Synthesis, characterization and properties of furan-containing difluoroboron complexes

Article abstract of DOI:10.1039/c6ra20489a

Novel difluoroboron β-diketonate complexes F1-F4 bearing a furan unit were synthesized and fully characterized. The effects of different substituents on the photoluminescence and redox properties of these new BF₂ complexes were investigated systematically. The absorption and emission maxima of complexes F1-F4 were red-shifted compared to those of reference substance F0. Among them, the complexes F2 with a rigid naphthalene moiety and F3 with an electron donating methoxyl group demonstrated stronger fluorescent emission intensity, much higher quantum yields and longer lifetime values relative to other complexes. Cyclic voltammetry measurements revealed the reversible reduction waves of these BF₂ complexes. DFT calculations supported the structural and spectroscopic data and confirmed the compositions of frontier molecular orbitals in the BF₂ complexes. These new complexes exhibited different emission colors in solvent and might have potential applications in emitting devices.

Full text of DOI:10.1039/c6ra20489a

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DOI: 10.1039/C6RA20489A
Journal Name
ARTICLE
Synthesis, characterization and properties of furan‐
containing difluoroboron complexes
Received 00th January 20xx,
Accepted 00th January 20xx
Chun Liu*, Hao Zhang and Jianzhang Zhao
Novel difluoroboron β‐diketonate complexes F1‐F4 bearing a furan unit were synthesized and fully characterized. The
effects of different substituents on the photoluminescence and redox properties of these new BF2 complexes were
investigated systematically. The absorption and emission maxima of complexes F1‐F4 were red‐shifted compared to
those of reference substance F0. Among them, the complexes F2 with a rigid naphthalene moiety and F3 with an
electron donating methoxyl group demonstrated stronger fluorescent emission intensity, much higher quantum yields and
longer lifetime values relative to other complexes. Cyclic voltammetry measurements revealed the reversible reduction
waves of these BF2 complexes. DFT calculations supported the structural and spectroscopic data and confirmed the
compositions of frontier molecular orbitals in the BF2 complexes. These new complexes exhibited different emission
colors in solvent and might have potential applications in emitting devices.
DOI: 10.1039/x0xx00000x
www.rsc.org/
1. Introduction
sensitized solar cells.36 Compared with thiophene, furan displays
similar HOMO and LUMO levels, structural similarity and
a
Boron‐containing materials often show impressive optical properties.
considerable degree of aromaticity. Most promisingly, furan can be
obtained from a variety of renewable biological feedstocks and be
decomposed easily, which make it attractive in the synthesis of green
materials.37, 38 Based on these advantages, furan has been widely used
1‐5
Difluoroboron β‐diketonate complexes, as a special type of them, are
classic fluorescent molecules with excellent properties, such as large
molar extinction coefficients, high quantum yields, intense emission,
outstanding photostability, high electron affinities and sensitivity to
the surrounding medium.6‐16 Hence, their charming performances have
made them a research focus, and these materials have been widely
employed in various fields, including lasers,6 semiconductors,17
fluorescent EL emitters,18 near‐IR probes,19 photo sensitizers,9 and
oxygen10 and mechanical sensors.20 In the past few years, many efforts
have been made to design and synthesize new difluoroboron β‐diketonate
derivatives with high contrast and strong emission. For example, a series
of 1,3‐diketone difluoroboron complexes with mechanochromic
luminescence were successively reported by Fraser et al.20‐27 Some
other BF2 1,3‐diketone derivatives based on triphenylamine and
carbazole moeties were found by Lu et al.14, 16, 28 The literature reports
disclose that the photoluminescence properties of such complexes
depend strongly on the structures of the β‐diketonate ligands whether
the fluorogens are in solution or in the solid state.29‐31
39
as a building block for the construction of organic materials.33,
Therefore, a deep study of organic materials containing furan units
does make great sense. However, as far as we know, among the most
of the reported BF2 β‐diketonate complexes, there are only few reports
on the properties and application of boron difluoride derivatives
40
containing
a
furan ring.9,
Thus, the development of novel
difluoroboron complexes with a furan ring and the investigation on the
structure‐property relationship are of great interest.
Herein, we report the design and synthesis of novel furan ring‐bearing
difluoroboron β‐diketonate complexes F1‐F4 (Scheme 1). Firstly, the
unsubstituted BF2 complex F0 was prepared by two steps. Then, with a
reference to the molecular structure of F0, different substituents were
introduced into the aromatic ring to form difluoroboron complexes F1‐F4
,
whose luminescence properties in combination with computational
chemistry were studied.
