Supramolecular Structures from Polycarbene Ligands and Transition Metal Ions

The synthesis of cylinder-type carbene complexes from polycarbene ligands and coinage metal ions via metal-controlled self-assembly has been explored. Imidazole reacts with 1,2,4,5-tetrabromobenzene or 1,3,5-tribromobenzene to give 1,2,4,5-tetrakis(1-imidazolyl)benzene (1) and 1,3,5-tris(1-imidazolyl)benzene (3), respectively. The tetrakisimidazolium salts of type H-4-2a,b(Br)(4) and the trisimidazolium salts of type H-3-4a,b(Br)(3) have been prepared by alkylation of the remaining free imines of the tetrakis- and trisimidazoles (H-4-2a(4+), H-3-4a(3+): R = n-butyl; H-4-2b(4+), H-3-4b(3+): R = ethyl). Polyimidazolium salts H-4-2a,b(PF6)(4) and H-3-4a,b(PF6)(3) have been synthesized by anion exchange from H-4-2a,b(Br)(4) and H-3-4a,b(Br)(3). Two equivalents of tetraimidazolium salt H-4-2a(Br)(4) or H-4-2a,b(PF6)(4) reacts with four equivalents of Ag2O to yield via self-assembly molecular cylinders of type [Ag-4(2a)(2)]Y-4 (Y- = [AgBr2](-) and/or Br-) or [Ag-4(2a,b)(2)](PF6)(4), respectively. Similarly, reaction of two equivalents of trisimidazolium salts H-3-4a(Br)(3) or H-3-4a,b)(PF6)(3) with three equivalents of Ag2O yields the molecular cylinder [Ag-3(4a)(2)](Y)(3) (Y- = [AgBr2](-) and/or Br-) or [Ag-3(4a,b)(2)](PF6)(3), respectively. Transmetalation of [Ag-4(2a,b)(2)](PF6)(4) with four equivalents of [AuCl(SMe2)] leads to the formation of the tetranuclear gold(I) complex [Au-4(2a,b)(2)](PF6)(4) with retention of the metallosupramolecular assembly. Analogously, transmetalation of [Ag-3(4a,b)(2)](PF6)(3) with three equivalents of [AuCl(SMe2)] or CuBr yields the trinuclear gold(I) complexes [Au-3(4a,b)(2)](PF6)(3) or the copper(I) complexes [Cu-3(4a,b)(2)](PF6)(3), respectively. Contrary to the metallosupramolecular assemblies of type [M-4(2a)(2)](4+) (M = Ag+, Au), tetrakisimidazolium salt H-4-2a(Br)(4) reacts with K2PtCl4 in the presence of NaOAc to yield the square-planar dinuclear complex [Pt-2(2a)Br-4].