Facile and environmentally friendly halogenation of BODIPYs in deep eutectic solvent

Article abstract of DOI:10.1016/j.dyepig.2014.07.024

A deep eutectic solvent based on choline chloride and 1,1,1,3,3,3- hexafluoro-2-propanol was prepared. This deep eutectic solvent was used as the reaction medium for halogenation of boron dipyrromethene in the presence of N-halosuccinimide, which delivere

Full text of DOI:10.1016/j.dyepig.2014.07.024

Dyes and Pigments 112 (2015) 274e279
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Facile and environmentally friendly halogenation of BODIPYs in deep
eutectic solvent
Liang Wang*, Kai-qiang Zhu, Qun Chen, Ming-yang He*
School of Petrochemical Engineering and Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, Changzhou University, Changzhou,
213164, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A deep eutectic solvent based on choline chloride and 1,1,1,3,3,3-hexafluoro-2-propanol was prepared.
This deep eutectic solvent was used as the reaction medium for halogenation of boron dipyrromethene in
the presence of N-halosuccinimide, which delivered the corresponding products in good to excellent
yields (79e94%) in short reaction time (usually within 30 min). Moreover, this deep eutectic solvent
could be easily prepared, recovered and reused for several runs without significant loss in the yields.
© 2014 Elsevier Ltd. All rights reserved.
Received 20 May 2014
Received in revised form
16 July 2014
Accepted 17 July 2014
Available online 28 July 2014
Keywords:
Deep eutectic solvent
Hexafluoroisopropanol
Halogenation
Boron dipyrromethene
Green chemistry
Fluorescent dye
1. Introduction
However, prolonged reaction time, relatively lower yields as well as
toxic reagents or solvents are still the issues to be addressed.
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) have
received much attention due to their unique properties including
high fluorescence quantum yields (Ff), large molar absorption
coefficients (ε), excellent thermal and photochemical stabilities
[1e3]. Recently, much effort has been spent on the decoration of
the BODIPY scaffold with functional groups to modify their pho-
tophysical properties, making them excellent fluorophores in
various fields [4e6]. Among them, halogenated BODIPYs are of
great interest since they are useful precursors for further func-
tionalization. For examples, 3,5-dihalogenated BODIPYs (Fig. 1A)
are generally modified via SNAr reactions and metal-catalyzed
cross-coupling reactions to provide more complex BODIPY de-
rivatives [7e10]. The 2,6-halogenated BODIPYs (Fig. 1B) are also
effective sensitizers for photodynamic therapy (PDT) [11,12] and
photocatalysts [13e15].
More recently, deep eutectic solvents (DESs) have invoked great
interest as green solvents or catalysts in organic reactions [19e22].
They are mainly prepared by combining a quaternary ammonium
salt with a hydrogen-bond donor. The unique properties such as
ready available, biodegradable, non-toxic, inexpensive and reusable
make them more advantageous than the conventional solvents. On
the other hand, it is well known that 1,1,1,3,3,3-hexafluoro-2-
propanol (HFIP) exhibits high hydrogen bonding donor ability,
low nucleophilicity and high ionizing power. Its utilization in
organic transformations has also been well-documented [23e26].
We believe that HFIP can be used to form a deep eutectic solvent
with a quaternary ammonium salt. Also, HFIP also can activate the
N-halosuccinimide via hydrogen bonding. Herein, we report the
preparation of a new DES (ChCl/HFIP) and halogenation reaction of
BODIPYs in such DES (Scheme 1).
Direct electrophilic halogenation of BODIPYs is well-
documented in literature. Using bromination as example, a series
of reaction systems including N-bromosuccinimide (NBS) [16],
bromine [17], NBS-AIBN [12] and CuBr2 [18] has been developed.
2. Experimental
2.1. Method and apparatus
All reagents were obtained from local commercial suppliers and
used without further purification. 1H NMR and 13C NMR spectra
were recorded using a Bruker Avance III 500-MHz spectrometer.
