Theoretical Study On The Carbon-Fluorine Bond Activation Involved By Group Ⅷ Transition Metal Complexes

Fluorine chemistry has been widely used in materials,medicines,pesticides and many other fields,which are closely related to human life and industrial production.In recent years,the increasing demand for the improvement of polyfluorinated compounds and the degradation of toxic fluorides has shifted research attention to the field of highly inert C-F bond activation.Transition metal compounds can be used to activate C-F bond stoichiometrically and catalytically.The d orbitals of transition metals can not only accept the σ bonding electrons of the C-F bond,but also can backdonate the d electrons to the σ antibonding orbital of the C-F bond,thereby effectively activating the C-F bond.Although transition metals have been active in the field of C-F bond activation,the selectivity of related reactions is easily affected by the electronic and steric effects of ligands,metal centers,solvents and other conditions.The detailed studies of the reaction mechanisms are less developed.In this dissertation,a series of C-F bond activation reactions involving transition metals of group Ⅷ are theoretically studied by using density functional theory.First,we proposed an alternative mechanism about Grignard-assisted Ni/Mg bimetallic cooperation of C-F bond cleavage for the Kumada-Tamao-Corriu cross-coupling between aryl fluorides and alkyl Grignard reagents,with Ni complexes with the bidentate phosphine ligands as the catalytic system.The detailed mechanism and the origin for the high selectivity have been probed from the aspects of geometry,principal interacting orbital analysis,NPA charges,and frontier molecular orbital theory.Subsequently,we theoretically predicted the C-F bond activation of Rh compounds with fluorine-substituted five-membered ring,and found that C-F bond activation was preferred to the corresponding C-H bond activation.Then we further extended the research to fluorine-substituted six-membered ring ligands and other metal center complexes of Group Ⅷ.In addition,we also took advantages of computational chemistry by designing several types of Pincer iridium complexes containing aromatic and non-aromatic moieties,in order to improve the reaction efficiency of(PCP)Ir(NBE)complexes reported in experiments.We found that when the N atom in the pyridine ring coordinated to the Ir center,the reaction barrier of the oxidative addition to the Csp3-F bond is greatly reduced,and the goal of regulating the reactivity of the substrate by modifying the ligand is successfully achieved.