BREAKING BONDS WITH ELECTRONS: STEPWISE AND CONCERTED REDUCTIVE CLEAVAGE OF C-Se BOND IN BENZYLSELENOCYANATES

CASTRO GODOY, WILBER D.; BOUCHET, LYDIA M.; SCHMIDT, LUCIANA C.; ARGÜELLO, JUAN E.

Carlos Paz

Conferencia; 13th Latin American Conference on Physical Organic Chemistry; 2015

The coupling between charge transfer and bond cleavage between two heavy atoms occurs in a large number of chemical, biochemical and catalytic processes, such as cleavage of C-halogen bonds in organic halides as well as other bonds. In this context, the concerted dissociative electron transfer model has been applied with success to both homogeneous and heterogeneous concerted dissociative electron transfers, including for C?halogen bonds, O?O bonds, but also N?halogen, N?S, S?C and S?Cl bonds.1We have recently described the electrochemical reduction of different phenacyl thiocyanates and phenacyl selenocyanates where the SCN and SeCN groups can be considered as pseudohalogen groups.2 These functional groups can also be used as a masked mercapto/seleno group, as wells as precursors toward the synthesis of sulphur/selenium-containing organic compounds.The electrochemical reduction of various substituted benzyl thiocyanates showed a change in the cleavage mechanism as a function of the substituent on the benzyl ring.3 However, the parent selenide derivatives have not been study yet.Then, in this work we have selected benzyl selenocianates (1a-c) bearing electron donor and withdrawing groups (Scheme 1). We also studied the concerted or stepwise nature of the bond breaking processes upon injection of electrons and provided a complete analysis of the reduction processes by using cyclic voltammetry (CV) and the concerted dissociative electron transfer model. For the p-nitrobenzyl selenocyanate (1c), a stepwise dissociative electron transfer mechanism with an anion radical as intermediate takes place, the electron being transitorily located on the π* orbital, before cleavage occurs at the Se?CN bond. However for benzylselenocyanate (1a) and p-methoxybenzyl selenocyanate (1b) the reduction is concerted with bond cleavage, with the electron going directly in the σ* orbital of the Se?CN bond.References:1.- Houmam, A. Chem. Rev., 2008, 108, 2190.2.- Bouchet, L. M.; Peñéñory, A. B.; Robert, M.; Argüello, J. E. RSC Advances, 2015, 5, 11753.3.- Hamed, E. M.; Doai, H.; McLaughlin, C. K.; Houmam, A. J. Am. Chem. Soc., 2006, 128, 6595.