Diezi Simon, Ferri Davide, Vargas Angelo, Mallat Tamas, Baiker Alfons
Department of Chemistry and Applied Biosciences, ETH Zurich, Hönggerberg, HCI, CH-8093 Zurich, Switzerland.
J Am Chem Soc. 2006 Mar 29;128(12):4048-57. doi: 10.1021/ja057586f.
In the Pt-catalyzed hydrogenation of 1,1,1-trifluoro-2,4-diketones, addition of trace amounts of cinchonidine, O-methyl-cinchonidine, or (R,R)-pantoyl-naphthylethylamine induces up to 93% ee and enhances the chemoselectivity up to 100% in the hydrogenation of the activated carbonyl group to an OH function. A combined catalytic, NMR and FTIR spectroscopic, and theoretical study revealed that the two phenomena are coupled, offering the unique possibility for understanding the substrate-modifier-metal interactions. The high chemo- and enantioselectivities are attributed to the formation of an ion pair involving the protonated amine function of the chiral modifier and the enolate form of the substrate. DFT calculations including the simulation of the interaction of a protonated amine with the enolate adsorbed on a Pt 31 cluster revealed that only the C-O bond next to the CF3 group of the substrate is in direct contact with Pt and can be hydrogenated. The present study illustrates the fundamental role played by the metal surface and indicates that also the enol form can be the reactive species in the hydrogenation of the activated ketone on chirally modified Pt.
在铂催化的1,1,1-三氟-2,4-二酮氢化反应中，添加痕量的辛可尼定、O-甲基辛可尼定或(R,R)-泛酰萘乙胺，可使对映体过量率高达93%，并将活化羰基氢化为羟基官能团的化学选择性提高到100%。一项结合催化、核磁共振和傅里叶变换红外光谱以及理论研究表明，这两种现象是相互关联的，为理解底物-改性剂-金属相互作用提供了独特的可能性。高化学选择性和对映选择性归因于涉及手性改性剂的质子化胺官能团和底物烯醇盐形式形成的离子对。包括模拟质子化胺与吸附在Pt₃₁簇上的烯醇盐相互作用的密度泛函理论计算表明，只有底物CF₃基团旁边的C-O键与Pt直接接触并可被氢化。本研究说明了金属表面所起的基本作用，并表明烯醇形式也可以是手性改性铂上活化酮氢化反应中的活性物种。
