Optically active co-ordination compounds. Part XX. Reactions of 1,10-phenanthroline co-ordinated to cobalt(III)

Abstract

The reactivity towards nitration and oxidation of the known ions D(+)-[Co(en)₂(phen)]³⁺ and D(+)-[Co(phen)₃]³⁺ has been studied. (+)[Co(en)₂(phen)] reacts rapidly at room temperature under normal nitrating conditions to give exclusively the 5-nitro-1, 10-phenanthroline derivative which is then slowly oxidised to the 1,10-phenanthroline-5,6-quinone (quinone hereafter) derivative. Both of these reactions occur with no racemisation at the cobalt.

The reactivity of D(+)-[Co(phen)₃]³⁺ towards nitration is much less; but D(+)-[Co(quinone)₃]³⁺ has been prepared without loss of optical activity, by oxidation with nitric acid–sulphuric acid in the presence of bromide ion. Several chemical correlations of optical configurations emerge from the various reactions and the circular dichroism spectra are discussed in relation to the configurations thereby revealed. The tris-bipyridyl cobalt(III) ion has been obtained optically active, and its properties are described.

A new synthesis of the free ligand 1,10-phenanthroline-5,6-quinone from the 5-nitro-derivative is described, together with a method for isolating the same compound from its cobalt complex.