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
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...
| Main Authors: | , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
American Chemical Society (ACS)
2017
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| Online Access: | http://hdl.handle.net/1721.1/108581 https://orcid.org/0000-0002-1788-4100 https://orcid.org/0000-0001-5827-3552 |
| Summary: | 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]). |
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