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.