Synthesis, characterization and photoluminescence properties of strong fluorescent BF2 complexes bearing (2-quinolin-2-yl)phenol ligands

Article abstract of DOI:10.1016/j.jfluchem.2012.03.006

Novel N,O bidentate BF₂ complexes were prepared in good to excellent yields through the coordination of (2-quinolin-2-yl)phenol and its derivatives with boron trifluoride etherate under mild conditions. These fluorine-boron complexes exhibited strong fluorescence both in organic solvents and in solid state. Their photophysical properties were thoroughly studied by absorption and fluorescence spectroscopy in various solvents. The electronic and site effects of substituents on phenolic and quinolinyl rings were found to have a profound impact on quantum yields. All these complexes were fully characterized by IR, ¹H, ¹³C, ¹⁹F NMR and microanalysis. The high quantum yields and large Stokes shifts make these compounds as potential fluorescent dyes.

Full text of DOI:10.1016/j.jfluchem.2012.03.006

Journal of Fluorine Chemistry 137 (2012) 93–98
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis, characterization and photoluminescence properties of strong
fluorescent BF2 complexes bearing (2-quinolin-2-yl)phenol ligands
*
Ru-Zheng Ma, Qi-Chao Yao, Xi Yang, Min Xia
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Novel N,O bidentate BF2 complexes were prepared in good to excellent yields through the coordination of
(2-quinolin-2-yl)phenol and its derivatives with boron trifluoride etherate under mild conditions. These
fluorine–boron complexes exhibited strong fluorescence both in organic solvents and in solid state. Their
photophysical properties were thoroughly studied by absorption and fluorescence spectroscopy in
various solvents. The electronic and site effects of substituents on phenolic and quinolinyl rings were
found to have a profound impact on quantum yields. All these complexes were fully characterized by IR,
1H, 13C, 19F NMR and microanalysis. The high quantum yields and large Stokes shifts make these
compounds as potential fluorescent dyes.
Received 16 October 2011
Received in revised form 1 March 2012
Accepted 5 March 2012
Available online 13 March 2012
Keywords:
(2-Quinolin-2-yl)phenols
N,O bidentate BF2 complexes
Strong fluorescence
Large Stokes shift
ß 2012 Elsevier B.V. All rights reserved.
High quantum yields
Photophysical properties
1. Introduction
green fluorescence and extraordinarily high quantum yields (>60%)
[33]. Inspired by these interesting findings, we were motivated to
The development of highly emissive dyes has been under the
focused research recently for their various applications. Among a
wide variety of fluorophores, organic difluoroboron complexes are
well-known for their strong emission intensity, large extinction
coefficients, high quantum yields, outstanding chem- and photo-
stability. Owning to these distinguished characteristics, BF2 com-
plexeshavethebroadapplicationsinphotodynamictherapy[1,2], as
electron-transport materials [3,4], fluorescent biolabels [5,6],
chemosensors [7,8] as well as photo sensitizers [9,10]. There are
mainly three types of these fluorine–boron complexes, classified as
N,N bidentate, O,O bidentate and N,O bidentate compounds. For the
formertwokindswhichhavebeenwelldocumentedandthoroughly
studied, BODIPY (boradipyrromethene) [11–17] and 1,3-dioxa-2-
borine [18–25] are their corresponding representatives. However,
N,O bidentate complexes, the isosteric analogues to the above two
types, have been rarely reported [26–29], especially those with
visible fluorescence [30–32].
discover other novel N,O bidentate BF2 complexes with remarkable
visible fluorescence characteristics.
