Structure and bonding of tetrylone complexes [(CO)₄W{E(PPh ₃)₂}] (E = C-Pb)

Quantum chemical calculations at the BP86 level with various basis sets (SVP, TZVPP, TZ2P+) have been carried out for transition metal complexes of carbodiphosphorane analogues E(PPh3)2 with E = C-Pb. The nature of the W(CO)4-E(PPh3) bonds was analysed with charge and energy decomposition methods. The equilibrium structures of the tetrylone complexes W(CO)4-E(PPh3)2 possess for E = C, Si, Ge a trigonal bipyramidal coordination at tungsten with the tetrylone ligand occupying an equatorial position. The heavier homologues with E = Sn, Pb exhibit a square pyramidal coordination at tungsten where the tetrylone ligand is at a basal position, while one phenyl group is found trans to the apical CO group which yields a hexacoordinated tungsten complex. The bond dissociation energies for the W(CO)4-E(PPh3)2 bonds are higher than for the W(CO)5-E(PPh3)2 homologues. The bonding analyses of the complexes show that the W-E bonds have a significant contribution from (CO)4W←E(PPh3)2 π-donation. All complexes W(CO)4-E(PPh3)2 are suitable targets for synthesis.