* Corresponding authors. Tel.: þ86 519 86330263; fax: þ86 519 86330251.
E-mail addresses: lwcczu@126.com (L. Wang), hemingyangjpu@yahoo.com
(M.-y. He).
http://dx.doi.org/10.1016/j.dyepig.2014.07.024
0143-7208/© 2014 Elsevier Ltd. All rights reserved.

L. Wang et al. / Dyes and Pigments 112 (2015) 274e279
275
2,6-Dibromo-4,4-difluoro-8-(4-chlorophenyl)-1,3,5,7-tetram
ethyl-4-bora-3a,4a-diaza-s-indacene (2c): red solid; m.p.
208e210 ꢀC (212e214 ꢀC) [18]; 1H NMR (500 MHz, CDCl3):
d
¼ 1.41
(s, 6H, CH3), 2.61 (s, 6H, CH3), 7.21e7.23 (d, J ¼ 10.0 Hz, 2H, ArH),
7.52e7.54 (d, J ¼ 10.0 Hz, 2H, ArH). 13C NMR (125 MHz, CDCl3):
d
¼ 154.4, 140.4, 140.3, 135.9, 132.8, 130.3, 129.8, 129.4, 128.6, 112.1,
13.9, 13.7.
2,6-Dibromo-4,4-difluoro-8-(4-nitrophenyl)-1,3,5,7-tetrame
thyl-4-bora-3a,4a-diaza-s-indacene (2d): red solid; m.p. > 250 ꢀC
(>300 ꢀC) [18]; 1H NMR (500 MHz, CDCl3):
¼ 1.38 (s, 6H, CH3),
d
2.64 (s, 6H, CH3), 7.55 (d, J ¼ 8.6 Hz, 2H, ArH), 8.44 (d, J ¼ 8.6 Hz, 2H,
Fig. 1. 3,5- and 2,6-dihalogenated BODIPYs.
ArH). 13C NMR (125 MHz, CDCl3):
138.6, 129.6, 124.6, 112.5, 14.0, 13.8.
d
¼ 155.3, 148.7, 141.2, 140.0,
NMR experiments are reported in
and were referenced to CDCl3
d
units, parts per million (ppm),
2,6-Dibromo-4,4-difluoro-8-(3,5-dinitrophenyl)-1,3,5,7-tetra
(d
7.26 or 77.0 ppm) as the internal
methyl-4-bora-3a,4a-diaza-s-indacene
(2e):
red
solid;
standard. The coupling constants J are given in Hz. Melting points
(m.p.) are determined with a MPA 100 apparatus and are not cor-
rected. Mass spectra (EI) were measured with Jeol JMS-DX300 and
Thermo Fisher LCQ instruments. Elemental analyses were obtained
using a PerkineElmer EA2400II analyzer.
m.p. > 250 ꢀC; 1H NMR (500 MHz, CDCl3):
d
¼ 1.37 (s, 6H, CH3), 2.64
(s, 6H, CH3), 8.56 (s, 2H, ArH), 9.23 (s, 1H, ArH). 13C NMR (125 MHz,
CDCl3):
15.4, 14.8. EI-MS: m/z
19H15BBr2F2N4O4: C, 39.90; H, 2.64; N, 9.80. Found: C, 39.87; H,
2.70; N, 9.76.
d
¼ 158.0, 149.0, 141.8, 138.8, 134.5, 130.7, 129.2, 122.6, 119.4,
¼
572 [M]þ. Anal. Calcd for
C
2.2. Preparation of ChCl/HFIP
2,6-Dibromo-4,4-difluoro-1,3,5,7-tetramethyl-8-methyl-4-
bora-3a,4a-diaza-s-indacene (2f): red solid; m.p. 221e223 ꢀC; 1H
Choline chloride (139.6 g, 100 mmol) and 1,1,1,3,3,3-hexafluoro-
2-propanol (25.2 g, 150 mmol) were placed in a round bottom flask
and stirred at 50 ꢀC. After 3 h, a homogenous colorless liquid
formed, which was used directly for the reactions without
purification.
