Electrostatic immobilisation of copper(I) and copper(II) bis(oxazolinyl)pyridine catalysts on silica: application to the synthesis of propargylamines via direct addition of terminal alkynes to imines

Abstract

Abstract-Copper(I) and copper(II) complexes of two bis(oxazolinyl)pyridines were immobilized on silica via electrostatic interactions. The catalytic activity of the immobilized catalysts in the direct addition of terminal alkynes to imines leading to propargylamines was investigated under a variety of reaction conditions. The performance of the immobilized catalysts compares very well with their homogeneous equivalents. When used in toluene, the catalysts could be recycled a number of times and maintained activity. This study is the first such report of the immobilization on silica in this manner of any bis(oxazolinyl)pyridine (pybox) complex.

Fast, solvent-free, highly enantioselective three-component coupling of aldehydes, alkynes, and amines catalysed by the copper(ii)pybox complex under high-vibration ball-milling

“…The catalyst recovery of the symmetric A 3 reaction had been extensively studied previously. [42][43][44][45][46][47] For the asymmetric A 3 reaction, catalysts and ligands were usually supported on silica gel, 48 polymers, 49 and Fe 3 O 4 nanoparticles for easy separation. 50 However, the poor performance induced by ligand furnishing and the dramatic drop of enantioselectivity in the recycling tests show the catalyst recovery still a challenging problem.…”

Recyclable Stereoselective Catalysts

“…Asymmetric addition of alkynes to imines promoted by Cu -Ph -PyBOX complex in ILs and water/stearic acid medium. Ph Ph-PyBOX * Alternatively, O ' Leary and co -workers immobilized a Cu(I) -and Cu(II) -Ph -PyBOX trifl ate complex on silica due to electrostatic interactions, but the catalyst ' s reusability was studied only during three cycles [68] . The immobilization of the Py -BOX ligand in a Wang resin did not provide a very recyclable system for the same transformation [69] .…”

Recent Developments in Asymmetric Alkynylation of Imines

“…An electrostatically immobilized phenylpybox Cu(I) triflate catalyst has been developed by O'Leary et al [50] and tested in the reaction of imine (82, R 1 = R 2 = Ph) and phenylacetylene in toluene (Scheme 47). The immobilized catalyst gave similar results in terms of conversion and enantioselectivity as the homogeneous catalyst, when the reaction was performed in refluxing toluene.…”