Regio- and Stereoselective Ring-Opening Metathesis Polymerization of Enantiomerically Pure Vince Lactam

The ring-opening metathesis polymerization (ROMP) of (+)-Vince lactam [(S)-azabicyclo[2.2.1]hept-5-en-3-one] (1) and its N-benzyl, N-trimethylsilyl (TMS), and N-tert-butoxycarbonyl (Boc) derivatives (2a c) is reported. Highly cis-syndiotactic (st) poly(Vince lactam) was readily accessible by using the cyclometalated ruthenium complex Ru[CH(2-OiPr-Ph)](Piv)(1-mesity1-3-C4H8-imidazol-2-ylidene) (Piv =2,2-dimethylpropanoate) (4); however, small amounts of trans double bonds (ca. 5%) formed. Highly cis-st (>98%) polymers were accessible by the action of the monoaryloxide pyrrolide (MAP) type complexes W(N-2,6-iPr(2)C(6)H(3))(CHCMe2Ph)(Pyr)(HMTO) (Pyr = pyrrolide, HMTO = 2,6-(2,4,6-Me3C6H2)(2)C6H3O) (7) and W(O)(CHCMe2Ph)(PMe2Ph)(Me(2)Pyr)(TPPO) (TPPO = 2,3,5,6-tetraphenylphenolate) (8). Complementary, cis-isotactic (>98% cis-it) polymers were prepared by the action of Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OBiphen) (OBiphen = 3,3'-di-tertbuty1-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate) (5) and its tungsten analogue W(N-2,6-Me2C6H3)(CHCMe2Ph)(OBiphen) (6). Notably, none of these Mo-and W-based initiators polymerize unprotected Vince lactam. Deprotection of poly(N-TMS Vince lactam) and poly(N-Boc Vince lactam) with neat trifluoroacetic acid allowed for the isolation of all-cis highly tactic poly(Vince lactam).