source: Macromolecules year: 2003 volume: 36 first page: 1446 last page: 1456 doi: 10.1021/ma021315x
Abstract: The ring-opening metathesis polymerization (ROMP) of two optically active 2,3-dicarboalkoxynorbornadienes derived from (S)-(-)-2-methyl-1-butanol and (R)-(-)-2-butanol were carried out in the presence of the [RuCl2(p-cymene)]2 catalyst precursor activated by trimethylsilyldiazomethane (TMSD). 1H and 13C NMR analyses showed that a high degree of stereoregularity was achieved and homonuclear proton-proton COSY spectroscopy indicated that the major trans fractions of the polymers were most likely isotactic, while the minor cis fractions were syndiotactic. Ring-opened metathesis polymers were also made from 2,3-dicarbomethoxynorbornadiene and exo,exo-2,3-dicarbomethoxy-5-norbornene. They were hydrogenated into the corresponding polynorbornanes using diimide. The NMR spectra of the reduced materials confirmed that the unsaturated parent polymers had an all-trans highly isotactic microstructure. A tentative mechanism involving arene loss, carbene formation, and monomer chelation is proposed to account for the observed stereoselectivities.