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

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-PrCH)NC(Ph)N(CH-2-OMe] () were synthesized and well-characterized. Treatment of rare-earth metal tris(alkyl)/tris(benzyl)/tris(amide) complexes Y(CHCHNMe-) or Y(CHSiMe)(THF) or LnN(SiHMe) (Ln = Sc, x = 1; Ln = Y, La, Sm, Lu, x = 2) with 1 equiv of gave the corresponding mono(amidinate) rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes [(2,6-PrCH)NC(Ph)N(CH-2-OMe)]Y(CHCHNMe-) (), [(2,6-PrCH)NC(Ph)N(CH-2-OMe)]Y(CHSiMe)(THF) (), and [(2,6-PrCH)NC(Ph)N(CH-2-OMe)]LnN(SiHMe) (Ln = Y, = 1 (); Ln = La, = 1 (); Ln = Sc, = 0 (); Ln = Lu, = 0 (); Ln = Sm, = 0 ()) in good isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction. In the presence of excess AlMe and on treatment with 1 equiv of [PhC][B(CF)], 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.