Synthesis, characterization and X-ray studies of new six-seven membered rings [4.5.0] heterobicyclic system of monomeric boronates

Article abstract of DOI:10.1016/j.ica.2012.03.055

Different tridentate ligands derived from ethanolamines and 2-hydroxyacetophenone, 2-hydroxybenzophenone and salicylaldehyde were reacted with two equivalents of phenylboronic acid to obtain compounds 6a-6f which are [4.5.0] heterobicyclic systems with a

Full text of DOI:10.1016/j.ica.2012.03.055

Inorganica Chimica Acta 390 (2012) 26–32
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization and X-ray studies of new six–seven membered
rings [4.5.0] heterobicyclic system of monomeric boronates
José María Rivera a, , Enrique Méndez a,e, Raúl Colorado-Peralta b, Susana Rincón c, Norberto Farfán b,
⇑
Rosa Santillán d
a Facultad de Ciencias Químicas, Universidad Veracruzana, Prolongación Oriente 6, No. 1009, Colonia Rafael Alvarado, Apartado, P.O. Box 215, CP 94340, Orizaba, Veracruz, Mexico
b Facultad de Química, Departamento de Química Inorgánica, Universidad Nacional Autónoma de México, Ciudad Universitaria, CP 04510, México DF, Mexico
c Departamento de Ingeniería Química-Bioquímica, Instituto Tecnológico de Mérida, Av. Tecnológico S/N, CP 97118, Mérida, Yucatán, Mexico
d Departamento de Química, Centro de Investigación y de Estudios Avanzados del IPN, Apartado P.O. Box 14-740, CP 07360, México DF, Mexico
e CIB-Doctorado en Ciencias Biomédicas, Universidad Veracruzana, Av. Dr. Luis Castelazo Ayala s/n, Colonia Industrial Anima, CP 91000, Xalapa, Veracruz, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Different tridentate ligands derived from ethanolamines and 2-hydroxyacetophenone, 2-hydroxybenzo-
phenone and salicylaldehyde were reacted with two equivalents of phenylboronic acid to obtain com-
pounds 6a–6f which are [4.5.0] heterobicyclic systems with a BꢀOꢀB structural unit. The boronates
were fully characterized and two heterobicyclic [4.5.0] structures have been analyzed by X-ray crystal-
lography, where a series of parameters such as bond distances, bond angles, torsion angles, tetrahedral
character at the boron atom and deviation of the boron atom from the mean plane have been evaluated.
Ó 2012 Elsevier B.V. All rights reserved.
Received 16 January 2012
Received in revised form 22 March 2012
Accepted 28 March 2012
Available online 13 April 2012
Keywords:
X-ray studies
Boronates
Tridentate ligands
NMR
1. Introduction
as reflux of toluene for 24 h. In turn, dimeric compounds were
formed when the ligands have zero, two, five or six methylene
Recently, there has been a considerable interest in the synthe-
sis, characterization and study of organoboron compounds, due
to a great variety of applications derived from these complexes
in different areas such as supramolecular chemistry [1,2]; boron
complexes have found application in medicinal chemistry, as anti-
cancer agents in boron neutron capture therapy [3,4]; as bioactive
materials, 10B is employed in the control of nuclear reactors as a
shield against the nuclear radiation [5]. Moreover, they also display
a wide range of applications in organic synthesis [6], for example,
in the synthesis of polyolefins, styrene, and substituted biphenyls
by the Suzuki reaction [7–10]; as materials with fluorescence
[11], electro optical and nonlinear optical properties which are
areas recently explored using boron chemistry [12,13]. In this con-
text, the synthesis and characterization of boron complexes ob-
tained from the condensation of 3-amino-phenylboronic acid and
1,3-diketones [14] and recently the synthesis, characterization
and X-ray studies of new fused five–six-membered rings, [4.3.0.]
heterobicyclic systems of monomeric boronates derived from opti-
cally active tridentate ligands [15] have been reported. Our previ-
ous studies have shown that fused five–six membered rings
compounds are obtained under strong reaction conditions such
units between the imino and hydroxyl group, using mild reactions
conditions such as reflux of THF for approximately 30 min [16]
(Scheme 1). In this work, tridentate ligands 5a–5f were allowed
to react with two equivalents of phenylboronic acid to give six
new [4.5.0] heterobicyclic boronates which possess two boron
atoms in the structure. The results from X-ray diffraction indicated
low strain present in the seven membered rings of the molecules as
well as the chair conformation and the tetrahedral character of the
boron atoms which is directly associated to the geometry [17,18]
and shows deviation from ideal values. The presence of two differ-
ent boron atoms in the structures suggests that these molecules
are intermediates in the reaction. One of the boron atoms (B1) is
tetrasubstituted forming a coordination bond to the nitrogen and
the other boron atom (B2) is trisubstituted with an empty p orbital.
These boronate units are connected by two covalent B–O and a
coordinative N ? B bond, which are responsible for hydrolytic sta-
bility of these molecules [19] (Scheme 2).
2. Experimental
2.1. Instrumentation
⇑
NMR spectra were recorded in CDCl3 and DMSO-d6 solutions on
Bruker Avance 300 spectrometer. Chemical shifts (ppm) are
Corresponding author. Tel.: +52 2721010934; fax: +52 2727240120.
