EPR characterization of new phosphavinyl sigma radicals

A number of radicals have be en added to 1,3-bis(2,4,6-tri-tert-butylphenyl)diphospha-allene at low temperature in cyclopropane solution. Addition of thiyl and alkoxyl radicals occurs regiospecifically to one of the phosphorus atoms leading to new phosphavinyl radicals, isoelectronic with vinyl radicals, which have been characterised by means of EPR spectroscopy. The results of ab initio calculations are in agreement with the experimentally determined spectral parameters and suggest that these radicals are bent, with a PCP bond angle of ca. 150 degrees. In contrast, silyl and germyl radicals appear to add to the carbon atom of the phospha-allene.