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Biliverdin-dimethylester (l), Mesobiliverdin-dimethylester (2) und 1 ',8'-Diathoxy-I',8'-didesoxobiliverdin-diathylester (4) bilden 1 : 1-Komplexe mit zweiwertigen Mn-, Co-, Ni-, Cuund Zn-Ionen. Die Komplexe liegen entweder in einer cyclischen, nahezu planaren ,,phlorinartigen" Konformation vor (Amax = 800-900 nm) oder in einer nicht naher charakterisierten, offenkettigen, ,,bilatrienartigen" Form (Amax = 650-700 nm). Die Komplexe weisen polarographische Stufen bei niedrigen Potentialen auf und gehen leicht irreversible Additionsreaktionen ein. In Essigsaureanhydrid gelang die fast quantitative Cyclisierung von Biliverdinkomplexen zu Oxaporphyrinen. Die chemischen Eigenschaften und Ergebnisse aus Modellberechnungen bei Biliverdinaten werden mit denen von Metalloporphyrinen verglichen. Metal Complexes of Biliverdin DerivativesBiliverdin dimethyl ester (l), mesobiliverdin dimethyl ester (2) and I ',8'-diethoxy-l',l'-dideoxobiliverdin diethyl ester (4) form 1 : I-complexes with divalent metal ions of Mn, Co, Ni, Cu and Zn. The complexes exist either in a cyclic near-planar, "phlorin-type" configuration (Amnx = 800-900 nm) or in an "open-chain" configuration (Amax = 650-700 nm). The complexes give rise to low polarographic oxidation and reduction potentials and undergo irreversible addition reactions. The metal complexes of biliverdjn cyclize in acetic anhydride quantitatively, yielding oxaporphyrins. The chemical properties of the biliverdins and the results of model calculations on these systems are compared with those of the corresponding porphyrins.Die Eigenschaften von Metallkompiexen des Biliverdin-dimethylesters (1) und seinen Derivaten wurden im Gegensatz zu den Metalloporphyrinen bisher kaum untersucht. Elektronenspektren 1,*.3) und Elementaranalysen1.2) sind in wenigen Fallen zuganglich, uber die Geometrie des Ligandenfeldes und die chemischen Eigenschaften der offenkettigen Tetrapyrroliiganden ist nichts bekannt. Unerwartete Eigenschaften bei von uns dargestellten Formylbiliverdinen4-6), der Wunsch das Eisenbiliverdin als mogliches Zwischenprodukt des biologischen Hamabbaus zum Biliverdin zu charakte-*) Korrespondenz bitte an diesen Autor unter dieser Adresse richten.

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have the same number of ring members and which, in addition to complexing sodium, rubidium, and cesium, also complex potassium. ( 5 ) solubilizes N a M n 0 4 in chloroform and benzene even more readily than (3). Remarkably, ( 5 ) is the only 18-membered ring compound described here which also solubilizes potassium permanganate, albeit not to the same extent as NaMn04. The thiophenophane ( 6 ) , on the other

Copolymers from styrene and 1-vinylimidazoles (4a-f), form low spin adducts with iron(I1) porphyrins and iron(II1) porphyrins, when the content of imidazolyl groups in the polymer is ten mole percent or more. With polymers having a content of imidazolyl groups of less then one mole percent, only high spin adducts are observed. With terpolymers, in which the porphyrin is covalently bound to the copolymer the same phenomenon is observed. Only the high spin Fe(I1) porphyrin adducts in the solid state adsorb molecular oxygen like cobalt(I1) porphyrins under the same conditions. Adsorptions and desorptions of oxygen are much slower in the cases of iron(I1) porphyrins than with the cobalt(I1) porphyrins. Electronic and ESR spectra as well as susceptibility measurements were used to characterize the reported spin states.Iron(I1) porphyrins (hemes) in proteins bind molecular oxygen and activate it for oxidations of various organic substrates, including the porphyrin periphery itself'.*). However, the porphyrins have t o be fixed in a monomeric state t o fulfill this task. If two heme molecules are allowed to react with one molecule of oxygen, rapid and irreversible oxidation t o the iron(II1) state takes place3). Therefore, the bioorganic approach t o produce stable or catalytically active oxygen complexes would be t o bind a few monomeric heme molecules t o rigid synthetic polymers. Wang4) has described the first successful experiment to bind oxygen reversibly to such a synthetic system. It needed, however, a 104-105 molar excess of I-phenylethylimidazole over heme to be active, and therefore, it represents a n extremely viscous solution which is dificult t o be tested as a catalytic system. A heme coordinated t o a copolymer of vinylimidazole and styrene5', and a cobalt porphyrin coordinated to a polystyrene containing some vinylimid-azole6' units, have been reported t o bind oxygen reversibly in the solid state. Many other reports o n the redox properties of heme-polymer adducts in solution have appeared'), but there is, t o our knowledge, only one report on the reversible binding of molecular oxygen').

Sutnwzary Octaethyloxophlorin (I) yields the stable radical direct oxidation of the zinc octaethyloxophlorin with (11) on aerial oxidation ; traces of such autoxidation oxygen or bromoacetamide. products are considered to account for the paramagnetism reported for oxophlorins.

Die Oxidation des Oxophlorins (I) mit z‐.

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.