E-mail address: chemax7@yahoo.com.mx (J.M. Rivera).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.03.055

J.M. Rivera et al. / Inorganica Chimica Acta 390 (2012) 26–32
27
R1
R2
R3
N
B
O
B
N
O
O
R3
R2
R1
2
R2
R1
R3
R1
R2
N
R3
O
N
2 C6H5B(OH)2
B
B
O
O
OH
Δ Tol, 1 Hr.
OH
3
R1
C
H
R2
B
(
O
Δ
H
To
)
l
,
3
6
H
N
B
r
s
.
R3
O
O
4
Scheme 1. Monomeric and dimeric boronates obtained using different reactions conditions.
relative to (CH3)4Si for 1H and 13C and BF3ꢁOEt2 for 11B. Coupling
constants are reported in Hz. Infrared spectra were recorded on a
Perkin–Elmer 16F-PC FT-IR spectrometer. Mass spectra were re-
corded on a Hewlett–Packard model 5989 engine, coupled to a
GC 5890 series II. Melting points were obtained on a Gallenkamp
MFB-595 apparatus and are uncorrected. Elemental analyses were
carried out on a FLASH (EA) 1112 series, thermo Finnigan appara-
tus. The X-ray diffraction study was determined on an Enraf–Non-
PLATON [23]. Molecular perspectives were drawn under ORTEP-3 [24],
and DIAMOND 2.1e drawing applications.
2.2. Reagents
All reactants and solvents were purchased from Aldrich chemi-
cal Co. and solvents were dried previous to use [25]. Single crystals
were grown using spectroscopic grade solvents.
ius-Fr590 Kappa-CCD (kMo
= 0.71073 Å, graphite monochro-
K
a
mator, T = 293 K, CCD rotating images scan mode) and the crystals
were mounted on a LINDEMANN tube. Absorption correction was
not necessary. All reflections data set were corrected for Lorentz
and Polarizations effects. Structure solution and refinement were
2.3. Synthesis
2.3.1. General method for the preparation of tridentate ligands 5a–5f
In order to prepare the tridentate ligands 5a–5f, equimolecular
quantities of the corresponding aminoalcohol and 2-hydroxyaceto-
phenone, 2-hydroxybenzophenone or salicylaldehyde, respec-
tively, were refluxed in ethanol for 1 h. The solvent and water
formed during the reaction were eliminated with a Dean–Stark
performed using the SHELX-S-97 program and then SHELX-L-97 pro-
gram was applied for refinement and output data [20,21]. All soft-
ware manipulations were done under the WINGX environment
program set [22]. Single crystal structure validation was done with

28
J.M. Rivera et al. / Inorganica Chimica Acta 390 (2012) 26–32
R2
R1
R3
R4
R1
R2
HO
OH
R5
6
3
R3
B
5
4
1
2
8
9
N
B
7
R4
R5
Tol
Δ
N
2
O
+
B
O
HO
O
17
16
OH
10
11
15
14
18
19
5a-5f
21
12
20
13
6a-6f
Compounds
R1
CH3
CH3
H
H
H
Ph
R2
R3
H
H
R4
CH3
H
R5
H
6a
6b
6c
6d
6e
6f
H
H
H
H
H
H
H
Ph
Ph
H
H
H
H
CH3
CH3
Ph
H
H
H
Scheme 2. Synthesis of oligodiboronates 6a–6f, derived from tridentate ligands 5a–5f and two equivalents of phenylboronic acid.
trap to yield yellow solids that were washed with methylene chlo-
ride and used without further purification. All tridentate ligands
5a–5f have already been published [26–33].
2.3.2.2. 2,4-diphenylbenzo[j]-9-Methyl-8-aza-1,3,5,2,4-trioxadibora-
cycloundec-8-ene. 6b. Compound 6b was synthesized from 0.50 g.
(2.79 mmol) of 5b and 0.68 g. (5.58 mmol) of phenylboronic acid.
The reaction was carried under reflux of toluene for 1 h, using a
Dean–Stark trap. The product was obtained as a yellow solid
0.87 g. (2.37 mmol), yield, 84%, mp: 203–207 °C. IR tmax (KBr):
3046, 3012, 2881, 1958, 1826, 1617 (C@N), 1556, 1437, 1335,
1272, 1149, 1083, 1026, 995, 951, 838, 747, 702, 641, 577, 506,
2.3.2. General method for the preparation of compounds 6a–6f
To prepare compounds 6a–6f one equivalent of the tridentate
ligands 5a–5f and two equivalents of the phenylboronic acid were
refluxed in toluene for 1 h. The solvent and water formed during
the reaction were eliminated to yield yellow solids that were
washed with methylene chloride and purified by recrystallization
using a mixture of chloroform hexane 2:1.
464, 420 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [d, ppm]: 2.57 (s,
.
