Gold complexes with N-heterocyclic carbene (NHC) ligands have been used in catalysis and medicinal chemistry. Often, complexes of the type (NHC)Au–X (X = halide) have been used. Replacing the halide ligand with a sulfur-based ligand can lead to more stable complexes with new functions. Ligands with sulfur/nitrogen heterocycles, such as mercaptopyridines or mercaptothiazolines, have also been used. In these complexes, the sulfur atom binds to the gold center and the nitrogen atom can potentially coordinate a second metal.

Daniel Mendoza-Espinosa, Autonomous University of the State of Hidalgo, Mineral de la Reforma, Mexico, and colleagues have prepared (NHC)Au^I–mercaptopyridine complexes (example pictured, Dipp = 2,6-diisopropylphenyl), as well as related heteronuclear Au/Pd complexes in which the pyridine nitrogen coordinates a palladium allyl chloride unit. The team prepared the Au(I) complexes from the corresponding chloride or iodide complexes via ligand exchange with either 2- or 4-mercaptopyridine and excess KOH in tetrahydrofuran (THF). The products were characterized using ¹H and ¹³C NMR spectroscopy, as well as single-crystal X-ray diffraction. The complexes show the expected linear (NHC)–Au–S coordination.

The heterometallic Au/Pd complexes were prepared from the synthesized gold complexes by the reaction with a palladium allyl chloride dimer in THF at 60 °C. The resulting bimetallic complexes might be useful in catalysis. The team also reacted the gold complexes with B(C₆F₅)₃ in the presence of ammonium fluoride and found that the pyridine nitrogen can form adducts of the type N_py–H–F–B(C₆F₅)₃. These complexes could be useful for the activation of small molecules.

• Synthesis and Reactivity of (NHC)Au^I–Mercaptopyridine Complexes,
  R. Evelyn Cordero-Rivera, David Rendón-Nava, Carlos Ángel-Jijón, Oscar R. Suárez-Castillo, Daniel Mendoza-Espinosa,
  Organometallics 2020.
  https://doi.org/10.1021/acs.organomet.0c00118