Transition Metal-catalyzed C-H Borylation And Carbon Dioxide Reduction:a Theoretical Study

In recent years,chemical reactions catalyzed by transition metals are an important class of catalytic reactions and one of the important methods in the synthesis of organic chemical reactions.Transition metal complexes are considered to be promising high-performance catalysts due to their potential high reactivity.It is very important to study the mechanism of transition metal complexes catalyzed reactions by theoretical methods to reveal the intrinsic nature of molecular reactions.In this dissertation,the theoretical study of transition metal-catalyzed C-H borylation and carbon dioxide reduction reactions was carried out,including the following contents:1.The reaction mechanism of cationic iridium catalysts for C-H borylation was investigated by density functional theory(DFT)method,including C-H borylation(1→3ortho→6ortho)and Ir-H borylation(6ortho→1)process.Combining multiple strategies of directing groups,coordinatively unsaturated metal center and cationic properties,a transition metal cationic iridium catalyst was designed with directing groups for C-H borylation that preserves ortho-selectivity while increasing the reactivity.Computational results show that the Gibbs free energy barrier of the C-H activation step(regioselectivity determining step)catalyzed by the cationic iridium catalyst is only 7.2 kcal/mol,indicating a higher activity than the neutral catalyst.The origin of the regioselectivity is explored,and the calculation results show that the ortho-C-H borylation pathway is more favorable than the meta-and para-pathways.Further catalyst modification demonstrated that the ortho-selectivity was attributed to the hydrogen-bonding interactions between the directing group and the substrate,although the ortho-position was sterically and electronically unfavorable.2.The mechanism of ruthenium-catalyzed amine-assisted carbon dioxide hydrogenation to methanol was explored by density functional theory.Amine-assisted carbon dioxide hydrogenation consists of five steps:carbon dioxide hydrogenation;carbamate hydrogenation;formamide hydrogenation;aminoalcohol decomposition and formaldehyde hydrogenation.The calculated total free energy barrier of amine-assisted carbon dioxide hydrogenation to methanol is 13.7 kcal/mol lower than that of direct carbon dioxide hydrogenation to methanol.It provides an important theoretical reference for the design and development of transition metal catalysts in carbon dioxide reduction.