An alternative method for the preparation of diphenylboron chelates. The crystal and molecular structures of (pyridine-2-acetyloximato)diphenylboron and (1-phenylazo-2-naphtholato)diphenylboron

Article abstract of DOI:10.1002/zaac.200500192

A convenient method for the preparation of diphenylboron chelates from ammonium tetraphenylborate is described. A variety of five- or six-membered O,O-, N,O- and N,N-chelates were obtained in yields from 60 to 90 %. The isolated compounds were characterized by elemental analysis, IR spectroscopy and multinuclear magnetic resonance spectroscopy (¹H, ¹³C, and ¹¹B). The crystal and molecular structures of (pyridine-2-acetyloximato)diphenylboron and (1-phenylazo-2-naphtholato) diphenylboron were determined by X-ray diffraction on single crystals.

Full text of DOI:10.1002/zaac.200500192

An Alternative Method for the Preparation of Diphenylboron Chelates.
The Crystal and Molecular Structures of (Pyridine-2-
acetyloximato)diphenylboron and (1-Phenylazo-2-naphtholato)diphenylboron
a,
a
a
a
,b
˜
Karl E. Bessler *, Elisabeth B. Dourado , Myller de S. Carvalho , Sebastiao S. Lemos , and Javier Ellena*
a
´
´
´
Brasılia Ϫ DF / Brazil, Instituto de Quımica, Universidade de Brasılia
b
´
Sa˜o Carlos Ϫ SP / Brazil, Instituto de Fısica de Sa˜o Carlos, Universidade de Sa˜o Paulo
Received April 18th, 2005.
Abstract. A convenient method for the preparation of diphenylbo-
ron chelates from ammonium tetraphenylborate is described. A va-
riety of five- or six-membered O,O-, N,O- and N,N-chelates were
obtained in yields from 60 to 90 %. The isolated compounds were
characterized by elemental analysis, IR spectroscopy and multinuc-
lear magnetic resonance spectroscopy (1H, 13C, and 11B). The cry-
stal and molecular structures of (pyridine-2-acetyloximato)diphe-
nylboron and (1-phenylazo-2-naphtholato)diphenylboron were de-
termined by X-ray diffraction on single crystals.
Keywords: Boron; Coordination chemistry; NMR spectroscopy;
Crystal structures
Introduction
dine-N-oxide (1) [10], maltol (2) [3] and 1-phenylazo-2-
naphthol (3) [11]), four of them are presented here for the
first time (LH ϭ β-alanine (4), pyridine-2-acetyloxime (5),
picolinic acid (6) and L-valine (7)).
At reaction times from 12 to 24h; the corresponding
diphenylboron chelates Ph2BL are obtained in high yields
(60 Ϫ 93 %). All compounds are characterized by IR and
multinuclear magnetic resonance spectroscopy (1H, 13C and
11B). The determination of the crystal and molecular struc-
tures by X-ray diffraction on single crystals reveals a six
membered O,N chelate for 3 and a five membered N,N che-
late for 5.
A large variety of tetrahedral boron chelates of the general
composition X2BL, for X ϭ H, F, Cl, alkyl, aryl, alkoxy,
aryloxy, acyloxy, etc. and a bidentate chelating anion L,
have been described in the past. Among these chelates the
diaryl species Ar2BL show outstanding thermal and hydro-
lytic stability [1]. Diphenylborinates Ph2BL are usually pre-
pared from the commercially available 2-aminoethanol
complex of diphenylborinic acid [2Ϫ6]. The n-butylester of
diphenylborinic acid has been employed for the preparation
of several aminoacid complexes [7]. Triphenylborane has
also been used as starting material [1]. Eventually di-
phenylboron chelates were obtained from trimethylborate
and phenylmagnesium bromide [8]. Diphenylboron com-
plexes with aminoacids have been obtained from the com-
mercially available sodium tetraphenylborate and ami-
noacid hydrochlorides [9]. We describe here the preparation
of diphenylboron complexes starting from the readily avail-
able and stable ammonium tetraphenylborate.
