Methacrylate Insertion into Cationic Diimine Palladium(II)−Alkyl Complexes and the Synthesis of Poly(alkene-block-alkene/carbon monoxide) Copolymers

The reaction of cationic Pd(II) diimine complex [(N∧N)Pd(Me)(L)][B(Arf)4] ((N∧N) = 2,3-bis(2,6-di-isopropylphenylimino)butane, Arf = 3,5-(CF3)2C6H3, L = Et2O) with methyl methacrylate results in 1,2-insertion regiochemistry that is opposite of that observed with methyl acrylate. The enthalpy of activation for MMA insertion is 4 kcal/mol higher than that for the corresponding MA insertion. The MMA-inserted complex can be employed for ethene or 1-hexene homopolymerization and their alternating copolymerization with carbon monoxide. Further, the quasi-living nature of the polymerizations allows the synthesis of poly(hexene-b-hexene/CO) and poly(ethene-b-ethene/CO) copolymers.