Copper(II) ion exchanged AlSBA-15: A versatile catalyst for intermolecular hydroamination of terminal alkynes with aromatic amines

The hydroamination reaction offers a very attractive route for the synthesis of alkylated amines and their derivatives with no byproduct formation. AlSBA-15 was synthesized by isomorphous substitution of aluminum into the framework of SBA-15, which induces the Brönsted acid sites, and these were exchanged with metal ions such as Cu2+, Zn2+, and Pd2+. The catalysts were characterized by XRD, N2-sorption, SEM, TEM, acidity measurements by FT-IR pyridine adsorption, H2-TPR, 27Al MAS NMR, and 29Si MAS NMR. Hydroamination of phenylacetylene (PhAc) with 2,4-xylidine has been used as a test reaction, which gave N-(1-phenylethylidene)-2,4-dimethylaniline with no byproduct formation. CuAlSBA-15 and CuAlMCM-41 showed around three times greater activity in hydroamination of PhAc compared with Cu-clay and Cu-beta, due to the moderate Lewis acidity of Cu2+ present in mesoporous supports. The performance of the CuAlSBA-15 was also determined with different alkynes and amines to evaluate the catalyst's general applicability in hydroamination reactions.