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- i Pr 2 C 6 H 3 )NC(Ph)N(C 6 H 4 -2-OMe] - ( HL ) were synthesized and well-characterized. Treatment of rare-earth metal tris(alkyl)/tris(benzyl)/tris(amide) complexes Y(CH 2 C 6 H 4 NMe 2 - o ) 3 or Y(CH 2 SiMe 3 ) 3 (THF) 2 or Ln[N(SiHMe 2 ) 2 ] 3 (THF) x (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- i Pr 2 C 6 H 4 )NC(Ph)N(C 6 H 4 -2-OMe)]Y(CH 2 C 6 H 4 NMe 2 - o ) 2 ( 1 ), [(2,6- i Pr 2 C 6 H 4 )NC(Ph)N(C 6 H 4 -2-OMe)]Y(CH 2 SiMe 3 ) 2 (THF) ( 2 ), and [(2,6- i Pr 2 C 6 H 4 )NC(Ph)N(C 6 H 4 -2-OMe)]Ln[N(SiHMe 2 ) 2 ] 2 (THF) n (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 AlMe 3 and on treatment with 1 equiv of [Ph 3 C][B(C 6 F 5 ) 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.