Group VI metal hexacarbonyl derivatives of some new fluorine substituted ditertiary phosphines

Complexes of the type [M(CO)4(PP′)] (M = Cr, Mo, W; PP′ = R2PCH2CH2PPh2, R = m-FC6H4(1a), R = p-FC6H4 (1b), R = m-CF3C6H4 (1c)) have been obtained from the reaction of appropriate metal hexacarbonyl with the corresponding ditertiary phosphine in methylcyclohexane/xylene. The order of ease of replacement of carbonyl by these phosphines was found in the sequence of Mo > Cr > W. The complexes [M(CO)4(PP′)] react with excess of pyridine to yield the trisubstituted complexes [M(CO)3(py)(PP′)] (M = Cr, Mo, W; py = pyridine; PP′ = 1a, 1b or 1c). All the complexes have been characterized by elemental analysis and IR and 1H NMR spectroscopy, and are assigned octahedral structures. Carbonyl force constants have been calculated from the (ν)(CO) stretching frequencies. 31P{1H}NMR spectra of [M(CO)4(PP′)] complexes reveal unusually large downfield shifts upon coordination, and these are explained in terms of a ring contribution. The values of the tungsten-phosphorus J(183W-31P) and phosphorusphosphorus J(31P31P′) coupling constants are discussed.