Synthesis and photophysical properties of aryl-substituted 2-borylbenzaldimines and their extended π-conjugated congeners

Article abstract of DOI:10.1021/jo202212s

Novel N-aryl-substituted 2-borylbenzaldimines 6 and related systems with extended π-framework 7 based on two borylbenzaldimine units linked by a spacer moiety were synthesized by condensation reactions of 2-(dimesitylboryl) benzaldehyde 3 with various amines 4 and diamines 5. All compounds were completely characterized including X-ray diffraction, especially in view of Lewis acid-base B-O and B-N interactions. The electronic as well as the photophysical properties of bisimines 7 were determined using cyclic voltammetry, UV/vis, and fluorescence spectroscopy and quantum chemistry. These compounds feature large Stokes shifts and reversible reduction waves. Interestingly, UV irradiation experiments unfold enhanced photostability for compounds 7 with an extended π-skeleton. By use of 1,8-diaminonaphthalene we observed the formation of a hitherto unknown BN-heterocyclic compound 9 fused with a perimidine skeleton. Structural and energetic aspects were evaluated by high level quantum chemical methods (DFT and SCS-MP2-calculations).

Full text of DOI:10.1021/jo202212s

Article
pubs.acs.org/joc
Synthesis and Photophysical Properties of Aryl-Substituted
2-Borylbenzaldimines and Their Extended π-Conjugated Congeners
Benedikt Neue,† Roland Frohlich,† Birgit Wibbeling,† Aiko Fukazawa,‡ Atsushi Wakamiya,§
̈
Shigehiro Yamaguchi,*,‡ and Ernst-Ulrich Wurthwein*,†
̈
†Westfalische Wilhelms-Universitat, Corrensstraße 40, 48149 Munster, Germany
‡Department of Chemistry, Graduate School of Science, Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan
§Institute for Chemical Research, Kyoto University Uji, Gokasho, Kyoto, 611-0011, Japan
̈
̈
̈
S
* Supporting Information
ABSTRACT: Novel N-aryl-substituted 2-borylbenzaldimines 6 and
related systems with extended π-framework 7 based on two boryl-
benzaldimine units linked by a spacer moiety were synthesized by
condensation reactions of 2-(dimesitylboryl)benzaldehyde 3 with
various amines 4 and diamines 5. All compounds were completely
characterized including X-ray diffraction, especially in view of Lewis
acid−base B−O and B−N interactions. The electronic as well as the
photophysical properties of bisimines 7 were determined using cyclic
voltammetry, UV/vis, and fluorescence spectroscopy and quantum
chemistry. These compounds feature large Stokes shifts and reversible
reduction waves. Interestingly, UV irradiation experiments unfold
enhanced photostability for compounds 7 with an extended π-skeleton.
By use of 1,8-diaminonaphthalene we observed the formation of a
hitherto unknown BN-heterocyclic compound 9 fused with a perimidine skeleton. Structural and energetic aspects were
evaluated by high level quantum chemical methods (DFT and SCS-MP2-calculations).
B−N coordination and the resulting influences on the photophysical
properties. Here we report the preparation and characterization
of a series of N-aryl 2-borylbenzaldimines and their extended
π-conjugated compounds with these BN-heterocycles as the termi-
nating units. The impact of the π-spacers on the photophysical and
electrochemical properties as well as on the photostability has been
studied.
