Metal-to-metal silyl migration and silicon-carbon bond cleavage/re-formation processes in the methylene/silyl complexes Cp{sup *}{sub 2}Ru{sub 2}({mu}-CH{sub 2})(SiR{sub 3})({mu}-Cl)
- Univ. of Illinois, Urbana, IL (United States). School of Chemical Sciences
Ruthenium methylene/silyl complexes of stoichiometry Cp{sup *}{sub 2}Ru{sub 2}({mu}-CH{sub 2})(SiR{sub 3})({mu}-Cl), where SiR{sub 3} = SiMe{sub 3} (1), SiEt{sub 3} (2), SiMe{sub 2}Et (3), and SiMe{sub 2}Ph (4), are produced when [Cp{sup *}RuCl]{sub 4} is treated with the appropriate dialkylmagnesium reagent, Mg(CH{sub 2}SiR{sub 3}){sub 2}. Each complex undergoes two fluxional processes as observed by variable-temperature {sup 1}H NMR spectroscopy. The low-temperature exchange process is migration of the SiR{sub 3} unit from one Ru center to the other, whereas the high-temperature process is the reversible re-formation of the C-Si bond between the silyl group and the bridging methylene unit. The activation parameters for the low-temperature exchange process in 1--4 are sensitive to the nature of the silyl group: {Delta}H{sup {double_dagger}} becomes smaller and {Delta}S{sup {double_dagger}} becomes more negative if the SiR{sub 3} group bears nonidentical or larger, more flexible substituents. This finding suggests that the transition state for this exchange process is crowded or characterized by different amounts of solvent reorganization depending on the SiR{sub 3} group involved. In contrast, the activation parameters for the high-temperature process in 1--4 are relatively independent of the nature of the silyl ligand. The small variation in the activation parameters for reformation of the C-Si bond is consistent with a noncrowded transition state in which the solvent reorganization is relatively independent of the nature of the SiR{sub 3} group.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Keck Foundation (United States); National Insts. of Health, Bethesda, MD (United States); National Science Foundation, Washington, DC (United States)
- DOE Contract Number:
- FG02-91ER45439
- OSTI ID:
- 354374
- Journal Information:
- Organometallics, Vol. 18, Issue 10; Other Information: PBD: 10 May 1999
- Country of Publication:
- United States
- Language:
- English
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