APPROACHES TO A CATHODIC ROUTE TO POLYPYRROLYLVINYLENES

Cathodic hydrodimerisation and cleavage reactions of 5-substituted pyrrole-2-carboxaldehydes have been explored with a view to developing an electroreductive route to polypyrrolylvinylenes. Polymers are formed by controlled potential reduction at mercury cathodes. Cyclic voltammetric and coulometric experiments together with detailed product analyses indicate that both hydrodimerisation and cleavage to highly reactive quinodimethane analogues are involved, In some cases carbanions are formed by cleavage, rather than quinodimethanes, and these undergo reaction with their precursor either via self-protonation or by nucleophilic attack. The key structural features of some of the pyrrolic polymers have been determined, notably using direct pyrolysis mass spectrometry (DPMS). They are highly coloured (red-black), paramagnetic, soluble in organic solvents, probably linear and with molecular weights (M(w)) in the region of 5500. Combustion microanalysis combined with DPMS suggests repeat units such as C7H7NO2, C6H6NO2 and C7H8NO2, i.e. reductive cleavage is not complete.