Rare-Earth Metal Complexes Supported by A Tridentate Amidinate Ligand: Synthesis, Characterization, and Catalytic...

To systematically investigate the dependence of the initiating group and metal size on polymerization performance, a family of rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes supported by a monoanionic tridentate amidinate ligand [(2,6-Pr₂C₆H₃)NC(Ph)N(C₆H₄-2-OMe]^- (HL) were synthesized and well-characterized. Treatment of rare-earth metal tris(alkyl)/tris(benzyl)/tris(amide) complexes Y(CH₂C₆H₄NMe₂-o)₃ or Y(CH₂SiMe₃)₃(THF)₂ or Ln[N(SiHMe₂)₂]₃(THF) (Ln = Sc, x = 1; Ln = Y, La, Sm, Lu, x = 2) with 1 equiv of HL gave the corresponding mono(amidinate) rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes [(2,6-Pr₂C₆H₄)NC(Ph)N(C₆H₄-2-OMe)]Y(CH₂C₆H₄NMe₂-o)₂ (1), [(2,6-Pr₂C₆H₄)NC(Ph)N(C₆H₄-2-OMe)]Y(CH₂SiMe₃)₂(THF) (2), and [(2,6-Pr₂C₆H₄)NC(Ph)N(C₆H₄-2-OMe)]Ln[N(SiHMe₂)₂]₂(THF) (Ln = Y, n = 1 (3); Ln = La, n = 1 (4); Ln = Sc, n = 0 (5); Ln = Lu, n = 0 (6); Ln = Sm, n = 0 (7)) in good isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction. In the presence of excess AlMe₃ and on treatment with 1 equiv of [Ph₃C][B(C₆F₅)₄], these complexes could serve as precatalysts for cationic polymerization of isoprene, in which the dependence of the polymerization activity and regioselectivity on the initiating group and metal size was observed.