Synthesis, crystal structure and non-linear optical properties of boronates derivatives of salicylideniminophenols

Article abstract of DOI:10.1016/j.jorganchem.2008.01.032

The condensation in one step of a series of salicylaldehydes and 2-amino-5-nitrophenol with 1-naphthylboronic acid, 2-naphthylboronic acid, and o-tolylboronic acid to give the corresponding boronates 1a-3a, 1b-3b and 1c-3d, is reported. The X-ray crystal structures of 1a, 2b and 3b allowed determining the α- and β-angle between the stilbene skeleton and the aryl or naphthylboronic fragments; these values are indicative of different conformations for the aryl moieties around the (B-C) boron-carbon bond which could potentially modulate the electronic properties on the boron stilbene compounds. All compounds were characterized by ¹H, ¹¹B and ¹³C NMR spectroscopy, UV, IR and mass spectrometry. Second- and third-order non-linear optical characterizations were also performed by EFISH and THG Maker Fringe techniques, respectively. Compounds 3a-3d containing an -N(Et)₂ donor group gave the best NLO response in second- and third-order.

Full text of DOI:10.1016/j.jorganchem.2008.01.032

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1321–1334
www.elsevier.com/locate/jorganchem
Synthesis, crystal structure and non-linear optical properties
of boronates derivatives of salicylideniminophenols
a
a,
a
b
*
´
´
´
Blanca M. Munoz , Rosa Santillan , Mario Rodrıguez , Jose Manuel Mendez ,
˜
b
b
c
d
´
Margarita Romero , Norberto Farfan , Pascal G. Lacroix , Keitaro Nakatani ,
e
e
´
´
Gabriel Ramos-Ortız , Jose Luis Maldonado
a Departamento de Quı´mica, Centro de Investigacio´n y de Estudios Avanzados del IPN, 07000, Apdo, Postal 14-740, Me´xico D.F., Mexico
b Facultad de Quı´mica, Departamento de Quı´mica Orga´nica, Universidad Nacional Auto´noma de Me´xico, Me´xico D.F. 04510, Mexico
c Laboratoire de Chimie de Coordination du CNRS, 205 Route de Narbonne, 31077 Toulouse, France
d Laboratoire de Photophysique et Photochimie Supramole´culaires et Macromole´culaires (UMR 8531 du CNRS), Ecole Normale Supe´rieure de Cachan,
Avenue du Pre´sident Wilson, 94235 Cachan, France
e
´
Centro de Investigaciones en Optica, A.P. 1-948, 37000 Leo´n, Gto., Mexico
Received 10 August 2007; received in revised form 18 January 2008; accepted 18 January 2008
Available online 26 January 2008
Abstract
The condensation in one step of a series of salicylaldehydes and 2-amino-5-nitrophenol with 1-naphthylboronic acid, 2-naphthylbo-
ronic acid, and o-tolylboronic acid to give the corresponding boronates 1a–3a, 1b–3b and 1c–3d, is reported. The X-ray crystal structures
of 1a, 2b and 3b allowed determining the a- and b-angle between the stilbene skeleton and the aryl or naphthylboronic fragments; these
values are indicative of different conformations for the aryl moieties around the (B–C) boron–carbon bond which could potentially mod-
ulate the electronic properties on the boron stilbene compounds. All compounds were characterized by 1H, 11B and 13C NMR spectros-
copy, UV, IR and mass spectrometry. Second- and third-order non-linear optical characterizations were also performed by EFISH and
THG Maker Fringe techniques, respectively. Compounds 3a–3d containing an –N(Et)2 donor group gave the best NLO response in
second- and third-order.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Boronates; NLO; 11B NMR; X-ray
1. Introduction
optics (NLO), where the three-coordinate species have been
more widely studied due to the fact that the vacant p orbi-
tal is a strong p-electron acceptor which can lead to signif-
icant delocalization with an adjacent organic p-system [7]
(Fig. 1).
Other boron species with NLO properties are the zwit-
terionic systems (Fig. 2), where the boron atom has a neg-
ative charge and the nitrogen is an ammonium salt. These
systems show high ground-state dipole moments and are
expected to have a small dipole moment in the first excited
singlet state [8].
The great versatility of boron chemistry has led to a
number of applications of these compounds in medicinal
[1], supramolecular [2] and materials chemistry [3]. In par-
ticular, stabilization through the formation of complexes
containing dative N ? B bond has been studied intensively
[4], some examples include the condensation of boronic
acids with ethanolamine [5] or amino acids [6].
The organic boron compounds are interesting species
with optoelectronic properties, in particular for non-linear
Complexes containing the N ? B coordinated bond
which are derived from pyridine and Lewis acids such as
BF3 or B(C6F5)3 present excellent NLO properties due to
the fact that formation of the pyridyl-boron complex leads
*
Corresponding author. Tel.: +52 55 50 61 37 25; fax: +52 55 50 61 33
89.
E-mail address: rsantill@cinvestav.mx (R. Santillan).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.01.032

1322
B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
B
N
B
B
B
S
S
N
Fig. 1. Dimesityl boron compounds with attractive NLO properties.
Me
Bu
Me
-
+
+
Me
Me
N
B
Bu
Bu
Me
Me
N
Bu
Me
Bu
-
-
+
B
Bu
Bu
Me
N
B
Bu
Bu
Me
Fig. 2. Borate Zwitterionic salts with high dipole moments.
R
R
to enhancement of the withdrawing effect and consequently
of second-order NLO properties [9] (Fig. 3).
It has been reported that compounds containing boron
and other elements such as bismuth exhibit promising
non-linear optical properties, for example, BiB3O6 (BIBO)
shows large second-harmonic generation (SHG) coefficient
compared to other known NLO borates such as BBO and
LiB3O5. In addition, bismuth borates crystallize in non-
centrosymmetric space group, this is an important prere-
quisite in the search toward solid state NLO properties
[10].
N
N
N
Cl
N
B
N
R
R
N
R
R
R = p-Tolylthio, p-tolylsulfonyl, SC8H17, SO2C8H17
Other compounds commonly employed in non-linear
optics are donor–acceptor substituted p-electron systems,
such as subphthalocyanines which exhibit good NLO prop-
erties. These compounds are planar and with excellent
physicochemical properties, including high aromaticity,
very good thermal and chemical stability (Fig. 4) [11].
We recently reported the synthesis and non-linear
optical properties of ‘‘push–pull” boron chromophores
containing the well-known stilbene backbone with an aryl-
boron (ArB) group (Fig. 5) [12]. The results suggest that
modulation could be achieved by rotation of the phenyl
around the boron–carbon bond. One of these boron chro-
mophores has been used for NLO dynamic holographic
imaging in photorefractive polymers [13].
Fig. 4. Boron complex of subphthalocyanines with NLO properties.
NO2
N
B
O
D
O
R
D = OMe, N(Et)2
R = H, Cl, OMe, Br, F, NO2, CHO
Fig. 5. Boron compounds derived from Schiff Bases with NLO properties.
Also, a series of boron complexes derived from hydroxy-
chalcones with borontrifluoride and diphenylborinic acid
has been reported [14] (Fig. 6). These boron complexes
exhibit a delocalized ‘‘push–pull” system. Unfortunately
they decomposed in solution, and in the solid state they
crystallized in centrosymmetric space groups, therefore
the NLO properties are canceled.
In continuation of our research, we designed a series of
push–pull boronates that contain an aryl- or naphtyl
Me
Me
Me
Me
N
N
B(C6F5)3
N
N
B(C6F5)3
N
N
BF3
Me
Me
Fig. 3. Pyridine-boron complex with NLO properties.

