Synthesis, characterization and X-ray studies of new chiral five-six-membered ring, [4.3.0] heterobicyclic system of monomeric boronates

Article abstract of DOI:10.1016/j.jorganchem.2011.03.006

Nine new boronates, six of them chiral, with five-six-membered ring heterobicycles were prepared by reaction of the Schiff bases and phenyl boronic acid. The boronates were fully characterized by spectroscopic techniques, NMR ¹H, ¹³C, ¹¹B, Infrared spectroscopy, mass spectrometry and elemental analysis. The reaction showed high diasteroselectivity, only in the case of compound 4c, containing a methyl substituent in the aliphatic moiety, the induction is low giving a 2:1 mixture of two diatereoisomers. The results showed that the preferred stereochemistry in the heterocycles is that where all substituents in the five membered ring and the phenyl group attached to boron atom are on the same side.

Full text of DOI:10.1016/j.jorganchem.2011.03.006

Journal of Organometallic Chemistry 696 (2011) 2420e2428
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and X-ray studies of new chiral five-six-membered
ring, [4.3.0] heterobicyclic system of monomeric boronates
,
b
c
d
José María Rivera a , Susana Rincón , Norberto Farfán , Rosa Santillan
*
a Facultad de Ciencias Químicas, Universidad Veracruzana, Prolongación Oriente 6 No. 1009, Colonia Rafael Alvarado, Apartado Postal 215, Orizaba 94340, Veracruz, México
b Departamento de Ingeniería Química-Bioquímica, Instituto Tecnológico de Mérida, Av. Tecnológico S/N, CP 97118, Mérida, Yucatán, México
c Facultad de Química, Departamento de Química Orgánica, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 México D.F., México
d Departamento de Química, Centro de Investigación y de Estudios Avanzados del IPN, Apdo. Postal 14-740, 07000 México D. F., México
a r t i c l e i n f o
a b s t r a c t
Article history:
Nine new boronates, six of them chiral, with five-six-membered ring heterobicycles were prepared by
reaction of the Schiff bases and phenyl boronic acid. The boronates were fully characterized by spec-
troscopic techniques, NMR 1H, 13C, 11B, Infrared spectroscopy, mass spectrometry and elemental analysis.
The reaction showed high diasteroselectivity, only in the case of compound 4c, containing a methyl
substituent in the aliphatic moiety, the induction is low giving a 2:1 mixture of two diatereoisomers. The
results showed that the preferred stereochemistry in the heterocycles is that where all substituents in
the five membered ring and the phenyl group attached to boron atom are on the same side.
Ó 2011 Elsevier B.V. All rights reserved.
Received 27 January 2011
Received in revised form
3 March 2011
Accepted 3 March 2011
Keywords:
Boronates
Tridentated ligands
NMR
X-ray
1. Introduction
envelope conformation, the tetrahedral character of the boron
atoms which is directly associated to the geometry [18,19] showed
In the last years there has been great interest in the study of
boron complexes due to the great number of applications found, for
example in medicinal chemistry, as anticancer agents directly
applied in the technique known as boron neutron capture therapy
used for the treatment of certain brain tumors [1], some boron
compounds also present cytotoxic activity [2e4]. Moreover, they
also display a wide range of applications in organic synthesis [5,6]
supramolecular chemistry [7], macrocyclic chemistry [8,9], organ-
ometallics [10], dendrimers [11,12] among others. Our group has
reported several studies on the N / B coordination bond [13e16]
and recently the synthesis and characterization of boron
complexes obtained from the condensation of 3-amino-
phenylboronic acid and 1,3-diketones [17].
In this paper, we describe the synthesis of nine new [4.3.0]
heterobicyclic boronates, derived from ethanolamines, as well as
the study of the structures and stereochemistry of the six
chiral boron complexes which were obtained with high Diastero-
selectivity. The results from X-ray diffraction indicated high strain
present in the five member rings of the molecules as well as the
deviation from ideal values. The configurational stability at the
boron atom is closely related to the size of the substituents attached
to the aliphatic carbons in the ethanol amine residues. In previous
studies it has been shown that the addition of phenyl boronic acid
to salicylidenimino alcohols produces dimeric (1ae1d) or mono-
meric (2) boronates [20,21] which are stable in air and are obtained
in high yields in one step synthesis. (Scheme 1).
These boronate units are connected by two covalent BꢀO and
coordinative N/B bonds, which are responsible for the hydrolytic
stability of these molecules [22,23]. Dimeric complexes have been
obtained when the ligands have zero (1a) [20], two (1b) [21], four
[24], five (1c) or six (1d) [21e] methylene units between the imino
and the hydroxyl groups. The studies indicated that formation of
the dimeric compound is favored because the monomeric systems
would be too strained owing to the tetrahedral geometry at the
boron atom, as well as its small atomic radius. When the imino
alcohol is substituted with three methylene groups, a monomeric
specie is obtained because the tridentate ligand permits the
formation of a stable [4.4.0] heterobicyclic system (2) [21e,25].
However, the use of harder reaction conditions, for example
toluene and 24 h of refluxing favored the monomeric especies than
the dimeric ones. In the present work, we describe the synthesis of
monomeric boronates (4ae4i) with five-six fused membered rings
* Corresponding author. Tel.: þ52 12727240120.
E-mail address: chemax7@yahoo.com.mx (J.M. Rivera).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.03.006

J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
2421
Scheme 1. Monomeric and dimeric boronates obtained with different methylene units
in the iminodialcohol moiety.
Scheme 3. Products from the reaction of 3c with phenyl boronic acid.
program was applied for refinement and output data [26,27]. All
software manipulations were done under the WINGX environment
program set [28]. Molecular perspectives were drawn under ORTEP-
3 [29], and Diamond 2.1e drawing applications.
derived from optically active ethanolamines (Schemes 2 and 3), as
well as the NMR and X-ray studies, this boronates can be apply in
assymetric synthesis as catalysts [26].
2. Experimental
2.2. Reagents
2.1. Instrumentation
All reactants and solvents were purchased from Aldrich Chem-
ical Co. and solvents were dried previous to use. Single crystals
were grown using spectroscopic grade solvents.
NMR spectra were recorded in CDCl3 and DMSO-d6 solutions on
Bruker Advance DPX 300 and Jeol Eclipse þ400 spectrometers.
Chemical shifts (ppm) are relative to (CH3)4Si for 1H and 13C and
BF3·OEt2 for 11B. Coupling constants are reported in Hz. Infrared
spectra were recorded on a PerkineElmer 16F-PC FT-IR spectrom-
eter. Mass spectra were recorded on a Hewlet-Packard model 5989
engine, coupled to an HP 5890 Series II GC. Melting points were
obtained on a Gallenkamp MFB-595 apparatus and are uncorrected.
