Two-electron oxidation of N,N,N ',N '-tetramethylphenylenediamine with a chromium(V) salen complex

The oxidation of tetramethylphenylenediamine (TMPD) with (salen) (CrO+)-O-V generates initially the 2-electron product TMPD2+, followed by the reaction with excess TMPD to yield the radical cation, TMPD center dot+. The kinetics of both TMPD/(salen) (CrO+)-O-V and TMPD/TMPD2+ reactions are acid-dependent, with TMPD being the most reactive form, and the doubly protonated TMPDH22+ exhibiting no discernible reactivity toward either (salen) (CrO+)-O-V or TMPD2+. The specific rate constants for the individual reactions are: TMPD/(salen) (CrO+)-O-V, k = (6.28 +/- 0.50) x 10(9) M-1 s(-1), TMPDH+/(salen) CrVO+, (3.89 +/- 0.31) x 10(5), TMPD/TMPD2+, (7.61 +/- 0.42) x 10(8), and TMPDH+/TMPD2+, (3.46 +/- 0.22) x 10(4).