Direct Observation of Reduction of Cu(II) to Cu(I) by Terminal Alkynes

X-ray absorption spectroscopy and in situ electron paramagnetic resonance evidence were provided for the reduction of Cu(II) to Cu(I) species by alkynes in the presence of tetramethylethylenediamine (TMEDA), in which TMEDA plays dual roles as both ligand and base. The structures of the starting Cu(II) species and the obtained Cu(I) species were determined as (TMEDA)CuCl2 and [(TMEDA)CuCl]2 dimer, respectively.