Theoretical Study On Asymmetric C-C Coupling Reaction With CO₂ Catalyzed By Copper And Nickel Complexes

Carbon dioxide,an abundance and non-toxic carbon source,is very stable and inert as it is in the highest oxidation state of carbon.Converting CO₂ to fuel molecule or fine chemicals is of great significance and challenge,especially the introducion of chiral center to carbon dioxide transformation.In recent years,with the development of chiral catalysts,the research on asymmetric catalytic conversion reactions has attracted the attention of researchers,and it has become a hot spot and frontier of organic synthetic chemistry.The earth-abundant transition metals?Ni,Cu,Fe,etc.?show high activity and selectivity in asymmetric catalytic conversion reactions of olefins.The introduction of CO₂ as a synthesizer into asymmetric catalytic conversion reactions is of great significance in the preparation of chiral products,the solution of climate warming and energy shortage.Moreover,employment of transition metal complexes as catalysts on CO₂ transformation is one of the hot research issues as the catalytic activity and enantioselectivity of transition metal complexes are facile to modulate by adjusting ligand structures and the catalytic mechiansms are easy to investigate.In addition,through theoretical study on asymmetric reaction of olefin with CO₂ catalyzed by transition metal complexes,scientific researchers understand and explain the roots of different selectivity in the reaction from a theoretical level,and use theoretical knowledge to predict more efficient catalysts,which will be of great significance to experimental research in this field.In this dissertation,the mechanism of asymmetric reductive hydroxymethylation reaction of styrene derivatives with CO₂ catalyzed by copper complexes was investigated by using density functional theory?DFT?.The calculation results indicate that the insertion of olefin into the Cu-H bond of L₁CuH catalyst is the determining step for enantioselectivity and regioselectivity and the following carboxylation step is rate determining step.Based on the analyses of frontier molecular orbitals,NPA charges and ligand-substrate interactions,the regioselectivity is premarily controlled by electronic effect and enantioselectivity is caused by the steric hindrance between ligand and substrate.The investigation of the ligand influences on enantioselectivity shows that ligand-substrate interactions controls the enantioselectivity.Additionally,the effect of non-axial chiral bisphosphine ligands on enantioselectivity was studied,and it was found that non-axial ligands are more flexible which can adjust the spatial structure to avoid steric exclusion.Secondly,the detailed mechanism of nickel complexes catalyzed hydrocarboxylation of olefins with CO₂ was studied using density functional theory.Two possible catalytic cycles were studied.The results indicate that the insertion of olefins into Ni-H bond is a key step in determining the regioselectivity and enantioselectivity,and it is rate determining step.Moreover,the more-nucleophilic Ni^I complex contained a vacant site that was available for the electrophilic attack of CO₂.Mn and H₂O play an important role in the formation of the active catalyst L₁NiH and in the entire catalytic cycle.