Elemental analyses were carried out on a thermo finnigan model
Flash 1112. The X-ray diffraction study was determined on an Enraf-
2.3. Synthesis
2.3.1. General method for the preparation of tridentate ligands 3b
and 3g
In order to prepare the tridentate ligands 3b and 3g, equimolar
quantities of the corresponding aminoalcohol and 2-hydrox-
ybenzophenone or 2-hydroxyacetophenone, respectively, were
refluxed in ethanol for 1 h. The solvent and the water formed
during the reaction were eliminated to yield yellow solids which
were washed with methylene chloride and used without further
purification. Tridentate ligands 3a, 3c, 3d, 3e, 3f, 3h and 3i have
already been published [21,30e34].
Nonius-Fr590 Kappa-CCD (lMoK ¼ 0.71073 Å, graphite mono-
a
chromator, T ¼ 293 K, CCD rotating images scan mode) and the
crystal was mounted on a LINDEMANN tube. Absorption correction
was not necessary. All reflections data set were corrected for Lorentz
and Polarization effects. Structure solution and refinement were
performed using the SHELX-S-97 program and then SHELX-L-97
Scheme 2. Synthesis of monomeric boronates 4ae4h with six and five membered rings, derived from optically active ethanolamines and phenyl boronic acid.

2422
J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
Scheme 4. Synthesis of boronates with [4.3.0] heterobicycles (4i) using as starting materials boronates with [4.5.0] heterobicycles (6i).
2.3.1.1. 2-[1-(2-hydroxy-(1R)-phenyl-ethylimino)-ethyl]-phenol
3b. Prepared from 2-hydroxyacetophenone (1.00 g, 7.34 mmol)
and (R)-(ꢀ)-phenylglycinol (1.00 g 7.34 mmol). The product was
obtained as a yellow solid (1.85 g, 7.24 mmol), yield 98%, mp:
95e97 ꢁC. IR ymax (KBr): 3059 (OH), 2839, 1611 (C¼N), 1449, 1340,
1285, 1149, 1068, 845, 753, 701, 636, 565, 524, 444 cmꢀ1 1H NMR
2.3.1.2. 2-[(2-hydroxy-1-phenyl-ethylimino)-phenyl-methyl]-phenol
3g. Prepared from 2-hydroxybenzophenone (1.00 g, 5.04 mmol)
and (R)-(ꢀ)-phenylglycinol (1.00 g 5.04 mmol). The product was
obtained as a yellow solid (1.48 g, 4.67 mmol), yield 92%, mp:
112e116 ꢁC. IR ymax (KBr): 3048 (OH), 2832, 1605 (C¼N), 1438, 1345,
1289, 1152, 1053, 841, 750, 712, 632, 560, 529, 512, 413 cmꢀ1 1H
(300 MHz, CDCl3) [
d
, ppm]: 2.36 (s, 3H, CH3), 3.98 (q, 1H,
NMR (300 MHz, CDCl3) [
d
, ppm]: 3.78 (dd, 1H, J ¼ 4.7 Hz, 6.4 Hz, H-
J ¼ 4.9 Hz, H-8), 4.01 (q, 1H, J ¼ 8.3, H-9a), 5.00 (dd, 1H,
J ¼ 2.6 Hz, 4.93 Hz, H-9b), 6.80 (t, 1H, J ¼ 7.2 Hz, H-5), 6.98 (d,
1H, J ¼ 8.4 Hz, H-3), 7.26e7.38 (m, 6H, H-4, H-11, H-12, H-13, H-
14, H-15), 7.52 (d, 1H, J ¼ 8.1 Hz, H-6). 13C NMR (75.46 MHz,
9a), 3.95 (dd, 1H, J ¼ 3.2 Hz, 8.2 Hz, H-9b), 4.5 (dd, 1H, J ¼ 3.5 Hz,
4.7 Hz, H-9a), 6.62 (t, 1H, J ¼ 8.2 Hz, H-5), 6.78 (dd, 1H, J ¼ 1.7 Hz,
6.2 Hz, H-3), 6.98 (d, 1H, J ¼ 8.2 Hz, H-6), 7.18e7.56 (m, 11H, H-4, H-
11, H-12, H-13, H-14, H-15, H-17, H-18, H-19, H-20, H-21). 13C NMR
CDCl3) [
d
, ppm] 15.6 (CH3), 65.7 (C-8), 68.6 (C-9), 117.6 (C-5),
(75.46 MHz, CDCl3) [d, ppm] 67.3 (C-8), 68.0 (C-9), 117.6 (C-5), 118.2
119.8 (C-3), 119.5 (C-1), 127.5 (C-12, 14), 128.1 (C-6), 128.8 (C-13),
129.2 (C-11, 15), 133.2 (C-4), 139.3 (C-10), 164.2 (C-2), 174.0 (C-7).
MS (m/z, %): 255 (Mþ, 28), 240 (3), 224 (100), 209(7), 183 (9), 165
(11), 146 (9), 136 (23), 120 (42), 103 (15), 91 (31), 77 (17). Anal.
Calc. for C16H17NO2: C, 75.27; H, 6.71; N, 5.49. Found C, 75.11; H,
6.52; N, 5.33%.
(C-3),119.2 (C-1), 127.3 (C-12, C-14), 127.8 (C-13), 128.5 (C-18), 128.6
(C-6), 128.9 (C-11, C-15), 129.2 (C-20), 132.0 (C-19), 133.0 (C-17),
133.7 (C-21), 136.5 (C-10), 137.9 (C-16), 139.8 (C-4), 163.6 (C-2),
175.6 (C-7). MS (m/z, %): 318 (Mþ, 1), 211 (100), 194 (4), 182 (2), 165
(2),132 (7),116 (5), 91 (9), 77 (2). Anal. Calc. for C21H19NO2: C, 79.47;
H, 6.03; N, 4.41. Found C, 79.27; H, 5.98; N, 4.36%.
Fig. 1. Molecular structures for compounds 4ae4c, 4g and 4i, hydrogens are omitted for clarity.

