Infrared Spectroelectrochemical Reduction of Iron Porphyrin Complexes
The spectroelectrochemistry of iron porphinones and their nitrosyl complexes were examined by infrared spectroscopy, as well as ferrous octaethylporphyrin nitrosyl. With the use of d8-THF, the solvent was transparent down to 1200 cm−1. For the porphinones, the reduction of the macrocycle ring could be observed by the changes in the νCO band and, for the nitrosyl complex, the changes in the nitrosyl ligand were directly observable from the νNO band. Formation of the ferrous complexes led to a small downshift in the νCO band. Further reduction to the formal Fe(“I”) complex led to more complex spectra which were interpreted with the help of density functional theory (DFT) calculations. The reduction of Fe(OEP)(NO) and its porphinone analogues was also examined. The reduction of the iron porphyrin and porphinone nitrosyl complexes lead to substantial decreases in the νNO band from 1665 to 1670 cm−1 to 1442−3 cm−1. The energy of the νNO band in the reduced complex was unaffected by the presence of carbonyl groups on the porphinone ring, indicating little additional delocalization of the electron density of the Fe-NO moiety because of the carbonyl groups. The identity of the νNO bands was confirmed with 15N substitution of the Fe(OEP)(NO) complex. The νCO band on the porphinone ring was found to be sensitive to the degree than electron density was delocalized to the ring.