Anodic Coupling of Diphenylbenzo[k]fluoranthene: Mechanistic and Kinetic Studies Utilizing Cyclic Voltammetry and Electrogenerated Chemiluminescence.

Upon oxidation at a platinum electrode, (7,12-diphenyl)benzo[k]fluoranthene (1) undergoes intermolecular dehydrogenative coupling to form bis-4,4'-(7,12-diphenyl)benzo[k]fluoranthene (2). Further oxidation of this product results in a much slower intramolecular coupling reaction that yields dibenzo{[f,f']-4,4',7,7'-tetraphenyl}diindeno[1,2,3-cd:1',2',3'-lm]perylene (3). 2 can be synthesized via bulk electrolysis of 1 and also by the chemical coupling of 4-bromo-7,12-diphenylbenzo[k]fluoranthene (4) with a nickel catalyst. Compounds 1-3 are capable of electrogenerated chemiluminescence (ECL), and their coupling reactions have been detected and followed using this technique. Cyclic voltammograms of 1 have been digitally simulated to provide mechanistic and kinetic insight into the initial intermolecular oxidative coupling reaction. Evidence supports an EC(2)()EE mechanism, in which the coupling of radical cations of 1 is the rate-limiting step. A second-order rate constant of k = 7500 M(-)(1) s(-)(1) has been determined for the dimerization process by fitting experimental data to theoretical working curves.