Electron transfer. 143. Reductions of benzopyrazine derivatives with indium(I)

Solutions of In(I)(aq) in 0.03–0.20 M H+ reduce quinoxaline (Q), phenazine (P), and the N-methylphenazonium cation (MP+) in kinetically separable steps, yielding first a colored radical, then a colorless dihydro compound. The initial stage of these reductions yields 2 equiv. of the radical, and the much slower second stage likewise entails loss of nearly 2 mol of radical per mol of In(I). Individual kinetic profiles exhibit no irregularities attributable to the intervention of In(II). Reactions of phenazine and its N-methylated cation are exceptionally photosensitive. Reductions of phenazine and quinoxaline to their radicals are favored by N-protonation, but reduction of the N-methyl cation is independent of [H+], as are the further reductions of both phenazonium radicals. Reduction of the quinoxalinium radical utilizes paths at two protonation levels (QHradical dot and QH2radical dot+). Although oxidants and reductant alike have access to 2 e− paths, observations in all three systems are consistent with reactions via successive 1 e− steps.