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

Abstract

Reaction of 1,3-bis(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate, [H(pyCH(2))(2)im]BF(4), with silver oxide in dichloromethane readily yields [Ag((pyCH(2))(2)im)(2)]BF(4), 1.BF(4)(). 1.BF(4) is converted to the analogous Au(I)-containing species, [Au((pyCH(2))(2)im)(2)]BF(4), 3, by a simple carbene transfer reaction in dichloromethane. Further treatment with two equivalents of AgBF(4) produces the trimetallic species [AuAg(2)((pyCH(2))(2)im)(2)(NCCH(3))(2)](BF(4))(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)]BF(4), 5, and [Au((py)(2)im)(2)]BF(4), 6, are made analogously to 1.BF(4) and 3 starting from 1,3-bis(2-pyridyl)-imidazol-2-ylidene tetrafluoroborate, [H(py)(2)im]BF(4). Addition of excess AgBF(4) to 6 yields the helical mixed-metal polymer, ([AuAg((py)(2)im)(2)(NCCH(3))](BF(4))(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) A. Colorless, monometallic [Hg((pyCH(2))(2)im)(2)](BF(4))(2), 8, is easily produced by refluxing [H(pyCH(2))(2)im)]BF(4) with Hg(OAc)(2) in acetonitrile. The related quinolyl-substituted imidazole, [H(quinCH(2))(2)im]PF(6), is produced analogously to [H(pyCH(2))(2)im]BF(4). [Hg((quinCH(2))(2)im)(2)](PF(6))(2), 9, is isolated in good yield as a white solid from the reaction of Hg(OAc)(2) and [H(quinCH(2))(2)im]PF(6). The reaction of [H(quinCH(2))(2)im]PF(6) with excess Ag(2)O produces the triangulo-cluster [Ag(3)((quinCH(2))(2)im)(3)](PF(6))(3), 11. All of these complexes were studied by (1)H 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.

Synthesis and Characterization of a Series of New Luminescent NHC‐Coordinated AuI–AgI Tetra‐ and Polymetallic Complexes Containing Benzoate‐Bridged Ag2 Dimers

“…For example, the bis(pyridyl)-substituted imidazole NHC ligand readily forms (Scheme 1) an Ag I -Au I helical polymer. [16] Interestingly, this material crystallizes in a chiral fashion with a statistical mixture of both the left-handed and righthanded crystals. Apart from the differences in helicity, the two enantiomers are completely identical with relatively small intermetallic separations of 2.8359(4) and 2.9042(4) Å.…”

Luminescence in Polymetallic Gold‐Heteronuclear Derivatives

“…The extended structures displayed very short alternating Au-Ag separations of 2.8359(4)À2.9042(4) Å . 32 This complex, like the carbene precursor, is luminescent in solution and in the solid state. In acetonitrile solution, it displays an emission at 345 nm, which originates from an electronic state centered at 284 nm, which is attributed to an intraligand fluorescent process.…”

Gold–Heterometal Interactions and Bonds

“…Thus, reaction with AgO 2 CCF 3 , in a 1 : 1 or 2 : 1 molar ratio, produces a tetranuclear species, [(C 6 F 5 )Au] 2 Ag 2 (m-Ph 2 PCH 2 SPh) 2 (m-O 2 CCF 3 ) 2 426a, with two gold and two silver atoms forming an Au-Ag-Ag-Au zigzag chain. The gold and silver atoms are bridged by the phosphorus ligand to afford an Au-Ag interaction of 3.0335 (8) [591].…”

“…In contrast, reaction of [Au{(py) 2 im} 2 ](BF 4 ) with AgBF 4 resulted in the heterometallic coordination polymer, [{AuAg{(py) 2 im} 2 (NCMe)}(BF 4 ) 2 ] n 430, regardless of the reaction conditions and stoichiometry used [591]. The chain polymer consists of Au(I) centers linearly coordinated to two carbene ligands alternating with Ag(I) centers bound to two of the pyridine rings from alternating Au(I) centers and to an acetonitrile molecule (distorted trigonal AgN 3 core).…”