Double-pillared cobalt Pacman complexes: synthesis, structures and oxygen reduction catalysis

Abstract

The syntheses and structures of binuclear cobalt complexes of a double-pillared cofacial Schiff-base pyrrole macrocycle (L) were determined and their activity as catalysts for the oxygen reduction reaction evaluated. The new binuclear cobalt complex, [Co(2)(L)], 1 was formed in good yield using a salt-elimination method and was characterised as adopting a cofacial structure in solution by NMR spectroscopy and as its THF and pyridine solvates in the solid state by X-ray crystallography. Using a variety of spectroscopic techniques, this complex was found to react reversibly with dioxygen to form a new paramagnetic complex. Furthermore, the new aqua-hydroxy double salt [Co(2)(μ-H(3)O(2))(py)(2)(L)][BF(4)] 2 was characterised by X-ray crystallography. In acidified benzonitrile solution, 1 behaves as a catalyst for the selective four-electron reduction of dioxygen to water and showed a large improvement in efficacy compared to its o-phenylene Schiff-base analogues.

High‐Yielding Synthesis of a Hetero‐Pacman Compound and the Characterization of Intermediates and Side‐Products

“…Catalytic O 2 reduction has been promoted by bimetallic platforms afforded by either cofacial Schiff-base calixpyrrole [14][15][16][17] or porphyrin Pacman systems. [18][19][20][21][22][23] Initially, the 4209 lated and characterized during the two-step synthesis procedure, including a hydroxylated version of the boronic acid substituted precursor molecule derived by a base-assisted rearrangement.…”

Terpyridine–Porphyrin Hetero‐Pacman Compounds

“…These bimetallic scaffolds are also competent in the activation and reduction of dioxygen. [50][51][52][53][54][55] To this end, metal-polypyridine complexes exhibit rich photo-and electrochemistry with regard to the activation of reactants, especially oxygen-based small molecules. Bis(terpyridine) Pacman compounds of diruthenium [56][57][58] and Pt À Ru [59] complexes have been prepared, but the preparation of a Pacman system that combines the attractive properties of a porphyrin active site and metal polypyridine in a single Pacman architecture has yet to be achieved.…”

Co3O4 nanoparticles anchored on nitrogen-doped reduced graphene oxide as a multifunctional catalyst for H2O2 reduction, oxygen reduction and evolution reaction

“…Designing bifunctional catalysts with good oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities would be highly beneficial to the development of metal-air batteries. However, developing catalysts for ORR and OER with high activity at low cost remain great challenges34. Platinum-based materials are known to be the most active electrocatalysts for the ORR and the OER.…”