NMR (500 MHz, CDCl3):
(s, 3H, CH3). 13C NMR (125 MHz, CDCl3):
17.4, 16.4, 13.6. EI-MS: m/z
420 [M]þ. Anal. Calcd for
14H15BBr2F2N2: C, 40.05; H, 3.60; N, 6.67. Found: C, 40.11; H, 3.52;
N, 6.70.
d
¼ 2.44 (s, 6H, CH3), 2.57 (s, 6H, CH3), 2.62
d
¼ 152.2, 141.9, 138.4, 29.7,
¼
C
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-pentyl-4-bor
a-3a,4a-diaza-s-indacene (2g): red solid; m.p. 216e218 ꢀC; 1H
2.3. General procedures for halogenation of BODIPYs
NMR (500 MHz, CDCl3):
2.44 (s, 6H, CH3), 2.57 (s, 6H, CH3). 13C NMR (125 MHz, CDCl3):
¼ 152.3, 147.3, 137.7, 130.5, 112.0, 32.5, 31.5, 29.0, 22.5, 15.5,
14.0, 13.7. EI-MS: m/z
476 [M]þ. Anal. Calcd for
18H23BBr2F2N2: C, 45.42; H, 4.87; N, 5.89. Found: C, 45.40; H,
4.91; N, 5.87.
d
¼ 0.93 (t, 3H, CH3), 1.36e1.66 (m, 8H),
A mixture of the BODIPY 1 (0.2 mmol) and either NBS or NIS
(0.48 mmol) in ChCl/HFIP (2 mL) was stirred at room temperature
for a certain time (usually < 30 min) according to the TLC (EtOAc/
petroleum, 1:5). After reaction, the mixture was extracted with
CH2Cl2, washed with H2O, dried over Na2SO4, and concentrated
under reduced pressure. The crude product was further purified
using column chromatography (EtOAc/petroleum ether or CH2Cl2/
hexane) to afford either the bromo-products 2 or the iodo-products
3. The ChCl/HFIP, which was insoluble in CH2Cl2, was readily
recovered by evaporation of the water and reused for the next run.
All the products were known compounds and were characterized
by comparison with authentic samples.
d
¼
C
2,6-Dibromo-4,4-difluoro-1,3,5,7-tetramethyl-8-undecyl-4-
bora-3a,4a-diaza-s-indacene (2h): red solid; m.p. 202e205 ꢀC; 1H
NMR (500 MHz, CDCl3):
18H, CH2), 2.44 (s, 6H, CH3), 2.57 (s, 6H, CH3), 3.70e3.74 (m, 2H,
CH2). 13C NMR (125 MHz, CDCl3):
d
¼ 0.88e0.91 (t, 3H, CH3), 1.22e1.65 (m,
d
¼ 152.3, 147.3, 137.7, 130.5, 112.0,
31.8, 31.7, 30.3, 29.0, 22.6, 18.4, 15.5, 14.1, 13.7. EI-MS: m/z ¼ 560
[M]þ. Anal. Calcd for C24H35BBr2F2N2: C, 51.46; H, 6.30; N, 5.00.
Found: C, 51.47; H, 6.25; N, 5.02.
2,6-Dibromo-4,4-difluoro-1,3,5,7-tetramethyl-8-phenyl-4-
bora-3a,4a-diaza-s-indacene (2a): red solid; m.p. 228e232 ꢀC
2,6-Dibromo-4,4-difluoro-1,3,5,7-tetramethyl-8-ethoxycarb
(229e231 ꢀC) [18]; 1H NMR (500 MHz, CDCl3):
d
¼ 1.36 (s, 6H, CH3),
onyl-4-bora-3a,4a-diaza-s-indacene (2i): red solid; m.p. > 250 ꢀC;
2.61 (s, 6H, CH3), 7.52e7.53 (m, 5H, ArH). 13C NMR (125 MHz,
1H NMR(500 MHz, CDCl3):
d
¼ 1.42e1.45(t, 3H), 2.13(s, 6H), 2.56 (s,
4.43e4.48 (q, 2H); 13C NMR(125 MHz, CDCl3):
d
¼ 164.5,
CDCl3):
13.6.
