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.