B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1323
C6H5
F
C6H5
O
F
plexes containing different boronic acids were prepared.
In addition, 3d containing an aldehyde group in the ortho
position was synthesized with the aim to fix the orientation
of the boronic acid fragment through an intramolecular
hydrogen contact with the phenolic oxygen. This molecule
was obtained in two steps, since the one step procedure
leads to a mixture of compounds (Scheme 2).
B
B
O
O
O
R
R
R = H, Cl, OMe
R = H, Cl, OMe
Fig. 6. ‘‘Push–pull” boron complexes derived from hydroxychalcones.
2.2. Spectroscopic data
boronic acid fragment in order to investigate the preferen-
tial conformation around the B–CPh bond and their poten-
tial application to modulate the NLO response using
different substituents. The complexes are stable and were
obtained in high yields through an easy one-step synthesis.
1
All compounds were characterized by H, 11B and 13C
NMR; selected data is summarized in Table 1. The singlets
between 8.15 and 8.77 ppm in the 1H NMR spectra of com-
pounds 1a–3a, 1b–3b, 1c–3c and 3d, correspond to the
imine proton and confirm the formation of the Schiff base.
The signals for H-22 are shifted to high frequencies (8.82,
8.81 and 8.84 ppm) for compounds 1a–3a which have a
1-naphthyl substituent, due to the existence of an intramo-
lecular interaction with the O-2 (phenolic moiety), as
confirmed by the solid state analysis of compound 1a
2. Results and discussion
2.1. Synthetic aspects
The tridentade ligands 1–3 were prepared by condensa-
tion of the appropriate salicylaldehyde with 2-amino-5-
nitrophenol [15,17]. The boron compounds 1a–3a, 1b–3b
and 1c–3c were obtained in one step by condensation of
the salicylaldehyde with 2-amino-5-nitrophenol and the
corresponding boronic acid. The reactions were carried
out under reflux of acetonitrile and a catalytic amount of
acetic acid from 2 to 8 h to give the corresponding boro-
nates in yields between 81% and 90% except for com-
pounds 2c (65%) and 3b (54%) (Scheme 1).
˚
(H-22ꢀ ꢀ ꢀO2 2.513(2) A).
1
The H NMR signals for the aryl and naphthyl rings
were assigned based on their COSY spectra which allow
correlation between the protons in the ring containing the
electron-withdrawing group and those of the ring with
the electron-donating group. The COSY spectra were nec-
essary because the multiplicity and chemical shifts of some
signals are very similar.
In the 13C NMR spectra of boron derivatives 1a–3a, 1b–
3b, 1c–3c and 3d, the signals for C2 are shifted to low fre-
quencies (157.1–158.9 ppm), with respect to the ligands
To modulate the NLO response through different con-
formations around the B–C bond, a series of boron com-
O
NH2
NO2
NO2
OH
H
N
+
EtOH
reflux
HO
OH
D
D
OH
D = H, OMe, N(Et)2
1 D = H
2 D = OMe
3 D = N(Et)2
12
13
6
7
O
NH2
NO2
8
1
NO2
5
11
N
B
OH
+
HO
OH
H
+
CH3CN
CH3CO2H
reflux
10
9
B
O
4
D
2
O
3
D
OH
R
R
D = H, OMe, N(Et)2
H
OMe
N(Et)2
D
R
22
14
17
23
15
16
21
20
1a
2a
3a
18
19
14
23
22
15
16
21
20
1b
1c
2b
2c
3b
3c
17
18
19
14
Me
19
18
15
16
17
Scheme 1. Synthesis of ligands 1–3 and boronates 1a–3a, 1b–3b and 1c–3c.

1324
B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
12
10
13
HO
OH
6
7
NO2
8
NO2
1
2
B
N
11
CH3CN
5
N
B
+
reflux, 8 h
9
HO
OH
O
N
O
4
N
O
3
14
15
19
18
O
3
16
17
3d
Scheme 2. Synthesis of boronate 3d.
Table 1
Table 2
Selected 1H, 11B, 13C NMR (ppm) and IR (cmꢁ1) data for compounds 1–
3, 1a–1c, 2a–2c and 3a–3d
Experimental absorption maxima (kmax in nm) and extinction coefficients
(e in dm3 molꢁ1 cmꢁ1) are compared to ZINDO calculated data for 1a, 2b,
and 3b
Compound 1H
NMR
13C NMR (ppm)
11B
IR
NMR (C@N)
Compounds
Experimental data
Computed data
C-2 C-4 C-7
C-9
(ppm)
(H-7)
(ppm) (cmꢁ1
)
kmax
e
kmax
f
1
375
376
436
456
461
511
76489
71215
89920
11700
22100
31104
1
9.01
8.97
8.79
8.77
8.55
8.73
8.61
8.63
8.55
8.34
8.15
8.33
8.39
161.2 134.5 165.5 151.7
161.6 165.3 161.8 146.0
167.2 159.2 152.5 144.4
1624
1620
1619
2
2
3
3
1a
2b
3b
402
412
434
0.44
0.35
0.74
1a
1b
1c
2a
2b
2c
3a
3b
3c
3d
158.3 139.7 152.7 157.7 9.8
158.9 140.4 152.9 158.7 8.6
158.5 139.9 148.6 157.8 9.3
161.1 169.8 151.3 157.6 9.8
161.0 169.6 153.0 157.5 8.0
161.1 169.9 151.2 157.7 9.2
160.5 157.1 148.4 156.9 9.5
157.5 161.1 148.6 157.1 8.3
157.1 160.6 148.5 157.0 9.1
157.2 160.0 148.7 156.4 8.8
1629
1626
1617
1608
1606
1613
1606
1606
1607
1607
of a concentrated mixture of CHCl3 and hexane. The
details of the crystal data and summary of the collection
parameters for compounds 1a, 2b and 3b are given in Table
3, selected bond distances and bond angles are compared in
Table 4 and the molecular structures are shown in Fig. 7.
Even if the boron compounds have similar structures, they
crystallize in different space groups. Compound 1a belongs
to the orthorhombic space group Icab, 2b to the triclinic
(161.2–167.2 ppm) owing to the coordination to boron. In
general the signal for the imine carbon (C-7) shows a
marked shielding effect (148.4–153.0 ppm) compared to
the ligands (152.5–165.5 ppm) due to increased delocaliza-
tion of the NEt2 substituent at the para position after for-
mation of the N ? B bond.
ꢀ
space group P1 and 3b to the monoclinic C2/c. Boron
Table 3
Crystal data for 1a, 2b and 3b
The 11B NMR spectra for the 10 new compounds show
one broad signal between 8.0 and 9.8 ppm indicative of tet-
racoordinated boron atoms [16]. In general, the C@N
stretching vibration bands for compounds 2a–2c and
3a–3d were shifted to lower wavenumbers in comparison
with the ligands, evidencing a decrease in strength as the
new N ? B dative bond is formed [17].
1a
2b
3b
Chemical formula
Formula weight
Crystal system
Space group
a (A)
b (A)
C23H15BN2O4 C24H17BN2O5 C27H24BN3O4
394.18
424.21
465.30
Orthorhombic Triclinic
Monoclinic
ꢀ
Icab
P1
C2=c
˚
˚
˚
17.3609(4)
17.9031(4)
24.5085(6)
90.0
9.9720(2)
11.7388(3)
19.7668(6)
73.9830(10)
88.8340(10)
66.7130(10)
2032.54(9)
4
24.5993(49)
19.9916(40)
11.6876(23)
90
109.973(30)
90
c (A)
Comparison of the absorption data for compounds 1a,
2b, 3b with the corresponding ligands evidences a red shift.
Moreover, this shift is observed both experimentally and
theoretically, as the push–pull character increases from 1a
to 3b. It is surprising that the modest shift (5 nm) induced
by the methoxy substituent when 1a and 2b are compared
can lead to unexpected NLO effects (vide infra) (see
Table 2).
a (°)
b, (°)
c (°)
V (A )
Z
90.0
90.0
7617.6(3)
16
293(3)
7979
3
˚
5402.02(627)
8
Temp (K)
293(2)
13909
8156
4909
293(2)
18060
5405
2346
Reflection collected
Reflection unique
Reflection observed
(4r)
4285
2501
2.3. Molecular structure
Number of variables
Final R (4r)
Final wR2
332
714
401
0.0462
0.1027
1.007
0.0564
0.1329
1.019
0.0715
0.175
0.965
For compounds 1a, 2b and 3c, it was possible to obtain
crystals suitable or X-ray diffraction by slow evaporation
Goodness-of-fit

