A synergistic {Cu2-W12O40} catalyst with high conversion for homo-coupling of terminal alkynes

Abstract

By the strategy of replacing the H₂O ligands in the “paddle wheel” shaped copper dimer Cu₂(OAc)₄(H₂O)₂ with polyoxometalate (POM) [H₂W₁₂O₄₀]⁶⁻ {W₁₂O₄₀} pro-ligands, a novel nano porous 2D network {[Cu₂(OAc)₄]₂(W₁₂O₄₀)}_n was obtained. The POM – copper centered redox reactions and stability of the compound were studied by cyclic voltammetry. Furthermore, the compound was found to be a super-efficient homogeneous catalyst (almost 100% conversion) in homo-coupling of terminal alkynes compared with its components and physical mixture under mild conditions with low amounts. The in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) results clearly show the changes of alkyne substances in the catalytic process and the X-ray photoelectron spectroscopy (XPS) results reveal the electron transfer from {W₁₂O₄₀} to Cu(II) to promote the C–H activation step during the homo-coupling of terminal alkynes. The synergistic Cu(II)-POM catalytic mechanism was proposed.