J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
2423
3062, 2928, 2864, 1638 (C¼N), 1553, 1473, 1451, 1314, 1265, 1169,
1076, 1021, 861, 752, 701, 649, 580, 524, 474 cmꢀ1 1H NMR
(300 MHz, DMSO-d6) [
d
, ppm]: 1.02 (d, 3H, J ¼ 6 Hz, CH3), 2.62 (s,
3H, CH3), 4.35 (m, 1H, H-8), 5.48 (d, 1H, J ¼ 5 Hz, H-9), 6.89 (t, 1H,
J ¼ 8.1 Hz, H-5), 7.08 (d, 1H, J ¼ 8.4 Hz, H-3), 7.18e7.26 (m, 3H, H-18,
H-20, H-13), 7.31 (t, 1H, J ¼ 8.1 Hz, H-4), 7.35e7.39 (m, 2H, H-12, H-
14), 7.39e7.44 (m, 2H, H-17, H-21), 7.48e7.54 (m, 4H, H-6, H-19, H-
11, H-15). 13C NMR (75.46 MHz, CDCl3) [
d, ppm]: 14.9 (CH3), 18.4
(CH3), 63.2 (C-8), 80.3 (C-9), 119.2 (C-5), 120.9 (C-1), 121.5 (C-3),
126.8 (C-18, 20), 127.2 (C-13), 127.5 (C-12, 14), 127.7 (C-19), 128.5 (C-
6), 128.6 (C-17, 21), 131.7 (C-11, 15), 137.0 (C-4), 139.9 (C-16), 161.1
(C-2), 167.0 (C-7). 11B NMR (96.29 MHz, CDCl3), [
d, ppm]: 5.6(h1/
¼ 260 Hz). MS (m/z, %): 354 (Mþ, 0.1), 278 (100), 248 (7), 162 (32),
2
117 (1), 91 (1). Anal. Calc for C23H22BNO2: C, 77.76; H, 6.24; N, 3.94.
Found C, 77.39; H, 6.29; N, 3.87%.
2.3.2.2. (2S,5R)-2-(Phenyl)benzo[j]-5-phenyl-7-methyl-6-aza-1,3-
dioxa-2-boracyclononen-6-ene 4b. Compound 4b was synthesized
from 0.30 g (1.55 mmol) of 3b and 0.183 g (1.55 mmol) of phenyl
boronic acid. The reaction was carried out in toluene under reflux,
using a DeaneStark trap during 24 h. The product was obtained as
Fig. 2. Molecular structure for compound 5f.
a yellow solid 0.29 g (1.04 mmol), yield, 67%, mp: 194e202 ꢁC
25
[a]
¼ þ 209.3 (c 0.097 CHCl3), IR ymax (KBr): 3061, 2930, 2868,
D
2.3.2. General method for the preparation of compounds 4ae4h
To prepare compounds 4ae4h, equimolar quantities of the
corresponding tridentate ligands 3ae3h and phenyl boronic acid,
were refluxed in toluene for 24 h. The solvent and the water formed
during the reaction were eliminated to yield yellow solids that were
then washed with methylene chloride and purified by recrystalli-
zation using chloroform.
1641 (C¼N), 1553, 1472, 1451, 1315, 1263, 1170, 1070, 1022, 859, 753,
702, 650, 526, 474 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [
d, ppm]:
2.36 (CH3), 4.02 (dd, 1H, J ¼ 7.7 Hz, 3 Hz, H-9a), 4.58 (dd, 1H,
J ¼ 7.7 Hz, 3.0 Hz, H-9b), 5.05 (dd, 1H, J ¼ 7.7 Hz, 3.0 Hz, H-8), 6.88
(t, 1H, J ¼ 8.0 Hz, H-5), 7.01 (d, 1H, J ¼ 8.0 Hz, H-3), 7.06e7.09 (m,
2H, H-18, H-20), 7.18e7.20 (m, 3H, H-12, H-13, H-14), 7.24e7.27 (m,
3H, H-17, H-19, H-21), 7.39e7.42 (m, 3H, H-4, H-11, H-15), 7.48 (dd,
1H, J ¼ 8.0 Hz, 3.0 Hz, H-6). 13C NMR (75.46 MHz, DMSO-d6) [
d,
2.3.2.1. (2S,4R,5S)-2-(Phenyl)benzo[j]-4-phenyl-5-methyl-7-methyl-
6-aza-1,3-dioxa-2-boracyclononen-6-ene 4a. Compound 4a was
synthesized from 0.30 g (1.11 mmol) of 3a and 0.14 g (1.11 mmol) of
phenyl boronic acid. The reaction was carried out in toluene under
reflux, using a DeaneStark trap during 24 h. The product was
ppm]: 18.6 (CH3), 65.7 (C-8), 70.5 (C-9), 119.2 (C-5), 120.8 (C-1),
121.1 (C-3), 127.3 (C-18, 20), 127.4 (C-13), 127.6 (C-12, 14), 128.2 (C-
6), 128.3 (C-19), 129.3 (C-17, 21), 131.1 (C-11, 15), 136.9 (C-4), 138.3
(C-16), 159.7 (C-2), 169.9 (C-7). 11B NMR (96.29 MHz, CDCl3), [
d,
ppm]: 6.1 (h1/2 ¼ 396 Hz). MS (m/z, %): 341 (Mþ, 0.3), 310 (4), 264
(100), 236 (2), 162 (20). Anal. Calc for C22H20BNO2: C, 77.44; H, 5.91;
N, 4.11. Found C, 77.93; H, 5.87; N, 4.11%.
obtained as a yellow solid 0.21 g (0.59 mmol), yield, 53%,
25
[
a]
¼ þ 87.4 (c 0.101 CHCl3), mp: 233e237 ꢁC. IR ymax (KBr):
D
Table 1
Crystallographic data for compounds 4a, 4b, 4c, 4i, 4g and 5f.
