Variable coordination of peroxide: The reaction of the Cu(I) complex-based on the BPMPD ligand with O₂ at low temperatures initially led to a μ-1,2 peroxo species (Cu ₂ O ₂ ). By addition of an acid (lutidinium triflate), this species can be reversibly converted into a μ-1,1-hydroperoxo complex, which is monitored using UV/Vis spectroscopy and X-ray absorption spectroscopy.

Copper-oxygen intermediates play an important role in nature as active species of many copper-containing enzymes. However, copper-oxygen intermediates have a key function not only in nature, but also in industry, for example as catalysts. Herein a study on a dinuclear copper complex is presented based on the literature known ligand BPMPD. This ligand combines features of the previously investigated systems (octadentate N-donor, like the MO8 system and pyridine donors, like the bdpdz system). Oxygenation of the Cu(I)-complex with O₂ at low temperature leads to the formation of a μ-1,2-peroxo intermediate (Cu ₂ O ₂ ), which is characterized with UV/Vis-, rRaman- and X-ray absorption spectroscopy (XAS), as well as by cryo-UHR-electrospray ionization mass spectrometry. The Cu ₂ O ₂ species can be reversibly converted into a μ-1,1-hydroperoxo intermediate (Cu ₂ OOH) by a reaction with lutidinium triflate and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), which can be monitored by UV/Vis and XAS. Furthermore, the reactivity of the Cu ₂ O ₂ species toward dihydroanthracene is investigated.