Abstract: A theoretical study on the isomerization mechanism between organorhenium alkylidene and alkylidyne complexes(Me)₂(NHR₃)Re(=CHR₁)(=NR₂) and(Me)₂(NHR₃)Re(≡CR₁)(NHR₂), where R₁,R₂, R₃=H,Me,Bu^t, were carried out with the density functional theory B3LYP method. The optimal structures of the transition states were located and the activation energies were calculated. The calculation results indicate that the intramolecular hydrogen transfer process is kinetically unfavorable because the high activation energies exists whatever the substituent is. The intermolecular hydrogen transfer process between two alkylidene complexes is less favorable either. The hydrogen transfer process between the alkylidene complex and the water molecule is favorable. The most favorable process is the hydrogen transfer process between the alkylidene complex and the chlorine hydride molecule where the chlorine hydride molecule acts as a bridge or a catalyst. The calculation results suggest that the effects of substituents on the reaction barriers of hydrogen transfer processes are almost the same for all the four processes considered in this work. For each process the most preferable substituents are the methyl or t-butyl group for R₁, the hydrogen atom for R₂, and t-butyl group for R₃. The calculation results also show that the additivity exists for the effects of substituents on the barriers of the α-hydrogen transfer reactions.

Key words: Organorhenium complex, Isomerization, Hydrogen transfer