Boronic ester of a phthalocyanine precursor with a salicylaldimino moiety

Article abstract of DOI:10.1016/j.jorganchem.2011.11.016

4-(4-Formyl-3-hydroxyphenoxy)phthalonitrile (3) and its condensation product with 2-aminophenol have been synthesized to reach 4-(3-hydroxy-4-(((2- hydroxyphenyl)imino)-methyl)phenoxy)phthalonitrile (5), a tridentate ligand possessing ONO binding sites. S

Full text of DOI:10.1016/j.jorganchem.2011.11.016

Journal of Organometallic Chemistry 699 (2012) 87e91
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Boronic ester of a phthalocyanine precursor with a salicylaldimino moiety
*
S¸ ennur Özçelik, Ahmet Gül
Department of Chemistry, Technical University of Istanbul, Maslak, TR-34469 Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
4-(4-Formyl-3-hydroxyphenoxy)phthalonitrile (3) and its condensation product with 2-aminophenol
have been synthesized to reach 4-(3-hydroxy-4-(((2-hydroxyphenyl)imino)-methyl)phenoxy)phthaloni-
trile (5), a tridentate ligand possessing ONO binding sites. Subsequent condensation of phenylboronic acid
with 5 afforded a novel boronic ester of a Schiff base with a phthalonitrile group (7). Boronate 7 displays
high stability and can be handled in air due to the presence of coordinative BeN and covalent BeO bonds in
its structure. The novel compounds were characterized by elemental analyses, IR, UVevis, mass, 1H-,
13C- and 11B NMR spectra.
Received 29 August 2011
Received in revised form
10 November 2011
Accepted 15 November 2011
Keywords:
Phthalonitrile
Schiff’s base
Ó 2011 Elsevier B.V. All rights reserved.
Boronate complex
Phenylboronic acid
1. Introduction
emitting diodes (OLEDs) or organic field effect transistors, photo-
responsive materials, and sensory and imaging materials [14].
There is considerable interest in the synthesis and character-
ization of organoboron compounds due to their interesting appli-
cations, for example in medicinal chemistry, as enzyme inhibition,
potent and selective serine protease inhibition. Likewise, organo-
boron compounds have been used as anticancer agents in boron
neutron capture therapy, a binary form of cancer treatment that
relies on delivering a compound containing boron-10 selectively to
tumour tissues prior to irradiation by neutrons [1e4]. Some boron
compounds also present cytotoxic activity [5]. Furthermore,
compounds containing boronic acids [RB(OH)2] or boronate esters
[RB(OR0)2] have been used extensively as intermediates in Suzu-
kieMiyaura cross-coupling reactions for a variety of applications
[2,6]. They also display a wide range of applications as materials
with fluorescence [7], electro-optical and non-linear optical prop-
erties [8e10]. Boron-based compounds of the type R2BOAr
(including many variations on Ar) have attracted a great deal of
attention as emitting materials due to their increased stability
The traditional organic synthesis of macrocyclic compounds
involves several steps, as a consequence, the products are obtained
in low yields. As an alternative method, coordinative connections
are preferred for the formation of a number of organic and inor-
ganic macrocycles and these processes usually occur through self-
assembly [15,16]. The presence of metal ions with the appropriate
ionic radius has also allowed the synthesis of coordinating systems
via the template effect [17,18].
Although boron takes part between metals and non-metals in
the periodic table of the elements, most of its physical and chemical
properties and those of the compounds derived from it are typical
for nonmetallic species. Its capacity to form coordinative bonds
with a series of ligands typically used for metal-complexation is the
most prominent feature in the chemistry of boron that reflects
a relationship to metal compounds [19,20]. Boron forms coordi-
native bonds with nitrogen, oxygen, sulphur or phosphorus atoms
with small charge separations. The ease of boron macrocyclic
synthesis is due to this versatility of boron atom to react with donor
atoms (e.g. N and O), thus favouring self-assembly processes [21].
The synthesis of boron macrocycles that contain coordinative
bonds between the nitrogen and boron atoms has been achieved
using the above method, and dimeric, trimeric, tetrameric and
pentameric species have been reported [15,22,23].
compared to aluminium-based emitters and the strong p-electron
accepting behaviour of the empty pz orbital at the boron centre
[11e13]. In addition, four-coordinated organoboron compounds
with a
p-conjugated chelate backbone have emerged recently as
highly attractive materials for a number of applications including
emitters and electron-transport materials for organic light-
The advantage of macrocyclic boronates lies in their easy, one
step synthesis from readily available starting materials [24]. The
presence of boron in the macromolecular structure gained unusual
and interesting properties to these macrocyclic boronates [7,8].
