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.