Hypovalent Radicals. 6. Electroreduction of Diazodiphenylmethane-Intermediacy of Ph2CN-. and PhC-.

Article abstract of DOI:10.1021/ja00547a007

The electrochemical reduction of diazodiphenylmethane (Ph2CN2) at a platinum cathode in DMF-0.1 F (n-Bu)4ClO4 has been shown to afford benzophenone azine ((Ph2C=N-)2) as the principal product, along with lesser amounts of Ph2CH2 and several other compounds.Product formation occurs by a chain process in which the carbene anion radical, Ph2C^-., is produced from electrogenerated Ph2CN2^-. by rapid loss of nitrogen.Ph2CH^-, the first-observed intermediate in Ph2CN2 electroreduction, is obtained from Ph2C^-. either by protonation followed by reduction or by hydrogen atom abstraction from a component of the solvent-electrolyte system.Propagation of the chain involves coupling of Ph2CH^- with Ph2CN2 to produce Ph2CH<*>N=CPh2 followed by proton transfer from this anion to Ph2C^-. to give (Ph2C=N-)2^2- and Ph2CH^., respectively.Regeneration of Ph2CN2^-. occurs by electron transfer from either (Ph2C=N-)2^2- or (Ph2C=N-)2^-. to Ph2CN2.Termination of the chain occurs upon protonation of Ph2CH^-.In the presence of the electroinactive proton donors, diethyl malonate and 2,2,2-trifluoroethanol, azine formation is interdicted and Ph2C=NNH2 and Ph2CH2 are the two major products.Studies of the Ph2CH2/Ph2C=NNH2 product ratio as a function of proton donor concentration and temperature have established that protonation (and other reactions) of Ph2CN2^-. occurs exclusively on terminal nitrogen while Ph2CH2 arises via Ph2C^-..No evidence was obtained for either hydrogen atom abstraction by or protonation of C_α of Ph2CN2^-..