(2-Quinolin-2-yl)phenol, which has a phenolic oxygen atom
and a quinolinyl nitrogen atom in the same molecular framework
and is capable of forming a six-membered chelate ring with an
electron-deficient center, is considered as a potential candidate for
the coordination with BF2 on N,O anchors. Fortunately, these
corresponding BF2 complexes exhibited characteristics such as
strong emission intensity, high quantum yield, large Stokes shift,
great absorption coefficient and robust chemical stability. It is
worth noting that the variation of substituents on phenolic or
quinolinyl rings was found to have a profound impact on the
photophysical performance of such BF2 chelates. Herein we
demonstrated the synthesis, structural analysis and spectroscopic
behaviors of these BF2 complexes bearing (2-quinolin-2-yl)phenol
ligands. In addition, their photophysical behaviors were thorough-
ly studied in various solvents as well.
In our previous work, we found that heterocyclic
b-enamino-
ketones like 3-(2-oxo-2-aryl-ethylidene)-3,4-dihydro-1H-quinoxa-
lin-2-ones and 3-(2-oxo-2-arylethylidene)-3,4-dihydrobenzo-
[1,4]oxazin-2-ones could be easily exploited as the effective ligands
to form the N,O bidentate difluoroboron complexes with strong
2. Results and discussion
2.1. Synthesis of complexes (6a–i)
In order to obtain the desired ligands (5a–i), two routes
(Scheme 1) were adopted depending on the different reactivity of
the acetyl group on the substituted 2-hydroxyacetophenones (1).
In cases where R3 and R4 were not electron-donating groups, the
* Corresponding author. Tel.: +86 571 86843757; fax: +86 571 86843757.
E-mail address: xiamin@zstu.edu.cn (M. Xia).
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2012.03.006

94
R.-Z. Ma et al. / Journal of Fluorine Chemistry 137 (2012) 93–98
Scheme 1. Route to synthesis of ligands and complexes.
corresponding ligands (5a–f) could be prepared through the
classical Friedla¨nder reaction (route A) [34], in which substituted
2-hydroxyacetophenones and substituted 2-aminobenzaldehydes
(2) were combined under strong basic conditions. However, when
R3 and R4 were electron-rich groups, the desired products could
not be gained in Friedla¨nder condensation due to the decrease of
acetyl reactivity. So another two-step strategy (route B) had to be
utilized [35], in which the intermediates 20-hydroxy-2-nitrochal-
cones (4) were formed in basic medium and underwent the
subsequent reductive coupling under acidic condition to form the
target ligands (5g–i).
2.2. Structural analysis
As all the complexes were of similar structures, complex 6c was
selected as a representative to carry out X-ray single crystal
diffraction study and its molecular structure is presented in Fig. 1.
The crystallographic data [36] clearly showed that there was a
quitesmalldihedralangle (about 108) betweenC2–C9 plane and C10
–
C15 plane due to the chelation of the BF2 group with 2-(quinolin-2-
yl)phenol ligand. Such great improvement of planarity imposed by
the chelation led to the more effective linkage between the
conjugative regions that were located on phenolic and quinolinyl
When 2-(quinolin-2-yl)phenol and its derivatives (5a–i) were
treated with excessive boron trifluoride etherate in the presence of
triethylamine, the novel BF2 complexes (6a–i) were generated
rapidly as yellowish or bright yellow microcrystals in good to
excellent yields. These compounds had robust chemical stability,
for their solids could be kept for several weeks without isolation
from air and moisture. More importantly, their fluorescence in
organic solutions was also insensitive to moisture.
rings. The extended p-electron delocalization on the complexes was
probably responsible for the variations of spectroscopic and
photophysical properties from those of the ligands. Additionally,
the excellent molecular planarity presented the fully efficient face-
to-face interaction when the molecules were aggregated in the solid
˚
state. Meanwhile, the distance (3.528 A) between the two molecular
planes was extraordinarily short. These elements could result in the
strong
p–p stacking interaction of the complexes.
Compared with the ligands, the melting points of the complexes
were elevated by nearly 100 8C correspondingly. Such a substantial
increase could be mainly attributed into two factors by the
introduction of the BF2 group: (i) the largely strengthened dipole–
dipole interaction due to the formation of zwitterions; (ii) the
much tighter
p–p stacking interaction due to the enhanced
planarity of the molecules.
