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ARTICLE
1-hexene and 1-octene.17 We modified the diarylphosphine
moiety by introducing methyl or trifluoromethyl groups to
study how the substituted diarylphosphine affects catalytic
behavior during selective ethylene oligomerization. Herein, we
report a catalytic system that has a high activity and selectivity
for 1-hexene (up to 99% purity) with only minor by-products.
The influence of ligands and activators was systematically
studied under various reaction conditions.
under vacuum to give a crude product, which was purified
as described below.
1: Diphenyl(1H-Pyrrol-1-yl)Phosphine
Following the general synthesis, the crude product as a yel-
low oil was purified by column chromatography, with ethyl
acetate:hexane (1:9) used as the eluent. The solvent was
removed under vacuum to give the product as a white solid
(0.266 g, 0.99 mmol, 21.7%). 1H NMR (300 MHz, CDCl3, d):
6.32 (dd, J 5 3.8, 1.9 Hz, 2H), 6.82 (td, J 5 3.8, 1.9 Hz, 2H),
7.23–7.31 (m, 4H), 7.38 (d, J 5 3.4 Hz, 6H); 13C NMR (150
MHz, CDCl3, d): 111.62, 125.64, 128.76, 129.86, 132.10,
137.14; 31P NMR (242 MHz, CDCl3, d): 47.79; purity 5 98%
on the basis of 31P NMR analysis. HRMS (ESI, m/z): [M 1 H]1
calcd for C16H15NP, 252.0942; found, 252.0930.
EXPERIMENTAL
General Considerations
All oligomerizations were carried out under an N2 atmo-
sphere using a glove box or by using standard Schlenk tech-
niques, except column chromatography at ambient
conditions. All solvents were dried and distilled prior to use
according to standard methods. Methylaluminoxane (MAO;
10 wt % in toluene) was purchased from Albemarle Corp.
(Baton Rouge, LA, USA). TIBA, pyrrole, 2,4-dimethylpyrrole,
2,5-dimethylpyrrole (DMP), triethylamine, tetrahydrofuran
(THF), and nonane were purchased from Sigma-Aldrich (St.
Louis, MO, USA). Chlorodiphenylphosphine, chlorodi(p-tolyl)-
2: 1-(Di-p-Tolylphosphino)Pyrrole
Following the general synthesis, pyrrole (0.31 mL, 4.4
mmol), Et3N (0.62 mL, 4.4 mmol), and chlorodi(p-tolyl)phos-
phine (0.22 g, 1 mmol) were used. The crude product as a
white oil was purified by column chromatography on silica
gel, with ethyl acetate:hexane (1:9) as the eluent. The solvent
was removed under vacuum to give the product as a white
solid (0.09 g, 0.32 mmol, 33.7%). Single crystals were
obtained by slow diffusion of hexane into a concentrated
solution of the product in THF at room temperature. 1H
NMR (300 MHz, CDCl3, d): 2.36 (s, 6H), 6.29 (dd, J 5 3.6, 1.7
Hz, 2H), 6.81 (dt, J 5 3.8, 2.0 Hz, 2H), 7.14–7.20 (m, 8H); 13C
NMR (150 MHz, CDCl3, d) 21.50, 111.36, 125.50, 129.52,
132.15, 133.93, 139.98; 31P NMR (242 MHz, CDCl3, d):
47.78; purity 5 94% on the basis of 31P NMR analysis. HRMS
(ESI, m/z): [M 1 H]1 calcd for C18H19NP, 280.12551; found,
280.1263.
phosphine,
bis(3,5-di(trifluoromethyl)phenyl)chlorophos-
phine, and methylcyclohexane were purchased from Alfa-
Aesar (Haverhill, MA, USA). Cr(acac)3 and CrCl3(THF)3 were
used as purchased from Strem Chemicals (Newburyport, MA,
USA). Hexane, ethyl acetate, methanol, and hydrogen perox-
ide (34.5 wt % aqueous solution) were purchased from Sam-
chun Pure Chemical Co. (Korea).
1
The H NMR spectra of the products were recorded at 25 8C
on a Fourier 300 NMR spectrometer (Bruker, Billerica, MA,
USA) with tetramethylsilane (TMS) as an internal reference.
The 13C NMR spectra and 31P NMR spectra of the products
were recorded at 25 8C with Avance III 600 equipment
(Bruker) and using TMS as an internal reference. The
oligomers (liquid products) were analyzed by gas chroma-
tography with a flame ionization detector (GC-FID) using
Agilent 6890 (Agilent Technologies, Santa Clara, CA, USA)
equipment with an Agilent J&W GC capillary column, with
nonane used as the internal standard. X-ray crystal data
were obtained using a SMART APEX II (Bruker) single-
crystal X-ray diffractometer equipped with a Bruker SMART
charge-coupled device (CCD) area detector. Mass spectra
3: Bis(3,5-Bis(Trifluoromethyl)Phenyl)(1H-Pyrrol-1-
yl)Phosphine
Following the general procedure, pyrrole (4.4 mmol), Et3N
(0.63 mL, 4.5 mmol), and bis(3,5-(trifluoromethyl)phenyl)-
chlorophosphine (0.49 g, 1 mmol) were used. The crude
product (3) was recrystallized in hexane to yield an ivory
solid, which was isolated and characterized immediately. 1H
NMR (300 MHz, CDCl3, d): d 5 6.45 (dd, J 5 1.8 Hz, 2H), 6.81
(dd, J 5 3.6, 1.8 Hz, 2H), 7.66 (d, J 5 6.6 Hz, 4H), 7.97 (s,
1
2H); 13C NMR (75 MHz, CDCl3, d): 114.12, 123.0 (q, JC–F
5 273 Hz), 124.58, 125.33, 131.82, 132.81, 139.36; 31P NMR
(242 MHz, CDCl3, d): 42.55; purity 5 93% on the basis of 31P
NMR analysis.
were recorded with
spectrometer.
a
Bruker micrOTOF-QII (ESI)
General Procedure for Ligand Synthesis
Pyrrole (1.4 mL, 20 mmol), Et3N (2.8 mL, 20 mmol), and
THF (6 mL) were charged to a Schlenk flask under an inert
3o: Bis(3,5-Bis(Trifluoromethyl)Phenyl)(1H-Pyrrol-1-
yl)Phosphine Oxide
The product 3 was purified by column chromatography on
silica gel, with ethyl acetate:hexane (1:9) as the eluent. On
recrystallization from hexane, a white solid was obtained,
which was isolated and dried under vacuum (0.17g, 0.32
mmol, 31.5%). Single crystals were obtained by slow diffu-
sion of hexane into a concentrated solution of the product in
THF at room temperature. 1H NMR (300 MHz, CDCl3, d):
6.53 (dd, J 5 4.3, 2.6 Hz, 2H), 6.84 (dd, J 5 4.3, 3.0 Hz, 2H),
8.11 (d, J 5 12.8 Hz, 4H), 8.18 (s, 2H); 13C NMR (150 MHz,
atmosphere.
Subsequently,
chlorodiphenylphosphine
(0.85 mL, 4.6 mmol) was added dropwise at 0 8C. The reac-
tion mixture was stirred for 10 min at 0 8C, and for 10 min
at room temperature, and then heated to reflux for a further
15 h. The colorless precipitate that formed was removed by
filtration and washed with THF. The combined filtrates were
evaporated to dryness under vacuum. The resulting oil was
re-dissolved in hexane and filtered. The solvent was removed
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