Supported rhodium nanoparticles obtained by Metal Vapour Synthesis as catalysts in the preparation of valuable organic compounds

Rhodium nanoparticles, derived from mesitylene-solvated rhodium atoms, deposited on g-Al2O3, are excellent catalysts for the selective hydrogenation of the double bond in a,b-unsaturated carbonyl compounds. The low metal loading Rh on g-Al2O3 catalyst, containing trioctylamine, TOA, as stabilizing agent of the metal nanoparticles, Rh(TOA)/g-Al2O3, 0.1 wt.% Rh, showed the highest catalytic activity. Using this catalyst 4-(6,-methoxy-2,-naphthyl)-3-buten-2-one was reduced to the anti-inflammatory drug 4-(6,-methoxy-2,-naphthyl)-butan-2-one, NabumetoneTM, with complete selectivity and under mild reaction conditions (room temperature, atmospheric pressure of hydrogen). Similarly, 2-acetyl-5,8-dimethoxy-3,4-dihydronaphthalene was hydrogenated with high selectivity (85%) to 2-acetyl-5,8-dimethoxy-1,2,3,4-tetrahydronaphthalene, precursor of antitumor anthracyclinic compounds, which was obtained chemically pure by crystallization. No leaching of rhodium was observed. The catalyst was completely recovered and, if reused, it works without loss of activity. 1H NMR DOSY analysis of the Rh(TOA)/mesitylene solution evidenced the presence of nanoparticles with a diameter of about 1.1 nm.