Dialkyllanthanide complexes containing new tridentate monoanionic ligands with nitrogen donors

Three new tridentate NNN ligand precursors, CH(3)C(2,6-((i)Pr)(2)C(6)H(3)NH)CHC(CH(3))(NCH(2)CH(2)-D) (D = NMe(2), NEt(2), N((CH(2)CH(2))(2)CH(2))), were synthesized. Subsequent metalations with in situ generated Ln(CH(2)SiMe(3))(3)(THF)(n) (Ln = Nd, Sm, Y, Lu) provided six solvent-free dialkyllanthanide complexes. Five of the lanthanide complexes were characterized by single-crystal X-ray diffraction, which showed that the pendant arm D bonds to the lanthanide ion in the solid state. The NMR spectra of these complexes in C(6)D(6) showed that such coordination is retained in solution. These dialkyllanthanide complexes show high activities for the ring-opening polymerization of epsilon-caprolactone, in which narrow-polydispersity polymers were produced. The size of the pendant arm has a significant effect on the molecular weight of the polymer obtained. In comparison to the Y complex with a -NMe(2) group, the Y complexes with -NEt(2) and -N((CH(2)CH(2))(2)CH(2)) groups yield much higher molecular weight polymer (60 000 vs 20 000).