Silylene Extrusion from Organosilanes via Double Geminal Si-H Bond Activation by a Cp*Ru(κ~2-P,N)~+ Complex: Observation of a Key Stoichiometric Step in the Glaser-Tilley Alkene Hydrosilylation Mechanism

摘要

Treatment of Cp*RuCI(k~2-P,N-2b) (2b = 2-MMe_2-3-PPr_2-indene) with TISO_3CF_3 produced the cyclometalated complex [4]~+SO_3CF_3- in 94% isolated yield. Exposure of [4]~+X~- (X = B(C_6F_5)_4 or SO_3CF_3) to Ph_2SiH_2 (10 equiv) or PhSiH_3 afforded the corresponding [Cp(μ-p.N-2b)(H)_2Ru=SiRPh]~+X~- complexes, [5]~+X~- (R = Ph; X = B(C_6F_5)_4, 82%; X = SO_3CF_3, 39%) and [6]~+X~- (R = H; X = B(C_6F_5)_4, 94%; X = SO_3CF_3, 95%). Notably, these transformations represent the first documented examples of Ru-mediated silylene extrusion via double geminal Si-H bond activation of an organosilane—a key step in the recently proposed Glaser-Tilley (G-T) alkene hydrosilylation mechanism. Treatment of [5]~+B(C_6F_5)_4~- with KN-(SiMe_3)_2 or [6]~+SO_3CF_3~- with NaN(SiMe_3)_2 afforded the corresponding zwitterionic Cp(μ-2-NMe_2-3-PPr_2-indenide)(H)_2Ru=SiRPh complex in 69% (R = Ph, 7) or 86% (R = H, 8) isolated yield. Both [6]~+X~- and 8 proved unreactive toward 1 -hexene and styrene and provided negligible catalytic turnover in the attempted metal-mediated hydrosilylation of these substrates with PhSiH3, thereby providing further empirical evidence for the required intermediacy of base-free Ru=Si species in the G-T mechanism. Isomerization of the P,N-indene ligand backbone in [6]~+X~-, giving rise to [Cp*(μ-1-PPr_2-2-NMe_2-indene)(H)_2Ru==SiHPh]~+X-([9]~+X~-), was observed. In the case of [9]~+SO_3CF_3~-, net intramolecular addition of the Ru=Si-H group across the styrene-like C=C unit within the ligand backbone to give 10 (96% isolated yield) was observed. Crystallographic characterization data are provided for [4]~+X~-, [5]~+X~-, [6]~+X~-, 8, and 10.