Catalytic activities of ruthenium(II) complexes in transition-metal-mediated living radical polymerization: Polymerization, model reaction, and cyclic voltammetry

Catalytic activities of ruthenium complexes were examined in the metal-cata lyzed living radical polymerization of methyl methacrylate (MMA) and in hal ogen exchange reactions between the dormant species and the ruthenium compl ex, along with cyclic voltammetry (CV). Among half-metallocene-type rutheni um(II) complexes, the activity increased in the order Ru(Cp)Cl(PPh3)(2) < R u(Ind)C1(PPh3)(2) < Ru(Cp*)Cl(PPh3)(2) (Cp = eta(5)-C5H5, Ind = eta(5)-C9H7 , CP* = eta(5)-C5Me5); namely, the lower the redox potential of the complex las measured by cyclic voltammetry), the faster the polymerization and the halogen exchange reaction. There were no apparent correlation, however, am ong the polymerization, the halogen exchange, and the redox potential for c omplexes of different structures such as Ru(Cp)Cl(PPh3)(2), RuCl2-(PPh3)(3) , and Ru(Tp)Cl(PPh3)(2) [Tp = hydrotris(1-pyrazolyl)borate]. Thus, the cata lytic activity of the complexes for the living radical polymerization can b e predicted from the halogen exchange reaction or their redox potential in some cases.