2.3. Spectroscopic behavior studies
In comparing the IR spectra of the ligands and the complexes,
the most obvious difference was the appearance of strong
vibrations in 1000–1200 cmꢀ1 region for complexes. This was
one of the most powerful pieces of evidence that the BF2 moiety
was successfully grafted into the complexes, as the tetravalent B–F
bond possesses its characteristic frequency in this region [37].
Moreover, the B–N vibrations (ꢁ920 cmꢀ1) [38] with moderate
intensity appeared in the IR spectra of the complexes. The
occurrence of these peaks could be also attributed to the effects
of the coordination.
Additionally, the disappearance of the downfield hydroxyl
proton signals from the 1H NMR spectra of the complexes was
Fig. 1. Molecular structure and
p–p stacking interaction of complex 6c.

R.-Z. Ma et al. / Journal of Fluorine Chemistry 137 (2012) 93–98
95
them had the 1:4 integration resonances in accord with the natural
abundance of boron isotopes. According to Gardinier’s assumption,
the vanished B–F couplings in the above two cases could be
presumably due in part to the fast relaxation of the quadrupolar
boron nucleus [48,49]. Furthermore, it was demonstrated from
Table 1 that the 19F chemical shifts were sensitive to the electronic
environments of the quinolinyl and phenolic rings. For complexes
with electron-rich groups on either the phenolic or the quinolinyl
rings, their 19F signals exhibited the upfield shifts. For a given
group, as its capability of donating electrons increased, the 19F
signal of its corresponding complex had a greater downfield shift.
For complex 6g and 6h, the different sites of methyl group on the
phenolic ring produced the distinct 19F chemical shifts. Moreover,
the 11B–19F coupling constants of our BF2 complexes were in the
range of 15.0–18.8 Hz, which were smaller than those (26.3–
30.0 Hz) in our early reported cases [33] but agreed well with those
in Itoh’s
b-enaminoketone complexes (17.1–17.9 Hz) [40] and
Flores–Parra’s benzimidazole complex (16.9 Hz) [38].
2.4. Photophysical property investigations
Fig. 2. 1H NMR spectra of ligand 5i and complex 6i (CDCl3; proton of hydroxyl on 5i).
The UV–Vis absorption and fluorescence data of the ligands and
the complexes are listed in Table 1. For absorption spectra,
remarkable red shifts of absorption peaks occurring from the
ligands to the complexes could be observed. Such red-shift effect
might be attributed to the dramatically extended delocalization of
conjugative electrons due to the improved planarity in the
complexes, which led to the increased energy levels of the HOMOs
in ground states and the decreased energy levels of the LUMOs in
excited states. Moreover, all of the complexes had the high molar
another solid proof for the chelation of the BF2 group with the
ligands. Moreover, due to the generation of permanently positive
charges on the N atoms of the complexes, the resulted deshielding
effect occurred on the protons and the carbon atoms to some
extent through the conjugation. This resulted in the changes of
split features for some signals and downfield shifts of whole signals
in the 1H NMR spectrum of a given complex, compared with signals
of the corresponding ligand. The 1H NMR spectra of ligand 5i and
complex 6i are shown in Fig. 2. It clearly illustrated that all of the
signals moved toward down field to a discernible degree after the
coordination. Similarly, the downfield shifts of the 13C signals
could also be clearly observed in the 13C NMR spectra of the
complexes. However, the detailed assignment of the 1H and 13C
signals of complexes was much more difficult.
