Mechanism and Scope of Stereospecific, Coordinative-Anionic Polymerization of Acrylamides by Chiral Zirconocenium Ester and Amide Enolates

Abstract

The mechanism and scope of the isospecific, coordinative-anionic polymerization of acrylamides, including N,N-dimethylacrylamide (DMAA), N,N-dimethylmethacrylamide (DMMA), and N-isopropylacrylamide (IPAA), using chiral ansa-zirconocenium ester and amide enolates, are reported. The zirconocenium ester enolate, rac-(EBI)Zr+(THF)[OC(OiPr)CMe2][MeB(C6F5)3]- [1; EBI = C2H4(Ind)2], effects highly isospecific and living polymerization of DMAA via a monometallic, intramolecular coordinative-conjugate-addition mechanism, with the resting intermediate during a “catalytic” propagation cycle being the cyclic amide enolate. The results leading to these key conclusions were derived from investigations of polymerization kinetics, polymer microstructures and chain-end groups, and block copolymerization behavior as well as modeling and isolation of the active propagating species. Specifically regarding the active species modeling, isolation, and characterization, neutral chiral amide enolate rac-(EBI)ZrMe[OC(NMe2)CMe2] (2...