Oxidation of copper(II) hydroxyporphyrin (oxophlorin); oxidative ring opening and formation of an ester-linked, dinuclear copper complex

Addition of copper(II) acetate to octaethyl(meso-hydroxy)porphyrin (H2OEPOH ) in THF under a dinitrogen atmosphere produces Cu-II(OEPOH), which has bee n isolated as red crystals and shown to have a meso-hydroxyporphyrin struct ure by UV-vis and EPR spectroscopy. Cu-II(OEPOH) undergoes oxidation by dio xygen to form a novel dinuclear copper complex {Cu-II(OEPOC(O)OEB)Cu-II}. T his dinuclear complex is composed of a copper(II) meso-substituted porphyri n portion (with a planar CuN4 unit), which is attached through an ester lin kage to a helical copper(II) tetrapyrrole that has been ring-opened through oxidative cleavage of a second molecule of Cu-II(OEPOH). The oxidative rin g-opening reaction resembles that of natural heme catabolism but is arreste d at a stage where the oxidized meso-carbon is still appended to the helica l open tetrapyrrole. A mechanism is suggested for this process.