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.
Debad
Jeff D.
JD
Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712.
Morris
Jonathan C.
JC
Magnus
Philip
P
Bard
Allen J.
AJ