Theoretical Studies On The Electronic Structures,Reaction Mechanisms,and Dinitrogen Complexation Of Iron Complexes

Iron complexes have received increasing attention in recent years because of the abun-dance,cheapness,good biocompatibility and relatively low toxic characteristics of iron ele-ment.Although experimentalists have made remarkable progress in this area,the related reac-tion mechanism,electronic structure,and factor governing reactivity and selectivity have re-mained unclear due to the limitation of current experimental approaches.Computational chemistry as a powerful tool is able to effectively deal with such systems.Studies on compli-cated electronic structure and reaction mechanism at the molecular and electronic levels would further help us design and explore new catalytic systems.Herein,the electronic struc-tures,reaction mechanisms,and the capability of dinitrogen complexation of a series of iron complexes were investigated by density functional theory?DFT?approaches.The complexation capability of dinitrogen with phosphine-ligated mononuclear iron complexes was investigated by DFT calculations.The results suggest that,in the cationic complex[Cp^*Fe?dippe?]⁺?Cp^*=?5-C₅Me₅;dippe = 1,2-bis?diisopropylphosphino?ethane?,relatively low electron density on Fe,small wiberg bond order index of Fe-P bond,low re-ducibility,and little contribution of Fe-orbital to the frontier molecular orbitals might cause the failure in dinitrogen complexation.Moreover,the second order stability energy analysis of the proposed existing cationic complex[Cp^*Fe?N₂??dippe?]⁺ reveals that the interaction be-tween Fe and dinitrogen is weak,which is not conducive to generate a stable dinitrogen coor-dination complex.Theoretical studies on single-electron oxidation of thiolate-bridged diiron complex[Cp^*Fe??-bdt?FeCp^*]?bdt = benzene-1,2-dithiolate?show that the oxidation event takes place at the iron center which doesn't coordinate to the phenyl ring of bdt.The bdt in this reaction serves as a dianion ligand rather than a monoanion radical although the C-C bond lengths of'phenyl ring show un-equidistant character.Further theoretical studies on continuous reduction of amino-bridged diiron sulfur complex[Cp^*Fe??-?²:?²-bdt???-NH₂?FeCp^*][BF₄]₂ reveal that the first reduction might occur at two metal centers,while the second reduction can be better viewed as a single-metal based process.Theoretical studies on the hydrosilylation of 1-octene with?Me₃SiO?₂MeSiH catalyzed by iron complex?'PrPDI?Fe?ⁱPrPDI = 2,6-?2,6-ⁱPr₂-C₆H₃N=CMe?₂C₅H₃N?have been carried out.The catalytically active species is proposed to be an octane-coordinated species,which is different from the general Chalk-Harrod mechanism of noble metal catalysis.The pathway in which hydrogen of silane is added to the ?-carbon of C=C double bond,and the formation of-anti-Markovnikov product is more favorable both kinetically and thermodynamically.And the auxiliary coordination of octane substrate in the reductive elimination step decreased the reac-tivity.Moreover,both dehydrogenative silylation and hydrogenation as side reactions are less favorable in this system.In summary,the theoretical studies in this thesis would be helpful for better understand-ing of the factor concerning with dinitrogen complexation and activation and would provide a theoretical basis for the design of iron-catalyzed reactions and nitrogen fixation systems.