Revealing the halide effect on the kinetics of the aerobic oxidation of Cu(I) to Cu(II)

In situ infrared (IR) and X-ray absorption near-edge structure (XANES) spectroscopic investigations reveal that different halide ligands have distinct effects on the aerobic oxidation of Cu(I) to Cu(II) in the presence of TMEDA (tetramethylethylenediamine). The iodide ligand gives the lowest rate and thus leads to the lowest catalytic reaction rate of aerobic oxidation of hydroquinone to benzoquinone. Further DFT calculations suggest that oxidation of CuI-TMEDA involves a side-on transition state, while oxidation of CuCl-TMEDA involves an end-on transition state which has a lower activation energy.