Stereoselective Ring-Opening Metathesis Polymerization (ROMP) of Methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate by Molybdenum and Tungsten Initiators

• Main Authors: Jeong, Hyangsoo (Contributor), Ng, Victor Wee Lin (Contributor), Borner, Janna (Contributor), Schrock, Richard Royce (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Chemistry (Contributor)
• Format: Article
• Language: English
• Published: American Chemical Society (ACS), 2017-05-02T15:38:54Z.
• Subjects: Article
• Online Access: Get fulltext

Ring-opening metathesis polymerization (ROMP) of methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate (PhEtNNBE; (S) and racemic) was investigated employing six molybdenum and tungsten imido alkylidene initiators and two tungsten oxo alkylidene initiators. Of the six initiators that we proposed should yield cis,syndiotactic-poly[(S)-PhEtNNBE], two molybdenum OHMT alkylidene initiators, Mo(NR)(CHMe2Ph)(pyr)(OHMT) (R = 1-adamantyl (Ad) or 2,6-Me[subscript 2]C[subscript 6]H[subscript 3] (Ar'); OHMT = O-2,6-mesityl[subscript 2]C[subscript 6]H[subscript 3]; pyr = pyrrolide), and two tungsten oxo alkylidene initiators, W(O)(CHMe[subscript 2]Ph)(2,5-dimethylpyrrolide)(PMe2Ph)(OR) (OR = OHMT or (R)-OBr[subscript 2]Bitet where (R)-Br[subscript 2]BitetOH = (R)-3,3'-dibromo-2'-(tert-butyldimethylsilyloxy)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2-ol), produced essentially pure cis,syndiotactic-poly[(S)-PhEtNNBE]. Essentially pure cis,isotactic-poly[(S)-PhEtNNBE] was formed when (S)-PhEtNNBE was polymerized by Mo(NAr')(CHCMe2Ph)(OBiphen[subscript CF3])(thf) or W(NAr')(CHCMe[subscript 2]Ph)((S)-OBiphenMe) (OBiphenCF3 = 3,3'-di-tert-butyl-5,5'-bistrifluoromethyl-6,6'-dimethyl-1,1'-biphenyl-2,2'-diolate; (S)-OBiphen[subscript Me] = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate). The best initiator for ROMP of rac-PhEtNNBE was Mo(NAd)(CHMe[subscript 2]Ph)(pyr)(OHMT) at 0 °C, which led to a polymer that is biased (∼80%) toward a cis,syndiotactic structure and that contains alternating enantiomers in the chain (cis,syndio,alt-poly[(rac)-PhEtNNBE]).
United States. Department of Energy (grant DE-FG0286ER13564)
Singapore. Agency for Science, Technology and Research (A*STAR International Fellowship)
Alexander von Humboldt-Stiftung (Feodor Lynen Research Fellowship)