Supramolecular Structures from Polycarbene Ligands and Transition Metal Ions

Abstract

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 H4-2a,b(Br)4 and the trisimidazolium salts of type H3-4a,b(Br)3 have been prepared by alkylation of the remaining free imines of the tetrakis- and trisimidazoles (H4-2a 4+, H3-4a 3+: R = n-butyl; H4-2b 4+, H3-4b 3+: R = ethyl). Polyimidazolium salts H4-2a,b(PF6)4 and H3-4a,b(PF6)3 have been synthesized by anion exchange from H4-2a,b(Br)4 and H3-4a,b(Br)3. Two equivalents of tetraimidazolium salt H4-2a(Br)4 or H4-2a,b(PF6)4 reacts with four equivalents of Ag2O to yield via self-assembly molecular cylinders of type [Ag4(2a)2]Y4 (Y− = [AgBr2]− and/or Br−) or [Ag4(2a,b)2](PF6)4, respectively. Similarly, reaction of two equivalents of trisimidazolium salts H3-4a(Br)3 or H3-4a,b)(PF6)3 with three equivalents of Ag2O yields the molecular cylinder [Ag3(4a)2](Y)3 (Y− = [AgBr2]− and/or Br−) or [Ag3(4a,b)2](PF6)3, respectively. Transmetalation of [Ag4(2a,b)2](PF6)4 with four equivalents of [AuCl(SMe2)] leads to the formation of the tetranuclear gold(I) complex [Au4(2a,b)2](PF6)4 with retention of the metallosupramolecular assembly. Analogously, transmetalation of [Ag3(4a,b)2](PF6)3 with three equivalents of [AuCl(SMe2)] or CuBr yields the trinuclear gold(I) complexes [Au3(4a,b)2](PF6)3 or the copper(I) complexes [Cu3(4a,b)2](PF6)3, respectively. Contrary to the metallosupramolecular assemblies of type [M4(2a)2]4+ (M = Ag+, Au+), tetrakisimidazolium salt H4-2a(Br)4 reacts with K2PtCl4 in the presence of NaOAc to yield the square-planar dinuclear complex [Pt2(2a)Br4].

Synthesis, Characterization and Luminescence of Silver(I) and Gold(I) Complexes Bearing a Diethyl Acetal Functionalized N-Heterocyclic Carbene

“…As solutions of 2 and 3 are not absorbing above 250 nm, the bands in the excitation spectra are indicative of electronic transitions originating from the aggregation via metal-metal interactions in the solid state. The very large Stokes shifts of ∼ 9470 cm −1 (2) and ∼ 22260 cm −1 (3) indicate severe distortions of the structures in the excited state. These observations are in accordance with an excimer/exciplex model.…”

“…Because NHC-Ag(I) complexes are versatile carbene transfer agents, they have been synthesized as stable intermediates in the course of many preparations of other transition metal NHCcomplexes [2]. They are conveniently accessible by the reaction of an imidazolium salt and Ag 2 O and feature a rich coordination chemistry.…”

“…NHC-Au(I) complexes are investigated due to numerous applications ranging from homogeneous catalysts for unique C-C, C-O, and C-N bond forming reactions [3,4] to pharmaceutical uses as anticancer, antiarthritis, and antibacterial agents [5,6]. The chemistry of gold is dominated by compounds of the metal in the oxidation state +1 in linearly coordinated complexes of the type NHC-Au-X or [(NHC) 2 Au]X, which are prepared by the reaction of (R 2 S)AuX (R 2 S = Me 2 S, tetrahydrothiophene; X = halide) with an NHC-Ag complex or the free carbene [7]. In the course of our studies on Ag(I), Au(I) and Au(III) complexes bearing NHCs functionalized with nitrogen donor atoms [8 -10], we became also interested in examples with oxygen containing side arms at a nitrogen atom of the NHC ligands.…”

Rotaxanes and pseudorotaxanes with threads containing pyridinium units

“…Recently N-heterocyclic carbenes have been widely investigated; they are used in construction of three-dimensional structures 54,55 and of metalla-macrocycles. 56,57 As an example of rotaxanes stoppered by palladium N-heterocyclic carbene may serve [2]rotaxane 12, obtained from bis(dipyridiniumyl)ethane 5 and dibenzo [24]crown-8 (DB24C8) in the presence of dimeric Pd(II)benzimidazolin-2-ylidene complex [PdBr 2 (i-Pr 2 -bimy)] 2 .…”

N‐heterocyclische Nitreniumliganden: ein fehlendes Bindeglied

“…Als Liganden bieten sie außerdem einige Vorteile, und zwar 1) den s-elektronenziehenden und p-elektronenliefernden Charakter des Stickstoffzentrums/der Stickstoffzentren des heterocyclischen Rings, 2) die sterische Abschirmung durch Substituenten an diesen Stickstoffzentren und 3) eine einfach und umfangreich modifizierbare Struktur. Aufgrund dieser Eigenschaften wurden NHCs als ausgezeichnete Liganden erkannt und auf verschiedenen Gebieten, darunter Katalyse [3] und Materialchemie, [4] ausgiebig verwendet. Infolge der raschen Entwicklung der NHC-Übergangsmetallchemie wurde auch das Koordinationsverhalten isovalenter NHC-Analoga mit weiteren Hauptgruppenelementen (aus den Gruppen 13-15) erforscht (A, Schema 1).…”