Pyrazole complexes of acyloxydialkylboranes

Article abstract of DOI:10.1016/S0022-328X(98)00824-9

The reaction of Me₃CCOOBEt₂ with pyrazole led to the formation of the stable addition complex 1, which was found to be monomeric in solution. The reaction of 9-H-9-borabicyclo[3.3.1]nonane (9-H-9-BBN)₂ with pyrazole and pivalic acid yielded a similar complex Me₃CCOO(9-BBN)-pzH 2. Crystallographic analysis of 2 revealed a dimeric structure due to the strong hydrogen bonding between azole hydrogen and carbonyl oxygen. The one boron-carbon bond of compound 1 cleaves readily with triethylborane at 20°C with the evolution of ethane, giving a species Me₃CCOO(BEt₂)₂pz 3 with a seven-membered heterocyclic ring as the main structural feature.

Full text of DOI:10.1016/S0022-328X(98)00824-9

Journal of Organometallic Chemistry 570 (1998) 31–37
Pyrazole complexes of acyloxydialkylboranes
Marek D a¸ browski, Tomasz Kli s´ , Sergiusz Luli n´ ski, Izabela Madura, Janusz Serwatowski *,
Janusz Zachara
Warsaw Uni6ersity of Technology, Faculty of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland
Received 6 April 1998; received in revised form 28 June 1998
Abstract
The reaction of Me CCOOBEt with pyrazole led to the formation of the stable addition complex 1, which was found to be
3
2
monomeric in solution. The reaction of 9-H-9-borabicyclo[3.3.1]nonane (9-H-9-BBN) with pyrazole and pivalic acid yielded a
2
similar complex Me CCOO(9-BBN)-pzH 2. Crystallographic analysis of 2 revealed a dimeric structure due to the strong hydrogen
3
bonding between azole hydrogen and carbonyl oxygen. The one boron–carbon bond of compound 1 cleaves readily with
triethylborane at 20°C with the evolution of ethane, giving a species Me CCOO(BEt ) pz 3 with a seven-membered heterocyclic
3
2 2
ring as the main structural feature. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Acyloxyboranes; Pyrazaboles; Pyrazole; Crystal structure; NMR spectroscopy
the protolytic reagent and is thought to be simple in the
case of water and alcohols and more complicated in the
case of primary amines. The formation of stable addi-
tion complexes of Me C–COOBEt with ammonia and
1
. Introduction
The substitution of acidic hydrogen in a pyrazole
molecule (pzH) with a dialkylboryl group leads to the
formation of the so-called tetraalkylpyrazaboles [1]
which exist usually as very stable dimers with a six-
membered B N ring. Standard syntheses of te-
3
2
primary amines was proved by K o¨ ster et al. [9].
We have found that pivalic acid or Me CCOOBEt
3
2
act as a catalysts also in the synthesis of 4,4,8,8-te-
2
4
traethylpyrazabole (TEP) from Et B and pzH. In this
3
traalkylpyrazaboles involve non-catalyzed reactions of
pzH with trialkylboranes or tetraalkyldiboranes(6) [2]
or, more recently, alkylation of B-halogenated pyraz-
aboles with lithium or magnesium alkyls [3]. The for-
mer require elevated temperatures, usually 130–150°C,
due to the great stability of the boron–carbon bond.
Carboxylic acids are well-known reagents which readily
cleave B–C bonds of trialkylboranes. The mechanism
of this cleavage was proposed earlier by Brown [4] and
Dessy [5,6]. Pivalic acid and/or its borylated derivatives
Me CCOOBR have been widely used for many years
paper we report the preparation and structural charac-
terization of addition complexes of Me CCOOBR
3
2
(
R=Et (1), R =1,5-cyclooctandiyl (2)) with pyrazole.
2
We suppose that
1
as well as its derivative
Me CCOO(BEt ) pz 3 are intermediates in the catalytic
3
2 2
cycle leading to the formation of TEP.
