Isolation and reactivity of an elusive diazoalkene

Most functional groups, especially those consisting of the abundant elements of organic matter—carbon, nitrogen and oxygen—have been extensively studied and only very few remain speculative due to their high intrinsic reactivity. In contrast to the well-explored chemistry of diazoalkanes (R2C=N2), diazoalkenes (R2C=C=N2) have been postulated in several organic transformations, but remain elusive long-sought intermediates. Here, we present a room-temperature stable diazoalkene, utilizing a dinitrogen transfer from nitrous oxide. This functional group shows dual-site nucleophilicity (C and N atoms) and features a bent C–C–N entity (124°) and a long N–N bond together with a remarkable low infrared absorption (1,944 cm–1). Substitution of N2 by an isocyanide leads to a vinylidene ketenimine. Furthermore, photochemically triggered loss of dinitrogen might proceed through a transient triplet vinylidene. We anticipate the existence of a stable diazoalkene functional group to pave an exciting avenue into the chemistry of low-valent carbon and unsaturated carbenes. Although diazoalkenes have been reported as reactive intermediates in organic chemistry, their detection and isolation remains challenging. Such species have previously only been detected at low temperatures in matrix-isolation studies. Now, a room-temperature stable diazoalkene has been reported, which shows dual-site nucleophilicity and can undergo N2 exchange or lose dinitrogen under irradiation.