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

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)(CHCMe 2 Ph)(Me 2 Pyr)(OAr) (X = arylimido, alkylimido, or oxo; Me 2 Pyr =2,5-dimethylpyrrolide; OAr = an aryloxide) were found to yield >98% cis, >98% syndiotactic poly(DCPD); they are W(N- t -Bu)(CHCMe 3 )(pyr)(OHMT) ( 2, OHMT = O-2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3, pyr = pyrrolide), W(N-2,6- i -Pr 2 C 6 H 3 )(CHCMe 2 Ph)(pyr)(OHMT) ( 3 ), W(O)(CHCMe 2 Ph)(Me 2 Pyr)(OHMT)(PPh 2 Me) ( 7, Me 2 Pyr =2,5-dimethylpyrrolide), W(O)(CHCMe 2 Ph)(Me 2 Pyr)(ODFT)(PPh 2 Me) ( 9, ODFT = O-2,6-(C 6 F 5 ) 2 C 6 H 3 ), and W(O)(CHCMe 2 Ph)(Me 2 Pyr)(OTPP)(PMePh 2 ) ( 10, OTPP = O-2,3,5,6-Ph 4 C 6 H). Two biphenolate alkylidene complexes, Mo(N-2,6-Me 2 C 6 H 3 )(CHCMe 2 Ph)( rac -biphen) ( 17 ) and W(N-2,6-Me 2 C 6 H 3 )(CHCMe 2 Ph)( rac -biphen) ( 22, biphen =3,3′-( t- Bu) 2 -5,5′-6,6′-(CH 3 ) 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 13 C 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 ( w c = 0.83 for syndiotactic and w c = 0.74 for isotactic ).