Although a great deal of BF2 1,3‐diketone derivatives have been
reported, the design of smart complexes with high performances still
remains a great challenge. On the other hand, furan, as with thiophene,
is a kind of important five‐membered aromatic heterocycle and its
derivatives are often used for designing and synthesizing novel organic
materials in recent years.32‐35 In 2009, Lin and coworkers synthesized
new metal‐free dyes with a furan moiety which can be used for dye‐
State key laboratory of fine chemicals, Dalian univeristry of Technology, Linggong
Road 2, Dalian 116024, China. E‐mail: cliu@dlut.edu.cn; Tel：+86‐411‐84986182
Electronic Supplementary Information (ESI) available. CCDC 1486089 and 1482992.
For ESI and crystallographic data in CIF or other electronic format.
See DOI: 10.1039/x0xx00000x
Scheme 1 Molecular structures of BF2 complexes F0‐F4
.
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2. Results and discussion
n‐hexane into a solution of F2 or F3 in chloroform. ThVeiewstrAurtcictluerOesnlinoef
DOI: 10.1039/C6RA20489A
complexes F2 and F3 are presented in Fig. 1 unambiguously. Selected
2.1 Synthesis and characterizations
crystallographic data are provided in Table S1 (see ESI†) and key bonding
parameters are given in Table 1. In the two molecules, it was found that the
β‐diketonate skeleton is almost planar and two fluorine atoms are
distributed over the different side of the diketonate six‐member ring. The
sp3 orbits hydridized at boron centre of F2 appear as a distorted tetrahedron
with bond angles O5‐B1‐O6 of 110.6°(2), slightly bigger than what is
observed in complex F3 (109.71°), and the angles of F1‐B1‐F2 are 111.3o(2)
and 112.18 o, respectively. Their average B‐O bond lengths are 1.48 Å and
1.49 Å, whose values are in accordance with the common difluroboron
diketonate analogues (1.48 Å).9 The two B‐F bonds in F2 and F3 are different
from each other, and the average B‐F bond length of F2 (1.372 Å) is slighter
longer than that of F3 (1.368 Å). From these data, we can find that the
electron density of boron atom in F3 is richer than that of F2 due to the
strong electron‐donating methoxyl group. All other bond lengths are typical
for difluoroboron β‐diketonate complexes.31
The synthetic routes of 1,3‐diketone ligands LF0‐LF4 and BF2 complexes F0‐
F4 are illustrated in Scheme 2. Firstly, the compound 3 was synthesized via
the Claisen condensation reaction of 4'‐bromoacetophenone with methyl‐2‐
furoate according to the literature.41 Then, 1,3‐diketone ligands LF1‐LF4
were synthesized by the Suzuki‐Miyaura coupling reactions between the
obtained aryl bromide and the corresponding arylboronic acids. Finally, the
BF2 complexes F1‐F4 could be easily prepared from the 1,3‐diketone ligands
LF1‐LF4 and boron trifluoride‐diethyl etherate in anhydrous CH2Cl2.
Similarly, compound F0 was synthesized and used as a reference
complex in this study. The target compounds F1‐F4 were characterized by
1H NMR, 13C NMR, 19F NMR spectroscopy, EI(ESI)‐TOF mass spectrometry
and X‐ray crystallographic analysis.
2.2 X‐ray crystallographic analysis of BF2 complexes
To further confirm their molecular structures, complexes F2 and F3 were
subjected to X‐ray single‐crystal diffraction studies. Single crystals of F2 and
F3 suitable for X‐ray diffraction analysis were obtained by slow diffusion of
(a) NaH, dry THF, HCl, 24 h; (b) Pd(PPh3)4, K2CO3, THF/H2O, N2, 18 h; (c) dry CH2Cl2, N2, 2h.
Scheme 2 Synthetic routes and structures for BF2 complexes F0‐F4
.
Fig. 1 ORTEP plots of F2 (left) and F3 (right) (30% probability ellipsoids, hydrogen atom labels have been omitted for clarity).
2 | J. Name., 2012, 00, 1‐3
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Table 1 X‐ray selected bond lengths(Å) and angles(°) around the boron atom in the BF2 complexes.
View Article Online
DOI: 10.1039/C6RA20489A
Complexes
CCDC number
1486089
B1‐O5
1.484(3)
1.494
B1‐O6
1.485(3)
1.499
B1‐F1
B1‐F2
O5‐B1‐O6
F1‐B1‐F2
111.3(2)
112.18
F2
F3
1.378(3)
1.355
1.366(3)
1.381
110.6(2)
109.71
1482992
Fig. 2 Normalized UV‐vis absorption (left) and fluorescence emission (right) spectra of BF2 complexes F0‐F4; c = 1.0 × 10‐5 mol∙dm‐3 in CH2Cl2, 25 oC.
