The theoretical studies on a series of α-hydrogen shift reactions between the alkylidene and alkylidyne organometallic molybdenum complexes R³R⁴Mo(≡CH)(CHR¹R²) and R³R⁴Mo(＝CH₂)(＝CR¹R²) were carried out with the density functional theory B3LYP method. The optimal structures of the reactants, transition states, and products were obtained and the reaction barriers and the relative energies of the reactants and products were calculated. Calculated results indicate that in all of the 16 transition states studied in this paper the sp² hybridization has been adopted by the central carbon atoms, from which the hydrogen atom has been shifted. The reaction barrier will be lowered by the substituents that delocalize the unpair electron in p_z orbital of the central carbon atom. The most preferable substituents are methyl groups for positions R¹ and/or R², due to the existence of a hyperconjugation effect between the p_z orbital of the central carbon atom and one of the C—H bond orbitals in methyl group. For the positons R³ and R⁴, the SiH₃ group is a favorite substituent. Calculated results also show that the first methyl group lowers the barriers as twice as the second one. The first silyl group lowers the barriers twice more than the second one. The second methyl group for positions R¹ and/or R² stabilizes the product as much as the first one. For positions R³ and/or R⁴, the first silyl group stabilizes the product while the second one will destabilize it.

Key words: organometallic molybdenum complex, α-hydrogen shift reaction, hyperconjugation effect