J. Zheng et al. / Dyes and Pigments 113 (2015) 502e509
503
2. Experimental
(m, 4H), 7.36e7.30 (m, 4H), 7.30e7.28 (m, 1H), 7.22e7.13 (m, 1H),
7.13e7.07 (m, 2H), 6.82 (d, 1H, J ¼ 7.9 Hz), 5.02 (s, 2H). 13C NMR
2.1. General
(125 MHz, CDCl3): d 162.27 (2C), 142.63 (1C), 140.18 (1C), 135.83
(1C), 129.46 (2C), 128.88 (2C), 127.96 (1C), 127.75 (1C), 127.29 (2C),
126.76 (1C), 123.29 (1C), 122.67 (1C), 121.46 (1C), 118.95 (1C), 114.42
(1C), 109.35 (1C), 43.24 (1C).
All of the chemicals used in the current study were purchased
from commercial vendors and used as received without further
purification, unless otherwise noted. All solvents were purified and
dried using standard methods prior to use. Fourier transform-
infrared (FTIR) spectra were performed using Thermo Nicolet
6700 spectrophotometer. Nuclear magnetic resonance (1H, 13C and
19F NMR) spectra were recorded on a Bruker AM 500 spectrometer
(Bruker) with chemical shifts reported as ppm at 500, 125 and
376 MHz, respectively, (in CDCl3, TMS as internal standard). Fluo-
rescence spectra were obtained with a F-7000 Fluorescence Spec-
2.4. Preparation of compounds 3ae3b
To a stirred solution of 2a (0.5 mmol, 0.1328 g) in degassed
anhydrous dichloromethane (20 mL), Et3N (10 mmol 1.5 mL) was
syringed under nitrogen atmosphere. After stirred for 20 min,
BF3$OEt2 (10 mmol, 1.25 mL) was successively added by syringe.
The mixture was stirred at room temperature overnight and com-
plete reaction was detected by TLC. The mixture was quenched with
water (20 mL), and extracted with dichloromethane (3 ꢁ 20 mL).
The organic layer was dried with MgSO4 and the solvent was
removed under reduced pressure. The residue was purified by silica
gel chromatography eluting (silica gel, ethyl acetate: petroleum
ether ¼ 1: 10) to afford clean complex 3a as a orange-yellow solid.
trophotomete in a solution of 100
were measured on a UV-2550.
mM. UVeVis absorption spectra
2.2. Preparation of compounds 1ae1b
A mixture of isatin (10.0 mmol, 1.4722 g), ethyl bromide
(10.0 mmol, 1.0905 g) and anhydrous K2CO3 (14.5 mmol, 2.0 g) in
DMF (10 mL) was stirred vigorously for 12 h at room temperature and
complete reactionwas detected by TLC analysis. The reaction mixture
was poured into water (100 mL) and the precipitate was concen-
trated to give crude product and recrystallized from EtOH [20].
2.4.1. 5-ethyl-3,3-difluoro-2-phenyl-3,5-dihydro-2H-[1,3,4,2]
oxadiazaborinino[6,5-b] indol-4-ium-3-uide (compound 3a)
Orange-yellow solid. Yield 0.1253 g, 80%. Mp 163e166 ꢀC. FTIR
(KBr, cmꢂ1) 2987.2, 1608.4, 1508.5, 1321.0, 1282.5, 1210.1, 1135.9,
1023.3, 761.8, 545.8, 432.0. 1H NMR (CDCl3, 500 MHz):
d 7.90e7.88
2.2.1. 1-ethylindole-2,3-dione (compound 1a)
Red solid. Yield 1.7110 g, 98%. Mp: 91e92 ꢀC (ref: 94 ꢀC) [20].
GCeMS: 175.0.
(m, 1H), 7.85e7.83 (m, 2H), 7.47e7.44 (m, 2H), 7.40e7.39 (m, 2H),
7.39e7.36 (m, 1H), 7.35e7.26 (m, 1H), 4.19 (q, 2H, J ¼ 7.4 Hz), 1.53 (t,
3H, J ¼ 7.4 Hz). 13C NMR (CDCl3, 125 MHz):
d 152.84 (1C), 145.16
(1C), 136.02 (1C), 128.94 (2C), 126.85 (1C), 126.54 (1C), 124.88 (1C),
123.29 (1C), 121.56 (1C), 120.72 (1C), 119.01 (2C), 110.74 (1C), 36.72
2.2.2. 1-benzylindole-2,3-dione (compound 1b)
From isatin and benzyl chloride as an orange-yellow solid. Yield
(1C), 13.45 (1C). 19F NMR (CDCl3, 376 MHz):
d
ꢂ130.94 (s,
2.3467 g, 99%. Mp:132e133 ꢀC (ref: 132 ꢀC) [21]. GCeMS: 237.0.