The 19F NMR spectra displayed a single quartet resonance in
nearly 1:1:1:1 area ratio, which revealed that the difluoroboron
chelates achieved more symmetric conformations in exchange-
averaged solution structures than in the ring-puckered static solid
structures due to the fast ring-flipping processes. This spectral
feature was similar to the results that were gained in Gardinier’s
detailed investigation on the 19F NMR spectra of BF2 complexes
[27]. In contrast to our BF2 complexes, the 19F NMR spectra of O,O
bidentate BF2 systems with 1,3-diketone ligands [39] showed two
sharp lines while and N,N bidentate BF2 complexes with
benzimidazole ligands [38] exhibited two broad signals. Both of
extinction coefficients, which suggested that largely permitted
p–
p
* electronic transitions occurred during the excitation of the
complexes. The absorption spectra of ligand 5i and complex 6i are
illustrated in Fig. 3.
Although the ligands did not show any fluorescence, the
complexes exhibited the intense fluorescence in their organic
solutions. The photographs of complex 6a, 6g and 6i in the CHCl3
solutions under daylight and a 365 nm ultraviolet lamp are shown
in Fig. 4.
The difference of fluorescence properties between the ligands
and the complexes was caused by the increase in rigidity of the 2-
(quinolin-2-yl)phenol skeleton of complexes due to the chelation
of the boron atoms. This reduced the loss of energy via
radiationless thermal vibrations [41]. A correlation could be
established between the quantum yields and the substituent
groups. Complexes with electron-donating groups had impres-
sively high quantum yields (6a, 6c, 6g–i) while those with
electron-withdrawing groups possessed less (6b, 6e) or even
Table 1
19F NMR chemical shifts and photophysical properties of ligands and complexes.a
Entry
labs (nm)b
Log
e
(L/(mol cm))
lem (nm)
Stokes shift (nm)
F
(%)d (solution)
d
(ppm) in 19F NMR
Ligand
Complex
Solid
Solutionc
a
b
c
d
e
f
361
353
348
343
350
361
355
351
357
385
381
380
363
382
396
387
382
394
4.43
4.20
4.13
4.00
3.98
4.36
4.06
4.23
4.44
454
484
487
–
441
477
463
–
56
96
83
–
81
31
48
<1
13
<1
57
77
86
ꢀ132.96
ꢀ131.07
ꢀ131.04
ꢀ130.06
ꢀ131.01
ꢀ131.99
ꢀ131.31
ꢀ131.08
ꢀ132.14
–
482
–
100
–
–
g
h
i
489
469
502
492
464
458
105
82
64
a
Both the absorption and emission spectra were measured in CHCl3 solution.
The absorption spectra were determined in ꢁ5.0 ꢂ 10ꢀ5 M solution.
The emission spectra were determined in ꢁ2.0 ꢂ 10ꢀ7 M solution.
The quantum yield was obtained by using quinine sulfate as the standard.
b
c
d

96
R.-Z. Ma et al. / Journal of Fluorine Chemistry 137 (2012) 93–98
Table 2
Photophysical properties of complex 6c in different solvents.
Entry
Solvent
labs (nm)a
lem (nm)b
Dl (nm)
1
2
3
4
5
6
7
Benzene
THF
381
377
376
376
365
364
345
461
464
465
470
481
487
–
80
87
CH2Cl2
89
Dioxane
Acetone
Acetonitrile
Methanol
94
116
123
–
a
The absorption spectra were determined in ꢁ5.0 ꢂ 10ꢀ5 M solution.
The emission spectra were determined in ꢁ2.0 ꢂ 10ꢀ7 M solution.
b
Unlike the typical BODIPYs which hardly fluoresce in solid state
[44], the complexes with fairly strong emission in solutions could
exhibit fluorescence in the solid state as well. It was assumed that
large Stokes shifts partly offset the self-quenching effect in the
solid state [45]. The emission maxima underwent the remarkable
Fig. 3. Spectra of ligand 5i and 6i (a: UV–Vis absorption of ligand 5i in CHCl3
solution; b: UV–Vis absorption of complex 6i in CHCl3 solution; c: fluorescence
emission of complex 6i in CHCl3 solution; d: fluorescence emission of complex 6i in
solid state).
red shifts in the solid state, which could be attributed to the
stacking induced by the more compact molecular aggregation in
the solid state.
