In light of frontier orbital theory, HOMO-LUMO gaps and singlet-triplet gaps provide a popular and well-justified measure of a molecule's reactivity. The low calculated singlet-triplet gap of around 0.5 eV for Fe(L1)(N) is consistent with the relatively reactive nature of analogous compounds with stabilized, carbene-type species such as CO and isocyanides. Notably, an S-T gap of almost 0.9 eV is predicted for Co(L1)(C), while even higher S-T gaps > 1 eV are predicted for the other carbido complexes examined, strongly suggesting that these complexes should exist as stable compounds.