N-Heterocyclic carbene silver(i), palladium(ii) and mercury(ii) complexes: synthesis, structural studies and catalytic activity

Abstract

The bis-benzimidazolium salts, 1,2-bis[2-(N-R-benzimidazolemethyl)phenoxy]ethane chloride (L1H2: R = Et, L2H2: R = nBu), 1,3-bis[2-(N-R-benzimidazolemethyl)phenoxy]propane chloride (L3H2: R = nPr, L4H2: R = nBu) and bis[N-R-benzimidazolemethyl]mesitylene 2X (L5H2: R = nBu, X = I; L6H2: R = PyCH2, X = Br and L7H2: R = PhCH2, X = Br), as well as their eight NHC silver(I), palladium(II) and mercury(II) complexes, [(L1Ag)2Ag2Cl4] (1), [L1(PdCl2CH3CN)2] (2), [(L2Ag)2AgCl2][AgCl2] (3), [(L3Ag2Cl2)n] (4), [(L4Ag2Cl2)n] (5), [L5HgI][HgI4]0.5 (6), [L6Hg][HgBr4] (7) and [L7Ag][(NO3)0.76Br0.24] (8) have been prepared and characterized. The complexes 1–8 adopt four different structures: (1) with bis-macrometallocycles connected via a Ag2Cl4 unit for 1 and via a AgCl2 unit for 3, (2) an open structure formed via one ligand and two metal atoms for 2, (3) 1D polymeric chains formed by the monomers of a cage-like cavity via weak Ag⋯Cl bonds (monomer: L3Ag2Cl2 for 4 and L4Ag2Cl2 for 5) and (4) a macrocyclic structure formed by one ligand and one metal for 6–8. In the crystal packing of these complexes, 1D supramolecular chains, 2D supramolecular layers and 3D supramolecular architectures are formed via intermolecular weak interactions, including π–π interactions, hydrogen bonds, C–H⋯π contacts and weak Hg⋯Br bonds. Particularly, the catalytic activity of the NHC palladium(II) complex 2 in Suzuki–Miyaura cross-coupling reactions was studied.