Theoretical Study On The Structure And Properties Of Boron Heterocyclic Carbene Formed By Charge Movement

Since the introduction of carbene(CH2)in 1835,there have been many researches on carbene in both experimental and theoretical aspects,of which the N-heterocyclic carbene(NHC)has attracted much attention due to its strong electron-donating ability.This paper theoretically designed 1-borabicyclo[1.1.0]2(3)butene(1BB)and 2-borabicyclo[1.1.0]1(3)butene(2BB)derivatives,and used the density functional theory,valance bond theory,ab initio,and chemical bond analysis methods studied the chemical bonds and properties of these two types of molecules.The main research content is as follows:1.1-Borabicyclo(1.1.0)but-2(3)-ene(1BB)is a singlet biradical with two single electrons which can form an ionic resonance structure by charge-shift.The ionic resonance structure is a B-heterocyclic carbene(BHC)which can act as carbene,Lewis base,L-and Z-type ligands to give adducts and complexes.Using the density functional theory B3LYP/6-311G**,ab initio CCSD(T)/aug-cc-PVDZ,valence bond(VB)theory BOVB/6-311G**and the block-localized wavefunction(BLW)methods,we designed four types of stable compounds(A-D)derived from 1BB.These derivatives of 1BB retain the unique features of 1BB,i.e.the single ionic resonance structure arising from the charge-shift.As a consequence,we have investigated the structure,stability and Wiberg bond orders(WBIs)of the Lewis adducts formed by A-D with Lewis acids(BePh2,BH3,AlH3,AlC13,C5BH5 and C13BH9),as well as the Cu(I),Ag(I)and Au(I)complexes bearing A-D ligands.Calculation results demonstrate that A-D can indeed react as carbenes.Interestingly,A-D,as L-type ligands,can attach to BePh2,BH33 AlH3,AIC13,C5BH5,C13BH9 and CuCl and form compounds with planar tetracoordinate carbon(ptC),while as Z-type ligands,A-D can bind to AgCl and AuCl and obtain complexes with planar tetracoordinate boron(ptB).In addition,we studied the binuclear complexes of ClAg(1BB)CuCl and CIAu(1BB)CuCl and found that A-D behave as both L-and Z-type ligands,in which these complexes contain both ptC and ptB.Thus,a kind of novel method for designing compounds with ptC and ptB is presented.Since these rationally designed compounds involve the elements of carbene,ptC,ptB,L-and Z-type ligands,they are expected to be useful in organic chemistry and organometallic field once they are experimentally synthesized.2.The Lewis adduct LB-LA and complexes LB-EH2-LA(E=Ge,Sn),LB=C3H2BX(X= Me,OH,Cl,NO2),LA= Beph2,AICl3 and BC5H5,were studied by density functional theory(DFT),include structure,the Wiberg bond indices(WBIs)and stability.The calculated results show that the enhancement of the electron-withdrawing ability of the substituent on the B atom of the Lewis base is unfavorable to electron donation for C3H2BX.The ability of BC5H5 to accept electrons due to the conjugated effect is stronger than Lewis acid Beph2 and AICl3.The 14-group dihydride GeH2 and SnH2 can be stabilized by Lewis base and Lewis acid,but the stability for SnH2 is weak.For the adducts A1-A12,the C-Be and C-Al bonds are weak coordination bonds,and the donor/acceptor C-B bond belonging to the covalent bond and ionic bond blending modes.For the complexes B1-B12 and C1-C12,the C-Ge,Ge-Be,Ge-Al,Sn-Be and Sn-Al bonds are coordination bonds,and the C-Sn bond are weak coordination bond,Ge-B and Sn-B bonds are generally covalent bonds.The corresponding three-and six-membered rings in A1-A12;B1-B12,and C1-C12 have aromaticity.In addition,we have found that the C atom of the Lewis base 2BB derivative produced by the ion resonance in the complex is ptC,so we proposed a new method to design a compound containing ptC.