Pyridine Substituted N-Heterocyclic Carbene Ligands as Supports for Au(I)−Ag(I) Interactions: Formation of a Chiral Coordination Polymer

Reaction of 1,3-bis(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate, [H(pyCH2)2im]BF4, with silver oxide in
dichloromethane readily yields [Ag((pyCH2)2im)2]BF4, 1·BF4. 1·BF4 is converted to the analogous Au(I)-containing
species, [Au((pyCH2)2im)2]BF4, 3, by a simple carbene transfer reaction in dichloromethane. Further treatment with
two equivalents of AgBF4 produces the trimetallic species [AuAg2((pyCH2)2im)2(NCCH3)2](BF4)3, 4, which contains
two silver ions each coordinated to the pyridine moieties on one carbene ligand and to an acetonitrile molecule in
a T-shaped fashion. Monometallic [Ag((py)2im)2]BF4, 5, and [Au((py)2im)2]BF4, 6, are made analogously to 1·BF4
and 3 starting from 1,3-bis(2-pyridyl)-imidazol-2-ylidene tetrafluoroborate, [H(py)2im]BF4. Addition of excess AgBF4
to 6 yields the helical mixed-metal polymer, {[AuAg((py)2im)2(NCCH3)](BF4)2}n, 7 which contains an extended Au(I)−Ag(I) chain with short metal−metal separations of 2.8359(4) and 2.9042(4) Å. Colorless, monometallic [Hg((pyCH2)2im)2](BF4)2, 8, is easily produced by refluxing [H(pyCH2)2im)]BF4 with Hg(OAc)2 in acetonitrile. The related quinolyl-substituted imidazole, [H(quinCH2)2im]PF6, is produced analogously to [H(pyCH2)2im]BF4. [Hg((quinCH2)2im)2](PF6)2,
9, is isolated in good yield as a white solid from the reaction of Hg(OAc)2 and [H(quinCH2)2im]PF6. The reaction
of [H(quinCH2)2im]PF6 with excess Ag2O produces the triangulo-cluster [Ag3((quinCH2)2im)3](PF6)3, 11. All of these
complexes were studied by 1H NMR spectroscopy, and complexes 3−9 were additionally characterized by X-ray
crystallography. These complexes are photoluminescent in the solid state and in solution with spectra that closely
resemble those of the ligand precursor.