Preparation of a coordinatively saturated μ-η2:η2-peroxodicopper(II) compound

Abstract

The synthesis and solution characterization of the mononuclear copper(I) complex [CuI(PyNMe3)(CH3CN)]+ (1) is described. This compound presents a Cs symmetric architecture as ascertained by NMR spectroscopy and corroborated by DFT calculations. The reactivity of 1 towards O2 in a CH3CN:THF 1:19 mixture at −100°C was monitored by UV–vis spectroscopy, which evidenced the formation of a new species (2) with a highly intense absorption at 353nm (ε>17200M−1cm−1) that was not stable even at this low temperature (t1/2=6min at −100°C). This spectroscopic signature is characteristic of μ-η2:η2-peroxodicopper(II) complexes, which typically exhibit one single intense absorption between 340 and 380nm. Despite the fact that such species are involved in the catalytic cycle of tyrosinase, a copper-based enzyme that ortho-hydroxylates phenols, attempts to hydroxylate phenolates by 2 turned out to be unsuccessful. Most probably, the rigid macrocyclic tetradentate architecture of the PyNMe3 ligand hinders simultaneous peroxide and phenolate coordination in the same copper center, a necessary step prior to the ortho-hydroxylation of this substrate.