2.3 UV‐visible absorption spectra
2.4 Fluorescent emission spectra
The UV‐vis absorption and fluorescence emission spectra for The substituents had significant influence on emission properties of the
complexes F0‐F4 in CH2Cl2 at 25 °C are summarized in Fig. 2 and the complexes (Fig. 2 and Table 2). The results show that the emission maxima
corresponding photophysical data are recorded in Table 2. The results of these BF2 complexes are red‐shifted for F1 (446 nm), F2 (510 nm), F3 (533
display that there are strong broad absorption bands at 386‐422 nm in nm), F4 (446 nm) compared to the reference compound F0 (422 nm).
this series of complexes, which are attributed to
π‐ π* transitions in Compared with F1, the donor group (‐OCH3) modified F3 resulted in an 87
the conjugated ring system. The longest absorption maxima of nm red‐shift and the rigid naphthalene ring modified F2 demonstrated a 64
complexes F1‐F4 are red‐shifted compared to those of F0, which nm red‐shift. Such a big red‐shift in F2 or F3 is attributed to their larger π‐
indicated an effective
π
‐conjugation in the BF2‐chelating system due conjugation systems. However, the withdrawing group (‐F) modified F4
F1 and displayed nearly the same emission properties. F2 and F3 showed yellow‐
to the introduction of aryl group. The spectra of complexes F0
,
F4 exhibit similar absorption bands. And the spectra of complexes F2 green emission with quantum yields Фf 0.40 and 0.37, respectively. F0, F1
and F3 display much wider absorption bands owing to the introduction and F4 yielded blue emission in CH2Cl2 with quantum yields of 0.12, 0.30 and
of a rigid naphthalene ring and an electron‐donating methoxyl group, 0.29, respectively. These results exhibit that the introduction of different
respectively.
functional groups on the para position of phenyl ring has a significant effect
on the emission properties of BF2 complexes.
Table 2 Photophysical data of BF2 complexes.
Complexes
Absorptiona λabs (nm)
Emission λem (nm)
Фfb
τf (ns)c
1.43
1.01
2.95
2.83
1.01
∆λst(nm)d
F0
F1
F2
F3
F4
386 sh(0.31), 402 (0.37)
398 sh(0.32), 412 (0.37)
418 (0.32)
422
446
510
533
446
0.12
0.30
0.40
0.37
0.29
20
34
92
422 (0.41)
111
398 sh(0.22), 412 (0.25)
34
a Measured in CH2Cl2 at a concentration of 10‐5 M and extinction coefficients (Ɛmax × 104 M‐1∙cm‐1）are shown in parentheses. b In CH2Cl2 relative to
[Ir(ppy)2acac] (Ф = 0.34, λex = 400 nm, under nitrogen atmosphere). c Measured in CH2Cl2 at a sample concentration of ca. 10‐5 M and the excitation
wavelength was set at 405.2 nm for F0‐F4. All fluorescence lifetimes were fitted with single‐exponential decays unless indicated. d ∆λst = λem‐λabs
.
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2.5 Electrochemical properties
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DOI: 10.1039/C6RA20489A
The electro‐chemical properties of F0‐F4 were examined using cyclic
voltammetry and the redox curves are shown in Fig. 3, and the
corresponding frontier orbital energy levels based on the redox data are
summarized in Table 3. Using [Bu4N]PF6 (0.1 M) as the supporting electrolyte,
values were obtained at a scan rate of 100 mV∙s‐1 with a saturated calomel
electrode (SCE) as the standard.42 The voltammograms displayed reversible
reduction waves for the complexes F0‐F4. The halfwave reduction potential
(Eꢀꢃꢁ/ꢂꢄ) for F1, F2, F3 and F4 were measured at ‐0.94, ‐0.93, ‐0.96 and ‐0.94 V,
which were close to that of F0 (‐0.92 V). Besides, no oxidation waves were
observed up to +2.0 V versus SCE. It was observed that the differences
among these curves are very small. When the para position of the phenyl
ring was linked with different substituent groups, the electron affinities of
the BF2 complexes didn’t change markedly. The facts suggested that the
electron‐accepting units were mainly located at the BF2‐chelating six
members ring and the furan ring (Fig. 4).
Fig. 3 Cyclic voltammograms of BF2 complexes F0‐F4 in CH2Cl2.
F0
F1
F2
F3
F4
LUMO
LUMO
LUMO
LUMO
LUMO
‐2.66 eV
‐2.67 eV
‐2.66 eV
‐2.59 eV
‐2.71 eV
HOMO
HOMO
HOMO
HOMO
HOMO
‐6.54 eV
‐6.31 eV
‐5.98 eV
‐5.90 eV
‐6.32 eV
Fig. 4 HOMO and LUMO energies (eV) of F0‐F4 calculated by using DFT at the B3LYP/6‐31G(d) level.
