A class of catalysts with unusually high activity for polymerizing vinyl monomers such as acrylates, methacrylates and styrene is described. The catalysts consists of a metal halide such as CuBr and FeBr2 ligated with multidentate amine-based ligands, for example N,N,N′,N′-tetra[(2-pyridal)methyl]ethylenediamine, and additives. The additives, which are tertiary amine compounds, can greatly increase the catalytic activity. The complex is capable of catalyzing a living polymerization reaction at a concentration of the complex below about 0.1 mol %.