Highly Fluorescent Red-Light Emitting Bis(boranils) Based on Naphthalene Backbone

Article abstract of DOI:10.1021/acs.joc.7b01001

Ten bis(boranils) differently substituted at the boron atom and iminophenyl groups were synthesized from 1,5-dihydroxynaphthalene-2,6-dicarboxaldehyde using a simple one-pot protocol. Their photophysical properties can be easily tuned in a wide range by the variation of substituents. Their absorption and emission spectral bands are significantly red-shifted (λ_max = 495-590 nm, λ_em = 533-683 nm) when compared with simple boranils, whereas fluorescence quantum yields are strongly improved to reach 83%. The attachment of pendant NO₂ and NEt₂ groups at the opposite positions of the π-conjugated bis(boranil) scaffold resulted in the formation of an unprecedented system featuring push-pull architecture.

Full text of DOI:10.1021/acs.joc.7b01001

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Note
Highly fluorescent red-light emitting
bis(boranils) based on naphthalene backbone
Mateusz Urban, Krzysztof Durka, Piotr Jankowski, Janusz Serwatowski, and Sergiusz Lulinski
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b01001 • Publication Date (Web): 03 Jul 2017
Downloaded from http://pubs.acs.org on July 3, 2017
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Highly fluorescent red-light emitting bis(boranils) based on naphthalene
backbone
[
a]
[a]
[b]
[a]
Mateusz Urban, Krzysztof Durka, * Piotr Jankowski, Janusz Serwatowski, Sergiusz
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[
a]
Luliński *
[
a]
Department of Physical Chemistry, and Chair of Inorganic Chemistry and Solid State
[
b]
Technology, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3,
0-664 Warszawa, Poland
0
E-mail:kdurka@gmail.com, serek@ch.pw.edu.pl
th
Dedicated to Prof. Tadeusz Marek Krygowski on the occasion of his 80 birthday
Abstract: Ten bis(boranils) differently substituted at the boron atom and iminophenyl groups
were synthesized from 1,5-dihydroxynaphthalene-2,6-dicarboxaldehyde using a simple one-
pot protocol. Their photophysical properties can be easily tuned in a wide range by the
variation of substituents. Their absorption and emission spectral bands are significantly red-
shifted (λmax = 495-590 nm, λem = 533-683 nm) when compared with simple boranils,
whereas fluorescence quantum yields are strongly improved to reach 83%. The attachment of
2 2
pendant NO and NEt groups at the opposite positions of the π-conjugated bis(boranil)
scaffold resulted in the formation of an unprecedented system featuring push-pull
architecture.
Currently, there is an increasing interest in various organoboron compounds due to
1
their specific optoelectronic properties. This enables their wide utilization in materials
chemistry with a special emphasis on the construction of optical and optoelectronic devices
including organic light emitting diodes (OLEDs), organic field-effect transistors as well as
2
photoresponsive materials. Specifically, boron complexes with (N,O)-bidentate Schiff base
ligands (boranils) have been described as promising fluorescent dyes with potential for bio-
3
labeling purposes and suitable emitters for electroluminescent devices (A, B Scheme 1). Free
ligands can be easily obtained by condensation reactions of appropriate salicylaldehydes and
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anilines. Since the starting materials are readily available, the access to a wide selection of
functionalized boranils including multicenter boron complexes is possible in a relatively
4
simple manner. On the other hand the photophysical properties of the reported multiboron
Schiff-base complexes are similar to their monoboron analogues with absorption and emission
maxima in the range of 350-450 nm and 470-520 nm, respectively, and quantum yields of
emission (QY) usually not exceeding 30%.
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Scheme 1. Mono- and mulitiboron complexes with salicydeneanilines.
A continuous search for related systems with improved optical properties has
prompted us to synthesize a group of strongly fluorescent red-light emitting bis(boranils) 1-10
derived from a ditopic tetradentate 1,5-dihydroxy-2,6-bis(N-phenyliminomethylene)-
naphthalene ligand. 1,5-Dihydroxynaphthalene-2,6-dicarboxaldehyde 14 is a key compound
en route to targeted Schiff base ligands and final boron complexes. It was obtained from
cheap and already accessible substrates (as 1,5-dihydroxynaphthalene) in a four-step protocol
with a satisfactory total yield of 56% (Scheme 2). Having the dialdehyde 14 in hand, we have
synthesized two referential bis(boranil) complexes bearing substituents frequently
encountered at the boron atom – fluorine atoms (1) or phenyl groups (2). It was expected that
the fluorination of B-phenyl rings will improve the stability of the complex due to an
5
increased boron Lewis acidity. Thus, we have prepared 2,6-difluorophenyl- (3) and
pentafluorophenyl (4) analogues. Further modification was achieved by rigidifying the
organoboron scaffold, which would restrict the rotation of substituents attached to boron atom
and limit the fluorescent quenching. Consequently, 10-hydroxyphenoxaborin was used as a
precursor for the synthesis of 5. In addition, the optical properties of the system can be easily
tuned by changing the length of the π-conjugated skeleton or by its substitution with electron-
withdrawing or electron-donating functional groups. Thus, we have obtained symmetrical
complexes 6-9 bearing two NO
2
(6, 7) or two NEt
2
(8, 9) groups. Finally, we have also
and NEt
obtained the push-pull system 10 derived from a Schiff base substituted with NO
2
2
located at the opposite terminal positions of the molecule. Complexes 2-9 were obtained in a
one-pot three-component reaction between dialdehyde 14, aniline and diarylborinic ester
2
R BOEt (or 10-hydroxyphenoxaborin). The advantage of this procedure over the commonly
applied multistep protocol is based on the fact that it omits the isolation of bis(anils) showing
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very weak solubility in organic solvents which hampers their conversion to targeted
bis(boranils). Exceptionally, the synthesis of 1 required the isolation of bis(anil) 15, which
was treated with nBuLi and BF
was isolated in the first step, and it was further reacted in one-pot protocol with 4-nitroaniline
and Ph BOEt. The isolation of final pure complexes is very simple as they are readily
3 2
OEt . In the case of push-pull system 10, the monoimine 16
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obtained after precipitation from solution in good yields (56-95%).
Scheme 2. Synthesis of bis(boranil) complexes 1-10.
The proper selection of organic materials for the OLED construction is not simple as
there are many parameters that may determine its final performance. The desired emitters
should be characterized by good optical parameters (high quantum yield), sufficient thermal,
hydrolytic and electrochemical stability as well as good solubility. The performed DSC
analyses (Figure S2-21, SI) show that the obtained diboron complexes are thermally stable as
evidenced by their high decomposition temperatures (270-440 °C). From the analysis of time-
depending UV-Vis absorption spectra (Figure S57-67, SI) it is evident, that the bis(boranil)s
3
e
are significantly more stable than monoboranils in respective dilute solutions, although for
some complexes the changes in band intensities are observed only after few days. This is
especially noticeable for nitro complexes 6 and 10. This naturally comes from the fact that
NO
2
functional group decreases the imine nitrogen basicity leading to weakening of N–B
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dative bond. On the other hand the fluorination of B-phenyl groups significantly increases
6 5 2 6 3
Lewis acidity of boron atoms. Thus, compounds 3, 4, 7 and 9 bearing two C F or 2,6-F C H
substituents at each boron centre are stable in solutions as their corresponding UV-Vis spectra
remain almost time independent. The CV measurements (Figure S22-S26) show that studied
bis(boranil) complexes are significantly more stable toward electrochemical oxidation and
reduction than monoboranils A and B. The most stable are diamino complexes 8 and 9 which
display reversible two-electron oxidation and reduction waves. The solubility of bis(boranils)
strongly varies with the N-phenyl and B-phenyl substitution pattern ranging from weakly
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soluble BF
polarity solvents such as PhMe). In general we have found that all complexes are soluble in
DMF and pyridine. Furthrmore, the introduction of C groups generally improves the
2
complex 1 to well soluble derivatives 4 and 8 (they are soluble even in the low
6 5
F
solubility although 9 is less soluble than its non-fluorinated analogue 8.
