Oxygen activation at a dicobalt centre of a dipyridylethane naphthyridine complex.

The mechanism of oxygen activation at a dicobalt bis-mu-hydroxo core is probed by the implementation of synthetic methods to isolate reaction intermediates. Reduction of a dicobalt(III, III) core ligated by the polypyridyl ligand dipyridylethane naphthyridine (DPEN) by two electrons and subsequent protonation result in the release of one water moiety to furnish a dicobalt(II, II) center with an open binding site. This reduced core may be independently isolated by chemical reduction. Variable-temperature H-1 NMR and SQUID magnetometry reveal the reduced dicobalt(II, II) intermediate to consist of two low spin Co(II) centers coupled antiferromagnetically. Binding of O-2 to the open coordination site of the dicobalt(II, II) core results in the production of an oxygen adduct, which is proposed to be a dicobalt(III, III) peroxo. Electrochemical studies show that the addition of two electrons results in cleavage of the O-O bond.