Phosphorus–phosphorus coupling constants in trifluoromethylphosphine group VIA metal complexes
Abstract
Phosphorus–phosphorus coupling constants, 2J(PP′), have been evaluated from 19F (and in certain cases 1H and 31P) n.m.r. spectra of cis-L2M(CO)4 complexes [L =(CF3)2PR or CF3PQ2; M = Cr, Q = H; M = Mo, Q = Cl, Br, H; R = Cl, Br, I, H]. The data, together with published values for the (CF3)2PF and CF3PF2 complexes, indicate that the magnitude of 2J(PP′) for the molybdenum series decreases in the order R = F > Cl > Br > l > H and Q = F > Cl ∼ Br H. The values for the CF3PH2 complexes are unusually small. The complexes cis-[(CF3)2PNMe2]2Mo(CO)4 and cis-[(CF3)2PNCS]2Mo(CO)4 are described and solution n.m.r. data suggest that intermolecular phosphine exchange is occurring.