The photophysical characteristics of complex 6c in various
solvents are tested and the results are listed in Table 2. The
absorption maximum underwent a hypsochromic shift with an
increase in solvent polarity. Such solvent-dependent behavior was
similar to the reported 1,3-enaminoketonatoboron difluorides [40]
p–p
nearly to zero (6d, 6f) quantum yields. It was assumed that the
groups on the phenolic rings were more influential on quantum
yields than those on the quinolinyl rings. For example, due to a
nitro group on the phenolic ring, both complexes 6f and 6d had
nearly zero quantum yields in spite of two methoxyl groups on the
quinolinyl ring for complex 6f. Similar case for complexes 6a and
6f, the quantum yields were dramatically reduced from 81% for 6a
to <1% for 6f when a nitro group was introduced on the phenolic
ring of complex 6f. Probably due to the heavy-atom effect which
caused an intersystem crossing to a nonradiative triplet state [42],
complex 6e which contained a bromo group at the quinolinyl ring
showed a largely decreased quantum yield. Undoubtedly, an
improved quantum yield could be gained whether an electron-
donating group was located on the quinolinyl or the phenolic ring.
It was interesting to notice that the complexes with the different
substitution positions of the same group on the phenolic ring gave
the different quantum yields, just like the case of complexes 6g
and 6h.
The emission spectrum of 6i in solution is presented in Fig. 3.
The excellent mirror image relationship between the absorption
and the emission spectra of the complexes demonstrated that the
distribution of the vibration energy levels in the S0 states was
analogous to that in the S1 excited states. Compared with the
widely observed small Stokes shifts of typical BODIPYs [43], the
large shift values in the range of 56–105 nm for our complexes
were quite impressive and promised to be helpful for the further
applications.
and implied that the peaks originated from the
p–p* transition.
Among all the investigated solvents, the blue shift up to 36 nm
could be observed between the absorption bands measured in
benzene and methanol.
The solvent-dependent correlation was also revealed from the
emission spectra and the solvent polarity, since it was found that the
peak gradually went through a bathochromic shift as the polarity of
the solvent increased. Among all the employed solvents, the longest
wavelength was at 487 nm in acetonitrile and the shortest one was
at 461 nm in benzene. For BF2 complexes, the excited states are
usually species with the larger dipole moments than the corre-
sponding ground states due to the rearrangement of the excited
electrons [46]. Therefore, the contribution of solvation to the
stabilization of excitedstate is much larger thanthat of ground state,
and such solvation effect is much greater in solvents with higher
polarity than in ones with lower polarity. Thus, a red-shift emission
is resulted when the electrons from the stabilized excited state fall
back to the ground state. However, the solution fluorescence was
completely quenched in methanol; this might be due to a strong
interaction to form an H-bond complex between the protic solvent
and the excited state [47]. The Stokes shifts turned over 80 nm and
the largest one was observed for 123 nm in acetonitrile. The large
Stokes shifts remarkably alleviated the self-absorption and were
beneficial for the performance of intense fluorescence.
Fig. 4. The photographs of samples in solution and in solid state.

R.-Z. Ma et al. / Journal of Fluorine Chemistry 137 (2012) 93–98
97
3. Conclusion
CDCl3):
1H, J = 7.6 Hz), 7.89 (m, 3H), 8.17 (t, 1H, J = 8.8 Hz), 8.51 (d, 1H,
J = 8.8 Hz), 8.95 (d, 1H, J = 9.2 Hz); 13C NMR (100 MHz, DMSO-d6):
117.08, 120.34, 120.47, 124.84, 124.92, 126.74, 127.64, 128.06,
128.41, 132.98, 135.64, 140.36, 142.81, 152.83, 156.39; Found: C,
66.83; H, 3.75; N, 5.16; Anal. Calc. for C15H10NOBF2: C, 66.90, H,
3.72; N, 5.20%.
