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 = Bu^tPF₂ and Bu^t₂PF; 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 PF_3–nBu^t_n(n= O–3) was assessed. It is proposed to use the quantity ΔJ/J_L(ΔJ=J_c–J_L; J_c= P–F or P–H coupling constant of the co-ordinated ligand; J_L= 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, Bu^t_nPF_3–n(n= 1–3) were calculated for a range of bond angles, on the assumption of a bond skeleton of C_3v symmetry. Evidence for an increase in bond angle from Bu^tPF₂ to Bu^t₃P was found.