Results and Discussion
Ammonium tetraphenylborate reacts with chelating agents
LH in refluxing toluene according to equation (1):
[NH4][B(C6H5)4] ϩ LH Ǟ (C6H5)2BL ϩ NH3 ϩ 2 C6H6
(1)
This method was applied for the preparation of a variety of
five- or six-membered O,O-, N,O- and N,N-chelates, three
of them have been described earlier (LH ϭ 2-hydroxypyri-
* Prof. Dr. Karl E. Bessler
´
Instituto de Quımica
´
Universidade de Brasılia
Caixa Postal 04478
´
70904-970 Brasılia DF / Brazil
E-mail: bessler@unb.br
Z. Anorg. Allg. Chem. 2005, 631, 1935Ϫ1940
DOI: 10.1002/zaac.200500192
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1935

K. E. Bessler, E. B. Dourado, M. de S. Carvalho, S. S. Lemos, J. Ellena
NMR spectra
upon coordination to boron atom. Satisfactory NMR data
for the maltolato complex 2 could only be obtained in
acetonitrile-d3 since it hydrolyses in water containing
DMSO-d6, even when an ampoule stored solvent was util-
ized.
1
The H- and 13C-NMR spectra of the Ph2B fragment in all
studied compounds show constant chemical shifts. In some
cases, the quaternary carbon atom (ipso) was only hardly
seen since it is a broad signal due to its coupling to both
10B and 11B isotopes. While the coordinated β-alaninate ex-
hibits a broad signal for the NH2 group at 6.78 ppm, the L-
valinate analog shows diastereotopic signals not only for
methyl groups but also for NH2 and Ph2B moieties in
consequence of the asymmetric center on the coordinated
The 11B chemical shift (δ) in R2B(chelate) complexes is
sensitive to a number of factors pertaining the resultant het-
erocyclic ring including i) its size, ii) the nature of the coord-
inating atoms, iii) substitution on the ring. The observed
11B resonances (δ) lie within the range of other reported
diphenylboron chelate compounds [5, 12].
L-valinate. Accordingly,
a
pseudotriplet centered at
6.29 ppm was assigned to one hydrogen atom from NH2,
which is coupling to its geminal hydrogen atom and also to
that attached to the asymmetric carbon atom. This could be
The crystal and molecular structure of (2-
acetylpyridineoximato)diphenylboron (5)
1
unequivocally confirmed with the aid of H{1H} selective
The molecular structure of 5 is shown in Fig. 1. Selected
bond lengths and angles are summarized in Table 1.
decoupling experiments. The other amino hydrogen signal
is overlapped with those of phenyl groups. Moreover, when
the spectrum was run in acetonitrile-d3 instead of dimeth-
ylsulfoxide-d6 a different pattern was observed. The amino
hydrogen atoms have appeared as broad signals at higher
magnetic fields (5.85 and 4.80 ppm) if compared to the
spectrum obtained in dimethylsulfoxide-d6. Furthermore,
the hydrogen atom bound to the asymmetric carbon atom
became clearly seen as a well-resolved doublet of triplet
centered at 3.61 ppm.
˚
Table 1 Selected bond lengths /A and angles /° for 5.
B-N(2)
B-N(1)
B-C(11)
B-C(21)
O-N(2)
1.581(2)
N(1)-C(5) 1.358(2)
1.589(2)
1.607(2)
1.615(2)
1.295(2)
N(2)-C(6)
C(5)-C(6)
C(6)-C(7)
1.314(2)
1.437(2)
1.489(2)
N(2)-B-N(1) 95.54(10) C(11)-B-C(21) 116.08(12)
N(2)-B-C(11) 111.84(12) C(1)-N(1)-B
N(1)-B-C(11) 110.33(11) C(6)-N(2)-B
128.61(14)
113.55(13)
N(2)-B-(C(21) 109.46(11) N(1)-C(5)-C(6) 110.33(13)
N(1)-B-C(21) 111.75(11) N(2)-C(6)-C(5) 109.49(13)
The 13C NMR spectra of all studied compounds present
the expected resonances. Those containing the 2-substituted
pyridine derivatives (5 pyridine-2-acetyloxime and 6 pico-
linic acid) have the C6-H (this numbering scheme is not in
agreement with the labeling of the crystallographic struc-
ture) position easily recognizable and they resonate at
higher magnetic fields (approximately 5 ppm) if compared
to the respective free precursor ligand molecules. This is a
consequence of the proximity of phenyl groups to C6-H as
has been pointed out for other diphenylboron chelates [4].
This interpretation is further supported by the fact that in
2-hydroxipyridine N-oxide there is almost no such change
The pyridine-2-acetyloximato ligand offers two chelating
possibilities: a six membered N,O- and a five membered
N,N-chelate, as shown below.
