Metal Acetylacetonates Covalently Anchored onto Amine Functionalized Silica/Starch Composite for the One-Pot Thioetherification and Synthesis of 2H-Indazoles

Abstract

This paper reports a series of novel metal acetylacetonates covalently anchored onto amine functionalized silica/starch composite, prepared by the Schiff condensation of metal acetylacetonates [Co(acac)2, Cu(acac)2, Pd(acac)2, Ru(acac)3, Mn(acac)3, Co(acac)3] with organically modified 3-aminopropyl silica/starch composite. Different metal acetylacetonates have been chosen with a view to select the most active heterogeneous catalyst. Among various catalysts, covalently anchored Cu(acac)2 onto amine functionalized silica/starch composite [ASS-Cu(acac)2] was found to be the most active and recyclable catalyst for the one-pot thioetherification and one-pot three component synthesis of 2H-indazoles via consecutive C–N and N–N bond formations. All the catalysts were characterized by FTIR, TGA and AAS analysis and the most active catalyst, [ASS-Cu(acac)2] was further characterized by SEM and TEM. The catalyst could be recovered by simple filtration and reused with almost consistent activity for four consecutive runs.