CH3), 3.82 (m, 1H, H-8a), 3.97 (m, 2H, H-8b, H-9a), 4.41 (m, 1H,
H-9b), 6.86 (t, 1H, J = 7.9 Hz, H-5), 7.21 (d, 1H, J = 8.3 Hz, H-3),
7.21–7.25 (m, 3H, H-6, H-12, H-14), 7.34–7.49 (m, 6H, H-4, H-11,
H-13, H-15, H-18, H-20), 7.57 (dd, 1H, J = 1.3 Hz, J = 6.9 Hz, H-19),
8.01 (d, 2H, J = 6.3 Hz, H-17, H-21). 13C NMR (75.46 MHz DMSO-
d6) [d, ppm]: 16.1 (CH3), 52.0 (C-8), 63.9 (C-9), 117.0 (C-1), 118.8
(C-5), 120.7 (C-3), 127.3 (C-6), 127.6 (C-18, C-20), 127.8 (C-12, C-
14), 128.5 (C-19), 130.3 (C-13), 131.1 (C-11, C-15), 137.2 (C-4),
2.3.2.1. (2R,6R)-2,4-diphenylbenzo[j]-6,9-dimethyl-8-aza-1,3,5,2,4-
trioxadiboracycloundec-8-ene. 6a. Compound 6a was synthesized
from 0.50 g (2.59 mmol) of 5a and two equivalents (0.63 g,
5.18 mmol) of phenylboronic acid. The reaction was carried out
under reflux of toluene for 1 h, using a Dean–Stark trap. The prod-
uct was obtained as a yellow solid 0.78 g. (2.04 mmol), yield, 79%,
159.4 (C-2), 170.2 (C-7).11
B NMR (96.29 MHz, DMSO-d6), [d,
ppm]: 3.5, 25.8 (h1/2 = 289, 674 Hz.). MS (m/z,%): 368 (M+, 0.2),
312 (3), 292 (46), 188 (100), 160 (2), 104 (1). Anal. Calc. for
mp: 95–100 °C. IR
1620 (C@N), 1554, 1441, 1408, 1335, 1276, 1156, 1079, 1025, 992,
854, 746, 702, 646, 580, 537, 504, 452 cmꢀ1 1H NMR (300 MHz,
tmax (KBr): 3070, 3011, 2976, 2881, 1914, 1830,
C22H21B2NO3: C, 71.60; H, 5.74; N, 3.80. Found C, 71.28; H, 5.94;
N, 3.86%.
.
DMSO-d6) [d, ppm]: 1.44 (d, 3H, CH3), 2.18 (s, 3H, CH3), 3.67 (dd,
1H, J = 4.7 Hz, J = 9.1 Hz, H-8a), 3.77 (d, 1H, J = 13.9 Hz, H-8b),
4.24 (q, 1H, J = 7.3 Hz, H-9), 6.87 (t, 1H, J = 7.7 Hz, H-5), 7.05 (d,
1H, J = 8.4 Hz, H-3), 7.22–7.31 (m, 3H, H-6, H-12, H-14), 7.33–
7.55 (m, 6H, H-4, H-11, H-13, H-15, H-18, H-20), 7.57 (d, 1H,
J = 8.4 Hz, H-19), 8.09 (d, 2H, J = 6.6 Hz, H-17, H-21). 13C NMR
(75.46 MHz, DMSO-d6) [d, ppm]: 15.9 (CH3), 22.5 (CH3), 56.2 (C-
8), 71.7 (C-9), 116.6 (C-1), 118.6 (C-5), 120.7 (C-3), 127.4 (C-6),
127.6 (C-18, C-20), 127.8 (C-12, C-14), 128.5 (C-19), 130.1 (C-13),
131.4 (C-11, C-15), 135.1 (C-17, C-21), 137.2 (C-4), 159.3 (C-2),
169.3 (C-7). 11B NMR (96.29 MHz, DMSO-d6), [d, ppm]: 3.4, 25.7.
(h1/2 = 286, 596 Hz.). MS (m/z,%): 383 (M+, 0.1), 306 (38), 262
(0.1), 234 (1), 202 (100), 162 (6), 105 (0.2). Anal. Calc. for
2.3.2.3.
(7R)-2,4-diphenylbenzo[j]-7-phenyl-8-aza-1,3,5,2,4-trioxa-
diboracyclo-undec-8-ene. 6c. Compound 6c was synthesized from
0.50 g. (2.07 mmol) of 5c and two equivalents 0.51 g. (4.14 mmol)
of phenylboronic acid. The reaction was carried out under reflux of
toluene for 1 h, using a Dean–Stark trap. The product was obtained
as a yellow solid 0.81 g. (1.89 mmol), yield, 91%, mp: 98–102 °C. IR
t
max (KBr): 3049, 2957, 2932, 1961, 1634 (C@N), 1559, 1442, 1310,
1191, 1151, 1076, 1027, 984, 882, 850, 755, 701, 650, 549,
452 cmꢀ1 1H NMR (300 MHz, CDCl3) [d, ppm]: 4.22 (dd, 1H,
.
J = 4.7 Hz, 7.7 Hz; H-8a), 4.84 (dd, 1H, J = 2.9 Hz, 9.5 Hz, H-9a),
4.98 (m, 1H, H-9b), 6.78 (t, 1H, J = 6.9 Hz, H-5), 7.09 (d, 1H,
J = 8.8 Hz, H-3), 7.21–7.32 (m, 5H, H-6, H-12, H-14, H-23, H-27),
7.38–7.54 (m, 9H, H-4, H-11, H-13, H-15, H-18, H-20, H-24, H-25,
H-26), 7.85 (s, 1H, H-7), 8.25 (d, 2H, J = 6.6 Hz, H-17, H-21). 13C
C23H23B2NO3: C, 72.12; H, 6.05; N, 3.66. Found C, 72.69; H, 6.15;
N, 3.71%.

