Pyrrolide-Supported Lanthanide Alkyl Complexes. Influence of Ligands on Molecular Structure and Catalytic Activity toward Isoprene Polymerization

作者：Yi Yang, Bo Liu, Kui Lv, Wei Gao, Dongmei Cui, Xuesi Chen and Xiabin Jing

关键字：ligands, lanthanide, C2-symmetric, binuclear, configuration, initiator

论文来源：期刊

具体来源：http://pubs.acs.org/doi/pdf/10.1021/om7003095

发表时间：2007年

The N,N-bidentate ligands 2-{(N-2,6-R)iminomethyl)}pyrrole (HL1, R = dimethylphenyl; HL2, R = diisopropylphenyl) have been prepared. HL1 reacted readily with 1 equiv of lanthanide tris(alkyl)s, Ln(CH2SiMe3)3(THF)2, affording lanthanide bis(alkyl) complexes L1Ln(CH2SiMe3)2(THF)n (1a, Ln = Lu, n = 2; 1b, Ln = Sc, n = 1) via alkane elimination. Reaction of the bulky ligand HL2 with 1 equiv of Ln(CH2SiMe3)3(THF)2 gave the bis(pyrrolylaldiminato) lanthanide mono(alkyl) complexes L22Ln(CH2SiMe3)(THF) (2a, Ln = Lu; 2b, Ln = Sc), selectively. The N,N-bidentate ligand HL3, 2-dimethylaminomethylpyrrole, reacted with Ln(CH2SiMe3)3(THF)2, generating bimetallic bis(alkyl) complexes of central symmetry (3a, Ln = Y; 3b, Ln = Lu; 3c, Ln = Sc). Treatment of the N,N,N,N-tetradentate ligand H2L4, 2,2‘-bis(2,2-dimethylpropyldiimino)methylpyrrole, with equimolar Lu(CH2SiMe3)3(THF)2 afforded a C2-symmetric binuclear complex (4). Complexes 3a, 3b, 3c, and 4 represent rare examples of THF-free binuclear lanthanide bis(alkyl) complexes supported by non-cyclopentadienyl ligands. All complexes have been tested as initiators for the polymerization of isoprene in the presence of AlEt3 and [Ph3C][B(C6F5)4]. Complexes 1a, 1b, and 3a show activity, and 1b is the most active initiator, whereas 2a, 2b, 3b, 3c, and 4 are inert. The microstructure of the resultant polyisoprene has a cis-1,4 or trans-1,4 configuration depending on the initiator applied.