Theoretical Studies On Ligand-controlled Catalytic Reactions Of ? Metal Complexes

Group ? transition metal complexes has been successfully applied in various chemical reactions.The use of functional ligands to control the activity and selectivity of the reaction is an important strategy to achieve this goal.Through the combination of theoretical computational chemistry and experimentation,the concept of"black box"is broken.It can not only avoid the blind design and synthesis reaction of chemists,but also improve scientific research efficiency.In this thesis,the mechanism of catalytic reaction is explored by density functional theory.Attempts are made to link the characteristics of the catalytic system with its reaction pathway,and provide research ideas for the design of new catalysts of ligand control reaction.In this paper,three important catalytic reaction mechanisms are studied:theoretical study on ligand-controlled cobalt-catalyzed selective C-H bond functionalization;theoretical study on ruthenium-catalyzed CO₂ hydrogenation;theoretical study on functional iridium-catalyzed formic acid dehydrogenation.First,the theoretical study on ligand-controlled cobalt-catalyzed selective C-H bond functionalization,cis-1,2-bis?diphenylphosphino?ethylene?dppen?and 1,3-bis?diphenyl-phosphino?propane?dppp?as ligands are discussed respectively.The mechanism of the cyclization reaction of the cobalt-catalyzed 1,6-enyne with aldehyde and the chemical selectivity origin show that:1.The reaction mechanism includes four steps:oxidative cyclization,aldehyde coordination,C-H bond metalation,reductive elimination.2.When dppen is used as a ligand,the ortho-C-H bond is metallized,resulted in hydroarylation product.The C-H bond metalation is the rate-determining step and selective origin.When dppp is used as a ligand,the carbonyl C-H bond is activated,resulted in hydroacylation product,and the rate-determining step is the oxidative cyclization.This conclusion is consistent with the experiment.Secondly,DFT study:the ligand-controlled rhodium-catalyzed CO₂ hydrogenation reaction.The reaction mechanism and catalyst activity origin are discussed.The calculation results show that:1.The reaction mechanism includes four steps:removing HCl,H₂ heterogeneous,hydride trnsfer,ligand exchange.2.The removal of HCl is the rate-determining step.The energy barrier of removing OH···Cl?28.5 kcal/mol?is lower than the energy barrier of removing NH···Cl?34.9 kcal/mol?.Complex 1 exhibits more good catalytic activity.This conclusion is consistent with the experiment.Thirdly,DFT study:the bifunctional Ir-catalyzed dehydrogenation reaction of formic acid.The mechanism of nitrogen of pyridine pendant is discussed.The calculation results show that:1.The reaction mechanism includes six steps:ligand exchange,deprotonation,CO₂generation,H₂ release,proton transfer,water coordination.2.Because that the nitrogen of pyridine acts as pendant,it can cooperate with the N-H structure of pyrazole at the 2nd position with the aid of water or formic acid.The energy barrier of hydrogen generation of the rate-determining step is lower,to promote the activity of the catalyst.This conclusion is consistent with the experiment.