Copper catalysts have been utilized in acetylene chemistry for more than 150 years. However, detailed mechanistic study in Cu/acetylene chemistry is still limited. The major barrier lies in the difficulty of accurate characterization of unstable catalytic intermediates. Specifically, determination of the valence state and coordination sphere of the Cu species is among the main challenges. X-ray absorption spectroscopy (XAS) is a powerful method for determining local geometric and electronic structure of metal catalysts under reaction conditions which could help gain valuable information for identifying important intermediates in catalytic reactions. In this work, direct XAS and electron paramagnetic resonance (EPR) spectroscopic evidence are provided for the reduction of Cu(II) to Cu(I) species by terminal alkynes in the presence of tetramethylethylenediamine (TMEDA). The structures of the starting Cu(II) species and the obtained Cu(I) species were also determined by EXAFS spectroscopy as (TMEDA)CuCl2 and [(TMEDA)CuCl]2, respectively. Given the extensive application of Cu/TMEDA/alkyne system, the oxidation state and structural information provided in the present work could shed light on Cu/acetylene chemistry and provide useful guidelines for designing new Cu/acetylene related reactions.

Direct observation of reduction of Cu(II) to Cu(I) by terminal alkynes

248th National Meeting (2014)

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