INTRODUCTION
■
Organic π-conjugated materials1 are of emerging interest for the
design and development of organic optoelectronics such as
organic light-emitting diodes (OLEDs)2 and organic field-effect
transistors (OFETs).3 The incorporation of main group
elements into π-conjugated frameworks was shown to be a
versatile method for tuning the photophysical and electronic
properties of these systems.4 Four coordinate boron-containing
π-conjugated compounds,5 especially of the N,C-chelate type,
have attracted interest because of their electronic and
photophysical properties.6,7 In particular, their photochromism
has been extensively studied by the group of Wang, who used
N-heteroaromatic rings, such as pyridine and indole, as the
boron-coordinating subunit.8,9 Imine-coordinating organo-
RESULTS AND DISCUSSION
■
Synthesis. Starting material for the synthesis of the imine
derivatives 6a−c and 7a−d is the 2-dimesitylborylbenzaldehyde
3 (Scheme 1). Its preparation was previously described.10,11
In addition to the published data, we were able to obtain
single crystals of the aldehyde 3 and to confirm the molecular
structure by X-ray diffraction12 (Figure 1). The molecular
structure in the solid state reveals the coordination of the Lewis
basic carbonyl oxygen atom to the Lewis acidic boron center
(B−O: 1.645(2) Å, CO: 1.2553(19) Å). The measured B−O
distance is in line with the value of 1.66 Å determined by
quantum chemical calculations.11
boron compounds were reported independently by Kawashima10
11
̈
and Gabbai. Kawashima used C6F5 substituents at the boron
̈
atom, whereas in the work of Gabbai et al. mesityl substituents
were employed. The latter work reports two examples with
aliphatic substituents on the imine nitrogen. We became
interested in the synthesis of more elaborate N-aryl-substituted
imine−organoboron Lewis acid−base pairs with larger π-systems
because the facile formation of the imine functionality should
enable us to produce a variety of novel π-systems having potential
for applications to organic electronics. To this end, it is crucial
with regard to the chemical and photostability of the imine-
coordinating boron compounds to study the substituent effects on
In order to get further insights into the bonding situation of
3, Wiberg bond index14 calculations using the NBO15 approach
as implemented in the GAUSSIAN 09 series of programs were
Received: October 27, 2011
Published: February 10, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of Compounds 3, 6, and 7 by Condensation of Dimesitylboryl Benzaldehyde 3 with Amines 4 or
Diamines 5
The synthesis of the imine derivatives 6a−c was accom-
plished by the condensation reaction of aldehyde 3 with various
amines 4/5 (1.0−1.1 equiv) using molecular sieves (Scheme 1).18
In addition to previous publications in which the preparation
of N-alkylated compounds was reported, we were now able to
synthesize fluorescent N-arylated BN-heterocycles 6a−c for
the first time by this method in moderate to excellent yield.11
Such systems offer the additional possibility to extend the
π-conjugation into the amine-derived part of the imino
compound.
The structure of compound 6a (crystal data were also ob-
tained for 6b; see the Supporting Information) was elucidated
by X-ray crystallography (Figure 2). The lengths of the B−N
Figure 1. Molecular structure of compound 3 in the crystal (Schakal
plot13).
performed.16 The Wiberg bond index of the coordinating B−O
interaction amounts to 0.489 (B−O) and for the CO-bond
to 1.48. For comparison, the isomer of 3-II with no direct B−O
coordination was also calculated. Here, the Wiberg bond index
of the CO bond has a value of 1.81, illustrating the severe
electronic changes induced by the coordination of boron by
oxygen in such compounds. This is well in line with the
calculated energy difference between 3 and 3-II of 9.4 kcal/mol
(SCS-MP2/6-311+G(d,p)//B3LYP6-31G(d)17) (Scheme 2).
Figure 2. Molecular structure of 6a in the crystal (Schakal plot).
and CN bonds 6a in the solid state were measured as
1.693(3) Å and 1.293(3) Å. The B−N bond length in 6a is
slightly elongated in comparison to the values reported in the
literature (1.627(3) and 1.630(4) Å for N-alkylated com-
pounds).11 This might be attributed to the different electronic
influences of the sterically more demanding aromatic
substituents or spacer units at the nitrogen atom.
Scheme 2. Relative Energies for 3 and 3-II [kcal/mol] (SCS-
MP2/6-311+G(d,p)//B3LYP/6-31G(d)+ZPE
The Wiberg bond indices for 6a are calculated to 0.560(B−N)
and 1.565(CN), indicating the stronger B−N-interaction
compared to the B−O-interaction in 3. The noncoordinating
structural isomer 6a-II has a Wiberg bond index of 1.759 for the
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CN bond. Compound 6a-II was found to be 10.7 kcal/mol
higher in energy compared to 6a (Scheme 3).
Scheme 4. Formation of Compound 9
Scheme 3. Relative Energies of 6a and 6a-II [kcal/mol]
(SCS-MP2/6-311+G(d,p)//B3LYP/6-31G(d)+ZPE)
For the preparation of the extended π-conjugated com-
pounds 7 with various π-spacers, the aldehyde 3 and the
corresponding diamines 5 were used in a 2−3:1 ratio (Scheme 1).
In some cases, the use of an excess amount of aldehyde was
necessary to prevent the formation of monocondensation
products. Purification was performed by recycling GPC or
recrystallization to obtain a series of the condensated compounds
7 in good to excellent yields. Compound 7a is poorly soluble in
various organic solvents, such as toluene, chlorinated solvents, or
ethers, whereas 6a can be dissolved as well in apolar as in various
other solvents. Extending the π-skeleton going from 7a to 7d
increases the solubility in solvents like benzene or toluene because
of the growing apolar character of the molecule by extending the
spacer moiety. While compound 6a was found to decompose after
a few hours (2−4) in benzene or dichloromethane solution, the
extended congeners 7 could be stored in solution over days. The
increasing chemical stability of compounds 7 in comparison to 6a
might be attributed to the sterically bulky dimesitylboryl subunits
on both sides of the spacer in 7. Therefore, the imine
functionalities in 7 might be less accessible for decomposition
reactions compared to the ones in 6a.