Table 3 Electrochemical properties and frontier orbital energy levels of all BF2 complexes.
Complexes
HOMO[eV] experimentalb
LUMO [eV] experimentalc
Eg[eV] experimentald
ꢅꢀꢃꢁ/ꢂꢄ [V]a
‐0.92
F0
F1
F2
F3
F4
‐6.50
‐6.35
‐6.23
‐6.10
‐6.35
‐3.48
‐3.46
‐3.47
‐3.44
‐3.46
3.02
2.89
2.76
2.66
2.89
‐0.94
‐0.93
‐0.96
‐0.94
a 0.1 M [Bu4N]PF6 in CH2Cl2, scan rate 100 mV∙s‐1, measured using a saturated calomel electrode (SCE) as the standard. b ELUMO = EHOMO + Eg.
c ELUMO (eV) = ‐e(4.4 + ERED). d Calculated from the onset of the absorption spectra by equation of Eg = hc/λ (h = 6.63×10‐34 J∙s, c = 3×108 m/s, 1 eV = 1.60×10‐19
J, λ (nm), Eg (eV)).
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2.6 Theoretical calculations
ARTICLE
4. Experimental
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DOI: 10.1039/C6RA20489A
The structures of BF2 complexes were optimized using density functional
theory (DFT)43 with the B3LYP functional and 6‐31G(d) basis set to
investigate the electronic structures and understand the nature of excited
states of our new BF2 complexes. All these calculations were performed with
the Gaussian 09 software package.44 The HOMO and LUMO energy
diagram of F0‐F4 was shown in Figure 4. It is clear that the HOMO and
LUMO densities of F0 are delocalized over the whole molecule. Except
F0, the LUMO densities in other complexes are mainly localized at the
BF2‐chelating unit and furan ring. And the LUMO levels are close to each
other, revealing that LUMO levels are not mainly influenced by the
4.1. Chemicals and measurements
4‐Bromoacetophenone and methyl‐2‐furoate were purchased from Alfa
Aesar. Arylboronic acid was purchased from Trusyn Chem‐Tech Co., Ltd,
China. Other chemicals were purchased from commercial sources and used
1
without further purification. H NMR, 13C NMR and 19F NMR spectra were
recorded on a 400 MHzVarian Unity Inova spectrophotometer. Mass spectra
were recorded with EI‐TOF‐HRMS and ESI‐HRMS spectrometer. The
intensities of the crystal data were collected on a BrukerSMART APEX II CCD
diffractometer with graphite‐monochromated Mo‐Kα (λ = 0.71073 Å) using
the SMART and SAINT programs. UV/Vis absorption spectra were recorded
on a Lambda 750S UV/vis/NIR spctrometer (Perkin Elmer). Fluorescence
emission spectra were obtained by HITACHIF‐7000 fluorescence
spectrophotometer. Luminescent quantum yields were measured with
[Ir(ppy)2acac] (Ф = 0.34, λex = 400 nm, in CH2Cl2, under degassed conditions)
using a standard method. Fluorescence lifetimes were determined on a
steady and transient state fluorometer (FLS920, Edinburgh Analytical
Instruments Ltd.) in a dichloromethane solution with excitation wavelength
at 405.2 nm. Cyclic voltammograms of the BF2 complexes were recorded on
an electrochemical workstation (BAS100B/W, USA) at room temperature in
a 0.1 M [Bu4N]PF6 solution under argon gas protection.
substituents
. In contrast, introducing an electron‐donating methoxyl or
a
rigid group 2‐naphthy on the benzene ring affects the HOMO level
significantly, resulting in a marked decrease in energy gap. The results
in Figure 4 show that the HOMO and LUMO energy diagrams of F1 are
almost the same as F4, which demonstrates that the introduction of a
fluorine into the molecule does not affect the performance. According to
the DFT calculations, the HOMO‐LUMO energy gaps are in order of 3.88
eV (F0) > 3.64 eV (F1) > 3.61 eV (F4) > 3.32 eV (F2) > 3.31 eV (F3),
which is in agreement with the emission spectra. The HOMO‐LUMO
energy levels and gaps are also established by using the experimental
data (Table 3). The experimental results are nearly in line with the
calculation values. With regard to the measuring conditions and basis
sets of calculations, the appropriate differences between experiment
findings and calculated values are acceptable. To gain an insight into the
absorption spectra of the complexes F0 ‐ F4, time‐dependent DFT (TD‐DFT)
was also used to investigate the electronic transitions on the optimized
ground‐state geometries. All these calculations were performed with the
Gaussian 09 software package. The electronic transition bands of the
complexes F0 ‐ F4 were listed in Table 4. For all the BF2 complexes, the
maximal absorption band originated from the electronic transition of HOMO
‐> LUMO. And the calculated λabs values of five complexes were ranked in the
order of F3 > F2 > F4 > F1 > F0. Within the error allowed, the changing trend
did not appear to be much different from the experiment results (Table 2).
