Monocyclopentadienyl complexes of niobium, tantalum and tungsten containing heterodifunctional P,O ligands

The reactions of P,O type ligands with the half-sandwich complexes [(η-C5R5)MCl4] (R5 = H5, Me5, iPrH4; M = Nb, Ta, W) have been investigated. Monodentate P-adducts were obtained with the β-amidophosphine Ph2PCH2C(O)NPh2, whereas in the case of the keto ligand Ph2PCH2C(O)Ph a spontaneous HCl elimination occurred to give direct access to the corresponding phosphinoenolate complexes. The crystal structures of [(η-C5H5)NbCl3{PPh2CHC(O)Ph}], [(η-C5H5)TaCl3{PPh2CHC(O)Ph}] and [(η-C5Me5)TaCl3{PPh2CHC(O)Ph}] have been determined. Interestingly, the acetamido derived phosphine Ph2PNHC(O)Me afforded O-adducts, which is an unusual bonding mode for a P,O ligand.