* Corresponding author. Tel.: þ90 212 285 68 27; fax: þ90 212 285 63 86.
E-mail address: ahmetg@itu.edu.tr (A. Gül).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.11.016

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S¸ . Özçelik, A. Gül / Journal of Organometallic Chemistry 699 (2012) 87e91
The use of tridentate ligands in coordination chemistry provides
Continuing our studies on the preparation and characterization
of boronated tetrapyrolle derivatives and their precursors [40,41],
in the present study we report the synthesis of a phthalonitrile
derivative possessing ONO binding sites and its phenylboronic
ester. The new compounds were fully characterized by elemental
analyses, FTIR, 1H NMR, 13C NMR, 11B NMR and UVevis spectral
data.
a facile means to stabilize transition metals [25] and main group
elements [26] taking advantage of the chelate effect. Thus, it has
been reported that tridentate ligands having an ONO donor set of
atoms react with main group elements to give stable heterocycles
[27]. The results of the studies based on these boronates have
shown that in all cases boron atom is tetracoordinated and forms
a dative bond with the nitrogen atom; the characteristics of the
dative bond as well as the rigidity of the tridentate ligands
employed gave rise to monomeric molecules and, through a self-
assembly procedure, to specific di-, tri- and tetrameric molecules
[28e30]. Moreover, the reaction is dependent on steric, as well as
electronic factors. All these compounds showed high hydrolytic and
oxidative stability [31] due to the presence of coordinative NeB and
covalent BeO bonds (the tetracoordination of the boron atoms)
[32,33]. In this context, the reactions between the molecules con-
taining nitrogen atoms as Lewis bases with compounds having
boron atoms as Lewis acids has been studied intensively [1,23,34].
Recently, there has been a great attention for boron products of
imines and related substrates prepared from the condensation of
boronic or borinic acid with polydentate Schiff base ligands which
can function in both bridging and chelating capacities [17,20,23,35].
These compounds have a number of applications, including their
use in bifunctional catalysis, molecular recognition, fluorescent
chemosensors, fungicidal additives, chiral sensors, electrolumi-
nescent devices, and non-linear optical studies [36]. Farfán et al.
[37] have investigated the imino DielseAlder reactions with orga-
noboron esters prepared by the condensation of the salicylaldi-
mines with phenylboronic acid (PhB(OH)2) or phenylborinic acid
(Ph2BOH) and have discovered that related systems are potential
candidates for third order non-linear optical studies. Their previous
studies reported the possible applications of boron adduct in Imino
DielseAlder (IDA) reaction as the presence of the coordination
bond between the nitrogen and boron atoms polarizes the imine
bond and increases the selective reactivity of this bond [38]. At
present, there is extending interest in this type of compounds
because of their being efficient catalysts in propylene polymeriza-
tion reactions via the formation of a boron cation [39].
2. Results and discussion
Scheme 1 shows the synthesis of the target phthalonitrile deriv-
atives 3, 5 and 7. In the first step of this study, 4-(4-formyl-3-
hydroxyphenoxy)phthalonitrile (3) waspreparedbya base-catalyzed
nucleophilic aromatic displacement of 4-nitrophthalonitrile (1) with
2,4-dihydroxybenzaldehyde (2). The reaction was carried out as
a single step synthesis by using K2CO3 as the base at room tempera-
ture in dry dimethylformamide under N2 atmosphere. It has been
reported that among the two phenolic OH groups in 2, the ortho-
hydroxy group was less acidic due to the intramolecular H-bonding
with the carbonyl group, making it possible to selectively react the
more acidic para-hydroxy group first using weaker bases or lower
temperatures [42]. Therefore, the product was compound 3, not
a mixture of isomers. The second step was the preparation of
aphthalonitrilederivative havinga Schiff’s basestructurerequired for
the esterification reaction with phenylboronic acid. 4-(3-Hydroxy-4-
(((2-hydroxyphenyl)imino)methyl)phenoxy)phthalonitrile (5) was
prepared through a condensation reaction between equimolar
amount of compound 3 and 2-aminophenol in ethanol with a yield of
82%. The subsequent reaction of compound 5 with phenylboronic
acid inTHF under reflux gave the desired boronate 7 in relatively high
yield (78%). In order to efficiently remove the byproduct water, the
reaction was performed in the presence of 3 Å molecular sieves.
