Sc and Y bis(alkyl) complexes supported by bidentate and tridentate amidinate ligands. Synthesis, structure and catalytic activity in polymerization of isoprene and 1-heptene

Abstract

A series of bis(alkyl) complexes {(tBu)C[N(2,6-Me₂C₆H₃)]₂}Ln(CH₂SiMe₃)₂(THF)_n (Ln = Y, n = 1 (1); Ln = Sc, n = 1 (2)), {2-[Ph₂P(O)]C₆H₄NC(tBu)N(2,6-Me₂C₆H₃)}Sc(CH₂SiMe₃)₂ (3), {2-[Ph₂P(NPh)]C₆H₄NC(tBu)N(2,6-Me₂C₆H₃)}Sc(CH₂SiMe₃)₂ (4) coordinated by bidentate (N,N) and tridentate (N,N,O; N,N,N) amidinate ligands are synthesized using an alkane elimination approach. Yttrium complex 1 demonstrated a half-life of ∼2.5 days at room temperature in benzene-D6 (C₆D₆) solution, whereas scandium complexes proved to be much more stable (25 d (2), 30 d (3) and 42 d (4)). Complexes 1–4 as a part of ternary catalytic systems 1–4/TB, HNB/AlR₃ (AlR₃ = AliBu₃, AliBu₂H; TB = [Ph₃C][B(C₆F₅)₄], HNB = [PhNHMe₂][B(C₆F₅)₄]) demonstrated high catalytic activity in isoprene polymerization and enable 80%–100% conversion of 1000 equivalents of monomer into polymer at 25 °C within 3–180 min. The isolated polyisoprenes feature predominantly cis-1,4-regularity (69.2%–87.3%) and polydispersities M_w/M_n = 2.26–8.92. Moreover, the binary (2/TB) and ternary (1–4/TB/10 AliBu₃) systems initiate 1-heptene polymerization providing 40%–100% conversion of 500 equivalents of monomer in 24 h at 25 °C giving polymer samples with M_n = 1.55–190.2 × 10³ and M_w/M_n = 1.55–3.87.