Oxidation of 1,10-phenanthroline by tetraoxomanganate(VI) and (VII). Preparation, structure and properties of 1H-cyclopenta[2,1-b:3,4-b′]dipyridine-2,5-dione

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Abstract
Oxidation of 1,10-phenanthroline with tetraoxomanganate(VI) gave good yields of ketone 3 and the previously unknown dione 5, formed by the unusual further oxidation of 3 at the 2 position of a pyridine ring. In contrast, use of the tetraoxomanganate(VII) gave the bipyridine diacid 2(69%), ketone 3(20%) and only a trace of the dione 5. The X-ray crystal structure of the anion of 5 indicates that the negative charge is located mainly on the 2-O rather than 5-O atom, with some delocalisation into the pyridine ring.