This novel bicyclic compound 7 is very stable to hydrolysis and
can be handled in air due to the presence of coordinative BeN and
covalent BeO bonds in its structure [43e45]. Furthermore, as the
strength of the BeN bond depends on the polarization of the
coordinative bond and the degree of substitution on the nitrogen
and boron atoms, the stability of this phenyl boron heterocycles 7
Scheme 1. Synthetic route for compounds 3, 5, 7 (i) DMF, K2CO3, r.t.; (ii) Ethanol, reflux; (iii) THF, reflux, molecular sieves.

S¸ . Özçelik, A. Gül / Journal of Organometallic Chemistry 699 (2012) 87e91
89
can be attributed to the strong acidity of the boron atom produced
by the electron-withdrawing behaviour of the phenyl group [46].
The preparation methods followed in the present study were
easy and afforded compounds 5 and 7 in relatively high yields.
Together with the fact that esterification reactions are essentially in
equilibrium with the precursors, a reaction mechanism based on
self assembly of these components can be proposed [47]. The
relatively high yield of the reaction in the present case can be
a consequence of this interaction.
Characterizations of the products involved a combination of
methods including elemental analysis, 1H and 13C NMR, UVevis,
FTIR, mass spectra and also 11B NMR for boronated compound.
Spectral data on the newly synthesized compounds are consistent
with the proposed structures.
electron density in the C]N bond [51]. Also, aromatic CH peaks
came out around 3068e2870 cmꢀ1 and the intense C^N peak was
observed at 2223 cmꢀ1
.
Most identical differences between 1H NMR spectra of
compounds 5 and 7 are the disappearance of OH chemical shifts in
the latter and appearance of new chemical shifts in the aromatic
region arising from the protons of benzene group condensed on to
the compound 5. The imine proton was observed at 8.19 ppm. The
aromatic protons appear in the range of 8.17e6.42 ppm.
The characteristic signal in the 13C NMR spectrum for the imine
group appeared at 151.64 ppm and shifted to higher field with
respect to that of compound 5 (164.75 ppm). The signals attributed
to the phenolic carbon atoms of phenylboronic acid moiety at
135.78, 135.66, 131.21, 128.28, 128.03 and 127.33 ppm also
confirmed the binding of phenylboronic acid with compound 5. The
existence of the N/B bond in compound 7 was also established by
11B NMR which showed a signal at 7.44 ppm, characteristic for the
tetracoordinated boron atom [52].
The IR spectrum of dinitrile compound 3 confirmed the
proposed structure by the disappearance of the aromatic eNO2
band at 1548 cmꢀ1 and the appearance of an intense new absorp-
tion at 1246 cmꢀ1 attributable to aromatic CeOeC [48]. In addition,
the characteristic C^N stretching vibrations appeared as a single
intense peak at expected frequency (2233 cmꢀ1) [49]. Furthermore,
2.1. UVevis spectra of compounds 2, 3, 5 and 7
the presence of aromatic CeH peaks around 3078e2971 cmꢀ1
,
C]O peak at 1738 cmꢀ1 and OeH peaks around 3300 cmꢀ1 in the IR
spectrum of 3 are the additional evidences for the formation of
compound 3 [50].
The compound 7 presented in this paper is an example of four-
coordinated organoboron compound that possesses a chelate
p
-conjugated backbone. In this kind of compounds, boron influ-
ences the electronic properties of the system by stabilizing the
chelate and enhancing the conjugation. These dual roles of boron
In the 1H NMR spectrum of 3, aromatic protons of benzaldehyde
group appeared at 7.76e7.72, 6.80e6.78 and 6.45 ppm as doublet,
doublet, singlet, respectively, while those of phthalonitrile groups
appeared at lower fields at 8.06, 7.84 and 7.43 ppm as doublet,
singlet, doublet, respectively. Also the CH]O and OeH protons
were observed as singlets at 11.00 and 9.87 ppm respectively. The
13C NMR of 3 exhibited the expected signals between 186.95 ppm
and 107.48 ppm for aromatic carbons. The carbon attached to the
OH group in the benzaldehyde part was observed at 157.23 ppm
and the signal for the formyl carbon was observed at 186.95 ppm.
Furthermore, the presence of nitrile groups in compound 3 was also
evidenced by signals at 116.72 and 115.65 ppm.
p
p
makes this class of compounds good candidates for their possible
use in OLEDs as emitters and electron-transport materials [14].
