Stepwise formation of organometallic macrocycles and triangular prisms containing 2,2′-bisbenzimidazole ligands

Abstract

A series of organometallic macrocycles have been constructed by an efficient “bottom-up” assembly methodology at ambient temperature. Treatment of [Cp*MCl₂]₂ (1a: M = Ir, 1b: M = Rh) with pyrazine or 4,4′-bipyridine (bpy) (1 : 1; Cp* = pentamethylcyclopentadienyl) at room temperature resulted in the formation of binuclear complexes [Cp*MCl₂]₂(pyrazine) and [Cp*MCl₂]₂(bpy) (M = Ir or Rh), which were then further reacted with AgOTf (Tf = O₂SCF₃) and 2,2′-bisbenzimidazole ligand (BiBzIm). Four organometallic macrocyclic complexes formulated as [Cp*₄Ir₄(BiBzIm)₂(pyrazine)₂](OTf)₄ (2a), [Cp*₄Rh₄(BiBzIm)₂(pyrazine)₂](OTf)₄ (2b), [Cp*₄Ir₄(BiBzIm)₂(bpy)₂](OTf)₄ (2c) and [Cp*₄Rh₄(BiBzIm)₂(bpy)₂](OTf)₄ (2d) each bearing 2,2′-bisbenzimidazole ligand and the half-sandwich Ir, Rh fragments were finally obtained in good yields. In a similar process, if a rigid ligand L (3-pyridyl-bian) was used as the linker, two novel metallacycles (3a and 3b) which enchased a silver atom in the centre were obtained. Organometallic triangular prisms 4a were synthesized via methods similar to those of the rectangles. [Cp*IrCl₂]₂ reacted with tridentate ligand 2,4,6-tri(4-pyridyl)-1,3,5-triazine (tpt) to give the corresponding trinuclear complexes [Cp*IrCl₂]₃(tpt), then further reacted with AgOTf and 2,2′-bisbenzimidazole ligand, leading to the formation of the prism-like complexes formulated as [Cp*₆M₆(BiBzIm)₆(tpt)₂](OTf)₆ (3a: M = Ir, 3b: M = Rh). All complexes were well characterized by ¹H NMR and IR spectroscopy, as well as elemental analyses. The molecular structures of 2a, 2b, 2c, 3a, 3b and 4a were characterized by single-crystal X-ray crystallography. We found that the prism-like hexanuclear complexes 4a displayed interesting host–guest chemistry.