Characterization of singly reduced iron(II) porphyrins

Journal Article · Wed Sep 16 04:00:00 EDT 1987 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00253a006· OSTI ID:5890935

Donohoe, R J; Atamian, M; Bocian, D F

Optical absorption, electron paramagnetic resonance (EPR), and resonance Raman (RR) spectra are reported for the one-electron reduction products of a series of Fe/sup II/ porphyrins. The porphyrins include 5,10,15,20-tetraphenylporphyrin (TPP), 2,7,12,17-tetrabromo-5,10,15,20-tetraphenylporphyrin (TPPBr/sub 4/), 2,7,12-tricyano-5,10,15,20-tetraphenylporphyrin (TPP(CN)/sub 3/), and 2,7,12,17-tetracyano-5,10,15,20-tetraphenylporphyrin (TPP(CN)/sub 4/). The iron complexes of these porphyrins represent a series in which the reduction potential is successively shifted to more positive values. The RR and EPR data demonstrate that for all of the complexes reduction results in a low-spin configuration for the metal ion. For (FeTPP)/sup -/ and (FeTPPBr/sub 4/)/sup -/, the unpaired electron resides in the metal d/sub z/sup 2// orbital; however, reduction results in the transfer of a significant amount of paired electron density to the macrocyle through ..pi.. back-bonding. Destabilization the metal d/sub z/sup 2// orbital via ligation of a single pyridine or CO molecule is insufficient to push the unpaired electron from the metal ion to the macrocycle. For (FeTPP(CN)/sub 3/)/sup -/ and (FeTPP(CN)/sub 4/)/sup -/, the unpaired electron resides primarily on the porphyrin ring although a small amount of unpaired density is shared with the metal ion through ..pi..-orbital interactions. The extensive interaction between the metal and porphyrin ..pi.. orbitals which is present in all of the complexes provides a mechanism for enhancing the oscillator strength of formally forbidden charge-transfer transitions. It is suggested that these charge-transfer absorptions are primarily responsible for the complicated optical spectra of the reduced complexes.

• Research Organization: Carnegie Mellon Univ., Pittsburgh, PA
• OSTI ID: 5890935
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:19; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
COMPLEXES
DATA
ELECTRON SPIN RESONANCE
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
IRON COMPLEXES
LASER SPECTROSCOPY
MAGNETIC RESONANCE
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
RAMAN SPECTROSCOPY
REDUCTION
RESONANCE
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES