Nanoscale Copper Particles Derived from Solvated Cu Atoms in the Activation of Molecular Oxygen Giovanni Vitulli,* ,† Maristella Bernini, † Sergio Bertozzi, † Emanuela Pitzalis, † Piero Salvadori, † Salvatore Coluccia, ‡ and Gianmario Martra ‡ Centro del CNR per le Macromolecole Stereordinate ed Otticamente Attive, via Risorgimento 35, 56126 Pisa, Italy, and Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, via P. Giuria 7, 10125 Torino, Italy Received August 7, 2001. Revised Manuscript Received November 13, 2001 Nanostructured Cu powders ranging from 3 to 4 nm in diameter have been prepared by the clustering of acetone solvated Cu atoms obtained via metal vapor synthesis (MVS). The copper nanoparticles are valuable catalytic precursors for the oxidation with molecular oxygen of a wide range of organic substrates under mild conditions and are largely more efficient than commercial Cu samples. Introduction Active metals are of large interest in preparative chemistry and catalysis. 1 Their behavior is strongly related to the particle size distribution, and nanostruc- tured metals are expected to have unusual electronic, optical, magnetic, and chemical properties, different from those of atomic or molecular species and bulk metals. 2 Chemical reduction of transition metal salts, 3 electrochemical methods, 4 ultrasounds, 5 and metal va- por chemistry 6 are promising preparative routes to these materials. In preparative routes involving metal vapor as re- agents, acetone was found to be a suitable organic ligand to prepare Au colloids from the corresponding solvated intermediates. 7 We report here that the reaction of Cu atoms with acetone and the further clustering at room temperature affords nanostructured Cu particles, av- eraging 3-4 nm in diameter, which are efficient cata- lytic precursors for the oxidation of organic substrates with molecular oxygen. Experimental Section Copper “commercial” (99%, RPE, from Carlo Erba) and copper “bronze” (99% for organic synthesis, from Aldrich) were used. Phenol, methanol, and pyridine (distilled and stored on KOH) had the highest purity grade from Fluka. Gaseous oxygen, from Rivoira, was 99.99% pure. 1 H NMR spectra were performed in CDCl3 solution on Varian 300 spectrometer, and mass spectra were performed using a VG analytical 70/70E spectrometer. Copper metal (0.25 g) loaded into a Sylvania W/Al2O3 crucible was evaporated over a 1 h period, under a dynamic vacuum of ca. 10 -4 Torr, and co-condensed with acetone (80 mL) at liquid nitrogen temperature, using a typical glass metal atom reactor. 8 The solid red-brown matrix obtained was allowed to melt, and the resulting brown solution was siphoned out under argon into a Schlenk flask. Acetone evaporation afforded 0.2 g of Cu powder. Electron micrographs were obtained with a JEOL 2000EX microscope equipped with polar piece and top entry stage. 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