Highly trans-1,4-Regular (Co)Polymerization of β-Myrcene and Isoprene by Amidinate Rare-Earth Metal Catalysts

Utilizing renewable resources to prepare elastomeric materials offers a viable solution to dwindling fossil reserves and heightened environmental concerns. As a result, the development of highly efficient catalysts for the highly stereoselective (co)polymerization of biobased monomers has garnered increasing attention. In this study, rare-earth metal bis(silylamide) complexes supported by a tridentate amidinate ancillary ligand, [(2,6-ⁱPr₂C₆H₃)NC(C₆H₅)N(C₆H₄-2-NMe₂)]Ln[N(SiHMe₂)₂]₂(THF)_n (Ln = Sc, n = 0 (1); Ln = Y, n = 0 (2); Ln = La, n = 1 (3); Ln = Nd, n = 0 (4); Ln = Sm, n = 0 (5); Ln = Lu, n = 0 (6)), were synthesized via amine-elimination reactions between the amidine (2,6-ⁱPr₂C₆H₃)NC(C₆H₅)NH(C₆H₄-2-NMe₂) and one equivalent of Ln[N(SiHMe₂)₂]₃(THF)_n. These rare-earth metal complexes were evaluated as precatalysts for both β-myrcene and isoprene polymerization. The ternary catalyst system comprising 5/[Ph₃C][B(C₆F₅)₄]/AlMe₃ achieved unprecedented high trans-1,4-selectivity in the polymerization of β-myrcene (∼100% selectivity). This catalyst system also exhibited controlled polymerization characteristics for trans-1,4-selective polymerization of isoprene (>99% selectivity). Diblock and statistical copolymers incorporating trans-1,4-polyisoprene segments and trans-1,4-polymyrcene segments were successfully synthesized. These results provide valuable insights for rational catalyst design to construct biobased polymers.