Substitution reactions at a bridging silicon ligand. Formation of a bis(μ-silylene) complex containing a trifluoroacetoxy group. Mechanistic studies of the site-exchange process of the hydride ligands

Article abstract of DOI:10.1021/om049328h

Treatment of a bis(μ-diphenylsilyl) complex, {Cp*Ru(μ- η²-HSiPh₂)}₂(μ-H)(H) (2a, Cp* = η⁵-C₅Me₅), with trifluoroacetic acid in toluene resulted in introduction of a trifluoroacetoxy group on a bridging silicon atom with concomitant loss of one phenyl group as benzene, affording a mixed-bridging bis(μ-silylene) complex, {Cp*Ru(μ-H)} ₂{μ-SiPh(OCOCF₃)}(μ-SiPh₂) (3b), in moderate yield. Nucleophilic addition of the acetoxy group took place in the intermediate μ-silyl,μ-silylene complex (Cp*Ru)₂(μ- η²-HSiPh₂)(μ-SiPh₂)(μ-CFs ₃CO₂)(μ-H)(H) (7), containing a bridging carboxylate group. The trifluoroacetoxy group of 3b underwent nucleopbilic displacement at the bridging silicon atom, which afforded the mixed-bridging bis(μ-silylene) complexes {Cp*Ru(μ-H)}₂(μ-SiPhX)(μ-SiPh₂) (3c, X = OMe; 3d, X = OH) upon treatment with methanol and aqueous KOH, respectively. VT NMR studies of 3b, 3c, 3d, {Cp*Ru(μ-H)} ₂(μ-SiPhMe)(μ-SiMe₂) (3e), and {Cp*Ru(μ-H) (μ-SiPhMe)}₂ (3f-syn) revealed a linear correlation between the electronic nature of the substituants on the bridging silicon atom and the activation parameters of the hydride site-exchange process occurring in the bis(μ-silylene) complex.