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)_0.76Br_0.24] (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.