Figure 4. Molecular structure of compound 9 (Schakal plot).
We were able to obtain the molecular structures of
compounds 7a and 7b by X-ray crystallography (for 7a, see
Figure 3). According to the crystal structure of 7a, the lengths
was isolated in 62% yield (Scheme 4). Its structure was
confirmed by X-ray analysis (Figure 4). This compound is
assumed to be formed by the intramolecular cyclization of
monocondensated product 8 followed by aerobic oxidation.
According to the crystal structure of 9, the B−N bond
(1.658 Å) is slightly shorter than those of 6a and 7a. The bond
lengths of the 6-membered ring formed amount to N1−C2
1.335(3) Å, C2−N2 1.328(3) Å, N2−C18 1.397(3) Å,
C18−C19 1.418(4) Å, C19−C10 1.417(4) Å, and N1−C10
1.424(3) Å. NICS(0)19 calculations (B3LYP/6-311+G(d)) give
values of −7.1 and −7.4 ppm for the rings of the naphthalene
subunit indicating aromatic character, whereas the NICS(0)
value for the pyrimidine subunit is calculated to 7.7 ppm, a
strong indicator for antiaromaticity.20
Photophysical and Electrochemical Properties. UV/vis
absorption and fluorescence spectra are shown in Figure 5. Table 1
provides the absorption and emission maxima and the quantum
yields for 6a and 7. The UV/vis spectra of compounds 6a and 7
show absorption maxima between 284 and 370 nm. The longest
absorption band or shoulder (in 6a ∼350 nm and 7a ∼370 nm)
can be attributed to the intramolecular charge transfer (ICT)
transition from the mesityl to the N-benzylidenearylidene-2-amine
part of the molecule (see below, quantum chemical calculations).
All compounds show emissions in the region of 569 to 583 nm.
The quantum yields for 6a and 7 were found to range from 3% to
10%. Notably, these compounds exhibit large Stokes shifts in
the range of 201−221 nm (9500−11100 cm−1), which suggest the
Figure 3. Molecular structure of 7a in the crystal (Schakal plot).
of the B−N and CN bonds amount to 1.688(4) Å and
1.292(4) Å, respectively, which are comparable to those of
compounds 6a and 6b. Wiberg bond indices for the B−N
bonds were calculated for 7a to 0.561 and 7b to 0.557. For the
CN bonds, Wiberg indices of 1.549 and 1.560 were obtained
(for Wiberg bond indices of other compounds, see the
Supporting Information).
An interesting reaction was observed when compound 3 was
condensated with 1,8-diaminonaphthalene. After workup and
recrystallization from dichloromethane, a perimidine derivate 9
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Figure 5. UV/vis (left) and fluorescence (right) spectra of compounds 6a (purple) 7a (red), 7b (blue), 7c (orange), and 7d (green) in CH2Cl2
(for details, see the Supporting Information).
Table 1. Photophysical Data for Compounds 6a and 7a−d in CH2Cl2
a
b
Absolute fluorescence quantum yield determined by a calibrated integrating sphere system. Could not be determined because the compound
underwent a photoreaction during the measurement.
potential utility as fluorescence dyes.21 For the pentacyclic 9, the
absorption maximum was found at 272 nm, while no fluorescence
was observed.
Quantum Chemical Calculations. DFT calculations were
carried out for 6a and 7a−d (B3LYP/6-31G(d)). Figure 7 depicts
the Kohn−Sham HOMO and LUMO orbitals of 6a and 7. For all
compounds 7, the HOMO-1 and the HOMO are quasi-
degenerate. They are each localized on one mesityl group of the
two bismesityl boron subunits, while the LUMO is delocalized
over the imine-containing π-conjugated skeleton. TD-DFT
calculations (B3LYP/6-31G(d), td=(nstates=20)) indicate that
the longest absorption bands for 6a and 7a−d are attributable to
the HOMO−LUMO transitions (with contributions of the
HOMO-1−LUMO-transitions in case of compounds 7). Thus,
these have the character of intramolecular charge-transfer
transitions (ICT) from the mesityl group to the π-skeleton.