The UVevis spectra of compounds 2, 3, 5 and 7 in THF are given
in Fig. 1. The UVevis spectrum of 2,4-dihydroxybenzaldehyde
presented three absorptions at 234, 278 and 313 nm in THF. The
phthalonitrile 3 exhibited bands at 246 and 268 nm with higher
absorbance values than those of compound 2 at 234 and 278 nm.
This increase in the absorbance values can be attributed to the
pep* transitions of the phenoxy group attached to the structure by
the aromatic substitution reaction of 2-nitrophthalonitrile (1) and
2,4-dihydroxybenzaldehyde (2). Furthermore, the band at 313 nm
disappeared in the UVevis spectrum of phthalonitrile 3. The
UVevis spectrum of phthalonitrile 5 was characterized by the
presence of three absorption maxima at 242, 280 and 345 nm. The
The formation of compound 5, the molecule with an ONO
binding core, was confirmed by the presence of OeH peaks around
3330 cmꢀ1, aromatic CH peaks around 3063e2964 cmꢀ1, C^N
peaks at 2200 cmꢀ1, aromatic CeOeC peaks around 1227 cmꢀ1 in
the IR spectrum. Schiff base structure of 5 was also confirmed by
the disappearance of CH]O absorption band (1738 cmꢀ1) and
appearance of an intense band attributed to the CH]N group at
1585 cmꢀ1. This imine proton was also well characterized by the
singlet peak at 8.73 ppm in 1H NMR spectrum. Due to the differ-
ences in their chemical environments, the protons of OH groups
showed different chemical shift values (14.14 ppm and 9.71 ppm)
and the aromatic protons were appeared in the range of
7.64e6.24 ppm.
broad maximum in 5 at 345 nm is due to the ne
transition of the azomethine group while the bands at 242 and
280 nm are due to the * electronic transitions. Significant
p* electronic
pep
spectral changes occurred in the spectrum of compound 5 after the
formation of boronate 7 through the condensation reaction of
phenylboronic acid and Schiff base 5. The peak at 345 nm of
compound 5 was blue shifted (by 35 nm) to 311 nm and its
absorbance value increased. In addition, the appearance of a broad
band around 430e440 nm indicated the formation of the proposed
boronate ester of the Schiff base with a phthalonitrile group [53,54]
(Fig. 1).
The 13C NMR spectrum of compound 5 showed aromatic
carbons in the range of
d 169.05 and 103.96 ppm. The azomethine
carbon appeared at 164.75 ppm and the nitrile carbons were
observed at 117.63 and 116.96 ppm. Also the aromatic carbon atoms
adjacent to the OH groups came out at 160.13 and 149.96 ppm.
The IR spectra for compound 7 showed the disappearance of the
bands corresponding to the OH groups, which are present in the
Schiff’s base 5 around 3330 cmꢀ1. Another important diagnostic
parameter would be the value of the BeN and BeO stretching
frequency. In the spectrum of compound 7, BeN and BeO peaks
appeared at 1440 cmꢀ1 and 1344e1312 cmꢀ1 respectively.
Furthermore, the formation of the NeB coordinative bond was
established by the observation of the CH]N stretching band at
1601 cmꢀ1. This band is shifted to higher wavenumbers compared
to the same band in the compound 5 (1585 cmꢀ1). This is due to the
BeN intramolecular coordination which serves to reduce the
In conclusion, three novel phthalonitrile derivatives, 4-
(4-formyl-3 hydroxyphenoxy)-phthalonitrile (3), 4-(3-hydroxy-4-
(((2-hydroxyphenyl)imino)methyl)-phenoxy)phthalonitrile (5) and
phenylboronic acid ester of 4-(3-hydroxy-4-(((2-hydroxyphenyl)
imino)-methyl)-phenoxy)phthalonitrile (7) have been prepared.
Phthalonitrile 7 displays high stability in air due to the presence of
coordinative BeO and dative BeN bonds in its structure. All of the
presented compounds in this paper were characterized by
elemental analyses, IR, UVevis, mass, 1H NMR, 13C NMR spectra and
11B NMR spectrum for boron compound. Spectral data and gradual
increase in their solubility confirmed the successful preparation of
the proposed phthalonitrile derivatives. Further studies to convert
the phthalonitrile precursors with or without boronic ester groups
to phthalocyanines are under investigation.

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S¸ . Özçelik, A. Gül / Journal of Organometallic Chemistry 699 (2012) 87e91
Fig. 1. Absorption spectra of compounds 2, 3, 5 and 7 in THF.