d
¼ 153.9, 142.1, 140.6, 134.4, 130.4, 129.5, 129.4, 127.8, 111.8,
6H),
d
154.6, 135.9, 129.8, 126.9, 122.8, 63.2, 13.8, 12.7, 10.5. EI-MS: m/
z ¼ 478 [M]þ. Anal. Calcd for C16H17BBr2F2N2O2: C, 40.21; H, 3.59; N,
5.86. Found: C, 40.16; H, 3.62; N, 5.80.
2,6-Dibromo-4,4-difluoro-8-(4-methoxyphenyl)-1,3,5,7-tetra
methyl-4-bora-3a,4a-diaza-s-indacene (2b): red solid; m.p.
238e240 ꢀC (236e238 ꢀC) [18]; 1H NMR (500 MHz, CDCl3):
d
¼ 1.47
2,6-Dibromo-4,4-difluoro-8-(morpholinomethyl)-1,3,5,7-tet
ramethyl-4-bora-3a,4a-diaza-s-indacene (2j): red solid; m.p.
(s, 6H, CH3), 2.62 (s, 6H, CH3), 3.91 (s, 3H, OCH3), 7.06 (d, J ¼ 8.65 Hz,
2H, ArH), 7.16 (d, J ¼ 8.65 Hz, 2H, ArH). 13C NMR (125 MHz, CDCl3):
228e231 ꢀC; 1H NMR (500 MHz, CDCl3):
(s, 3H, CH3), 2.47 (s, 3H, CH3), 2.60 (s, 3H, CH3), 3.74 (t, 4H, CH2), 3.76
d
¼ 2.32 (s, 3H, CH3), 2.39
d
¼ 160.6, 153.7, 142.3, 140.6, 130.9, 130.8, 129.1, 128.8, 126.3, 114.8,
111.7, 55.4, 13.9, 13.7.
Scheme 1. 2,6-dihalogenation of BODIPYs in ChCl/HFIP.
Scheme 2. Preparation of ChCl/HFIP.

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L. Wang et al. / Dyes and Pigments 112 (2015) 274e279
C18H22BBr2F2N3O: C, 42.81; H, 4.39; N, 8.32. Found: C, 42.78; H,
3.31; N, 8.35.
2,6-Dibromo-4,4-difluoro-8-(4-((2-hydroxybenzylidene)ami
no)phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene
(2k): red solid; m.p. 236e238 ꢀC; 1H NMR (500 MHz, CDCl3):
d
¼ 1.23e1.55 (m, 6H, CH3), 2.57 (s, 6H, CH3), 6.96e6.99 (m, 2H,
ArH), 7.05e7.44 (m, 6H, ArH), 8.72 (s, 1H). 13C NMR (125 MHz,
CDCl3):
¼ 163.5, 161.3, 155.7, 149.2, 143.0, 141.0, 133.7, 133.6,
132.5, 131.5, 129.3, 129.0, 122.0, 121.4, 119.2, 119.0, 117.6, 117.4,
115.4, 18.5, 14.6. EI-MS: m/z
601 [M]þ. Anal. Calcd for
26H22BBr2F2N3O: C, 51.95; H, 3.69; N, 6.99. Found: C, 51.91; H,
3.65; N, 7.02.
Scheme 3. Model bromination reactions in ChCl/HFIP.
d
(t, 4H, CH2), 3.85 (s, 2H, CH2). 13C NMR (125 MHz, CDCl3):
d
¼ 154.8,
¼
C
154.0, 142.2, 142.0, 140.4, 132.4, 131.8, 121.7, 119.7, 67.1, 55.7, 54.1,
17.5, 17.4, 16.5, 14.5. EI-MS: m/z ¼ 505 [M]þ. Anal. Calcd for
Table 1
Bromonation of BODIPYs.a
a
Reaction conditions: 1 (0.2 mmol), NBS (2.4 equiv), DES (2 mL), 25 ꢀC, 30 min, isolated yields.