2. Results and discussion
3
2
as active catalysts in protolysis of trialkylboranes [7,8].
The mechanism of this catalysis depends on the type of
The reaction of Me C–COOBEt with pyrazole in
the molar ratio 1:1 afforded the addition complex 1 as
an oily liquid, according to Eq. 1 (Scheme 1).
3
2
The presence of the hydrogen bond in the molecule
of 1 has been confirmed by the solution infrared spec-
*
Corresponding author. Fax: +48 22 6282741; e-mail: ser-
wat@ch.pw.edu.pl
0022-328X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00824-9

32
M. D a¸ browski et al. / Journal of Organometallic Chemistry 570 (1998) 31–37
ture with ethane evolution. It is well-known that com-
plexes of Et B with nitrogen donors have generally a
3
significant dynamic character [10] and we have also
11
proved this for Et B*pzH complex by B-NMR exper-
3
iments which showed the dependence of the chemical
shift on the Et B:pzH molar ratio. The mode of forma-
3
tion of complex 1 remains essentially the same as
described above. Nevertheless, it should be stressed that
Scheme 1.
the protolysis of Et B with pivalic acid in the system
3
trum which exhibits a broad band of the associated NH
Et B/pzH, i.e. the formation of Me CCOOBEt , is
3
3
2
−
1
group in the range of 3300–2300 cm . The molecular
weight determination of 1 in benzene, points to a
monomeric structure in solution. These results allowed
to conclude that the additional stabilization of the
molecule is reached owing to the intramolecular hydro-
gen bonding and the formation of the seven-membered
ring structure. This observation can also be supported
by the fact that our attempts to obtain the correspond-
ing complex of type 1 with imidazole were unsuccessful.
slowed down by the competition of the much stronger
base pzH (rapid cleavage of Et B by pivalic acid in the
3
absence of pzH is observed at 0°C [8]).
Another species of type 1 was synthesized in a one-
pot reaction from (9-H-9-BBN) , pyrazole and pivalic
2
acid, as is shown below (Eq. (2)):
3
Me CCOOH+pzH+1/2(9-H-9-BBN)2
“
Me CCOO(9-BBN)-pzH
(2)
3
1
3
In the C-NMR spectrum of 1, three signals of the
three non-equivalent carbon atoms of the pyrazole ring
are observed, which is in agreement with the structure
Compound 2 is a crystalline solid moderately air-stable
slow decomposition after several days was observed). 2
(
1
proposed for 1. However, the H-NMR spectrum
in comparison with 1, is more stable, which is confi-
1
shows that complex 1 has a dynamic character (on the
rmed by its H-NMR spectrum, where two doublets of
1
H-NMR time scale). As a result two hydrogen atoms
two hydrogen atoms: H3 and H5 are observed (at room
temperature). Molecular weight measurements revealed
that 2 exists in solution as a monomer (Scheme 2). The
solution infrared spectrum of 2 suggests the existence of
an intramolecular hydrogen bond N–H–O (the broad
H3 and H5 bound to carbon atoms C3 and C5 become
equivalent and give, at room temperature, one broad-
ened signal. The process is slowed down below 0°C
where two well resolved doublets appear in the spec-
trum. The nature of this process is somewhat unclear
and it could be explained in different ways. One possi-
bility is the slow dissociation of 1 with subsequent
exchange of pyrazole. However, flipping of the pyrazole
ring in a molecule of 1 cannot be completely excluded
although it would involve a transfer of azole hydrogen
to carbonyl oxygen. Complex 1 is stable and can be
stored at room temperature during several weeks with-
out decomposition. It is also stable during several hours
−
1
band with a maximum at 3125 cm ).
The X-ray structure analysis of 2 shows that there
are two independent dimers in the unit cell located over
crystallographic centres of symmetry as shown in Fig.
