Cobalt complexes of pyrrolecarboxamide ligands as catalysts in nitro reduction reactions: influence of electronic substituents on catalysis and mechanistic insights

Abstract

This work presents two square-planar Co(III) complexes within a N₄ coordination sphere created by two related pyrrolecarboxamide ligands. Both complexes functioned as catalysts for the hydrazine-mediated reduction of aromatic, heterocyclic, as well as aliphatic nitro substrates. Binding studies provided evidence that the square-planar Co(III) complexes bind two equivalents of a substrate whereas mechanistic studies established the involvement of a Co³⁺–Co²⁺ based redox cycle in the catalysis. The Co(III) complex having electron-withdrawing –Cl substituents on the ligand was noted to be a much better catalyst than the one with electron-donating –CH₃ substituents.