Photoreduction of Iron(iii)porphyrins

Abstract

Abstract— Ferrideuteroporphyrin in benzene, water or micelle solutions containing primary or secondary alcohols as well as in pure or basic 2‐propanol solutions is clearly reduced to the ferrous state by continuous light irradiation in the Soret region. Quantum yields range between 4 × 10−4 and 3 × 10−2 depending on the solvents used and on the coordination state of the ferric porphyrin. As inferred from laser pulse photolysis experiments, the primary chemical step appears to be the homolytic cleavage of the bond between the ferric ion and a coordinated alcoholate anion leading to the ferrous porphyrin and the alkoxy radical. This cleavage is found to occur within less than 50 ns. The alkoxy radical rearranges leading to the α‐hydroxyalkyl radical which reacts with excess ferric porphyrin leading to further reduction. The reaction rate constant for the reaction of α‐hydroxyisopropyl radicals is found to be k = (2.1 ± 0.3) × 108M−1 s−1 in pure 2‐propanol. As expected, this rate is greatly increased in basic 2‐propanol where α‐hydroxyisopropyl radicals deprotonate.

Photoreduction of iron protoporphyrin IX chloride in non‐ionic triton X‐100 micelle studied by electronic absorption and resonance Raman spectroscopy

“…2(D)], as observed by others. 6 Although acid-base equilibrium presumes coordination of the iron center by two water molecules in acidic conditions, close association of the negatively charged chloride ion in the coordination sphere of iron is indicated by the observation of the 10 mode at 1631 cm 1 , which is close to 1632 cm 1 reported for the same mode in Fe III PPCl complex by Spaulding et al 41 The charge neutralization of the bis-aqua complex Fe III PP(H 2 O) 2 with a single Cl may cause one axial water molecule to bind differently to the other, giving a near fivecoordinated configuration. This is confirmed by the presence of a band at 644 nm in the absorption spectrum [ Fig.…”

A survey of the iron ligand-to-metal charge transfer chemistry in water

“…As this molecule acts like a reservoir for the small molecule NO it can be considered as photo-trigger molecule with huge impact for medical and biological research. 87 Inspired by the ability of Fe(III)-porphyrins to bind to alcohols and to form the respective oxygen-centred radical after a LMCT activation step, 91,92 the group of Tsuchida investigated a system consisting of (tetraphenylporphyrinato)Fe(III) complex with four alkyl phosphocholine ligands as well as an axially Scheme 11 Application of iron-LMCT on the photooxidation of cyclic ketones. 81 Scheme 12 Iron-assisted oxidation of arsenic.…”