B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1325
Table 4
˚
Selected bond lengths (A) and angles (°) for 1a, 2b and 3b
˚
Lengths (A)
Angles (°)
1a
2b
3b
1a
2b
3b
O(1)–B(1)
O(2)–B(1)
B(1)–N(1)
B(1)–C(14)
C(1)–C(7)
C(7)–N(1)
N(1)–C(8)
1.498(2)
1.458(2)
1.585(2)
1.607(2)
1.427(3)
1.296(2)
1.411(2)
1.497(3)
1.456(3)
1.594(3)
1.606(4)
1.420(4)
1.296(3)
1.416(3)
1.464(4)
1.509(4)
1.572(4)
1.605(5)
1.388(4)
1.324(4)
1.396(4)
O(1)–B(1)–O(2)
O(2)–B(1)–C(14)
O(1)–B(1)–C(14)
O(1)–B(1)–N(1)
O(2)–B(1)–N(1)
N(1)–B(1)–C(14)
111.16(13)
112.41(14)
113.12(14)
100.13(13)
106.61(13)
112.60(14)
112.4(2)
113.5(2)
111.5(2)
99.55(18)
107.51(19)
111.5(2)
111.3(2)
110.3(3)
112.9(3)
108.0 (3)
99.5(2)
114.0(3)
Fig. 7. X-ray molecular structure of compounds 1a, 2b and 3b.
compounds 1a and 3b contain one crystallographically
independent molecule while 2b has two independent mole-
cules that show the same structure in the asymmetric unit.
The bond distance observed in the dative N ? B and cova-
lent B–O bonds, as well as the angle values are very similar
in the three derivatives. Compounds 1a, 2b and 3b contain
four-coordinated boron atoms with tetrahedral character
values of 74% (1a), 75% (2b) and 76% (3b) [18], therefore
the delocalization of the p system is not optimal. The val-
ues for the intramolecular N ? B dative bonds are 1.585
bridged boronates [19] but similar to the values reported
in other monomeric boronates [12].
˚
In turn, the N(1)–C(7) [1.324 (5) A] bond length for
compound 3b is significantly longer than that of 2b
˚
[N(1)–C(7) 1.296 (3)] A and 1a [N(1)–C(7) 1.296 (2)] show-
ing the influence of the electron donor groups. These com-
pounds are bent along the N ? B bonds as expected in this
family of boronates, as a result of the tetrahedral geometry
around the boron atom. The angles around this boron
atom are close to tetrahedral and the shorter value (around
100°) corresponds to O(1)–B–N. The slight folding in the
molecular skeleton decreases the p-conjugation pathway
˚
˚
˚
(2) A, 1.594 (3) A and 1.572 (5) A for 1a, 2b and 3b respec-
tively, which are shorter than dimeric, oligo- and oxo-

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B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
the 2-naphtyl. The 1-naphtyl (Fig. 8) shows two intramo-
˚
lecular hydrogen bonds (H22ꢀ ꢀ ꢀO2 2.513(2) A, H15ꢀ ꢀ ꢀN1
N
˚
2.536 (18) A) which are less than the sum of the van der
B1
O
O1
˚
˚
Waals radii (Hꢀ ꢀ ꢀO 2.77 A, Hꢀ ꢀ ꢀN 2.75 A) [20]. In the solid
state, the naphthyl fragment linked to the boron atom is
perpendicular to the organic ligand, as reported for the
(dppy)B-2-naphthyl complex [21].
14
23
α
The molecular packing diagrams of 1a, 2b and 3b are
depicted in Fig. 8. Compound 1a shows a p–p stacking
intermolecular interaction between the aromatic rings with
Scheme 3. The a-angle in boronate compounds.
˚
a contact distance of 3.218 (3) A that is shorter than the
and the NLO response. An important difference between
the three molecular structures is observed in the relative
orientation of the 1- and 2-naphthyl moiety with respect
to the stilbene backbone which could lead to variations
in NLO properties. Using the definition of the rotation a-
angle (O1–B1–C14–C23) shown in Scheme 3, the crystal
structure provides values of ꢁ67.3°, +4.3° and +1.1° for
1a, 2b and 3b, respectively. Interestingly, the a-angle in
1a depends on the nature of the substituent bonded to
the ortho carbons in the aryl moiety. The results show that
the 1-naphthyl group modifies the angle much more than
˚
value reported for (dppy)B-2-naphthyl (3.40 A)[21]. Also,
the p–p stacking interaction between naphthyl groups
˚
shows a value of 3.29 (3) A. The crystal packing of 2b
shows a chain arrangement; within each chain and there
is p–p stacking interaction with ligand/ligand rings contact
˚
distances of 3.275(4) A that is almost the same as that of
˚
(dppy)B–F (3.28 A) [22] but shorter than the (dppy)-
˚
B–C6H4-2(OEt) (3.342 A) probably due to steric effects [21].
In 3b, two molecules are linked by two hydrogen bonds
˚
˚
(CHꢀ ꢀ ꢀO–N 2.527(5) A, CHꢀ ꢀ ꢀO–N 2.556 (6) A) of the
Fig. 8. Intermolecular interaction in the crystal packing of 1a, 2b and 3b.

B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1327
complex–N(Et)2ꢀ ꢀ ꢀO2N-complex resulting in a head–tail
are available. The results and relevant NLO parameters
are presented in Table 6, and compared to the experimen-
tal studies in Table 5.The main two orbitals involved in
the intense and low lying (1 ? 2) transitions of the chro-
mophores are compared in Fig. 9. The major differences
are observed at the level of the occupied orbitals, which
mostly reflect the contribution of the donor fragment to
the ground state electron density. Indeed, H (1a), MeO
(2b) and N(Et)2 (3b) contribute <0.1%, 8.5%, and
11.3%, respectively, to the electron density of the related
orbitals 70, 77, 86, in full agreement with their relative
donating strengths. In the case of 2b, the data gathered
in Table 6 reveals the contribution of additional excita-
tions to the low energy 1 ? 2 transition, which arise from
orbital 69. This orbital is localized on the nitro group,
which leads to an unexpected reduction of the charge
transfer and finally to a reduction of b1?2. A qualitative
picture for the lowering of the charge transfer process is
provided in Fig. 10. Although a methoxy group is present
in 2b, it turns out not to be significantly involved in the
charge transfer process. By contrast, and despite a lack
of strong donor group, an important donating character
(black contribution in Fig. 10) seems to be devoted to
the conjugated bridge of 1a, leading to a rather large
NLO response.A final discussion has to be conducted
on the rather large experimental difference observed
between 2b and 2c (Table 5). Indeed, while 1a and 1b exhi-
bit similar NLO response with experimental b ꢂ l value
around 90 ꢂ 10ꢁ30 cm5 esuꢁ1 D, and 3a, 3b, and 3c exhi-
bit b ꢂ l value around 500 ꢂ 10ꢁ30 cm5 esuꢁ1 D, in
agreement with the fact that the aryl-boronated fragment
is not engaged in the charge transfer, the large b ꢂ l dif-
ference (59.1 and 137.9 ꢂ 10ꢁ30 cm5 esuꢁ1 D, for 2b and
2c, respectively) is somewhat surprising. Without struc-
tural data for 2c, it is not possible to conclude unambigu-
ously on the origin of this difference. In a previous
investigation [12], we have pointed out that short contacts
between the aryl fragments and the oxygen atoms of the
boron coordination sphere had the potential to lead to
significant b enhancement. If hydrogen bonding is possi-
ble between O1 and the substituted boronic fragments,
one can infer that it should more likely take place in 2c
than in 2b. However, the change in hyperpolarizability
chain (Fig. 8). These contacts are less than the sum of
P
˚
the van der Waals radii ( rvdWH–O = 2.7 A) [20]. For
molecular materials the p–p stacking interactions and
hydrogen bonds might be beneficial in terms of charge
transfer [23].
2.4. NLO properties
(a) Second-order: the experimental hyperpolarizabilities
(b) for compound 1a, 1b, 2b, 2c, 3a–3c, were measured
by the electric field-induced second harmonic (EFISH)
technique and the data are shown in Table 5. Attempts
to carry out measurements on the ligands were unsuc-
cessful due to their insolubility in chloroform. The data
clearly reveals that b is larger for the compound contain-
ing the -N(Et2) group as donor.Except for 2b, the expla-
nation that NLO effects are ultimately related to the
intense charge transfer between electron donating and
accepting fragment, is in agreement with the simple,
but widely used ‘‘2 level” model [24]:
3e2f1!2Dl1!2
2mE31!2
E41!2
ꢁꢀ
2
ꢀ
ꢁ
b1!2
¼
ꢂ
2
E21!2 ꢁ ð2ꢀhxÞ
E21!2 ꢁ ðꢀhxÞ
ð1Þ
In this model, E1?2 is the energy of the transition between
the ground and the first excited state, f1?2 (oscillator
strength) is its intensity and Dl1?2 the change in dipole
moment occurring during the transition. Increasing the
strength of the donor acceptor substituents usually pro-
vide f and Dl enhancements and reduce the transition en-
ergy, which together lead to a larger molecular
hyperpolarizability.To provide a rationale for the unex-
pected behaviour of 2b, the electronic features have been
analysed in the 1a–2b–3b series, for which structural data
Table 5
Experimental (EFISH and THG) and computed (ZINDO) data for the
boronate derivatives 1a–1c, 2b–2c and 3a–3d
a
Compounds Experimental
(EFISH) data b ꢂ l (ZINDO)
(10ꢁ30 cm5 esuꢁ1 D) data
Computed b2level Experimental
l (D) (THG)
data v(3)
(ꢂ10ꢁ12 esu)c
1a
1b
1c
2b
2c
3a
3b
3c
3d
87.9
10.7
4.6
12.1
11.0
18.2
1.55
1.58
1.42
Table 6
92.8b
Low energy transitions and relevant parameters (absorption maxima,
oscillator strengths dipole moment changes, and compositions of the
configuration interaction), for 1a, 2b, and 3b
59.1b
137.9
485.9
535.0
497.9
1.10
4.05
5.07
5.01
5.67
Compound Transitions kmax (nm)
f
Dl (D) Composition of
CI expansion
14.2
1a
2b
1 ? 2
1 ? 2
402
412
0.44 5.0
0.35 2.5
v70?73 (68%)
v77?79 (48%)
v69?80 (15%)
v69?79 (12%)
v86?88 (78%)
Compounds 1, 2, 3, 1c and 2a were not sufficiently soluble to be measured
in EFISH and TGH was not measured for 2b.
a
3b
1 ? 2
434
0.74 2.9
Calculated from Eq. (1).
b
Measured in a 9:1 CHCl3:DMSO mixture.
v(3) for fused silica = 3.1 ꢂ 10ꢁ14 esu.
Orbital 72(73) is the HOMO(LUMO) for 1a, orbital 78(79) is the
HOMO(LUMO) for 2b, orbital 87(88) is the HOMO(LUMO) for 3b.
c

