Dichloro(o-isopropoxyphenylmethylene)(tricyclohexylphosphine)ruthenium is a well-defined, second-generation Grubbs catalyst, specifically known as Grubbs Catalyst II. It is an organometallic complex featuring a ruthenium center coordinated by a benzylidene ligand, a tricyclohexylphosphine (PCy3) ligand, and two chloride ligands. The o-isopropoxy substituent on the benzylidene moiety is a key structural feature that influences its reactivity and stability. This complex is a cornerstone reagent in synthetic organic chemistry and materials science, primarily due to its exceptional activity and functional group tolerance in olefin metathesis reactions, including ring-closing metathesis (RCM), cross-metathesis (CM), and ring-opening metathesis polymerization (ROMP). Its primary industrial and research application lies in the synthesis of complex organic molecules, advanced polymers, and functional materials. In the context of materials chemistry, it is extensively used to synthesize conjugated polymers and precision macromolecular architectures for organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and other organic electronic devices. Compared to the first-generation catalyst, Grubbs Catalyst II offers significantly higher activity and thermal stability, making it suitable for a broader range of substrates and more demanding reaction conditions. It is typically handled under an inert atmosphere (argon or nitrogen) due to its sensitivity to air and moisture.