FT-IR and Theoretical Analysis of the Characteristic Bonding Properties in the Multiplet Metal Porphyrin Carbene Complexes

FT-IR and theoretical studies of the d^6 and d^7-porphyrin carbene complexes revealed that the metal–Ccarbene bond is a double bond in the singlet state, while the metal–Ccarbene bond is a single bond in the multiplet state. Since the radical on the Ccarbene delocalized to the (alpha)-carbonyl group, the stretching of the C=O double bond shifted downward in the multiplet states.