The optical properties of obtained complexes were investigated by UV-Vis absorption
and photoluminescence spectroscopy (Figure 1, Table 1). In order to elucidate the
solvatochromic nature of emission bands, the emission spectra were recorded in
dichloromethane and PhMe solutions. To provide an additional insight into electronic
structures of studied diboron complexes and the features of molecular orbitals involved in the
6
7
electronic transitions, we have performed TD-DFT calculations on the PBE0 /6-31G(d,p)
level of theory.
The studied bis(boranil) complexes present long-wave absorption bands in PhMe and
CH
coefficients for 1-5 are relatively high ranging from 12600-13600 M cm in PhMe and
2 2
Cl in range of 495-584 nm and 497-589 nm, respectively. The molar absorption
-
1
-1
-1
-1
1
3800-15400 M cm in CH
at the N-aryl moieties (up to 38400 M cm in PhMe and 44500 M cm in CH
Depending on the substitution pattern the longest-wavelength emission maxima span in range
of 538-664 nm in PhMe and 533-683 nm in CH Cl with QY reaching 83% in PhMe (7) and
1% in CH Cl (5). Both the absorption and emission bands are significantly red-shifted in
comparison with vast majority of reported boranils. For instance, the BF
2
Cl
2
, and significantly increase after introduction of NEt
2
groups
-
1
-1
-1
-1
2
Cl ).
2
2
2
8
2
2
3
,4
2
2
(1) and BPh (2)
bis(boranil) complexes absorb and emit at the wavelengths shifted by ca. 130 nm (absorption)
and ca. 65 nm (emission) with respect to corresponding monoboron complexes A and B. The
bathochromic shift of absorption and emission bands can be attributed to an increased length
of the π-conjugated skeleton. Another important feature of studied bis(boranils) are moderate
-
1
Stokes shifts (ΔS) values of 1450-2800 cm . They are significantly smaller than ΔS values
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-1
obtained for A and B monoboranils (ca. 6000 cm ), reflecting a higher structural rigidity of
former complexes.
Among studied systems compound 1 is characterized by the shortest wavelength of
absorption and emission (λabs = 495 nm, λem = 533 nm in CH
2
2
Cl ) accompanied by the
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-1
smallest Stokes shift value of 1440 cm . The introduction of BPh
2
(2) leads to the substantial
2
c,3d,8
red-shift of absorption and emission bands (λabs = 529 nm, λem = 594 nm in CH
2
Cl
2
).
In
addition, the fluorescence quantum yield increases from 52% (1) to 76% (2) in CH
2
Cl
2
.
Importantly, in both cases these QYs significantly exceed the values obtained for respective
monoboron complexes A (3%) and B (7%). According to expectations, the further
modification of organoboron core (either by introducing the fluorine substituents or oxaborine
scaffold) only slightly influences the absorption and emission wavelengths (Table 1, 2-5).
Simultaneously, the QYs are high for these systems (70-81%).
Figure 1. Absorption spectra of 1-5 (a) and 6-10 (b) in PhMe. Normalized emission spectra of
1
-5 (c), 6-10 (d) recorded in PhMe at room temperature. Photographs of 1-10 in DCM (e).
2 2
Table 1. Photophysical data for 1-10 in CH Cl /PhMe, respectively.
[a]
-
1
-1
QY
λ
abs / nm
ε / M cm
λem / nm
/
%
A
368
400
8100
4600
14700/-
466
534
3
7
3e
B
1
2
3
4
5
6
[
d]
495/497
529/536
534/538
533/531
545/549 [
541(565)
533/538 52/54
13900/12700 594/602 76/70
14700/13200 585/592 81/76
15400/12600 580/580 80/81
13800/13600 599/605 81/77
[c]
b]
[
b] 16000/-
642/643 48/63
/
536(570)
7
553/549
13100/18200 620/613 66/83
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560(576)
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589(604)
/584
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/
[
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[
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[
a] Fluorescence standard: Coumarin 153 (A, 1), Rhodamine 6G (2-4), Rhodamine 101 (5-7), Cresyl
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violet (8-10); [b] Values in brackets obtained after band deconvolution using second derivative
method; [c] Due to insufficient solubility, ε values were not determined; [d] It was impossible to
obtain the reliable value due to very weak fluorescence.
TD-DFT calculations show that for 1-5 vertical excitations are observed
predominantly due to electron transition from the orbital (usually HOMO) located at the
central part of the molecule (naphthalene ring and O–B–N chelate moieties) and LUMO
orbital which is delocalized over the entire π -conjugated skeleton. The energy gap of
bis(boranils) can be further modified by extending the conjugation with electron-withdrawing
NO
2
(6, 7) or electron-donating NEt
2
(8, 9) functional groups attached at the C4-position of
substituent stabilizes the HOMO and LUMO
the N-phenyl ring. The introduction of 4-NO
2
energy levels, but since the LUMO is delocalized over entire skeleton and HOMO is restricted
to the centre of the molecule, the lowering of LUMO orbital is more pronounced. Thus,
HOMO-LUMO energy gap decreases leading to red-shifted absorption and emission with
respect to 1-5 (6: λabs = 565 nm, λem = 642 nm in CH
group (8, 9) pushes the HOMO and LUMO energy levels up, however as HOMO orbital is
additionally extended on N-(4-NEt )Ph groups its elevation is more pronounced than LUMO
inducing again a significant red-shift of emission (8: λabs = 576 nm, λem = 664 nm in CH Cl ).
2 2 2
Cl ). In turn, the introduction of 4-NEt
2
2
2
The dinitro complexes undergo uncommon blue-shift of emission (22-30 nm) upon the
5
fluorination of B-phenyl groups (6→7). This is accompanied by the sizable increase of QY
from 63% to 83% in PhMe, and from 48% to 66% in CH
BPh with a B(C groups in diamino complexes (8→9) induces a sizable red-shift of
emission of 17 nm in PhMe and 39 nm in CH Cl , and reduces QY from 40% to 33% in
. At this point it is noticeable that these values are high
2 2
Cl . In contrast, the replacement of a
2
6 5 2
F )
2
2
PhMe and from 29% to 10% in CH
2 2
Cl
for such red-emitters.
2 2
In 10 the location of NO and NEt groups at the terminal parts of a quasi-linear
conjugated system leads to the formation of a push-pull rod-type architecture. The TD-DFT
calculation show that electron excitation can be interpreted in terms of charge transfer from
2 2
the naphthalene ring and N-(4-NEt )Ph group to the N-(4-NO )Ph group. The absorption
maximum of 10 (λabs = 560 nm, PhMe) is close to the values for corresponding NO
2
(6) and
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NEt
2
(8) complexes. In turn, the emission wavelength is red-shifted (λem = 664 nm, PhMe)
with respect to both symmetrical derivatives.
Concerning bis(boranils) 1-7, the solvent polarity only slightly affects their absorption
and emission wavelengths, although it is interesting to note that emission is slightly blue-
shifted in more polar solvents (Table S6, ESI). In turn, amino derivatives undergo sizable red-
shift of emission wavelengths with the increase of solvent polarity. This is especially
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noticeable for red-light emitter 9, which emission in CH
2 2
Cl (λem = 683 nm) and THF (λem =
7
14 nm) approaches close to the NIR region. According to expectations, the bathochromic
shift of emission bands is accompanied by the reduction of QY values. Finally, preliminary
results of solid state (powder) photoluminescence of 4 and 7 show that QY are reduced to
9
13% and 6%, respectively. This is accompanied by red-shift of emission wavelength of ca.
30-35 nm (Figure S55-56). Both effects are most likely caused by aggregation, thus further
studies should be performed (e.g., in blends) to improve solid-state luminescence.