d 7.04 (m, 1H), 7.08 (m, 1H), 7.54 (t, 1H, J = 8.0 Hz), 7.69 (d,
Herein we described the synthesis, structural analysis, spectral
and photophysical property studies of the novel BF2 complexes
bearing 2-(quinolin-2-yl)phenol ligands. The preparation of these
complexes was performed in good to excellent yields under mild
conditions with simple work-up procedures. These dyes displayed
solvent-sensitive absorption and emission features. The electronic
and site effect of substituents played an important role in the
quantum yields of the corresponding complexes. The strong
emission in solutions and in solid state as well as the impressive
large Stokes shifts and the high quantum yields made these
compounds as useful fluorescent materials. Further work on the
development of their potential applications is underway and will
be reported soon.
d
Complex 6d: 71% yield, m.p. > 300 8C; IR (KBr):
1553 (C55C), 1117 (B–F), 929 (B–N) cmꢀ1 1H NMR (400 MHz,
CDCl3): 7.35 (d, 1H, J = 8.8 Hz), 7.91 (t, 1H, J = 7.6 Hz), 8.11 (t, 1H,
n 1615 (C55N),
;
d
J = 7.6 Hz), 8.39 (d, 1H, J = 8.4 Hz), 8.47 (d, 1H, J = 9.2 Hz), 8.71 (d,
1H, J = 8.4 Hz), 8.96 (d, 1H, J = 8.4 Hz), 9.14 (d, 1H, J = 9.2 Hz), 9.26
(s, 1H); 13C NMR (100 MHz, DMSO-d6):
d 118.48, 118.78, 118.95,
124.31, 126.88, 126.94, 127.27, 128.06, 131.29, 139.07, 139.42,
143.56, 155.56, 155.43, 165.96; Found: C, 57.25; H, 2.90; N, 8.86;
Anal. Calc. for C15H9N2O3BF2: C, 57.31; H, 2.86; N, 8.91%.
4. Experimental
Complex 6e: 77% yield, m.p. 294–295 8C; IR (KBr):
n 1607 (C55N),
1555 (C55C), 1089 (B–F), 927 (B–N) cmꢀ1 1H NMR (DMSO-d6):
;
d
4.1. Apparatus and materials
6.99 (d, 1H, J = 8.8 Hz), 7.54 (d, 1H, J = 8.8 Hz), 7.70 (t, 1H,
J = 7.2 Hz), 7.87 (t, 1H, J = 8.4 Hz), 8.10 (t, 2H, J = 8.4 Hz), 8.37 (s,
1H), 8.45 (d, 1H, J = 8.8 Hz), 8.63 (d, 1H, J = 8.8 Hz); 13C NMR
All the reagents used were analytically pure and some
chemicals were further purified by recrystallization or distillation.
(100 MHz, DMSO-d6):
d 110.11, 118.58, 120.17, 120.92, 126.65,
Melting points were determined by
a
X-4 micro melting
126.90, 127.36, 127.99, 130.18, 131.12, 134.52, 138.77, 143.81,
156.07, 159.02; Found: C, 51.67; H, 2.52; N, 4.06; Anal. Calc. for
C15H9NOBF2Br: C, 51.73; H, 2.58; N, 4.02%.
instrument and the thermometer was uncorrected. The 1H NMR
(400 MHz), 13C NMR (100 MHz) and 19F NMR (376 MHz) spectra
were obtained on a Bruker Avance II DMX400 spectrometer using
CDCl3 or DMSO-d6 as the solvent. The 1H NMR and 13C NMR
experiments were carried out using trimethylsilane as the internal
standard and the 19F NMR spectra were recorded using CF3COOH
(ꢀ76.5 ppm) as the external standard. FT-IR spectra were
performed using KBr pellets on a Nicolet Avatar spectrophotome-
ter. The absorption spectra were measured on a Shimadzu UV
2501(PC)S UV–Vis spectrometer and the fluorescence spectra were
acquired on a Perkin-Elmer LS55 spectrophotometer.
