Ab initio MO study on cationic phosphenium complexes of group 6 transition metals, fac- and mer-[(bpy)(CO)3M{PN(Me)CH2CH2NMe}]+ (M = Mo, W)

Quantum mechanical ab initio calculations at the RHF level of theory using effective core potentials (ECP) for the metals and several all-electron basis sets are reported for the facial and meridional isomers of cationic phosphenium complexes of group 6 transition metals, [(bpy)(CO)(3)M{PN(Me)CH2CH2NMe}](+) (M = Mo,W). Fully optimized geometries using the ECP by Stevens et al. are in good agreement with the experimental parameters' for the related complex. The theoretically predicted relative thermodynamic stability of the meridional and facial isomers of Mo and W complexes also agrees well with experimental behavior. Structural consideration, M-P(phosphenium) bond rotational behavior, and Mulliken charge and orbital. population analysis of component atoms in the central part based on the computational results reveal that (i) a phosphenium ligand has strong pi-electron accepting character, which is stronger than that of a CO ligand, and (ii) a phosphenium ligand gets pi-donation predominantly from a transition metal and little from amino groups being substituents on the phosphenium phosphorus, though a metal-free phosphenium has such pi-donation from N to P. Energy profiles in terms of phosphenium rotation along the M-P bond is also discussed.