Efficient polyoxometalate (POM)-based Lewis acid-base catalysts of the rare-earth-metal-contg. POMs (TBA6RE-POM, RE = Y3+, Nd3+, Eu3+, Gd3+, Tb3+, or Dy3+) were designed and synthesized by reactions of (TBA)4H4[ﾎｳ-SiW10O36] (TBA = Bu4N) with RE(acac)3 (acac = acetylacetonato). TBA6RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic O-enriched surfaces of neg. charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, resp. Consequently, cyanosilylation of carbonyl compds. with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-contg. POMs via the simultaneous activation of coupling partners on the same POM mols. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C=O bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examd., the Nd-contg. POM showed remarkable catalytic performance for cyanosilylation of various kinds of structurally diverse ketones and aldehydes, giving the corresponding cyanohydrin trimethylsilyl ethers in high yields (13 substrates, 94-99%). In particular, the turnover frequency (714,000 h-1) and the turnover no. (23,800) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts. [on SciFinder(R)]
各種検索
サポート
ヘルプ