J.M. Rivera et al. / Inorganica Chimica Acta 390 (2012) 26–32
29
NMR (75.46 MHz, CDCl3) [d, ppm]: 60.5 (C-8), 67.4 (C-9), 118.7 (C-
1), 118.9 (C-5), 119.8 (C-3), 127.4 (C-6), 128.1 (C-18, C-20), 129.1
(C-12, C-14), 129.5 (C-19), 129.7 (C-24, C-26), 130.4 (C-13), 131.4
(C-11, C-15), 132.7 (C-25), 135.1 (C-23, C-27), 135.7 (C-17, C-21),
138.6 (C-4), 162.3 (C-2), 165.8 (C-7). 11B NMR (96.29 MHz, CDCl3),
[d, ppm]: 3.9, 28.8. (h1/2 = 235, 752 Hz.). MS (m/z,%): 430 (M+, 1),
354 (45), 326 (3), 312 (5), 250 (100), 210 (1), 148 (3), 78 (1). Anal.
Calc. for C27H23B2NO3: C, 75.22; H, 5.38; N, 3.25. Found C, 75.39; H,
5.43; N, 3.29%.
1550, 1443, 1407, 1335, 1279, 1189, 1154, 1072, 1029, 951, 841,
757, 702, 647, 569, 529 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [d,
.
ppm]: 2.18 (s, 3H, CH3), 3.44 (dd, 1H, J = 3.9 Hz, J = 8.1 Hz, H-8a),
3.54 (d, 1H, J = 6.2 Hz, 8b), 4.13 (dd, 1H, J = 4.0 Hz, J = 6.9 Hz, H-
9), 6.68 (t, 1H, J = 7.3 Hz, H-5), 7.09 (d, 1H, J = 8.2 Hz, H-3), 7.24–
7.36 (m, 4H, H-6, H-12, H-14, H-26), 7.37–7.48 (m, 8H, H-4, H-
11, H-13, H-15, H-18, H-20, H-24, H-27), 7.51–7.65 (m, 3H, H-19,
H-23, H-25), 8.07 (dd, 2H, J = 1.3 Hz, J = 7.9 Hz, H-17, H-21). 13C
NMR (75.46 MHz, DMSO-d6) [d, ppm]: 20.6 (CH3), 60.7 (C-8), 71.4
(C-9), 118.4 (C-5), 119.9 (C-1), 120.5 (C-3), 126.8 (C-22), 127.3
(C-6), 127.4 (C-18, C-20), 127.6 (C-26), 128.2 (C-12, C-14), 129.2
(C-19), 129.7 (C-24), 131.8 (C-25), 132.1 (C-11, C-15), 132.9 (C-
27), 135.2 (C-23), 135.8 (C-17, C-21), 137.1 (C-4), 161.9 (C-2),
168.3 (C-7). 11B NMR (96.29 MHz, DMSO-d6), [d, ppm]: 3.8, 25.7
(h1/2 = 293, 714 Hz.). MS (m/z,%): 444 (M+, 1), 368 (56), 340 (1),
264 (100), 224 (1), 146 (2), 104 (1). Anal. Calc. for C28H25B2NO3:
C, 75.55; H, 5.66; N, 3.15. Found C, 75.28; H, 5.52; N, 3.17%.
2.3.2.4. (6S,7R)-2,4-diphenylbenzo[j]-6,7-diphenyl-8-aza-1,3,5,2,4-tri-
oxadiboracycloundec-8-ene. 6d. Compound 6d was synthesized
from 0.50 g. (1.58 mmol) of 5d and two equivalents (0.38 g,
3.16 mmol) of phenylboronic acid. The reaction was carried out
under reflux of toluene for 1 h, using a Dean–Stark trap. The prod-
uct was obtained as a yellow solid 0.58 g. (1.15 mmol), yield, 73%,
mp: 94–98 °C. IR tmax (KBr): 3029, 3007. 2975, 1958, 1629 (C@N),
1557, 1493, 1454, 1396, 1306, 1185, 1130, 1082, 946, 893, 830,
757, 701, 653, 599, 515, 452 cmꢀ1
.
1H NMR (300 MHz, DMSO-d6)
2.3.2.7. 2,11-diphenyl-dibenzo[h,j]-16-methyl-6,15-diaza-1,3,10,12-
tetraoxa-2,11-diboracyclooctadeca-6,15-diene. 8b. Compound 8b
was synthesized from 0.50 g (1.37 mmol) of 6b and 0.22 g.
(1.37 mmol) of. 2-[(2-hydroxy-ethylimino)-methyl]-phenol 7b.
The reaction was carried out under reflux of THF. The product
was obtained as a white solid 0.49 g. (0.94 mmol), yield, 70%,
mp: 203–207 °C. IR tmax (KBr): 3044, 2932, 2871, 2755, 1966,
1640 (C@N), 1610, 1555, 1482, 1458, 1437, 1343, 1313, 1273,
1200, 1111, 1075, 1017, 962, 927, 873, 825, 752, 709, 652, 629,
455, 410 cmꢀ1. MS (m/z,%): 516 (M+, 0.2), 439 (M+–C6H5, 1), 425
(3), 250 (3), 220 (4), 188 (27), 174 (100), 148 (13), 132 (4), 91
(3), 77 (23). Anal. Calc. for C31H30B2N2O4: C, 72.13; H, 5.86; N,
5.43. Found C, 72.29; H, 6.03; N, 5.39%.
[d, ppm]: 5.15 (d, 1H, J = 2.9 Hz, H-8), 6.44 (d, 1H, J = 2.7 Hz, H-9),
6.82 (t, 1H, J = 7.7 Hz, H-5), 6.92 (m, 2H, H-29, H-33), 7.01–7.16
(m, 7H, H-3, H-6, H-12, H-14, H-25, H-30, H-32), 7.23–7.30 (m,
3H, H-19, H-23, H-27), 7.36–7.52 (m, 7H, H-4, H-13, H-18, H-20,
H-24, H-26 H-31), 7.74 (dd, 2H, J = 1.4 Hz, J = 6.4 Hz, H-11, H-15),
8.05 (s, 1H, H-7), 8.09 (dd, 2H, J = 1.3 Hz, J = 6.3 Hz, H17, H-21).
