Chiral Silver and Gold Rings: Synthesis and Structural, Spectroscopic, and Photophysical Properties of Ag and Au Metallamacrocycles of Bridging NHC Ligands
datasetposted on 09.05.2011 by Cristina Carcedo, James C. Knight, Simon J. A. Pope, Ian A. Fallis, Athanasia Dervisi
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The synthesis and silver(I) and gold(I) coordination chemistry of a new chiral, bidentate N-heterocyclic carbene (NHC) dehydrohexitol derivative (3) are reported. The imidazolium salt [H23][PF6]2 reacts with Ag2O and Au(tht)Cl (tht = tetrahydrothiophene) precursors to form the isostructural 18-membered metallamacrocyclic dimers [Ag2(μ-3)2][PF6]2 and [Au2(μ-3)2][PF6]2 and the monocarbene complex [(AuCl)2(μ-3)]. Single-crystal X-ray structures have been determined for the bis-imidazolium precursor [H23][PF6]2 and corresponding Ag(I) and Au(I) complexes of ligand 3. Comparison between the X-ray-derived structures and solution-phase NMR data for [Ag2(μ-3)2][PF6]2 and [Au2(μ-3)2][PF6]2 demonstrate that the complexes adopt a conformation in solution different from that found in the solid state, implying a conformational flexibility of the metallamacrocycle in solution. Both [(AuCl)2(μ-3)] and [Au2(μ-3)2][PF6]2 are emissive in the solid state at ca. 380 nm (λex = 295 nm). Time-resolved luminescence measurements indicate different excited-state lifetimes for the two species, with [(AuCl)2(μ-3)] measured at 35 ns and [Au2(μ-3)2][PF6]2 at 379 ns. The chiroptical properties of the silver and gold NHC complexes have been studied by circular dichroism (CD).