Rare-earth metal bis(alkyl)s that bear a 2-pyridinemethanamine ligand: Dual catalysis of the polymerizations of both isoprene and ethylene
作者:Jian, ZB;Cui, DM
关键字:yttrium alkyl complexes,olefin polymerization,ethene polymerization,organoyttrium cations, living polymerization
New pyridinemethanamido-ligated rare-earth metal bis(alkyl) complexes [C5H4N-CH(Me)-NC6H3(iPr)2]Ln(CH2SiMe3)2(THF) (Ln = Sc (1), Y (2), Lu (3)) have been prepared at 0 °C via a protonolysis reaction between rare-earth metal tris(alkyl)s and the corresponding 2-pyridinemethanamine ligand and fully characterized by NMR and X-ray diffraction analysis. Bis(alkyl) complexes 1–3 are analogous monomers of THF solvate, where the ligand bonds to the metal center in a κN:κN-bidentate mode. Complexes 1–3, in combination with [Ph3C][B(C6F5)4], showed a good activity towards isoprene polymerization to give polyisoprene with a main 3,4-selectivity (60%–66%); in particular the yttrium catalyst system, 2/[Ph3C][B(C6F5)4], displayed a living mode. By contrast, only the precatalyst 2 exhibited activity for isoprene polymerization in the presence of [PhNMe2H][B(C6F5)4]. The influence of alkylaluminium (AlR3, R = Me, Et, iBu) and the metal center on the polymerization of isoprene was also studied, and it was found that addition of AlMe3 to the catalyst systems could lead to a dramatic change in the microstructure of the polymer from 3,4-specific to 1,4-selective (89%–95%), but the ionic radius of the central metal had little influence on the selectivity. In addition, by using the 1(Sc)/[Ph3C][B(C6F5)4]/10 AliBu3, the polymerization of ethylene was also achieved with moderate activity (up to 3.2× 105 g (PE) molSc−1 h−1bar−1) and narrow polydispersity (Mw/Mn = 1.19–1.28); while the effect of temperature on the activity was discussed. Such dual catalysis for the polymerizations of both isoprene and ethylene is rare.