(1,3-Dimesitylimidazolidin-2-ylidene)(2-isopropoxybenzylidene)ruthenium(VI) chloride, also known as the Hoveyda-Grubbs catalyst 2nd generation, is a ruthenium-based olefin metathesis catalyst. Its structure features a chelating benzylidene ligand with an isopropoxy group and a saturated N-heterocyclic carbene (NHC) ligand, which enhances its stability and activity compared to first-generation catalysts. This catalyst is widely used in organic synthesis for ring-closing metathesis (RCM), cross-metathesis (CM), and ring-opening metathesis polymerization (ROMP). Its high functional group tolerance and air stability make it a preferred choice for complex molecule synthesis, including pharmaceuticals and natural products. The catalyst operates via a dissociative mechanism, where the isopropoxy group coordinates to the ruthenium center, facilitating initiation. The compound is typically a green crystalline solid, stable under inert atmosphere but sensitive to prolonged exposure to air and moisture. It is commercially available and a standard tool in synthetic chemistry laboratories for constructing carbon-carbon double bonds efficiently.