In summary, bis(boranils) derived from a ditopic tetradentate 1,5-dihydroxy-2,6-bis(N-
phenyliminomethylene)naphthalene ligand are very efficient orange-to-red emitters with QY
exceeding 80%. Their photophysical properties are easily tuned in a wide range either by
varying the substitution on boron atom or by extending the π-conjugation with electron-
withdrawing (NO
2 2 2
) or electron-donating (NEt ) functional groups. The introduction of NO
and NEt at terminal parts of the molecule gave rise to an unprecedented push-pull system
2
with electron transition possessing charge transfer character. The absorption band for this
compound is similar, while emission significantly red-shifted with respect to bis(boranil)
2
bearing two NEt groups. The promising features of obtained bis(boranils), i.e., improved
stability (thermal, hydrolytic, electrochemical) and strong fluorescence in a red region of the
visible spectrum, would be beneficial for a construction of highly efficient organic red-light
emitting diodes. In our opinion, the most appropriate candidate for such applications would be
complexes 4 and 8, as they feature strong red-shifted emission, high stability, and good
solubility in most organic solvents.
Experimental Section
General comment. All the used reagents were provided by Aldrich Chemical
Company. THF was dried by heating to reflux with sodium or potassium and benzophenone,
and distilled under argon. Starting materials (halogenated benzenes, trialkyl borates, n-BuLi
(10M in hexane), t-BuLi (1.7 M in pentane), DMF, benzoyl chloride, dimethoxymethane)
were used as received without additional purification, with exception of 1,5-
dihydroxynaphthalene, which was recrystallized from acetonitrile with activated charcoal.
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Reactions and manipulations involving air and moisture-sensitive reagents were carried out
under an argon atmosphere.
1
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19
Characterization Data: H, B, C and F NMR spectra were recorded on a Bruker
1
13
Advance III 300 MHz and Agilent NMR 400 MHz DDR2 spectrometers. H and C chemical
1
1
shifts were referenced to TMS using known chemical shifts of solvent residual peaks. B and
1
9
13
3 2 3
F NMR chemical shifts are given relative to BF ·Et O and CFCl , respectively. In the C
0
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NMR spectra the resonances of boron-bound carbon atoms were not observed in most cases
as a result of their broadening by the quadrupolar boron nucleus. HR-MS analyses were
performed on a GCT Premiermass spectrometer equipped with EI ion source and a Maldi
SYNAPT G2-S HDMS spectrometer equipped with ESI ion source, both spectrometers
equipped with TOF mass analyzers. Compound 1 was insufficiently soluble in organic
13
solvents to record reliable C spectra even after prolonged acquisition.
Experimental procedures – general comment: The synthesis of BF
2
monoboranil A
has not been described and it is given below whereas another referential compound B was
3
e
obtained according to the published procedure. Complexes 2-10 were synthesized according
to a protocol developed by us recently which involves a one-pot three-component reaction
between dialdehyde 14, aniline and diarylborinic esters Ar
2
BOR (Ph
2
B(OEt), (2,6-dF-
3e
Ph)
and corresponding dialkyl arylboronates ArB(OR)
2 6 5 2
B(OiPr), (C F ) B(OEt)). The latter components were generated in situ from aryllithium
3
e
2
. An intermediate borinic ate-complex
] Li was quenched with TMSCl or 2 M ethereal HCl affording diarylborinic ester
BOR. Diphenylborinic ester Ph BOEt was isolated and purified by distillation whereas
-
+
2 2
[R B(OR)
Ar
2
2
fluorinated analogues were unstable at elevated temperatures and therefore, they were
prepared and used without isolation. In the case of 5, 10-phenoxaborin was used as a boron
10
precursor. Complex 1 was obtained from bis(anil) 15, which was treated with nBuLi and
BF
first step, which was further reacted in one-pot protocol with one equivalent of 4-nitroaniline
and diphenylborinic ester Ph BOEt.
Synthesis of substrates: 2,6-dibromo-1,5-dihydroxynaphthalene (11): To a
suspension of 1,5-dihydroxynaphthalene (10.0 g, 62.4 mmol) in CHCl (200 mL), a solution
of bromine (20.0 g, 125 mmol) in CHCl (15 mL) was added dropwise at 0 °C. A mixture was
warmed up to room temperature and stirred for 3 hours. A solid product was filtered, washed
with CHCl (50 mL) and hexane (50 mL), and dried under vacuum to give pure 2,6-dibromo-
,5-dihydroxynaphthalene as a beige powder (17.7 g, yield 89%). M.p. 213-215 °C
3 2
·Et O. The synthesis of bis(boranil) 10 required the isolation of mono(imine) 16 in the
2
3
3
3
1
1
6
(decomposition is observed). H NMR (400 MHz, Acetone-d ) δ = 8.55 (s, OH), 7.74 (d, J =
13
1
8
6
.9 Hz, 2H, naph), 7.58 (d, J = 8.9 Hz, 2H, naph) ppm; C{ H} NMR (75 MHz, Acetone-d )
6 2 2
δ = 150.2, 130.4, 126.8, 116.3, 105.9 ppm. Anal. Calcd. for C10H Br O : C, 37.77; H, 1.90.
Found: C, 37.64; H, 1.95.
1
,5-bis(methoxymethoxy)-2,6-dibromonaphthalene (12): To a suspension of NaH
60% oil dispersion, 3.36 g, 84 mmol) in anhydrous DMF (10 mL), a solution of 11 (12.1 g,
8 mmol) in anhydrous DMF (20 mL) was added dropwise at –5 °C. After ca. one hour a gas
evolution ceased, and a solution of chloromethyl methyl ether MOMCl (6,79 g, 84 mmol) in
Et O (20 mL) was added dropwise over one hour at –5 °C. During the addition a mixture
thickened and was diluted with Et O (50 mL). The mixture was stirred for 5 hours at 0 °C. A
beige slurry was poured onto vigorously stirred ice cold water (40 mL). CH Cl (110 mL) was
added to dissolve suspended solids. Phases were separated. Water layer was extracted twice
with CH Cl (2 × 25 mL). Combined organic phases were washed with 5% NaHCO (50 mL)
and brine (50 mL) and dried with MgSO . Volatiles were removed under vacuum to obtain a
(
3
2
2
2
2
2
2
3
4
brown solid. It was washed with hexane (30 mL) and dried under vacuum to give pure 1,5-
bis(methoxymethoxy)-2,6-dibromonaphthalene as a beige crystalline solid (12.04 g, yield 78
1
%
). M.p. 115-116 °C. H NMR (300 MHz, Acetone-d
6
) δ = 7.97 (d, J = 8.9 Hz, 2H, naph),
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1
7
.77 (d, J = 8.9 Hz, 2H, naph), 5.31 (s, 4H,-OCH
2
O-), 3.69 (s, 6H, -OCH
3
) ppm; C{ H}
NMR (101 MHz, Acetone-d
Calcd for C14H14Br O : C, 41.41; H, 3.48. Found: C, 41.24; H, 3.59.
2 4
6
) δ =152.1, 132.0, 131.2, 121.3, 114.5, 101.3, 58.4 ppm. Anal.
1,5-bis(methoxymethoxy)naphthalene-2,6-dicarboxaldehyde (13): A solution of 12
(10.20 g, 25 mmol) in anhydrous THF (150 mL) was added dropwise to a stirred solution of
nBuLi (10 M, 6.3 mL, 63 mmol) in anhydrous THF (100 mL) over 40 min at –70 °C. After
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
.5 hours anhydrous DMF (5 mL, 65 mmol) was added dropwise at –70 °C. A mixture was
slowly warmed up to 0 °C and H SO (1.5 M) was added to reach pH = 4. The precipitated
solid was filtered, washed with cold EtOH (2 × 10 mL), Et O (2 × 15 mL), hexane (15 mL)
2
4
2
and dried under vacuum to give pure 1,5-bis(methoxymethoxy)naphthalene-2,6-
dicarboxaldehyde as a bright yellow powder (6.7 g, 88%). M.p. 151-153 °C. H NMR (400
MHz, CDCl ) δ = 10.55 (s, 2H, -CHO), 8.08 (d, J = 8.8 Hz, 2H, naph), 7.98 (d, J = 8.8 Hz,
3
2
CDCl
16 16 6
C H O
1
13
1
H, naph), 5.28 (s, 4H, -OCH
2
O-), 3.67 (s, 6H, -OCH
) δ = 190.2, 159.1, 133.1, 128.2, 124.1, 120.4, 102.3, 58.5 ppm. Anal. Calcd for
: C, 63.15; H, 5.30. Found: C, 62.88; H, 5.15.
