New Hg(II)–N-heterocyclic carbene complexes of compartmental ligands with a suitable topology for a η1-arene–Hg(II) close interaction

A new Hg(II)–N-heterocyclic carbene (NHC) complex (1) of the form [(NHC)2-μ-Hg]·2PF6 was synthesized from the reaction of Hg(II) acetate with a meta-xylyl-linked bis-imidazolium salt (η1-areneC–H model). The complex was characterized using elemental analysis, nuclear magnetic resonance (1H, 13C and HMQC), and single-crystal X-ray diffraction techniques. X-ray structural studies on complex 1 revealed a linear coordination of the Hg ion with both carbene centers of the ligand. In addition, a strong interaction between the Hg ion and a carbon atom of the aryl ring of the ligand was also observed. This interesting interaction is further supported by a downfield chemical shift of the 1H NMR signal for the arene-H that interacts with mercury (δ 0.88 compared to the free ligand). In a related meta-arylene-bis(imidazol-2-yliden-1-ylmethyl) Hg(II) complex (2) with a methyl group between the bridges, synthesized in analogy to complex 1, no such interaction between the Hg ion and the aryl ring was observed.

Graphical abstractA Hg(II)–NHC complex (1) displayed an interesting close interaction between η1-areneC and Hg(II). However, no such interaction was observed in complex 2, whose ligand topology was tainted.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New Hg(II)–NHC complexes (1 and 2) of meta-xylyl bridged bis-carbenes were reported. ► Complexes were characterized by elemental, NMR and X-ray diffraction analyses. ► Complex 1 displayed an interesting close interaction between η1-areneC and Hg(II). ► In complex 2, a methyl between the bridging CH2 groups prevented the interaction.