1328
B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
(b) Third-order: the cubic non-linear responses for the
series 1a–3a, 1b–3b, 1c–3c and 3d were estimated
through the use of third-harmonic generation (THG)
Maker-fringes technique [25] exciting at the IR wave-
length of 1200 nm. This technique allowed us to calcu-
late the third-order non-linear susceptibility v(3) of our
boron chromophores dispersed into polymer films. The
THG measurements were performed on thin polymer
(polystyrene: PS) films doped with the boronates at a
loading level of 30 wt.% (weight percent). At this doping
level the samples exhibit a third-order non-linear suscep-
tibility of the order v(3) ꢃ 10ꢁ12 esu. The v(3) values for
each boronate are summarized in Table 5 (note that
for compounds 2a and 2b, THG data are not reported
since optical quality in polymer films was not accept-
able, i.e., they exhibit strong light scattering at the
fundamental and harmonic wavelengths). Thus, except
for 2c, our measurements show that there exists a corre-
lation between the quadratic and cubic non-linear
responses which are ultimately related to charge
transfer transitions involving donor and acceptor
substituents. For instance, the largest nonlinearities
were observed for the compounds 3a–3d having the
very strong donor N(Et)2 group which lead to the high-
est b ꢂ l ꢃ 500 ꢂ 10ꢁ30 cm5 esuꢁ1 D and v(3) ꢃ 5 ꢂ
10ꢁ12 esu for the quadratic and cubic cases, respectively.
Interestingly, the THG measurements also show that
despite a lack of strong donor group in 1a, 1b and 1c,
this series exhibit a larger NLO response compared with
2c which possesses a methoxy group (OMe) with higher
donating strength. Unfortunately, for the reasons above
mentioned, it was not possible to measure the cubic non-
linearity of 2b to contrast it with the quadratic non-lin-
ear behaviour previously discussed. So, depending on
the donor group it was found that the films doped with
the boronates have a third-order non-linear susceptibil-
ity v(3) that varied from 35 up to 180 times the values
corresponding to the standard reference used in our
experiments, i.e., fused silica. It is worth to mention that
the choice of using THG as a technique to measure v(3)
allowed us to measure pure electronic NLO effects at
infrared wavelength (important for photonic applica-
tions such as high bandwidth all-optical switching).
B
B
73
70
molecule 1a
B
79
77
B
molecule 2b
B
88
86
B
molecule 3b
Fig. 9. Main orbitals involved in the charge transfer process for 1a, 2b,
and 3c. Orbitals 70(73), 77(79) and 86(88) are occupied (unoccupied)
orbitals, defined in Table 6.
B
3. Conclusions
Ten new boronates with H, OMe and N(Et2) donor
groups (series 1a–c, 2a–c and 3a–d, respectively) were syn-
thesized easily in good yields, and the NLO properties were
investigated for the first time for both quadratic (EFISH
experiments) and cubic (THG Maker-fringes experiments)
orders. The X-ray crystal structures show that the stilbene
fragments reveal a planar array in the ligands and are bent
in the boron complexes. The weak intramolecular interac-
tion for compound 1a observed in solution was retained
in the solid state. The increase of the ‘‘a” and ‘‘b” angle
B
Fig. 10. Comparison of the charge transfer processes in 2b (top) and 1a
(bottom). White (black) contributions are indicative of increase (decrease)
of the electron density upon 1 ? 2 transition.
is not observed between 3b and 3c, as well. This suggests
that an explanation based only on this short contact is
probably not fully reliable.

B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1329
can be attributed to the presence of naphthyl groups, which
could be used to modulate the electronic properties of the
rigid stilbene skeleton, and finally the optical properties
of the materials. At the second-order level, the observation
of an enhancement of 2–3 times of the NLO response
between compounds 2b and 2c suggests that the presence
of additional bulky p-conjugated substituents (e.g. naph-
thyl) in the proximity of the charge transfer pathway of
push–pull NLO chromophores has the potential to modu-
late the molecular conformation, the electronic features of
the bridge and finally to affect the overall NLO response.
Nevertheless, at the third-order level, the NLO modulation
induced by a bulky substituent resulted rather weak,
though the substitution of electronic donor groups
enhanced between 3.5 and 4.5 the non-linear response.
The nonlinearities in these kind of molecules, which up
to now have received a limited attention, could deserve
further investigation in a perspective of developing
boron-based non-linear materials with potential applica-
tions in photonics.
were found by Fourier map difference and refined aniso-
tropically. Some hydrogen atoms were found by Fourier
map differences and refined isotropically. The remaining
hydrogen atoms were geometrically modelled and are
not refined.
4.3. NLO measurements
Second-order: the experimental hyperpolarizabilities (b)
were investigated by electric field induced second harmonic
(EFISH) technique [29,30]. The data were recorder using
picosecond Nd:YAG pulsed (10 Hz) laser operating at
1.064 lm. The outcoming Stokes-shifted radiation at
1.907 lm generated by Raman effect in a hydrogen cell
(1 m long, 50 bar) was used as the fundamental beam for
second harmonic generation (SHG). The centrosymmetry
of the solution was broken by dipolar orientation of the
chromophores with a high voltage pulse pulse (5 kV) syn-
chronized with the laser pulse. The SHG signal was selected
through a suitable interference filter, detected by a photo-
multiplier, and recorded on
oscilloscope.
a Tektonic TDS 620
4. Experimental
4.1. Instrument
4.3.1. Theoretical methods
All starting materials were purchased from Aldrich. Sol-
vents were used without further purification. Melting
points were recorded on a Electrothermal 9200 apparatus
and are uncorrected. Infrared spectra were measured on a
FT-IR Perkin-Elmer GX spectrophotometer using KBr
The all-valence INDO (intermediate neglect of differen-
tial overlap) method [31], was employed for the calculation
of the electronic transitions, to analyze the origin of the
charge transfer at the atomic level. Calculations were per-
formed using the INDO/1 Hamiltonian incorporated in
the commercially available MSI software package ZINDO
[32]. The monoexcited configuration interaction (MECI)
approximation was employed to describe the excited states.
The 100 lowest energy transitions between the 10 highest
occupied molecular orbitals and the 10 lowest unoccupied
ones were chosen to undergo CI mixing.
Third-order: these molecules were studied in solid state
(solid films) using the guest(molecule)–host(polymer)
approach. Ratios of 70:30 wt.% of polystyrene (PS) and
boronates 1a, 2c, 3a–3d were dissolved in chloroform while
1b–1c were dissolved in tetrahydrofuran. The solid films
were deposited on fused silica substrates (1 mm-thick) by
using the spin coating technique. The prepared films had
typical thickness between 50 and 300 nm with good optical
quality showing negligible light scattering at visible and
NIR wavelengths. Absorption spectra of spin-coated films
were obtained with a spectrophotometer (Perkin–Elmer
Lambda 900). Sample thickness was measured by using a
Dektak 6 M profiler.
1
pellets. H, 11B and 13C NMR spectra were recorded on
a Bruker avance DPX 300, Jeol GX 270 and Jeol Eclipse
+400 spectrometers. Chemical shifts (ppm) are relative to
1
(CH3)4Si for H and 13C and to BF3(OEt2) for 11B. Ultra-
violet spectra were obtained with a Perkin–Elmer Lambda
12 spectrophotometer. Mass spectra were recorded on a
Hewlett–Packard 5989A spectrometer. Elemental analyses
were carried out on a Thermo Finnigan Flash EA 1112
elemental microanalyzer.
4.2. X-ray data collection and structure determination
In all cases the single crystals suitable for X-ray struc-
tural studies were obtained by slow evaporation from
mixtures of CHCl3 and hexane. The crystal data were
recorded on an Enraf Nonius Kappa-CCD (k Mo
˚
Ka = 0.71073 A, graphite monochromator, T = 293 K-
CCD rotating images scan mode). The crystals were
mounted on a Lindeman tube. Absorption corrections
were performed using the SHELX-A [26] program. All reflec-
tion dataset were corrected for Lorentz and polarization
effects. The first structure solution was obtained using
the SHELXS-97 program and then SHELXL-97 program was
applied for refinement and output data [26]. All software
manipulations were done under the WIN-GX environment
program set [27]. Molecular perspectives were drawn
under ORTEP3 drawing application [28]. All heavier atoms
THG Maker-fringes setup is reported elsewhere [33].
Briefly, it consisted of a Nd-YAG laser-pumped optical
parametric oscillator (OPO) that delivered pulses of 8 ns
at a repetition rate of 10 Hz. A fundamental wavelength
of 1200 nm (idler beam) was used. The output of the
OPO system was focused into the films with a 30-cm
focal-length lens to form a spot with a radius of approxi-
mately 150 lm. Typical energies in our measurements were

