Pyrrolide-Supported Lanthanide Alkyl Complexes. Influence of Ligands on Molecular Structure and Catalytic Activity toward Isoprene Polymerization
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posted on 2020-04-02, 14:53 authored by Yi Yang, Bo Liu, Kui Lv, Wei Gao, Dongmei Cui, Xuesi Chen, Xiabin JingThe 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.