The crystal structure of 5 contains discrete molecules of
the type (b) chelate with a distorted tetrahedral coordi-
nation on the boron atom. The same coordination mode
was found in several pyrinine-2-acetyloximato transition
metal complexes [13Ϫ15]. The endocyclic N-B-N angle is
quite small (95.54°), whereas the exocyclic C-B-C angle is
enlarged (116.08°). It is noteworthy that the two B-N bond
˚
lengths B-N(1) with 1.589(2) A (pyridine nitrogen atom)
˚
and B-N(2) with 1.581(2) A (oxime nitrogen atom) are simi-
lar to each other and are situated in the range of the lowest
3
2
˚
values (below 1.60 A) found for Bsp -Nsp bonds [16]. The
B-N(2) bond length is compatible with the corresponding
C-N distance in (salicylaldoximato)diphenylboron [17]. In
the diphenylboron chelate 5 the oxime CϭN bond C(6)-
˚
N(2) with 1.314(2) A is slightly lengthened by 2.8 % com-
pared to the free oxime with 1.278 A. However, the N-O
bond is considerably shortened by 7.9 % from 1.406 A in
the free oxime [18] to 1.295(2) A, similar to N-O distances
˚
Fig. 1 An ORTEP view of the molecular structure of 5. The dis-
placement ellipsoids are drawn at the 50 % probability level. H
atoms have been omitted for clarity.
˚
˚
1936
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 1935Ϫ1940

An Alternative Method for the Preparation of Diphenylboron Chelates.
˚
Table 2 Selected bond lengths /A and angles /° for 3.
B(1)-O(1)
B(1)-C(111)
B(1)-C(121)
1.514(3)
1.596(3)
1.607(3)
B(2)-O(2)
B(2)-C(221)
B(2)-C(211)
1.516(3)
1.596(4)
1.6)4(3)
B(1)-N(2)
1.615(3)
1.326(2)
1.291(2)
1.372(3)
1.436(3)
1.390(3)
B(2)-N(22)
1.617(3)
1.325(2)
1.294(2)
1.364(3)
1.439(3)
1.392(3)
O(1)-C(140)
N(11)-N(12)
N(11)-C(149)
N(12)-C(131)
C(140)-C(149)
O(2)-C(240)
N(21)-N(22)
N(21)-C(249)
N(22)-C(231)
C(240)-C(249)
O(1)-B(1)-C(111)
O(1)-B(1)-C(121)
C(111)-B(1)-C(121)
O(1)-B(1)-N(12)
C(111)-B(1)-N(12)
C(121)-B(1)-N(12)
C(140)-O(1)-B(11)
N(12)-N(11)-C(149)
N(11)-N(12)-B(1)
O(1)-C(140)-C(149)
N(11)-C(149)-C(140)
107.2(2)
108.4(2)
117.9(2)
102.7(2)
111.1(2)
108.5(28)
116.8(2)
117.9(2)
121.9(2)
120.6(2)
121.3(2)
O(2)-B(2)-C(211)
O(2)-B(2)-C(221)
C(211)-B(2)-C(221)
O(2)-B(2)-N(22)
C(211)-B(2)-N(22)
C(221)-B(2)-N(22)
C(240)-O(2)-B(2)
N(22)-N(21)-C(249)
N(21)-N(22)-B(2)
O(2)-C(240)-C(249)
N(21)-C(249)-C(240)
107.8(2)
109.8(2)
115.5(2)
102.0(2)
112.4(2)
108.5(2)
115.6(2)
117.5(2)
120.5(2)
120.1(2)
121.3(2)
Fig. 2 An ORTEP view of the asymmetric unit of 3. The displace-
ment ellipsoids are drawn at the 50 % probability level. H atoms
have been omitted for clarity.
0.80 and 0.23, respectively, from the OCCN(1) least square
˚
plane. The NϭN-distance (1.293 A) is slightly longer than
found in pyridine N-oxides [19]. The chelate ring is nearly
planar, the boron atom being displaced by 0.098(2) A from
˚
˚
the mean value for aromatic azo compounds (1.254 A) [19].
The B-N distance of 1.616 A indicates a strong B-N bond,
being slightly shorter compared to B-N distances observed
in boron O,N-chelates involving coordination of azine ni-
trogen atoms [22, 23]. On the other hand the B-O bond
˚
the C2N2 plane which is almost coplanar with the pyridine
ring (dihedral angle between the least square planes of
3.22(5)°). Displacement of the O atom from the chelate
˚
C2N2 plane is 0.040(1) A.
˚
length of 1.515 A is situated at the upper limit of the corre-
sponding values found in boron chelates with phenolic B-O
bonds [8, 22, 23].
