Living ROMP of exo-norbornene esters possessing PdIISCS pincer complexes or diaminopyridines

Isomerically pure exo-norbornene esters containing either a Pd-II 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 k(p) values are highly dependent upon the isomeric purity but completely independent of the terminal diaminopyridine or Pd-II 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.