Abstract：
Herein the reaction mechanism and the origin of stereoselectivity of asymmetric hydrogenation of oximes to hydroxylamines catalyzed by the cyclometalated iridium (III) complexes with chiral substituted single cyclopentadienyl ligands (Ir catalysts A1 and B1) under acidic condition were unveiled using DFT calculations. The catalytic cycle for this reaction consists of the dihydrogen activation step and the hydride transfer step. The calculated results indicate that the hydride transfer step is the chirality-determining step and the involvement of methanesulfonate anion (MsO-) in this reaction is of importance in the asymmetric hydrogenation of oximes catalyzed by A1 and B1. The calculated energy barriers for the hydride transfer steps without an MsO- anion are higher than those with an MsO- anion. The differences in Gibbs free energies between TSA5-1fR/TSA5-1fS and TSB5-1fR/TSB5-1fS are 13.8/13.2 (ΔΔG‡ = 0.6 kcal/mol) and 7.5/5.6 (ΔΔG‡ = 1.9 kcal/mol) kcal/mol for the hydride transfer step of substrate protonated oximes with E configuration (E-2a-H+) with MsO- anion to chiral hydroxylamines product R-3a/S-3a catalyzed by A1 and B1, respectively. According to the Curtin-Hammet principle, the major products are hydroxylamines S-3a for the reaction catalyzed by A1 and B1, which agrees well with the experimental results. This is due to the non-covalent interactions among the protonated substrate, MsO- anion and catalytic species. The hydrogen bond could not only stabilize the catalytic species, but also change the preference of stereoselectivity of this reaction.
摘要：
本文使用DFT计算揭示了在酸性条件下，具有手性取代的单环戊二烯基配体的环金属化铱（III）配合物（Ir催化剂A1和B1）催化的肟不对称氢化为羟胺的反应机理和立体选择性起源。该反应的催化循环由二氢活化步骤和氢化物转移步骤组成。计算结果表明，氢化物转移步骤是手性确定步骤，甲磺酸根阴离子（MsO-）参与该反应对于A1和B1催化的肟的不对称氢化具有重要意义。没有MsO-阴离子的氢化物转移步骤的计算能垒高于具有MsO-阴离子的那些。TSA5-1fR/TSA5-1fS和TSB5-1fR/TSB5-1fS之间的吉布斯自由能差异为13.8/13.2（ΔΔG=0.6kcal/mol）和7.5/5.6（ΔΔΔG=1.9kcal/mol）kcal/mol，分别由具有E-2a羟基胺和M3a阴离子结构的底物质子化肟的氢化物转移根据Curtin-Hammet原理,A1和B1催化反应的主要产物是羟胺S-3a，与实验结果吻合良好。这是由于质子化底物之间的非共价相互作用，MsO-阴离子和催化物种。氢键不仅可以稳定催化物种，但也改变了该反应的立体选择性的偏好。