Complex 6f: 84% yield, m.p. > 300 8C; IR (KBr):
1543 (C55C), 1095 (B–F), 929 (B–N) cmꢀ1 1H NMR (400 MHz,
CDCl3): 4.00 (s, 6H), 7.31 (d, 1H, J = 9.2 Hz), 7.75 (m, 1H), 8.04 (m,
1H), 8.39 (d, 1H, J = 7.6 Hz), 8.71 (m, 1H), 8.88 (d, 1H, J = 8.8 Hz),
9.14 (m, 1H); 13C NMR (100 MHz, DMSO-d6):
56.08, 56.13,
n 1621 (C55N),
;
d
d
102.67, 107.09, 116.33, 116.48, 120.06, 123.95, 125.20, 129.17,
136.48, 140.84, 142.58, 146.74, 150.49, 154.63, 159.25; Found: C,
54.47; H, 3.51; N, 7.42; Anal. Calc. for C17H13N2O5BF2: C, 54.53; H,
3.47; N, 7.48%.
Complex 6g: 91% yield, m.p. 264–265 8C; IR (KBr):
n 1620 (C55N),
4.2. General procedure for synthesis of complex (6a–i)
1560 (C55C), 1100 (B–F), 920 (B–N) cmꢀ1 1H NMR (DMSO-d6):
;
d
2.39 (s, 3H), 7.11 (d, 1H, J = 8.4 Hz), 7.35 (d, 1H, J = 8.8 Hz), 7.67 (m,
2H), 7.89 (m, 2H), 8.16 (d, 1H, J = 8.8 Hz), 8.49 (d, 1H, J = 8.8 Hz),
At room temperature, triethylamine (2 mmol) was added to the
solution of ligand (1 mmol) in benzene (3 mL), the resulted
mixture was stirred for 20 min and then boron trifluoride etherate
(3 mmol) was added. The mixture was stirred at 50 8C for 1 h and
yellowish solid was gradually precipitated out from the solution.
After cooling to room temperature, the mixture was filtrated and
the solid was washed several times by ether and dried in air. For
microanalysis, the solid was recrystallized in the benzene/hexane
mixture.
8.95 (d, 1H, J = 9.6 Hz); 13C NMR (100 MHz, DMSO-d6):
d 20.84,
117.11, 120.07, 124.71, 124.80, 124.89, 126.45, 127.56, 127.93,
128.37, 129.63, 132.89, 136.84, 142.64, 152.88, 154.33; Found: C,
67.91; H, 4.19; N, 5.01; Anal. Calc. for C16H12NOBF2: C, 67.82; H,
4.24; N, 4.95%.
Complex 6h: 94% yield, m.p. 257–259 8C; IR (KBr):
n 1616 (C55N),
1553 (C55C), 1086 (B–F), 909 (B–N) cmꢀ1 1H NMR (DMSO-d6):
;
d
2.40 (s, 3H), 6.84 (d, 1H, J = 8.0 Hz), 7.00 (s, 1H), 7.64 (t, 1H,
J = 7.6 Hz), 7.76 (d, 1H, J = 8.4 Hz), 7.87 (t, 2H, J = 7.6 Hz), 8.08 (d,
1H, J = 8.8 Hz), 8.43 (d, 1H, J = 8.8 Hz), 9.92 (d, 1H, J = 8.8 Hz); 13C
Complex 6a: 81% yield, m.p. 272–273 8C; IR (KBr):
1556 (C55C), 1110 (B–F), 923 (B–N) cmꢀ1 1H NMR (400 MHz,
CDCl3): 4.02 (s, 3H), 4.14 (s, 3H), 7.00 (m, 1H), 7.03 (m, 1H), 7.18
(m, 1H), 7.46 (t, 1H, J = 7.6 Hz), 7.82 (d, 1H, J = 8.0 Hz), 7.93 (d, 1H,
J = 8.8 Hz), 8.28 (m, 2H); 13C NMR (100 MHz, DMSO-d6):
56.20,
n 1622 (C55N),
;
d
NMR (100 MHz, DMSO-d6): d 21.25, 118.04, 118.17, 119.03,
121.91, 123.15, 127.44, 127.90, 128.03, 129.27, 132.05, 139.01,
143.96, 146.95, 152.32, 155.31; Found: C, 67.86; H, 4.28; N, 4.89;
Anal. Calc. for C16H12NOBF2: C, 67.82; H, 4.24; N, 4.95%.
