Theoretical Study On The Hydrogenation Reaction Catalyzed By Dual Sites Ligand-assisted Catalyst

Catalytic hydrogenation play important applications in the field of organic synthesis and is a hot issue of interest in the field of catalytic science.The design and synthesis of highly active and selective catalysts has been an important challenge in this field.In recent years,transition metal catalysts using metal-ligand cooperation strategy(MLC)have been widely used in catalytic hydrogenation,in which functional auxiliary ligands will participate in the bond formation and bond breaking processes,and participate in the activation of chemical bonds together with the metal center,thus effectively reducing the reaction activation free energy barrier and improving the catalyst activity.However,traditional metal-ligand cooperation catalysts only have a single catalytic mode,and their catalytic driving force regulation methods are limited when facing multi-step tandem reactions,and this problem restricts the further enhancement of the activity of traditional metal-ligand cooperation catalysts.To solve this problem,dual-site ligand-assisted catalysts have emerged to exploit the differences in the activation of chemical bonds by different metal-ligand cooperation mechanisms,enabling the catalysts to achieve autonomous selection of dominant paths in mediating multi-step reactions.However,there are still many problems to realize the rational design of dual-site ligand cooperation catalysts.First,there are many different types of ligand cooperation mechanisms,and the functional ligands can be structurally located at both the first and second ligand levels,and the differences in catalyst spatial structure will lead to differences in catalytic activity.In addition,during the bridging of different stages of the catalytic cycle in a multi-step reaction,if dual sites have high transfer energy barriers to each other,this will bring about a single mechanism selectivity.The aim of this paper is to use density functional theory and computational chemistry to theoretically study representative dual-site ligand cooperation catalysts,to elucidate their mechanistic selectivity and influencing factors,and to provide a reference for the rational design of new dual-site ligand-assisted catalysts at the theoretical level.This paper consists of four chapters,the main contents of which are as follows:Chapter 1: Introduction.It mainly introduces the catalytic model of traditional metal-ligand cooperation mechanism and the current status and research significance of dual sites ligand cooperation catalysts.Next,some theoretical bases for conducting simulations are introduced,and finally the main research contents and innovations of this paper are described.Chapter 2: Mechanistic insight into borrowing-hydrogen N-alkylation catalyzed by an MLC catalyst with dual proton-responsive sites.Metal-ligand cooperation catalysis is one of the most important concepts in the field of organo-metallic catalysis.However,diverse functional ligands result in ambiguous mechanisms and constrain the understanding of MLC catalysis.Herein,a theoretical study based on density functional theory calculations is performed to shed light on the mechanistic preference of borrowing-hydrogen N-alkylation catalysed by a ruthenium complex with dual proton-responsive sites.The results suggest that the reaction pathway mediated by the α-NH site requires overcoming a higher activation energy barrier(31.4 kcal/mol)compared with the γ-NH site due to the ligand distortion after protonation.Nevertheless,the instability caused by the ligand distortion does not transform into catalytic activity for the subsequent hydrogenation reaction.In contrast,the γ-NH site facilitates the rate-determining hydride transfer step(21.1 kcal/mol)via non-covalent interaction instead of participating in the bond formation and breaking process,which is found to be a more plausible mechanism.These findings demonstrate the versatile role of ligand N-H functionality,which may provide useful guidance for the design of new MLC catalysts in the future.Chapter 3: Theoretical study on the transfer hydrogenation catalyzed by Shvo-type dual sites ligand cooperation catalyst.In this chapter,we investigate in detail the site-selectivity and mechanism-selectivity of the Shvo-type ruthenium catalyst for the transfer hydrogenation reaction of acetophenone using computational chemistry based on density functional theory and on experimental grounds.The results show that only the O-H group on this catalyst ligand is catalytically active and preferentially selects the MLC mechanism for the transfer hydrogenation reaction.Compared with the MLC mechanism,the higher activation energy barrier of the MPV reaction path due to the distortion of the transition state structure of the key step makes the MPV reaction path less likely to occur.And neither of the two MPV reaction pathways formed metal hydrides,and unlike the conventional MPV reaction mechanism,the O-H functional groups on the ligands were involved or assisted in the catalytic reaction.These discoveries on the catalytic transfer hydrogenation mechanism of Shvo-type dual sites ligand cooperation catalysts are expected to provide useful guidance for the design of novel catalysts in the future.Chapter 4: Conclusion and outlook.This chapter summarizes the research work in this paper,presents the current challenges of metal-ligand cooperation catalysis and dual-site ligand cooperation catalysis,and provides an outlook on the rational design of future dual sites ligand-assisted catalyst.