Carbene Cation Radicals: The Kinetics of Their Formation from Diazoalkane Cation Radicals and Their Reactions

Article abstract of DOI:10.1021/ja00251a002

The unimolecular decomposition reacions of trhree diazoalkane (diazodiphenylmethane and related compounds) cation radicals were studied in acetonitrile, methanol, and mixed solvent.Kinetic studies, using transient electrochemical methods, show that the reaction rates are insensitive to solvent, the presence of nucleophiles, and the nature and concentration of electrolytes.At temperatures above 300 K the competing second-order reactions, observed to minor extents at lower temperatures, were insignificant.Arrhenius activation energies were observed to be the order of 16 kcal/mol with entropies of activation close to zero.It is suggested that the rate-determining step in all cases is unimolecular loss of dinitrogen (reaction i) to generate the reactive carbene cation radicals.The carbene cation radicals show reaction patterns that exhibit both electrophilic and Ar2C=N2^.+ -> Ar2C^.++N2 radical-like facets.In acetonitrile complex reaction mixtures were obtained suggesting that the carbene cation radicals react rather indiscriminately.In more nucleophilic methanol, the major products were Ar2C(OMe)2, Ar2C=O, and Ar2CHOMe in proportions depending strongly on the structure of the carbene cation radical.