Theoretical Studies On Transfer Hydrogenation Of Ketones And C-H Bond Functionalization Of 2-pyrdiones With Alkynes Catalyzed By Transition Metal Complexes

This thesis focuses on the theoretical studies of the reactions of transfer hydrogenation of ketones and C-H bond functionalization of 2-pyrdiones with alkynes catalyzed by transition metal(TM)complexes.The following contents are included:one is the theoretical study on pH-dependent transfer hydrogenation(TH)of acetophenone catalyzed by cyclometallated single-site Ru complexes,and the other is theoretical study on C-H bond functionalization of 2-pyrdiones with alkynes catalyzed by Rh(?)complexes.The research results of this text are as follows:1.The reaction mechanism of pH-dependent transfer hydrogenation of acetophenone or dehydrogenation of formic acid catalyzed by[(?6-arene)RUCl(?2-N,N-dmobpy)]+ complex in aqueous media has been investigated using density functional theory(DFT)method.TM-catalyzed TH of ketones with formic acid as hydrogen source proceeds via two steps:the formation of a metal hydride and the transfer of the hydride to the substrate ketone.The calculated results show that the ruthenium hydride formation is the rate-determining step(RDS)via the ion-pair mechanism with an energy barrier of 14.1 kcal/mol.The experiments show that the dihydrogen release process of formic acid and the hydride transfer process to produce alcohol are competitive under different pH environment.The investigation explores the feasibility of two pathways under different pH environment.Under acidic condition,the free energy barrier of dihydrogen release pathway is 4.5 kcal/mol higher than that hydride transfer pathway,suggesting that the hydride transfer pathway is more favorable than the dihydrogen release pathway.However,under strongly acidic condition,the dihydrogen release pathway is more favorable than the hydride transfer pathway.Meanwhile,under basic condition,the active species[(?6-arene)Ru(H2O)(?2-N,N-dmobpy)]2+is easily deprotonated to form the hydroxo complex[(?6-arene)Ru(OH)(?2-N,N-dmobpy)]+which leads to a termination of reaction.Such single-site cyclometallated Ru catalysts are predicted to be able to drive H2-hydrogenation under acidic condition.The dihydrogen activation mode of this reaction adopts an ion-pair mechanism,which is metal-solvent cooperation in nature.Such single-site cyclometallated Ru catalysts are predicted to be able to drive H2-hydrogenation under acidic condition.The dihydrogen activation mode of this reaction adopts an ion-pair mechanism,which is metal-solvent cooperation in nature.2.Changing the reaction pathway of Rh(?)-catalyzed chelation-.assisted C-H bond functionalization of 2-pyrdiones with alkynes has been realized by variation of the reaction conditions.The alkenylation product,the alkenylation rearrangement product,the alkenylation annulation product and the[4+2]oxidation annulation product were obtained,respectively.Experimental mechanistic studies indicate that the involvement of A6 as a reaction intermediate in these catalytic processes and the C-H activation step is reversible.The reaction mechanism of Rh(?)-catalyzed chelation-assisted C-H bond functionalization of 2-pyrdiones with internal alkynes has been investigated using DFT method integrating with experiments.The calculated results show that C6-H bond activation is the RDS of the formation of A6 via the concerted metalation-deprotonation(CMD)mechanism with a free energy barrier of 20.1 kcal/mol.Interestingly,the free energy barrier for the reverse reaction of C6-H activation is only 12.2 kcal/mol(from A3 to TSA2-3),suggesting that the C6-H activation step is reversible.Path a(the alkenylation product 3)is the advantage pathway in the case of the EtOH solvent and AcOH additive,and the RDS of the formation of product 3aa is C6-H activation with a free energy barrier of 20.1 kcal/mol.Path b(the alkenylation rearrangement product 4aa)is the advantage pathway in the case of the DCE solvent and TFA additive,and the RDS of the formation of product 4aa is intramolecular nucleophilic aromatic substitution(SNAr)with a free energy barrier of 27.4 kcal/mol.Path c(the alkenylation annulation product 5aa)is the advantage pathway in the case of the DCE solvent and PivOH additive,and the RDS of the formation of product 5aa is C3'-H activation with a free energy barrier of 24.1 kcal/mol.Which is in good agreement with experimental results.These experimental and theoretical works proved the important role of solvents and acid additives for the chemoselectivity of this switchable Rh(?)-catalyzed C-H bond functionalization of 2-pyrdiones with alkynes.This work reveals the nature of this reaction,which could provide a theoretical guide for similar works.