Cho Woo Kyung, Lee Jungkyu K, Kang Sung Min, Chi Young Shik, Lee Hee-Seung, Choi Insung S
Department of Chemistry and School of Molecular Science (BK21), Center for Molecular Design and Synthesis, KAIST, Daejeon 305-701, Korea.
Chemistry. 2007;13(22):6351-8. doi: 10.1002/chem.200601791.
Gold had been considered to be an extremely inert metal, but recently it was found that nanometer-sized gold particles on metal-oxide supports acted as catalysts for simple organic reactions, such as oxidation and hydrogenation, even at or below room temperature. Herein, we report that gold nanoparticles (AuNPs) of zero oxidation state (Au0) are catalytically active for a C--C bond-forming reaction, the cyanosilylation of aldehydes. The AuNP-catalyzed cyanosilylation proceeded smoothly at room temperature with 0.2 wt % loading of AuNPs. The reactions of aromatic aldehydes were almost quantitative, except for benzaldehyde derivatives containing the electron-withdrawing NO2 group, and alpha,beta-unsaturated aromatic aldehydes were the most reactive substrates. The reactions also went smoothly for aliphatic aldehydes. Mechanistic studies indicated that the reactions proceeded both homogeneously and heterogeneously: homogeneous catalysis by leached gold species and heterogeneous catalysis by the adsorption of the reactants (aldehydes and trimethylsilyl cyanide) onto AuNPs. The ratio of homogeneous and heterogeneous catalysis was estimated to be approximately 4:1.
金一直被认为是一种极其惰性的金属，但最近发现，负载在金属氧化物载体上的纳米级金颗粒即使在室温或室温以下，也能作为简单有机反应（如氧化和氢化反应）的催化剂。在此，我们报道零氧化态的金纳米颗粒（AuNP）对醛的氰基硅基化反应（一种碳-碳键形成反应）具有催化活性。在室温下，当AuNP负载量为0.2 wt%时，AuNP催化的氰基硅基化反应顺利进行。除了含有吸电子基团NO2的苯甲醛衍生物外，芳香醛的反应几乎是定量的，α,β-不饱和芳香醛是最具反应活性的底物。脂肪醛的反应也进行得很顺利。机理研究表明，该反应以均相和非均相两种方式进行：浸出的金物种进行均相催化，反应物（醛和三甲基硅基氰）吸附在AuNP上进行非均相催化。均相催化与非均相催化的比例估计约为4:1。
