The interaction of iron carbonyls, Fe(CO) 5 , Fe 2 (CO) 9 and Fe 3 (CO) 1 2 with Me 3 NO occurs according to a one-electron redox-disproportionation scheme giving rise to iron carbonyl radical anions: Fe 2 (CO) 8 . - (1), Fe 3 (CO) 1 2 . - (2), Fe 3 (CO) 1 1 . - (3) and Fe 4 (CO) 1 3 . - (4). The role of Me 3 NO, inducing CO-substitution, consists of the generation of reactive 17-electron species with a labile coordination sphere in which the substitution for other ligands occurs, resulting from fast ligand and electron exchange in the confines of the ETC-reaction.