3. Experimental
132.47 (Ar CH), 123.1 (Ar CH), 122.57 (Ar CH), 119.65 (Ar C), 116.72
(C^N), 115.65 (C^N), 115.31 (Ar C), 113.81 (Ar CH), 108.86 (Ar C),
107.48 (Ar CH); UVevis (THF): lmax/nm: 246, 268; Calcd. for
C15H8N2O3: C, 68.18; H, 3.05; N, 10.60%. Found: C, 68.27; H, 3.25; N,
10.54%.
All reagents and solvents were of reagent grade quality, obtained
from commercial suppliers. The solvents were storedover molecular
sieves (4 Å). 4-Nitrophthalonitrile (1) was synthesized as reported in
the literature [55]. 2,4-Dihydroxybenzaldehyde (2) and phenyl-
boronic acid were used as supplied commercially. The progress of
the reactions was monitored by TLC (SiO2). IR spectra were recorded
on a PerkineElmer Spectrum One FTIR (ATR sampling accessory)
spectrophotometer, electronic spectra in the UVevis region were
recorded with an Scinco S-3100 single beam UV/vis PDA spectro-
photometer. 1H NMR spectra were recorded on a Varian UNITY
INOVA 500 MHz spectrophotometer using TMS as internal refer-
ence. 13C- and 11B NMR spectra were recorded on a Bruker Ultra
Shield Plus 400 MHz spectrometer. Boron trifluouride diethyl
etherate was used as an external standard in 11B NMR spectra.
Elemental analyses were performed on a Thermo Flash EA 1112.
3.2. Synthesis of 4-(3-hydroxy-4-(((2-hydroxyphenyl)imino)
methyl)phenoxy)phthalonitrile (5)
To a solution of 200.0 mg (0.757 mmol) 3 in 20 ml of ethanol,
a solution of 2-aminophenol (90.8 mg, 0.832 mmol) in 15 ml of
ethanol was added. The reaction mixture was refluxed for 24 h and
then the hot mixture was filtered. The filtrate was evaporated to
dryness to give compound 5 as a golden brown solid. Yield: 0.220 g
(82%). m.p. 214 ꢁC. FTIR nmax/cmꢀ1: 3330 (OH), 3063e2964 (AreH),
2220 (C^N), 1585 (CH]N), 1510, 1458, 1342, 1227 (CeOeC), 1099,
1035, 829, 745, 666; 1H NMR (d6-DMSO): 14.14 (1H, s, OH), 9.71 (1H,
s, OH), 8.73 (1H, s, CH]N), 8.19 (1H, d, J ¼ 7.9 Hz, AreH), 7.64 (1H, s,
AreH), 7.28 (1H, d, J ¼ 7.8 Hz, AreH), 7.13 (1H, d, J ¼ 7.6 Hz, AreH),
7.05e7.03 (1H, m, AreH), 6.94 (1H, d, J ¼ 7.4 Hz, AreH), 6.82 (1H, m,
AreH), 6.66e6.61 (1H, m, AreH), 6.39 (1H, d, J ¼ 7.5 Hz, AreH), 6.24
(1H, s, AreH); 13C NMR (d6-DMSO): 169.05 (Ar CeO), 164.75
(CH]N), 160.13 (Ar C), 156.26 (Ar C), 149.96 (Ar C), 143 (Ar C),
134.39 (Ar CH), 133.53 (Ar CH), 126.13 (Ar CH), 124.60 (Ar CH),
124.43 (Ar CH), 119.39 (Ar CH), 119.01 (Ar CH), 117.63 (C^N), 116.96
(C^N), 116.23 (Ar CH), 114.40 (Ar C), 112.09 (Ar C), 109.37 (Ar CH),
106.40 (Ar C), 103.96 (Ar CH); UVevis (THF): lmax/nm: 242, 280,
345; Calcd. for C21H13N3O3: C, 70.98; H, 3.69; N, 11.83%. Found: C,
71.12; H, 3.45; N, 11.75%.
3.1. Synthesis of 4-(4-formyl-3-hydroxyphenoxy)phthalonitrile (3)
4-Nitrophthalonitrile (1.0 g, 5.78 mmol) and 2,4-
dihydroxybenzaldehyde (1.197 g, 8.66 mmol) were dissolved in
10 ml dry DMF. After dissolution, finely ground anhydrous potas-
sium carbonate (4.2 g, 30 mmol) was added in portions over 2 h
with efficient stirring. The reaction mixture was stirred vigorously
at room temperature under N2 for 48 h. The progress of the reaction
was monitored by TLC. The reaction mixture was poured into
250 ml of cold water and stirred for 30 min. The pH of the solution
was adjusted to 1 by addition of 1 N HCl solution. The precipitated
solid was filtered, washed with water until the filtrate was neutral.
