Synthesis and Characterization of a (μ-ρ2:ρ2-Peroxido)dicopper(II) Complex with N,N′,N-Triisopropyl-cis,cis-1,3,5-triaminocyclohexane (R3TACH, R = iPr): Selective Preparation of (μρ2:ρ2-Peroxido)dicopper(II) and Bis(μ-oxido)dicopper(III) Species Regulated by Substituent Groups

The new CuI complex of N,N',N?-triisopropyl-cis,cis-1,3,5-triaminocyclohexane (iPr3TACH), [Cu(iPr3TACH)(MeCN)](X), immediately reacts with dioxygen at 80 degrees C to give a (mu-?2:?2-peroxido)dicopper(II) complex. This observation is significantly different from the previously reported cases of bis(mu-oxido)dicopper(III) complexes that were generated by the reaction of copper(I) complexes of other TACH ligands (Et3TACH, iBu3TACH, and Bn3TACH) with dioxygen under the same reaction conditions. Such selective preparations have been explained in terms of the structural specificity provided by the TACH ligands that surround the metal centers. The obtained (mu-?2:?2-peroxido)dicopper(II) complex exhibits ortho-hydroxylation of a phenolate to ortho-quinone with ca. 50?% yield based on the peroxido intermediate. The bis(mu-oxido)dicopper(III) complexes with other TACH derivatives are not capable of oxygenation of phenolate. The (mu-?2:?2-peroxido)dicopper core is discussed in the context of the reaction mechanism of tyrosinase.