1330
B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
set at 1 mJ per pulse at sample position (corresponding to
peak intensities of ꢃ0.18 GW/cm2). The third-harmonic
beam, as a bulk effect, emerging from the films was
separated from the pump beam by using a color filter
and detected with a PMT and a Lock-in amplifier. The
THG measurements were performed for incident angles
in the range from ꢁ40° to 40° with steps of 0.27°. All the
experiment was computer controlled.
In the Maker-fringes technique, the third-harmonic
peak intensity I3x from the substrate-film structure is com-
pared to one produce from the substrate alone. Then, the
non-linear susceptibility v(3) in a film of thickness Lf is
determined from [34]:
5), 7.02–7.05 (2H, m, H-3, H-17), 7.16 (1H, t, J = 8.0 Hz,
H-16), 7.45–7.52 (4H, m, H-4, H-6, H-13, H-20), 7.61
(1H, t, J = 7.9 Hz, H-21), 7.66 (1H, dd, J = 1.9, 8.0 Hz,
H-15), 7.77 (1H, d, J = 7.9 Hz, H-19), 7.80 (1H, d,
J = 2.2 Hz, H-10), 7.83 (1H, dd, J = 2.2, 8.8 Hz, H-12),
8.77 (1H, s, H-7), 8.82 (1H, d, J = 7.9 Hz, H-22); 13C
NMR (100 MHz, CDCl3) d (ppm): 110.8 (C-10), 114.8
(C-13), 115.1 (C-12), 119.3 (C-1), 120.9 (C-3), 121.0
(C-5), 124.6 (C-16), 125.4 (C-20), 125.6 (C-21), 128.4
(C-19), 128.5 (C-15), 128.9 (C-17), 129.5 (C-22), 132.0
(C-6), 133.9 (C-18), 135.5 (C-23), 135.6 (C-11), 139.7
(C-4), 149.9 (C-8), 152.7 (C-7), 157.7 (C-9), 158.3 (C-2);
11B NMR (96 MHz, CDCl3) d (ppm): +9.79 (h1/2
=
192 Hz); Elemental Anal. Calc. for C23H15O4N2-
B–C2H3N: C, 68.99; H, 4.17; N, 9.65. Found: C, 68.51;
H, 4.20; N, 9.17%.
ꢂ
ꢃꢂ
ꢃ
1=2
ð3Þ 2 Lc;s
I3f x
I3sx
vð3Þ ¼ vs
ð2Þ
p
Lf
where v(s3) and Lc,s are the non-linear susceptibility and
coherence length, respectively, for the substrate at the fun-
damental wavelength. In our calculation, we considered
v(s3) = 3.1 ꢂ 10ꢁ14 esu and Lc,s = 9 lm for the fused silica
substrate [33]. In any case, our samples satisfied the condi-
tion Lf ꢄ Lc,s in which Eq. (2) is valid.
4.4.3. 2-(2-Naphthyl-(30-nitrobenzo[d]))-1,3-dioxa-6-aza-
2-boracyclonon-6-ene (1b)
Compound 1b was obtained from 0.120 g (1.00 mmol)
of 2-hydroxybenzaldehyde, 0.150 g (1.00 mmol) of
2-amino-5-nitrophenol and 0.170 g (1.00 mmol) of 2-naph-
thylboronic acid. The product was obtained as a yellow
solid (0.350 g), yield 87%, m.p. 140–142 °C. IR (KBr) mmax
(cmꢁ1): 3382, 3321, 3109, 3052, 1626 (C@N), 1546, 1524,
1467, 1378, 1338, 1293, 1263, 1227, 1155, 1122, 1065,
977, 934, 867, 821 753. UV/Vis (CHCl3); kmax (nm) (e):
462 (4870). MS m/z (%): 395 (M++1, 25), 394 (M+, 86),
4.4. Syntheses
The following procedure was used in the syntheses of all
boron compounds described herein. Equimolecular
amounts of 4-diethylaminosalicylaldehyde (4-methoxysali-
cylaldehyde or salicyladehyde), 2-amino-5-nitrophenol
and the corresponding arylboronic or naphthylboronic
acids were refluxed in a mixture of acetonitrile and acetic
acid (9:1 ratio) for 6–12 h and allowed to cool to room tem-
perature. The solid precipitate was collected by filtration
under vacuum and washed with hexane, followed by
recrystallization from chloroform–hexane.
1
393 (30), 364 (4), 267 (100), 221 (61) 127 (6); H NMR
(400 MHz, CDCl3) d (ppm): 7.02 (1H, t, J = 7.5 Hz,
H-5), 7.29 (1H, d, J = 8.4 Hz, H-3), 7.34–7.42 (3H, m,
H-15, H-18, H-21), 7.48 (1H, d, J = 7.5 Hz, H-6), 7.58
(1H, d, J = 8.6 Hz, H-13), 7.63–7.72 (4H, m, H-4, H-16,
H-19, H-20), 7.74 (1H, s, H-23), 7.86 (1H, dd, J = 2.0,
8.6 Hz, H-12), 7.93 (1H, d, J = 2.0 Hz, H-10), 8.55 (1H,
s, H-7); 13C NMR (75 13C MHz, CDCl3) d (ppm): 110.7
(C-10), 115.4 (C-13), 115.6 (C-12), 119.4 (C-1), 121.1
(C-3), 121.5 (C-5), 125.9 (C-21), 126.1 (C-18), 127.4 (C-16),
127.9 (C-20), 128.4 (C-19), 128.9 (C-15), 131.2 (C-23)
132.7 (C-6), 133.2 (C-17), 133.9 (C-22), 136.2 (C-11),
140.4 (C-4), 150.3 (C-8), 152.9 (C-7), 158.7 (C-9), 159.0
(C-2); 11B NMR (128 MHz, CDCl3) d (ppm): +8.61
(h1/2 = 128 Hz).
4.4.1. 2-(2-Hydroxybenzylideneamino)-5-nitrophenol (1)
Compound 1 was obtained from 0.120 g (1.00 mmol) of
2-hydroxybenzaldehyde and 0.150 g (1.00 mmol) de
2-amino-5-nitrophenol. The product was obtained as a
red solid (0.190 g), yield 74%, m.p. 216–218 °C. UV/Vis
(CHCl3); kmax(nm) (e): 375 (76489). The spectroscopic
characterization has been previously reported [15].
4.4.4. 2-(2-Methylbenzo-(3-nitrobenzo[d]))-(benzo[h])-
1,3-dioxa-6-aza-2-boracyclonon-6-ene (1c)
4.4.2. 2-(1-Naphthyl-(30-nitrobenzo[d]))-1,3-dioxa-6-aza-
2- boracyclonon-6-ene (1a)
Compound 1c was obtained from 0.120 g (1.00 mmol) of
2-hydroxybenzaldehyde, 0.150 g (1.00 mmol) of 2-amino-5-
nitrophenol and 0.130 g (1.00 mmol) of o-tolylboronic
acid. The product was obtained as an orange solid
(0.320 g), yield 89%, m.p. 204–206 °C. IR (KBr) mmax
(cmꢁ1): 3392, 3216, 3063, 1617 (C@N), 1585, 1542, 1464,
1379, 1338, 1263, 1179, 1064, 995, 953, 872, 819, 754,
754. MS m/z (%): 357 (M++1, 3), 358 (M+, 10), 267
Compound 1a was obtained from 0.120 g (1.00 mmol)
of 2-hydroxybenzaldehyde, 0.150 g (1.00 mmol) of
2-amino-5-nitrophenol and 0.170 g (1.00 mmol) af 1-naph-
thylboronic acid. The product was obtained as an orange
solid (0.320 g), yield 81%, m.p. 150–152 °C. IR (KBr) mmax
(cmꢁ1): 3397, 3055, 2250, 1629 (C@N), 1588, 1545, 1520,
1463, 1381, 1341, 1293, 1261, 1154, 1125, 1070, 1042,
997. UV/Vis (CHCl3); kmax(nm) (e): 456 (11700). MS m/z
1
(100), 237 (25), 221 (38); H NMR (300 MHz, CDCl3) d
1
(%): 394 (M+, 65), 364 (3), 267 (100), 221 (50); H NMR
(ppm): 2.72 (3H, s, CH3), 6.89–6.94 (2H, m, H-6, H-16),
(400 MHz, CDCl3) d (ppm): 6.94 (1H, dt, J = 7.6, 0.9 H-
6.98 (1H, t, J = 7.2 Hz, H-5), 7.07–7.16 (3H, m, H-3,