13C NMR (75.46 MHz, DMSO-d6) [d, ppm]: 74.1 (C-8), 75.9 (C-9),
115.7 (C-1), 119.3 (C-5), 120.2 (C-3), 126.4 (C-29, C-33), 127.6 (C-
6), 127.8 (C-18, C-20), 128.0 (C-31), 128.3 (C-12, C-14), 129.0 (C-
23, C-27), 129.3 (C-19), 130.7 (C-30, C-32), 130.9 (C-13), 131.0
(C-11, C-15), 132.5 (C-25), 133.9 (C-22), 135.6 (C-17, C-21), 139.2
(C-4), 139.3 (C-28), 160.5 (C-2), 165.6 (C-7). 11B NMR
(96.29 MHz, DMSO-d6), [d, ppm]: 4.4, 28.9 (h1/2 = 337, 626 Hz.).
MS (m/z,%): 507 (M+, 2), 430 (94), 326 (100), 296 (10), 234 (4),
148 (14), 105 (2), 78 (1). Anal. Calc. for C33H27B2NO3: C, 78.15; H,
5.37; N, 2.76. Found C, 78.23; H, 5.39; N, 2.88%.
2.4. Results and discussion
Reacting different ethanolamines with 2-hydroxyacetophe-
none, salicylaldehyde or 2-hydroxybenzophenone afforded triden-
tate ligands 5a–5f in high yields. The subsequent reaction of
these ligands 5a–5f with two equivalents of phenylboronic acid
under reflux of toluene for 1 h gave compounds 6a–6f in yields
between 72% and 91% (Scheme 2). All compounds (6a–6f) were
soluble in common solvents and were characterized by mass
spectrometry, IR, 1H, 13C, 11B NMR and elemental analysis. Due
to the formation of a new chiral center at the boron atom it is
possible to induce its stereochemistry [15]. All compounds except
6b have a chiral center at the aliphatic carbons of the ethanol-
amine moiety, which favors the formation of only one diastereo-
isomer. In the case of compounds 6a, 6e and 6f that have a
methyl group at the aminoacid fragment and afforded a pair of
diastereoisomers in a 2:1 ratio, as established by 1H NMR spec-
troscopy (Scheme 3). The major product has the methyl and the
phenyl groups on the same side, this is attributed to the small
size of the methyl group that could not induce high diastereose-
lectivity, in consequence the attack of phenylboronic acid took
place from both faces of the molecule. This observation is in
agreement with previous results that have shown that the pre-
ferred product possesses the stereochemistry with all the substit-
uents on the same side (syn) [15]. Compound 6a crystallized in a
non centrosymmetric P212121 space group and the X-ray diffrac-
tion showed that the preferred stereochemistry is that where
the methyl and phenyl group are on the same side. As we men-
tioned earlier, we found that reaction of ethanolamines with
phenylboronic acid in THF during 30 min, leads to the formation
of a very insoluble solid that corresponds to the dimeric com-
pounds, however, changing the reaction conditions to toluene
24 h the product obtained was a monomeric [4.3.0] heterobicyclic
system. Surprisingly, we could obtain six–seven membered rings
2.3.2.5. (6R)-2,4-diphenylbenzo[j]-6-methyl-8-aza-1,3,5,2,4-trioxa-
diboracycloundec-8-ene. 6e. Compound 6e was synthesized from
0.50 g. (2.79 mmol) of 5e and two equivalents 0.68 g. (5.58 mmol)
of phenylboronic acid. The reaction was carried under reflux of tol-
uene for 1 h, using a Dean–Stark trap. The product was obtained as
a yellow solid 0.74 g. (2.0 mmol), yield, 72%, mp: 100–104 °C. IR
tmax (KBr): 3050, 3016, 2928, 2868, 1901, 1640 (C@N), 1560,
1482, 1441, 1405, 1376, 1346, 1271, 1192, 1155, 1072, 1082,
852, 746, 700, 658, 558, 515, 456, 423 cmꢀ1 1H NMR (300 MHz,
.
CDCl3) [d, ppm]: 1.25 (d, 3H, CH3), 3.37 (m, 1H, H-8a), 3.94 (d,
1H, J = 13.1 Hz, H-8b), 4.69 (m, 1H, H-9), 6.87 (t, 1H, J = 7.7 Hz, H-
5), 7.05 (d, 1H, J = 8.1 Hz, H-3), 7.24–7.32 (m, 3H, H-6, H-12, H-
14), 7.34–7.58 (m, 6H, H-4, H-11, H-13, H-15, H-18, H-20), 7.60
(d, 1H, J = 7.7 Hz, H-19), 8.1 (dd, 2H, J = 1.5 Hz, J = 6.7 Hz, H-17,
H-21). 13C NMR (75.46 MHz, CDCl3) [d, ppm]: 20.1 (CH3), 64.5 (C-
8), 66.7 (C-9), 115.2 (C-1), 119.1 (C-5), 119.8 (C-3), 127.5 (C-6),
127.6 (C-18, C-20), 127.9 (C-12, C-14), 130.5 (C-19), 131.2 (C-13),
131.6 (C-11, C-15), 135.0 (C-17, C-21), 138.6 (C-4), 161.4 (C-2),
164.2 (C-7). 11B NMR (96.29 MHz, CDCl3), [d, ppm]: 3.7, 25.8. (h1/
2 = 286, 854 Hz.). MS (m/z,%): 369 (M+, 0.3), 292 (51), 247 (1),
188 (100), 148 (3), 91 (0.2). Anal. Calc. for C22H21B2NO3: C, 71.60;
H, 5.74; N, 3.80. Found C, 71.74; H, 5.84; N, 3.86%.