Then the solid product was dissolved in ethanol and the solution
was refluxed for 30 min in the presence of activated carbon. The hot
solution was filtered and then the solvent was evaporated to
dryness. The solid product was washed with hexane and dried in
3.3. Synthesis of compound 7
100 mg (0.28 mmol) of compound 5 was dissolved in 25 ml THF
and then poured into a solution of benzenboronic acid (34 mg,
0.28 mmol) in 15 ml THF. The reaction mixture was refluxed in
100 ml round bottom flask charged with 3 Å molecular sieves
(1.20 g) in order to remove the water released from the esterifica-
tion reaction. After 6 h reflux, the mixture was filtered to remove
the molecular sieves. The solvent was evaporated under reduced
pressure and the product was washed with hexane. Yield: 97 mg
(78%). m.p. 140 ꢁC. FTIR nmax/cmꢀ1: 3068e2870 (AreCH), 2223
(C^N), 1601 (CH]N), 1556, 1471, 1440, 1344, 1312, 1258, 1232
vacuo. Yield: 0.488
g :
(32%); m.p. 181 ꢁC. FTIR nmax/cmꢀ1
3300(broad, OeH), 3078e2971 (AreH), 2233 (C^N), 1738 (C]O),
1656 (C]C), 1591, 1483, 1457, 1374, 1309, 1246 (CeOeC), 1168, 1098,
1042, 980, 876, 815, 666. 1H NMR (d6-DMSO): 11.00 (1H, s, OH), 9.87
(1H, s, CH]O), 8.06 (1H, d, J ¼ 7.9 Hz, AreH), 7.84 (1H, s, AreH), 7.74
(1H, d, J ¼ 7.7 Hz, AreH), 7.43 (1H, d, J ¼ 7.4 Hz, AreH), 6.79 (1H, d,
J ¼ 7.4 Hz, AreH), 6.45 (1H, s, AreH); 13C NMR (d6-DMSO): 186.95
(CH]O), 164.95 (Ar C), 160.58 (Ar C), 157.23 (Ar C), 136.30 (Ar CH),

S¸ . Özçelik, A. Gül / Journal of Organometallic Chemistry 699 (2012) 87e91
91
(CeOeC), 1177, 1119, 1087, 1015, 945, 859, 802, 746, 699; 1H NMR
(CDCl3): 8.19 (1H, s, CH]N), 8.17 (1H, d, J ¼ 8.1 Hz, AreH), 7.69e7.67
(1H, s, AreH), 7.53 (1H, d, J ¼ 8.2 Hz, AreH), 7.46e7.43 (2H, m,
AreH), 7.35e7.33 (3H, m, AreH), 7.26 (1H, d, J ¼ 7.8 Hz, AreH), 7.21
(1H, m, AreH), 7.11e7.06 (1H, m, AreH), 7.00e6.98 (1H, m, AreH),
6.91 (1H, d, J ¼ 7.6 Hz, AreH), 6.83 (1H, d, J ¼ 7.9 Hz, AreH), 6.42
(1H, s, AreH); 13C NMR (CDCl3): 169.92 (Ar CeOeB), 163.77 (Ar C),
160.81 (Ar CeOeB), 157.25 (Ar C), 151.64 (CH]N), 150.35 (Ar C),
144.60 (Ar CH), 135.78 (Ar CH-meta-B), 135.66 (Ar CH-meta-B),
133.57 (Ar CH), 131.21 (Ar C-ortho-B), 128.28 (Ar CH-para-B),
128.03 (Ar CH-para-B), 127.33 (Ar CH-para-B), 125.56 (Ar CH),
121.44 (Ar CH), 120.32 (Ar CH), 119.42 (Ar CH), 117.14 (Ar CH), 115.73
(C^N), 115.20 (C^N), 114.77 (Ar C), 114.42 (Ar CH), 112.17 (Ar C),
110.42 (Ar CH), 107.05 (Ar C), 105.66 (Ar CH); 11B NMR, (CDCl3,
ppm): 7.44 (s, tetracoordinated B); UVevis (THF): lmax/nm: 242,
280, 311, 429; Calcd. for C27H16BN3O3: C, 73.49; H, 3.65; N, 9.52%.
Found: C, 73.65; H, 3.45; N, 9.75%.
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