Covalently immobilized indium(III) composite (In/SiO2) as highly efficient reusable catalyst for A3-coupling of aldehydes, alkynes and amines under solvent-free conditions

We describe the synthesis and application of a silica-xerogel-supported indium(III) composite (In/SiO2). Using X-ray photoelectron spectroscopy, by the first time it was possible to identify that the indium is bonded to the silica through covalent In-O-Si bonds. The N-2 adsorption/desorption isotherms revealed that the In/SiO2 composite presents pores with diameters between 1 and 4 nm, which allows it to be used as a heterogeneous catalyst. Thus, this composite was used as catalyst in an A(3)-coupling reaction with several aldehydes, amines and acetylenes, leading to the formation of propargylamines in good-to-excellent yields in solvent-free conditions, using both conventional heating and microwave irradiation (MW). The recyclability was evaluated under both conditions and no considerable reduction in the yields was observed after four cycles. (c) 2015 Elsevier B.V. All rights reserved.