Donor-substituted phosphanes – surprisingly weak Lewis donors for phosphenium cation stabilisation

Abstract

Paradoxically, N- and O-donor substituted tri-arylphosphanes are shown to be weaker donors than PPh₃ when binding the soft Lewis acid moiety [PPh₂]⁺. This arises from internal solvation and rehybridisation at phosphorus, precluding chelation and increasing steric demand, in direct contrast to coordination modes observed for metal complexes.