C-s-Ligated ansa-zirconocene bis- and mono(ester enolate) complexes incorporating the diphenylmethylidene- (cyclopentadienyl)(9-fluorenyl) ligand, upon activation with appropriate activators, are highly active catalysts for the syndiospecific polymerization of MMA at ambient temperature, leading to the production of PMMA with high syndiotacticity (mr = 94%) and glass transition temperature (T-g = 139 C).