Theoretical Studies of the Relative Stabilities of Transition Metal Alkylidyne (CH3)2M(⋮CH)(X) and Bis(alkylidene) (CH3)M(CH2)2(X) Complexes

Density functional molecular orbital calculations at the B3LYP level were performed to investigate the relative stabilities of the tautomeric pairs of transition metal alkylidyne (CH 3 ) 2 M(⋮CH)(X) and bis(alkylidene) (CH 3 )M( CH 2 ) 2 (X) complexes (M = W, Mo, Os, and Ru; X = Cl, CH 3, CF 3, SiH 3, and SiF 3 ). Calculation results indicate that the relative stabilities of the bis(alkylidene) tautomers increase with the increasing π-accepting ability of X for the W and Mo complexes. When X is a silyl ligand, it is found that the tautomeric pair for W or Mo have similar stabilities. These results have been explained in terms of π interaction between ligand X and the electron density in the metal−alkylidyne/alkylidene bonds. For the Os and Ru complexes, the bis(alkylidene) tautomers are found more stable no matter what X is. The stabilities of the bis(alkylidene) tautomers for these d 2 metal complexes have been related to the bonding characteristic of the orbital that accommodates the two metal d electrons.