Successive Si−H/Si−C Bond Cleavage of Tertiary Silanes on Diruthenium Centers. Reactivities and Fluxional Behavior of the Bis(μ-silylene) Complexes Containing μ-Hydride Ligands

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Abstract

A series of μ-silylene complexes was synthesized by way of sequential Si−H and Si−C bond scission of tertiary silanes on diruthenium centers generated from Cp*Ru(μ-H)4RuCp* (1; Cp* = η5-C5Me5). While both bis- and mono(μ-diphenylsilylene) complexes, {Cp*Ru(μ-SiPh2)(μ-H)}2 (3a) and {Cp*Ru(μ-H)}2(μ-SiPh2) (4a), were obtained in the case of Ph3SiH, the reactions of 1 with Ph2MeSiH and PhMe2SiH exclusively afforded bis(μ-silylene) complexes, {Cp*Ru(μ-SiPhMe)(μ-H)} (3b-syn/anti) and {Cp*Ru(μ-H)}2(μ-SiPhMe)(μ-SiMe2) (3c), respectively. The Si−C bond scission proceeded via prior π-coordination of the phenyl group of the intermediary formed silyl groups, which was supported by the fact that the reaction of 1 with (CH2CH)RSiH2 (R = Ph, Me) afforded exclusively the mono(μ-silylene) complex {Cp*Ru(μ-H)}2(μ-SiEtR) (4b, R = Me; 4c, R = Ph) as a result of intramolecular coordination of the vinyl group. Reaction of a mixture of 3b-syn and 3b-anti with PMe3 afforded the bis(μ-silylene) complex {Cp*Ru(μ-SiPhMe)}2(PMe3)(H)2 (5), which adopted only the syn structure with respect to the two bridging silylene ligands. Isomerization of the anti to the syn form arose from rotation of the bridging silylene ligands, which was confirmed by the VT-NMR studies of 3b-syn and 3c. While reactions of 3 with H2 and CO afforded respectively the bis(μ-silyl) complexes {Cp*Ru(μ-η2-HSiR2)}2(μ-H)(H) (2) and bis(μ-silylene) complexes containing two terminal carbonyl groups {Cp*Ru(CO)(μ-SiR2)}2 (6), liberation of the bridging silylene ligand of 4 was observed during the reaction with H2 and CO, together with formation of the mono(μ-silylene) complex {Cp*Ru(CO)}(μ-CO)(μ-SiR1R2) (8a, R1 = R2 = Ph; 8b, R1 = Me, R2 = Et; 8c, R1 = Ph, R2 = Et). X-ray diffraction studies were performed on 3c, 4a,b, 5, and 8a,b, and they clearly demonstrated the bridging silylene structures of these complexes.

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