Table 4 Main orbital transitions calculated with TD‐DFT.
4.2 Synthesis of compound 3 and ligand LF0
1‐(4‐Bromophenyl)‐3‐(furan‐2‐yl)propane‐1,3‐dione( compound 3). Sodium
hydride (0.24 g, 10.0 mmol) was added rapidly to a dry flask containing a
solution of methyl‐2‐furoate (0.64 mL, 6.0 mmol) in 10 mL of dry THF. The
mixture was heated to 66 °C. 1‐(4‐Bromophenyl)ethanone (1.0 g, 5.0 mmol)
in 10 mL of dry THF was added dropwise to the mixture. The reaction
mixture was refluxed under an atmosphere of nitrogen for 24 h. Then the
mixture was poured into water and neutralized with hydrochloric acid until
pH = 7. And then the mixture was extracted three times with ethyl acetate.
After the solvent was removed, the residue was purified by column
chromatography (silica gel). Eluent: (ethyl acetate/petroleumether, v/v =
100/1), yellow solid, yield: 84%; 1H NMR (400 MHz, CDCl3, 25 °C) δ 7.96 (d,
J = 8.6 Hz, 1H), 7.83 (d, J = 1.9 Hz, 1H), 7.82 – 7.81 (m, 1H), 7.65 – 7.59 (m,
3H), 6.73 (s, 1H), 6.60 (dd, J = 3.6, 1.7 Hz, 1H) (Fig. S1).
Complexes
λcal a (nm)
365.44
397.01
438.21
439.93
401.13
f b
Composition c (%)
H ‐> L (70)
F0
F1
F2
F3
F4
0.9468
1.2008
0.6045
0.9196
1.1682
1‐(Furan‐2‐yl)‐3‐phenylpropane‐1,3‐dione( ligand LF0). Sodium hydride
(0.048 g, 2.0 mmol) was added rapidly to a dry flask containing a solution of
methyl‐2‐furoate (0.128 mL, 1.2 mmol) in 10 mL of dry THF. The mixture was
heated to 66 °C. Acetophenone (0.12 g, 1.0 mmol) in 10 mL of dry THF was
added dropwise to the mixture. The reaction mixture was refluxed under an
atmosphere of nitrogen for 24 h. Then the mixture was poured into water
and neutralized with hydrochloric acid until pH = 7. And then the mixture
was extracted three times with ethyl acetate. After the solvent was removed,
the residue was purified by column chromatography (silica gel). Eluent:
(ethyl acetate/petroleumether, v/v = 100/1), yellow solid, yield: 75%. 1H
NMR (400 MHz, CDCl3, 25 °C) δ 7.96 (d, J = 7.2 Hz, 2H), 7.61 (d, J = 0.9 Hz,
1H), 7.54 (t, J = 7.3 Hz, 1H), 7.47 (t, J = 7.4 Hz, 2H), 7.24 (d, J = 3.5 Hz, 1H),
6.76 (s, 1H), 6.58 (dd, J = 3.5, 1.7 Hz, 1H) (Fig. S2).
H ‐> L (71)
H ‐> L (69)
H ‐> L (69)
H ‐> L (71)
a Calculated electronic transition band in CH2Cl2. b Calculated oscillator
strength in CH2Cl2. c H represents HOMO and L represents LUMO.
3. Conclusions
In summary, new furan ring‐bearing BF2 complexes F1‐F4 have been
prepared and their structures were characterized by means of NMR, MS and
single crystal diffraction, and their spectroscopic and electrochemical
properties were investigated. Among these new compounds, the absorption
and emission maxima of F2 and F3 were considerably red‐shifted compared
to those of F0 and F1 owing to the extended π‐conjugation system. Also,
F2 and F3 exhibited the stronger fluorescent emission intensity, much higher
quantum yields and longer lifetime values relative to other complexes.
These complexes have excellent optical and electrochemical
properties and may be served as new emitting materials. Further
investigations on their potential applications are in progress.