Taking these similarities into consideration, the different photo-
stabilities between 6a and 7 may be attributable to the different
NMR Experiments. To confirm the photochemical stability
difference between systems 6a and 7 we prepared NMR
samples of both compounds, irradiated these with a UV lamp
(366 nm, distance sample lamp: 3 cm), and measured proton
NMR spectra after various irradiation periods. Figure 6 depicts
the changes observed in the NMR spectra with time. Obviously,
compound 7d undergoes no structural change even after pro-
longed irradiation time, whereas new peaks appear in the
spectra of the mono-BN-heterocyclic system 6a, which de-
composes completely within 4 h of UV irradiation. This is seen
from the decreasing intensity of the mesityl signals at 2.18 and
2.04 ppm, while new signals arise.
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Figure 6. Time-dependent 1H NMR spectra of 6a (top/left) and 7d (top/right, 8.0−0 ppm) after incremental periods of irradiation (with UV light
(standard: anisole, solvent C6D6) and magnified spectra of 6a region: 5.7−4.4 ppm (bottom/left) and 2.4−1.8 ppm (bottom/right).
degree of delocalization of the LUMO in 6a compared to 7. The
considerably higher degree of delocalization in 7 might impede
possible photorearrangement reactions, since here the energy
might be dispersed over the spacer and the adjacent second BN-
heterocyclic system.9
within the systems. In addition, we also studied the oxidation
potential of 7a as an example for molecules of type 7. An
irreversible oxidation process was observed in CH2Cl2 at 0.1 V s−1
scan rate, suggesting that the radical cation formed might be
unstable under the measurement conditions.
Summary. In this work, we present the synthesis and
characterization of novel imine-based BN-heterocycles, espec-
ially imines with N-aryl substituents 6 and related bisimines
with extended π-conjugation 7. The latter compounds contain a
spacer moiety which interconnects two BN-heterocyclic
systems. We observed that these molecules show enhanced
chemical stability compared, e.g., to the phenyl derivative 6a
containing a single BN-heterocyclic unit. UV/vis and
fluorescence and cyclic voltammetric measurements revealed
that compounds of type 7 show large Stokes shifts and high
electrochemical stability, which indicate their possible utility in
organic optoelectonic materials, such as fluorescence dyes and
semiconducting materials.22 Furthermore, compounds 7 also
do not undergo photoisomerization as it was previously ob-
served in four coordinate boron compounds substituted with
mesityl groups. The lack of photoisomerization reactions is
advantageous for technical applications.9 Additionally, we syn-
thesized a novel pentacyclic molecule 9 containing a perimidine
skeleton fused with a BN-heterocycle.
a
Table 2. Electrochemical Data for Compounds 7
b,
c
c
compd
Epc (V)
E1/2 (V)
7a
7b
7c
7d
−2.06
−1.98
−2.14/−2.21
−2.08/−2.38
−1.96/−2.15
b
−2.18/−2.32
−2.19/−2.50
−1.88/−2.24
a
In THF with Bu4N+PF6−, scan rate 100 mV s−1. Cathodic peak
c
potential vs Fc/Fc+. Reduction potentials vs Fc/Fc+
Cyclic Voltammetry. To assess the electrochemical
properties of 7a−d, cyclic voltammetric measurements were
carried out. The results are summarized in Table 2, and the
cyclic voltammograms are shown in Figure 8.
Reversible reduction waves were found in all cyclic voltammo-
grams of 7. Compound 7a shows one (E1/2 = −1.98 V) and 7b−d
two reversible reduction waves, respectively. In the latter cases, due
to the large conjugated system, the generation of dianionic species
seems to be reasonable. The change from the phenylene (7a) to
the naphthyl spacer (7b) shifts the first reduction potential to
more negative values (E1/2 = −1.98 V for 7a and E1/2 = −2.14 V
for 7b). These values are comparable to those reported for the
BN-coordinating thienylthiazoles dimers, which were suggested as
electron-transporting materials.6 Reversibility was also found at
higher scan rates (0.2 V s−1), demonstrating a fast redox process
EXPERIMENTAL SECTION
■
Compounds 6 were synthesized by condensation reaction of dimesityl
benzaldehyde 311 with amines (1 equiv or small excess) in CH2Cl2.
[1-(2-(Dimesitylboranyl)phenyl)meth-(E)-ylidene]-
phenylamine (6a). A 1.11 g (3.13 mmol) portion of 3 was dissolved
in 60 mL of dry CH2Cl2. Subsequently, 0.35 mL (3.19 mmol)
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Figure 7. Photophysically relevant molecular orbitals with energies (in eV) of 6a and 7a−d: HOMO-1 (left), HOMO (center), LUMO (right)
(B3LYP/6-31G(d), isocontour value 0.02) (for LUMO+1, excitation energies and oscillator strengths, see the Supporting Information).
