Phosphorus–fluorine chemistry. Part XXVIII. Fluorophosphines with bulky substituents as ligands in transition metal carbonyl complexes

Abstract

Bis(t-butyl)fluorophosphine, the first stable dialkylfluorophosphine, and the corresponding difluorophosphine, were evaluated with regard to their ligand properties. A series of transition-metal carbonyl derivatives of types (CO)3NiL, (CO)5ML, cis-(CO)4MoL2, cis-(CO)3MoL3(L = ButPF2 and But2PF; M = Cr, Mo, W) was prepared. Using i.r. and n.m.r. data (1H, 19F, 31P) the relative π-acceptor character of the phosphines in the series PF3–nButn(n= O–3) was assessed. It is proposed to use the quantity ΔJ/JL(ΔJ=Jc–JL; Jc= P–F or P–H coupling constant of the co-ordinated ligand; JL= P–F or P–H coupling constant of the free ligand) as a measure of the π-donor strength of the metal carbonyl fragments, M(CO)x(M = Ni, x= 3; M = Cr, W, x= 5; or M = Mo, x= 3–5). 31 P Chemical-shift values of the free phosphines, ButnPF3–n(n= 1–3) were calculated for a range of bond angles, on the assumption of a bond skeleton of C3v symmetry. Evidence for an increase in bond angle from ButPF2 to But3P was found.