4.3 Synthesis of ligands LF1‐LF4
A mixture of corresponding arylboronic acids (1.0 mmol), compound 3
(0.147 g, 0.5 mmol), and K2CO3 (0.14 g, 1.0 mmol) in distilled water (9 mL)
and THF (15 mL) was charged and then Pd(PPh3)4 (20 mg) was added under
an atmosphere of nitrogen. The mixture was refluxed for 24 h under
nitrogen. After cooling to room temperature, the mixture was extracted
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δ 182.2, 171.2, 149.5, 148.0, 139.2, 130.6, 129.5, 129.1, 128.9, 128.8, 127.7,
127.4,121.6, 114.3, 92.5 (Fig. S16). 19F NMR (376 MHz, CDViCewl A2rt5icle°CO)nlδine‐
with ethyl acetate for three times. Then the organic phase was combined
and dried over anhydrous Na2SO4. Removing the solvent under reduced
pressure, the residue was purified by column chromatography (silica gel).
DOI: 10.1039/C6RA20489A
3,
140.34, ‐140.40 (Fig. S17). 11B NMR (160 MHz, CDCl3) δ 1.07 (Fig. S18).
HRMS‐EI (m/z): calcd for C19H13BF2O3 [M]+ 338.0926; found 338.0934 (Fig.
S19). Anal. Calcd. for C19H13BF2O3: C, 67.49; H, 3.88; found: C, 67.62; H, 3.78.
1‐([1,1'‐biphenyl]‐4‐yl)‐3‐(furan‐2‐yl)propane‐1,3‐dione (ligand LF1).45 Elue
nt:(ethyl acetate/petroleumether, v/v = 300/1), yellow solid, yield: 73%. 1H
NMR (400 MHz, CDCl3, 25 °C) δ 8.04 (d, J = 8.3 Hz, 2H), 7.71 (d, J = 8.3 Hz, 3
H), 7.68 – 7.59 (m, 3H), 7.48 (t, J = 7.5 Hz, 2H), 7.40 (t, J = 7.3 Hz, 1H), 6.81 (s,
1H), 6.60 (dd, J = 3.3, 1.5 Hz, 1H) (Fig. S3).
2,2‐difluoro‐4‐(furan‐2‐yl)‐6‐(4‐(naphthalen‐2‐yl)phenyl)‐2H‐1,3,2‐
dioxaborinin‐1‐ium‐2‐uide (complex F2). Yellow solid, yield: 51%. H NMR
1
(400 MHz, CDCl3, 25 °C) δ 8.26 (d, J = 8.6 Hz, 2H), 8.15 (s, 1H), 7.93 (ddd,
J = 15.9, 11.0, 6.8 Hz, 5H), 7.83 – 7.75 (m, 2H), 7.63 (d, J = 3.7 Hz, 1H),
7.58 – 7.50 (m, 2H), 7.16 (s, 1H), 6.75 (dd, J = 3.7, 1.7 Hz, 1H) (Fig. S20).
13C NMR (100 MHz, CDCl3, 25 °C) δ 182.2, 171.2, 149.4, 147.9, 136.5,
133.5, 133.3, 130.6, 129.6, 128.9, 128.5, 127.9, 127.7, 126.9, 126.7,
1‐(furan‐2‐yl)‐3‐(4‐(naphthalen‐2‐yl)phenyl)propane‐1,3‐dione (ligand LF2).
Eluent: (ethyl acetate/petroleumether, v/v = 200/1), yellow solid, yield: 73%.
1H NMR (400 MHz, CDCl3, 25 °C) δ 8.15 – 8.03 (m, 2H), 8.01 – 7.81 (m, 5H),
7.79 (d, J = 8.6 Hz, 1H), 7.76 – 7.65 (m, 1H), 7.64 (s, 1H), 7.59 – 7.47 (m, 3H),
6.84 (s, 1H), 6.61 (s, 1H) (Fig. S4). 13C NMR (100 MHz, CDCl3, 25 °C) δ 182.1,
177.6, 167.7, 151.1, 146.1, 145.1, 137.3, 133.6, 133.5, 133.0, 132.3, 130.9,
129.0, 128.8, 128.7, 128.3, 127.7, 127.6, 127.5, 126.6, 126.5, 126.3, 125.2,
115.8, 112.7, 92.7 (Fig. S5) HRMS‐ESI (m/z): calcd for C23H16O3 [M+Na] +
363.0997; found [M+Na]+363.0991 (Fig. S6).
124.9, 121.6, 114.3, 92.5 (Fig.S21).
19F NMR (376 MHz, CDCl3, 25 °C) δ ‐
140.36, ‐140.43 (Fig. S22). 11B NMR (160 MHz, CDCl3) δ 1.16 (Fig. S23).
HRMS‐EI (m/z): calcd for C23H15BF2O3 [M]+ 388.1082; found 388.1078 (Fig.
S24). Anal. Calcd. for C23H15BF2O3: C, 71.17; H, 3.89; found: C, 71.03; H, 3.82.