d
56.62, 104.45, 105.70, 114.90, 116.38, 120.04, 120.29, 124.06,
126.12, 134.48, 137.67, 140.46, 149.81, 150.44, 154.55, 155.41;
Found: C, 61.88; H, 4.21; N, 4.19; Anal. Calc. for C17H14NOBF2: C,
61.98; H, 4.25; N, 4.25%.
Complex 6i: 83% yield, m.p. 243–244 8C; IR (KBr):
n 1617 (C55N),
1557 (C55C), 1109 (B–F), 910 (B–N) cmꢀ1 1H NMR (DMSO-d6):
;
d
3.88 (s, 3H), 6.62 (m, 2H), 7.61 (t, 1H, J = 7.6 Hz), 7.84 (m, 3H), 8.00
(d, 1H, J = 9.2 Hz), 8.37 (d, 1H, J = 9.2 Hz), 8.87 (d, 1H, J = 8.8 Hz);
13C NMR (100 MHz, DMSO-d6):
d 55.69, 102.51, 110.03, 116.69,
124.29, 124.38, 124.47, 126.98, 127.43, 128.08, 128.35, 132.73,
142.19, 152.65, 158.73, 166.06; Found: 64.28; H, 3.96; N, 4.72;
Anal. Calc. for C16H12NO2BF2: C, 64.20; H, 4.01; N, 4.68%.
Complex 6b: 76% yield, m.p. 262–264 8C; IR (KBr):
1586 (C55C), 1099 (B–F), 930 (B–N) cmꢀ1 1H NMR (400 MHz,
CDCl3): 7.04 (m, 1H), 7.19 (m, 1H), 7.54 (t, 1H, J = 7.6 Hz), 7.62 (d,
1H, J = 8.4 Hz), 7.83 (m, 2H), 8.13 (d, 1H, J = 8.8 Hz), 8.46 (d, 1H,
J = 8.8 Hz), 8.96 (m, 1H); 13C NMR (100 MHz, DMSO-d6):
117.31,
n 1614 (C55N),
;
d
d
120.43, 120.67, 124.18, 124.28, 124.38, 125.97, 126.87, 129.24,
129.47, 136.12, 139.66, 142.43, 153.57, 156.44; Found: C, 59.39; H,
3.01; N, 4.56; Anal. Calc. for C15H9NOBF2Cl: C, 59.31; H, 2.96; N,
4.61%.
Acknowledgments
We are grateful for the financial support from the Natural
Science Foundation of Zhejiang Province (Y4100034) and Zhejiang
Provincial Key Innovation Team (2010R50038).
Complex 6c: 86% yield, m.p. 264–265 8C; IR (KBr):
n 1609 (C55N),
1560 (C55C), 1085 (B–F), 922 (B–N) cmꢀ1 1H NMR (400 MHz,
;

98
R.-Z. Ma et al. / Journal of Fluorine Chemistry 137 (2012) 93–98
[24] D. Rohde, C.-J. Yan, L.-J. Wan, Langmuir 22 (2006) 4750–4757.
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