Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Nat Chem. 2010 Jan;2(1):61-5. doi: 10.1038/nchem.467. Epub 2009 Nov 29.
Selective coupling of oxygenates is critical to many synthetic processes, including those necessary for the development of alternative fuels. We report a general process for selective coupling of aldehydes and methanol as a route to ester synthesis. All steps are mediated by oxygen-covered metallic gold nanoparticles on Au(111). Remarkably, cross-coupling of methanol with formaldehyde, acetaldehyde, benzaldehyde and benzeneacetaldehyde to methyl esters is promoted by oxygen-covered Au(111) below room temperature with high selectivity. The high selectivity is attributed to the ease of nucleophilic attack of the aldehydes by the methoxy intermediate-formed from methanol on the surface-which yields the methyl esters. The competing combustion occurs via attack of both methanol and the aldehydes by oxygen. The mechanistic model constructed in this study provides insight into factors that control selectivity and clearly elucidates the crucial role of Au nanoparticles as active species in the catalytic oxidation of alcohols, even in solution.
含氧物的选择性偶联对于许多合成过程至关重要，包括开发替代燃料所需的过程。我们报告了一种通过含氧金属金纳米粒子在 Au(111)上介导的醛和甲醇选择性偶联的一般方法，用于酯合成。值得注意的是，在室温以下，含氧 Au(111)促进甲醇与甲醛、乙醛、苯甲醛和苯乙醛的交叉偶联，生成甲酯，具有高选择性。高选择性归因于醛的亲核攻击容易发生，甲醇在表面上形成的甲氧基中间体——生成甲酯。竞争燃烧通过甲醇和醛都被氧攻击发生。本研究构建的机理模型提供了控制选择性的因素的深入了解，并清楚地阐明了 Au 纳米粒子作为醇催化氧化中活性物种的关键作用，即使在溶液中也是如此。