1. The molecular structure of one of these dimers is
presented in Fig. 2. Both dimers are chemically identi-
cal as confirmed by precise geometry analyses; the bond
lengths (Table 1) are the same within 3|, but this is not
the case for some angles, e.g. B(1)–O(11)–C(31) and
B(2)–O(21)–C(81), suggesting slight differences in the
geometry of these dimers.
at 60°C in CDCl . Neat 1 decomposes rapidly only
3
above 100°C to give TEP and pivalic acid.
The synthesis of 1 was also accomplished starting
from the triethylborane-pyrazole complex and pivalic
acid. This reaction proceeds rapidly at room tempera-
The comparison of adequate torsion angles (Table 5)
leads to a conclusion that there are two different con-
formers, possibly due to crystal packing. The biggest
Scheme 2.

M. D a¸ browski et al. / Journal of Organometallic Chemistry 570 (1998) 31–37
33
one signal at 10.3 ppm in the region typical for the
tetracoordinated boron atom bonded to one oxygen,
1
one nitrogen and two carbon atoms. The H- and
1
3
C-NMR spectra point to a symmetrical arrangement
of the pyrazole ring. In the infrared spectrum an ab-
−
1
sorption band of the CꢀO group at 1590 cm
is most
noteworthy as it occurs in the range typical for the
carbonyl group coordinating the boron atom [9,15].
Compound 3 is stable and decomposes rapidly only
above 100°C to give TEP and Me C–COOBEt . 3 can
3
2
be also synthesized by borylation of 1 with Me C–
3
COOBEt . However, the best method which yielded the
2
desired product free of impurities was the one-pot
synthesis from 1 equivalent of pivalic acid, 1 equivalent
of pzH and 2 equivalents of Et B. Probably an impor-
3
š
š
tant role in the Et B /H exchange is played by the
2
carbonyl group, which coordinates the boron atom
analogously as it was proved in the reaction of car-
boxylic acids with R B. Unfortunately, we were unable
3
to synthesize a crystalline compound of type 3 in order
to confirm the proposed structure by X-ray diffraction.
The attempt to obtain a similar compound from 2 and
9
-H-9-BBN failed due to side reactions. Finally, the
Fig. 1. Packing diagram of 2.
treatment of 1 equivalent of benzoic acid and 1 equiva-
lent of 3,5-dimethylpyrazole with 2 equivalents of Et B
3
difference for torsion angles are within conformation of
the boron atom, pz and the carboxylic group. The
boron atom for dimer 2B lies on the opposite side of
the pz plane than the O(21) atom. This is confirmed by
different sign of the torsion angles for B(1)–N(11)–
N(12)–C(23) and B(2)–N(21)–N(22)–C(73), respec-
tively. The distance of boron atoms from pz planes for
resulted in the evolution of only 1 equivalent of ethane
and a crystalline complex of PhCOOBEt2 with 3,5-
dimethylpyrazole 4 was isolated. This complex was
found to be inert in the protolysis of Et B, even at
3
elevated temperature, which can clearly be explained by
the steric influence of methyl groups. The question
whether the methyl group in the ortho position to the
˚
NH bond hinders the coordination of the Et B
3
dimer 2A is 0.131(3) and 0.051(3) A for dimer 2B [11].
molecule by the carbonyl group sufficiently to prevent
subsequent protolysis or rather the formation of the
appropriate rotamer in which the distance between
carbonyl and NH groups is small, remains open.
Centrosymmetric dimers are formed due to the rela-
tively strong hydrogen bonding resulting in the forma-
tion of the 14-membered heterocyclic ring (Fig. 2).
˚
The N…O% distance of 2.722(2) A observed for pair
In conclusion, pyrazole complexes of Me C–
3
2
A–2A% is slightly shorter than that for the pair 2A–2A%
COOBEt2 were found to have interesting structural
properties in the liquid as well as in the solid state. The
specific arrangement of NH and carbonyl groups in the
molecule of 1 is responsible for the much higher activity
of the azole hydrogen in the cleavage of the boron–car-
bon bond in the molecule of triethylborane than it is
observed in the case of pyrazole. The role of complexes
of type 1 and 3 in the catalyzed synthesis of te-
traalkylpyrazaboles will be investigated.
