Theoretical Mechanistic Study Of Selective C-C/C-S Bond Actiavtion And Formation Reaction By Ni/B And Ni/Ir Synergistic Catalysis

Activation of carbon-carbon?C-C?bond and construction of carbon-heteroatom?C-X,X=N,O,P,S?bond is a growing field in organic chemistry,because of the powerful and wide applications in synthesis and catalytic reactions.It is worth noting that the cooperative catalysis strategy has been successfully applied to selectively activate C-C or construct C-X bonds in recent years.As we all know,it is not easy to clarify such reaction mechanism experimentally considering the highly reactive intermediates.In contrast,theoretical calculations have become essential to provide meaningful information of structures and properties of molecules as well as mechanisms and selectivities of reactions.Therefore,with the aid of density functional theory,this thesis selects two synergistic catalytic reactions?C-C bond activation and C-S bond cross-coupling?to solve the mechanistic issues.Such conclusions would provide inspiration for experimental chemists to further design synergistic catalytic system.The first chapter of this thesis gives an introduction of catalysis,synergistic catalysis,methodologies used in mechanistic studies,and briefly reviewed the achievements and challenges of C-C bond activation and C-X bond formation.The second chapter summarizes the density functional theory?DFT?method,basis set,solvation model,transition state theory and the analysis of potential energy surface.The third and fourth chapters are the summary of the research projects in my master study,as shown below:1.The cooperative mechanism of Ni?0?/Lewis acid catalyzed carbocyanation of alkyne with 2,3,5,6-tetrafluorobenzonitrile was investigated using the DFT method.Our calculations indicate that the most feasible catalytic cycle consists of the oxidative addition of C-CN bond to the Ni?0?center,alkyne insertion into the C?aryl?-Ni?II?bond and reductive elimination.Notably,the Lewis acid?LA?interacting with the cyano nitrogen atom of the substrate can play a significant effect on activating the C-CN bond while suppressing C-H and C-F bond activations.The origin of lower C-CN activation barrier in the presence of LA can be attributed to the remarkably enhanced charge transfer?CT?amount from the Ni_cat 3d orbital to C-CN?*+?*antibonding molecular orbital and the little decrease of interaction energy between Ni-catalyst and substrate.In the C-F and C-H bond activations in the presence of LA,on the contrary,the significant decrease interaction energy between Ni-catalyst and substrate and almost no change of charge transfer amounts are the origin of the larger bond activation barrier.Thus,LA is essential to make C-CN bond weaker than other bonds,which is well agreed with the experimental observation.Such conclusions shed new lights for understanding the selectivity of C-CN bond activation and would provide inspiration for experimental chemists to further design TMs/LA synergistic catalytic system.This paper is published on Organometallics,2018,37,2594-2601.2.Photoredox-mediated iridium/nickel dual catalysis has successfully triggered a series of traditionally challenging carbon-heteroatom cross-coupling reactions.However,detailed mechanisms,such as the catalytic cycles for dual catalysts and the role of base additive,remain controversy in these reactions.In this study,a highly chemoselective C-S cross-coupling of thiols with heteroaryl iodides has been investigated by DFT calculations and emission quenching experiments.Interestingly,the oxidation state modulation mechanism merging oxidative quenching(Ir^III-*Ir^III-Ir^IV-Ir^III)and nickel catalytic cycles(Ni^II-Ni^I-Ni^III-Ni^I-Ni^II)is favorable.It is consisted of four major steps:pyridine mediated proton-coupled electron transfer,oxidative addition of heteroaryl iodides with Ni?I?-halide complex,reductive elimination and single-electron transfer.In contrast,the radical mechanism initiated by reductive quenching of*Ir^III with thiols is impracticable because oxidative addition or?-bond metathesis from Ni?II?-thiolate intermediate is highly energy-demanding.This study will hopefully benefit the future understanding of such photoredox-mediated dual catalytic system.This paper is published on ACS Catalysis,2019,9,3858-3865.