Theoretical Study On The Nature Of Donor-acceptor Bonds In Half-sandwich Organometallics

Due to the metal carbon bond,organometallics exhibited a special redox,conductive,and catalytic properties.Therefore they aroused widespread concern.Among them,half-sandwich type organometallic compounds are very important metal organic catalysts,it is of great significance to carry out the theoretical research on the bonding nature of donor-acceptor bond in these compounds.In this thesis,we studied the stability and donor-acceptor bond in dinuclear organometallics CpM1-M2Cl3(M1,M2=B,Al,Ga,In;Cp=?5-C5H5).We also have analyzed the interactions of transition metal(TM)hydrides CpM(PMe3)(L)2H(M=Cr,Mo,W;L=PMe3,CO)with poor,moderate,and strong proton donors HX(NH3,H2O,and HF).The nature of dihydrogen bonds(DHBs)in these complexes are analyzed.All of the geometry optimizations and natural bond orbital(NBO)analysis have been calculated using the GAUSSIAN09 program package.The topological analyses of electron density of molecule have been studied using AIMALL program,AIM2000 program and TopMod program.The energy decomposition analysis(EDA)has been performed using the ADF2008.01 program.This thesis mainly includes the following two aspects:1?The geometries and stabilities of the dinuclear organometallics CpM 1-M2Cl3(M1,M2=B,Al,Ga,In;Cp=?5-C5Hs)have been investigated by density function theory(DFT)at M06L/6-311G(d,p)level.The nature of donor-acceptor M1?M2 bond has been studied based on atoms in molecules(AIM)theory,energy decomposition analysis(EDA)and natural bond orbital(NBO)analysis.Results show that it is the electronegativity of M atom determines the stability and covalent character of the dinuclear organometallics CpM1-M2Cl3.The larger electronegativity M as the donor is more stable than it as the acceptor in the donor-acceptor bond,and the donor-acceptor has more covalent character.The strength and the polarity of M1?M2 donor-acceptor bond are determined by the periodicity of M atom.As the period number of M1 atom is smaller than M2,the strength of M1?M2 bond is larger than M2?M1 bond.For the homonucleardinuclear organometallics,the polarity of the M-M bond increases with the increasing atomic number of M atom.And for the heteronuclear complexes,the polarity of the M1-M2 bond also increases in the sequence of M2=B,Al,Ga,and In,for the same M1 atom.2?In this work we have analyzed the interactions of transition metal(MH)hydrides CpM(PMe3)(L)2H(M=Cr,Mo,W;L=PMe3,CO)with poor,moderate,and strong proton donors HX(NH3,H2O,and HF)and focus on the DHBs in these complexes.In this study,we studied all important factors that can affect the DHBs:transition metal,proton-donor and substituent group.Electrostatic potential(ESP)analysis,topological(AIM)analysis and non-covalent interactions index(NCI)analysis of the electron density,and energy decomposition analysis(EDA)were applied to better understand the nature of the dihydrogen bonds(MH?-…H?+X)in CpM(PMe3)(L)2H…HX(M=Cr,Mo,W;L=PMe3,CO;X=F,OH,NH2).The calculated results show that the MH?-…H?+X bonds and M…H?+X bonds both can be form.The transition metal is the main influence factor for the directionality of dihydrogen bonds.Electron-rich 5d metal(W in this case)hydrides have a greater chance of forming M…H?+X bonds rather than MH?-…H?+X bonds.The stronger proton donor involves,the stronger DHBs form.The substituting of CO makes it difficult to form a dihydrogen bond.Both electrostatic interactions and orbital interactions play important roles in dihydrogen interactions,and steric interactions are weak.The interaction energies are also determined by the proton donor.As the proton-donating ability of HX increases,the interaction energies decrease.When PMe3 is substituted by CO,the interaction energies increase.