2.3.2.6.
(6R)-2,4-diphenylbenzo[j]-6-methyl-9-phenyl-8-aza-1,3,5,
2,4- trioxadiboracycloundec-8-ene. 6f. Compound 6f was synthe-
sized from 0.50 g. (1.96 mmol) of 5f and two equivalents (0.48 g,
3.92 mmol) of phenylboronic acid. The reaction was carried out
under reflux of toluene for 1 h, using a Dean–Stark trap. The prod-
uct was obtained as a yellow solid 0.72 g. (1.63 mmol), yield, 81%,
mp: 97–101 °C. IR tmax (KBr): 3049, 3016, 2982, 1963, 1610 (C@N),

30
J.M. Rivera et al. / Inorganica Chimica Acta 390 (2012) 26–32
R1
R1
CH3
O
CH3
O
H
H
N
B
N
B
B
B
O
O
O
O
R1= CH3 6a
R1= H
6e
R1= Ph 6f
6-syn
6-anti
Scheme 3. Diatereoisomers obtained by reaction of ligands 5a, 5e and 5f with phenylboronic acid.
CH3
CH3
N
B
N
O
N
B
O
O
OH
B
N
THF
+
Δ
O
B
O
OH
O
O
7b
6
8
Scheme 4. Synthesis of noncentrosymmetric dimeric compound 8b.
Fig. 1. Molecular structures for compounds 6a and 6b, hydrogens are omitted for clarity.
[4.5.0] heterobicyclic systems using toluene after 1 h of reaction.
These results indicate that reaction of tridentate ligands 5a-5f can
lead to the synthesis of the kinetic compound 2 (THF 1/2 h), the
thermodynamic compound 4 (Toluene 36 h) and the intermediate
of the reaction 3 (toluene 1 h) (Scheme 1). This was confirmed
when compound 8b was obtained by reaction of 6b and triden-
tate ligand 7b in THF for 1 h (Scheme 4).
signals between 25.7 and 28.9 ppm, for the tricoordinated boron
atom [26–40]. The signals in the 13C NMR spectra for the imine
group appear at 169.3, 170.2, 165.5, 165.6, 164.2 and 168.3 ppm
for 6a–6f, respectively, and it was confirmed by the band for
(C@N) in the infrared spectra at 1610 and 1640 cmꢀ1.The mass
spectrometric analysis gave the molecular ions in low abundance
and the base peak corresponds to the [M+–C6H5] fragment ions
[16,26,27]. Compound 8b was insoluble in all common solvents
and the structure was confirmed by IR (C@N at1640 cmꢀ1), mass
spectrometry and elemental analysis. The mass spectra gave the
molecular ion at 516 (M+, 0.2) which corresponds to the molecular
weight of 8b.
2.4.1. Spectroscopic properties
The existence of the N ? B coordination bond was established
by 11B NMR which shows the signals between 3.40 and
4.40 ppm, characteristic for the tetracoordinated boron atom and

J.M. Rivera et al. / Inorganica Chimica Acta 390 (2012) 26–32
31
0
2.4.2. X-ray analyses of 6a and 6b
and 1.597(3) ÅA, respectively, similar to those observed in boron
complexes [26–30]. Significant differences are found between the
B(1)–O(1) (1.470(4) and 1.469(3) Å) and B(1)–O(2) (1.449(4)–
1.438(3) Å) bond distances for 6a and 6b, respectively, and show
that the shorter bonds length correspond to the aliphatic oxygen
in the seven member rings (Table 2). The bond angles around the
tetracoordinated boron atom are in the range from 107.1° to
113.2° and the bond angles around the tricoordinated boron atom
are in the range from 114.7° to 125.8° for compounds 6a and 6b
(Table 2). The average value for the bond angles in the seven mem-
bered rings are 120.78° and 120.88° for 6a and 6b, respectively,
which are larger than those observed in five–six membered rings
values, indicating lower ring strain [16,26]. The values for the tet-
rahedral character (THC) [18] of the tetracoordinated boron atoms
are 93% and 90% for 6a and 6b, respectively, these values show that
the boron atom is less distorted than in five–six membered ring
compounds [15]. The deviations of the boron atom from the mean
plane of the six membered rings C(2)–C(1)–C(7)–N(1)–B(1)–O(1)
in 6a and 6b are ꢀ0.052 and ꢀ0.048 Å, respectively, showing that
the largest deviation corresponds to compound 6a, which has a
methyl group in the iminic carbon. The dihedral angles for the
O1–B1–C10–C15 fragment in compounds 6a and 6b are
ꢀ59.0(4)° and 52.8(2)° which are indicative that the gauche con-
formation is the preferred one around the CꢀB bond. Compound
6a crystallized in the non centrosymmetric space group P212121
Compounds 6a and 6b crystallized and the X-ray structures for
these compounds are shown in Fig. 1. The crystallographic data are
summarized in Table 1. The structure of compound 6a showed that
the phenyl group attached to the tetracoordinated boron atom is in
the same face as the methyl group, is in agreement with previous
results [15]. The N ? B bond distances for 6a and 6b are 1.587(5)
Table 1
Crystallographic data for compounds 6a and 6b.
