Investigations of dioxygen activation mechanisms by dimetal complexes

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<Reversible four electron redox conversion of dioxygen by copper complexes > A series of copper(I) complexes ([Cu(L)]^+) having tripodal tetradentate ligands (L) was synthesized and reactivity of their complexes with O_2 was investigated. Reaction of copper(I) complexes ([Cu(L)]^+ generated bis(μ-oxo)dicopper(III) complexes, which showed reversible conversion to copper(I) complexes by bubbling of N_2. Furthermore, it was also found that bis(μ-oxo)dicopper(III) complexes have monooxygenase activity for the supporting ligands. Reactivity can be modulated by stereochemical electronic effect of the supporting ligands<Reaction intermediates of nickel complexes having a variety of dioxygen active species formed by the reaction with H_2O_2> Reaction of a bis(μ-hydroxo)Ni(II)_2 having a series of tetradentate tripodal ligands having methyl substituents with H_2O_2 at low temperature resulted in a successive formation a bis(μ-oxo)Ni(III)_2 a bis(μ-superoxo)Ni(II)_2, and a bis(μ-alkylperoxo)Ni(II)_2 complexes as the intermediates for the conversion of a methyl substituent of ligands to carboxylate and alkoxide ligands<Reversible O-O bond cleavage and formation of a peroxo group of an iron(III) complex having a peroxycarbonate> A peroxcarbonate iron(III) complex ([Fe(qn)_2(O_2C(O)O)]^-(1)) was synthesized. The complex is stable at -35℃ in acetonitrile, whereas it decomposes at 20℃. Decomposition of an ^<18>O-labeled [Fe(qn)_2(^<18>O-^<18>OC(O)O)]^-complex (1-^<18>O-^<18>O) at 20℃ in acetonitrile was investigated by resonace Raman and ESI-MS spectroscopies. They revealed that the ^<18>O-^<18>O of the peroxocarboante ligand is converted through ^<16>O-^<18>OC(O)O and ^<18>O-^<16>OC(O)O to ^<16>O-^<16>OC(O)O during thermal decomposition. This is the first example which showed reversible O-O bond cleavage and formation for iron complexes