Rare-Earth-Metal Complexes Bearing Phosphazene Ancillary Ligands: Structures and Catalysis toward Highly Trans-1,4-Selective (Co)Polymerizations of Conjugated Dienes
作者：Weifeng Rong, Dongtao Liu, Huiping Zuo, Yupeng Pan, Zhongbao Jian, Shihui Li and Dongmei Cui
关键字：Staudinger reaction;zwitterionic; polyisoprene; trans-1,4-selectivity; dibutylmagnesium
论文来源：期刊
具体来源：http://pubs.acs.org/doi/pdf/10.1021/om300967h
发表时间：2012年
The
bis-arylated phosphazene compounds [HN(PPh2NAr)2] (Ar =
phenyl (HL1), 2,6-dimethylphenyl (HL2),
2,6-diisopropylphenyl (HL3)) and the imidodiphosphinate compound
HN(PPh2O)2 (HL4) have been prepared via
the Staudinger reaction. Treatment of the neutral compounds HL1, HL2,
and HL3 with Ln(CH2SiMe3)3(THF)2 (Ln
= Sc, Y, Lu) generated the solvent-free bis(alkyl) complexes L1Ln(CH2SiMe3)2 (Ln
= Sc (1a), Y (1b), Lu (1c)), L2Sc(CH2SiMe3)2 (2a),
L3Y(CH2SiMe3)2 (3b),
and L3Lu(CH2SiMe3)2 (3c),
respectively. The reaction between HL4 and Y(CH2SiMe3)3(THF)2 gave
the rare zwitterionic complex 4b. Lithiation of the ligand HL1 by nBuLi
followed by a metathesis reaction with Nd(BH4)3(THF)3 afforded
the corresponding complex L1Nd(BH4)2(THF)2 (5).
Complexes 1 upon incorporation of [Ph3C][B(C6F5)4]
and AliBu3 led to ternary systems that initiated
isoprene polymerization with high activities, among which complex 1a was
the first example of a scandium catalytic precursor providing
trans-1,4-selectivity (90.0%), while the lutetium analogue 1c had
medium trans-1,4-selectivity (54.3%) and the yttrium complex 1b exhibited
high cis-1,4-selectivity (76.3%). The ternary system based on the
zwitterion 4b displayed the highest activity for the isoprene
polymerization among these complexes and gave cis-1,4-regularity-enriched
polyisoprene (70.6%). Highly stereospecific homopolymerizations of isoprene
(trans-1,4-content: 97.0%) and butadiene (trans-1,4-content: 94.0%) were achieved
by using the borohydrido complex 5 upon the activation of
dibutylmagnesium. The copolymerization of isoprene and butadiene with1a/[Ph3C][B(C6F5)4/AliBu3]
gave randomly arranged trans-1,4-regulated polybutadiene and polyisoprene
sequences. The kinetics study displayed competitive polymerization rates
of rBD = 2.89 and rIP =
0.41. The thermal behaviors of the (co)polymers were investigated.
