New rare earth metal bis(alkyl)s bearing an iminophosphonamido ligand. Synthesis and catalysis toward highly 3,4-selective polymerization of isoprene
作者：Li, SH,Miao, W,Tang, T,Dong, WM,Zhang, XQ,Cui, DM
關鍵字：lanthanide alkyl complexes; stereospecific polymerization; 1,3-diene polymerization; diene polymerization; methyl-methacrylate; butadiene; reactivity; copolymerization; ethylene; neodymium
論文來源：期刊
具體來源：http://pubs.acs.org/doi/abs/10.1021/om700945r
發表時間：2008年
New rare earth metal bis(alkyl) complexes [(NPNPh)Ln(CH2SiMe3)2(THF)] (NPNPh: N(Ph)PPh2═NC6H2Me3-2,4,6; Ln = Sc (3a), Ln = Y (3b), Ln = Lu (3c)) and [(NPNPy)Sc(CH2SiMe3)2(THF)] (NPNPy = N(Py)PPh2═NC6H2Me3-2,4,6) (3d)) have been prepared via protonolysis reaction between rare earth metal tris(alkyl)s and the corresponding iminophosphonamines. Complexes 3a?d are analogous monomers of THF solvate. Each metal ion coordinates to a η2-chelated NPN ligand and two cis-located alkyl groups, adopting tetrahedron geometry. The scandium complex [(NPNPh)Sc(CH2SiMe3)2(THF)] in combination with [PhNHMe2][B(C6F5)4] and AliBu3 forms the first non-Cp-ligated rare earth metal based catalyst system to provide extremely high activity and 3,4-selectivity for the polymerization of isoprene. The resultant high molecular weight polymer (Mn = 99 × 104) with narrow molecular weight distribution (PDI = 1.55) has a 3,4-regularity up to 94.7% (Tp = –40 °C, toluene, 2 h, 100% yield). The complexes 3b and 3c, with a larger ionic radius, are less regioselective, and 3d, with an electron-donating pyridyl moiety, is inert. The probable initiation species and mechanistic scenario are also presented.
