Synthesis and Structure of Dinuclear Silver(I) and Palladium(II) Complexes of 2,7-Bis(methylene)naphthalene-Bridged Bis-N-Heterocyclic Carbene Ligands

We synthesized a series of new Ag-2(bis-NHC)(2) complexes from the corresponding bisimidazolium salts tethered with 2,7-dimethylnaphthalene-bridged bis-NHC ligands. The reaction proceeded in a selective manner, and the Ag-2(bis-NHC)(2) complexes were isolated in good to high yields. The Ag complexes were converted to the Pd-2(bis-NHC)(2) complexes efficiently. It is important to choose proper conditions for the conversion of the silver complexes to the palladium complexes, depending on the structure of the ligand: the effect of the counteranion was significant. The structures of the complexes were studied by X-ray crystallographic analyses and compared with the corresponding monodentate NHC complexes. The catalytic activity of the Pd complexes for the Mizoroki-Heck reaction was examined.