Density Functional Theory Studies On Remote C-H Bond Functoinalizations Catalyzed By Palladium Complexes And Nickel Complexes

Achieving the site-selective activation of C-H bonds,especially the long-range C-H bonds,is a major challenge in the area of direct C-H bonds functionalization.At present,the widely-accepted strategies to controll the site-selectivities are with the help of appropriate guided group and ligand.In the C-H bond functionalizations fields,the remote C-H bond functionalization is rarely reported.Although some remote C-H bond functionalizations,such as aromatic ring p-C-H bond and chain olefins substrate?-C_sp3-H bond,have been accomplised with template-guided strategies and olefin isomerization strategies,the theoretical research involving remote C-H bond activations are really limited.It is of great significance to the design of catalystic system,the optimization of reaction conditions and the development of synthesis methods through the DFT study on the remote activation of C-H bonds catalyzed by transition metals.By studying the insight mechanism of the remote C-H bond activation at the molecular level,we can master the characteristics of those reactions and get further mechanitic insight of the remote C-H bond activation.This thesis is based on the recently reported two remote C-H bond functionalization experiments.The reaction mechanism and the origins of the-selectivity of remote C-H functionalization catalyzed by palladium and nickel complexes have been systematically studied by means of density functional theory?DFT?.The main research contents and conclusions are summarized as follows:?1?The alkylation reaction of remote?-C_sp3-H bonds of aliphatic amine derivatives was studied by a noval dimer palladium acetate catalytic model.In the bimetallic catalytic mechanism,two palladium metal play different roles respectively,which means that one palladium center is used to bind with the substrate through coordination interaction and the other acts as an active center of this reaction.The reaction process can be simply divided into four steps:N-H bond activation,C-H bond activation,C-Pd bond insertion and the protonation.Among those,the C-H bond activation stepis not only the rate-limiting step,but also the site-selectivity determining step.The calculation shows that the energy barriar for?-C_sp3-H bond activation is lower than that for achiveing the other two?-C_sp3-H bonds,and?-C_sp3-H bond activation is an irreversible process,so the?-C_sp3-H bond is activated preferentially.Thus,the selectivity of the reaction occurs at the?-site,which reasonably explains the origin of the special site selectivity.Contrary to dimer model,the insertion step of C-Pd bond was the rate-limiting step and the position-selective determining step in the monomer palladium acetate catalytic mechanism.Finally,based on the theoretical computation,we predict a noval Ni-Pd?OAc?₄ catalyst,which can also catalyze this reaction in a manner like the dimer Pd₂?OAc?₄.?2?The mechanism of Ni-catalyzed regioselective?,?-diarylation of unactivated olefin was studied.The reaction processes include five steps:C-I bond oxidation addition,C=C bond migretinsertion,ring contraction,transmetalation and reduction elimination.Among them,the oxidation of C-I bond is the rate-limiting step and the site-selectivity of the reaction is determined by the ring contraction step.It was found that the isomerization of olefin catalysed by Ni-complex leading to the formation of a more stable five-membered intermediates via the ring contraction of six-membered intermediates,which finally attribute to the?,?-diarylation products.With the help of phosphine ligands,Ni complexs could experience a series of flexible configuration isomerizations and attribute to ring contraction process.In addition,the imine guided group plays an key role in selectivitly transformation.