Synthesis of chiral molybdenum ROMP initiators and all-cis highly tactic poly(2,3-(R)2norbornadiene) (R = CF3 or CO2Me)

Polymerization of Enantiomerically Pure 2,3-Dicarboalkoxy Norbornadienes and 5,6-Disubstituted Norbornenes by Well-Characterized Molybdenum ROMP catalysts

“…8 The tacticity of these polymers is the same as the bias observed foricis polymers prepared using Mo(CHCMe 2 Ph)(NAr)[OCMe(CF 3 ) 2 12 as the initiator. 7 Therefore both high trans, highly tactic and high cis, highly tactic polymers can now be prepared.…”

“…4 poly(NBDF6). 8 It was proposed that the isopropyl substituents in the NAt ligand are sterically too encumbering in that particular circumstance to allow the syn rotamer to react exclusively to give cis polymer, some trans polymer is formed via anti rotamers.…”

“…Unfortunately, neither NBDF6 nor DCMNBD is chiral, and therefore 13 C NMR methods analogous to those that have been used so extensively to argue for a given tacticity of polymers prepared from enantiomerically pure (or highly enriched) norbornenes 9 -14 cannot be employed here. However, since the proton NMR spectrum of cis,tactic polyDCMNBD relatively simple 8 we realized that it should be possible to determine the tacticity of 2,3-dicarboalkoxy norbornadienes that contain a chiral group in the ester directly and relatively quickly by proton NMR methods. It also should be possible to determine the tacticity of i$JIIl ]mmmll i 0 0 0l n n 0 0 * t4 0 enantiomerically pure 5,6-disubstituted norbornenes, if high trans or high cis, highly tactic 0 polymers can be prepared.…”

Metathesis by Molybdenum and Tungsten Catalysts

“…37 In 1993 initiators that contain a biphenolate ligand (e.g., 2 in Figure 1) were found to direct an olefin to one side of the initial M=C bond and all subsequent M=C bonds to give a cis,isotactic polymer (e.g., equation 3 for norbornene itself). 38 Enantiomorphic site control of polymer formation is complemented by the more recent development of MAP initiators (e.g., 1, 3, or 4) that promote formation of cis C=C bonds (vide supra) and in the process, formation of cis,syndiotactic polymers as a consequence of the chirality at the metal switching with each insertion of monomer into the M=C bond (stereogenic metal control). 39 Hydrogenation of pure cis,isotactic or cis,syndiotactic polymers made from norbornene 40 or dicyclopentadiene 41 yields isotactic or syndiotactic hydrocarbon polymers that are crystalline, high melting, relatively stable to oxygen, and therefore of commercial value.…”

Asymmetric catalysts for stereocontrolled olefin metathesis reactions

“…6 The first suggestion that these complexes may also catalyze the enantioselective synthesis of small organic molecules appeared in 1993. 7 Henceforward, the quest for asymmetric olefin metathesis catalysts began and still goes on. However, due to their electron deficient character (14 VE-d 4 ) these Mo-complexes are sensitive to moisture and oxygen.…”