230
Y. Song et al. / Dyes and Pigments 137 (2017) 229e235
application prospects in electrochromic display.
1.6 Hz, 2H), 7.61(d, 8.7 Hz, 2H), 1.50(s, 9H). 13C NMR (100 MHz,
DMSO-d 152.63, 150.05, 146.47, 140.75, 130.22, 127.12, 120.45,
118.31, 79.34, 28.06. HRMS Found: [M] 270.1371; molecular for-
6
) d
þ
ꢂ
2
. Experimental
þ
ꢂ
mula C16
2982,1724,1598,1536,1492, 1405,1322, 1241, 1158, 1049, 1022, 810,
H N O requires [M] 270.1368. IR (KBr): n 3238, 3182,
18 2 2
2.1. Materials and apparatus
ꢀ
1
7
69 cm .
CB[6] and CB[7] were prepared and purified according to
method described in the literature [21,22]. Other chemicals were
commercially available and used without further purification. NMR
spectra were measured on a Brüker AM-400 spectrometer. The ITC
measurements were carried out on a GE MicroCal ITC200. The
UVeVis absorption spectra were obtained on a Varian Cary 100
spectrometer and a Varian Cary Eclipse (1-cm quartz cell was used).
The MS spectra were recorded on a 4800 Plus M-TOF/TOF analyzer
2.2.5. 4-(4-pyridinyl)-Benzenamine (7)
6 (1.67 g, 6.2 mmol) was dissolved in the mixture of methanol
(40 mL) and concentrated hydrochloric acid (8 ml). The solution
ꢁ
was stirred at 80 C for 4 h. All the solvent was then removed under
reduced pressure and the residue was washed with sodium car-
bonate aqueous solution (5%) and water respectively. 7 (1.03 g, 98%)
ꢁ
1
was obtained pure enough as a white solid. m.p. 232e234 C. H
NMR (400 MHz, DMSO-d
8.48(d, J ¼ 5.9 Hz, 2H), 7.55(m, 4H),
(
AB SCIEX, USA) and a LCT Premier XE mass spectrometer. All
6
) d
13
electrochemical measurements were performed by using a Versa-
Stat II electrochemical workstation (Princeton Applied Research,
USA).
6.66(d, J ¼ 8.5 Hz, 2H), 5.52(s, 2H). C NMR (100 MHz, DMSO-d
6
)
d
150.22, 149.87, 147.13, 127.42, 123.33, 119.38, 114.01. HRMS Found:
þ
ꢂ
þ
ꢂ
[M]
270.1371; molecular formula
11 10 2
C H N requires [M]
2
70.1368. IR (KBr):
ꢀ
1320, 1287, 1226, 1188, 999, 816 cm .
n
3432, 3311, 3175, 1642, 1585, 1529, 1489, 1412,
1
2
2
.2. Synthesis
0
.2.1. 1,1 -Bis(2,4-dinitrophenyl)-4,4'-bipyridinium dichloride (2)
2.2.6. Bis[4-(4-pyridinyl)phenyl] viologen (BPPV)
0
4
,4 -Bipyridine (3.2 g, 20 mmol) and 2,4-dinitrochlorobenzene
2 (0.704 g, 1.25 mmol), 7 (0.53 g, 3.1 mmol) and ethanol (35 mL)
were added into a 100 mL round bottom flask. The mixture was
(
14.1 g, 70 mmol) were dissolved in acetonitrile (10 mL) and the
ꢁ
resulting solution was refluxed for 48 h. During the reaction, a pale
yellow precipitate was formed. The reaction mixture was then
cooled to room temperature and the precipitate was collected by
filtration and washed with a small amount of ethanol/water. The
product was dried in vacuo to yield 2 as a yellow powder (10.0 g,
8
stirred for 80 h at 80 C, then cooled to room temperature and
concentrated under reduced pressure. Ethyl acetate (100 ml) was
added and the precipitate was collected, washed with the mixture
of ethanol/water (10:1) and dried in vacuo. BPPV was obtained as a
ꢁ
1
yellow solid (480 mg, 72%). m.p. >250 C. H NMR (400 MHz, D
9.41(d, J ¼ 6.7 Hz, 2H), 8.76(d, J ¼ 6.7 Hz, 2H), 8.63(d, J ¼ 5.6 Hz,
2H), 8.08(d, J ¼ 8.6 Hz, 2H), 7.93(d, J ¼ 8.6 Hz, 2H), 7.88(d, J ¼ 5.6 Hz,
2
O)
1
9%). H NMR (400 MHz, D
2
O)
d
9.40 (d, J ¼ 7.0 Hz, 4H), 9.33(d,
d
J ¼ 2.5 Hz, 2H), 8.86(m, 6H), 8.22(d, J ¼ 8.7 Hz, 2H).
