 Cobalt(III)-carbene radicals have found catalytic applications in cyclopropanation reactions, as well as in a variety of other catalytic radical-type ring-closing reactions.Theoretical calculations and EPR studies confirmed their radical-type behaviour and explained the bonding interactions underlying the stability of the carbene radical.Stable carbene radicals of other metals are known, but the catalytically relevant cobalt(III)-carbene radicals have thus far only been synthesized as long-lived reactive intermediates.