L. Wang et al. / Dyes and Pigments 112 (2015) 274e279
277
2,6-Dibromo-4,4-difluoro-8-((bis(chloromethyl)amino)meth
yl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (2l): red
J ¼ 10.0 Hz, 2H, ArH), 7.15e7.17 (d, J ¼ 10.0 Hz, 2H, ArH). 13C NMR
(125 MHz, CDCl3):
d
¼ 160.6, 153.7, 142.3, 140.6, 130.9, 130.8, 129.1,
solid; m.p. 217e219 ꢀC; 1H NMR (500 MHz, CDCl3):
d
¼ 2.43 (s, 3H,
CH3), 2.45 (s, 3H, CH3), 2.51 (s, 3H, CH3), 2.60 (s, 3H, CH3), 3.00 (t,
2H, CH2), 3.56 (t, 2H, CH2). 13C NMR (125 MHz, CDCl3):
128.8, 126.3, 114.8, 111.7, 55.4, 13.8, 13.6.
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-(4-chlorophen
d
¼ 155.0,
yl)-4-bora-3a,4a-diaza-s-indacene (3c): red solid;
m.p.
¼ 1.43
154.5, 142.4, 142.2, 140.4, 132.5, 131.9, 121.9, 119.9, 57.1, 51.9, 42.0,
203e204 ꢀC (207e209 ꢀC) [27]; 1H NMR (500 MHz, CDCl3):
d
17.5, 17.4, 16.5, 14.5. EI-MS: m/z ¼ 531 [M]þ. Anal. Calcd for
(s, 6H, CH3), 2.64 (s, 6H, CH3), 7.20 (d, J ¼ 10.0 Hz, 2H, ArH), 7.52 (d,
C
16H18BBr2Cl2F2N3: C, 36.13; H, 3.41; N, 7.90. Found: C, 36.10; H,
J ¼ 10.0 Hz, 2H, ArH). 13C NMR (125 MHz, CDCl3):
d
¼ 157.2, 145.1,
3.38; N, 7.84.
139.7, 135.8, 133.2, 131.2, 129.8, 129.4, 85.9, 17.2, 16.1.
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-phenyl-4-bora
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-(4-nitropheny
-3a,4a-diaza-s-indacene (3a): red solid; m.p. 194e196 ꢀC
l)-4-bora-3a,4a-diaza-s-indacene (3d): red solid; m.p. > 250 ꢀC
(195e197 ꢀC) [27]; 1H NMR (500 MHz, CDCl3):
d
¼ 1.38 (s, 6H, CH3),
(>300 ꢀC) [27]; 1H NMR (500 MHz, CDCl3):
2.66 (s, 6H, CH3), 7.54 (d, J ¼ 7.5 Hz, 2H, ArH), 8.42 (d, J ¼ 7.5 Hz, 2H,
d
¼ 1.38 (s, 6H, CH3),
2.65 (s, 6H, CH3), 7.52e7.53 (m, 5H, ArH). 13C NMR (125 MHz,
CDCl3):
16.9.
d
¼ 156.8, 145.4, 141.4, 134.7, 131.3, 129.5, 129.4, 127.8, 85.7,
ArH). 13C NMR (125 MHz, CDCl3):
129.5, 124.7, 114.0, 14.9, 14.7.
d
¼ 158.1, 148.6, 141.7, 141.6, 138.1,
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-(4-methoxyph
enyl)-4-bora-3a,4a-diaza-s-indacene (3b): red solid; m.p.
