Preparation and ESR of phosphorus spiro compounds. Part II: Stereo‐isomerization of organo‐phosphorus radicals

Abstract

Abstract The synthesis of bis{2,2î‐(5,5î‐dimethoxy)biphenylenephosphonium and bis {2,2′‐(5,5′‐dimethylamino)biphenylene}phosphonium salts is described. The related spiro phosphoranyl radicals II and III, 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′‐biphenylene)phosphoranyl radical I. In this investigation we found also that the radical obtained by photolysis of bis(2,2′‐biphenylene)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.