Phlorin anion

The methyliron(lll) corrphycene complex has been prepared and is stable in the absence of dioxygen the methylcobalt(lll) complex is stable even in the presence of dioxygen. 153 Radiol)ftic reduction occurs at the metal center to produce Fe(ll) and Co(l) corrphycenes, which are also stable upon further radiolytic reduction in neutral solutions they yield species with chlorin-like spectral signatures. In alkaline solutions, species with phlorin-anion-like characteristics are produced. 153 ... 

The anion radicals of metalloporphyrins are reported to give rise to broad single-line esr signals. They are thought to arise from the presence of an unpaired electron in the doubly degenerate eg orbital [Hush (97, 98)]. Phlorin anion radicals yield esr spectra with extensive hyperfine splittings which have not so far been interpreted [Hush (97)]. 

A dramatic difference was observed in the behavior of porphyrin radical anions that contain phenyl v . pyridinium substituents at the meso positions. It was suggested that the radical anions decay either via protonation, to form a neutral radical, or disproportionation, to form a dianion, which then protonates very rapidly. The dianion can take-up a proton at a meso site to form a phlorin anion or take up two protons at a pyrrole ring to form a chlorin. 

A ring localized hydrogenation can be a consequence of the disproportionation of photochemically formed 7t-anion radicals. Such a process was found [243] to proceed in aqueous solutions containing two gold(III) porphyrins Au(Por)Cl, where Por = TMPyP or TPyP, and electron donors (EDTA or TEA), jt-radicals abstract protons from HaO+ ions (pH < 4) and give the parent porphyrin complexes Au(Por)Cl and reduced phlorins Au(H2Por)Cl. 

Highly electropositive ions deactivate the porphyrin towards oxidants. The Sn(IV)-porphyrinates present an extreme here. They are totally stable against molecular bromine but can easily be photoreduced to form porphyrin anion radicals and, in proton-containing solvents, phlorins (Fuhrhop and Lumbantobing, 1970). Both porphyrin Ji-anion radicals and the protonated neutral phlorin radicals usually produce absorption bands around 850 nm (see Sec. 6.5). The lifetimes of a-anion radicals of metalloporphyrins as obtained by pulse radiolysis are also dependent on the central metal ions. Sb(V) and Sn(IV) produce stable... 

Figure 6.4.2 Spectroscopic titration of magnesium-octaethyl-porphyrinate with NBS in chloroform/methanol to yield the corresponding Ji-radical. Here the cation radicals reversibly add methoxide anions to give electroneutral phlorin radicals.

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