In contrast to the copper or nickel bis-chelates [20, 21],
the naphthalene C-N bond is by 5 % shorter compared to
the phenyl C-N bond.
The crystal and molecular structure of (1-phenylazo-
2-naphtholato)diphenylboron (3)
Complexes of 2-hydroxyazo compounds may have either a
five membered (c) or a six membered (d) chelate structure.
Experimental Section
Materials and Equipment
Solvents and reagent grade starting materials were used as received
from commercial suppliers. A FISIONS CHNS micro analyser
mod. EA 1108 was used for the CHN analyses. Melting points are
uncorrected. The infrared spectra (KBr pellets, 4000-400 cmϪ1
)
The six-membered version (d) was found for bis-chelates
of copper(II) [20] and nickel(II) [21]. The crystal structure
of 3 confirms the coordination mode (d) of the azo ligand,
which has been proposed earlier from spectroscopic data
[11]. This is the first example for a crystal structure of a
boron complex involving an azo ligand. Selected bond
lengths and angles are summarized in Table 2. The asym-
metric unit of 3 consists of two crystallographically non
equivalent molecules, as shown in Figure 2. The two mol-
ecules differ mainly in the torsion angles between the B-
phenyl groups and in minor conformational changes of the
chelate ring. In the following discussion the indicated bond
lengths and angles correspond to approximate mean values
from the two independent molecules. The boron atom
shows a distorted tetrahedral coordination with the exo-
cyclic C-B-C- angle of 116.7° and the endocyclic N-B-O
angle of 102.3°. The chelate ring has a considerably puck-
ered conformation. The B and N(2) atoms are displaced by
were recorded on a BOMEM BM 100 FT-IR spectrometer. UV-
VIS absorption spectra were obtained with a Beckmann DU 650
equipment. All NMR spectra were recorded on a Varian MER-
CURY plus (M-300) spectrometer operating at 300.07, 75.46, and
96.27 MHz for 1H, 13C, and 11B, respectively. The 1H, 13C{1H},
and 11B{1H} NMR spectra were obtained in CDCl3, CD3CN or
DMSO-d6 as solvents at 25 °C. Chemical shifts (δ) are given in
ppm relative to SiMe4 (internal reference for 1H and 13C), and neat
BF3OEt2 (external reference for 11B). They are positive if the signal
was shifted to higher frequencies than the standard. The solutions
were placed in 5 mm (o.d.) NMR tubes and deuterated solvents
were used as internal lock. All 11B NMR spectra have been sub-
tracted from the background signal of the NMR tube by using the
VNMR 6.1C software.
Crystal structure determinations
X-ray diffraction data collections ( scans andscans with κ offsets)
were performed on an Enraf-Nonius Kappa-CCD diffractometer
Z. Anorg. Allg. Chem. 2005, 631, 1935Ϫ1940
zaac.wiley-vch.de
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1937

K. E. Bessler, E. B. Dourado, M. de S. Carvalho, S. S. Lemos, J. Ellena
Table 3 Crystal data and structure refinement for 3 and 5.
5
3
Empirical formula
Formula weight
Temperature /K
Wavelength /A
Crystal system
Space Group
C19H17BN2O
300.16
150(2)
C28H21BN2O
412.28
293(2)
0.71073(6)
orthorhombic
Pna21
a ϭ 29.0810(6)
b ϭ 10.1207(1)
c ϭ 15.2138(3)
˚
0.71073(6)
monoclinic
P21/n
a ϭ 8.4114(3)
b ϭ 17.2554(8)
c ϭ 10.8552(5)
β ϭ 97.890(3)
4
˚
Unit cell dimensions /A, °
Z
8
3
˚
Cell volume /A
1560.6(1)
1.277
4477.7 (1)
1.223
Calculated density /(g/cm3)
Absorption coefficient /mmϪ1
F(000)
0.079
632
0.074
1728
Crystal size /mm3
0.30x0.22x0.14
3.73 to 25
Ϫ9 Յ h Յ 9
Ϫ20 Յ k Յ 20
Ϫ12 Յ l Յ 12
7812
0.30x0.25x0.08
3.02 to 26
Ϫ35 Յ h Յ 35
Ϫ12 Յ k Յ 10
Ϫ17 Յ l Յ 18
25363
Theta range for data collection /°
Index ranges
Reflections collected
Independent reflections
Completeness to theta /%
Max. And min. transmission
Data / restraints / paramters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
2714 [R(int) ϭ 0.0496]
θ ϭ 25.00°: 99.0
8364 [R(int) ϭ 0.0666]
θ ϭ 26.00°: 98.9
0.9941 and 0.9782
8364 / 1 / 578
0.998 and 0.845
2714 / 0 / 209
1.033
R1 ϭ 0.0419, wR2 ϭ 0.1038
R1 ϭ 0.0564, wR2 ϭ 0.1133
1.004
R1 ϭ 0.0457, wR2 ϭ 0.0804
R1 ϭ 0.0974, wR2 ϭ 0.0926
0.0100(8)
Extinction coefficient
Largest diff. Peak and hole (e/ A )
3
˚
0.168 and Ϫ0.185
0.124 and Ϫ0.150
(95 mm CCD camera on κ-goniostat) using graphite-monochrom-
ated MoKα radiation (0.71073 A). Data were collected with a re-
dundancy of 4. The final unit cell parameters were based on all
reflections. Data collections were made using the COLLECT pro-
gram [24]; integration and scaling of the reflections were performed
with the HKL Denzo-Scalepack system of programs [25]. Multi-
scan absorption correction was applied [26].