Compound
4a
4b
4c
4g
4i
5f
Chemical formula
Formula weight
Space group
Crystal system
Crystal size (mm)
a (Å)
C23H22BNO2
355.23
P 212121
Orthorhombic
0.2 x 0.2 x 0.1
9.7792(4)
12.7252(6)
15.3413(6)
90
C22H20BNO2
341.20
P 21
Monoclinic
0.1 x 0.1 x 0.1
8.6473(2)
10.9323(3)
10.6276(3)
90
C17H18BNO2
279.13
P 21
Monoclinic
0.12x0.1x0.1
8.6619(5)
9.9421(6)
17.0126(11)
90
C27H22BNO2
403.28
P 21
Monoclinic
0.2x0.1x 0.1
8.3990(3)
10.7430(3)
12.0826(4)
90
C16H16BNO2
265.11
P 21/n
Monoclinic
0.1x.05x .05
8.5671(2)
9.6308(2)
17.2100(4)
90
C21H22BNO2
331.21
P 212121
Orthorhombic
0.12x0.1x0.1
7.09570(10)
13.0448(3)
20.5644(5)
90
b (Å)
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
90
90
112.5290(10)
90
92.584(4)
90
92.7180(10)
90
92.8220
90
90
90
Formula units per cell
4
2
4
3
4
4
dcalc (g cm-3
)
1.236
1.221
1.267
1.230
1.242
1.156
F (000)
752
360
592
424
560
704
Temperature of measurement (K)
q
No. of reflections collected
293(2)
3.47-27.50
4161
4181
2534
0.0447
0.0879
1.002
293(2)
4.15-27.49
3840
3848
3108
0.0393
0.0883
1.048
293(2)
3.87-27.48
5699
3218
1921
0.0771
0.2084
1.011
293(2)
4.15-27.53
4756
4767
3416
0.0494
0.1170
1.033
293(2)
3.44-27.46
23752
24680
2166
0.0485
0.1127
1.011
293(2)
3.42-27.48
12053
12094
3366
0.0398
0.0812
1.034
Limits (ꢁ)
No. of independent reflections
No. of observed reflections, (Fo)2>4
s
(Fo)2
P
P
R ¼
jFoj ꢀ jFcjj= jFoj
P
P
Rw ¼ ½ wðjFoj ꢀ jFcjÞ2= wFo2ꢂ1=2; w ¼ 1=s2
Goodness-of-fit
s
No. of parameters
333
316
190
285
246
305
Maximun
Drmin (e Å-3
Drmax (e Å-3
D
/
)
)
s
0.014
-0.115
0.118
-0.010
-0.109
0.102
-0.068
-0.383
0.196
0.032
-0.141
0.173
0.055
-0.144
0.231
0.057
-0.130
0.138

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J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
2.3.2.4. (2S,5R)-2-(Phenyl)benzo[j]-5-phenyl-6-aza-1,3-dioxa-2-bor-
acyclononen-6-ene 4d. Compound 4d was synthesized from 0.30 g
(1.24 mmol) of the ligand 3d and 0.15 g (1.24 mmol) of phenyl
boronic acid. The reaction was carried out in toluene under reflux,
using a DeaneStark trap during 24 h. The product was obtained as
a yellow solid 0.26 g (0.79 mmol), yield, 64%, mp: 210e215 ꢁC
25
[a
]
¼ þ 189.3 (c 0.092 CHCl3), IR ymax (KBr): 3059, 2935, 2872,
D
1635 (C¼N), 1548, 1470, 1455, 1319, 1259, 1158, 1067, 1029, 845, 759,
712, 657, 514, 521, 479, 423 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [
d,
ppm]: 4.23 (dd, 1H, J ¼ 8.0 Hz, 5.0 Hz, H-9a), 4.83 (dd, 1H, J ¼ 8.0 Hz,
3.0 Hz, H-9b), 5.02 (dd, 1H, J ¼ 8.0 Hz, 3.0 Hz, H-8), 7.06 (t, 1H,
J¼ 8.0 Hz, H-5), 7.15 (d,1H, J ¼ 8.0 Hz, H-3), 7.18e7.21 (m, 2H, H-18, H-
20), 7.21e7.23 (m, 3H, H-12, H-13, H-14), 7.25e7.28 (m, 3H, H-17, H-
19, H-21), 7.40e7.42 (m, 3H, H-4, H-11, H-15), 7.61 (dd,1H, J ¼ 8.0 Hz,
Fig. 3. Envelope conformation for the five membered rings in compounds 4a and 4i.
2.5 Hz, H-6), 7.84 (s, 1H, H-7). 13C NMR (75.46 MHz, DMSO-d6) [
d,
ppm]: 64.8 (C-8), 71.5 (C-9),119.8 (C-5),121.4 (C-1),122.3 (C-3),128.1
(C-18, C-20), 127.0 (C-13), 128.2 (C-12, C-14), 128.5 (C-6), 128.6 (C-
19), 129.7 (C-17, C-21), 131.8 (C-11, C-15), 137.0 (C-4), 138.5 (C-16),
2.3.2.3. (4R)-2-(Phenyl)benzo[j]-4-methyl-7-methyl-6-aza-1,3-
dioxa-2-boracyclononen-6-ene 4c. Compound 4c was synthesized
from 0.30 g (1.55 mmol) of the ligand 3c and 0.19 g (1.55 mmol) of
phenyl boronic acid. The reaction was carried out in toluene under
reflux, using a DeaneStark trap during 24 h. The product was
160.0 (C-2), 165.8 (C-7). 11B NMR (96.29 MHz, CDCl3), [
d, ppm]: 4.7
(h1/2 ¼ 297 Hz). MS (m/z, %): 327 (Mþ, 0.1), 251 (100), 223 (0.5), 173
(0.2),149 (4), 90 (0.1), 78 (0.1). Anal. Calc for C21H18BNO2: C, 77.09; H,
5.55; N, 4.28. Found C, 77.16; H, 5.50; N, 4.26%.
obtained as a yellow solid 0.23 g (0.82 mmol), yield, 53%, mp:
25
148e152 ꢁC [
a
]
D
¼ ꢀ 216.1 (c 0.079 CHCl3), IR ymax (KBr): 3065,
2969, 2925, 2856, 1650 (C¼N), 1607, 1556, 1476, 1455, 1380, 1349,
2.3.2.5. (4S,5R)-2-(Phenyl)benzo[j]-4-phenyl-5-phenyl-6-aza-1,3-
dioxa-2-boracyclononen-6-ene 4e. Compound 4e was synthesized
from 0.30 g (0.94 mmol) of the ligand 3e and 0.11 g (0.94 mmol) of
phenyl boronic acid. The reaction was carried out in toluene under
reflux, using a DeaneStark trap during 24 h. The product was
1320, 1274, 1181, 1116, 1086, 1029, 997, 943, 874, 846, 751, 705, 642,
581, 523, 486, 450 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [
d, ppm]:
1.48 (d, CH3), 2.42 (s, CH3), 3.60 and 3.93 (m, 2H, H-8a, 8b), 4.27 (m,
1H, H-9), 6.85 (t,1H, J ¼ 7.0 Hz, H-5), 7.13e7.19 (m, 4H, H-3, H-12, H-
13, H-14), 7.45 (m, 2H, H-11, 15), 7.45e7.52 (m, 2H, H-4, H6). 13C
obtained as a yellow solid 0.24 g (0.59 mmol), yield, 63%, mp:
NMR (75.46 MHz, CDCl3) [d, ppm]: 18.3 (CH3), 20.8 (CH3), 57.6 (C-8),
25
122e130 ꢁC [
a
]
¼ ꢀ14.9 (c 0.114 CHCl3), IR ymax (KBr): 3063,
71.0 (C-9), 118.8 (C-5), 119.8 (C-1), 120.7 (C-3), 127.1 (C-13), 127.2 (C-
12, C-14), 128.5 (C-6), 132.0 (C-11, C-15), 136.6 (C-4), 160.5 (C-2),
D
2958, 2921, 2869, 1645 (C¼N), 1609, 1553, 1494, 1454, 1384, 1291,
166.1 (C-7).11B NMR (96.29 MHz, CDCl3), [
d, ppm]: 6.0 (h1/
1256,1215,1176,1154,1126,1050,1026, 979, 919, 876, 805, 759, 700,
630, 597, 565, 544, 517, 455 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [
d,
¼ 241 Hz). MS (m/z, %): 279 (Mþ, 0.2), 202 (100),174 (0.3),101 (13),
2
ppm]: 4.52 (d, 1H, J ¼ 7.0 Hz, H-8), 5.04 (d, 1H, J ¼ 7.0 Hz, H-9), 6.82
77 (23). Anal. Calc for C17H18BNO2: C, 73.15; H, 6.50; N, 5.02. Found
C, 73.42; H, 6.79; N, 4.95%.
