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