Colorless prismatic crystals; soluble in acetone, acetonitrile, chloro-
form and toluene. Mp 125Ϫ127 °C. Calc. for C17H14BNO2
(275.11): C 74.22; H 5.13; N 5.09 %. Found: C 75.12; H 4.98; N
5.28 %.
NMR spectra (CDCl3, δ/ppm): 1H 6.75 (ddd, J ϭ 7.8, 6.6, 1.1 Hz, 1H), 7.01
(dd, J ϭ 8.7, 1.1 Hz, 1H), 7.19-7.33 (m, 6H), 7.50-7.56 (m, 5H), 8.02 (dd,
J ϭ 6.5, 1.1 Hz, 1H). 13C 111.01, 113.60, 126.92, 127.28, 130.93, 131.66,
138.44, 145.2, 156.60. 11B 15.5. IR (KBr, cmϪ1): 3093 ms, 3057 ms, 3005 m,
1630 vs, 1567 ms, 1519 vs, 1453 ms, 1432 ms, 1361 ms, 1263 ms, 1213 s,
1189 ms, 1150 s, 930 ms, 903 s,881 s, 758 s, 738 s, 704 vs, 613 ms, 582 m,
421 m.
˚
The structures were solved by direct methods with SHELXS-97
[27]. The model was refined by full-matrix least squares on F2 with
SHELXL-97 [28]. All the hydrogen atoms were stereochemically
positioned and refined with the riding model [29]. Hydrogen atoms
of the CH and CH2 groups were set isotropic with a thermal par-
ameter 20 % greater than the equivalent isotropic displacement par-
ameter of the atom to which each one was bonded. This percentage
was set to 50 % for the hydrogen atoms of the CH3 and OH groups.
Data collections and experimental details for the complexes are
summarized in Table 3. The programs SHELXL-97 [28], and OR-
TEP-III [29] were used within WinGX [30] to prepare materials
for publication.
(Maltolato)diphenylboron (2)
Reaction time 12 h. The resulting solution is hot filtered and cooled
on ice. The crystallized product is filtered off and air-dried. Yield
62 %. Colorless crystal leaflets, soluble in acetonitrile and DMSO.
Mp 200-202 °C. Calc. for C18H15BO3 (290.13): C 74.52; H 5.21 %.
Found: C 74.52; H 5.46 %.
NMR spectra (CD3CN, δ/ppm): 1H 2.52 (s, 3H, CH3), 6.99 (d, J ϭ 5.1 Hz,
1H), 7.14-07.27 (m, 6H, CHarom), 7.39-7.44 (m, 4H, CHarom), 8.31 (d, J ϭ
5.1 Hz, 1H). 13C 14.97, 107.15, 127.43, 128.13, 132.47, 151.68, 153.04,
161.29, 176.16. 11B 17.6. IR (KBr, cmϪ1): 1638 s, 1572 vs, 1560 vs, 1468 vs,
1432 ms, 1298 s, 1270 m, 1251 m, 1209 s, 1105 m, 942 ms, 904 ms, 881 s,
859 ms, 828 ms, 754 s, 744 s, 708 s, 647 ms, 616 ms, 588 m, 537 m.
Syntheses
General procedure
NH4BPh4 and the reactant LH (1.0 mmol respectively) are kept
under reflux at 135Ϫ140 °C in 25 mL toluene until the evolution of
ammonia has ceased (controlled with a pH-strip in the gas phase).
