Theoretical Study On The Properties Of π（B≡B）…M Bond Formed By Diboron Compounds And The Cu/Fe Catalyzed CO₂ Hydroboration Reduction Mechanism

The transition metal complex of boron is an important object in organometallic chemistry.The transition metalπ-diboryne compounds formed between transition metals and diboryne are the key intermediates in synthesis and catalytic reactions,and they show fascinating photophysical properties.Unravelling of their electronic structure and bonding characteristics are helpful to understand their photophysical properties and make better use of these compounds.Although CO₂ is the best C1 source with the merits of abundant reserves,low price,non-toxic and non-flammable,the reactions containing CO₂only would occur under serious conditions due to its inert nature.CO₂ utilization can resolve the serious climate warming problems and provide a new development direction in energy usage.Recently,CO₂was found to be reduced by HB（pin）catalyzed by Cu/Fe bimetallic metal complex under mild conditions,so as to realize the effective utilization of CO₂.The thesis contains two parts.In the first section,the structures of the complexes formed between different numbers of MCl（M=Cu,Au,Ag）and diboryne have been studied by density functional theory.The natures ofπ（B≡B）…M interactions are analyzed by electron density topological analysis,energy decomposition and natural bond orbital（NBO）theory.In the second section,the detailed mechanism of hydroboration reduction of CO₂ catalyzed by[LCu-Fp]has been systematically investigated by DFT calculations,the chemical selectivity of the studied reaction,as well as the role of CO₂ in the adjustment of chemical selectivity,are clarified.This paper mainly includes the following two parts:1.The interactions between n MCl（n=1,2,3;M=Cu,Au,Ag）and B₂IDip₂（IDip₂=1,3-bis（2,6-dimethylphenyl）imidazol-2-ylidene）are investigated at M06L/def2-SVP level.The nature ofπ（B≡B）…M interactions was characterized within the framework of energy decomposition analysis,natural bond orbital analysis,atoms in molecule theory,and electron localization function method.The calculated results show that the M atom of MCl interacts with two boron atoms of B₂IDip₂ to form anη²-coordinated structure.Theπ（B≡B）…M interactions belong to the Dewar-Chatt-Duncanson（D-C-D）model,the charge transfers from IDip toπ（B≡B）bonds first and then fromπ（B≡B）bonds to the MCl.Inπ（B≡B）…M interactions,electrostatic interactions are dominant,and orbital interactions are important.The strengths ofπ（B≡B）…M interactions increase in the sequence of M=Ag,Cu,and Au for the same n.The formation ofπ（B≡B）…M interaction weakens the B≡B and B-C bonds in B₂IDip₂.In particular,the B≡B bonds become increasingly weaker with increasing number of MCl,followed by M=Ag,Cu,and Au.2.The detailed mechanism of[LCu-Fp]heterobimetallic-catalyzed hydroboration reduction of CO₂ has been systematically investigated at PBEPBE-D3/def2-TZVP//PBEPBE-D3/def2-SVP level.Our calculated results show that the catalytic reaction contains three steps,[LCu-Fp]catalyst activated by HB（pin）to form[LCu-H]and Fp B（pin）,CO₂hydroboration catalyzed by[LCu-H],and CO₂-assited formate decarbonylation by Fp B（pin）.HCO₂B（pin）can be obtained catalyzed by[LCu-H].It is the reversible CO₂ coordination to Fp^-drive the Fp^-away the B（pin）⁺,the formation of B（pin）⁺would facilitate the transformation of HCO₂B（pin）to（pin）BOB（pin）,not the directly CO₂ coordinates to Fp or substituted the CO of Fe.The chemoselectivity of the title reaction can be controlled by the reaction conditions.Using nonpolar solvent,HCO₂B（pin）is the main product of the CO₂reduction at mild conditions.Enhancing the polarity of the solution or under the UV/V is radiation,the yield rate of（pin）BOB（pin）would increase.