Theoretical Mechanistic Study And Catalyst Design Of Photo-mediated C-X(X=N,O) Cross Coupling Reaction

The construction of carbon-heteroatom（C-X）bonds is of great significance in many fields such as medicine,chemical industry,energy and has always been hot research in chemical synthesis.Among of the synthesis methods,the cross-coupling reaction is generally considered to be the synthetic strategy with the most economic efficiency.In recent decades,various classical coupling reactions,such as Chan-Lam and Ullmann-Goldberg,have been developed and reported to achieve the various C-X bond constructions.However,high temperatures,high costs and long reaction times were usually required during these strategies.With the rapid rise of photoredox catalysis,the photo-mediated transition metal-cooperative dual catalytic strategy has been revealed to be one of the most powerful and efficient approaches to realize C-X cross-coupling reactions.This dual-catalytic system,which benefits from a unique excited-state single electron transfer（SET）process,is especially conducive to the construction of C（sp³）-X coupling products.However,expensive photocatalysts,such as iridium（ruthenium）polypyridine complexes,fine chemical organic photosensitizers,etc.,are indispensable in the photocatalytic process.Moreover,the active photoelectrons make the reaction mechanism more complicated.Therefore,clarifying the reaction mechanism of metallaphotoredox catalysis and developing efficient and broad-spectrum photocatalysts can further promote the development of C-X cross-coupling reactions.In this dissertation,quantum chemical methods and molecular dynamics methods were used to systematically study the mechanism of photo-mediated synergistic catalysis of C-X（X=N,O）cross-coupling reactions,and further rationally design low-cost and broad-spectrum photoredox catalysts,which has been successfully verified by our experiments.The content of the thesis includes six chapters.The first chapter is an introduction,which systematically introduces the research progress of photoredox synergistic catalysis of C-X cross-coupling reactions.The second chapter is the main theoretical basis and calculation methods.The third to sixth chapters are the main research contents of the thesis:1.The reaction mechanism of visible light-mediated Ir^Ⅲ/Ni^Ⅱbimetallic synergistic catalysis of C（sp²）-N cross-coupling was investigated in detail by density functional theory（DFT）calculations.The results show that the radical mechanism merging photocatalyst reductive quenching(Ir ^Ⅲ-*Ir ^Ⅲ-Ir ^Ⅱ-Ir ^Ⅲ)and nickel catalytic cycles(Ni ^Ⅱ-Ni ^Ⅲ-Ni ^Ⅱ-Ni ^Ⅱ)is the most favorable.The main steps consist of exogenous base-mediated SET and hydrogen atom transfer（HAT）,Ni（Ⅱ）-mediated radical trapping,and rate-determiningσ-bond metathesis,respectively.In addition,different from previous reports,the rate-determining step of C-N coupling exists an“electron flow”phenomenon,which is conducive to theσ-bond metathesis process.This work provides new mechanistic insights for metallaphotoredox-catalyzed C-N cross-coupling and theoretical basis for rational design of efficient photocatalysts.2.The mechanism of the photo-mediated Ir ^Ⅲ/Cu ^Icatalyzed C（sp³）–N coupling reactions was investigated by DFT calculations.The results indicate that the favorable mechanism consists of the photocatalytic cycle(Ir^Ⅲ?*Ir^Ⅲ?Ir^Ⅱ?Ir^Ⅲ)and the copper catalytic cycle(Cu^I?Cu^Ⅱ?Cu^Ⅲ?Cu^I).In addition,the differences between Ir^Ⅲ/Cu^Isynergistic catalysis and Cu ^Isingle catalysis have been further explored and analyzed for achieving this C（sp³）-N cross-coupling reaction.The“springboard”effect of photocatalysts in dual catalysis can better match the energy level of the SET process and initiate a faster SET process.This work will contribute to a deeper understanding of the nature of photocatalytic decarboxylation reactions and provide a theoretical basis for further development of novel cross-coupling reactions.3.Based on the research experience of the above C-N coupling mechanisms,a high-efficiency and broad-spectrum Na I-PPh₃/Cu Br photoredox catalytic system was developed through computational design combined with experimental verification,and successfully achieved a series of C（sp³）-O/N cross-coupling reaction.The studies show that the donor-acceptor complex can be transformed into triplet excited species through a rapid intersystem crossing process,and decarboxylated by illumination to generate alkyl radicals.The C（sp³）-O/N cross-coupling products were successfully obtained via Cu ^I-mediated radical trapping,inter-molecular SET,base-mediated proton transfer,and reductive elimination,avoiding the kinetically unfavorable Cu^Ⅲreductive elimination.This theoretical calculation-driven organic synthesis strategy is expected to provide new perspectives and ideas for the future development of novel C（sp³）-X cross-coupling reactions.4.The mechanism of the two-dimensional carbon-nitrogen material synergizing Ni（Ⅱ）catalyst to realize C-O cross-coupling reaction was systematically studied by combining quantum chemical and molecular dynamics calculations.In the photoredox catalysis,the carbon-nitrogen materials generate electrons and holes on the conjugated C atoms and N atoms by photoexcitation,respectively.Through the analysis of molecular adsorption and electron transfer efficiency,it can be determined that the Ni（Ⅱ）-mediated electron trapping process is the main reason for the quenching of carbon-nitrogen materials,initiating the Ni catalytic cycle to obtain C-O coupling products.In addition,the quenching experiments further proved that Ni（Ⅱ）molecules can quench carbon-nitrogen photocatalysts better than other molecules.This result provides a theoretical basis for 2D materials for photoredox catalyzed C-X cross-coupling.