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-methyl-4-bora
-3a,4a-diaza-s-indacene (3e): purple solid; m.p. 201e203 ꢀC; 1H
198e200 ꢀC (196e198 ꢀC) [27]; 1H NMR (500 MHz, CDCl3):
d
¼ 1.42
NMR (500 MHz, CDCl3):
d
¼ 2.46 (s, 6H, CH3), 2.61 (s, 6H, CH3), 2.62
¼ 155.1,143.0,141.1,132.2,
(s, 6H, CH3), 2.62 (s, 6H, CH3), 3.94(s, 3H, OCH3) 7.04e7.06 (d,
(s, 3H, CH3). 13C NMR (125 MHz, CDCl3):
d
Table 2
Iodonation of BODIPYs.a
a
Reaction conditions: 1 (0.2 mmol), NIS (2.4 equiv), DES (2 mL), 25 ꢀC, 15 min, isolated yields. For product 3i, 4.8 equivalent of NIS was used.

278
L. Wang et al. / Dyes and Pigments 112 (2015) 274e279
85.8, 19.8, 17.9, 16.0. EI-MS: m/z ¼ 514 [M]þ. Anal. Calcd for
with NIS quickly to give the diiodo substituted BODIPYs (3a~3i) in
good to excellent yields within 15 min (82e92%).
C
14H15BF2I2N2: C, 32.72; H, 2.94; N, 5.45. Found: C, 32.70; H, 2.90; N,
5.48.
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-pentyl-4-bor
a-3a,4a-diaza-s-indacene (3f): red solid; m.p.193e195 ꢀC; 1H NMR
(500 MHz, CDCl3):
¼ 0.93e0.96 (t, 3H, CH3), 1.23e1.66 (m, 8H,
CH2), 2.43 (s, 6H, CH3), 2.61 (s, 6H, CH3). 13C NMR (125 MHz, CDCl3):
One of the most important advantages employing DES as sol-
vent or catalyst is their recyclability. Thus, the recycling experi-
ments were carried out using bromination of BODIPY 1a as the
model reaction. After completion of the reaction, dichloromethane
and water were added and the mixture was stirred for five minutes.
The dichloromethane layer containing the starting substrate and
product was separated. The aqueous medium was then dried under
vacuum at 80 ꢀC to recover the DES. Results showed that the DES
could be reused several times with only a gradual decrease in the
yield (90%, 90%, 88% and 85%).
d
d
¼ 155.2, 142.2, 131.9, 128.7, 86.8, 32.5, 31.5, 29.3, 22.5, 18.5, 16.1,
14.0. EI-MS: m/z ¼ 570 [M]þ. Anal. Calcd for C18H23BF2I2N2: C, 37.93;
H, 4.07; N, 4.91. Found: C, 37.90; H, 4.11; N, 4.95.
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-undecyl-4-bor
a-3a,4a-diaza-s-indacene (3g): red solid; m.p. 178e180 ꢀC; 1H
NMR (500 MHz, CDCl3):
18H, CH2), 2.44 (s, 6H, CH3), 2.60 (s, 6H, CH3), 3.67e3.72 (m, 2H,
CH2). 13C NMR (125 MHz, CDCl3):
31.9, 31.6, 30.3, 29.6, 29.4, 29.3, 22.7, 18.9, 18.3, 16.1, 14.1. EI-MS: m/
z ¼ 654 [M]þ. Anal. Calcd for C24H35BF2I2N2: C, 44.06; H, 5.39; N,
4.28. Found: C, 44.10; H, 5.37; N, 4.33.
d
¼ 0.87e0.90 (t, 3H, CH3), 1.21e1.60 (m,
4. Conclusion
d
¼ 155.0, 146.5, 142.3, 131.3, 86.4,
In summary, a facile and environmentally friendly protocol has
been developed for dihalogenation of BODIPYs using ChCl/HFIP as
solvent and N-halosuccinimide as the halogen source. The reaction
completed within 15e30 min to afford the dihalogenated BODIPYs
in good to excellent yields. Moreover, the DES ChCl/HFIP can be
easily recovered and reused for several runs.