Figure 8. Cyclic voltammograms of compounds 7 (measured in THF, Bu4N+PF6−, scan rate 100 mV s−1).
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of aniline was added to the stirring mixture. The compound was
purified by washing with pentane. Yellow crystals were obtained by
recrystallization from CH2Cl2 to give 1.20 g (2.71 mmol, 87%) of
crude product was heated to reflux in toluene and filtrated hot. To
obtain single crystals, the solid was recrystallized from CH2Cl2 to give
0.30 g (0.39 mmol, 79%) as pale yellow crystals. Mp: > 300 °C. IR
compound 6a. Mp: 170−171 °C. IR (neat): v = 3017 cm−1 (w), 2970
(neat): v = 2974 cm−1 (w), 2959 (w), 2922 (w), 2913 (w), 1603 (s),
̃
̃
(m), 2961 (m), 2920 (m), 2868 (w), 2849 (w), 1603 (s), 1595 (s),
1574 (m), 1537 (vs), 1491 (s), 1470 (s), 1443 (vs), 1412 (m), 1379
(m), 1358 (s), 1283 (w), 1261 (m), 1234 (m), 1202 (m), 1136 (m),
1578 (w), 1533 (vs), 1499 (m), 1470 (m), 1447 (s), 1412 (w), 1379
(w), 1356 (w), 1263 (w), 1229 (w), 1200 (vs), 1163 (w), 1142 (w),
1015 (m). UV/vis (CH2Cl2): λabs (v, ε) = 317 nm (31546 cm−1, 2.23 ×
̃
1113 (w), 1024 (m), 1015 (m). UV/vis (CH2Cl2): λabs (v, ε) =
10−4 M−1 cm−1), 370 nm (27027 cm−1, sh). Fluorescence (CH2Cl2):
̃
1
304 nm (32895 cm−1, 1.16 × 10−4 M−1 cm−1), 350 (28571 cm−1, sh).
λem (v) = 583 nm (17153 cm−1), λ = 370 nm. Φf: 0.04. H NMR
̃
exc
Fluorescence (CH2Cl2): λem (v) = 570 nm (17544 cm−1), λ
=
(THF-d8, 399.65 MHz): δ = 1.73 ppm (s, 24H), 1.75 (s, 12H), 6.51
(bs, 8H), 6.95 (s, 4H), 7.23 (t, J = 8.0 Hz, 2H), 7.33 (t, J = 8.0 Hz,
2H), 7.60 (d, J = 8.0 Hz, 2H), 7.80 (d, J = 8.0 Hz, 2H), 8.83 (s, 2H).
13C NMR (THF-d8, 100.40 MHz): δ = 21.0 ppm, 125.8, 126.3, 127.9,
̃
exc
370 nm. 1H NMR (C6D6, 300.13 MHz): δ = 2.05 ppm (s, 12H), 2.19
(s, 6H), 6.77 (bs, 4H), 6.79−6.85 (m, 4H), 7.00 (td, 1H, J = 7.2 Hz,
J = 0.9 Hz, 1H), 7.10 (td, 1H, J = 7.2 Hz, J = 0.9 Hz, 1H), 7.26 (dt, J =
7.5 Hz, J = 0.9 Hz, 1H), 7.34 (s, 1H), 7.84 (d, J = 7.5 Hz, 1H). 13C
NMR (C6D6, 75.47 MHz): δ = 21.0 ppm, 25.7, 125.2, 125.4, 126.3,
127.9, 128.3, 130.4, 131.8, 132.9, 134.2, 137.3, 141.3, 145.9, 170.0. 11B
NMR (C6D6, 128.15 MHz): δ = 8.37 ppm. HRMS(ESI): calcd for
C31H32BNNa 452.2521, found 452.2522. Anal. Calcd for C31H32BN
(429.40): C, 86.71; H, 7.51; N, 3.26. Found: C, 86.49; H, 7.50; N, 3.17.
The X-ray crystal structure data of 6a can be found in the Supporting
Information.
130.7, 132.0, 133.5, 134.4, 138.6, 146.4, 173.0. 11B NMR (THF-d8,
128.15 MHz): δ = 10.02 ppm. HRMS(ESI): calcd for C56H58B2N2Na
803.4679, found 803.4699. Anal. Calcd for C56H58B2N2 (780.70): C,
86.15; H, 7.49; N, 3.59. Found: C, 85.89; H, 7.44; N, 3.39. X-ray crystal
structure data of 7a can be found in the Supporting Information.
