Preparation and ESR characterization of polyalkyl-s-indacenyl anion-radicals from polyalkyl-1,5-dilithio-s-indacenes

Polyalkyl-(or chloropolyalkyl)-s-indacenyl anion radicals were obtained from the organodilithium derivatives of the corresponding substituted-1,5-dihydro-s-indacenes by three different methods: (i) UV photolysis, (ii) oxidation by a ferrocenium salt, (iii) single electron transfer reaction from an electron rich olefin. The last reaction (iii) involves transient formation of an unstable polyalkyl-lithio-s-indacenyl imidazolidinium salt. The same salt, obtained by another way by reacting 1,3-dimethylimidazolidinium chloride with the polyalkyl-1,5-dilithio-s-indacene, also leads to the corresponding lithium polyalkyl-s-indacenyl anion radical. All lithium polyalkyl-s-indacenyl anion radicals studied were characterized from their ESR spectra. They present a characteristic symmetrical spin distribution. On the contrary a Rhodium-COD polyalkyl-s-indacene radical presents a non symmetrical spin distribution.