1,5-dihydroxynaphthalene-2,6-dicarboxaldehyde (14): A suspension of 13 (6.32 g, 21
3
) ppm; C{ H} NMR (101 MHz,
3
mmol) in THF (100 mL) and hydrochloric acid (6 M, 100 mL) was refluxed for 4 hours. The
mixture was cooled to 0 °C. The obtained solid was filtered, washed with water to reach a
neutral pH. Then it was then washed with cold ethanol (15 mL), hexane (20 mL), and dried
under vacuum to give pure 1,5-dihydroxynaphthalene-2,6-dicarboxaldehyde as a yellow
crystalline solid (4.14 g, 91% yield). M.p. 240-245 °C. H NMR (300 MHz, CDCl
1
3
) δ =
1
2
2.42 (s, 2H, -OH), 10.06 (s, 2H, -CHO), 8.00 (d, J = 8.5 Hz, 2H, naph), 7.61 (d, J = 8.5 Hz,
13
1
H, naph); C{ H} NMR (101 MHz, CDCl
: C, 66.67; H, 3.73. Found: C, 66.57; H, 3.79.
,6-bis(N-phenyliminomethyl)-1,5-dihydroxynaphthalene (15): A mixture of aniline
3
) δ = 197.0, 160.4, 128.9, 127.1, 117.2, 115.3
8 4
ppm. Anal. Calcd for C12H O
2
(0.30 mL, 3.3 mmol), 14 (325 mg, 1.5 mmol) and TsOH (19 mg) in PhMe (10 mL) was
refluxed in a Dean-Stark apparatus for 6 hours. After cooling to room temperature the mixture
was filtered and the precipitate was washed with cold Et
vacuum to give pure 15 as a brown crystalline solid (0.45 g, yield 82%). M.p. 208-210 °C. H
NMR (400 MHz, DMSO-d ) δ = 14.93 (d, J = 4.5 Hz, 2H, OH), 9.10 (d, J = 4.5 Hz, 2H,
N=CH), 7.65 (d, J = 8.6 Hz, 2H, naph), 7.60-7.47 (m, 10H, Ar), 7.38-7.30 (m, 2H, Ph) ppm;
2
O (2 × 10 mL) and dried under
1
6
1
3
1
C{ H} NMR (101 MHz, DMSO-d
20.5, 114.3, 112.1, 39.5 ppm; Anal. Calcd for C24
Found: C, 78.51; H 4.83; N 7.69.
-[N-(4’-(N’,N’-diethylamino)phenyliminomethyl)]-1,5-dihydroxynaphthalene-2-
6
) δ =165.5, 160.6, 144.2, 129.7, 129.0, 128.0, 127.0,
1
18 2 2
H N O
: C, 78.67; H, 4.95; N 7.65.
6
carboxaldehyde (16): A solution of 4-(N,N-dietylamino)aniline (1.30 g, 7.9 mmol) in PhMe
(100 mL) was added dropwise over 6 hours to refluxed mixture of 16 (1.50 g, 6.9 mmol) in
PhMe (300 mL). Water released during reaction was removed using Dean-Stark apparatus. A
mixture was stirred and refluxed for two hours and cooled to rt. A brown precipitate was
filtered off on a Büchner funnel, washed with PhMe (2 × 50 mL), hexane (10 mL) and dried
under vacuum to obtain bis(anil) – 2,6-bis[N-(4’-(N’,N’-diethylamino)phenyliminomethyl)]-
1,5-dihydroxynaphthalene (16; 0.69 g). The filtrate was concentrated on a rotary evaporator to
obtain the crude product as a red solid (2.11 g). It was purified by recrystallization from
PhMe-hexane (v/v = 5:1) and dried under vacuum. The pure imine 16 was isolated as red
1
needles (1.36 g, 54%). Decomposition starts at 154 °C (M.p. 190 °C). H NMR (300 MHz,
Acetone-d
N=CH), 7.98 (d, J = 8.6 Hz, 1H), 7.72 (d, J = 8.6 Hz, 2H), 7.58 (d, J = 8.8 Hz, 1H), 7.45 (d, J
= 9.1 Hz, 2H), 6.81 (d, J = 9.1 Hz, 2H), 3.46 (q, J = 7.0 Hz, 4H, NCH ), 1.19 (t, J = 7.0 Hz,
6
) δ = 15.67 (s, 1H, OH), 12.53 (s, 1H, OH), 10.13 (s, 1H, CHO), 8.96 (s, 1H,
2
1
3
1
6
H, CH
3
) ppm; C{ H} NMR (101 MHz, Acetone-d
6
) δ = 209.9, 198.7, 156.4, 128.9, 127.4,
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2
2
2
2
2
2
2
2
2
3
3
3
3
3
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5
5
5
5
5
5
5
5
5
6
1
6
23.1, 117.2, 115.7, 112.9, 112.8, 45.1, 12.9 ppm. Anal. Calcd for C22
.12; N, 7.73. Found: C, 72.79; H, 6.24; N, 7.78.
22 2 3
H N O : C, 72.91; H,
2
Ethoxydiphenylborane (Ph BOEt): Bromobenzene (13.5 mL, 86 mmol) was added
dropwise to a stirred solution of nBuLi (9.0 mL, 90 mmol) in THF (120 mL) at –78 °C. A
white suspension of PhLi was formed. After 1 hour of stirring diethyl phenylboronate
2 2
(PhB(OEt) ) (15.10 g, 85 mmol) dissolved in Et O (15 mL) was added dropwise at –78 °C.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
The resulting thick white slurry was stirred for ca. 30 min and then allowed to reach room
temperature. A mixture was treated with TMSCl (13 mL, 100 mmol) and heated to 40 °C.
After 15 minutes LiCl precipitated from the solution. A mixture was stirred for 2 hours and
then volatiles were removed under vacuum. Et
was filtered under argon atmosphere. The precipitate was washed three times with Et
30 mL) and the combined colourless filtrate was concentrated in vacuo. A crude product was
purified by distillation under reduced pressure to give ethoxydiphenylborane as a colourless
liquid boiling at 90-101 °C (1 Tr) (15.4 g, 86%). It is air and moisture sensitive, so it should
2
O (30 mL) was added and the obtained slurry
O (3 ×
2
1
be stored and handled under an inert atmosphere. H NMR (400 MHz, CDCl
3
) δ = 7.94-7.75
), 1.52 (t, J = 7.0 Hz, 3H,
) δ = 45.4 ppm; C{ H} NMR (101 MHz, CDCl ) δ
(m, 4H, Ph), 7.70-7.45 (m, 6H, Ph), 4.38 (q, J = 7.0 Hz, 2H, OCH
2
1
1
13
1
CH
3
) ppm; B NMR (128 MHz, CDCl
3
3
= 134.2, 130.1, 127.7, 63.7, 17.8 ppm.
Synthesis of boranils: Difluoroboron salicylideneaniline complex (A): nBuLi (10 M,
0.50 mL, 5.0 mmol) was added dropwise to a solution of salicylideneaniline (0.97 g, 4.9
mmol) in THF (20 mL) at –70 °C. Mixture was warmed up to – 50 °C and stirred for 30 min.
