Copper(II)‐TEMPO Interaction

Copper(II) complexes with N-oxyl reactants such as TEMPO can selectively oxidize alcohols to aldehydes or ketones. The proposed copper intermediates of the oxidation reaction were extensively theoretically studied, but they never experimentally detected. Here, we present an analysis “frozen” that contain without α-hydrogen atoms, thus preventing oxidation. copper(II)-TEMPO a bipyridine-type ancillary ligand isolated by electrospray ionization mass spectrometry and investigated spectroscopically cryogenic photodissociation spectroscopy. vibrational characteristics suggest retains its unpaired electron even upon coordination copper(II). In agreement, electronic spectra TEMPO-copper(II) show characteristic band for gaseous copper(II) complexes. These results contradict interpretations some previous density functional theory (DFT) analyses possible intermediates. experimental data confronted theoretical obtained pure DFT (OPBE, TPSS) hybrid (TPSSH, B3LYP) calculations. methods favor different ground states capture various aspects demonstrating multiconfigurational character