Making Copper(0) Nanoparticles in Glycerol: A Straightforward Synthesis for a Multipurpose Catalyst

Small zero-valent copper nanoparticles (CuNPs) have been straightforwardly prepared from Cu(I) and Cu(II) precursors in glycerol and in the presence of polyvinylpyrrolidone as stabilizer. Thanks to the negligible vapor pressure of the solvent, these original nano-systems could be directly characterized in glycerol as well as in the solid state, exhibiting relevantly homogeneous colloidal dispersions, also even after catalysis. CuNPs coming from the well-defined coordination complex di-mu-hydroxobis[(N,N,N',N'-tetramethylethylenediamine)copper(II)] chloride {[Cu(kappa(2)-N,N-TMEDA)(mu-OH)](2)Cl-2} have been highly efficient in C-C and C-heteroatom bond formation processes. This new catalytic system has proved its performance in C-N couplings and in the synthesis of differently substituted propargylic amines through cross-dehydrogenative couplings, multi-component reactions such as A(3) (aldehydealkyne-amine) and KA(2) (ketone-alkyne-amine) couplings, as well as in the formation of heterocycles such as benzofurans, indolizines, and quinolines under smooth conditions. No significant copper amount was detected in the extracted organic compounds from the catalytic phase by inductively coupled plasma-atomic emission spectroscopic (ICP-AES) analyses, proving a highly efficient immobilization of copper nanoparticles in glycerol. From a mechanistic point of view, spectroscopic data (infrared and ultraviolet-visible spectra) agree with a surface-like catalytic reactivity.