Amphoteric reactivity of a putative Cu(II)-mCPBA intermediate

In copper-based enzymes, Cu-hydroperoxo/alkylperoxo species are proposed as key intermediates for their biological activity. A vast amount of literature is available on the functional and structural mimics of enzymatic systems with heme and non-heme ligand frameworks to stabilize high valent metal intermediates, mostly at low temperatures. Herein, we report a reaction between [Cu^I(NCCH₃)₄]⁺ and meta-chloroperoxybenzoic acid (mCPBA) in CH₃CN that produces a putative Cu^II(mCPBA) species (1). 1 was characterized by UV/Vis, resonance Raman, and EPR spectroscopies. 1 can catalyze both electrophilic and nucleophilic reactions, demonstrating its amphoteric behavior. Additionally, 1 can also conduct electron transfer reactions with a weak reducing agent such as diacetyl ferrocene, making it one of the reactive copper-based intermediates. One of the most important aspects of the current work is the easy synthesis of a Cu^II(mCPBA) adduct with no complicated ligands for stabilization. Over time, 1 decays to form a Cu^II paddle wheel complex (2) and is found to be unreactive towards substrate oxidation.