3 2
Then it was cooled to –70 °C and BF ·Et O (0.61 mL, 5.0 mmol) was added dropwise. A
cooling bath was removed and a mixture was left to warm up to the room temperature. After 2
hours a mixture was cooled to 0 °C and filtered. The solid was washed with water (3 × 10
mL), cold EtOH (2 × 5 mL) and hexane (15 mL), and dried under vacuum to obtain pure
compound A as a light yellow powder (0.85 g, 69%). M.p. 226-228 °C. H NMR (300 MHz,
DMSO-d
1
6
) δ = 9.20 (s, 1H, N=CH), 7.83 (ddd, JHH = 7.7, 1.8, 0.6 Hz, 1H, Ar), 7.75 (ddd, JHH
=
8.3, 7.3, 1.8 Hz, 1H, Ar), 7.71–7.64 (m, 2H, Ar), 7.62–7.48 (m, 3H, Ar), 7.17–7.09 (m, 2H,
11
19
Ar) ppm; B NMR (96 MHz, DMSO-d
MHz, DMSO-d ) δ = –132.28 - –132.54 (m) ppm; C{ H} NMR (75 MHz, DMSO-d
166.4, 158.4, 142.1, 139.0, 133.7, 129.4, 129.0, 123.6, 120.4, 118.3, 116.1 ppm. Anal. Calcd
6
) δ = 0.56 (t, JBF = 16.1 Hz) ppm; F NMR (282
1
3
1
6
6
) δ =
for C13
H10BF
2
NO: C, 63.72; H, 4.11; N, 5.72. Found: C, 63.56; H, 3.94; N, 5.85.
2
,6-bis(N-phenyliminomethyl)-1,5-dihydroxynaphthalene bis(difluoroboron) complex
(1): 15 (0.45 g, 1.2 mmol) was dissolved in anhydrous PhMe (45 mL) at 50 °C. A dark red
solution was rapidly cooled in dry ice – acetone bath and nBuLi (10M, 0.25 mL, 2.5 mmol)
was added dropwise at –78 °C. A cooling bath was removed and a mixture was slowly
warmed up to 50 °C, and stirred for 4 hours, then cooled and left overnight with stirring at
room temperature. The obtained orange slurry was cooled to –78 °C and BF
2
and then gently refluxed for 4 hours. The formation of a bright orange precipitate was
observed. It was cooled to room temperature and filtered. The obtained solid (very fine
powder) was washed with PhMe (2 × 7 mL) and acetone (10 mL), and dried in air flow. A
crude product was transferred to small beaker and stirred vigorously with water for 20 min.
Then it was filtered, washed with EtOH (50%, 2 × 5 mL), EtOH (100%, 2 × 5 mL) and Et
(3 × 5 mL), and dried under vacuum. 1 was obtained as a fine orange powder (0.39 g, yield
3 2
·Et O (0.30 mL,
.5 mmol) was added, the mixture become darker. It was slowly warmed to room temperature
2
O
1
6
1
2
8%). Decomposition >430 °C (does not melt). H NMR (300 MHz, DMSO-d
6
) δ = 9.38 (s,
H, N=CH), 8.04 (d, J = 8.6 Hz, 1H, naph) 7.90 (d, J = 8.6 Hz, 1H, naph), 7.75 (d, J = 7.2 Hz,
11
19
H, NPh), 7.67-7.52 (m, 3H, NPh) ppm; B NMR (96 MHz, DMSO-d
6
) δ = 0.9 ppm; F
NMR (282 MHz, DMSO-d
6
) δ = –130.43 ppm; FTIR (ATR) ν = 3071, 3043, 1621, 1580,
1
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494, 1487, 1435, 1361, 1249, 1197, 1113, 1092, 1207, 980, 720, 687, 604 cm ; HRMS (EI):
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
+
calcd. for C24
16 2 4 2 2
H B F N O [M] 462.1334; found 462.1332.
2
,6-bis(N-phenyliminomethyl)-1,5-dihydroxynaphthalene
bis(diphenylborinic)
complex (2): Ethoxydiphenylborane (Ph
2
BOEt) was dissolved in EtOH (10 mL) followed by
the addition of aniline (0.40 mL, 4.4 mmol) and 14 (0.43 g, 2.0 mmol). Immediately, the
resulting solution turned red. A mixture was stirred for 15 hours and the precipitation of the
bis(boranil) was observed. The obtained thick orange slurry was filtered. The solid was
washed with water (20 mL), EtOH (30 mL), Et
product was transferred to a small flask, stirred vigorously with Et
Then it was filtered, washed with Et O (20 mL) and dried under vacuum to give 2 as an
orange powder (1.32 g, 95% yield). M.p. 299-301 °C. H NMR (300 MHz, Acetone-d
.04 (s, 2H, N=CH), 7.81 (d, J = 8.6 Hz, 2H, naph), 7.60 (d, J = 8.6 Hz, 2H, naph), 7.49-7.42
m, 8H, Ph), 7.28 (s, 10H, Ph), 7.15 – 7.03 (m, 12H, Ph) ppm; C{ H} NMR (101 MHz,
Acetone-d ) δ = 165.2, 161.8, 146.7, 134.6, 132.2, 129.6, 129.2, 129.1, 128.1, 127.7, 127.2,
125.7, 117.3, 115.3 ppm; FTIR (ATR) ν = 3069, 3047, 3008, 1611, 1565, 1490, 1475, 1432,
423, 1349, 1182, 1144, 1097, 981, 879, 718, 702, 690, 596, 555 cm ; HRMS (EI): calcd. for
C H B N O [M] 694.2963; found 694.2958.
48 36 2 2 2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
O (10 mL) and hexane (20 mL). A crude
2
O (20 mL) for 4 hours.
2
1
6
) δ =
9
(
13
1
6
-
1
1
+
2
,6-bis(N-phenyliminomethyl)-1,5-dihydroxynaphthalene bis[bis(2,6-difluorophenyl)-
borinic] complex (3): 1,3-difluorobenzene (0.37 mL, 3.8 mmol) was added dropwise to a
stirred solution of nBuLi (0.38 mL, 3,8 mmol) in Et O (20 mL) at –78 °C. After ca. 30 min
2
diethyl 2,6-difluorophenylboronate (0.81 g, 3.8 mmol) was added dropwise. The mixture was
stirred for ca. 30 min. A cooling bath was removed and a mixture was allowed to warm up to
10 °C. It was treated with the ethereal HCl (2 M, 1.9 mL, 3.8 mmol) resulting in the
formation of ethoxybis(2,6-difluorophenyl)borane. A mixture was warmed up to 30 °C. After
h aniline (0.40 mL, 4.4 mmol) and 14 (0.39 g, 1.8 mmol) were added, resulting in a red
coloration of the mixture. The mixture was stirred for 10 hours at 60 °C. An orange
precipitate was formed. It was cooled to ca. 0 °C; an orange precipitate was filtered and
washed with hexane (20 mL). The crude product was transferred to a small flask and stirred
–
1
vigorously with Et
2
O (30 mL) for 3 hours. Precipitate was filtered, washed with water (20
mL), EtOH (20 mL) and hexane (20 mL), and dried under vacuum to give 3 as a bright orange
powder (1.33 g, 79% yield). M.p. 353-355 °C. H NMR (300 MHz, DMSO-d
2H, N=CH), 7.68 (d, J = 8.7 Hz, 2H, naph), 7.62 (d, J = 8.7 Hz, 2H, naph), 7.44 (m, 4H, Ar),
.40-7.26 (m, 6H, Ar), 7.23-7.08 (m, 4H, Ar), 6.72 (t, J = 8.4 Hz, 8H, Ar) ppm; H NMR (400
MHz, DMF-d ) δ 9.36 (s, 2H, N=CH), 7.79 (d, J = 8.7 Hz, 2H, naph), 7.74 (d, J = 8.7 Hz, 2H,
naph), 7.61 (d, J = 7.7 Hz, 4H, Ar), 7.43 – 7.36 (m, 4H, Ar), 7.36 – 7.31 (m, 2H, Ar), 7.18 (tt,
1
6
) δ = 9.29 (s,
1
7
7
1
9
J = 8.2, 6.5 Hz, 4H, Ar), 6.74 (t, J = 8.4 Hz, 8H, Ar) ppm. F NMR (282 MHz, DMSO-d
6
) δ
) δ = 166.3 (dd, JCF = 243.5,
4.7 Hz) , 164.5, 162.4, 159.6, 144.8, 131.1, 130.0, 129.9 (t, JCF = 11.5 Hz), 128.9, 127.8,
ꢀ
13
1
= –103.29 (t, J = 7.1 Hz) ppm; C{ H} NMR (101 MHz, DMF-d
7
1
1
23.7, 116.2, 114.6, 110.9 (d, JCF = 29.8 Hz). FTIR (ATR) ν = 3069, 3041, 1611, 1560, 1492,
478, 1479, 1442, 1351, 1247, 1218, 1183, 1095, 977, 916, 871, 783, 714, 692, 589, 510 cm
HRMS (EI): calcd. for C48
-
1
1
+
;
H
28
B
2
F
8
N
2
O
2
[M] 838.2209; found 838.2221.
