Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd-Catalyzed CO/Vinyl Arene Polyketone Synthesis

Two pyrene-tagged iminopyridines (NN) were used to synthesize neutral and monocationic, palladium(II) complexes, [Pd(Me)Cl(NN)] and [Pd(Me)(MeCN)(NN)][PF6]. The monocationic complexes generated active catalysts in the CO/vinyl arene copolymerization, leading to polyketones with yields and molecular weight strongly dependent on N-N, with the ketimine catalysts one order of magnitude more productive than the aldimine counterpart. The stereochemistry of polyketones synthesized with the aldimine catalyst was found to be dependent on the vinyl comonomer: prevailingly syndiotactic copolymers were obtained for styrene, prevailingly isotactic copolymers were produced for 4-methyl styrene, and atactic macromolecules were formed for 4-tert-butyl styrene. The statistical analysis demonstrated that the control of the stereochemistry switched from enantioselective site control for 4-methyl styrene to a combination of chain-end and enantioselective site control for styrene.