B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1331
H-17, H-18), 7.52 (1H, d,J = 8.0 Hz, H-19), 7.57 (1H, t,
J = 7.2 Hz, H-4), 7.65 (1H, d, J = 8.4 Hz, H-13), 7.82–
7.85 (2H, m, H-10, H-12), 8.73 (1H, s, H-7); 13C NMR
(75 MHz, CDCl3) d (ppm): 22.2 (CH3), 110.9 (C-10),
114.8 (C-13), 115.2 (C-12), 119.4 (C-1), 120.9 (C-3), 121.2
(C-5), 124.2 (C-16), 128.0 (C-18), 130.4 (C-17), 131.2 (C-
6), 132.6 (C-19), 135.8 (C-15) 139.9 (C-4), 141.8 (C-11),
150.0 (C-8), 152.5 (C-7), 157.8 (C-9), 158.4 (C-2); 11B
NMR (96 MHz, CDCl3) d (ppm): +9.3 (h1/2 = 192.6 Hz).
Elemental Anal. Calc. for C20H15BN2O4 C, 67.07; H,
4.22; N, 7.82. Found: C, 66.63; H, 4.25; N, 7.85. HRMS
calcd m/z for C20H15BN2O4[M++H]+: 359.1197; Found:
359.1202 error 1.2 ppm.
7.67 (1H, d, J = 6.9 Hz, H-15), 7.75 (1H, d, J = 2.2 Hz,
H-10), 7.78 (1H, d, J = 7.0 Hz, H-19), 7.80 (1H, dd,
J = 2.2, 8.4 Hz, H-12), 8.60 (1H, s, H-7), 8.81 (1H, d,
J = 7.7 Hz, H-22); 13C NMR (100 MHz, CDCl3) d
(ppm): 56.0 (OCH3), 102.9 (C-3), 110.4 (C-10), 111.8 (C-5),
113.4 (C-1), 113.8 (C-13), 115.2 (C-12), 124.6 (C-16),
125.3 (C-20), 125.5 (C-21), 128.3 (C-15), 128.4 (C-19),
128.8 (C-17), 129.5 (C-22), 133.4 (C-6), 133.9 (C-18),
135.5 (C-23), 136.3 (C-11), 149.1 (C-8), 151.3 (C-7), 157.6
(C-9), 161.1 (C-2), 169.8 (C-4); 11B NMR (128 MHz,
CDCl3) d (ppm): +9.77 (h1/2 = 64 Hz). Elemental Anal.
Calc. for C24H17BN2O5 C, 67.95; H, 4.04; N, 6.60. Found:
C, 67.46; H, 4.15; N, 6.83%. HRMS calcd m/z for
C24H17BN2O5 [M++H]+: 425.1303; Found: 425.1306 error
0.6 ppm.
4.4.5. 2-(2-Hydroxy-4-methoxybenzylideneamino)-5-
nitrophenol (2)
Compound 2 was obtained from 0.150 g (1.00 mmol)
of 2-hydroxy-4-methoxy-benzaldehyde and 0.150 g
(1.00 mmol) of 2-amino-5-nitrophenol. The product was
obtained as an orange solid (0.270 g), yield 94%, m.p.
232-234 °C. IR (KBr) mmax (cmꢁ1): 3431(OH), 2979, 2895,
2470, 1620 (C@N), 1583, 1513, 1458, 1332, 1238, 1142,
1074, 947, 867, 811, 783, 741. UV/Vis (CHCl3);
4.4.7. 2-(2-Naphthyl-(30-nitrobenzo[d]))-(400-methoxy-
benzo[h])-1,3-dioxa-6-aza-2-boracyclonon-6-ene (2b)
Compound 2b was obtained from 0.150 g (1.00 mmol)
of 2-hydroxy-4-methoxy-benzaldehyde, 0.150 g (1.00 mmol)
of 2-amino-5-nitrophenol and 0.170 g (1.00 mmol) of
2-naphthylboronic acid. The product was obtained as an
orange solid (0.370 g), yield 87%, m.p. 220–222 °C. IR
(KBr) mmax (cmꢁ1): 3041, 2927, 2842, 1606 (C@N), 1582,
1528, 1384, 1337, 1293, 1234, 1170, 1122, 1067, 1042,
1021, 966, 933, 875, 820, 800, 782. UV/Vis (CHCl3); kmax
(nm) (e): 461 (22100). MS m/z (%): 425 (M++1, 9), 424
k
max(nm)(e): 376 (71215). MS m/z (%): 289 (M++1, 18),
288 (M+, 100), 271 (11), 241 (24), 199 (7), 165(6), 151 (9),
124 (14), 78 (4); 1H NMR (400 MHz, DMSO-d6) d
(ppm): 3.78 (3H, s, OCH3), 6.36 (1H, d, J = 2.2 Hz, H-3),
6.45 (1H, dd, J = 2.2, 8.8 Hz, H-5), 7.45 (1H, d,
J = 8.8 Hz, H-6), 7.48 (1H, d, J = 8.8 Hz, H-13), 7.62
(1H, d J = 2.2, 8.8 Hz, H-12), 7.66 (1H, d, J = 2.2 Hz,
H-10), 8.97 (1H, s, H-7); 13C NMR (68 MHz, DMSO-d6)
d (ppm): 56.0 (OMe), 101.6 (C-3), 107.8 (C-5), 111.4
(C-10), 113.6 (C-1), 114.7 (C-12), 120.1 (C-13), 134.9
(C-6), 141.4 (C-8), 145.9 (C-11), 152.6 (C-9), 162.5 (C-7),
165.2 (C-2), 166.8 (C-4). Elemental Anal. Calc. for
C14H12N2O5 C, 58.33; H, 4.19; N, 9.71. Found: C, 58.99;
H, 4.27; N, 10.03%. HRMS calcd m/z for C14H12N2O5
[M++H]+: 289.0818; Found: 289.0821 error 0.7 ppm.
1
(M+, 34), 297 (100), 267 (10), 251 (67); 127 (3); H NMR
(400 MHz, CDCl3) d (ppm): 3.65 (3H, s, OMe), 6.31 (1H,
dd, J = 2.2, 8.8 Hz, H-5), 6.41 (1H, d, J = 2.2 Hz, H-3),
7.03–7.07 (2H, m, H-18, H-21), 7.12 (1H, d, J = 8.0 Hz,
H-15), 7.19 (1H, d, J = 8.8 Hz, H-6), 7.33 (1H, d,
J = 8.0, Hz, H-16), 7.36-7.44 (2H, m, H-19, H-20), 7.44
(1H, s, H-23), 7.47 (1H, d, J = 8.7 Hz, H-13), 7.52 (1H,
d, J = 2.2 Hz, H-10), 7.56 (1H, dd, J = 2.2, 8.7 Hz,
H-12), 8.63 (1H, s, H-7); 13C NMR (100 MHz, DMSO-
d6) d (ppm): 56.0 (OMe), 102.6 (C-3), 109.0 (C-10), 110.9
(C-5), 113.4 (C-1), 115.0 (C-13), 115.2 (C-12), 125.3,
125.4 (C-18, C-21), 126.7 (C-16), 127.3, 127.8 (C-20,
C-19), 128.6 (C-15), 130.2 (C-23), 132.7 (C-17), 133.2
(C-22), 134.2 (C-6), 136.9 (C-11), 148.6 (C-8), 153.0
(C-7), 157.5 (C-9), 161.0 (C-2), 169.6 (C-4); 11B NMR
(128 MHz, DMSO-d6) d (ppm): +8.0 (h1/2 = 320 Hz). Ele-
mental Anal. Calc. for C24H17O5N2B: C, 67.98; H, 4.01;
N, 6.60. Found: C, 67.21; H, 4.18; N, 6.49%. HRMS calcd
m/z for C24H17BN2O5 [M++H]+: 425.1303; Found:
425.1303 error 0.07 ppm.
4.4.6. 2-(1-Naphthyl-(30-nitrobenzo[d]))-(400- methoxy-
benzo[h])-1,3-dioxa-6-aza-2-boracyclonon-6-ene (2a)
Compound 2a was obtained from 0.150 g (1.00 mmol)
of 2-hydroxy-4-methoxy-benzaldehyde, 0.150 g (1.00 mmol)
of 2-amino-5-nitrophenol and 0.170 g (1.00 mmol) of 1-
naphthylboronic acid. The product was obtained as an
orange solid (0.270 g), yield 64%, m.p. 260-262 °C. IR
(KBr) mmax (cmꢁ1): 3040, 2945, 2843, 1608 (C@N), 1582,
1527, 1469, 1382, 1337, 1293, 1234, 1171, 1121, 1069,
1042, 1021, 964, 934, 875, 819, 801, 782. UV/Vis (CHCl3);
4.4.8. 2-(2-Methylbenzo-(3-nitrobenzo[d]))-
(methoxybenzo[h])-1,3-dioxa-6-aza-2-boracyclonon-6-ene
(2c)
Compound 2c was obtained from 0.150 g (1.00 mmol) of
2-hydroxy-4-methoxy-benzaldehyde, 0.150 g (1.00 mmol)
of 2-amino-5-nitrophenol and 0.130 g (1.00 mmol) of o-tol-
ylboronic acid. The product was obtained as an orange
solid (0.250 g), yield 65%, m.p. 230–232 °C. IR (KBr) mmax
(cmꢁ1): 2928, 1613 (C@N), 1582, 1529, 1471, 1385, 1335,
k
max(nm) (e): 460 (8740). MS m/z (%): 425 (M+ + 1, 1) 424
(M+, 6), 297 (100), 267 (16), 251 (44), 208 (11), 127 (8);
1H NMR (400 MHz, CDCl3) d (ppm): 3.75 (3H, s,
OCH3), 6.42 (1H, d, J = 2.2 Hz, H-3), 6.49 (1H,
dd,J = 2.2, 8.8 Hz, H-5), 7.05 (1H, d,J = 6.9 Hz,
H-17), 7.19 (1H, t, J = 6.9 Hz, H-16), 7.37 (1H, d,
J = 8.8 Hz, H-6), 7.47 (1H, t, J = 7.0 Hz, H-20), 7.54
(1H, d, J = 8.4, H-13), 7.61 (1H, t, J = 7.0 Hz, H-21),

