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Stereospecific Ring-Opening Metathesis Polymerization (ROMP) of endo-Dicyclopentadiene by Molybdenum and Tungsten Catalysts

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journal contribution
posted on 28.04.2015, 00:00 by Benjamin Autenrieth, Hyangsoo Jeong, William P. Forrest, Jonathan C. Axtell, Antje Ota, Thomas Lehr, Michael R. Buchmeiser, Richard R. Schrock
We report an examination of the ring-opening metathesis polymerization (ROMP) of endo-dicyclopentadiene (DCPD) by 10 well-defined molybdenum-based and 16 tungsten-based alkylidene initiators. Five tungsten-based MAP (monoaryloxide pyrrolide) initiators with the general formula W­(X)­(CHCMe2Ph)­(Me2Pyr)­(OAr) (X = arylimido, alkylimido, or oxo; Me2Pyr =2,5-dimethylpyrrolide; OAr = an aryloxide) were found to yield >98% cis, >98% syndiotactic poly­(DCPD); they are W­(N-t-Bu)­(CHCMe3)­(pyr)­(OHMT) (2, OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3, pyr = pyrrolide), W­(N-2,6-i-Pr2C6H3)­(CHCMe2Ph)­(pyr)­(OHMT) (3), W­(O)­(CHCMe2Ph)­(Me2Pyr)­(OHMT)­(PPh2Me) (7, Me2Pyr =2,5-dimethylpyrrolide), W­(O)­(CHCMe2Ph)­(Me2Pyr)­(ODFT)­(PPh2Me) (9, ODFT = O-2,6-(C6F5)2C6H3), and W­(O)­(CHCMe2Ph)­(Me2Pyr)­(OTPP)­(PMePh2) (10, OTPP = O-2,3,5,6-Ph4C6H). Two biphenolate alkylidene complexes, Mo­(N-2,6-Me2C6H3)­(CHCMe2Ph)­(rac-biphen) (17) and W­(N-2,6-Me2C6H3)­(CHCMe2Ph)­(rac-biphen) (22, biphen =3,3′-(t-Bu)2-5,5′-6,6′-(CH3)4-1,1′-biphenyl-2,2′-diolate), were found to yield >98% cis, >98% isotactic poly­(DCPD). Cis, syndiotactic or cis, isotactic poly­(DCPD)­s (made with 50–1000 equiv of DCPD) are accessible within seconds to minutes in dichloromethane at room temperature. No isomerization or cross-linking reactions are observed, and addition of a chain transfer reagent (1-hexene) or the use of THF as a solvent does not decrease the stereospecificity of the polymerizations. Cis, syndiotactic and cis, isotactic poly­(DCPD)­s can be distinguished readily from each other by 13C NMR spectroscopy. Hydrogenation of each stereoregular poly­(DCPD) produces H-poly­(DCPD)­s that have melting points near 270 °C (syndiotactic) or 290 °C (isotactic) and high crystallinities (wc = 0.83 for syndiotactic and wc = 0.74 for isotactic).