N,N′-Bis[1-(2-(dimesitylboranyl)phenyl)meth-(E)-ylidene]-
naphthalene-1,5-diamine (7b). A 0.71 g (2.00 mmol) portion of of
3 was dissolved in 20 mL of dry CH2Cl2. Subsequently, 0.16 g (1.00
mmol) of 1,5-diaminonaphthalene in 80 mL of dry CH2Cl2 was slowly
added to the stirring mixture. After 18 h of stirring, the resulting yellow
solid was washed with CH2Cl2 to give 0.64 g (0.76 mmol, 76%) as a
light orange solid. Colorless crystals were obtained by recrystallization
[1-(2-(Dimesitylboranyl)phenyl)meth-(E)-ylidene]-
naphthalen-1-ylamine (6b). For the synthesis of compound 6b,
0.35 g (1.00 mmol) of 3 was dissolved in 50 mL of dry CH2Cl2. Then
0.14 g (1.00 mmol) of 1-naphthylamine in 50 mL of dry CH2Cl2 was
added, and the mixture was stirred for 18 h. The compound was
purified by washing with hexane to give 0.21 g (0.44 mmol, 44%) of
from dichloromethane. Mp: 295−296 °C. IR (neat): v = 2970 cm−1
̃
(m), 2961 (m), 2943 (m), 2934 (m), 2928 (m), 2920 (m), 2359 (vs),
2342 (vs), 1595 (vs), 1576 (m), 1533 (vs), 1506 (s), 1487 (w), 1466
(s), 1447 (vs), 1406 (vs), 1379 (s), 1358 (vs), 1325 (w), 1315 (w),
1267 (s), 1246 (m), 1219 (vs), 1206 (s), 1190 (m), 1177 (vs), 1159
(s), 1146 (s), 1109 (m), 1076 (m), 1063 (w), 1015 (vs). UV/vis
compound 6b as colorless crystals. Mp: 196−197 °C. IR (neat): v =
̃
2976 cm−1 (w), 2959 (w), 2924 (m), 2916 (m), 2361 (m), 2342 (w),
2332 (w), 1597 (vs), 1574 (s), 1539 (vs), 1510 (m), 1466 (m), 1441
(vs), 1410 (m), 1395 (m), 1375 (s), 1360 (s), 1339 (w), 1304 (w),
1283 (w), 1263 (s), 1231 (m), 1209 (vs), 1186 (w), 1169 (m), 1161
(m), 1140 (s), 1107 (w), 1097 (w), 1086 (s), 1070 (w), 1053 (w),
1018 (s). 1H NMR (C6D6, 300.13 MHz): δ = 2.16 ppm (bs, 6H), 2.18
(bs, 12H), 6.74 (bs, 4H), 6.99−7.18 (m, 4H), 7.24−7.27 (m, 2H),
7.33−7.39 (m, 1H), 7.43 (s, 1H), 7.49 (t, J = 8.4 Hz, 2H), 7.93 (t, J =
7.2 Hz, 2H). 13C NMR (C6D6, 75.48 MHz): δ = 20.9 ppm, 25.7,
122.3, 124.2, 125.7, 125.9, 126.4, 126.6, 127.9, 128.3, 130.3, 132.5,
132.9, 134.3, 137.7, 141.6, 142.0, 171.8. 11B NMR (C6D6, 96.29 MHz):
δ = 11.34 ppm. HRMS(ESI): calcd for C35H34BNH 480.2858, found
480.2858. Anal. Calcd for C35H34BN (479.46): C, 87.68; H, 7.15; N,
2.92. Found: C, 87.06; H, 7.30; N, 2.85. The X-ray crystal structure
data of 6b can be found in the Supporting Information.
(CH2Cl2): λabs (v, ε) = 289 nm (34602 cm−1, 2.98 × 10−4 M−1 cm−1),
̃
351 nm (28490 cm−1, 1.20 × 10−4 M−1 cm−1). Fluorescence (CH2Cl2):
1
λem (v) = 572 nm (17483 cm−1), λ = 370 nm. Φf: 0.04. H NMR
̃
exc
(C6D6, 399.65 MHz): δ = 2.02 ppm (bs, 24H), 2.10 (bs, 12H), 6.65−
6.71 (m, 11H), 6.97 (d, J = 8.4 Hz, 2H), 7.03 (t, J = 7.2 Hz, 3H), 7.22
(d, J = 7.2 Hz, 2H), 7.40 (s, 2H), 7.64 (d, J = 7.2 Hz, 2H), 7.81 (d, J =
7.2 Hz, 2H). 13C NMR (C6D6, 100.40 MHz): δ = 20.8 ppm, 24.8,
122.3, 122.4, 124.9, 125.8, 126.6, 128.4, 130.0, 130.1, 130.4, 130.5,
132.5, 133.1, 134.6, 137.6, 141.1, 141.9, 172.0. 11B NMR (C6D6,
128.15 MHz): δ = 12.66 ppm. HRMS(ESI): calcd for C60H60B2N2H
831.5016, found 831.5021.
