Main Group Metal Mediated Hydrogenation Reactions and Catalysis

利用分子氢作为清洁还原剂进行不饱和化合物的催化加氢反应是石油化工和有机合成中最重要的反应之一。大多数氢化催化剂都是由贵金属制成的，这些贵金属通常有毒且与生物不相容。近年来，人们对更环境友好和更便宜的碱金属和碱土金属氢化物催化剂越来越感兴趣，这些催化剂通常以二聚物甚至更高的低聚物形式存在。在温和的条件下，显着的主族金属催化剂被报道用于活化的共轭烯烃和甚至未活化的1-烯烃以及醛亚胺（PhHC=NR，R = tBu，iPr，Ph）的氢化。然而，详细的催化机制，特别是潜在的（金属）合作和（配体）的空间效应，了解这样的催化体系往往仍然不清楚。最近，与道格拉斯W.在Stephan等人的实验组中，我们已经证明了二聚碱金属配合物M_2L_2（M = Li，Na，K; L = tBu_2P，NCy_2），K_2L_2（L = N（SiMe_3）_2）和（C_6 H_5CH_2K）_2可以促进可逆的H_2-活化，甚至与CO/H_2混合物反应形成新的C-C链和C-H键。由于大型金属氢化物催化剂的复杂电子结构，与不饱和底物和溶剂分子的额外相互作用以及潜在的广泛探索的反应路径是必需的，这种催化氢化反应的详细机理研究是计算上的挑战。在本项目中，基于高效的GFN 2-xTB方法，（构象和反应路径探索），色散校正的低成本DFT（快速结构筛选）和高水平色散校正DFT方法（精确的结构和能量，必要时以高度相关的DLPNO-CCSD（T）为基准），采用多层次理论方法有效探索各种反应路径，以便更详细地确定催化机制。本项目旨在通过与实验的紧密结合，深入理解主族金属催化剂催化加氢反应的机理，并合理设计环保、廉价的新一代加氢催化剂。

The catalytic hydrogenation of unsaturated compounds using molecular dihydrogen (H2) as a clean reducing agent is one of the most important reactions in petroleum and chemical industry as well as organic synthesis. Most hydrogenation catalysts are derived from precious transition-metals that are often toxic and bio-incompatible. Recently, there is an increasing interest in more environment-friendly and cheaper alkaline and alkaline earth metal hydride catalysts that are usually found as dimers and even higher oligomers. Remarkable main-group-metal catalysts were reported for the hydrogenation of activated conjugated alkenes and even unactivated 1-alkenes as well as aldimines (PhHC=NR, R = tBu, iPr, Ph) under mild conditions. However, the detailed catalytic mechanism and especially the potential (metal) cooperative and (ligand) steric effects for understanding such catalytic systems often remain unclear. Very recently, together with Prof. Douglas W. Stephan's experimental group, we have demonstrated that dimeric alkaline metal complexes M2L2 (M = Li, Na, K; L = tBu2P, NCy2), K2L2 (L = N(SiMe3)2) and (C6H5CH2K)2 can facilitate reversible H2-activation and even reactions with a CO/H2 mixture to form new C-C chain and C-H bonds. Because of the complicated electronic structure of large metal hydride catalysts, additional interactions with unsaturated substrate and solvent molecules as well as potentially extensive exploration of reaction paths is required, detailed mechanistic studies of such catalytic hydrogenation reactions are computationally challenging. In this project, based on the efficient GFN2-xTB method (conformational and reaction paths exploration), dispersion-corrected low-cost DFT (fast structure screening), and high-level dispersion-corrected DFT methods (accurate structures and energies, highly correlated DLPNO-CCSD(T) as benchmark when necessary), a multi-level theoretical approach is adopted to efficiently explore various reaction paths, in order to identify the catalytic mechanisms in great detail. Through close interplay with experiment, this project aims at a deep mechanistic understanding of hydrogenation reactions catalyzed by main group metal catalysts as well as a rational design of environment-friendly and cheap new-generation hydrogenation catalysts.