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Novel Dendritic PNP Chromium Complexes: Synthesis, Characterization, and Performance on Ethylene Oligomerization
Author(s) -
Wang Jun,
Gao Rui,
Zhang Na,
Tan Xiangkun,
Wang Libo,
Ma Lili,
Shi Weiguang
Publication year - 2017
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.201700162
Subject(s) - methylaluminoxane , chemistry , chromium , selectivity , ethylene , oligomer , catalysis , ethylenediamine , tetrahydrofuran , polymer chemistry , solvent , medicinal chemistry , inorganic chemistry , organic chemistry , polymerization , metallocene , polymer
Three dendritic PNP ligands with ethylenediamine, 1,4‐butanediamine, 1,6‐diaminohexane as bridged groups are synthesized in good yields, respectively. Three dendritic PNP chromium complexes ( C1 – C3 ) are prepared with the ligands and chromium( III ) chloride tetrahydrofuran complex (CrCl 3 ( THF ) 3 ) as materials. The dendritic PNP ligands and the synthetic chromium complexes are fully characterized by spectroscopic and analytical methods. All chromium complexes activated with methylaluminoxane ( MAO ) exhibited moderate activities on ethylene oligomerization (7.90 × 10 4 – 2.15 × 10 5 g (mol Cr h) −1 ] and had better selectivity for C 6 and C 8 oligomer, reaching up to 81%. The chromium complex ( C1 ) activated with diethylaluminium chloride (Et 2 AlCl) has higher catalytic activity than the chromium complex C1 activated with MAO , although the chromium complex ( C1 ) activated with Et 2 AlCl had lower selectivity for C 6 and C 8 oligomer. The effects of solvent and reaction parameters on ethylene oligomerization are also studied using the chromium complex C1 as pre ‐ catalyst and MAO as co ‐ catalyst. Under optimized conditions ([complex] = 2 μmol, Al/Cr = 500, 25 °C, 0.9 MP a ethylene, 30 min), the catalytic activity of complex C1 in toluene is 2.15 × 10 5 g (mol Cr h) −1 and the selectivity for C 6 and C 8 oligomer is 36.76%. In addition, the structure of complexes significantly affects both the catalytic activity and the selectivity on ethylene oligomerization.