Influence of Lewis Acid and Solvent in the Hydrosilylation of Aldehydes and Ketones with Et3SiH; Tris(pentafluorophenyl)borane B(C6F5)3 versus Metal Triflates [M(OTf)3; M = Sc, Bi, Ga, and Al] – Mechanistic Implications
✍ Scribed by Peter Bach; Andrea Albright; Kenneth K. Laali
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 140 KB
- Volume
- 2009
- Category
- Article
- ISSN
- 1434-193X
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✦ Synopsis
Abstract
The scope of the B(C~6~F~5~)~3~‐catalyzed hydrosilylation of (X)Ph–CH=O and (X)Ph–C(R)=O was expanded to include a large set of substitutents (X = H, p‐Me, o‐Me, p‐F, o‐F, p‐Cl, p‐Br, p‐NO~2~, m‐NO~2~, p‐Et; R = Me or CF~3~). Reactions proceed at room temperature with high chemoselectivity in a host of solvents (toluene, benzene, CCl~4~, 1,2‐dichloroethane, 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(C~6~F~5~)~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)~3~‐catalyzed reactions thus represent a practical method for the synthesis of dibenzyl ethers. Remarkably, substantial amounts of dibenzyl ether was formed in the B(C~6~F~5~)~3~‐catalyzed reactions, when MeCN was used as solvent. Mechanistic implications of these Lewis acid catalyzed reactions are discussed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)