AB-INITIO CALCULATIONS FOR THE ADDITION OF ETHYLENE TO METAL HYDROGENAND METAL METHYL BONDS IN HYDRIDE AND ALKYL COMPLEXES OF TI, AL, AND B

The addition of ethylene to the metal-hydrogen and metal-methyl bonds in the complexes H2MR (M = Ti, Al, B; R = H, CH3) is investigated by t he ab initio SCF MO LCAO quantum-chemical method with a split-valence basis set of Gaussian functions. The structure of a transition state f or the addition of coordinated ethylene and the energy profile for the general reaction of ethylene addition are calculated. The role of ele ctronic and steric factors in this reaction is analyzed using boron co mplexes as an example. It is shown that the electronic mechanism of th e insertion of ethylene into the M-R bond is determined by the electro n-density transfer from the sigma-bonded orbital of the M-R bond to th e pi-antibonding orbital of ethylene. A concept is suggested that att ributes the chemical reactivity of the M-R bonds to the relation of s- , p-, and d-orbital interactions contributing to the bond formation. T he activation energy is increased with increasing s character and is d ecreased with increasing d character.