2,6-bis(N-phenyliminomethyl)-1,5-dihydroxynaphthalene bis[bis(pentafluorophenyl)-
borinic] complex (4): Pentafluorobromobenzene (0.50 mL, 4.0 mmol) was added dropwise to
a stirred solution of nBuLi (0.42 mL, 4.2 mmol) in Et O (20 mL) at –78 °C. After ca. 20 min
diethyl pentafluorophenylboronate (C B(OEt) ) (1.18 g, 4.4 mmol) was added dropwise.
Subsequently the mixture was stirred for ca. 40 min and the ethereal HCl (2 M, 2.1 mL, 4.2
mmol) was added. A cooling bath was removed and a mixture was allowed to slowly reach
room temperature and was stirred for 1 h to give ethoxybis(pentafluorophenyl)borane
2
6
F
5
2
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4
4
5
5
5
5
5
5
5
5
5
5
6
(
C
6
F
5
)
2
BOEt. In the next step, aniline (0.38 mL, 4.2 mmol) and 14 (0.41 g, 1.9 mmol) were
added. A mixture was stirred for 24 hours at room temperature. Then it was cooled to –50 °C,
an orange precipitate was filtered and washed with hexane (20 mL). A crude product was
transferred to a small flask and stirred vigorously with water (20 mL) for 0.5 h. The product
was filtered, washed with warm EtOH (50 mL) and hexane (20 mL), and dried under vacuum
to give 4 as a bright orange powder (1.51 g, yield 76%). M.p. 350-353°C. H NMR (300
MHz, Acetone-d
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
) δ = 9.37 (s, 2H, N=CH), 7.85 (d, J = 8.8 Hz, 2H, naph), 7.82 (d, J = 8.8
1
1
Hz, 2H, naph), 7.59-7.51 (m, 4H, NPh), 7.50-7.38 (m, 6H, NPh) ppm; B NMR (96 MHz,
1
9
Acetone-d
8F), –157.90 (t, J = 20.0 Hz, 4F), –165.41 (ddd, J = 23.4, 20.0, 9.2 Hz, 8F) ppm; C{ H}
NMR (101 MHz, Acetone-d ) δ = 166.5, 159.6, 150.8–147.8 (m), 144.8, 142.8-139.8 (m),
39.5-136.2 (m), 132.0, 130.5, 130.4, 120.0, 124.4, 117.1, 116.6 ppm; FTIR (ATR) ν = 1646,
610, 1545, 1517, 1458, 1347, 1292, 1283, 1185, 1113, 1094, 983, 966, 774, 718, 690, 557
6 6
) δ = 1.7 ppm; F NMR (282 MHz, Acetone-d ) δ = –135.15 (dd, J = 23.4, 9.2 Hz,
1
3
1
6
1
1
-
1
+
cm ; HRMS (ESI): calcd. for C48
16 2 20 2 2
H B F N O [M] 1054.1079; found 1054.1062.
2
,6-bis(N-phenyliminomethyl)-1,5-dihydroxynaphthalene bis(phenoxaborin) complex
(
(
5): To a solution of 10-hydroxyphenoxaborin (0.667 g, 3.4 mmol) in acetone (5 mL), aniline
0.40 mL, 4.4 mmol) and solution of 14 (0.371 g, 1.7 mmol) in acetone (25 mL) were added.
An immediate coloration of the mixture was observed. The mixture was stirred for 18 hours at
room temperature, resulting in the formation of a bright red precipitate. The precipitate was
filtered, washed with acetone (20 mL) and Et
a small flask and stirred vigorously with Et
filtered, washed with Et O (10 mL) and dried under vacuum to give 5 as a bright orange
powder (0.70 g, 56%). M.p. 402-410°C. H NMR (300 MHz, DMSO-d
N=CH), 7.60 (d, J = 8.7 Hz, 2H, naph), 7.57 (dd, J = 7.4, 1.8 Hz, 4H, oxaborin), 7.51 (d, J =
2
O (20 mL). A crude product was transferred to
2
O (20 mL) for 1.5 h. The pure product was
2
1
6
) δ = 9.09 (s, 2H,
8
7
.7 Hz, 2H, naph), 7.25 (ddd, J = 8.3, 7.1, 1.8 Hz, 4H, oxaborin), 7.20-7.15 (m, 6H, NPh),
.05 (dd, JHH = 8.3, 0.7 Hz, 4H, oxaborin), 6.99-6.90 (m, 8H, NPh, oxaborin) ppm; H NMR
1
(400 MHz, Pyridine-d
5
) δ = 8.90 (s, 2H, N=CH), 7.98 (dd, J = 7.6, 0.8 Hz, 4H, oxaborin),
7
.75 (d, J = 8.8 Hz, 2H, naph), 7.49 (d, J = 8.7 Hz, 2H, naph), 7.39–7.34 (m, 8H, Ar), 7.17–
1
3
1
7.02 (m, 14H, Ar) ppm.; C{ H} NMR (101 MHz, pyridine) δ = 165.0, 160.8, 157.2, 146.2,
33.9, 132.4, 127.6, 124.9, 124.2, 124.0, 123.7, 123.3, 116.8, 115.4, 114.6 ppm.; FTIR (ATR)
ν = 3066, 3009, 1616, 1594, 1565, 1491, 1428, 1345, 1296, 1279, 1217, 1198, 1181, 1165,
1
-1
1
C
145, 1088, 997, 900, 815, 784, 753, 725, 691, 556 cm ; HRMS (EI): calcd. for
+
48
H
32
B
2
N
2
O
4
[M] 722.2548; found 722.2521.
2
,6-bis[N-(4’-nitrophenyl)iminomethyl)]-1,5-dihydroxynaphthalene
bis(diphenyl-
borinic) complex (6): To solution of ethoxydiphenylborane (Ph
anhydrous 2-MeTHF (15 mL), 14 (0.22 g, 1.0 mmol) and 4-nitroaniline (0.30 g, 2.2 mmol)
were added. The mixture was warmed up to 50 °C and stirred for 24 h. After cooling a pink
precipitate was filtered, washed with Et
2
BOEt) (0.66 g, 3.1 mmol) in
2
O (5 × 5 mL) and hexane (2 × 5 mL), and dried under
vacuum. The pure compound 6 was obtained as a pink, fine powder (0.70 g, 90%). M.p. 326-
1
3
28 °C. H NMR (400 MHz, DMF-d
Hz, 2H), 7.76–7.68 (m, 6H), 7.54–7.47 (m, 8H), 7.23–7.08 (m, 12H) ppm. C NMR (101
MHz, DMF-d ) δ = 166.7, 161.4, 150.8, 147.0, 134.0, 131.5, 127.3, 126.8, 126.5, 124.4,
117.2, 114.6, 112.9 ppm. FTIR (ATR) ν = 3067, 3004, 1606, 1557, 1520, 1473, 1342, 1294,
7
) δ = 9.42 (s, 2H), 8.28–8.19 (m, 4H), 7.78 (d, J = 8.9
1
3
7
-
1
1
196, 1177, 1141, 1094, 1070, 992, 984, 904, 881, 738, 704, 603, 550, 444 cm . HRMS (EI):
+
calcd. for C48
7
34 2 4 6 34 2 4 6
H B N O [M] 784.2664; found 784.2679. Anal. Calcd for C48H B N O : C,
3.50; H, 4.37; N, 7.14. Found: C, 73.65; H, 4.64; N, 7.05.
