Preparation and ESR of phosphorus spiro compounds : part III

The synthesis of 2,2'-biphenylenediphenylphosphonium, 2,2'-biphenylenephenylbenzylphosphonium and 2,2'-biphenylenephenyl(p-nitrophenyl)phosphonium salts is described. The related phosphoranyl radicals I, IV and V, generated by electrochemical reduction, are measured by ESR spectroscopy. A similar procedure is followed for the radicals II and III; related phosphonium compounds are described in the literature. The small values of the phosphorus doublet splitting constants are an indication for a tetrahedron (T) like configuration of the phosphorus. The odd electron is delocalized in the aromatic ligands and the five 3-d orbitals of the phosphorus. It is shown that the spin- and odd electron density distribution depends on the electron affinity of the aryl ligands. This is confirmed by quantum chemical calculations.