˚
(
2.784(3) A), where typical N…O distances lie within
˚
2
.79–2.68 A [12] (Tables 2 and 3).
Complex 1 reacts rapidly with triethylborane in hep-
tane at room temperature with ethane evolution. The
product obtained was as an oily liquid, after evapora-
tion of the solvent. Spectroscopic data and molecular
weight determination indicated that the borylation of 1
resulted in the formation of a new heterocyclic system
3
, consisting of seven-membered CO B N and pyrazole
2 2 2
fused rings, according to Eq. 3 (Scheme 3).
Compound 3 represents a new type of a pyrazolylbo-
rane adduct, although similar species where the car-
boxyl group is replaced by hydrogen, -OH as well as
3
. Experimental section
1
13
11
H-, C-, B-NMR as well as IR spectra were
-
SH groups were reported [2,13]. On the other hand,
recorded at room temperature (unless otherwise noted).
Chemical shifts are given in ppm relative to TMS in H-
1
species possessing a six-membered CO B N ring, where
2
2
13
the pz ring is replaced by the bridging -NH group, are
and C-NMR spectra and relative to Et O*BF in
2
2 3
11
11
also known. [9,14]. The B-NMR spectrum of 3 shows
B-NMR spectra. The solvent was CDCl (NMR spec-
3

34
M. D a¸ browski et al. / Journal of Organometallic Chemistry 570 (1998) 31–37
Fig. 2. ORTEP [18] plot of the molecular structure of one of the independent centrosymmetric dimers of Me CCOO(9-BBN)-pzH 2. Thermal
3
ellipsoids are drawn at 50% probability level; the hydrogen atoms, except NH groups, are omitted for clarity.
tra). Molecular weight determinations were performed
cryoscopically in benzene. Triethylborane, 98%, was
received from MPI f u¨ r Kohlenforschung, M u¨ lheim/
Ruhr. Pyrazole and pivalic acid were received from
under reduced pressure. The product (51.0 g, yield 99%)
was obtained as a colourless oily liquid.
1
H-NMR (300 MHz) l: 10.1 (br, 1H, NH), 7.64 (d,
2H, CH), 6.45 (t, 1H, CH), 0.65 (t, 9H, CH ), 0.42 (q,
3
1
1
Aldrich,
and
were
laboratory
grade.
(2,2-
6H, CH ); B-NMR (96.24 MHz) l: 0.0; IR (CCl4):
2
−
1
Dimethyl)propanoiloxydiethylborane was synthesized
as described in the literature [8]. All reactions were
carried out under dry argon using standard Schlenk
techniques. Pyrazole and benzoic acid were dried in
vacuo prior to use. Solvents were dried by conventional
methods. Other reagents were used without
purification.
3450 cm
(sharp, N–H).
3
.2. Preparation of the addition complex of
Me C–COOBEt with pzH (1)
3
2
A solution of pyrazole (2.26 g, 33.2 mmol) in chloro-
form (10 ml) was dropped in during 30 min to the
solution of Me C–COOBEt (5.68 g, 33.5 mmol) in
3
2
chloroform (10 ml) at 0°C. The solvent was removed in
vacuo, to give 1 (7.90 g, yield 100%) as a colourless
liquid.