Compound
6a
6b
Chemical formula
Formula weight
Space group
Crystal system
Crystal size (mm3)
Unit cell dimensions
a (Å)
C23H23B2NO3
C22H21B2NO3
369.02
Cc
383.04
P212121
Orthorhombic Monoclinic
0.2 ꢂ 0.1 ꢂ 0.1 0.2 ꢂ 0.1 ꢂ 0.1
8.2208(3)
14.6103(6)
17.4739(8)
90
90
90
14.8600(3)
14.4010(4)
10.8940(3)
90
122.5560(10)
90
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Formula units per cell
4
3
dcalc (g cmꢀ3
F(000)
T (K)
)
1.212
808
293(2)
3.64–27.47
4680
0.936
582
293(2)
3.60–27.46
4013
and it presents weak intermolecular interactions between
0
h (°)
O1–H13 with a distance of 2.635 ÅA and between O2–H13 with
0
Reflections collected
a distance of 2.688 ÅA, the angles between O1–H13–C13 and
O2–H13–C13 are 152.8° and 143.9°, respectively [41,42] (Fig. 2).
The conformation in the seven member ring in molecules 6a and
6b is chair, in 6a C8 is above the plane formed by C9, O3, B1 and
N1, B2, O2 (Fig. 3).
Independent reflections
4700
2690
0.0538
0.1191
4095
3104
0.0415
0.0619
Observed reflections, (Fo)2 > 4
r
(Fo)2
P
P
R = |Fo| ꢀ |Fc||/ |Fo|
P
P
Rw = [ w(|Fo| ꢀ |Fc|)2/ wFo
]
1/2, w = 1/r2
2
(all data)
Goodness-of-fit (GOF)
No. of parameters
1.077
265
0.992
270
Maximum
D
D
D
/
)
)
r
ꢀ0.041
ꢀ0.119
0.122
0.047
ꢀ0.108
0.157
qmin (e Åꢀ3
qmax (e Åꢀ3
Table 2
Selected bond distances (Å) and bond angles (°) for compounds 6a and 6b.
Compound
6a
6b
Bond distances (Å)
N(1)–C(8)
N(1)–C(7)
C(1)–C(7)
C(7)–C(22)
B(1)–O(1)
B(1)–O(2)
B(1)–N(1)
B(1)–C(10)
B(2)–O(2)
B(2)–O(3)
B(2)–C(16)
1.467(4)
1.294(4)
1.451(5)
1.510(5)
1.470(4)
1.449(4)
1.587(5)
1.590(5)
1.341(5)
1.371(5)
1.556(5)
1.468(3)
1.305(3)
1.449(3)
1.505(3)
1.469(3)
1.438(3)
1.597(3)
1.614(3)
1.332(3)
1.367(3)
1.569(4)
Bond angles (°)
N(1)–B(1)–O(1)
N(1)–B(1)–O(2)
N(1)–B(1)–C(10)
O(1)–B(1)–C(10)
O(2)–B(1)–C(10)
O(1)–B(1)–O(2)
C(7)–N(1)–B(1)
C(8)–N(1)–C(7)
B(1)–O(2)–B(2)
O(2)–B(2)–O(3)
O(2)–B(2)–C(16)
O(3)–B(2)–C(16)
109.1(3)
108.4(3)
109.5(3)
110.0(3)
112.2(3)
107.6(3)
125.0(3)
121.3(3)
142.4(3)
125.8(4)
119.5(4)
114.7(3)
109.0(15)
109.0(17)
108.1(15)
110.3(17)
113.2(17)
107.1(16)
124.5(16)
122.9(18)
142.3(18)
125.0(2)
119.7(2)
115.2(2)
Deviation from mean plane (Å)
Plane: C(2)–C(1)–C(7)–N(1)–B(1)–O(1)
Fig. 2. Intermolecular interactions for compound 6a, hydrogens are omitted for
clarity.
B(1) ꢀ 0.052
B(1) ꢀ 0.048

32
J.M. Rivera et al. / Inorganica Chimica Acta 390 (2012) 26–32
Fig. 3. Chair conformation in the seven member ring in compounds 6a and 6b.
[4] A.H. Soloway, W. Tjarks, B.A. Barnum, F.G. Rong, R.F. Barth, I.M. Codogni, J.G.
2.5. Conclusions
Wilson, Chem. Rev. 98 (1998) 1515.
[5] M.A. Grassberger, F. Turnowsky, J. Hildebrandt, J. Med. Chem. 27 (1984) 947.
[6] M. Suginome, L. Uehlin, A. Yamamoto, M. Murakami, Org. Lett. 6 (2004) 1167.
[7] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457.
[8] A. Suzuki, Pure Appl. Chem. 63 (1991) 419.
[9] A. Suzuki, J. Organomet. Chem. 576 (1999) 147.
[10] J.H. Kirchhoff, M.R. Netherton, I.D. Hill, G.C. Fu, J. Am. Chem. Soc. 124 (2002)
13662.
[11] Z.Q. Liu, Q. Fang, D.X. Cao, D. Wang, G.B. Xu, Org. Lett. 6 (2004) 2933.
[12] C.D. Entwistle, T.B. Marder, Angew. Chem. Int. Ed. Engl. 41 (2002) 2927.
