Conformational aspects of mononuclear and heterobinuclear metal complexes containing the bent metallocene thiolate fragment /
| Main Author: | |
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Bent metallocene thiolate complexes of group 4-6 metals adopt either an endo or an exo conformation of the thiolate ligands relative to the Cp ligands. A series of para substituted bent niobocene thiolate complexes (Nb^lV, d^1 C[p2]Nb(S-p-C6H4X) 2 where X = OCH3, CH3, H, Cl and CF3 were synthesized to systematically examine the electronic effects of the thiolate ligands on the structure and physical properties of the complexes while minimizing steric differences within the series. X-ray crystal structures of the complexes where X = OCH3, CH3, H, and CF3 revealed a preference for the exo conformation while both neutral and cationic (Nb^V , d^0) forms of X = Cl were found to adopt the endo form. The neutral complex must adopt the endo conformation due to factors other than electronic considerations alone. The substituents were found to affect solution spectra (UV-vis, CV and NMR) in a uniform fashion. Heterobimetallic complexes containing the d^0 bent titanocene thiolate fragment show ^1H NMR Cp signal equilibration resulting from fluxionality of the thiolate ligand. The ΔG for the interconversion of endo-anti and endo-syn conformations for Cp2Ti(μ-S-p-C6H4X)2Mo(CO) 4 where X = OCH3, CH3, H and Cl ranged from 52 to 55 kJ/mol as determined from half height line widths a t the coalescence temperature from VT ^1H NMR spectra. A bond breaking process was probed as a possible mechanism for the Cp signal equilibration by the reaction of CO with the complexes Cp2Ti(μ-S-p-C6 H4 X)2Mo(CO)4 where X = OCH3 and Cl to form Mo(CO)6 . For the dissociative mechanism, ΔG was calculated at the coalescence temperature (NMR) of the respective complexes and found to be 88.1 kJ/mol (268 K) for X = OCH3 and 88.3 kJ/mol (258 K) for X = Cl. The bond breaking mechanism was rule out as the mechanism of interconversion as determined by comparison of the ΔG+ for the bond breaking process and the ΔG+ calculated from the VT ^1H NMR data. Pyramidal inversion of sulfur would be a more reasonable choice for the mechanism of fluxionality. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xv, 158 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |