Ansa -Chromocene isocyanide Complexes ................................ ... 39 3.3.1. {1,1’ -(trans -1,2 -diphenylethano) dicyclopentadienyl} (ferroc enyl isocyanide) chromium(II) ......... 39 3.3.2. Bis {1,1’ -(trans -1,2 -diphenylethano) dicyclopentadienyl} (1,1’ -ferrocenyldiisocyanide) chromium(II) ................................ ................................ ................................ ................................ .... 40 3.3.3. Bis {1,1’ -(tetramethylethan o) dicyclopentadienyl} (1,1’ -ferroceny ldiisocyanide) chromium(II) ... 41 3.3.4. Bis {1,1’ -(tetrame thylethano) dicyclopentadienyl} (1,4 -phenylene diisocyanide ) chromium(II ) ... 41 3.4. Chemical Oxidation of Heteronuclear Complexes ................................ ................................ ................ 42 3.4.1. Oxidation of {1,1’ -(trans -1,2 -diphenylethano) dicyclo pentadienyl} (ferrocenylisocyanide) chromium(II) ................................ ................................ ................................ ................................ .... 42 3.4.2. Oxidation of Bis {1,1’ -(trans -1,2 -diphenylethano) dicyclo pentadienyl} (1,1’ -ferrocenyl - diisocyanide) chromium(II) ................................ ................................ ................................ .............. 43 3.5. Determination of the Effective Magnetic Moments ................................ ................................ ............... 44 3.5.1. Johnson Matthey Magnetic Susceptibility Balance ................................ ................................ .......... 44 3.5.2. Evans Method using the NMR Device ................................ ................................ ............................. 45 3.5.3. Correction Values ................................ ................................ ................................ ............................. 46 1able of Contents II 4. Results .......................................................................................................................... 47 4.1. Electrochemistry of Ansa -Chromocene Complexes ................................ ................................ .............. 47 4.2. Generation of ansa -Chromocene(III) halide Complexes ................................ ................................ ...... 49 4.3. Synthesis, Physical and Electronic Properties of Hetero nuclear and Homobinuclear Ansa - Chromocene isocyanide Complexes ................................ ................................ ................................ ...... 54 0.3.1. Synthesis of Ferrocenylisocyanide De rivatives ................................ ................................ ................ 54 4.3.1.1. Synthesis of Ferrocenylisocyanide ................................ ................................ ......................... 54 4.3.1.2. Synthesis of Ferrocenyldiisocyanide: ................................ ................................ ..................... 56 4.3.2. New Synthetic Route to Ansa -Chromocene isocyanides ................................ ................................ .. 57 4.3.3. Synthesis of Neutral Polynuclear Ansa -Chromocene isocyanides ................................ ................... 59 4.3.4. Characterization with NMR - and IR -Spectroscopy ................................ ................................ .......... 60 4.3.5. Ligand Exchange with CO ................................ ................................ ................................ ............... 67 4.3 .6. Electrochemistry and X -Ray Single Crystal Structures ................................ ................................ ... 68 4.3.7. UV -VIS Spectroscopy ................................ ................................ ................................ ...................... 76 4.4. Chemical Oxidation of Heteronuclear A nsa -Chromocene isocyanide Complexes .............................. 77 4.4.1. Oxidation of 3 and 4a with the Ferrocenylium Cation as well as Benzoquinone ............................. 77 4.4.2. Determination of the Effective Magnetic Moments ................................ ................................ ......... 82 5. Discussion ..................................................................................................................... 85 6. Conclusions ................................................................................................................... 91 7. Future Work .................................................................................................................
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