Highly 3,4-selective living polymerization of isoprene with rare earth metal fluorenyl N-heterocyclic carbene precursors
作者：Wang, BL ,Cui, DM ; Lv, K
關鍵字：yttrium alkyl complexes; stereospecific polymerization; 1,3-diene polymerization; metathesis polymerization; styrene polymerization; diene polymerization; catalytic-activity; ancillary ligand; butadiene; copolymerization
論文來源：期刊
具體來源：http://pubs.acs.org/doi/abs/10.1021/ma702505n
發表時間：2008年
Fluorenyl modified N-heterocyclic carbene ligated rare earth metal bis(alkyl) complexes, (Flu-NHC)Ln(CH2SiMe3)2 (Flu-NHC = (C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6); Ln = Sc (1a); Ln = Y (1b); Ln = Ho (1c); Ln = Lu (1d)), were synthesized and fully characterized by NMR and X-ray diffraction analyses. Complexes 1b?d with the activation of AliBu3 and [Ph3C][B(C6F5)4] exhibited high activity, medium syndio- but remarkably high 3,4-regio-selectivity, and the unprecedented livingness for the polymerization of isoprene. Such distinguished catalytic performances could be maintained under various monomer-to-initiator ratios (500?5000) and broad polymerization temperatures (25?80 °C). The resultant polymers are crystalline, having syndiotactically enriched (racemic enchainment triad rr = 50%, pentad rrrr = 30%) 3,4-regulated (99%) microstructure and high glass-transition temperatures (40?49 °C). In contrast, complex 1a was almost inert, while complexes bearing indenyl modified N-heterocyclic carbene moiety, (Ind-NHC)Ln(CH2SiMe3)2 (Ind-NHC = C9H6CH2CH2(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (2a); Ln = Y (2b); Ln = Ho (2c); Ln = Lu (2d)), also showed low activity or selectivity. These differences in catalytic performance could be attributed mainly to the electronics and spacial sterics of the metal center of these precursors.
