Highly <i>trans</i> -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-^<i>i</i>Pr₂C₆H₃)NC(C₆H₅)N(C₆H₄-2-NMe₂)]Ln[N(SiHMe₂)₂]₂(THF)_n (Ln = Sc, <i>n</i> = 0 (<b>1</b>); Ln = Y, <i>n</i> = 0 (<b>2</b>); Ln = La, <i>n</i> = 1 (<b>3</b>); Ln = Nd, <i>n</i> = 0 (<b>4</b>); Ln = Sm, <i>n</i> = 0 (<b>5</b>); Ln = Lu, n = 0 (<b>6</b>)), were synthesized via amine-elimination reactions between the amidine (2,6-^<i>i</i>Pr₂C₆H₃)NC(C₆H₅)NH(C₆H₄-2-NMe₂) and one equivalent of Ln[N(SiHMe₂)₂]₃(THF)_<i>n</i>. These rare-earth metal complexes were evaluated as precatalysts for both β-myrcene and isoprene polymerization. The ternary catalyst system comprising <b>5</b>/[Ph₃C][B(C₆F₅)₄]/AlMe₃ achieved unprecedented high <i>trans</i>-1,4-selectivity in the polymerization of β-myrcene (∼100% selectivity). This catalyst system also exhibited controlled polymerization characteristics for <i>trans</i>-1,4-selective polymerization of isoprene (>99% selectivity). Diblock and statistical copolymers incorporating <i>trans</i>-1,4-polyisoprene segments and <i>tran</i>s-1,4-polymyrcene segments were successfully synthesized. These results provide valuable insights for rational catalyst design to construct biobased polymers.