The reaction of cobalt(III) octaethylcorrole (CoOEC) with ethyl diazoacetate (EDA) under a nitrogen atmosphere led to the formation of bridged complexes with the carbene moiety inserted into one of the cobalt-nitrogen bonds. The bridged complexes underwent unique thermal isomerization, presumably via the transiently formed axial carbene complex. One of the thermodynamic isomers was characterized by H-1 NMR and mass spectroscopic methods.