3
.1. Preparation of the Et B pzH complex
3
ꢀ
Et B (31.0 g, 0.32 mol) was added to a suspension of
3
pyrazole (21.1 g, 0.31 mol) in heptane (100 ml). The
rate of dropping in was adjusted to maintain the tem-
Table 2
Selected bond angles (°)
perature below 15°C. After the addition of Et B the
3
solvent and the excess of Et B were evaporated off
3
O(11)–B(1)–C(11)
O(11)–B(1)–C(15)
C(11)–B(1)–C(15)
115.0(2)
107.3(2)
107.4(2)
O(21)–B(2)–C(61)
O(21)–B(2)–C(65)
C(61)–B(2)–C(65)
O(21)–B(2)–N(21)
C(61)–B(2)–N(21)
C(65)–B(2)–N(21)
B(2)–O(21)–C(81)
N(22)–N(21)–B(2)
C(73)–N(22)–H(2)
N(21)–N(22)–H(2)
O(22)–C(81)–O(21)
115.4(2)
107.1(2)
106.9(2)
105.4(2)
111.6(2)
110.2(2)
126.0(2)
123.8(2)
129.0(2)
120.0(2)
123.3(2)
Table 1
Selected bond lengths (A)
˚
O(11)–B(1)–N(11) 104.2(2)
C(11)–B(1)–N(11)
C(15)–B(1)–N(11)
B(1)–O(11)–C(31)
N(12)–N(11)–B(1) 124.1(2)
C(23)–N(12)–H(1) 126.5(1)
N(11)–N(12)–H(1) 122.9(1)
O(12)–C(31)–O(11) 123.4(2)
111.9(2)
110.8(2)
124.3(2)
O(11)–C(31)
O(11)–B(1)
O(12)–C(31)
N(11)–N(12)
N(11)–B(1)
N(12)–H(1)
1.300(2)
1.521(3)
1.221(2)
1.338(2)
1.600(3)
0.89(2)
O(21)–C(81)
O(21)–B(2)
O(22)–C(81)
N(21)–N(22)
N(21)–B(2)
N(22)–H(2)
1.304(3)
1.524(3)
1.219(3)
1.343(2)
1.603(3)
0.84(2)

M. D a¸ browski et al. / Journal of Organometallic Chemistry 570 (1998) 31–37
35
Table 3
Selected torsion angles (°)
N(12)–N(11)–B(1)–O(11)
C(31)–O(11)–B(1)–N(11)
B(1)–O(11)–C(31)–O(12)
C(21)–N(11)–B(1)–O(11)
C(21)–N(11)–B(1)–C(11)
N(12)–N(11)–B(1)–C(11)
C(21)–N(11)–B(1)–C(15)
B(1)–N(11)–N(12)–C(23)
C(31)–O(11)–B(1)–C(11)
C(31)–O(11)–B(1)–C(15
N(12)–N(11)–B(1)–C(15)
N(11)–B(1)–C(11)–C(12)
B(1)–N(11)–C(21)–C(22)
B(1)–O(11)–C(31)–C(32)
98.0(2)
−62.6(2)
0.7(3)
−74.6(3)
160.5(2)
−26.9(3)
40.6(3)
N(22)–N(21)–B(2)–O(21)
C(81)–O(21)–B(2)–N(21)
B(2)–O(21)–C(81)–O(22)
C(71)–N(21)–B(2)–O(21)
C(71)–N(21)–B(2)–C(61)
N(22)–N(21)–B(2)–C(61)
C(71)–N(21)–B(2)–C(65)
B(2)–N(21)–N(22)–C(73)
C(81)–O(21)–B(2)–C(61)
C(81)–O(21)–B(2)–C(65)
N(22)–N(21)–B(2)–C(65)
N(21)–B(2)–C(61)–C(62)
B(2)–N(21)–C(71)–C(72)
B(2)–O(21)–C(81)–C(82)
91.7(2)
−69.4(2)
7.1(3)
−91.1(3)
142.9(3)
−34.3(4)
24.3(4)
−174.5(2)
60.3(3)
177.9(2)
54.2(3)
179.8(2)
−146.8(2)
−63.0(2)
173.7(2)
−177.8(2)
173.1(2)
−153.0(2)
−61.4(3)
−177.5(2)
−172.4(2)
Table 4
Anal. Found: C, 59.84; H, 9.93; N, 11.92. Anal. Calc.
