Living ROMP of <i>exo</i>-Norbornene Esters Possessing Pd^II SCS Pincer Complexes or Diaminopyridines

Abstract

Isomerically pure exo-norbornene esters containing either a PdII SCS pincer complex or a diaminopyridine unit were synthesized, polymerized, and copolymerized by ring-opening metathesis polymerization using a ruthenium initiator. All polymerizations are living under mild reaction conditions. A comparison between the pure exo monomers and the commonly employed 80:20 endo/exo mixtures was carried out. The exo-norbornene isomers exhibit significantly higher rates of propagation under milder conditions when compared to the endo/exo mixtures. Kinetic studies have shown that the kp values are highly dependent upon the isomeric purity but completely independent of the terminal diaminopyridine or PdII SCS Pincer functional groups. The living character of the polymerization has allowed for the first block copolymerization of norbornene metal-containing pincer complexes and diaminopyridine-based hydrogen-bonding receptors.