Syntheses, electrochemistry and reactivities of pyridine amide complexes of chromium(III) and manganese(III)

Abstract

Reactions of anhydrous CrCl3 with H2bpb and H2bpc [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; H2bpc = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene] in dimethylformamide and manganese(III) acetate with H2bpc in methanol, yielded the respective [CrIII(bpb)Cl]·xH2O, [CrIII(bpc)Cl]·H2O and [MnIII(bpc)(O2CMe)] complexes. The electrochemistry of the chromium(III) amide complexes has been studied by cyclic voltammetry. They exhibit reversible oxidation couples with E°values ranging from 0.28 to 0.80 V vs. ferrocenium-ferrocene. Except for [CrIII(bpb)(CN)2]- which has a quasireversible reduction couple at -1.97 V, the electrochemical reductions are irreversible. The complexes [CrIII(bpb)(H2O)2]ClO4, [CrIII(bpb)Cl(MeOH)] and [MnIII(bpc)(O2CMe)] have been shown to catalyse olefin epoxidation by iodosobenzene. With [Mn(bpc)(O2CMe)], catalytic oxidation of alkanes by PhIO has also been observed. An oxygen-rebound mechanism involving a Mnv=O or a Crv=O intermediate is proposed for the PhIO oxidation reactions.