Mono-, di-, and trinuclear luminescent silver(I) and gold(I) N-heterocyclic carbene complexes derived from the picolyl-substituted methylimidazolium salt: 1-methyl-3-(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate

The N-heterocyclic carbene (NHC) precursor, 1-methyl-3-(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate, [HCH(3)im(CH(2)py)]BF4, reacted with AgBF4 in the presence of aqueous NaOH to produce the silver complex [Ag(CH(3)im(CH2PY))(2)]BF4 (1) which was then reacted with Au(tht)Cl to form the corresponding gold(l) complex, [Au(CH(3)im(CH2PY))(2)]BF4 (2). Complex 2 reacted with 1 equiv of AgBF4 to produce the mixed-metal species [AuAg(CH(3)im(CH2PY))(2)](BF4)(2) (3). The reaction of 2 with 1 equiv of Au(tht)Cl followed by metathesis with NaBF4 produces the dimetallic gold complex [Au-2(CH(3)im(CH2PY))(2)](BF4)(2) (4). The reaction of [Ag(CH(3)im(CH2PY))(2)]BF4 (1) with 1 equiv of AgBF4 produces the trinuclear [Ag-3(CH(3)im(CH2PY))(3)(NCCH3)(2)](BF4)(3) (5) complex, which appears to dissociate into a dimetallic complex in solution. Complexes 1-5 were characterized by H-1 NMR, C-13 NMR, UV-vis, luminescence spectroscopy, elemental analysis, mass spectrometry, and X-ray crystallography. The CH(3)im(CH2PY) ligands in 3 are arranged in a head-to-head fashion spanning a Au-Ag separation of 3.0318(5) angstrom with the carbene portion of the ligand remaining coordinated to the Au(I) center. In 4, the ligands are arranged in a head-to-tail fashion with an Au-Au separation of 3.1730(5) angstrom. In 5, the ligands bridge the nearly symmetrical Ag-3 triangular core with short Ag-Ag separations of 2.7765(8), 2.7832(8), and 2.7598(8) angstrom. All of these complexes, including the ligand precursor, are intensely luminescent in solution and the solid state.