(t, 1H, J ¼ 7.0 Hz, H-5), 6.95 (d, 1H, J ¼ 8.0 Hz, H-3), 7.08 (d, 1H,
Table 2
Selected bond distances (Å), bond angles (ꢁ) and dihedral angles (ꢁ) for compounds 4a, 4b, 4c, 4g, 4i and 5f.
Compound
4a
4b
4c
4g
4i
5f
Bond distances (Å)
N(1)-C(8)
N(1)-C(7)
O(1)-C(2)
O(2)-C(9)
C(8)-C(9)
B(1)-O(1)
B(1)-O(2)
B(1)-N(1)
B(1)-C(10)
Bond angles (ꢁ)
C(8)-N(1)-B(1)
N(1)-B(1)-O(2)
B(1)-O(2)-C(9)
O(2)-C(9)-C(8)
C(9)-C(8)-N(1)
C(7)-N(1)-B(1)
N(1)-B(1)-O(1)
1.476(3)
1.290(3)
1.335(3)
1.418(3)
1.545(3)
1.490(3)
1.440(3)
1.605(3)
1.614(4)
1.482(2)
1.288(2)
1.343(2)
1.420(2)
1.542(3)
1.475(2)
1.442(2)
1.590(2)
1.608(3)
1.465(3)
1.294(3)
1.345(3)
1.412(4)
1.523(5)
1.475(3)
1.444(3)
1.588(3)
1.620(4)
1.485(4)
1.302(4)
1.336(4)
1.402(5)
1.549(6)
1.477(5)
1.440(5)
1.591(5)
1.617(5)
1.466(2)
1.290(19)
1.346(19)
1.412(2)
1.522(3)
1.484(2)
1.445(2)
1.582(2)
1.615(2)
1.4807(19)
1.2903(19)
1.3320(19)
——
1.547(2)
1.491(2)
1.442(2)
1.607(19)
1.617(2)
108.96(17)
100.64(16)
110.46(16)
105.26(18)
99.00(15)
123.07(17)
102.91(17)
116.77(17)
117.00(2)
108.41(14)
99.83(14)
108.3(2)
101.5(2)
112.5(2)
108.3(2)
101.5(2)
123.7(2)
106.1(19)
116.1(2)
119.0(2)
116.2(2)
109.2(3)
100.6(3)
108.4(3)
109.3(3)
101.0(3)
123.7(3)
107.6(3)
119.1(2)
118.8(3)
117.3(3)
108.27(13)
101.55(12)
112.27(13)
108.46(14)
101.28(14)
124.38(13)
106.00(12)
116.89(12)
118.61(13)
116.39(14)
117.95(11)
104.15(12)
——
107.27(14)
106.63(18)
101.98(15)
124.07(14)
107.07(15)
118.03(12)
118.11(15)
116.91(15)
——
109.94(12)
122.24(13)
107.76(11)
124.83(12)
119.14(14)
122.48(15)
B(1)-O(1)-C(2)
C(2)-C(1)-C(7)
C(1)-C(7)-N(1)
116.64(19)
Dihedral angles (ꢁ)
O(1)-B(1)-C(10)-C(15)
O(2)-B(1)-C(10)-C(11)
N(1)-B(1)-C(10)-C(15)
N(1)-B(1)-C(10)-C(11)
Deviation from mean plane (Å)
Plane: C(2)-C(1)-C(7)-N(1)-B(1)-O(1)-B(1)
Plane: B(1)-N(1)-C(8)-C(9)-O(2)
-5.5(3)
64.9(2)
14.8(2)
55.5(2)
127.8(17)
-0.8(3)
60.1(4)
10.4(4)
-60.0(4
124.4(3)
2.6(2)
-5.74(19)
49.73(19)
112.73(16)
-67.73(18)
42.1(3)
111.4(2)
-72.6(3)
-52.3(3)
-119.2(3)
60.9(3)
-50.0(2)
-115.8(16)
63.5(19)
-0.305
C(9) -0.236
0.228
O(2) -0.246
-0.26
C(8) -0.171
-0.212
O(2) 0.207
0.254
C(8) 0.173
0.100
——

J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
2425
(0.8), 206 (0.1), 148 (3), 117 (0.2), 78 (0.2). Anal. Calc for
C22H20BNO2: C, 77.44; H, 5.91; N, 4.11. Found C, 77.40; H, 6.01; N,
4.06%.
2.3.2.7. (2S,5R)-2-(Phenyl)benzo[j]-5-phenyl-7-phenyl-6-aza-1,3-
dioxa-2-boracyclononen-6-ene 4g. Compound 4g was synthesized
from 0.30 g (0.94 mmol) of 3g and 0.11 g (0.94 mmol) of phenyl
boronic acid. The reaction was carried out in toluene under reflux,
using a DeaneStark trap during 24 h. The product was obtained as
a yellow solid 0.21 g (0.53 mmol), yield, 56%, mp: 221e224 ꢁC
25
[a
]
¼ þ381.0 (c 0.114 CHCl3), IR ymax (KBr): 3066, 3006, 2940,
D
2864, 1606 (C¼N), 1546, 1453, 1393, 1340, 1268, 1192, 1150, 1106,
1015, 951, 844, 818, 741, 701, 651, 619, 533, 499, 437, 406 cmꢀ1 1H
NMR (300 MHz, DMSO-d6) [
d
, ppm]: 4.12 (d, 1H, J ¼ 5.0 Hz, H-8),
4.44 (d, 1H, J ¼ 7.0 Hz, H-9b), 4.64 (d, 1H, J ¼ 4.0 Hz, H-9a), 6.79 (t,
1H, J ¼ 8.0 Hz, H-5), 7.08e7.13 (m, 2H, H-3, H-23), 7.08e7.23 (m, 8H,
H-13, H-17, H-18, H-19, H-20, H-21, H-24, H-25), 7.23e7.25 (m, 2H,
H-12, H-14), 7.40e7.55 (m, 6H, H-4, H-6, H-11, H-15, H-26, H-27).
Fig. 4. Bond distances correlation for compounds 4ae4c, 4g, 4i and 5f.