[13] H. Reyes, B.M. Muñoz, N. Farfán, R. Santillan, S. Rojas-Lima, P.G. Lacroix, K.
Nakatani, J. Mater. Chem. 12 (2002) 2898.
[14] V. Barba, R. Hernández, R. Santillan, N. Farfán, Inorg. Chim. Acta 363 (2010)
4112.
[15] J.M. Rivera, S. Rincón, N. Farfán, R. Santillán, J. Organomet. Chem. 696 (2011)
2420.
[16] V. Barba, D. Cuahutle, M.E. Ochoa, R. Santillan, N. Farfán, Inorg. Chim. Acta 303
(2000) 7.
[17] S. Toyota, M. Oki, Bull. Chem. Soc. Jpn. 65 (1992) 1832.
[18] H. Höpfl, J. Organomet. Chem. 581 (1999) 129.
[19] T. Mancilla, R. Contreras, B. Wrackmeyer, J. Organomet. Chem. 307 (1986) 1.
[20] G.M. Sheldrick, Acta Cryst. A64 (2008) 112.
[21] G.M. Sheldrick, SHELX-97. Programs for Crystal Structure Analysis (Release 97-
2). University of Göttingen, Germany, 1997.
Six new heterobicyclic systems of monomeric boronates with
two fused rings, one of which is seven-membered while the other
is six-membered were prepared in good yields. The reaction of tri-
dentate ligands with two equivalents of phenylboronic acid leads
to oligoboronates (6a–6f). It is possible to obtain boronates with
fused five–six membered rings by heating oligoboronates 6a–6f,
or by reacting only one equivalent of the phenylboronic acid and
one equivalent of the tridentate ligands under reflux of toluene
during 24 h. Reacting compounds 6a–6f with tridentate ligands
gave to dimeric compounds (kinetic compounds). These results al-
low to conclude that boronates with fused six–seven membered
rings are very stable, as evidenced by the bond angles in the seven
member rings; in turn, dimeric compounds can be obtained by the
reaction of compounds 6a–6f with tridentate ligands. This kind of
compounds could find application as chiral inductors in the Suzuki
reaction.
[22] L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
[23] A.L. Spek, J. Appl. Cryst. 36 (2003) 7.
Acknowledgements
[24] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[25] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemical, 3th ed.,
Pergamon Press, New York, 1988.
[26] H. Höpfl, N. Farfán, J. Organomet. Chem. 547 (1997) 71.
[27] H. Höpfl, M. Sánchez, V. Barba, N. Farfán, S. Rojas, R. Santillan, Inorg. Chem. 37
(1998) 1679.
[28] N. Farfán, H. Höpfl, V. Barba, M.E. Ochoa, R. Santillan, E. Gómez, A. Gutiérrez, J.
Organomet. Chem. 581 (1999) 70.
The authors acknowledge financial support from Consejo Nac-
ional de Ciencia y Tecnología (CONACyT), Fondo Mixto Veracruz
(127835) and PAPIIT IN-214010. Thanks are given to I.Q. Geiser
Cuellar Rivera for mass spectra, Q.F.B. Ma. Luisa Rodríguez Pérez
for NMR spectra, and Q.F.B. José Vicente Rivadeneira.
[29] N. Farfán, R. Santillan, H. Höpfl, Main Group Chem. News 7 (1999) 3.
[30] V. Barba, R. Luna, D. Castillo, R. Santillan, N. Farfán, J. Organomet. Chem. 604
(2000) 273.
Appendix A. Supplementary material
[31] V. Barba, R. Xochipa, R. Santillan, N. Farfán, Eur. J. Inorg. Chem. 1 (2004)
118.
[32] G. Bernardinelli, D. Fernandez, R. Gosmini, P. Meier, A. Ripa, P. Schupfer, B.
Treptow, E.P. Kundig, Chirality 12 (2000) 529.
[33] C. Jiang, Z. Ming, Q. Tan, D. Qian, T. You, Enantiomer 7 (2002) 287.
[34] N. Farfán, T. Mancilla, D. Castillo, G. Uribe, L. Carrillo, P.J. Nathan, R. Contreras,
J. Organomet. Chem. 381 (1990) 1.
[35] N. Farfán, R. Contreras, Heterocycles 23 (1985) 2989.
[36] H. Nöth, B. Wrackmeyer, Nuclear Magnetic Resonance Spectroscopy of Boron
Compounds, Springer-Verlag, New York, 1978.
CCDC 270362 and 270360; contains the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.03.055.
References
[37] B. Wrackmeyer, Annu. Rev. NMR Spectrosc. 20 (1988) 61.
[38] A.R. Siedle, Annu. Rev. NMR Spectrosc. 20 (1988) 205.
[39] W.G. Henderson, E.F. Mooney, Annu. Rev. NMR Spectrosc. 2 (1969) 219.
[40] D. Reed, Chem. Soc. Rev. 22 (1993) 109.
[1] G.R. Desiraju, Angew. Chem. Int. Ed. Engl. 34 (1995) 2311.
[2] C.J. Davis, P.T. Lewis, D.R. Billodeaux, F.R. Fronczek, J.O. Escobedo, R.M.
Strongin, Org. Lett. 3 (2001) 2443.
[41] A. Bondi, J. Phys. Chem. 68 (1964) 441.
[42] A. Bondi, J. Phys. Chem. 70 (1966) 3006.
[3] M.F. Hawthorne, M.W. Lee, J. Neuro-Oncol. 62 (2003) 33.