Electrostatic Contributions to the Stability of an End-on Cupric Superoxide

We recently reported the presence of strong, local electrostatic fields in the secondary coordination sphere of a phosphinimine-decorated CuI complex, [(P3tren)CuI]+ (1). Here, we show that the low-temperature oxygenation of 1 yields a long-lived, three-fold symmetric η1-cupric superoxide complex, [(P3tren)CuII(O2)]+ (2). This latter complex was shown to abstract hydrogen atoms from 2,6-di-tert-butyl-4-methoxy phenol (KIE = 3.0 ± 0.3) and oxidize a cuprous tris(2-pyridylmethyl)amine complex to form a heteroleptic di(cupric)-μ-1,2-peroxide complex (4). The thermal stability of 2 was observed to be uncommonly high for sterically unprotected cupric superoxide complexes in this geometry (t1/2 = 10.4 h at -85 °C). Density functional theory (DFT) calculations implicate a unique electrostatic stabilization of the π*v orbital of the O2 unit, and the thermal stability of 2 is discussed in the context of the CuI/II redox potential of 1, the steric bulk in the complex’s secondary coordination sphere, and intramolecular electrostatic interactions.