The Non-innocent Role of Spin Traps in Monitoring Radical Formation in Copper-Catalyzed Reactions

Abstract

Spin traps, like 5,5-dimethyl-1-pyrroline N-oxide (DMPO), are commonly used to identify radicals formed in numerous chemical and biological systems, many of which contain metal-ion complexes. In this study, continuous wave electron paramagnetic resonance and hyperfine spectroscopy are used to prove the equatorial ligation of DMPO(-derived) molecules to Cu(II), even in the presence of competing nitrogen bases. The experimental data are corroborated with density functional theory calculations. It is shown that 14N HYSCORE can be used as a fingerprint method to reveal the coordination of DMPO(-derived) molecules to Cu(II), an interaction that might influence the outcome of spin-trapping experiments and consequently the conclusion drawn on the mechanism under study.