Formation and Reactivity of a Biomimetic Hydroperoxocopper(II) Cryptate

Abstract

AbstractCopper(II)‐hydroperoxo species are proposed as key intermediates in the catalytic cycles of copper‐monooxygenase enzymes that perform C–H bond hydroxylation. Herein we report on the oxidation chemistry of a copper(II) complex with a coordinating cryptand based on a peralkylated tetradentate tris(2‐aminoethyl)amine (tren) moiety. X‐ray crystallography of the copper(II) acetate complex of this cryptand revealed that the copper(II) ion is in a square‐pyramidal environment, with the cryptand acting only as a tridentate ligand. This geometry is conserved in solution and likely results from restraints imposed by the semi‐rigid cryptand. Reaction of this complex with basic hydrogen peroxide in methanol led to the decomposition of the complex with an oxygen‐atom transfer to the ligand, as evidenced by mass spectrometry analysis after reaction and demetallation. Low‐temperature stopped‐flow experiments (down to –90 °C) support the formation of a copper(II)‐hydroperoxo intermediate, CuOOH, before ligand oxygenation occurs. It is proposed that this intermediate performs the oxygen‐atom transfer to a weak benzylic C–H bond of the cryptand, thereby mimicking the behavior of dopamine‐β‐hydroxylase.