Linear versus bent bonding in metal-phosphinidene complexes: Theoretical studies of the electrophilic phosphinidene complexes [(Cp)(CO)2Mtriple bond; length of mdashPMe)]+, [(Cp)(CO)3Mdouble bond; length as m-dashPMe)]+ (M = Cr, Mo, W)

Density functional theory calculations have been performed for the title phosphinidene complexes using the exchange correlation functionals BP86 and B3LYP. The optimized bond lengths and angles of the model compounds are in excellent agreement with experiment. The M–P bond lengths in linear phosphinidene complexes correspond to a Pauling bond order of ∼ 3. The bent geometries at phosphorus in the bent metal phosphinidene complexes are consistent with the presence of a trivalent phosphorus(III) center which is singly bonded to carbon and doubly bonded to transition metal. The analysis of the delocalized Kohn-Sham orbitals shows the polarization of the M–P σ bonding orbitals towards the phosphorus atom in the Mtriple bond; length of mdashPMe bonds, while in the Mdouble bond; length as m-dashPMe bond, the contributions of metal and phosphorus are almost the same. In the linear phosphinidene complexes the contributions of the covalent bonding ΔEorb are more than the electrostatic interaction ΔEelstat. The bent phosphinidene complexes have a lower degree of covalent bonding than the linear phosphinidene complexes. The major differences between the linear and bent phosphinidene complexes are found in the degree of π-bonding. The Mtriple bond; length of mdashPMe bonds show a true M–P π bond and a deviated π bond due to slight bent M–P–C bond angles. The Mdouble bond; length as m-dashPMe bonds show a true M–P π bond and a lone-pair on phosphorus.