Theoretical Study On The Structure And Catalytic Properties Of Charged Chemically Bonded Molecules And Their Complexes

Since the concept of planar tetracoordinate carbon(ptC)was proposed by Hoffmann,the studies involving ptC have been about half century.However,only a few of compounds with ptC were observed experimentally.Theoretical calculations indicated that 2-Me-2-borabicyclo[1.1.0]but-1(3)-ene(2-Me-2BB)can be ligands to form stable complexes with Cu,Ag and Au.In this thesis,we have further investigated the bonding and stability of the derivatives of 2-Me-2BB and the complexes of d-block elements bearing the derivatives of 2-Me-2BB ligand,as well as the reactions of C-H bond activation in methane and propane catalyzed by Pd-complexes having the derivatives of 2-Me-2BB ligands.The main content of this thesis includes three parts as follows:1.We have theoretically investigated the stability,chemical bonding,and coordination ability of the 2-Me-2-borabicyclo[1.1.0]but-1(3)-ene(2-Me-2BB)molecule using density functional theory and ab initio molecular dynamics(AIMD)simulations.Calculated results indicated that 2-Me-2BB is both thermodynamically and kinetically stable.The C=C bonds in 2-Me-2BB contain a ? bond and a charge shift(CS)bond,which were different from those in 1-Me-borirene and cyclopropylene.Moreover,2-Me-2BB can be a ? donor,leading to the formation of TM(2-Me-2BB)Ln complexes containing planar tetracoordinate carbon(ptC)with transition metals(TM=Sc-Cu),in which the lone electron pair of 2-Me-2BB results from its ionic resonance form.The lengths and Wiberg bond indices of the TM-ptC bond in TM(2-Me-2BB)Ln(TM=Sc-Cu)reveal that 2-Me-2BB can be a ligand similar to N-heterocyclic carbene.Therefore,2-Me-2BB and its derivatives are promising molecules to obtain complexes with ptC.The natural charges on TM atoms in TM(2-Me-2BB)Ln(TM=Sc-Cu)complexes range from-0.97 to 1.54e,indicating that such complexes with ptC might have potential applications in catalytic chemistry.2.Five new palladium(II)complexes have been designed as the model catalysts for methane to methyl trifluoroacetate conversion.All these compounds are analogues of the well-established(bis-NHC)PdBr2 complex(NHC,N-heterocyclic carbenes),derived by complexing the palladium(II)metal ion with the derivatives of bis-2-borabicyclo[1.1.0]but-1(3)-ene(bis-2BB)ligands using the sp2 carbons.Our density functional theory calculation results suggest that the(bis-2BB)PdBr2 catalysts outperform the popular(bis-NHC)PdBr2 complex in the desired catalytic process,and further reveal that the charge-shift bonding in the bis-2BB ligands contributes to the improved catalytic performance.These findings may spark new ideas for experimental design of more efficient organometallic catalysts for C-H bond activation and functionalization.3.Using density functional theory(DFT),we have investigated the conversion of propane to propyl trifluoroacetate catalyzed by five kinds of(bis-2BB)PdBr2 complexes(bis-2BB is the derivatives of bis-2-borabicyclo[1.1.0]but-1(3)-ene).Calculated results indicate that the(bis-2BB)PdBr2 catalysts are superior to the popular(bis-NHC)PdBr2 complex in the desired catalytic process,consistent with the previous results of the conversion of methane to methyl trifluoroacetate catalyzed by(bis-2BB)PdBr2 complexes.Moreover,calculated natural charges and Wiberg bond index(WBI)values involving Pd(?)reveal that the charge-shift(CS)bonding characteristics in the bis-2BB ligands contributes to the improved catalytic performance of the(bis-2BB)PdBr2 complexes.Thus,we suggested that Pd(?)-catalysts having the ligands with CS bond might be promising organometallic catalysts for the activation and functionalization of C-H bond in alkanes.