N,N′-Bis[1-(2-(dimesitylboranyl)phenyl)meth-(E)-ylidene]-
naphthalene-1,4-diamine (7c). A 0.08 g (0.50 mmol) portion of
1,4-diaminonapthalene was dissolved in 20 mL of dry CH2Cl2. The
mixture was slowly added to a solution of 0.35 g (1.00 mmol) of 3 in
80 mL of dry CH2Cl2. After addition, the solution was stirred for 17 h.
Subsequently, the crude product was purified by recycling GPC (in
toluene) to give 0.41 g (0.49 mmol, 98%) of 7c as a yellow solid. Mp:
Anthracen-2-yl[1-(2-(dimesitylboranyl)phenyl)meth-(E)-
ylidene]amine (6c). A 0.35 g (1.00 mmol) portion of 3 was dissolved
in 50 mL of dry CH2Cl2. Then, 0.20 g (1.02 mmol) of anthracen-2-
amine in 100 mL of dry CH2Cl2 was added. To purify compound 6c,
the crude product was recrystallized from CH2Cl2 to give 0.53 g
(0.99 mmol, 99%) as yellow crystals. Mp: 225−226 °C. IR (neat): v =
̃
3048 cm−1 (vw), 3019 (vw), 2974 (w), 2955 (w), 2914 (w), 2878 (vw),
2868 (vw), 2853 (vw), 1628 (vw), 1603 (s), 1574 (w), 1531 (vs), 1495
(vw), 1470 (w), 1443 (vs), 1408 (w), 1379 (w), 1366 (w), 1354 (w),
1335 (w), 1312 (vw), 1283 (vw), 1265 (w), 1223 (m), 1188 (w), 1171
(w), 1155 (w), 1140 (m), 1105 (w), 1080 (vw), 1024 (w), 1015 (m).
1H NMR (C6D6, 300.21 MHz): δ = 2.15 ppm (s, 10H), 2.18 (s, 6H), 6.78
(bs, 4H), 6.89−6.97 (m, 1H), 7.02−7.07 (m, 1H), 7.12−7.16 (s, 1H),
7.20−7.23 (m, 2H), 7.36 (d, J = 7.5 Hz, 1H), 7.46 (d, J = 9.0 Hz, 1H),
7.58 (s, 1H), 7.57−7.58 (m, 1H), 7.69−7.72 (m, 2H), 7.90 (d, J = 7.5 Hz,
1H), 7.96 (d, J = 8.4 Hz, 2H). 13C NMR (C6D6, 75.47 MHz): δ = 20.9
ppm, 25.7, 123.4, 123.9, 125.5, 126.0, 126.4, 126.6, 127.3, 128.4, 128.3,
128.4, 128.5, 128.7, 130.5, 130.6, 130.8, 131.8, 132.5, 132.6, 133.0, 134.3,
137.4, 141.4, 142.6, 170.0. 11B NMR (C6D6, 96.29 MHz): δ = 10.26 ppm.
HRMS(ESI): calcd for C39H36BNH 530.3014, found 530.3005. Anal.
Calcd for C39H36BN (529.52): C, 88.46; H, 6.85; N, 2.65. Found: C,
88.09; H, 6.77; N, 2.57.
234−235 °C. IR (neat): v = 2963 cm−1 (m), 2940 (m), 2920 (m),
̃
2361 (m), 2340 (m), 1703 (w), 1601 (s), 1578 (m), 1535 (vs), 1445
(vs), 1412 (m), 1379 (m), 1358 (m), 1267 (m), 1233 (m), 1211 (vs),
1163 (m), 1144 (m), 1103 (w), 1059 (w), 1016 (m). UV/vis
(CH2Cl2): λabs (v, ε) = 289 nm (34602 cm−1, 2.57 × 10−4 M−1 cm−1),
̃
370 nm (27027 cm−1, 1.19 × 10−4 M−1 cm−1). Fluorescence (CH2Cl2):
1
λem (v) = 571 nm (17513 cm−1), λ = 370 nm. Φf: 0.03. H NMR
̃
exc
(C6D6, 399.65 MHz): δ = 2.09 ppm (bs, 12H), 2.12 (bs, 24H), 6.68
(bs, 8H), 6.80−6.83 (m, 2H), 7.00−7.07 (m, 4H), 7.12−7.16 (m, 2H),
7.33 (d, J = 7.2 Hz, 2H), 7.58 (s, 2H), 7.58−7.61 (m, 2H), 7.79 (d, J =
7.2 Hz, 2H). 13C NMR (C6D6, 100.40 MHz): δ = 20.8 ppm, 25.4,
120.0, 122.5, 126.3, 126.4, 126.9, 128.6, 129.3, 129.9, 130.1, 130.4,
132.6, 133.0, 135.0, 137.7, 141.5, 142.6, 171.6. 11B NMR (C6D6,
128.15 MHz): δ = 16.17 ppm. HRMS(ESI): calcd for C60H60B2N2K
869.4575, found 869.4582. Anal. Calcd for C60H60B2N2 (830.75): C,
86.75; H, 7.28; N, 3.37. Found: C, 86.00; H, 7.42; N, 3.21.
