N-Heterocyclic Carbene Palladium Complexes Bearing Carboxylate Ligands and Their Catalytic Activity in the Hydroarylation of Alkynes

The synthesis and reactivity of palladium
acetate/trifluoroacetate complexes stabilized by the presence of N-heterocyclic carbene (NHC) ligands are described. The structures and coordination characteristics
of both (IPr)Pd(OAc)2 (1) and (IPr)Pd(OOCCF3)2(H2O)
(2) were elucidated by spectroscopic and X-ray diffraction
studies. The structure of 1 shows a novel coordination
of the anions in a monomeric complex, with one acetate
anion acting as a monodentate ligand while the second
one coordinates through both oxygens. The NHC ligands
in 1 and 2 are stable under acidic conditions. The
complexes were used as precatalysts in the hydroarylation of alkynes. Using this simple protocol, a number of
arenes react with various alkynes to produce stilbenes.