Mechanism involving a preceding structural change in homogeneous redox catalysis

Abstract

In this work we report examples of a preceding structural change in homogeneous redox catalysis. This behavior was encountered in the catalyzed reduction of xanthylideneanthrone, 1 , and thioxanthylideneanthrone, 2 . The neutral form of each of these compounds exists in two structures, a minor form (B) and a major form (A). However, in the anion radicals, the preference is reversed with B − predominating over A − . Normal redox catalysis would involve the reduced form of the catalyst, Q, reacting in an uphill reaction with A to produce A − and P, the oxidized form of the catalyst. The unfavorable reaction would be driven by the rapid conversion of A − to B − . In the case of 1 and 2 , however, Q instead reacts with the minor form, B, and the extent of catalysis can be used to evaluate the rate and equilibrium parameters for the preceding structural change, the A ⇌ B reaction.