SYNTHESES, ELECTROCHEMISTRY AND REACTIVITIES OF PYRIDINE AMIDE COMPLEXES OF CHROMIUM(III) AND MANGANESE(III)

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 [Cr(III)(bpb)Cl].xH2O, [Cr(III)(bpc)Cl].H2O and [Mn(III)(bpc)(O2CMe)] complexes. The electrochemistry of the chromium(III) amide complexes has been studied by cyclic voltammetry. They exhibit reversible oxidation couples with E-degrees values ranging from 0.28 to 0.80 V vs. ferrocenium-ferrocene. Except for [Cr(III)(bpb)(CN)2]- which has a quasireversible reduction couple at -1.97 V, the electrochemical reductions are irreversible. The complexes [Cr(III)(bpb)(H2O)2]ClO4, [Cr(III)(bpb)Cl(MeOH)] and [Mn(III)(bpc)(O2CMe)] have been shown to catalyse olefin epoxidation by iodosobenzene. With [Mn(bpc)(O2CMe)], catalytic oxidation of alkanes by PhlO has also been observed. An oxygen-rebound mechanism involving a Mn(v) = O or a Cr(v) = O intermediate is proposed for the PhlO oxidation reactions.