Silylene extrusion from organosilanes via double geminal Si-H bond activation by a Cp*Ru(k2-P,N)+ complex:: Observation of a key stoichiometric step in the Glaser-Tilley alkene hydrosilylation mechanism

Treatment of (CpRUCI)-R-*(k(2)-P,N-2b) (2b = 2-NMe2-3-(PPr2)-Pr-i-indene) with TISO3CF3 produced the cyclometalated complex [4]+SO3CF3- in 94% isolated yield. Exposure of [4]X-+(-) (X = B(C6F5)(4) or SO3CF3) to Ph2SiH2 (10 equiv) or PhSiH3 afforded the corresponding [Cp-*(mu-P,N-2b)(H)(2)Ru=SiRPh]X-+(-) complexes, [5]X-+(-) (R = Ph; X = B(C6F5)(4), 82%; X = SO3CF3, 39%) and [6]X-+(-) (R = H; X = B(C6F5)(4), 94%; X=SO3CF3, 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+(C6F5)(4)(-) with KN-(SiMe3)(2) or [6]+SO3CF3- with NaN(SiMe3)(2) afforded the corresponding zwitterionic Cp-*(mu-2-NMe2-3-(PPr2)-Pr-i-indenide)(H)(2)Ru=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-*(mu-1-(PPr2)-Pr-i-2-NMe2-indene)(H)(2)Ru=SiHPh]X-+(-)([9]X-+(-)), was observed. In the case Of [9]+SO3CF3-, 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.