In Crystallo Wolff Rearrangement of a Metalated Diazoester: Structural Confirmation of the Singlet Carbene Wolff-Intermediate

-C-C(O)-OEt) is reported as a fleeting intermediate in the photoinitiated fragmentation of a diazoester ligand. Frozen solution and crystal matrix isolation experiments enabled the spectroscopic, magnetic, crystallographic, and computational characterization of this highly reactive species. All methods confirmed a singlet ground state for the WR metallocarbene, which is stabilized by π interactions with the carboxyl substituent, thus complementing computational and transient spectroscopy studies for classic organic WR reactions.