1332
B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1299, 1237, 1171, 1139, 1062, 1022, 963, 870, 818, 752, 731.
UV/Vis (CHCl3); kmax(nm) (e): 461 (22800). MS m/z (%):
388 (M+, 3), 297 (100), 267(5), 251 (47), 208 (14), 91(5);
1H NMR (270 MHz, CDCl3) d (ppm): 2.68 (3H, s, CH3),
3.83 (3H, s, OCH3), 6.49 (1H, d, J = 2.4 Hz, H-3), 6.52
(1H, dd, J = 8.4, 2.4 Hz, H-5), 6.87–6.95 (2H, m, H-16,
H-19), 7.05–7.10 (2H, m, H-17, H-18), 7.36 (1H, d,
J = 8.4 Hz, H-6), 7.52 (1H, d, J = 8.4 Hz, H-13), 7.76
(1H, d, J = 2.2, Hz, H-10), 7.79 (1H, dd, J = 8.4, 2.2 Hz,
H-12), 8.55 (1H, s, H-7); 13C NMR (75 MHz, CDCl3) d
(ppm): 22.3 (CH3), 56.2 (OCH3), 102.9 (C-3), 110.5 (C-
10), 111.8 (C-5), 113.6 (C-1), 113.9 (C-13), 115.2 (C-12),
124.2 (C-16), 127.9 (C-18), 130.4 (C-17), 131.2 (C-19),
133.7 (C-6), 136.5 (C-15), 141.8 (C-11), 149.1 (C-8), 151.2
(C-7), 157.7 (C-9), 161.1 (C-2), 169.9 (C-4); 11B NMR (96
MHz, CDCl3) d (ppm): +9.17 (h1/2 = 193 Hz). Elemental
Anal. Calc. for C21H17O5N2B: C, 64.98; H, 4.41; N, 7.22.
Found: C, 65.43; H, 4.12; N, 7.01%. HRMS calcd m/z
for C21H17O5N2B [M++H]+: 389.1303; Found 389.1308
error 1.2 ppm.
CH3), 3.32 (4H, m, N–CH2), 6.06 (1H, d, J = 2.4 Hz,
H-3), 6.27 (1H, dd, J = 9.2, 2.4 Hz, H-5), 7.11 (1H, d,
J = 7.4 Hz, H-17), 7.19 (1H, t, J = 7.4 Hz, H-16), 7.21
(1H, d, J = 9.2 Hz, H-6), 7.35 (1H, d, J = 8.6, Hz, H-13),
7.45 (1H, t, J = 7.8 Hz, H-20), 7.58 (1H, t, J = 7.8 Hz,
H-21), 7.65 (1H, d, J = 7.4 Hz, H-15), 7.69 (1H, d,
J = 2.2 Hz, H-10), 7.76 (1H, dd, J = 8.6, 2.2 Hz, H-12),
7.77 (1H, d, J = 7.8 Hz, H-19), 8.34 (1H, s, H-7), 8.84
(1H, d, J = 7.8 Hz, H-22); 13C NMR (100 MHz, CDCl3)
d (ppm): 12.8 (CH3), 45.2 (N–CH2), 99.4 (C-3), 107.8
(C-5), 109.6 (C-10), 110.6 (C-1), 112.1 (C-13), 115.3
(C-12), 124.7 (C-16), 125.1 (C-20), 125.3 (C-21), 127.9
(C-15), 128.3 (C-19), 128.7 (C-17), 129.8 (C-22), 133.9
(C-18), 134.2 (C-6), 135.7 (C-23), 138.9 (C-18), 147.5
(C-8), 148.4 (C-7), 156.9 (C-9), 157.1 (C-4), 160.5 (C-2);
11B NMR (128 MHz, CDCl3) d (ppm): +9.5 (h1/2
=
256, Hz); Elemental analysis Calc. for C27H24O4N3B: C,
69.74; H, 5.16; N, 9.03. Found: C, 69.51; H, 5.77; N, 8.87%.
4.4.11. 2-(2-Naphthyl-(30-nitrobenzo[d]))-
(400- diethylaminobenzo[h])-1,3-dioxa-6-aza-2-
boracyclonon-6-ene (3b)
4.4.9. 2-4-(Diethylamino-2-hydroxybenzylideneamino)-
5- nitrophenol (3)
Compound 3b was obtained from 0.190 g (1.00 mmol)
of 4-diethylaminosalicylaldehyde, 0.150 g (1.00 mmol) of
2-amino-5-nitrophenol and 0.170 g (1.00 mmol) of 2-naph-
thylboronic acid. The product was obtained as a red solid
(0.250 g), yield 54%, m.p. 198–200 °C. IR (KBr) mmax
(cmꢁ1): 3045, 2974, 1606 (C@N), 1573, 1526, 1448, 1420,
1331, 1246, 1187, 1139, 1067, 959, 932, 866, 821, 745.
UV/Vis (CHCl3); kmax(nm) (e): 511 (63900). MS m/z (%):
466 (M++1, 6), 465 (M+, 18), 338 (100), 308 (10), 292
(31), 248 (15), 220 (3), 127 (10); 1H NMR (400 MHz,
CDCl3) d (ppm): 1.25 (6H, t, CH3), 3.46 (4H, m,
N–CH2), 6.33 (1H, dd, J = 9.5, 2.6 Hz, H-5) 7.35 (IH, d,
J = 2.6 Hz, H-3), 7.18 (1H, d, J = 9.5 Hz, H-6), 7.29 (1H,
d, J = 8.6 Hz, H-13), 7.33–7.36 (2H, BB0, H-18, H-21),
7.49 (1H, d, J = 8.4 Hz, H-15), 7.66 (1H, d, J = 8.4 Hz,
H-16), 7.69–7.71 (2H, AA0, H-19, H-20), 7.79 (1H, dd,
J = 2.2, 8.6 Hz, H-12), 7.81 (1H, s, H-23), 7.83 (1H, d,
J = 2.2 Hz, H-10), 8.15 (1H, s, H-7); 13C NMR (75 MHz,
CDCl3) d (ppm): 31.2 (N–CH2), 45.5 (CH3), 99.3 (C-3),
107.8 (C-5), 109.1 (C-10), 110.5 (C-1), 112.5 (C-13), 115.6
(C-12), 125.4 (C-18, C-21), 126.9 (C-16), 127.7 (C-19),
128.2 (C-20), 129.1 (C-15), 130.5 (C-23), 133.1 (C-17),
133.5 (C-22), 134.6 (C-6) 138.4 (C-11), 147.5 (C-8), 148.6
(C-7), 157.1 (C-9), 157.5 (C-2), 161.1 (C-4); 11B NMR
(128 MHz, CDCl3) d (ppm): +8.3 (h1/2 = 128 Hz); Elemen-
tal Anal. Calc. for C27H24O4N3B: C, 69.69; H, 5.2; N, 9.03.
Found: C, 69.38; H, 5.08; N, 8.89%.
Compound 3 was obtained from 0.190 g (1.00 mmol) of
4-(diethylamino)-salicylaldehyde and 0.150 g (1.00 mmol)
of 2-amino-5-nitrophenol. The product was obtained as a
red solid (0.230 g), yield 69%, m.p. 254–256 °C. IR (KBr)
mmax (cmꢁ1): 3436, 2938, 1619 (C@N), 1586, 1523, 1397,
1339, 1230, 1124, 1073, 1017, 945. UV/Vis (CHCl3);
k
max(nm) (e): 436 (89920). MS m/z (%): 329 (M+, 97),
314 (100), 300 (14), 286 (8); 1H NMR (400 MHz,
DMSO-d6) d (ppm): 1.12 (6 H, t, CH3), 3.39 (4H, q,
N–CH2), 5.94 (1H, d, J = 2.2 Hz, H-3), 6.32 (1H, dd,
J = 2.2, 8.8 Hz, H-5), 7.27 (1H, d, J = 8.8 Hz, H-6), 7.46
(1H, d, J = 8.4 Hz, H-13), 7.62–7.64 (2H, m, H-10, H-
12), 8.77 (1H, s, H-7), 13C NMR (68 MHz, DMSO-d6) d
(ppm): 12.7 (Me), 44.7 (CH2–N), 98.4 (C-3), 104.8 (C-5),
110.3 (C-10), 111.2 (C-12), 111.9 (C-1), 119.2 (C-13),
135.2 (C-6), 141.6 (C-8), 145.8 (C-11), 153.2 (C-9), 156.8
(C-7), 159.1 (C-4), 168.9 (C-2). HRMS calcd m/z for
C17H19N3O4 [M++H]+: 330.1448; Found 330.1451 error
0.8 ppm.
4.4.10. 2-(1-Naphthyl-(30-nitrobenzo[d]))-
(400- diethylaminobenzo[h])-1,3-dioxa-6-aza-2-
boracyclonon-6-ene (3a)
Compound 3a was obtained from 0.190 g (1.00 mmol)
of 4-diethylaminesalicylaldehyde, 0.150 g (1.00 mmol) of
2-amino-5-nitrophenol and 0.170 g (1.00 mmol) of 1-naph-
thylboronic acid. The product was obtained as a red solid
(0.410 g), yield 88%, m.p. 238–240 °C. IR (KBr) mmax
(cmꢁ1): 3037, 2972, 2930, 2380, 1606 (C@N), 1572, 1526,
1446, 1418, 1375, 1328, 1244, 1185, 1135, 1063, 1039,
959, 932, 862, 819, 788. UV/Vis (CHCl3); kmax(nm) (e):
506 (34060). MS m/z (%): 466 (M++1, 7) 465 (M+, 23),
4.4.12. 2-(2-Methylbenzo-(3-nitrobenzo[d]))-
(diethylaminobenzo[h])-1,3-dioxa-6-aza-2-boracyclonon-6-
ene (3c)
Compound 3c was obtained from 0.190 g (1.00 mmol) of
4-diethylaminosalicylaldehyde, 0.150 g (1.00 mmol) of
2-amino-5-nitrophenol and 0.130 g (1.00 mmol) of o-tolyl-
boronic acid. The product was obtained as a red solid
1
338 (100), 308 (16), 292 (30), 248 (15), 220(3), 127 (5); H
NMR (400 MHz, CDCl3) d (ppm): 1.12 (3H, t, J = 7.1,

