Mapping the Pathway to Organocopper(II) Complexes Relevant to Atom Transfer Radical Polymerization

The rare organocopper­(II) complex [Cu­(Me6tren)­(CH2CN)]+ (Me6tren = tris­(2-(dimethylamino)­ethyl)­amine) has emerged as an important model of potential byproducts in copper-catalyzed atom transfer radical polymerization. This complex has been generated by controlled potential electrolysis of [Cu­(Me6tren)­(NCMe)]2+ in the presence of BrCH2CN. Time-resolved UV–vis and continuous wave and pulse electron paramagnetic resonance (EPR) spectra identified [Cu­(Me6tren)­Br]+ as an intermediate. Hyperfine sublevel correlation and electron nuclear double resonance spectroscopy of samples at different timepoints reveal signals that are assigned to a C-bound cyanomethylate ligand, with distinct 14N and 1H hyperfine coupling constants in comparison with the corresponding N-bound acetonitrile and bromido complexes. The experimental EPR data are supported by density functional theory calculations to understand how the geometries of the species involved produce distinct spectroscopic signatures, and a clear picture of how this unusual organocopper­(II) complex is formed has emerged.