N,N′-Bis[1-(2-(dimesitylboranyl)phenyl)meth-(E)-ylidene]-
benzene-1,4-diamine (7a). A solution of 0.53 g (1.50 mmol) of
compound 3 in 40 mL of dry CH2Cl2 was prepared. Then, 0.05 g
(0.50 mmol) of p-phenylenediamine dissolved in 40 mL of dry CH2Cl2
was added slowly. The mixture was stirred for 48 h. Afterwards the
N,N′-Bis[1-(2-(dimesitylboranyl)phenyl)meth-(E)-ylidene]-
9H-fluorene-2,7-diamine (7d). A 0.29 g (1.50 mmol) portion of
2,7-diaminofluorene was dissolved in 20 mL of dry CH2Cl2 and added
slowly to a stirred solution of 1.07 g (3.00 mmol) of 3 in 80 mL of dry
CH2Cl2. After 12 h, the reaction mixture was filtrated and the crude
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The Journal of Organic Chemistry
Article
mixture was purified by GPC to give 1.25 g (1.44 mmol, 96%) as
ACKNOWLEDGMENTS
■
yellow crystals. Mp: 194−195 °C. IR (neat): v = 2924 cm−1 (w), 2914 (w),
̃
This work was supported by the IRTG 1143 Munster-Nagoya
(Deutsche Forschungsgemeinschaft (DFG, Bad Godesberg))
and the Fonds der Chemischen Industrie (Frankfurt).
̈
1605 (s), 1584 (s), 1557 (s), 1535 (s), 1514 (w), 1464 (s), 1433 s),
1416 (m), 1358 (m), 1333 (w), 1314 (w), 1306 (w), 1296 (w),
1263 (m), 1200 (s), 1175 (s), 1150 (s), 1111 (w), 1096 (w), 1038
(w), 1020 (w). UV/vis (CH2Cl2): λabs (v, ε) = 325 nm (30769 cm−1,
̃
sh), 354 (28249 cm−1, 2.73 × 10−4 M−1 cm−1). Fluorescence (CH2Cl2):
REFERENCES
■
1
λem (v) = 569 nm (17575 cm−1), λ = 370 nm. Φf: 0.10. H NMR
̃
exc
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10−4 M−1 cm−1), 325 nm (30770 cm−1, 1.20 × 10−4 M−1 cm−1), 339 nm
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ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for the new compounds; time-
dependent spectra of NMR experiments; fluorescence measure-
ments; graphics of the crystal structures showing thermal
ellipsoids with 50% probability; optimized Cartesian coor-
dinates (B3LYP/6-31G(d) and SCS-MP2/6-311+G(d,p)//
B3LYP/6-31G(d)+ZPE energies for the calculated structures;
details of TD-DFT calculations; Wiberg bond indices obtained
from NBO calculations (B3LYP/6-311G(d,p)); NICS calcu-
lations (B3LYP/6-311+G(d,p)). This material is available free
of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
■
(11) García-Hernan
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dez, Z.; Gabbaï, F. P. Z. Naturforsch. 2009, 64b,
Corresponding Author
(12) Data sets were collected with CCD diffractometers equipped
with a rotating anode generator. Programs used: data collection
COLLECT (Nonius B.V., 1998) and CrystalClear (Rigaku Corp.,
2000), data reduction Denzo-SMN (Otwinowski, Z.; Minor, W.
Methods Enzymol. 1997, 276, 307−326.) and CrystalClear (Rigaku
*E-mail: (E.-U.W.) wurthwe@uni-muenster.de, (S.Y.)
yamaguchi@chem.nagoya-u.ac.jp.
Notes
The authors declare no competing financial interest.
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