Study On The Selective Mechanism Of Co(?)/Rh(?) Complex Catalyzed The Activation Of Ene/alyne CH

Transition metal cobalt and rhodium belong to the same subgroup and own excellent catalytic function.It has been widely applied in transition metal C-H functionalization.Recently,a number of studies have drawn much attention in cobalt because of its earth-abundant,low-cost and low toxicity.While Rh~?II catalysts have been proved to be among the most useful because of high functional group compatibility and their unique reactivity.The cobalt and rhodium catalyst have excellent performance in many of the reactions,such as catalytic asymmetric synthesis,carbon-carbon bonds coupling,and the formation of the new C-O bond,C-N bond,and it would realize to improve the economy of the atom,shorten the reaction time,improve the reaction of stereoselectivity and regioselectivity,improve the efficiency of catalytic,etc.In summary,transition-metal-catalyzed C-H functionalization has beenan important way to realize the construction of new materials,and has great application value in the field of pharmaceutical synthesis and material.In this study,the progress of related research results in recent years is briefly reviewed,using the classic method of density functional theory(DFT)study and reveal the mechanism of transition-metal-catalyzed C-H functionalization.The Rh(?)-catalyzed C-H activation of benzamide derivatives with a,a-difluoromethylene alkynes was studied by DFT calculations to elucidate the selectivity controlled by different O-substituted groups(OPiv versus OMe).The reactions share a similar process that involves N-H deprotonation,C-H activation and alkyne insertion to form a 7-membered rhodacycle.Then the reaction pathway bifurcates for the two different directing groups.For OPiv,the following step involves concerted ipso attack and pivalate migration,methanol nucleophilic addition and protonation to generate hydroarylation products.For OMe,the subsequentpathwaycontains the firstb-F elimination,intramolecular aminorhodation and the secondb-F elimination to produce[4+1]annulation products.The N-O bond strength and the coordination of O-substituted groups to Rh are responsible for the selectivity.The carbonyl oxygen in OPiv group provides crucial rhodium-oxygen interaction,which essentially stabilizes 7-membered intermediate and thus facilitates concerted ipso attack and pivalate migration process,while the much stronger N-O bond of OMe-containing 7-membered rhodacycle promotes theb-F elimination.In addition,the Co(?)-catalyzed three-component C-H bond addition cascade with highly stereoselective was also studied by DFT calculations,and elucidated the factors for stereoselectivity.The reaction proceeds via four sequential steps:C-H activation,alkene insertion,C-C bond formed and protodemetalation.The insight into the mechanism of the above two reactions have been promoted a deep understanding of the transition metal catalyzed C-H activation,and it provides a method of guidance for the mechanism of the reactions and the reference for the design of the new mechanism and catalyst.