Schiff base complex of metal ions supported on superparamagnetic Fe3O4@SiO2 nanoparticles: An efficient, selective and recyclable catalyst for synthesis of 1,1-diacetates from aldehydes under solvent-free conditions

We report a new multistep method for preparing functionalized superparamagnetic Fe3O4@SiO2 possessing high saturation magnetization. During the first step, Fe3O4@SiO2 nanosphere core-shell is synthesized using nano-Fe3O4 as the core, TEOS as the silica source and PVA as the surfactant. Then, Schiff base complex of metal is synthesized from the reaction between Schiff base and metal acetates [Co(OAc)(2), Mn(OAc)(2), Ni(OAc)(2), Cu(OAc)(2), Hg(OAc)(2), Cr(OAc)(3) and Cd(OAc)(2)] on the Fe3O4@SiO2 surface. The structural and magnetic properties of functionalized magnetic silica are identified by transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) instruments. Moreover, functionalized Fe3O4@SiO2 possessed a superparamagnetic characteristic with saturation magnetization value of about 34 emu/g. NMR, FT-IR, elemental analysis and XRD were also used for the identification of these structures. The catalytic ability of Fe3O4@SiO2/Schiff base complex of metal ions was found to be an efficient nanocatalyst for the conversion of aldehydes to their corresponding 1,1-diacetates compounds under mild and solvent-free conditions at room temperature. This method gives notable advantages such as excellent chemoselectivity, mild reaction condition, short reaction times and excellent yields. Also, the aforementioned nanocatalyst can be easily recovered by a magnetic field and reused for subsequent reactions for at least 5 times without noticeable deterioration in catalytic activity. (C) 2012 Elsevier B.V. All rights reserved.