Strategic Design and Refinement of Lewis Acid鈥揃ase Catalysis by Rare-Earth-Metal-Containing Polyoxometalates

详细信息    查看全文

• 作者：Kosuke Suzuki ; Midori Sugawa ; Yuji Kikukawa ; Keigo Kamata ; Kazuya Yamaguchi ; Noritaka Mizuno
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：June 18, 2012
• 年：2012
• 卷：51
• 期：12
• 页码：6953-6961
• 全文大小：366K
• 年卷期：v.51,no.12(June 18, 2012)
• ISSN：1520-510X

文摘

Efficient polyoxometalate (POM)-based Lewis acid鈥揵ase catalysts of the rare-earth-metal-containing POMs (TBA₆RE-POM, RE = Y³⁺, Nd³⁺, Eu³⁺, Gd³⁺, Tb³⁺, or Dy³⁺) were designed and synthesized by reactions of TBA₄H₄[纬-SiW₁₀O₃₆] (TBA = tetra-n-butylammonium) with RE(acac)₃ (acac = acetylacetonato). TBA₆RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic oxygen-enriched surfaces of negatively charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, respectively. Consequently, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-containing POMs via the simultaneous activation of coupling partners on the same POM molecules. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C鈺怬 bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examined, the neodymium-containing 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鈥?9%). In particular, the turnover frequency (714鈥?00 h^鈥?) and the turnover number (23鈥?00) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts.