AbstractThe scope of the B(C6F5)3âcatalyzed hydrosilylation of (X)PhâCH=O and (X)PhâC(R)=O was expanded to include a large set of substitutents (X = H, pâMe, oâMe, pâF, oâF, pâCl, pâBr, pâNO2, mâNO2, pâEt; R = Me or CF3). Reactions proceed at room temperature with high chemoselectivity in a host of solvents (toluene, benzene, CCl4, 1,2âdichloroethane, and methylcyclohexane), or under solventless conditions, with hydrosilylation yields ranging from 85 to 95 % (for aldehydes) and 71 to 100 % (for ketones) and no noticeable solvent dependency of hydrosilylation yields. Replacing B(C6F5)3 for M(OTf)3 (M = Bi, Al, Ga, Sc) causes a dramatic change in chemoselectivity, forming dibenzyl ether and benzylated solvent (with toluene and benzene), with hydrosilylation products becoming negligible in most cases. The M(OTf)3âcatalyzed reactions thus represent a practical method for the synthesis of dibenzyl ethers. Remarkably, substantial amounts of dibenzyl ether was formed in the B(C6F5)3âcatalyzed reactions, when MeCN was used as solvent. Mechanistic implications of these Lewis acid catalyzed reactions are discussed.(© WileyâVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)