Article
Sun et al.
carrier gas nitrogen. The initial oven temperature was 60 °C held
for 3 min, and then raised with a gradient of 20 °C/min to 170 °C
and held for 5 min. The temperature of the FID and injection were
250 °C.
ionic liquid solutions. In general, chlorinated aromatics (5.0
mmol), nickel-complex catalyst (0.25 mmol) and zinc powder (50
mmol) are put together in molten [Bmim]Br (5.0 mL) with H2O
(1.0 mL), the whole mixture was held at 70 °C under ambient at-
mosphere for 7 hours. The final reaction mixture was quenched
with water (20 mL) and then extracted with n-heptane for three
times (3 ´ 10 mL). The obtained organic layer was further used
for the chemical analysis to determine the concentrations of vari-
ous products by GC analysis.
Preparation of Ni[phen]2(PF6)2. A solution of 1,10-phen-
anthroline (2 mmol) in ethanol (15 mL) was heated to 60 °C and
added drop-wise to a solution of Nickel chloride (1 mmol) in wa-
ter (10 mL) at 60 °C with continuous stirring for 7 hrs. After cool-
ing to room temperature, saturated aqueous KPF6 was added and
resulted in immediate precipitation of the complexes, strongly
colored hexafluorophosphate salts. The complexes were col-
lected by vacuum filtration and washed with water for several
times till the absence of Cl-, tested with AgNO3 (0.1 M). The solid
was then washed with ethanol for two times (2 ´ 5 mL) and air
dried. Then the solid complexes were purified by a recrystalliza-
tion procedure, where acetonitrile and dicholoromethane were
used as the solvent. Finally, large prismatic violet crystals with
formula of [Ni(phen)2](PF6)2 were obtained. The synthesized
product was further confirmed by NMR method.18 The yield can
reach 87% (664.03 mg).
Recycling reactions for the hydrodechlorination. The re-
cycling performance of the synthesized nickel-complex catalysts
was investigated by using 4-methylchlorobenzene as the sub-
strate. All the recycling experiments were implemented with the
details described in hydrodecholorination reaction procedure. Af-
ter the hydrodecholorination reaction, the catalyst and ionic liq-
uid were separated from the reaction product and Zn powder by
adding 20 mL n-heptane and followed by centrifugation.
RESULTS AND DISCUSSION
Firstly, we investigated the effect of the ligand in cat-
alyst and ionic liquids on the hydrodechlorination effi-
ciency. As shown in Table 1, the change of the ligand in
both catalyst and ionic liquids did introduce dramatic dif-
ference in the hydrodechlorination of chlorobenzene.
Recent studies indicated that the hydrodecholorina-
tion reactions are categorized as electrophilic reaction, it is
rational to expect that the electron-donating ability linked
with different molecule structures might have dramatic in-
fluence on the hydrodechlorination efficacy. From entries
1 to 3, it can be seen that the combination of nickel com-
plexe catalysts and ionic liquid was effective for the hy-
drodechlorination process. Between Ni[bpy]3(PF6)2 and
Ni[phen]2(PF6)2, the former molecule possess higher space
resistance and worse electron-donating capability. To be
linked with the catalysis performance, it is further illus-
trated that the electron-donating and space resistance need
to be considered together. Compaed with the highest hy-
drodechlorination efficiency ever reported,20 >95% con-
version rate,20 present design only gave moderate effi-
ciency. However, the combination between Ni-catlayst and
ionic liquid is still attractive, mainly due the low cost.
As one potential function for ionic liquid, acting as
the solvent in hydrochlorination reaction,22 the mass trans-
port rate should be the controlling factor for the reaction ki-
netics. Entries 3, 4, 5, 6 in Table 1 showed that the yields of
benzene decrease significantly with the increase in the
number of alkyl substituents, from butyl to decyl. The in-
Preparation of Ni[bpy]3(PF6)2. Ni(OAc)2×4H2O (2.48 g,
10 mmol) was dissolved in ethanol (300 mL) and refluxed at 60 oC
with stirring for 10 min. Solid 2,2¢-Dipyridyl (4.686 g, 30 mmol)
was then added and refluxed at 60 oC for 7 hrs. The solution was
cooled, with the product precipitated from solution as the hexa-
fluorophosphate salt by addition of NH4PF6 (325 mg, 2 mmol).
The pink product, [Ni(bhy)3](PF6)2, was collected by vacuum fil-
tration, washed with cold water and ether, and then air dried. Then
the solid complexes were purified by a recrystallization proce-
dure, where acetonitrile and ether were used as the solvent. Fi-
nally, large prismatic violet-pink crystals with formula of
[Ni(bhy)3](PF6)2 were obtained. The synthesized product was fur-
ther confirmed by NMR method.19 The yield can reach 90%
(664.03 mg). Fig. 1 shows the molecule structures of Ni[phen]2
(PF6)2 and Ni[bpy]3(PF6)2.
General procedures for nickel-catalyzed hydrodechlo-
rination reactions. Aseries of the nickel catalysts were tested for
the hydrodechlorination reaction of aryl chlorides in aqueous
Fig. 1. Nickel complexes.
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© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim J. Chin. Chem. Soc. 2013, 60, 1365-1370