cis-Diazene (diimide) has been implicated as an intermediate in stereospecific reductions by in situ generated diazene1and in nitrogenase action on nitrogen.2This molecule and itsrather well-studied trans isomer3,4have been the objects of anumber of theoretical studies.5Yet, only fragmentary andinconclusive evidence has been reported for the direct observation of the cis isomer.6,7We now report the isolation of theclosest homologue of cis-diazene, cis-methyldiazene, and itsinfrared spectrum. Based on the assignment of this spectrum, we conclude that cis-diazene is yet to be observed. © 1979, American Chemical Society. All rights reserved.