Dual Behavior of Cationic Palladium Pentafluorophenyl Complexes as Catalysts for the Homopolymerization of Acrylates and of Nonpolar Olefins

[Pd(Pf)(NCMe)(N-N)]BF4, (Pf = C6F5; N-N = ethylenediamine (en, 1), 2,2'-bipyridine (2), (2,6-(PrC6H3)-Pr-i)N=C(Me)C(Me)=N(2,6-(PrC6H3)-Pr-i) (diimine, 3)) are very efficient initiators of the radical polymerization of alkyl acrylates. Mechanistic studies reveal that the polymerization of methyl acrylate with 1 starts by the insertion of the monomer into the Pd-aryl bond of the catalyst to give [Pd{CH(CO2Me)CH(2)Pf}(N-N)(NCMe)]BF4, (N-N = en (5), diimine (7)). In contrast to the case for other cationic palladium complexes, the presence of a Pf group does not allow the formation of C,O-palladacycles with a suitable ring size. This allows complex 5 (or 7) to decompose not only by beta-H elimination but also by homolytic cleavage of the Pd-C bond in the light. The radical species generated in this process start the polymerization. Complex 1 is also a very efficient catalyst in the vinyl addition polymerization of norbornene by an insertion mechanism. Complex 3 polymerizes ethylene. Although complexes 1 and 3 are versatile polymerization initiators by two different mechanisms, neither copolymerization of methyl acrylate and norbornene with 1 nor that of methyl acrylate and ethylene with 3 were successful, leading to either very low yields or mixtures of homopolymers.