CONTROLLING FACTORS OF STEPWISE VERSUS CONCERTED REDUCTIVE CLEAVAGES - ILLUSTRATIVE EXAMPLES IN THE ELECTROCHEMICAL REDUCTIVE BREAKING OF NITROGEN HALOGEN BONDS IN AROMATIC N-HALOSULTAMS

The cyclic voltammetry of the reductive cleavage of N-fluoro-, N-chloro-, and N-bromosaccharin sultams and of their 4-nitro-substituted analogues was investigated in acetonitrile at an inert electrode. This series of compounds provides particularly clear evidence that the two main factors governing the occurrence of a stepwise or a concerted mechanism in reductive cleavages are the energy of the pi* orbital, possibly accommodating the incoming electron, and the strength of the breaking bond. In the concerted cases, application of the theory of dissociative electron transfer allowed the estimation of the nitrogen-halogen bond dissociation energy and of the standard potential and intrinsic barrier of the reaction. The standard potential for the reduction of the nitrogen-centered sultam radicals could also be determined from the oxidation of the amide ion obtained from the reductive cleavage of the halosultams or from the deprotonation of the sultams.