Theoretical Studies On The Mechanisms Of Functionalization Of Alkenes Catalyzed By Nickel And Cobalt Complexes

The functionalization of alkenes catalyzed by transition metal complexes can synthesize multi-site products economically and efficiently,providing a favorable synthetic tool for constructing complex chemical structures.Compared with precious metals such as palladium,rhodium and iridium,the first transition period metals such as nickel and cobalt,which are cheap and abundant in the earth's crust,have received extensive attention in recent years due to their unique chemical reactivity.The functionalization of alkenes catalyzed by transition metal complexes such as nickel and cobalt therefore has the advantage of high atom economy and is more in line with the development concept of green chemistry.The functionalization strategy of alkenes shows many excellent reaction characteristics in organic synthesis,and has the advantages of high reaction selectivity and wide range of reaction substrates.Compared with the rapid development of experimental chemistry,the research on the mechanism of olefin functionalization catalyzed by transition metal complexes is relatively lagging,and the experimental process often fails to capture key intermediates,which brings great challenges to the elaboration of the mechanism.In response to this research difficulty,we selected two important types of transition metal nickel/cobalt complexes catalyzed olefin functionalization reactions,and conducted a systematic theoretical study on the chemical reaction mechanism and selectivity using density functional theory methods.The main contents include the following two parts:(1)The C-H bond activation of imine catalyzed by nickel metal complexes was systematically studied.The reaction path producing the ?,?-diarylation products mainly includes the following steps: oxidative addition of C-I bond,insertion of alkenes into Ni-C bond,?-H elimination,transmetallization and reduction elimination of C-C bond.The regioselectivity of the reaction is determined by the ?-H elimination step.Our calculation results show that in the presence of organophosphine ligands,the yield of ?,?-diarylation products can be increased,the speed determining step of the reaction can be changed,the overall energy barrier of the reaction can be reduced,and the production of heck products can be reduced.Our calculation results reasonably explain the effect of the ligand on the reaction product.(2)The mechanism for the cobalt-catalyzed asymmetric coupling reaction between alkenes and alkynes in the presence of N,P bidentate ligands was investigated systematically.The reaction pathway leading to the formation of chiral trans-isomers mainly includes the following steps: cycloaddition of alkenes,alkynes and cobalt complexes,reduction elimination of C-C bond,isomerization of single bond rotation,cycloaddition with ethylene again,?-H elimination and reduction elimination of C-H bond.In the step of olefin insertion into Co-C bond,the chirality of the product is produced,while in the step of isomerization,the E-type and Z-type of the product are distinguished.Due to the particularity of the electronic configuration of cobalt(I),the calculation results of possible singlet,triplet and open shell singlet states of cobalt complexes are discussed in detail,and the optimal reaction path is obtained.The above-mentioned study on the mechanism of functionalization of alkenes catalyzed by nickel and cobalt complexes will help to further understand the difference in the electronic structure of 3d and 4d transition metals and the resulting difference in catalytic activity.Our calculated results may be also helpful for the mechanism design of related reactions and the design of new transition metal catalysts.