APPROACHES TO A CATHODIC ROUTE TO POLYPYRROLYLVINYLENES

Cathodic hydrodimerisation and cleavage reactions of 5-substituted pyr role-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 voltamme tric and coulometric experiments together with detailed product analys es indicate that both hydrodimerisation and cleavage to highly reactiv e quinodimethane analogues are involved, In some cases carbanions are formed by cleavage, rather than quinodimethanes, and these undergo rea ction with their precursor either via self-protonation or by nucleophi lic attack. The key structural features of some of the pyrrolic polyme rs have been determined, notably using direct pyrolysis mass spectrome try (DPMS). They are highly coloured (red-black), paramagnetic, solubl e 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. reduc tive cleavage is not complete.