Phosphane lone-pair energies as a measure of ligand donor strengths and relation to activation energies

Using density-functional theory as implemented in the projector- augmented wave method, we have calculated structures, energy levels, structures of the protonated forms, and proton affinities of the phosphanes PH₃, PF₃, P(CF₃)₃, PMe₃, P(NMe₂)₃, P(C₆H₅)₃, P(p-C₆H₄OMe₂)₃, and P(p-C₆H₄NMe₂)₃. The donor strengths of the phosphanes are discussed in terms of lone-pair energies and proton affinities. The influence of the donor ability of the phosphane ligands on the protonolytic cleavage of the metal-carbon bond in [NiCl(CH₂CH₂NH₃)(PR₃)₂]⁺ complexes has been studied. A linear relationship between the lone-pair energies of the phosphanes and the activation barrier has been established. (C) 2000 Elsevier Science B.V.