1F), ꢂ131.00 (s, 1F). HRMS (ESI-TOF) found: [M þ H]þ 314.1273,
molecular formula C16H14BF2N3O, requires [M þ H]þ 314.1271.
2.3. Preparation of compounds 2ae2b
2.4.2. 5-benzyl-3,3-difluoro-2-phenyl-3,5-dihydro-2H-[1,3,4,2]
oxadiazaborinino[6,5- b]indol-4-ium-3-uide (compound 3b)
Deep-yellow solid. Yield 0.3758 g, 84%. Mp: 145e149 ꢀC. FTIR
(KBr, cmꢂ1) 3060.5, 1634.0, 1508.1, 1458.1, 1266.7, 1183.4, 1133.0,
A mixture of 1a (5.0 mmol, 0.8755 g), phenylhydrazine hydro-
chloride (5.0 mmol, 0.7325 g) in DMF (10 mL) was stirred vigor-
ously at room temperature overnight. The reaction mixture was
poured into water (100 mL) and extracted with ethyl acetate
(3 ꢁ 20 mL). The combined organic layer was dried with MgSO4 and
the solvent was removed under reduced pressure. The residue was
purified by silica gel chromatography eluting (silica gel, ethyl ace-
tate: petroleum ether ¼ 1:5) leading to phenylhydrazone derivative
2a as a yellow solid [22].
1023.8, 881.3, 757.9, 555.4. 1H NMR (500 MHz, CDCl3):
d 7.89e7.86
(m, 3H), 7.48 (t, 2H, J ¼ 1.9 Hz), 7.45e7.28 (m, 8H), 7.17 (d, 1H,
J ¼ 7.4 Hz), 5.27 (s, 2H). 13C NMR (125 MHz, CDCl3):
d 153.14 (1C),
145.20 (1C), 136.28 (1C), 133.48 (1C), 129.30 (2C), 128.92 (2C),
128.72 (1C), 127.67 (2C), 127.11 (1C), 126.59 (1C), 125.03 (1C), 123.13
(1C), 121.58 (1C), 120.90 (1C), 118.95 (1C), 114.46 (1C), 111.62 (1C),
45.52 (1C). 19F NMR (CDCl3, 376 MHz):
d
ꢂ130.96 (s, 1F), ꢂ131.02 (s,
2.3.1. 1-ethylindole-3-phenylhydrazone (compound 2a)
1F). HRMS (ESI-TOF) found: [M þ H]þ 376.1436, molecular formula
Yellow solid. Yield 0.8220 g, 62%. Mp: 78e79 ꢀC. 1H NMR
C
21H16BF2N3O, requires [M þ H]þ 376.1427.
(500 MHz, CDCl3)
d
12.83 (s, 1H), 7.68 (d, 1H, J ¼ 7.5 Hz), 7.38e7.37
(m, 4H), 7.31e7.29 (m, 1H), 7.14e7.11 (m, 1H), 7.08e7.05 (m, 1H),
6.93 (d, 1H, J ¼ 7.9 Hz), 3.89 (q, 2H, J ¼ 7.3 Hz), 1.35 (t, 3H, J ¼ 7.3 Hz).
GCeMS: 265.0.
3. Results and discussion
3.1. Synthesis
2.3.2. 1-benzylindole-3-phenylhydrazone (compound 2b)
Preparation of the substituted isatin-phenylhydrazone de-
rivatives (precursor 2) and their corresponding boron complexes
(BODIHY 3) is shown in Scheme 1. To inhibit the H atom on the N
Yellow solid. Yield 1.3566 g, 83%. Mp: 138e139 ꢀC. 1H NMR
(500 MHz, CDCl3):
d
12.84 (s, 1H) 7.69 (d, 1H, J ¼ 7.3 Hz) 7.68e7.37
Scheme 1. The synthesis of the precursor 2 and the BODIHY 3.