EPR CHARACTERIZATION OF NEW PHOSPHAVINYL SIGMA-RADICALS

A number of radicals have be en added to ,3-bis(2,4,6-tri-tert-butylph enyl)diphospha-allene at low temperature in cyclopropane solution. Add ition of thiyl and alkoxyl radicals occurs regiospecifically to one of the phosphorus atoms leading to new phosphavinyl radicals, isoelectro nic 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 tha t these radicals are bent, with a PCP bond angle of ca. 150 degrees. I n contrast, silyl and germyl radicals appear to add to the carbon atom of the phospha-allene.