2
,6-bis[N-(4’-nitrophenyl)iminomethyl)]-1,5-dihydroxynaphthalene
bis[bis(penta-
fluorophenyl)borinic] complex (7): Compound 7 was prepared as described for 4 using:
2
pentafluorobromobenzene (0.79 g, 3.1 mmol), nBuLi (10 M, 0.31 mL, 3.1 mmol), Et O (20
1
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5
6
7
8
9
2
mL), diethyl pentafluorophenylboronate (0.84 g, 3.1 mmol), HCl/Et O (2 M, 1.55 mL, 3.1
mol), 14 (0.32 g, 1.5 mmol) and 4-nitroaniline (0.45, 3.3 mmol) in anhydrous 2-MeTHF (65
mL). The mixture was stirred at room temperature for 24 hours and concentrated on rotary
evaporator. The obtained solid was product was washed with Et
precipitate was washed with Et O (3 × 5 ml), water (2 × 5 ml), EtOH (5 ml) and Et
to give pure 7 as a dark pink powder (1.03 g, yield 60%). M.p. 338-340 °C. H NMR (300
MHz, Acetone-d ) δ = 9.59 (s, 2H, N=CH), 8.38–8.30 (m, 4H, naph), 7.91–7.82 (m, 8H, NAr)
ppm; H NMR (400 MHz, Pyridine-d ) δ = 10.02 (s, 2H, N=CH), 8.44 (d, J = 8.8 Hz, 4H, Ar
, 8.22 (d, J = 8.9 Hz, 2H, naph), 8.05 (d, J = 8.9 Hz, 4H, Ar), 7.90 (d, J = 8.8 Hz, 2H, naph)
2
O (10 ml) and filtered. The
2
2
O (5 ml)
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6
1
5
)
1
1
19
ppm B NMR (96 MHz, Acetone-d
6
) δ = 2.0 (s) ppm; F NMR (282 MHz, Acetone-d
6
) δ = –
1
9
1
1
35.20 (dd, J = 23.4, 9.2 Hz, 8F), –157.17 (t, J = 23.4 Hz, 4F), –164.92 (ddd, J = 23.4, 20.0,
.2 Hz, 8F) ppm; C{ H} NMR (101 MHz, Pyridine-d ) δ = 168.1, 160.6, 148.9, 148.6,
5
48.4–147.6 (m), 143.0–139.7 (m), 139.5–136.4 (m), 132.5, 128.9, 125.9, 125.5, 124.2,
13
1
17.4, 117.3 ppm. FTIR (ATR) ν = 1646, 1610, 1561, 1531, 1518, 1549, 1346, 1291, 185,
-
1
+
1092, 970, 860, 718, 689, 532, 438 cm ; HRMS (ESI): calcd. for C48
1144.0780; found 1144.0807.
14 2 20 4 6
H B F N O [M]
2
,6-bis[N-(4’-(N’,N’-diethylaminophenyl)iminomethyl)]-1,5-dihydroxynaphthalene
bis(diphenylborinic)complex (8): Compound 8 was prepared as described for 6 using:
ethoxydiphenylborane Ph BOEt (0.43 g, 2.0 mmol), anhydrous THF (15 mL), 14 (0.19 g, 0.9
mmol) and 4-(N,N-diethylamino)aniline (0.35 g, 2.1 mmol). The mixture was stirred at 50 °C
for 48 h and filtered. The obtained product was washed with THF (2 × 10 mL) and Et O (2 ×
0 mL), and dried under vacuum to give 8 as a brown powder (0.51 g, yield 68%). M.p. 315-
2
2
1
1
316 °C. H NMR (300 MHz, CDCl
7.52-7.45 (m, 4H, Ar), 7.24–7.09 (m, 7H, Ar), 7.00–6.88 (m, 2H, Ar), 6.45–6.36 (m, 2H),
3
) δ = 8.33 (s, 1H, N=CH), 7.86 (d, J = 8.6 Hz, 1H, naph),
1
3
1
3
.29 (q, J = 7.1 Hz, 4H, NCH
CDCl ) δ = 160.6, 159.2, 147.6, 134.3, 133.8, 131.2, 127.0, 126.3, 126.0, 125.5, 115.7, 115.1,
10.9, 44.5, 12.6 ppm; FTIR (ATR) ν = 3066, 3041, 3012, 2972, 2931, 2891, 1609, 1590,
2 3
), 1.11 (t, J = 7.1 Hz, 6H, CH ) ppm; C{ H} NMR (101 MHz,
3
1
1
-
1
567, 1514, 1350, 1267, 1193,1140, 1093, 982, 881, 820, 701, 607, 530 cm ; HRMS (ESI):
+
calcd. for C56
54 2 4 2
H B N O [M+H] 837.4511; found 837.4530.
2
,6-bis[N-(4’-(N’,N’-diethylaminophenyl)iminomethyl)]-1,5-dihydroxynaphthalene
bis[bis(pentafluorophenyl)borinic)] complex (9): Compound 9 was prepared as described for
4 using: pentafluorobromobenzene (0.74 g, 3.0 mmol), nBuLi (10 M, 0.30 mL, 3.0 mmol),
THF (70 mL), diethyl pentafluorophenylboronate (0.89 g, 3.3 mmol), HCl/Et O (2M, 1.50
2
mL, 3.0 mol), 14 (0.22 g, 1.0 mmol) and 4-(N,N-diethylamino)aniline (0.36 g, 2.2 mmol). A
mixture was stirred at room temperature for 72 hours. The precipitation of the product was not
observed. Solvents were removed under vacuum to obtain a dark solid. CH
with stirring and after 20 min a brown solid was filtered off. It was washed with water (2 × 10
mL), EtOH (2 × 5 mL) and Et O (2 × 5 mL). After drying under vacuum pure compound 9
was obtained as a brown powder (0.76 g, yield 60%). M.p. 303-305 °C. H NMR (300 MHz,
CDCl ) δ = 8.38 (s, 2H, N=CH), 7.81 (d, J = 8.7 Hz, 2H, naph), 7.35 (d, J = 8.7 Hz, 2H,
naph), 7.09 (d, J = 9.0 Hz, 4H, Ar), 6.50 (d, J = 9.0 Hz, 4H, Ar), 3.34 (q, J = 7.2 Hz, 8H,
2 2
Cl was added
2
1
3
1
NCH
N=CH), 8.20 (d, J = 8.7 Hz, 2H, naph), 7.73 (d, J = 8.7 Hz, 2H, naph), 7.64–7.53 (m, 4H, Ar),
.69 (d, J = 9.2 Hz, 4H, Ar), 3.11 (q, J = 6.9 Hz, 8H, NCH ), 0.91 (t, J = 6.9 Hz, 12H, CH
) δ = –134.83 (dd, J = 23.6, 9.0 Hz, 2F), –156.30 (t, J =
2 3 5
), 1.15 (t, J = 7.2 Hz, 12H, CH ) ppm; H NMR (300 MHz, Pyridine-d ) δ = 9.41 (s, 2H,
6
2
3
)
19
ppm.; F NMR (376 MHz, CDCl
2
1
3
1
3
1
0.4 Hz, 1F), –163.58 - –163.89 (m, 2F) ppm; C{ H} NMR (101 MHz, Pyridine-d
60.8, 158.3, 149.2, 148.8 – 148.5 (m), 142.5-139.4 (m), 139.3-136.4 (m), 131.4, 127.9,
5
) δ =
125.1, 116.9, 116.6, 111.8, 44.8, 12.8 ppm.; FTIR (ATR) ν = 2974, 2937, 2874, 1646, 1613,
1
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7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
-1
1
(
591, 1569, 1517,1459, 1352, 1286, 1274, 1194, 1093, 977, 919, 815, 684 cm ; HRMS
+
ESI): calcd. for C56
-[N-(4’-nitrophenyl)iminomethyl)]-6-[N’-(4’’-(N’’,N’’-diethylaminophenyl)-
iminomethyl)]-1,5-dihydroxynaphthalene bis(diphenylborinic) complex (10): To solution of
ethoxydiphenylborane ((C BOEt) (0.66 g, 3.1 mmol) in anhydrous 2-MeTHF (25 mL)
compound 16 (0.36 g, 1.0 mmol) was added. The mixture was warmed to 50 °C and stirred
for 17 hours. Then 4-nitroanilne (0.15 g, 1.05 mmol) was added and a mixture was stirred for
2 hours at 50 °C. Volatiles were removed under reduced pressure to obtain a dark solid. Et
was added with stirring and after 20 min a dark precipitate was filtered. It was washed with
Et O (5 × 10 mL) and hexane (2 × 10 mL), and dried under vacuum. The pure compound 10
was obtained as a violet powder (0.54 g, 67%). M.p. 270-275 °C. H NMR (400 MHz,
Acetone-d ) δ = 9.20 (s, 1H, N=CH), 8.92 (s, 1H, N=CH), 8.20-8.12 (m, 2H, Ar), 7.78 (d, J =
8.7 Hz, 2H, naph), 7.63-7.53 (m, 4H, Ar), 7.51-7.42 (m, 8H, Ar), 7.19-7.03 (m, 14H, Ar),
.57–6.49 (m, 2H, Ar), 3.35 (q, J = 7.0 Hz, 4H, NCH ), 1.09 (t, J = 7.0 Hz, 6H, CH );
) δ = 163.01, 162.98, 160.3, 158.8, 150.5, 147.8, 146.9,
34 2 20 4 2
H B F N O [M+H] 1197.2627; found 1197.2646.
