Two inorganic–organic hybrid silver-polyoxometalates as reusable catalysts for one-pot synthesis of propargylamines via a three-component coupling reaction at room temperature†
By the combination of Ag-complexes and Keggin POMs, two novel inorganic–organic silver–polyoxometalates hybrids, [Ag3L2(DMSO)2][PW12O40]·4DMSO (1) and [(Ag2L2)2][SiW12O40]·10DMSO·2H2O (2) (L = 4-(2-pyridyl)-6-(4-pyridyl)-2-aminopyrimidine), were synthesized and characterized. Interestingly, the silver atoms in compound 1 are three-coordinated with the AgNO model; however, the Ag atoms of compound 2 were surrounded by four N atoms of the organic ligands and displayed a distorted tetrahedral configuration. Importantly, compound 1 showed high catalytic activities for the three-component coupling reaction of alkynes and secondary amines along with formaldehyde, which resulted in a series of propargylamine derivatives in higher yields (up to 99%). Furthermore, the Ag–POM catalyst was easily recovered by filtration and reused for three cycles without a significant loss in catalytic activity. A tentative mechanism is also proposed for this transformation.