2,6-Diiodo-4,4-difluoro-1,3,5,7-tetramethyl-8-ethoxycarbon
yl-4-bora-3a,4a-diaza-s-indacene (3h): red solid; m.p. > 250 ꢀC;
1H NMR(500 MHz, CDCl3):
d
¼ 1.44e1.41 (t, 3H, CH3), 2.16 (s, 6H,
CH3), 2.62 (s, 6H, CH3), 4.43e4.47(q, 2H, CH2). 13C NMR(125 MHz,
CDCl3):
d
¼ 164.8, 158.8, 128.8, 128.5, 85.5, 63.2, 16.2, 15.3, 13.8. EI-
Acknowledgments
MS: m/z ¼ 572 [M]þ. Anal. Calcd for C16H17BF2I2N2O2: C, 33.60; H,
3.00; N, 4.90. Found: C, 33.63; H, 2.96; N, 4.91.
We gratefully thank the National Natural Science Foundation of
China (21302014), the Natural Science Foundation for Colleges and
Universities of Jiangsu Province (13KJB150002), the Jiangsu Key
Laboratory of Advanced Catalytic Materials and Technology
(BM2012110), and ordinary university graduate student research
innovation projects of Jiangsu province (No. KYZZ_0303) for
financial support.
2,2’,6,6’-tetraiodo-4,4,4’,4’-difluoro-1,1’,3,3’,5,5’,7,7’-octamet
hyl-4,4ˊ-dibora-3a,3a’,4a,4a’-tetraaza-s-indacene (3i): red solid;
m.p. > 250 ꢀC; 1H NMR (500 MHz, CDCl3):
d
¼ 2.14 (s, 6H, CH3), 2.58
(s, 6H, CH3). 13C NMR (125 MHz, CDCl3):
d
¼ 156.0, 138.6, 128.9,
128.5, 127.6, 13.8, 12.2. EI-MS: m/z ¼ 998 [M] þ. Anal. Calcd for
C
26H24B2F4I4N4: C, 31.30; H, 2.42; N, 5.62. Found: C, 31.35; H, 2.37;
N, 5.57.
Appendix A. Supplementary data
3. Results and discussion
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2014.07.024.
Initially, DES (ChCl/HFIP) was prepared by simple mixing
choline chloride with HFIP at 50 ꢀC till a clear solution was obtained
(Scheme 2). The ratio of ChCl/HFIP was 1:1.5 as confirmed by
NMR analysis. DSC analysis clearly showed that the melting point
of ChCl/HFIP was ꢁ37.2 ꢀC. Moreover, ChCl/HFIP was very stable
and could be easily stored on the shelf without decomposition.
With this DES in hand, we began to investigate the halogenation
reaction. Encouragingly, it was found that upon simple mixing of
BODIPY 1a (0.2 mmol) and N-bromosuccinimide (NBS, 2.4 equiv) in
ChCl/HFIP (2 mL), the reaction proceeded rapidly to provide the
corresponding dibromo-BODIPY 2a in 90% yield within 30 min
(Scheme 3). Other choline-based eutectic mixtures such as choline
chlorideeurea, choline chlorideemalonic acid, choline chlor-
ideeglycerol and choline chloride- p-toluenesulfonic acid were also
evaluated for this reaction. However, BODIPY 1a was not soluble in
these DESs, thus only trace amount of products were obtained.
On the basis of above result, the scope of the BODIPYs was
examined and the results were summarized in Table 1. Generally, all
of the reactions proceeded smoothly to afford the dibromo-BODI-
PYS (2a~2l) in good to excellent yields (79e94%). For the meso-aryl
substituted BODIPYs 1a~1e and those bearing electron-
withdrawing groups, such as a nitro group, relatively lower yields
were recorded. The meso-ethoxycarbonyl substituted BODIPY was
less active than the meso-alkyl substituted BODIPYs. Other BODIPYs
modified with morpholine, schiff base functions and bis(chlor-
omethyl)amine also showed good compatibilities to deliver the
products in good yields.
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