J ¼ 7.0 Hz, H-6), 7.25e7.39 (m, 16 H, H-4, H-11, H-12, H-13, H-14, H-
13C NMR (75.46 MHz, CDCl3) [
d, ppm]: 68.4 (C-8), 71.6 (C-9), 118.8
15, H-17, H-18, H-19, H-20, H-21, H-23, H-24, H-25, H-26, H-27),
8.07 (s, 1H, H-7). 13C NMR (75.46 MHz, CDCl3) [
d, ppm]: 78.4 (C-8),
(C-5), 120.5 (C-3), 121.3 (C-1), 127.2 (C-19), 127.4 (C-18, C-20), 127.7
(C-12, C-14), 127.8 (C-13), 128.2 (C-24), 128.5 (C-17, C-21), 128.7 (C-
26),129.1 (C-25), 129.25 (C-23), 131.5 (C-27),131.6 (C-6), 131.7 (C-11,
C-15), 132.3 (C-22), 137.3 (C-4), 140.7 (C-16), 161.4 (C-2), 172.3 (C-7).
80.2 (C-9), 117.0 (C-3), 118.8 (C-5), 119.2 (C-1), 127.3 (C-12, C-14),
128.1 (C-24, C-26), 128.2 (C-13), 128.25 (C-6), 128.27 (C-18, C-20),
128.3 (C-23, C-27), 128.9 (C-11, C-15), 131.8 (C-19), 132.6 (C-25),
138.8 (C-4), 139.5 (C-16), 140.3 (C-22), 160.0 (C-2), 166.0 (C-7). 11B
11B NMR (96.29 MHz, CDCl3), [
d, ppm]: 6.5. (h1/2 ¼ 257 Hz). MS (m/z,
%): 402 (Mþ, 0.3), 326 (100), 298 (2), 248 (2), 224 (10), 208 (1), 146
(3), 104 (1). Anal. Calc for C27H22BNO2: C, 80.41; H, 5.50; N, 3.47.
Found C, 80.18; H, 5.44; N, 3.42%.
NMR (96.29 MHz, CDCl3), [
d
, ppm]: 4.4 (h1/2 ¼ 385 Hz). MS (m/z, %):
402 (Mþ, 0.4), 326 (100), 296 (3), 211 (3), 148 (3), 148 (1), 116 (0.2),
91 (0.2), 77 (0.1). Anal. Calc for C27H22BNO2: C, 80.41; H, 5.50; N,
3.47. Found C, 80.23; H, 5.38; N, 3.41%.
2.3.2.8. (Rac)-2-(Phenyl)benzo[j]-7-phenyl-6-aza-1,3-dioxa-2-bor-
acyclononen-6-ene 4h. Compound 4h was synthesized from 0.30 g
(1.24 mmol) of 3h and 0.15 g (1.24 mmol) of phenyl boronic acid.
The reaction was carried out in toluene under reflux, using
a DeaneStark trap during 24 h. The product was obtained as
a yellow solid 0.29 g (0.89 mmol), yield, 71%, mp: 151e154 ꢁC, IR
ymax (KBr): 3055, 2963, 2928, 2870, 1601 (C¼N), 1543, 1490, 1449,
1364, 1323, 1258, 1180, 1090, 1060, 1005, 902, 877, 832, 742, 699,
2.3.2.6. (2S,4R,5S)-2-(Phenyl)benzo[j]-4-phenyl-5-methyl-6-aza-1,3-
dioxa-2-boracyclononen-6-ene 4f. Compound 4f was synthesized
from 0.30 g (1.17 mmol) of 3f and 0.14 g (1.17 mmol) of phenyl
boronic acid. The reaction was carried out in toluene under reflux,
using a DeaneStark trap during 24 h. The product was obtained as
a yellow solid 0.27 g (0.79 mmol), yield, 67%, mp: 236e241 ꢁC
25
[
a]
¼ þ 65.9 (c 0.097 CHCl3), IR ymax (KBr): 3065, 2979, 2935,
D
630, 573, 531, 442 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [
d, ppm]:
2864, 1651 (C¼N), 1608, 1552, 1474, 1454, 1404, 1292, 1225, 1177,
1145, 1094, 1023, 992, 923, 882, 816, 746, 703, 642, 571, 518, 485,
3.04 (dd, 1H, J ¼ 3.5 Hz, J ¼ 9.0 Hz, H-8b), 3.36 (dd, 1H, J ¼ 3.0 Hz,
J ¼ 5.0 Hz, H-8a), 3.85 (m, 1H, H-9a), 4.18 (m, 1H, H-9b), 6.72 (t, 1H,
J ¼ 6.0 Hz, H-5), 6.83 (d, 1H, J ¼ 6.0 Hz, H-6), 7.04 (d, 1H, J ¼ 8.0 Hz,
H-3), 7.18e7.31 (m, 4H, H-12, H-13, H-14, H-20), 7.42e7.44 (m, 1H,
J ¼ 7 Hz, H-4), 7.48e7.57 (m, 2H, H-18, H-21), 7.64 (t, 1H, J ¼ 8.0 Hz,
H-19), 7.69 (d, 2H, J ¼ 7.0 Hz, H-11, H-15), 8.39 (d, 1H, J ¼ 8.0 Hz, H-
461, 425 cmꢀ1 1H NMR (300 MHz, DMSO-d6) [
d, ppm]: 0.92 (d, 3H,
J ¼ 7.0 Hz, CH3), 4.19 (m, 1H, H-8), 5.38 (d, 1H, J ¼ 5.0 Hz, H-9), 6.85
(t, 1H, J ¼ 7.5 Hz, H-5), 6.98 (d, 1H, J ¼ 8 0.0 Hz, H-3), 7.12e7.23 (m,
4H, H-13, H-18, H-19, H-20), 7.28e7.38 (m, 2H, H-17, H-21),
7.32e7.42 (m, 2H, H-4, H-6), 7.48e7.62 (m, 4H, H-11, H-12, H-14, H-
15), 8.38 (s, 1H, H-7). 13C NMR (75.46 MHz, CDCl3) [
d, ppm]: 15.4
17), 13C NMR (75.46 MHz, CDCl3) [
d, ppm]: 53.1 (C-8), 60.4 (C-9),
(CH3), 66.9 (C-8), 80.0 (C-9), 118.7 (C-1), 119.1 (C-5), 120.5 (C-3),
126.4 (C-18, C-20), 127.4 (C-13), 127.3 (C-12, C-14), 127.1 (C-19),
128.3 (C-17, C-21), 130.8 (C-6), 131.0 (C-11, C-15), 137.6 (C-4), 139.2
118.1 (C-5), 118.2 (C-1), 119.1 (C-3), 126.9 (C-13), 127.4 (C-12, C-14),
128.2 (C-26), 128.5 (C-24), 129.0 (C-25), 129.9 (C-27), 130.3 (C-23),
132.1 (C-11, C-15), 132.5 (C-6), 132.6 (C-22), 136.5 (C-4), 160.7 (C-2),
(C-16), 158.2 (C-2), 161.5 (C-7). 11B NMR (96.29 MHz, CDCl3), [
d,
174.7 (C-7). 11B NMR (96.29 MHz, CDCl3), [
d, ppm]: 3.9(h1/
ppm]: 5.9 (h1/2 ¼ 192 Hz). MS (m/z, %): 341 (Mþ, 0.1), 264 (100), 234
¼ 298 Hz) MS (m/z, %): 327 (Mþ, 0.1), 250 (100), 224 (0.1), 208
2
(0.1), 174 (3), 146 (0.1), 78 (0.1). Anal. Calc. for C21H18BNO2: C, 77.09;
H, 5.55; N, 4.28. Found C, 77.01; H, 5.68; N, 4.22%.
