Silver(I), palladium(II) and mercury(II) NHC complexes based on bis-benzimidazole salts with mesitylene linker: Synthesis, structural studies and catalytic activity

The diimidazolium salts bis[1-R-imidazoliumylmethyl]mesitylene·2X (1: R = PhCH2, X = Br− and 2: R = Et, X = PF6−) and the dibenzimidazolium salts bis[1-R-benzimidazoliumylmethyl]mesitylene·2X (3: R = nPr, X = I−; 4: R = PhCH2, X = I−), as well as their four NHC silver(I), palladium(II) and mercury(II) complexes, {[mesitylene(CH2imyPhCH2)2]2Ag2·Ag2Br4}n (6), {mesitylene[(CH2imyPhCH2)PdCl2(CH3CN)]2} (7), {mesitylene[(CH2imyEt)2Hg2(CHCN)][HgI4]} (8) and {[mesitylene(CH2bimynPr)2HgI][HgI4]0.5} (9), as well as one anionic complex {[1,3-bis(1-benzylbenzimidazolemethyl)mesitylene][HgI4]} (5) (imy = imidazol-2-ylidene and bimy = benzimidazol-2-ylidene), have been prepared and characterized. In the complex 6, the macrometallocycles formed by two precursor 1 and two silver(I) atoms are connected together via Ag2Br4 unit to form a 1D polymeric chain. Complex 7 adopted an open structure formed by one precursor 1 and two Pd(II) atoms. In complex 8, a bidentate dicarbene from precursor 2 and a doubly deprotonated acetonitrile coordinate with two Hg(II) atoms to afford a funnel-like structure. The 10-membered macrometallocycle of 9 was formed by one precursor 3 and one Hg(II) atom. In the crystal packings of these compounds, 1D supramolecular chains, 2D supramolecular layers or 3D architectures are formed via intermolecular weak interactions, including π–π interactions, hydrogen bonds, C–H···π contacts and weak Hg···N and Hg···I bonds. Additionally, the catalytic activity of the NHC palladium(II) complex 7 in Suzuki–Miyaura cross-coupling reaction was studied.

Graphical abstractA series of new NHC silver(I), palladium(II) and mercury(II) complexes containing mesitylene linkers were prepared and characterized. The catalytic performance of the palladium complex is studied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Four NHC Ag(I), Pd(II) and Hg(II) complexes have been prepared and characterized. ► These NHC metal complexes adopt four different conformations. ► A doubly deprotonated acetonitrile is contained in complex 8. ► The crystal packings of the compounds are formed via weak interactions. ► NHC Pd(II) complex 7 is an effective catalyst for Suzuki–Miyaura reaction in air.