Evaluation of ruthenium-based complexes for the controlled radical polymerization of vinyl monomers

New complexes of the type RuCl2(p-cymene)L where the ligand L is either a p hosphine or a stable triazolinylidene carbene have been tested and compared to the Grubbs' benzylidene complex RuCl2(=CHPh)(PCy3)(2) as catalyst precu rsors for the controlled atom transfer radical polymerization (ATRP) of met hyl methacrylate and of various para-substituted styrenes. Kinetic data and Hammett rho constants are reported, as well as the X-ray structure of the ortho-metallated triazolinylidene-ruthenium(II) complex RuCl(p-cymene)[1,2- phenylene[3,4-diphenyl-1H-1,2,4-triazol-1-yl-5(4H)-ylidene]].