Kieffer Ian A, Treich Nicholas R, Fernandez Jordan L, Heiden Zachariah M
Department of Chemistry, Washington State University, Pullman, WA 99164, USA.
Dalton Trans. 2018 Mar 12;47(11):3985-3991. doi: 10.1039/c7dt04929c.
Hydride transfer promoted by the coordination of a substrate molecule to a Lewis acid is a critical step in many catalytic transformations. This computational study investigates the nature of the interaction between a polar substrate molecule and a Lewis acid by examining the influence of Lewis acid strength on the ability to reduce (transfer a hydride to) the coordinated substrate molecule. To investigate this interaction, the coordination of 10 probe substrates to seven Lewis acids was analyzed. Coordination of the probe substrate molecules to a Lewis acid resulted in a more favorable reduction of the substrate molecule by 20-70 kcal mol. Further examination of the coordination of the substrate molecules to Lewis acids of varying Lewis acid strengths resulted in a direct linear correlation between the ability of the Lewis acid-substrate adduct to accept a hydride and the Lewis acid strength. The linear correlations also revealed that between 44 and 70% of the Lewis acidity of the Lewis acids translated to the Lewis acid-substrate adducts. From the results obtained in this study, the minimum Lewis acid strength needed to activate the substrates for the reduction with [BH] and the implications of employing a Lewis acid to promote the reduction of an unsaturated polar substrate in catalytic reactions are also described.
底物分子与路易斯酸配位促进的氢化物转移是许多催化转化中的关键步骤。这项计算研究通过考察路易斯酸强度对还原（将氢化物转移至）配位底物分子能力的影响，来探究极性底物分子与路易斯酸之间相互作用的本质。为研究这种相互作用，分析了10种探针底物与7种路易斯酸的配位情况。探针底物分子与路易斯酸配位导致底物分子的还原更有利，能量降低20 - 70千卡/摩尔。进一步考察底物分子与不同路易斯酸强度的路易斯酸的配位情况，发现路易斯酸 - 底物加合物接受氢化物的能力与路易斯酸强度之间存在直接线性关系。线性关系还表明，路易斯酸44%至70%的路易斯酸度转化到了路易斯酸 - 底物加合物中。根据本研究获得的结果，还描述了用[BH]还原底物所需的最低路易斯酸强度，以及在催化反应中使用路易斯酸促进不饱和极性底物还原的意义。
