THE STRUCTURE OF DIPHOSPHAALLENIC RADICAL CATIONS AS EVIDENCED BY EPREXPERIMENTS AND AB-INITIO CALCULATIONS

The isotropic hyperfine coupling constants of the diphosphaalkene radi cal cation have been measured by EPR spectroscopy after electrochemica l oxidation of ArP=C=PAr (and ArP=C-13=PAr) in tetrahydrofuran (THF), The two P-31 constants as well as the C-13 coupling are close to 90 MH z, Taking HPCPH as a model compound, the structure has been assessed, by extensive ab initio calculations including correlation effects at t he MP2 and MCSCF levels of theory, It is found that oxidation of the a llenic -P=C=P- structure leads to the formation of two rotamers with H PPH dihedral angles of 45 degrees and 135 degrees. These two structure s are compatible with the Jahn-Teller distortion of allene, The calcul ated hyperfine constants support the EPR results.