First characterization of phosphoenol radical cations in solution and the kinetics of the mesolytic P-O bond cleavage in sterically shielded enoxy-phosphorus compounds after one-electron oxidation

The new phosphoenols 1-6 and 9 have been synthesized starting from stable s imple enols. Upon chemical or electrochemical oxidation, for the first time phosphoenol radical cations could be characterized in solution by cyclic v oltammetry and EPR spectroscopy. The preparative one-electron oxidation of the model systems afforded the benzofurans indicating an unprecedented meso lytic P-O bond cleavage. Using cyclic voltammetry the kinetics of this step was determined in dichloromethane and acetonitrile. A rationale to account for the selectivity of the mesolytic P-O bond cleavage is given. According ly, reactive species P+(OEt)(2) (16) and P-.(=O)(OEt)(2) (18) can be genera ted selectively by mesolytic cleavage. At high scan rates, the partially re versible oxidation wave 1(.+)reversible arrow 1(++) could be monitored indi cating that the dication of enol phosphate 1 is relatively stable.