Silver(I) complexes as efficient source for silver oxide nanoparticles with catalytic activity in A3 coupling reactions

Abstract

New silver(I) complexes [Ag7(μ4-Cl)(μ3-Cl)2(μ2-Cl)3(MPI)6] (1), and [Ag(μ3-I)(BI)]n (2) [MPI=1-(4-methoxyphenyl)-1H-imidazole; BI=1-Benzylimidazole] have been prepared starting with AgX (X=Cl, I) and 1-(4-methoxyphenyl)-1H-imidazole/1-Benzylimidazole. The complexes have been characterized by elemental analysis, IR, 1H NMR, and electronic absorption spectroscopy. Molecular structure of the complexes 1 and 2 were determined crystallographically. Complex 1 has a twofold axis with Ag3 in special position and bisecting the Ag4–Ag4′ vector. It contains six 1-(4-methoxyphenyl)-1H-imidazole molecules and seven chlorine atoms bridging the seven silver atoms. Complex 2 exists as a one-dimensional (1D) polymeric chain of [(μ3-I)Ag(μ3-I)Ag] fragments bridged via the 1-Benzylimidazole ligand. The weak argentophilic Ag⋯Ag interaction distances in complexes 1 and 2 are 3.1014(4)Å–3.2998(15)Å, respectively. The complexes 1 and 2, yielded silver oxide nanoparticles on pyrolysis and were characterized by PXRD and TEM. The catalytic properties of the resulting silver oxide nanoparticles and the silver(I) complexes have also been studied for A3-coupling of amines, alkynes and aldehydes in microwave which gave moderate to good yields of propargylamines. Silver(I) complexes exhibit higher catalytic activity compared to silver oxide nanoparticles. The silver oxide nanoparticles as well as silver(I) complexes could be separated easily from the reaction mixture and reused at least four to five times without significant loss of the catalytic activity.