(1-Phenylazo-2-naphtholato)diphenylboron (3)
Reaction time 20 h. The resulting deep red solution is filtered and
the filtrate evaporated to dryness. Yield 92 %. Red prismatic crys-
tals; soluble in usual organic solvents. Recryst. from methanol. Mp
195 °C. Calc. for C28H21BN2O (412.30): C 81.57; H 5.13; N 6.79 %.
Found: C 81.72; H 4.96; N 6.81 %.
(2-Pyridinolato-N-oxide)diphenylboron (1)
Reaction time 15 h. The resulting cold solution is filtered and the
filtrate evaporated to dryness. Yield 93 %. Recryst. from ethanol.
1938
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 1935Ϫ1940

An Alternative Method for the Preparation of Diphenylboron Chelates.
NMR spectra (CDCl3, δ/ppm): 1H 7.11-7.30 (m), 7.39-7.47 (m), 7.56-7.62
(m), 7.67 (dd, J ϭ 8.1, 0.6 Hz), 7.91 (d, J ϭ 9.0 Hz), 8.42 (dd, J ϭ 8.1,
0.5 Hz). 13C 120.58, 121.33, 124.47, 125.74, 126.86, 127.21, 128.24, 128.93,
129.53, 129.58, 129.74, 132.49, 142.48, 148.08, 154.79. 11B 1.2. IR (KBr,
cmϪ1): 1617 m, 1589 m, 1556 m, 1508 s, 1489 m, 1456 m, 1443 m, 1432 m,
1384/1357 vs, 1294 ms, 1280 ms, 1212 s, 1191 ms, 1146 s, 1007 ms, 963 m,
919 m, 887 ms, 838 ms, 751 vs, 720 m, 702 s, 689 s, 662 m, 563 m, 489 m. UV-
VIS (CHCl3, λmax nm/logε) 330/3.879, 414/4.008, 498/4.177.
131.42, 148.0 (Carom); 173.60 (COO). 11B 6.3. IR (KBr, cmϪ1): 3270 ms,
3206 m, 3099 s, br, 1702 vs, 1603 s, 1434 ms, 1339 ms, 1316 ms, 1276 s, 1246 s,
1170 m, 1008 m, 954 ms, 868 m, 762 m, 740/734 m, 711 s, 680 m, 643 m,
593 m, 503 m.
Supplementary Information Ϫ Supplementary Crystallographic
data have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication nos. CCDC 265848 &
265849 for compound 5 and 3, respectively.. Copies of available
material can be obtained, free of charge on application to the Di-
rector, CCDC, 12 Union Road, Cambridge CH2 1EZ, UK (fax:
ϩ44-1223-336-033 or e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk).
(β-Alaninato)diphenylboron (4)
Reaction time 20 h. The solid product is filtered off, air-dried and
washed with water. Yield 93 %. Colorless crystal needles; soluble
in DMSO. Recryst from methanol. Mp 255 °C (dec.). Calc. for
C15H16BNO2 (253.11): C 71.18; H 6.37; N 5.53 %. Found: C 71.20;
H 6.06; N 5.78 %.
NMR spectra (DMSO-d6, δ/ppm): 1H 2.46 (t, J ϭ 6.4 Hz, 2H, CH2), 2.84 (t,
br, 2H, NCH2), 6.78 (s, br, 2H, NH2), 7.06-7.12 (m, 2H, p-C6H5), 7.15-7.22
(m, 4H, m-C6H5), 7.38-7.44 (m, 4H, o-C6H5). 13C 30.03 (CH2), 35.50 (CH2),
125.67, 127.07, 130.81, 149.30, 169.41 (COO). 11B 3.0. IR (KBr, cmϪ1):
3171 vs, br, 3110 vs, br, 3001 ms, 2910 m, 1643 vs, 1607 s, 1432 ms, 1418 m,
1361 vs, 1313 ms, 1268 m, 1228 m, 1206 m, 1178 m, 1158 s, 1050 m, 998 ms,
917 ms, 893 m, 841 m, 738 s, 703 s.
Acknowledgements. The authors are indebted to Prof Dr. Dr. h.c. J.
Strähle (University of Tübingen) for the use of the diffractometer.
Financial support from the Brazilian Agencies CNPq (Proj. no
471314/2003-0) and FINEP (Proj. no 0970/01 CT-INFRA) is grate-
fully acknowledged.
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7.8, 5.7, 1.2 Hz, 1H), 8.46 (ddd, J ϭ 7.8, 1.2 Hz, 1H), 8.64 (ddd, J ϭ 7.8,
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