13
2
H). C NMR (100 MHz, D
2
O) d 155.99, 150.98, 145.53, 144.12,
2
.2.2. (4-Bromophenyl)carbamic acid tert-butyl ester (4) [23]
Into a 250 mL round bottom flask were added p-bromoaniline
141.62, 138.32, 130.36, 127.29, 125.36, 125.24. HRMS (m/z):
2þ
2þ
[M ꢀ 2Cl] calcd. for 232.1001; found: HRMS Found: [M ꢀ 2Cl]
2þ
(
5.16 g, 30 mmol), di(tert-butyl) carbonate (7.86 g, 36 mmol) and
dichloromethane (100 mL). To the stirred solution triethylamine
1 mL, 7 mmol) was added dropwise in 6 h and stirring continued
232.0996; molecular formula C32
H N
24 4
Cl
2
requires [M ꢀ 2Cl]
232.1001. IR (KBr):
n
ꢀ
3421, 3095, 3060, 1632, 1601, 1489, 1440, 1406,
1
(
1217, 1003, 820 cm
.
for additional 10 h at room temperature. The solvent was then
removed under reduced pressure and the residual was submitted to
3. Result and discussion
a silica gel column, after eluted with CH
white solid (4.0 g, 49%). H NMR (400 MHz, DMSO-d
2
Cl
2
, 4 was obtained as a
9.5 (s, 1H),
1
6
)
d
3.1. Synthesis
7.42(s, 4H), 1.47 (s, 9H).
The synthetic route of BPPV was shown in Scheme 1. Alkyl-
substituted viologens were commonly prepared from the direct
alkylation of 4,4 -bipyridine, while aromatic-substituted viologens
2
.2.3. 4-(Boc-amino)benzeneboronic acid pinacol ester (5) [24]
A mixture of bis(pinacolato)diboron (10.5 g, 41.5 mmol), 4
0
(
7.75 g, 28.5 mmol), Pd(dppf)Cl
2
(0.79 g, 1.1 mmol) and potassium
were usually not because of the low reactivity of both bipyridine
and aromatic halides. The preparation of aromatic-substituted
viologens adopts generally the route of Zinke reaction, that is,
displacing the 2,4-dinitroaniline units of the bipyridinium salt 2
with aromatic amines. The key aromatic amine in this work is 4-(4-
pyridinyl)-benzenamine 7, which can theoretically synthesized
from the Suzuki coupling between a pyridine borate and a bro-
moaniline, or between an aniline borate and a bromopyridine. It is
believed that the using of an electron rich borate and an electron
deficient halide favors the coupling [25,26], and as a result, the later
strategy was carried out. The coupling of Boc-protected aniline
borate 5 with bromopyridine indeed gave 6 in good yield (83%). 6
was then converted to 7 quantitatively by the deprotection of the
Boc-group. The final Zinke reaction was carried out by refluxing 2
and 7 in ethanol and the desired BPPV precipitated out from the
acetate (7.0 g, 71.4 mmol) in dry dioxane (100 mL) was added into a
2
1
50 mL round bottom flask. The mixture was stirred for 12 h at
ꢁ
10 C under the protection of argon. After being cooled to room
temperature, it was filtered and the filtrate was concentrated on a
rotary evaporator. The residue was subjected to column chroma-
tography over silica gel (PE/EA 10:1) to give 5 (3.26 g, 36%) as a
white solid. 1H NMR (400 MHz, DMSO-d
)
d
9.53(s, 1H), 7.56(d,
6
J ¼ 8.5 Hz, 2H), 7.47(d, J ¼ 8.5 Hz, 2H), 1.48(s, 9H), 1.29(s, 12H).
2
.2.4. [4-(Pyridin-4-yl)phenyl]carbamic acid tert-butyl ester (6)
A solution of 5 (4.08 g, 13 mmol), 4-bromopyridine hydrochlo-
ride (2.92 g, 15 mmol), potassium carbonate (6 g, 43.4 mmol) and
Pd (dppf)Cl
was stirred for 12 h at 120 C in argon. After being cooled to room
temperature, the mixture was filtered and the filtrate was
concentrated. The residue was subjected to column chromatog-
raphy over silica gel (PE/EA 12:1) to give 6 (2.90 g, 83%) as a white
2
(0.40 g, 0.55 mmol) in dioxane/water (65 mLþ5 mL)
ꢁ
1
13
solution. The H and C NMR spectra (Figs. S12 and S13) of BPPV in
O display six proton and ten carbon signals, respectively, which
D
2
agree with the symmetric structure. Further identification was
ꢁ
1
solid. m.p. 177e179 C. H NMR (400 MHz, DMSO-d
8
6
)
d
9.60(s, 1H),
conducted by high resolution mass spectrometry, as shown in
2þ
.58(d, J ¼ 6.1 Hz, 2H), 7.75(dd, J ¼ 8.7, 1.6 Hz, 2H), 7.67(dd, J ¼ 6.1,
Fig. S14, the peak at m/z ¼ 232.0996 corresponds to the [M ꢀ 2Cl]