2,2‐difluoro‐4‐(furan‐2‐yl)‐6‐(4'‐methoxy‐[1,1'‐biphenyl]‐4‐yl)‐2H‐1,3,2‐
dioxaborinin‐1‐ium‐2‐uide (complex F3). Yellow solid, yield: 64%. H NMR
1
(400 MHz, CDCl3, 25 °C) δ 8.18 (d, J = 8.6 Hz, 2H), 7.79 (d, J = 0.8 Hz, 1H),
7.73 (d, J = 8.6 Hz, 2H), 7.61 (dd, J = 11.1, 6.2 Hz, 3H), 7.11 (s, 1H), 7.02 (d, J =
8.8 Hz, 2H), 6.73 (dd, J = 3.7, 1.6 Hz, 1H), 3.88 (s, 3H) (Fig. S25). 13C NMR (100
MHz, CDCl3, 25 °C) δ 182.2, 170.9, 167.7, 160.5, 149.3, 148.5, 147.6,
131.5, 130.9, 129.9, 129.6, 128.8, 128.5, 127.0, 121.4, 114.6, 114.2,
92.4, 55.4 (Fig. S26). 19F NMR (376 MHz, CDCl3, 25 °C) δ ‐140.50, ‐140.57 (Fig.
S27). 11B NMR (160 MHz, CDCl3) δ 1.06 (Fig. S28). HRMS‐ESI (m/z): calcd for
C20H15BF2O4 [M+Na]+ 391.0927; found [M+Na]+ 391.0921 (Fig. S29). Anal.
Calcd. for C20H15BF2O4: C, 65.25; H, 4.11; found: C, 65.05; H, 4.22.
1‐(furan‐2‐yl)‐3‐(4'‐methoxy‐[1,1'‐biphenyl]‐4‐yl)propane‐1,3‐dione (ligand
LF3). Eluent: (ethyl acetate/petroleumether, v/v = 200/1), yellow solid, yield:
69%. 1H NMR (400 MHz, CDCl3, 25 °C) δ 8.02 (d, J = 8.4 Hz, 2H), 7.67 (d, J =
8.4 Hz, 2H), 7.66 – 7.55 (m, 4H), 7.01 (dd, J = 8.8, 2.2 Hz, 2H), 6.80 (s, 1H),
6.60 (dd, J = 3.4, 1.6 Hz, 1H), 3.87 (s, 3H) (Fig. S7). 13C NMR (100 MHz, CDCl3,
25 °C) δ 182.1, 177.5, 151.1, 146.1, 145.1, 139.9, 133.5, 130.9, 128.9, 128.8,
128.1, 127.5, 127.3, 127.2, 115.7, 112.7, 92.7, 31.6 (Fig. S8). HRMS‐ESI (m/z):
calcd for C20H16O4 [M+Na]+ 343.0942; found [M+Na]+ 343.0947 (Fig. S9).
2,2‐difluoro‐6‐(4'‐fluoro‐[1,1'‐biphenyl]‐4‐yl)‐4‐(furan‐2‐yl)‐2H‐1,3,2‐
dioxaborinin‐1‐ium‐2‐uide (complex F4). Yellow solid, yield: 64%. H NMR
1
1‐(4'‐fluoro‐[1,1'‐biphenyl]‐4‐yl)‐3‐(furan‐2‐yl)propane‐1,3‐dione
(ligand
(400 MHz, CDCl3, 25 °C) δ 8.20 (d, J = 8.2 Hz, 2H), 7.81 (s, 1H), 7.73 (d, J = 8.3
Hz, 2H), 7.64 (dd, J = 7.7, 4.7 Hz, 3H), 7.19 (t, J = 8.5 Hz, 2H), 7.13 (s, 1H),
6.83 – 6.69 (m, 1H) (Fig. S30). 13C NMR (100 MHz, CDCl3, 25 °C) δ 182.2,
171.2, 149.5, 148.0, 139.2, 130.9, 130.6, 129.5, 129.1, 128.9, 128.8, 127.7,
127.3, 121.6, 114.3, 92.5 (Fig. S31). 19F NMR (376 MHz, CDCl3, 25 °C) δ ‐
140.34, ‐140.40, ‐140.97 (Fig. S32). 11B NMR (160 MHz, CDCl3) δ 1.07 (Fig.
S33). HRMS‐EI (m/z): calcd for C23H15BF2O3 [M]+ 356.0832; found 356.0833
(Fig. S34). Anal. Calcd. for C20H15BF2O4: C, 64.08; H, 3.40; found: C, 64.27; H,
3.53.
