A copper(II)–hydroperoxo complex, [Cu(Me₆-tren)(OOH)]⁺ (2), and a copper(II)–cumylperoxo complex, [Cu(Me₆-tren)(OOC(CH₃)₂Ph)]⁺ (3), were synthesized by reacting [Cu(Me₆-tren)(CH₃CN)]²⁺ (1) with H₂O₂ and cumyl-OOH, respectively, in the presence of triethylamine. These intermediates, 2 and 3, were successfully characterized by various physicochemical methods such as UV-vis, ESI-MS, resonance Raman and EPR spectroscopies, leading us to propose structures of the Cu(II)–OOR species with a trigonal-bipyramidal geometry. Density functional theory (DFT) calculations provided geometric and electronic configurations of 2 and 3, showing trigonal bipyramidal copper(II)–OOR geometries. These copper(II)–hydroperoxo and –cumylperoxo complexes were inactive in electrophilic and nucleophilic oxidation reactions.