Pyrrolide-Supported Lanthanide Alkyl Complexes. Influence of Ligands on Molecular Structure and Catalytic Activity toward Isoprene Polymerization
writer：Yi Yang, Bo Liu, Kui Lv, Wei Gao, Dongmei Cui, Xuesi Chen and Xiabin Jing
keywords：ligands, lanthanide, C2-symmetric, binuclear, configuration, initiator
source：期刊
specific source：http://pubs.acs.org/doi/pdf/10.1021/om7003095
Issue time：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.
