Syntheses and Reactivity of Diiorn-, Dicobalt-, and Dicopper-Dioxygen Complexes

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Diiron-dioxygen and dicopper-dioxygen complexes play an important role in the reversible binding and activation of O_2 in biological and catalytic processes. We developed various diiron (II) and dicopper (I) complexes as functional models for O_2 transport proteins such as Hemerythrin (Fe_2) and hemocyanin (Cu_2) and mono-oxygenase such as methane monooxygenases (Fe_2 or Cu_n).Diiron Complexes : Only a few structurally and spectroscopically characterized diiron-dioxygen complexes have been reported. In order to synthesize the diiron-dioxygen complexes, it is important to control the ligand environment which is suitable for O_2 binding by two iron ions and stabilizes the mu-peroxo species toward irreversible oxidation. For this purpose, a series of dinucleating ligands with sterically hindered pyridyl and imidazolyl groups has been developed, which has an N_6O donor set with a phenolate or alkoxide bridging group. They form five-coordinate dinuclear [Fe_2 (L) (RCO_2)]^<2+> with an exoge … More nous carboxylate bridge, which react with O_2 to form mu-peroxo species. It was found that thermal stability toward irreversible oxidation and dioxygen affinity of those complexes are highly dependent on the stereochemistry and the electron donor ability of dinucleating ligands and bridging carboxylate. Finally we have succeeded in preparation and structural characterization of a cis-mu-1,2-peroxo diiron complex which is the first example of a crystallographically characterized diiron-dioxygen complex that binds O_2 reversibly at ambient temperature.Dicopper Complexes : A series of copper (I) complexes ([Cu (L)]^+) having tripodal tetradentate ligands ((R_1R_2NCH_2CH_2)_3N : L) was synthesized. Reactivity of those complexes with O_2 was investigated. They form trans-mu-1,2-peroxo species at low temperature. It was found that stereochemistry and thermal stability of dioxygen complexes are highly dependent on the steric bulkiness of substituents (R). We have succeeded in structural characterization of a trans-mu-1,2-peroxo species ([Cu ((BnHNCH_2CH_2)_3N)]_2 (O_2)), where benzyl (Bn) groups form a cavity around Cu^<2+>-O_2^<2->-Cu^<2+> moiety, which stabilizes peroxo species. Less