Synthesis Of Rare Earth Metal Bis(Alkyl) Complexes Bearing Pyrrolidinyl-functionalized Mono(Cyclopentadienyl)Ligand And Their Performace In Isoprene Polymerization

A series of neutral rare earth metal bis(alkyl) complexes supported by the pyrrolidinyl-functionalized cyclopentadienyl, indenyl, fluorenyl ligands were synthesized and well-characterized. The neutral rare earth metal bis(alkyl) complexes could serve as cationic catalyst precursors for the region-selective polymerization for of isoprene.1. Alkyl elimination of rare earth metal tris(alkyl) complexes Ln(CH2SiMe3)(THF)2with1equivalent of [C5Me4H-SiMe2-NC4H8] in THF at room temperature, afforded a series of neutral rare earth bis(alkyl) complexes (C5Me4-SiMe2-NC4H8)Ln(CH2SiMe3)2(THF)n (Ln=Y (1), n=2; Lu (2), n-2). Complex1-2was characterized by elemental analysis, IR spectroscopy, and NMR spectroscopy.2. Alkyl elimination of rare earth metal tris(alkyl) complexes Lu(CH2SiMe3)(THF)2with1equivalent of [C9H7-SiMe2-NC4H8] in THF at room temperature, afforded a neutral rare earth bis(alkyl) complexes (C9H6-SiMe2-NC4H8)Lu(CH2SiMe3)2(THF)2(3). Complex3was characterized by elemental analysis, IR spectroscopy, and NMR spectroscopy.3. One-pot reaction of LnCl3with1equivalent of [C13H8-SiMe2-NC4H8]Li, followed by the introduction of two equivalents of LiCH2SiMe3in THF at room temperature, afforded the afforded a series of neutral rare earth bis(alkyl) complexes (C13H8-SiMe2-NC4H8)Ln(CH2SiMe3)2(THF)(Ln=Y (4), Lu (5)). The complex4-5was well-characterized by elemental analysis, FI-IR spectroscopy, NMR spectroscopy and X-ray crystallography. The metal center is coordinated by one pyrrolidinyl-Flu ligand in η1/k1constrained geometry configuration mode, and the metal center is four-coordinated to form a distorted tetrahedron geometry.4. Upon activated with1equivalent of borate ([Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4]) in toluene at room temperature,4-5became active for isoprene polymerization, while1-3showed no activity toward isoprene polymerization under the same polymerization conditions. In the presence of excess of Al’Bu3, the polymerization activity of3-5dramatically increased, and1-2were also active for isoprene polymerization in toluene at room temperature. All these polymerization showed regio-selectivity, and the resulting polymers were characterized by GPC and1H NMR.