Nanostructured Metal Oxides Prepared from Schiff Base Metal Complexes: Study of the Catalytic Activity in Selective Oxidation and C–C Coupling Reactions

Abstract

Schiff base Cu(II), Co(II), Ni(II), Cr(III) and Fe(III) complexes have been synthesized via the reaction of the 2-amino-3-hydroxy-4-bromopyridine with 2-chloro-5-nitrobenzaldehyde and different transition metal salts. The complexes have been characterized by several methods. In addition, the prepared complexes were tested as precursors for the synthesis of their corresponding metal oxides nanoparticles by controlled aerobic thermal decomposition at 500 °C. The structure, composition, morphology and particle size of the prepared nanostructured metal oxides were characterized by FTIR, X-ray powder diffraction and by scanning and transmission electron microscopy. In addition, the corresponding materials have been tested as catalysts in the heterogeneous selective “solvent free” oxidation of benzyl alcohol giving high selectivities to benzaldehyde. In addition, the nanostructured metal oxides gave, in general, higher conversions than those of the starting Schiff base metal complexes. Finally, the nanostructured metal oxides have been treated with an organometallic Pd(II) precursor to prepare Pd-doped metal oxides, which have been tested as catalysts in two different C–C coupling reactions, namely, the coupling reaction between iodobenzene and phenylboronic acid and the double coupling of iodobenzene with 2,6-dibromopyridin. In all cases interesting conversions and yields were observed for the nanostructured metal oxides.