Qin Hua-Li, Zhao Chuang, Leng Jing, Kantchev Eric Assen B
State Key Laboratory of Silicate Materials for Architectures, School of Chemistry, Chemical Engineering, and Life Science, Wuhan University of Technology, 122 Luoshi Road, Wuhan, 430070, Hubei, P.R. China.
School of Chemistry and Chemical Engineering, Hefei University of Technology, 193 Tunxi Road, Hefei, 230009, Anhui, P.R. China.
Chemistry. 2017 Nov 13;23(63):15997-16003. doi: 10.1002/chem.201703096. Epub 2017 Oct 19.
The [(dppe)RhCl]-catalysed ring expansion of 2-methylbenzocyclobutenone has been proposed to occur by C-C oxidative addition to rhodaindanone, β-hydride elimination, hydrorhodation and C-C reductive elimination. DFT calculations [IEFPCM(1,4-dioxane, 383.15 K)/PBE0/DGDZVP level of theory] here confirm this mechanism. As proposed, oxidative addition into CHMe-CO bond is preferred over the alternative CHMe-aryl insertion. The barriers of oxidative addition, β-hydride elimination hydrorhodation, and reductive elimination are 23.6 (rate-determining), 8.9, 10.4, and 13.1 kcal mol , respectively. Therefore, the β-hydride elimination/hydrorhodation steps to/from an octahedral Rh -hydride serve as a fast equilibrating hydrogen shuffle flanking the two slower C-C bond breaking/making steps. This is consistent with the weak kinetic isotope effect observed experimentally when 2-CH and 2-CD benzocyclobutenone react competitively in a 1:1 ratio. The reaction barriers calculated with more modern, dispersion interaction-corrected methods (SMD/M06 and IEFPCM/ωB97xD) follow identical trends.
已提出[(dppe)RhCl]催化的2-甲基苯并环丁烯酮的扩环反应是通过碳-碳氧化加成生成铑茚满酮、β-氢消除、氢化铑化和碳-碳还原消除来进行的。此处的密度泛函理论计算[IEFPCM(1,4-二氧六环，383.15 K)/PBE0/DGDZVP理论水平]证实了这一机理。如所提出的，氧化加成到CHMe-CO键比另一种CHMe-芳基插入更有利。氧化加成、β-氢消除、氢化铑化和还原消除的势垒分别为23.6（速率决定）、8.9、10.4和13.1 kcal·mol⁻¹。因此，八面体铑氢化物的β-氢消除/氢化铑化步骤作为一个快速平衡的氢转移，位于两个较慢的碳-碳键断裂/形成步骤两侧。这与当2-CH和2-CD苯并环丁烯酮以1:1比例竞争性反应时实验观察到的较弱动力学同位素效应一致。用更现代的、考虑色散相互作用校正的方法（SMD/M06和IEFPCM/ωB97xD）计算的反应势垒遵循相同的趋势。