LF4). Eluent: (ethyl acetate/petroleumether, v/v = 200/1), yellow green solid,
yield: 68%. 1H NMR (400 MHz, CDCl3, 25 °C) δ 8.04 (d, J = 8.4 Hz, 2H), 7.73 –
7.63 (m, 4H), 7.62 – 7.57 (m, 2H), 7.17 (t, J = 8.6 Hz, 2H), 6.81 (s, 1H), 6.61
(dd, J = 3.5, 1.6 Hz, 1H) (Fig. S10). 13C NMR (100 MHz, CDCl3, 25 °C) δ 182.1,
181.2, 177.5, 152.4, 151.1, 147.7, 146.1, 145.7, 144.1, 134.5, 133.6, 129.6,
129.0, 128.9, 128.8, 128.4, 127.6, 127.5, 127.2, 116.0, 115.8, 112.7, 92.7 (Fig.
S11). HRMS‐EI (m/z): calcd for C19H13FO3 [M]+ 308.0849; found 308.0847 (Fig.
S12).
4.3 Synthesis of complexes F0‐F4
4.4 X‐ray structural analysis
Boron trifluoride–diethyl etherate (0.13 mL, 1.0 mmol) was added to a
solution of the corresponding ligand (0.2 mmol) in dry dichloromethane
(15 mL) under nitrogen. The reaction mixture was heated to 60 oC and
stirred for 2 h. After removal of the solvent, the residue was purified
by chromatography on silica gel (petroleumether/dichloromethane,
v/v = 1/1).
Crystals suitable were grown by slow diffusion of n‐hexane into the
respective solutions of F2 or F3 in chloroform at room temperature.
Reflection data were collected at 296 (2) K using a graphite monochromator
with Mo‐K radiation (λ= 0.71073 Å) on a Bruker SMART APEX(II) CCD
α
diffractometer. The collected frames were processed with the software
SAINT and an absorption correction (SADABS) was used to the collected
reflections. The resulting structure was solved by the Direct or Patterson
methods (SHELXTL 97) in conjunction with standard difference Fourier
techniques and then refined by full‐matrix least‐square technique on F2. All
2,2‐difluoro‐4‐(furan‐2‐yl)‐6‐phenyl‐2H‐1,3,2‐dioxaborinin‐1‐ium‐2‐uide
1
(complex F0).46 Yellow solid, yield: 79%. H NMR (400 MHz, CDCl3, 25 °C) δ
8.15 (d, J = 7.6 Hz, 1H), 7.80 (s, 1H), 7.69 (d, J = 7.3 Hz, 1H), 7.63 (d, J = 3.7 Hz,
1H), 7.56 (t, J = 7.8 Hz, 1H), 7.11 (s, 1H), 6.75 (dd, J = 3.7, 1.5 Hz, 1H) (Fig. hydrogen atoms were positioned geometrically and non‐hydrogen atoms
S13). 11B NMR (160 MHz, CDCl3) δ 1.06 (Fig. S14). Anal. Calcd. for C13H9BF2O3:
were refined anisotropically. Relevant crystal data for the structures are
C, 59.59; H, 3.46; found: C, 59.43; H, 3.28.
collected in the ESI.†
6‐([1,1'‐biphenyl]‐4‐yl)‐2,2‐difluoro‐4‐(furan‐2‐yl)‐2H‐1,3,2‐dioxaborinin‐1‐
ium‐2‐uide (complex F1). Yellow solid, yield: 64%. 1H NMR (400 MHz, CDCl3,
25 °C) δ 8.22 (d, J = 8.6 Hz, 2H), 7.83 – 7.75 (m, 3H), 7.70 – 7.66 (m, 2H), 7.63
(d, J = 3.7 Hz, 1H), 7.51 (dd, J = 9.9, 4.7 Hz, 2H), 7.45 (d, J = 7.2 Hz,1H), 7.14 (s,
1H), 6.75 (dd, J = 3.7, 1.7 Hz, 1H) (Fig. S15). 13C NMR (100 MHz, CDCl3, 25 °C)
Acknowledgements
The authors thank the financial support from the National Natural Science
Foundation of China (21276043 and 21421005) and Open Fund of Key
6 | J. Name., 2012, 00, 1‐3
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DOI: 10.1039/C6RA20489A
Graphical Abstract
Synthesis, characterization and properties of
furan-containing difluoroboron complexes
Chun Liu*, Hao Zhang and Jianzhang Zhao
[*] Dr. C. Liu, Corresponding Author.
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Linggong Road 2, Dalian
116024, China.
Tel.: +86-411-84986182
E-mail: cliu@dlut.edu.cn
New β-diketonate difluoroboron complexes (F1-F4) containing a furan ring have been developed, and
their luminescence properties have been investigated systematically.