B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
1333
(0.420 g), yield 90%, m.p. 126–128 °C. IR (KBr) mmax
(cmꢁ1): 3109, 2975, 1607 (C@N), 1573, 1526, 1448, 1419,
1377, 1331, 1245, 1185, 1138, 1065, 1012, 960, 932, 857,
818, 787, 749, 729. UV/Vis (CHCl3); kmax (nm) (e): 490
(16990). MS m/z (%): 430 (M++1, 3), 429 (M+, 11), 338
(100), 308 (13), 292 (31), 264 (6), 248 (17) 220 (3); 1H
NMR (300 MHz, CDCl3) d (ppm): 1.22 (6H, t, CH3),
2.71 (3H, s, CH3), 3.32–3.53 (4H, m, N–CH2), 6.17 (1H,
d, J = 2.4 Hz, H-3), 6.32 (1H, dd, J = 9.2, 2.4 Hz, H-5),
6.93 (1H, t, J = 7.0 Hz, H-16), 7.00 (1H, d, J = 7.0 Hz,
H-17), 7.08 (1H, dd, J = 7.0, 1.7 Hz, H-18), 7.14 (1H, d,
J = 7.0 Hz, H-19), 7.23 (1H, d, J = 9.2 Hz, H-6), 7.38
(1H, d, J = 8.6 Hz, H-13), 7.72 (1H, d, J = 2.2, Hz,
H-10), 7.78 (1H, dd, J = 8.6, 2.2 Hz, H-12), 8.33 (1H, s,
H-7); 13C NMR (75 MHz, CDCl3) d (ppm): 12.8 (CH3),
22.4 (CH3), 45.4 (N–CH2), 99.3 (C-3), 107.9 (C-5), 109.5
(C-10), 110.8 (C-1), 112.2 (C-13), 115.3 (C-12), 124.1
(C-17), 127.5 (C-19), 130.2 (C-18), 131.3 (C-16), 134.4
(C-6), 138.1 (C-15), 141.9 (C-11) 147.5 (C-8), 148.5 (C-7),
157.0 (C-9), 157.1 (C-2), 160.6 (C-4); 11B NMR (96 MHz,
CDCl3) d (ppm): +9.1 (h1/2 = 202 Hz). HRMS calcd m/z
for C24H24BN3O4 [M++H]+: 430.1932; Found: 430.1937
error 0.2 ppm.
can be obtained free of charge from The Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Acknowledgements
The authors thank the UNAM (PAPIIT IN-203207)
and CONACyT-CNRS for financial support and the schol-
arship to B.M. Munoz, and the ENS Cachan, International
˜
Scholarship Program. We also thank M. Leyva for X-ray
´
diffraction and V. Gonzalez and G. Uribe for NMR
spectra.
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87%, m.p. 246–248 °C. IR (KBr) mmax (cmꢁ1): 3123, 2975,
1686, 1607 (C@N), 1574, 1526, 1448, 1420, 1380, 1332,
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J = 2.4 Hz, H-3), 6.32 (1H, dd, J = 9.2, 2.4 Hz, H-5),
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(1H, d, J = 8.6 Hz, H-13), 7.68 (1H, d, J = 2.2 Hz, H-10),
7.77 (1H, dd, J = 8.6, 2.2 Hz, H-12), 7.97 (1H, dd,
J = 6.2, 2.7 Hz, H-16), 8.39 (1H, s, H-7), 10.94 (1H, s,
HCO); 13C NMR (100 MHz, CDCl3) d (ppm): 12.8
(CH3), 45.4 (N–CH2), 99.2 (C-3), 108.2 (C-5), 109.4
(C-10), 110.6 (C-1), 112.1 (C-13), 115.6 (C-12), 127.1
(C-16), 127.7 (C-17), 131.7 (C-19), 132.3 (C-18), 134.4
(C-6), 137.7 (C-15), 139.6 (C-11) 147.4 (C-8), 148.7 (C-7),
156.4 (C-9), 157.2 (C-2), 160.0 (C-4), 196.3 (COH); 11B
NMR (128 MHz, CDCl3) d (ppm): +8.8 (h1/2 = 256 Hz).
HRMS calcd m/z for C24H22BN3O5 [M++H]+: 444.1725;
Found 444.1727 error 0.4 ppm.
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1334
B.M. Mun˜oz et al. / Journal of Organometallic Chemistry 693 (2008) 1321–1334
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