2.3.2.9. (Rac)-2-(Phenyl)benzo[j]-7-methyl-6-aza-1,3-dioxa-2-bor-
acyclononen-6-ene 4i. Compound 4i was synthesized from 0.30 g
(0.81 mmol) of 6i. The reaction was carried out in toluene under
reflux, using a DeaneStark trap during. The product was obtained
as a yellow solid 0.18 g (0.49 mmol), yield, 60%, mp: 180e184 ꢁC. IR
ymax (KBr): 3044, 3000, 2936, 1612 (C¼N), 1553, 1479, 1454, 1400,
1325, 1274, 1143, 1106, 1036, 985, 954, 865, 814, 784, 754, 704, 657,
634, 614, 567, 499, 441 cmꢀ1 1H NMR (300 MHz, CDCl3) [
d, ppm]:
2.53 (s, CH3), 3.99 (m, 2H, H-8), 4.12 (m, 1H, H-9a), 4.30 (m, 1H, H-
9b), 6.86 (t,1H, J ¼ 7.0 Hz, H-5), 7.13 (d,1H, J ¼ 7.1 Hz, H-3), 7.14e7.19
(m, 3H, H-12, H-13, H-14), 7.33e7.37 (m, 2H, H-11, H-15), 7.41e7.50
(m, 2H, H-4, H-6). 13C NMR (75.46 MHz, CDCl3) [
d, ppm]: 18.3 (CH3),
Fig. 5. Bond angles correlation for the compounds 4ae4c, 4g, 4i and 5f.
50.0 (C-8), 62.8 (C-9), 119.1 (C-5), 119.7 (C-1), 121.0 (C-3), 127.2 (C-

2426
J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
Fig. 6. Conformations of the [4.3.0] heterobicycles in compounds 4a, 4b, 4c, 4g and 4i.
13), 127.4 (C-12, C-14), 128.4 (C-6), 131.6 (C-11, C-15), 136.8 (C-4),
obtained from the reaction between the ligand 3i and 2 equivalents
of phenyboronic acid, refluxing 6i in toluene for one day gave 4i and
2,4,6-triphenylboroxine (Scheme 4).
In the attempts to crystallize compound 4f, the hydrolysis
product 5f was obtained (Fig. 2). The structure of 5f showed that
the five member ring has been opened, most likely as the result of
its greater reactivity owing to ring strain.
160.0 (C-2), 166.9 (C-7). 11B NMR (96.29 MHz, CDCl3), [
d, ppm]: 5.9.
(h1/2 ¼ 221 Hz). MS (m/z, %): 264 (Mþ, 0.2), 234 (0.3), 188 (100), 162
(16), 146 (7), 117 (3), 91 (3), 77 (13). Anal. Calc. for C16H16BNO2: C,
72.49; H, 6.08; N, 5.28. Found C, 72.11; H, 5.92; N, 5.18%.
2.4. Results and discussion
2.4.1. Spectroscopic Properties
Reaction of ethanolamines with salicylaldehyde, 2-hydrox-
yacetophenone or 2-hydroxybenzophenone afforded tridentate
ligands 3ae3i in high yields. Subsequent reaction of these ligands
3ae3h with phenyl boronic acid under reflux of toluene for 24 h
gave boronates 4ae4h in yields between 53 and 71% (Scheme 2), All
compounds including the tridentate ligands were characterized by
mass spectrometry, IR, 1H, 13C, elemental analysis and 11B NMR for
boron compounds. Due to the formation of a new chiral center at
the boron atom it is possible to induce its stereochemistry.
Compounds 4a, 4b, 4d, 4e, 4f, and 4g all have a phenyl group at the
aliphatic carbons (Scheme 2) hence the formation of only one
diastereoisomer can be attributed to the big size of the phenyl
group that induces the attack of the boron atom just in one face of
the molecule. In the case of compound 4c we observed in 1H NMR
spectroscopy the formation of two different compounds in 2:1
a ratio which correspond to the pair of diastereoisomers 4c-syn and
4c-anti (Scheme 3), where the major product has the methyl and
phenyl group in the same side. The methyl group in compound 4c
could not induce diastereoselectivity because of its small size, in
consequence the attack took place in both faces of the molecule. It
is worth to mention that the preferred stereochemistry is that
where all substituents are on the same side (syn), in the case of
compounds 4h and 4i they do not have chiral atoms and the
products correspond to the enantiomeric mixture.
The existence of the N/B bond in compounds 4ae4i was
established by 11B NMR which shows the signals between 6.5 and
3.9 ppm, characteristic for the tetracoordinated boron atom
[14e24]. The characteristic signal in the 13C NMR spectra for the
imine group appears between 161.5 and 174.7 ppm, and it was
confirmed by the band for (C¼N) in the infrared spectra, between
1601 and 1651 cmꢀ1. The mass spectra give the molecular ions in
low abundance, and a base peak corresponds to the [MþeC6H5] ion
in agreement with previous results [21]. In the case of compound 4c
the reaction provides a 2:1 mixture of both diastereomers 4c-syn
and 4c-anti, this behavior was attributed to the small size of the
methyl group compared with the other substituents, which causes
that asymmetric induction was poor, and the new chiral center
generated on the boron atom is R in 4c-syn in the case of major
product. (Scheme 3)
2.4.2. X-ray analyses of 4a, 4b, 4c, 4g, 4i and 5f
The compounds 4a, 4b, 4c, 4g, 4i and 5f provided crystals
suitable for Xeray analyses. The X-ray structures for these
compounds are shown in Figs.1 and 2. The crystallographic data are
summarized in the (Table 1). The structures of compounds 4a, 4b,
4c, 4g, 4i showed that the phenyl group attached to the boron atom
prefers the position in the same face of the other substituents, and
the phenyl group in the five membered ring is big enough to induce
the configuration at the boron atom (Fig. 3). In compounds 4a and
4i, the position of C(9) deviates by ꢀ0.236 Å from the mean plane B
In the preparation of compound 4i following the same method
failed because the formation of the dimeric compound is very fast,
therefore it was necessary to prepare the compound 6i, which was

J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
2427
Fig. 7. Intermolecular interactions in structure 5f.
(1)eN(1)-C(8)-C(9)-O(2), and that of C(8) deviates by 0.173 Å from
the same plane, respectively. The N / B bond distances for 4a, 4b,
4c, 4g and 4i are 1.605(3), 1.590(2), 1.588(3), 1.591(5) and 1.582(2)
and they are similar to those observed in boron complexes [21].