1
Crystal data and refinement data for 2
for C H BN O : C, 60.52; H, 9.74; N, 11.76. H-NMR
1
2
23
2
2
(
500 MHz, 273 K) l: 15.3 (br, 1H, NH), 7.65 (d, 1H,
Empirical formula
Formula weight
Crystal class
C16H27BN O
2 2
290.21
Triclinic
P1
(
CH), 7.60 (d, 1H, CH), 6.38 (t, 1H, CH), 1.21 (s, 9H,
(
(
1
BCH ), 8.7 (BCH CH ); B-NMR, l (96.24 MHz): 7.0;
IR (CCl ): 3300–2300 cm
1
3
CH ) C), 0.8–0.5 (m, 10H, B(C H ) ); C-NMR, l
3
3
2
5 2
50.28 MHz): 185.7 (CꢀO), 134.7 (CH), 130.3 (CH),
Space group
Unit cell parameters
05.4 (CH), 39.7 ((CH ) C), 27.3 (CH ) C, 11.8 (br,
3
3
3 3
˚
1
1
a (A)
10.419(1)
12.642(2)
14.611(2)
70.065(9)
74.857(9)
81.99(1)
1743.7(3)
4
1.105
632
0.20×0.32×0.38
0.071
2
2
3
˚
b (A)
−
1
−1
(N–H···O), 1700 cm
4
˚
c (A)
(
CꢀO···H).
h(°)
i (°)
k(°)
3
2
.3. Reaction of (9-H-9-BBN) with pyrazole and
2
˚
3
V (A )
,2-dimethylpropanoic acid
Z
Dcalc. (Mg m−3)
F(000)
A solution of pivalic acid (0.204 g, 2.0 mmol) and pzH
0.130 g, 2.0 mmol) in toluene (7 ml) to a cooled (0°C)
solution of (9-H-BBN) (0.243 g, 1.0 mmol) in toluene
(
Crystal size (mm)
Absorption coefficient
2
−
1
(
mm
)
(
5 ml) was added. The cooling bath was removed and the
˚
Radiation
Mo–Kh (u=0.71073 A),
graphite-monochromated
293(2)
reaction was allowed to warm up to room temperature.
Hydrogen (42 Nml, 95%) evolved. Evaporation of the
solvent afforded a crystalline solid 2 (0.55 g, yield 96%).
Anal. Found: C, 67.58; H, 9.80; N, 9.85. Anal. Calc. for
C H BN O : C, 66.25; H, 9.32; N, 9.66. H-NMR (300
MHz): (1.13, s, 9H, t-Bu); (1.1–1.9, m, 14H, 9-BBN);
Temperature (K)
Scan type
2q range for data collection 4.06–50.10
Standard reflections
Crystal decay (%)
Index ranges
q−2q
1
Two measured every 70 reflections
2.19
05h 512, −145k 515,
1
6
27
2
2
(
6.40, t, 1H, pz); (7.60, d, 1H pz), (7.76, d, 1H, pz);
−
165l517
1
1
−1
B-NMR (96.24 MHz) l: 6.3; IR (CCl ): 3125 cm
4
Reflections collected
Independent reflections
Reflections observed
6227
−
1
(
N–H···O), 1690 and 1630 cm
(CꢀO···H).
5867 (Rint=1.71%)
3339
[
I\2|(I)]
3
.4. Preparation of Me CCOO(BEt ) pz 3 in the
3
2 2
2
Refinement method
Weighting scheme
Full-matrix least-squares on F
reaction of the Me CCOOH*pzH complex with Et B
3
3
2
2
2
w=1/[| (F )+(0.0668·P) , where
o
2
o
2
P=(F +F )/3
c
Et B (6.0 g, 61.2 mmol) was added at −20°C to the
3
Data/restraints/parameters
Final R indices (observed
data)
R indices (all data)
Goodness-of-fit on F
Extinction coefficient
Largest difference peak and +0.179 and −0.127
hole (e A
5866/0/536
R =0.0480, wR =0.1118
1 2
solution of Me CCOOH*pzH (4.18 g, 24.6 mmol) in
3
heptane (15 ml). During 1 h the temperature was raised
gradually to 20–30°C. To complete the reaction the
solution was stirred for 10 min at 55°C. The total volume
of ethane evolved was 1.05 Nl (95%). After evaporation
of the solvent a colourless, oily liquid 3 was obtained
R =0.0975, wR =0.1334
1 2
0.985 (all) 1.143 (observed)
0.006(1)
2
˚
−3
)
(
7.50 g, yield 100%).

