Coordination Variations within Binuclear Copper Dioxygen-Derived (Hydro)Peroxo and Superoxo Species; Influences upon Thermodynamic and Electronic Properties.

Copper ion is a versatile and ubiquitous facilitator of redox chemical and biochemical processes. These include the binding of molecular oxygen to copper(I) complexes where it undergoes stepwise reduction-protonation. A detailed understanding of thermodynamic relationships between such reduced/protonated states is key to elucidate the fundamentals of the chemical/biochemical processes involved. The dicopper(I) complex [Cu ^I ₂ (BPMPO ^- )] ¹⁺ {BPMPOH = 2,6-bis{[(bis(2-pyridylmethyl)amino]methyl}-4-methylphenol)} undergoes cryogenic dioxygen addition; further manipulations in 2-methyltetrahydrofuran generate dicopper(II) peroxo [Cu ^II ₂ (BPMPO ^- )(O ₂ ^2- )] ¹⁺ , hydroperoxo [Cu ^II ₂ (BPMPO ^- )( ^- OOH)] ²⁺ , and superoxo [Cu ^II ₂ (BPMPO ^- )(O ₂ ^•- )] ²⁺ species, characterized by UV-vis, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies, and cold spray ionization mass spectrometry. An unexpected EPR spectrum for [Cu ^II ₂ (BPMPO ^- )(O ₂ ^•- )] ²⁺ is explained by the analysis of its exchange-coupled three-spin frustrated system and DFT calculations. A redox equilibrium, [Cu ^II ₂ (BPMPO ^- )(O ₂ ^2- )] ¹⁺ ⇄ [Cu ^II ₂ (BPMPO ^- )(O ₂ ^•- )] ²⁺ , is established utilizing Me ₈ Fc ⁺ /Cr(η ⁶ -C ₆ H ₆ ) ₂ , allowing for [Cu ^II ₂ (BPMPO ^- )(O ₂ ^•- )] ²⁺ /[Cu ^II ₂ (BPMPO ^- )(O ₂ ^2- )] ¹⁺ reduction potential calculation, E °' = -0.44 ± 0.01 V vs Fc ^+/0 , also confirmed by cryoelectrochemical measurements ( E °' = -0.40 ± 0.01 V). 2,6-Lutidinium triflate addition to [Cu ^II ₂ (BPMPO ^- )(O ₂ ^2- )] ¹⁺ produces [Cu ^II ₂ (BPMPO ^- )( ^- OOH)] ²⁺ ; using a phosphazene base, an acid-base equilibrium was achieved, p K _a = 22.3 ± 0.7 for [Cu ^II ₂ (BPMPO ^- )( ^- OOH)] ²⁺ . The BDFE _OO-H = 80.3 ± 1.2 kcal/mol, as calculated for [Cu ^II ₂ (BPMPO ^- )( ^- OOH)] ²⁺ ; this is further substantiated by H atom abstraction from O-H substrates by [Cu ^II ₂ (BPMPO ^- )(O ₂ ^•- )] ²⁺ forming [Cu ^II ₂ (BPMPO ^- )( ^- OOH)] ²⁺ . In comparison to known analogues, the thermodynamic and spectroscopic properties of [Cu ^II ₂ (BPMPO ^- )] O ₂ -derived adducts can be accounted for based on chelate ring size variations built into the BPMPO ^- framework and the resulting enhanced Cu ^II -ion Lewis acidity.