Cathodic oligomerisation of bis(diazo) compounds of the indenofluorene series Part 2. Kinetic and mechanistic aspects

Abstract

The time dependence of the disappearance of diazo groups during the constant-current electrolysis indimethylformamide solution at a platinum cathode of two bis(diazo)indenofluorenes (1) and (2) giving oligomeric polyazines has been investigated. The form of the diazo group concentration vs. time curves shows that chain reactions are involved and the slopes place limits on the chain lengths. By interruption of the current after partial reaction it was possible to show, using an adaptation of methodology previously developed to explain the electrochemical reduction of 9-diazofluorene, that for (1) the chain-termination process is kinetically of the first order in the chain carrier; kinetic, parameters for the propagation and termination processes in homogeneous solution were obtained. The discrepancy between the observed concentration/time curve for continuous electrolysis and that calculated from these kinetic parameters provides information on the initiation step, yielding a consistent picture of a chain carrier formed from four monomer units. Similarly it has been shown that the results for (2) best fit a reaction scheme involving, in the early stages, a trimeric chain carrier which is partitioned between chain transfer to monomer and termination by dimerisation. Details of these processes are discussed, and the way in which the mechanistic schemes permit interpretation of the differing molecular-weight distributions in the final products from (1) and (2) are explained. Supporting evidence is provided by voltammetric experiments on the related monodiazo compound (5) and thermolytic studies of (1)–(3) in solution.