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(pyCH(2))(2)im]BF4, with silver oxide in dichloromethane readily yields [Ag((pyCH(2))(2)im)(2)]BF4, 1.BF4. 1.BF4 is converted to the analogous Au(I)-containing species, [Au((pyCH(2))(2)im)(2)]BF4, 3, by a simple carbene transfer reaction in dichloromethane. Further treatment with two equivalents of AgBF4 produces the trimetallic species [AuAg2((pyCH(2))(2)im)(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)(2)im)(2)]BF4, 5, and [Au((py)(2)im)(2)]BF4, 6, are made analogously to 1.BF4 and 3 starting from 1,3-bis(2-pyridyl)-imidazol-2-ylidene tetrafluoroborate, [H(py)(2)im]BF4. Addition of excess AgBF4 to 6 yields the helical mixed-metal polymer, {[AuAg((py)(2)im)(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) Angstrom. Colorless, monometallic [Hg((pyCH(2))(2)im)(2)](BF4)(2), 8, is easily produced by refluxing [H(pyCH(2))(2)im)]BF4 with Hg(OAC)(2) in acetonitrile. The related quinolyl-substituted imidazole, [H(quinCH(2))(2)im]PF6, is produced analogously to [H(pyCH(2))(2)im]BF4. [Hg((quinCH(2))(2)im)(2)](PF6)(2), 9, is isolated in good yield as a white solid from the reaction of Hg(OAc)(2) and [H(quinCH(2))(2)im]PF6. The reaction of [H(quinCH(2))(2)im]PF6 with excess Ag2O produces the triangulo-cluster [Ag-3((quinCH(2))(2)im)(3)](PF6)(3), 11. All of these complexes were studied by H-1 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.