Synthesis of new coordination complexes of MF5(M = Nb, Ta), and insights into the Ta(V) reduction

The pentafluorides of niobium and tantalum reacted with benzophenone (Ph2CO), (2-diphenylphosphino)phenol (DPPPh) and 4-fluorobenzonitrile affording adducts corresponding to the asymmetric (Ph2CO and DPPPh) and symmetric (4-fluorobenzonitrile) cleavage of the tetranuclear structure of MF5. The products were characterized by elemental analysis, IR and multinuclear NMR spectroscopy. A selection of Ta(V) complexes was investigated in the attempt to obtain tantalum tetrafluoride derivatives, which are almost unknown in the literature. The reactions with cobaltocene in dichloromethane afforded unidentified paramagnetic materials and [CoCp2][TaF6], characterized by X-ray diffraction.