Co(II) Immobilized on Functionalized Magnetic Hydrotalcite (Fe3O4/HTNH2- CoII): A Green and Magnetically Recyclable Bifunctional Nanocatalyst for the Synthesis of Xanthenes

Hydrotalicites (HTs) and magnetic hydrotalcites (MHTs) have been widely studied as promisingsupporting materials for catalysts in organic reactions. Hydrotalictes as a layer double hydroxide(LDH) with abundant surface hydroxyl groups consist of alternating cationic(Mg6Al2(OH)16+2 anionic (CO32-) interlayers and Mg–Al mixed oxides which are chemicallyactive sites (strong basic sites) for use in catalytic reactions and also act as the anchoring sitesfor metal nanoparticles. By considering the fact that the separation of hydrotalcite-based catalystsfrom the reaction mixture is difficult to some extent, replacement of conventional separationmethods with magnetic separation approaches is a fascinating technique. Thus, incorporationof magnetic nanoparticles (MNPs) into the hydrotalcite structure provides easy separationof catalysts from the reaction mixture using a simple magnetic bar along with the preventionof MNP agglomeration, as well. A variety of amines and other functional groups havebeen utilized in nanoparticle preparation as stabilizers on surface of MHTs, which could beuseful for immobilization of metal ions [1,2]. In recent times, xanthene derivatives have greatlydrawn the attention of organic chemists as they are important motifs in a variety of biologicallyactive compounds [3]. In summary we have successfully synthesized COII immobilizedon functionalized magnetic hydrotalcite (Fe3O4/HT-NH2-COII) from readily available startingmaterials. The applicability of nanocatalyst was explored in the synthesis of of xanthene derivativesthrough reaction aldehydes with 2-naphtol at 90 °C under solvent free conditions inexcellent yields.