Acta Chimica Sinica ›› 2021, Vol. 79 ›› Issue (9): 1164-1172.DOI: 10.6023/A21050236 Previous Articles     Next Articles



王英辉a, 魏思敏b,*(), 段金伟a, 王康a   

  1. a 长安大学 理学院 西安 710064
    b 陕西中医药大学 陕西中药资源产业化省部共建协同创新中心 咸阳 712083
  • 投稿日期:2021-05-28 发布日期:2021-09-17
  • 通讯作者: 魏思敏
  • 基金资助:
    项目受国家自然科学基金(21705029); 项目受国家自然科学基金(21804066); 陕西省高校科协青年人才托举计划(20190307); 陕西省自然科学基金(2021JQ-221); 长安大学中央高校基本科研业务费专项资金(300102120303); 陕西省教育厅自然科学研究项目(19JK0233)

Mechanism of Silyl Enol Ethers Hydrogenation Catalysed by Frustrated Lewis Pairs: A Theoretical Study

Yinghui Wanga, Simin Weib(), Jinwei Duana, Kang Wanga   

  1. a College of Science, Chang'an University, Xi'an 710064, China
    b Co-construction Collaborative Innovation Center for Chinese Medicine Resources Industrialization by Shaanxi & Education Ministry, Shaanxi University of Chinese Medicine, Xianyang 712083, China
  • Received:2021-05-28 Published:2021-09-17
  • Contact: Simin Wei
  • Supported by:
    National Natural Science Foundation of China(21705029); National Natural Science Foundation of China(21804066); Young Talent Fund of University Association for Science and Technology in Shaanxi, China(20190307); Natural Science Foundation of Shaanxi Province(2021JQ-221); Fundamental Research Funds for the Central Universities, CHD(300102120303); Special Scientific Research Plan of Education Department of Shaanxi Province(19JK0233)

Silyl enol ethers have attracted enormous attention as they could serve as a test bed for the development of novel frustrated Lewis pairs (FLPs) catalytic systems. However, the reaction mechanism of hydrogenation catalysed by metal-free FLPs for these compounds to the corresponding secondary alcohols remains elusive to a large extent in previous studies. We thus performed a thorough investigation on the reaction mechanism by density functional theory (DFT). To illustrate the reaction mechanism of FLPs-catalysed hydrogenation for silyl enol ethers, trimethyl((1-phenylvinyl)oxy)silane (Me-TMS) was chosen as the prototype substrate and toluene as the solvent, where the FLPs were generated by ethylbis(perfluorophenyl)- borane (Et-B(C6F5)2) and tri-tert-butylphosphine (t-Bu3P). The M06-2X functional in connection with 6-31+G(d) basis set was used to optimize the structures of related species including in the Gibbs free energy profiles, and the energies were obtained at M06-2X/6-311++G(d,p) level of theory, where the solvent effect was simulated with the integral equation formalism, polarized continuum mode (IEF-PCM) in both calculations. Our results suggest that the FLPs-catalysed hydrogenation of silyl enol ethers in toluene begins with the formation of B-P-FLPs followed by hydrogen activation, proton transfer and hydride transfer to complete the process. It is obvious from the Gibbs free energy profile that the proton transfer is rate-determining step, the formation of B-P-FLPs and proton transfer are endothermal and the hydride transfer is no barrier. This indicates that the amount of H2 and prototype substrate have significant influence on the FLPs-catalysed hydrogenation of silyl enol ethers. A higher temperature (328.15 K) is disadvantageous to hydrogenation reaction catalysed by FLPs but the reaction could be accelerated under higher pressure (4040 kPa). The Gibbs free energy profile calculations for trimethyl((1-phenylprop-1-en-1-yl)oxy)silane (Et-TMS) and tert-butyldimethyl((1-phenylvinyl)oxy)silane (Me-TBS) reveal that substituent group may inhibit the hydride transfer as the absence of a suitable construction for R-H-transfer, where the hydride does not direct to the C+ of silyl enol ethers and the distance between C+ and hydride is longer. These results would be helpful to design another novel FLPs-catalysed hydrogenation reaction for silyl enol ethers.

Key words: frustrated Lewis pairs, silyl enol ethers, hydrogenation, density functional theory