2
6 5 2
F )
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
O
2
1
6
6
2
3
13
1
C{ H} NMR (101 MHz, CDCl
3
1
1
C
34.1, 133.8, 133.6, 132.3, 131.1, 127.4, 127.3, 127.0, 126.8, 126.5, 125.9, 125.8, 125.5,
24.4, 116.8, 115.9, 115.2, 115.1, 110.9, 44.5, 12.6 ppm; HRMS (ESI): calcd. for
+
52
H
44
B
2
N
4
O
4
[M+H] 811.3627; found 811.3638.
Optical properties: The UV-Vis absorption spectra were recorded using a Hitachi
UV-2300II spectrometer. The emission spectra were recorded using a Hitachi F-7000
spectrofluorometer, equipped with a photomultiplier detector, calibrated using Spectral
Fluorescence Standard Kit certified by BAM Federal Institute for Materials Research and
1
1
Testing. The measurements were performed at room temperature, according to published
1
2
procedures. Suprasil quartz cuvettes (10.00 mm) were used. 1.5 nm slits were used for
absorption and 2.5 nm slits were used for emission spectra. To eliminate any background
emission, spectrum of pure solvent was subtracted from the samples’ spectra. QY were
determined in diluted solutions (A < 0.1 for longest wavelength band) by comparison with
known standards: Coumarin 153 in ethanol (c = 4·10 mol · dm ), Rhodamine 6G in ethanol
c = 9·10 mol · dm ), Rhodamine 101 in methanol (c = 3·10 mol·dm ) and Cresyl violet
-
6
-3
-
7
-3
-7
-3
(
-6
-3
perchlorate in ethanol (c = 1·10 mol · dm ). Concentration of bis(boranil) solutions were in
-6
-3
the range of 1-3·10 mol · dm (concentration was adjusted to reach absorbance similar to
that for reference solution at the excitation wavelength). To calculate the QY the following
formula was used:
1 − 10!!!"
!
ꢀ
ꢀ
!
!
QY = QY ∙
∙
∙
!
!
!"
1 − 10!!
!
ꢀ!"
ꢀ
!"
where F is the relative integrated photon flux of sample (x) and standard (st), A is the
absorbance at the excitation wavelength, n is the refractive index of used solvents.
ꢀ
ꢀ!" · ꢀ!"
ꢀ
=
ꢀ! ꢀꢀ!"
=
ꢀꢀ!"
ꢀ
ꢀ!"
Photon fluxes (F) were calculated by integration of corrected spectra (I
c
), obtained by
multiplication of intensity of emission spectra (I) by photon energy and division by the
spectral responsivity (s) in corresponding wavelengths (λem). All measurements were carried
out at room temperature. For compound A, 1 referenced standards were used: Coumarine 153
(
r r r
QY = 0.38); 2-4: Rhodamine 6G (QY = 0.95); 5-7: Rhodamine 101 (QY = 1.00); 8-10
1
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Cresyl violet perchlorate (QY
IUPAC report. The following excitation wavelengths (nm) were used: 370 (A), 400 (B), 440
r
= 0.56). The QY for these standards were adopted from
13
(
1 – DCM), 465 (1 – toluene), 500 (2-4 – toluene), 503 (2-4 – DCM), 531 (5 – toluene), 533
(5-7 – DCM; 6 - toluene), 540 (7 – toluene), 550 (8, 10 – DCM), 555 (7, 10 – toluene), 563 (9
– DCM), 571 (9 – toluene).
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Absolute fluorescence quantum yields of 4 and 7 in solid state (powders) were determined
using FLS980 (Edinburgh Instruments) fluorescence spectrometer, equipped with an
integrating sphere, with BENFLEC inside coating, from Edinburgh Instruments.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Acknowledgements
This work was supported by the National Science Centre (Narodowe Centrum Nauki, Grant
No. UMO-2015/19/D/ST5/00735). The X-ray measurements were undertaken at the
Crystallographic Unit of the Physical Chemistry Laboratory, Chemistry Department,
University of Warsaw. We would like to thank prof. Krzysztof Woźniak from University of
Warsaw. Authors thank The Interdisciplinary Centre of Mathematical and Computational
Modelling in Warsaw (grant no. G33-14) for providing computer facilities. Support from
Aldrich Chemical Company, Milwaukee, WI, USA, through the donation of chemicals and
equipment is gratefully acknowledged.
Supporting Information
Detailed information regarding X-ray structures of complexes 4 and 9, DSC, electrochemical
measurements, spectroscopic measurements, time-dependent UV-Vis experiments,
computational studies as well as copies of NMR spectra are gathered in the Supporting
Information.
References:
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Chem. Soc. Rev. 2013, 42, 8416. (c) Frath, D.; Massue, J.; Ulrich, G.; Ziessel, R.
Angew. Chem. Int. Ed. 2014, 53, 2290.
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8
46. (b) Mellerup, S. K.; Rao, Y.-L.; Amarne, H.; Wang, S. Org. Lett. 2016, 18, 4436.
(c) Benelhadj, K.; Massue, J.; Ulrich, G. New J. Chem. 2016, 40, 5877. (d) Pais, V. F.;
Ramírez-López, P.; Romero-Arenas, A.; Collado, D.; Nájera, F.; Pérez-Inestrosa, E.;
Fernández, R.; Lassaletta, J. M.; Ros, A.; Pischel, U. J. Org. Chem. 2016, 81, 9605. (e)
Saint-Louis, C. J.; Magill, L. L.; Wilson, J. A.; Schroeder, A. R.; Harrell, S. E.;
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H.-Y.; Paine, T. D.; Rachford, A. A. Dyes Pigm. 2017, 141, 83.
1
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(
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(
(
b) Frath, D.; Azizi, S.; Ulrich, G.; Retailleau, P.; Ziessel, R. Org. Lett. 2011, 13, 3414.
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Dobkowski, J.; Wnuk, P.; Buczyńska, J.; Pszona, M.; Orzanowska, G.; Frath, D.;
Ulrich, G.; Massue, J.; Mosquera-Vázquez, S.; Vauthey, E.; Radzewicz, C.; Ziessel, R.;
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