CCC-Pincer Bis(carbene) Lanthanide Dibromides. Catalysis on Highly cis-1,4-Selective Polymerization of Isoprene and Active Species
writer：Kui Lvand Dongmei Cui
keywords：CCC-pincer; cis-1,4 selectivity; isoprene; active specie
source：期刊
specific source：具體來源：http://pubs.acs.org/doi/pdf/10.1021/om1002039
Issue time：2010年
A series of CCC-pincer 2,6-xylenyl
bis(carbene)-ligated rare-earth metal dibromides (PBNHC)LnBr2(THF) ((PBNHC) =
2,6-(2,4,6-Me3C6H2NCHCHNCCH2)2C6H3; Ln = Sc (1), Y (2), La (3), Nd (4), Sm (5),
Gd (6), Dy (7), Ho (8), Tm (9), Lu (10)) have been synthesized. Upon activation
with AlR3 (R = Me, Et, iBu) and [Ph3C]+[B(C6F5)4]?, complexes 2, 4, 6, 7, and 8
exhibited high activity and cis-1,4 selectivity (99.6%, 25 °C) toward the
polymerization of isoprene, although complexes 1, 3, 5, 9, and 10 were inert.
The selectivity was not affected by the nature of the central metal and AlR3
and was maintained at elevated temperatures up to 80 °C (97.4%). The yttrium
hydrido aluminate cation [(PBNHC)Y(μ-H)2AliBu2]+ was identified as the active
species according to NMR spectroscopic analysis.