Significant differences were between B(1)eO(1) 1.490(3)-1.475(2)
Å and B(1)-O(2) 1.440(3)-1.445(2) Å bond distances, and showed
that the shorter bond lengths correspond to the aliphatic oxygen in
the five member rings (Table 2). The bond angles around the boron
atom for compounds 4a, 4b, 4c, 4g and 4i are in the range between
99.83ꢁ and 116.04ꢁ (Table 2). The average value for the bond angles
in five membered rings are 104.92ꢁ, 104.82ꢁ, 106.42ꢁ, 105.68ꢁ
and 106.36ꢁ for 4a, 4b, 4c, 4g and 4i respectively, which are better
than those observed in six and seven membered rings values, due
to the higher strain of five membered rings, while the values
observed for similar 6 and 7 member rings heterocycles are 117.1ꢁ
(3) and 118.8ꢁ (3) which indicate lower ring strain [35]. Figs. 4 and 5
show that bond lengths and angles in five and six member rings are
similar.
The values for the tetrahedral character (THC) [19] for boron
atoms are 66.5%, 74.2%, 75.7%, 77.1% and 75.3% for 4a, 4b, 4c, 4g and
4i respectively, these values show that the boron atom is more
distorted in the derivative of ephedrine because it has two
substituents in the aliphatic carbons directly bonded to the five
membered ring, consequently it presents the largest ring strain and
the lower THC.
The deviations of the boron atom from the mean plane of the
six-membered ring C(2)eC(1)-C(7)eN(1)-B(1)eO(1) in 4a, 4b, 4c,
4g and 4i are 0.305, ꢀ0.228, 0.261, 0.100 and 0.212 Å respectively,
showing again that the largest deviation of the boron atom from
the mean plane corresponds to compound 4a, which has two
substituents on the aliphatic carbons and presents the less THC.
The dihedral angles for the O1-B1-C10-C15 fragment in
compounds 4a, 4b, 4c, 4g and 4i are ꢀ5.5ꢁ, ꢀ64.9ꢁ, ꢀ0.8ꢁ, 60.1ꢁ and
2.6ꢁ which are indicative of two conformations preferred around
CꢀB bond, eclipsed and gauche.
In the Fig. 6 are shown the different conformations of the [4.3.0]
heterobicycle for 4a, 4b, 4c, 4g and 4i, the six-members ring is
almost planar and the boron atom is deviated from the mean
plane ꢀ0.305, 0.228, ꢀ0.26, ꢀ0.212, 0.254, 0.100 Å for 4a, 4b, 4c, 4g
and 4i, respectively (Table 2) and the five member ring has an
envelope conformation with different atoms out of the mean plane
for 4a C(9) ꢀ0.236 Å, for 4b O(2) ꢀ0.246 Å for 4c C(8) ꢀ0.171 Å for
4g O(2) 0.207 Å and 4i C(8) 0.173 Å. Fig. 4 shows that the bond
lengths are very similar, in all compounds. However, in the Fig. 5
shows that bond angles have small differences in the compounds
4a, 4b, 4c, 4g and 4i.
The structure for compound 5f is shown in the Fig. 2, this
compound corresponds to the open five membered ring, which was
obtained by reaction of water with 4f and proved that the five
member ring is less stable than the six member ring. The THC value
for compound 5f is close to a tetrahedral (85.2%) due to loss of ring
strain.
The deviations of the boron atom from the mean plan of six
membered ring in 5f is 0.254 Å The N/B bond length for 5f is 1.607
(19), and is larger than the 4a, 4b, 4c, 4g and 4i, Fig. 4 show that
bond lengths are similar to the compounds 4a, 4b, 4c, 4g and 4i, but
the bond angles are expectedly rather different.
Structure 5f shows intermolecular hydrogen bond interactions
of O2 with H3A with a distance of 1.889 Å and O3 with H2A with
a distance of 2.103 Å, in both cases the distances are less than the
sum of the van der Walls radii (Fig. 7) [36].
2.5. Conclusions
Two new tridentate ligands and nine boronates (six of them
chiral) were synthesized in good yields. The reaction of the tri-
dentate ligands with phenyl boronic acid lead to monomeric bor-
onates (4ae4h), with exception of compound 4i, which was
obtained from compound 6i. Although, it was possible to obtain
boronates with six and seven membered rings employing two

2428
J.M. Rivera et al. / Journal of Organometallic Chemistry 696 (2011) 2420e2428
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equivalents of phenyl boronic acid, an adequate control of the
reaction conditions, lead to the preparation of boronates with six
and five membered rings, which were thermodynamically more
stable. However, six and seven membered rings heterobicycles are
intermediates which upon heating conduce to the monomeric
compounds with six and five member heterobicyclic rings. We
conclude that five membered rings are strained as revealed through
the bond angles in five member rings which were 104.92ꢁ, 104.82ꢁ,
106.42ꢁ, 105.68ꢁ and 106.36ꢁ for 4a, 4b, 4c, 4g and 4i, respectively.
Ring opening in compound 5f is due to the presence of water in the
solvent used to crystallize the compound. This kind of compounds
could have some applications as chiral inductors.
[17] V. Barba, R. Hernández, R. Santillán, N. Farfán, Inorg. Chim. Acta 363 (2010)
4112.
Acknowledgments
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J. Organomet. Chem. 581 (1999) 70;
The authors acknowledge financial support from Consejo
Nacional de Ciencia y Tecnología (CONACyT) Fondo Mixto Veracruz
(127835) and PAPIIT IN-214010 Thanks are given to Consejo
Superior de la Investigación Científica in Spain for the award of
a license for the use of the Cambridge Crystallographic Data Base
and Geiser Cuéllar for mass spectra, Q. Ma. Luisa Rodríguez for NMR
spectra, I.Q. Jobo Lara Faticati.
c) N. Farfán, R. Santillan, H. Höpfl, Main Group Chem. News 7 (1999) 3;
d) V. Barba, R. Luna, D. Castillo, R. Santillan, N. Farfán, J. Organomet. Chem. 604
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31.
Appendix A. Supplementary material
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(7) (2000).
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17A (1979) 618;
b) H. Höpfl, M. Sánchez, V. Barba, N. Farfán, Can. J. Chem. 76 (1998) 1352.
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[27] G.M. Sheldrick, University of Göttingen, Göttingen, 1993.
[28] A.L. Spek, J. Appl. Cryst. 36 (2003) 7.
CCDC no. 264752, 259940, 264751, 264749, 264753 and 264750
for 4a, 4b, 4c, 4g, 4i and 5f respectively, contain the supplementary
crystallographic 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.
[29] L. Farrugia, J. Appl. Cryst 30 (1997) 565.
[30] L. Farrugia, J. Appl. Cryst. 32 (1999) 837.
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