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.