36
M. D a¸ browski et al. / Journal of Organometallic Chemistry 570 (1998) 31–37
Table 5
Anal. Found: C, 62.66; H, 10.71; N, 9.40. Calc. for
4
1
Atomic coordinates (×10 ) and equivalent isotropic displacement
parameters (A ×10 )
C H B N O : C, 62.79; H, 10.54; N, 9.15. H-NMR
1
6
32
2
2
2
2
3
˚
(
(
300 MHz) l: 7.55 (d, 2H, CH), 6.28 (t, 1H, CH), 1.26
13
s, 9H, (CH ) C), 0.70–0.55 (m, 20H, B(C H ) ); C-
3
3
2
5 2
Atom
x
y
z
Ueq
48(1)
NMR (50.28 MHz) l: 189.9 (COO), 136.6 (CH), 104.6
O(11)
O(12)
N(11)
N(12)
B(1)
4148(2)
7316(1)
8648(1)
8829(1)
9866(2)
8098(2)
8875(2)
9594(2)
8970(3)
8061(3)
7326(2)
6548(2)
7140(3)
8091(3)
8543(3)
9394(3)
10220(3)
7656(2)
6720(2)
7139(2)
6435(3)
5694(2)
2692(1)
829(1)
2248(1)
1163(2)
2833(2)
2338(2)
2567(2)
3780(3)
4398(2)
4159(2)
4681(3)
4152(3)
2859(3)
2673(2)
1870(3)
918(2)
798(1)
584(1)
1133(1)
943(2)
391(2)
−749(2)
(
8
(
CH), 41.0 ((CH ) C), 27.1 ((CH ) C), 14.7 (br, BCH ),
3 3 3 3 2
1
1
5482(2)
2521(2)
2901(2)
3037(3)
3461(3)
2247(3)
1016(4)
696(3)
65(1)
45(1)
53(1)
43(1)
49(1)
70(1)
91(1)
84(1)
58(1)
76(1)
86(1)
70(1)
69(1)
85(1)
70(1)
46(1)
54(1)
97(1)
119(1)
113(1)
54(1)
62(1)
48(1)
53(1)
47(1)
52(1)
66(1)
94(1)
78(1)
60(1)
83(1)
91(1)
70(1)
66(1)
80(1)
69(1)
50(1)
72(1)
146(2)
159(2)
162(2)
.9 (BCH CH ). B-NMR (96.24 MHz) l: 10.3; IR
2 3
−
1
CCl ): 1590 cm
(CꢀO···B).
4
3
.5. Preparation of PhCOOBEt*pz*H 4 in the reaction
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(21)
C(22)
C(23)
C(31)
C(32)
C(41)
C(42)
C(43)
O(21)
O(22)
N(21)
N(22)
B(2)
C(61)
C(62)
C(63)
C(64)
C(65)
C(66)
C(67)
C(68)
C(71)
C(72)
C(73)
C(81)
C(82)
C(91)
C(92)
C(93)
2
−1076(2)
−893(3)
128(3)
of PhCOOH with pzH and Et B
3
(
pz*=3,5-dimethylpyrazolyl)
1902(3)
2525(3)
3224(4)
4085(3)
1781(3)
1690(3)
2405(3)
5241(2)
6232(2)
7058(3)
7124(4)
5527(3)
8628(2)
8640(2)
10749(2)
11196(2)
10122(3)
10818(2)
12305(3)
12649(4)
11821(3)
10336(3)
9566(4)
9923(5)
10059(4)
10994(3)
11589(3)
11700(3)
8038(2)
6528(3)
5923(3)
6132(4)
6044(4)
463(2)
Et B (3.90 g, 39.8 mmol) was added at 0°C to the
3
−163(3)
−1242(3)
−1375(2)
2061(2)
2457(2)
1729(2)
851(2)
solution of PhCOOH (2.02 g, 16.6 mmol) and pz*H
1.60 g, 16.6 mmol) in heptane (15 ml). The mixture
was stirred for 2 h at ambient temperature, then was
heated for 30 min at 70°C. Cooling to room tempera-
ture afforded colourless crystals of 4 (3.85 g, yield
(
8
1%). Anal. Found: C, 66.95; H, 8.10; N, 10.00. Anal.
