Reactivity of a Titanocene Pendant Si-H Group toward Alcohols. Unexpected Formation of Siloxanes from the Reaction of Hydrosilanes and Ph3COH Catalyzed by B(C6F5)3

The reaction of [Cp(eta(5)-C5H4CH2SiMe2H)TiCl2] (1; Cp = eta(5)-C5H5) and methanol in the presence of catalytic amounts of B(C6F5)(3) afforded a complex with a pendant silyl ether group, [Cp(eta(5)-C5H4CH2SiMe2OMe)TiCl2] (2), in good yield. The analogous reaction of 1 and Ph3COH resulted in the unexpected formation of [CpTiCl2{mu-eta(5):eta(5)-(C5H4)CH2SiMe2OSiMe2CH2(C5H4)}TiCl2,Cp] (4). The formation of siloxanes from the reaction of 2 equiv of hydrosilane with Ph3COH mediated by B(C6F5)(3) has a general applicability and proceeds in two consecutive steps: (i) transfer of the hydroxyl group from the trityl moiety to the silicon atom and (ii) silylation of the silanol formed in situ with the second equivalent of hydrosilane. The different hydrosilane reactivity toward Ph3COH in comparison with other alcohols can be attributed to the easy generation of the borate salt [Ph3C](+)[(C6F5)(3)B(mu-OH)B(C6F5)(3)](-) (5) under catalytic conditions. The intramolecular Si-H and Ti-Cl exchange in 1 is catalyzed by B(C6F5)(3) in the presence of no alcohol. This process affords presumably a transient titanocene hydrido chloride, which is either chlorinated to give [Cp(eta(5)-C5H4CH2SiMe2Cl)TiCl2] (3) in CD2Cl2 or decomposes into several paramagnetic Ti(III) species in toluene-d(8). Complex 3 was independently synthesized from 1 and Ph3CCl in a good yield.