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Abstract. The synthesis of 2,2'-biphenylenediphenylphosphonium, 2,2'-biphenylenephenyIbenzylphosphonium 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 I1 and 111; 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.

The synthesis of bis{2,2'-(5,5'-dimethoxy)biphenylenephosphonium and bis {2,2'-(5,5'-dimethylamino)biphenylene}phosphonium salts is described. The related spiro phosphoranyl radicals I1 and 111, generated by electrochemical reduction, are measured by means of ESR spectroscopy. We observed the same small values of the phosphorus doublet splitting constants as for the bis(2,2'-bipheny1ene)phosphoranyl radical I.In this investigation we found also that the radical obtained by photolysis of bis(2,T-bipheny1ene)phosphorane at -120° appeared to be identical with the radical obtained by electrochemical reduction of the bis(2,2'-biphenylene)phosphonium ion. Irradiation of the phosphorane which has a trigonal bipyramidal (TBP) configuration results in a cleavage of the equatorial hydrogen atom. The small values of the phosphorus doublet splitting constants give rise to a tetrahedron like (T) configuration in which the unpaired electron is delocalized in the aryl ligands. We also discuss the associative character of these radicals in dependence on the temperature.