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,
[HCH3im(CH2py)]BF4, reacted with AgBF4 in the presence of aqueous NaOH to produce the silver complex
[Ag(CH3im(CH2py))2]BF4 (1) which was then reacted with Au(tht)Cl to form the corresponding gold(I) complex,
[Au(CH3im(CH2py))2]BF4 (2). Complex 2 reacted with 1 equiv of AgBF4 to produce the mixed-metal species
[AuAg(CH3im(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 [Au2(CH3im(CH2py))2](BF4)2 (4). The reaction of [Ag(CH3im(CH2py))2]BF4 (1)
with 1 equiv of AgBF4 produces the trinuclear [Ag3(CH3im(CH2py))3(NCCH3)2](BF4)3 (5) complex, which appears to
dissociate into a dimetallic complex in solution. Complexes 1−5 were characterized by 1H NMR, 13C NMR, UV-vis,
luminescence spectroscopy, elemental analysis, mass spectrometry, and X-ray crystallography. The CH3im(CH2py)
ligands in 3 are arranged in a head-to-head fashion spanning a Au−Ag separation of 3.0318(5) Å 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) Å. In 5, the ligands bridge the nearly symmetrical Ag3 triangular
core with short Ag−Ag separations of 2.7765(8), 2.7832(8), and 2.7598(8) Å. All of these complexes, including the
ligand precursor, are intensely luminescent in solution and the solid state.