Theoretical Study:the Origin Of Metallphotoredox And Its Catalytic Mechanism Of C(sp~3)-H Bond Functionalization

In recent years,chemists have developed a novel catalytic approach that combines transition metal-catalyzed ground-state reactions with photoredox-mediated excited-state reactions.This method is known as metallaphotoredox catalysis.Owing to its ability to precisely control the synthesis of complex organic molecules,metallaphotoredox catalysis enables the directional synthesis of reactions and has emerged as a hot research topic in the field.However,detecting key active intermediates experimentally remains challenging due to the ambiguity of single-or double-electron transfer processes and the involvement of highly active radical species in metallaphotoredox catalysis.Quantum chemical calculations play a critical role in photophysical and photochemical processes,the catalytic mechanisms of transition metal complexes,and the electronic properties of intermediates.In this paper,we primarily discuss the synergistic nature of photocatalysis and transition-metal catalysis,as well as the mechanisms underlying inert chemical bond functionalization through theoretical calculations.Our goal is to achieve accurate organic synthesis and design a new class of photo-mediated synergistic catalytic systems that can advance the development of novel chemical bond functionalizations in synthetic organic chemistry.In this paper,the mechanism of C（sp³）-H bond functionalization catalyzed by combining the photocatalyst with transition metal catalyst（nickel or copper）was systematically studied by theoretical calculations.The content of the paper includes six chapters.The first chapter is the introduction;the second chapter is the theoretical basis and calculation method;the third to sixth chapters are the main contents of the paper:1.Firstly,the Ir ^Ⅲ/Ni ^Ⅱand Ir ^Ⅲ/Ni⁰metallaphotoredox catalysis have been theoretically investigated using density functional theory（DFT）,molecular dynamics,and time-dependent density functional theory computations,with the aryl esterification reaction of benzoic acid and aryl bromide as a model system.Our findings suggest that an electron transfer mechanism is applicable to Ir^Ⅲ/Ni^Ⅱmetallaphotoredox catalysis,while an energy transfer mechanism is suitable for the Ir ^Ⅲ/Ni⁰combination.The Ir ^Ⅲ/Ni ^Ⅱmetallaphotoredox catalysis successfully constructs a Ni^Ⅰ-Ni ^Ⅲcatalytic cycle,avoiding the challenging reductive elimination（RE）of Ni（Ⅱ）species.In constrast,RE occurs from the triplet excited-state Ni（Ⅱ）species in the Ir^Ⅲ/Ni⁰metallaphotoredox catalysis.Furthermore,the triplet excited-state Ni（Ⅱ）species,exhibiting the metal-to-ligand charge transfer（MLCT）character,can resemble a Ni（Ⅲ）center to promote RE.This work explores the mechanism of metallaphotoredox catalysis,providing valuable insights for further research on inert chemical bond functionalization.2.Building on the aforementioned investigation of metallaphotoredox mechanisms,we have conducted DFT calculations to examine the highly regioselective Ir（Ⅲ）/Ni（Ⅱ）-metallaphotoredox catalyzed hydroalkylation of unsymmetrical internal alkynes with etherα-hetero C（sp³）-H bonds.Our findings predict a novel radical mechanism that merges oxidative quenching(Ir^Ⅲ-*Ir^Ⅲ-Ir^IV-Ir^Ⅲ)and nickel catalytic cycles(Ni ^Ⅱ-Ni ^Ⅲ-Ni^Ⅰ-Ni ^Ⅲ-Ni ^Ⅱ)for this C（sp³）-H functionalization to construct C（sp³）-C（sp²）bonds.Importantly,we have also evaluated the thermodynamic performance of redox potentials,as well as the kinetic exploration of energy barriers and electron-transfer rates for the corresponding electron transfer processes.Additionally,steric effects play a significant role in determining the regioselectivity of alkyne oxidative hydrometallation.In short,we anticipate that these mechanistic insights will contribute to a deeper understanding of effective Ir/Ni cooperative catalysis and inspire future advancements in C（sp³）-H functionalization research.3.A challenging[W₁₀O₃₂]^4-/Ni metallaphotoredox catalyzed C（sp³）-H arylation of alkane has been investigated by DFT calculations.These calculations reveal that the superficial active center,located in the bridged oxygen of*[W₁₀O₃₂]^4-,is responsible for the abstraction of foreign hydrogen atoms and the activation of C（sp³）-H bonds.Specifically,when comparing three common mechanisms for nickel catalysis induced by Ni⁰,Ni^Ⅰ,and Ni ^Ⅱto construct C-C bonds,the nickel catalytic cycle induced by Ni^Ⅰactive catalyst proves to be favorable in both kinetics and thermodynamics.Ultimately,a radical mechanism merging([W₁₀O₃₂]^4--*[W₁₀O₃₂]^4--[HW₁₀O₃₂]^4--[W₁₀O₃₂]^4-)decatungstate reductive quenching cycle,([HW₁₀O₃₂]^4--[H₂W₁₀O₃₂]^4--[HW₁₀O₃₂]^4-)electron relay,and(Ni^I-Ni^Ⅱ-Ni^I-Ni^Ⅲ-Ni^I)nickel catalytic cycle is proposed to be the most advantageous.We hope that this work would provide a better understanding of the unique catalytic activity of decatungstate anion for the direct functionalization of C（sp³）-H bonds.4.The C（sp³）-H trifluoromethylation of pyrrolidine,mediated by[W₁₀O₃₂]^4-photocatalysis and Cu catalysis,is theoretically investigated by DFT.Our analysis reveals that the hydrogen atom transfer（HAT）,responsible for C（sp³）-H bond activation catalyzed by[W₁₀O₃₂]^4-,is the regioselectivity-determining step.Moreover,β-regioselective activation of pyrrolidine occurs more easily thanα-regioselective one due to the enhanced activity of the distalβ-C-H bond upon protonation.A linear relationship between the steric volume of the protective group on pyrrolidine and the C-H bond selectivity has been demonstrated.In other words,the larger the steric volume of the protective group,the easier it is to obtain a single C_β-H bond activation product.This theoretical analysis could provide guidance for achieving high-selectivity target products in experimental settings.