Main Group Metal Mediated Hydrogenation Reactions and Catalysis

以分子二氢(H2)为清洁还原剂的不饱和化合物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。大多数加氢催化剂都来自贵重的过渡金属，这些金属往往是有毒的和生物不相容的。近年来，人们对更环保、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体甚至更高的低聚物的形式存在。据报道，在温和的条件下，主族金属催化剂对活化的共轭烯烃甚至未活化的1-烯烃以及醛二胺(PhHC=NR，R=TBU，IPR，Ph)的加氢反应具有显著的催化活性。然而，详细的催化机理，特别是潜在的(金属)协同和(配体)空间效应对于理解这类催化体系往往还不清楚。最近，我们与道格拉斯·W·斯蒂芬教授的实验小组一起证明了二聚碱金属络合物M2L2(M=Li，Na，K；L=tBu2P，NCy2)，K2L2(L=N(SiMe3)2)和(C6H5CH2K)2可以促进可逆的H2活化，甚至与CO/H2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电子结构复杂，需要与不饱和底物和溶剂分子进行额外的相互作用，以及潜在的广泛的反应路径探索，因此对这类催化加氢反应的详细机理研究在计算上是具有挑战性的。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)和高级色散校正的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)，采用多层次的理论方法来有效地探索各种反应路径，以便更详细地确定催化机理。通过与实验的密切互动，本项目旨在深入了解主族金属催化剂催化加氢反应的机理，合理设计环境友好、价格低廉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.