An oxygen-bridged bimetallic [Cu–O–Se] catalyst for Sonogashira cross-coupling†
Most non-palladium catalysts employed in Sonogashira cross-coupling work at high temperatures of 120–140 °C and with well-defined ligands. Palladium-based catalysts with bulky and electron-rich phosphine ligands generally show the best performance for the above-mentioned cross-coupling procedure. Herein, we report a new protocol for Csp–Csp2 Sonogashira cross-coupling between a terminal alkyne and aryl halide using the cheap and commercially available catalyst CuSeO3·2H2O. The title reaction proceeds using a variety of terminal alkynes, affording diaryl or aryl–alkyl acetylenes in high yields under mild conditions in the absence of ligands. Alkyl acetylenes, ethynylsilanes, and alkynols are efficiently coupled with aryl iodides and aryl bromides. The mechanism of the reaction was evaluated using computational DFT studies. To the best of our knowledge, this is the first example of the use of an oxygen-bridged copper-based bimetallic catalyst for Csp–Csp2 Sonogashira cross-coupling reactions under mild conditions. The reaction is palladium-free up to a limit of 0.2 ppm.