1250(2)
1759(3)
357(3)
Calc. for C H BN O : C, 67.15; H, 8.10; N, 9.79.
1
6
23
2
2
1
H-NMR (200 MHz) l: 14.2 (br, 1H, NH), 8.15 (m,
H, Ph), 7.53–7.38 (m, 3H, Ph), 5.88 (s, 1H, pz*), 2.35
1994(3)
4590(1)
5012(1)
5160(1)
5438(2)
4203(2)
3312(2)
2975(2)
2713(3)
3420(3)
3784(2)
2958(3)
2121(3)
2479(2)
5812(2)
6489(2)
6233(2)
4904(2)
5114(2)
5754(3)
4128(3)
5679(4)
2
(
11
s, 6H, Me), 0.79 (s, 10H, BEt2);
B-NMR (64.16
MHz) l: 8.8.
3
.6. Crystal Structure of 2
A sample of 2 (0.3 g) was dissolved in toluene (15 ml)
at 25°C. Slow cooling in a 0°C freezer gave crystals
suitable for X-ray analysis. Crystal data, data collection
and refinement parameters for 2 are summarized in
Table 4. A single crystal was measured on a Siemens P3
diffractometer at room temperature. The unit cell was
determined by the automating indexing of 24 well cen-
tered reflections. Two standard reflections were moni-
tored every 70 measurements; no significant crystal
decay was detected during data collection. After correc-
tion for the Lorentz-polarization effect and crystal de-
composition, the equivalent reflections were averaged.
The structure was solved by direct methods using the
SHELXS-86 [16] program which revealed the position
of the oxygen, nitrogen, boron atoms and the majority
of the carbon atoms. The distribution of the peaks
showed that the compound crystallizes with two inde-
1746(2)
1897(2)
777(4)
2301(4)
2724(4)
Ueq is defined as one third of the trace of the orthogonalized Uij
tensor.
pendent molecules in the asymmetric unit. Full-matrix
least-squares refinement method against F values was
2
carried out by using the SHELXL-93 [17] program. All
non-hydrogen atoms were refined with anisotropic dis-
placement parameters. Hydrogen atoms of tert-butyl
groups were refined with fixed geometry, riding on their
carrier atoms, with fixed isotropic displacement
parameter equal to 1.5 times the value of the equivalent
isotropic displacement parameter of the parent carbon.
For the other hydrogen atoms positional and isotropic
thermal parameters were refined. The magnitude of the
t
Scheme 3.
thermal parameters observed for one of the Bu-groups

M. D a¸ browski et al. / Journal of Organometallic Chemistry 570 (1998) 31–37
37
[
3] C.M. Clarke, M.K. Das, E. Hanecker, et al., Inorg. Chem. 26
1987) 2310.
(
atoms C(91), C(92), C(93) suggests a possibility of
(
some rotational disorder about the C(81)–C(82) bound
which was not modelled. Final results gave R =0.048
and wR =0.1118. Atomic coordinates for the non-hy-
[
4] H.C. Brown, N.C. H e´ bert, J. Organomet. Chem. 255 (1983) 135.
5] H. Toporcer, R.E. Dessy, S.I.E. Green, J. Am. Chem. Soc. 87
(1965) 1236.
1
[
2
drogen atoms and equivalent isotropic displacement
coefficients are presented in Table 5.
[6] H. