2,5-DIAZACYCLOPENTADIENYUDENE: A STANDARD CARBENE OR A HIGHLY REACTIVE DIRADICAL ?

Abstract
2,5-Diazacyclopentadienylidene (2H-imidazolylidene), generated either by photolysis or thermolysis from 2-diazo-2H-imidazole, reacts with benzene derivatives to give mainly a mixture of o-, m-, and p-substituted 2-phenylimidazoles. The carbene shows a strong diradical character, in sharp contrast with the well-known behavior of cyclopentadienylidene.