Linear versus bent bonding in metal-phosphinidene complexes: Theoretical studies of the electrophilic phosphinidene complexes [(Cp)(CO)2MPMe)]+, [(Cp)(CO)3M=PMe)]+ (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 similar to 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 sigma bonding orbitals towards the phosphorus atom in the M PMe bonds, while in the M=PMe bond, the contributions of metal and phosphorus are almost the same. In the linear phosphinidene complexes the contributions of the covalent bonding Delta E-orb are more than the electrostatic interaction Delta E-elstat. 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 pi-bonding. The M PMe bonds show a true M-P pi bond and a deviated pi bond due to slight bent M-P-C bond angles. The M=PMe bonds show a true M-P pi bond and a lone-pair on phosphorus. (C) 2009 Elsevier B. V. All rights reserved.