Heterocyclic free radicals. Part 1. 4,5-Diazafluorene derivatives of Koelsch’s free radical: an EPR and metal-ion complexation study

Abstract

Heteroaromatic precursors to nitrogen substituted derivatives of Koelsch’s free radical have been prepared by the condensation of 4,5-diazafluorene with a fluorenylidene or diazafluorenylidene. These compounds appear coloured and can exist in different tautomeric forms. An improved one pot synthesis of 4,5-diazafluorenone has been developed by the oxidative ring contraction of 1,10-phenanthroline with aqueous potassium permanganate. Aza derivatives of Koelsch’s free radical are easily generated by oxidation of the appropriate precursors with K₃Fe(CN)₆. Treatment of 9-[(9H-4,5-diazafluoren-9-ylidene)phenylmethyl]-9H-fluoren-9-yl radical with CuCl₂ in EtOH gives a brown precipitate of a 1∶1 radical–ligand complex.