Unusual Stability of an End‐on Superoxido Copper(II) Complex under Ambient Conditions

Superoxido copper complexes play an important role as usually short‐lived intermediates in biology and chemistry. The unusual stability of an end‐on superoxido copper complex observed in an oxygen‐enhanced atom transfer radical polymerization (ATRP) led to a detailed mechanistic investigation of the formation of [Cu II (Me 6 tren)(O 2 ⋅ − )] + (Me 6 tren=tris(2‐dimethyl‐aminoethyl)amine) under ambient conditions. The persistence of the superoxido copper complex could be explained by a reaction cycle including the peroxido complex [(Me 6 tren) 2 Cu II 2 (O 2 )] 2+ together with [Cu I (Me 6 tren)(DMSO)] + and [Cu II (Me 6 tren)(OH)] + in the overall reaction.