Indazolin‑<i>s</i>‑ylidene–N-Heterocyclic Carbene Complexes of Rhodium, Palladium, and Gold: Synthesis, Characterization, and Catalytic Hydration of Alkynes

A novel series of Indy-N-heterocyclic carbene ligands (Indy = indazolin-<i>s</i>-ylidene) have been developed and investigated. Via a mild Ag carbene transfer route, these new carbene ligands reacted with rhodium, palladium, and gold salts to yield the corresponding air-stable metal complexes. The product complexes were characterized by NMR spectroscopic methods and X-ray diffraction analysis. The electronic properties of these complexes were modified by the introduction of different substituents at the coordinated NHC ligands. Catalytic properties of the gold complex were evaluated in the hydration of alkynes to give the corresponding ketone products. This new type of gold N-heterocyclic carbene complex showed a high catalytic activity in the hydration of alkyne at room temperature.