Busygin Igor, Taskinen Antti, Nieminen Ville, Toukoniitty Esa, Stillger Thomas, Leino Reko, Murzin Dmitry Yu
Laboratory of Organic Chemistry, Abo Akademi University, FI-20500 Turku/Abo, Finland.
J Am Chem Soc. 2009 Apr 1;131(12):4449-62. doi: 10.1021/ja809070g.
Assessing the origin of asymmetric induction in heterogeneously catalyzed hydrogenation is a challenging task. In this work, hydrogenation of a chiral compound, (R)-1-hydroxy-1-phenyl-2-propanone [(R)-PAC], in toluene over cinchonidine modified and unmodified Pt/Al(2)O(3) was studied. To reveal the detailed reaction mechanism and the origin of stereoselectivity in the Pt-catalyzed hydrogenation of the CO double bond, the structures and energies of several adsorption modes of (R)-PAC as well as whole reaction paths for hydrogenation were investigated on Pt(111) by density functional theory (DFT). In agreement with experimental results, the theoretically obtained potential energy profiles for the studied hydrogenation mechanisms implied that (1R,2S)-1-phenyl-1,2-propanediol is formed in excess with respect to the other diastereomeric product diol, (1R,2R)-1-phenyl-1,2-propanediol. Generally, if the elementary hydrogen addition step was thermodynamically more favorable on one of the two diastereotopic faces, it was also kinetically preferred on the same face, and vice versa. Pairwise addition of hydrogen was the most energetically favorable mechanism. Adsorption and hydrogenation of other structurally similar chiral alpha-hydroxyketones, (R)-3-hydroxy-2-butanone and (R)-2-hydroxy-1-cyclohexanone, were also studied computationally on Pt(111). The results showed that cluster model DFT calculations can be used to assess (dia)stereoselectivity in metal-catalyzed hydrogenation of even such complex organic molecules as studied here.
评估非均相催化氢化中不对称诱导的起源是一项具有挑战性的任务。在这项工作中，研究了手性化合物（R）-1-羟基-1-苯基-2-丙酮[（R）-PAC]在甲苯中于辛可尼定修饰和未修饰的Pt/Al₂O₃上的氢化反应。为了揭示Pt催化的CO双键氢化反应的详细机理和立体选择性的起源，采用密度泛函理论（DFT）在Pt（111）上研究了（R）-PAC的几种吸附模式的结构和能量以及氢化反应的整个路径。与实验结果一致，理论上获得的所研究氢化机理的势能剖面图表明，相对于另一种非对映体产物二醇（1R，2R）-1-苯基-1,2-丙二醇，（1R，2S）-1-苯基-1,2-丙二醇过量生成。一般来说，如果在两个非对映异位面之一上，基本的氢加成步骤在热力学上更有利，那么在同一面上它在动力学上也更受青睐，反之亦然。成对加氢是能量上最有利的机理。还在Pt（111）上通过计算研究了其他结构相似的手性α-羟基酮（R）-3-羟基-2-丁酮和（R）-2-羟基-1-环己酮的吸附和氢化反应。结果表明，簇模型DFT计算可用于评估甚至像本文所研究的这种复杂有机分子在金属催化氢化中的（非对映）立体选择性。
