Metalloporphyrins in Polymeric Matrices, Micelles, and Vesicles, IV. Photochemical and Peroxide Oxidations of Magnesium Octaethylporphyrinate in the Presence of Polymeric and Monomeric Imidazole Derivatives

Abstract

Magnesium octaethylporphyrin (MgOEP) in foils of polystyrene was oxygenated quantitatively by visible light and oxygen to yield the corresponding formylbilinate. In poly[1‐phenylethyleneco‐1‐(1‐imidazolyl)ethylene] (95:5 or 78:22 mol %) the quantitative formation of MgOEP cation radical was observed. The photooxygenation was fully suppressed in this copolymer. This is explained with a physical quenching of singlet oxygen by imidazole. — Oxidation of MgOEP with benzoyl peroxide in the presence of imidazole yields either octaethyl‐5‐imidazolylporphyrin or 10‐benzoyloxy‐octaethyl‐5,15‐diimidazolylporphyrin and other highly substituted porphyrins. The latter produces only one absorption band (λmax ≈︁ 560 nm) in the visible range and yields isoporphyrins (λmax ≈︁ 900 nm) in a reversible reaction with an excess of benzoyl peroxide. The same reaction with the imidazole‐containing copolymer leads to a covalent binding of MgOEP. The reversible formation of an isoporphyrin is observed with molecular oxygen.

Synthesis of imidazole and imidazolium porphyrins

“…The cnmr spectra were recorded at 100 MHz. All starting materials were commercially available; 4-(imidazol-1-yl)benzaldehyde was prepared according to literature procedures [12]. Pyrrole and benzaldehyde were vacuum transferred immediately prior to use; all other reagents were used without further purification.…”

Synthesis of Imidazole and Imidazolium Porphyrins.

“…The cnmr spectra were recorded at 100 MHz. All starting materials were commercially available; 4-(imidazol-1yl)benzaldehyde was prepared according to literature procedures [12]. Pyrrole and benzaldehyde were vacuum transferred immediately prior to use; all other reagents were used without further purification.…”

“…Porphyrins with heterocyclic substitutions on the periphery have been utilized to form a variety of arrays and coordination modes to metal centers [1][2][3][4][5][6]. Specifically, imidazoles covalently attached to porphyrins have been used to form non-covalent arrays through the binding of an imidazole nitrogen to a metal inside of a second porphyrin [7][8][9][10][11][12][13].…”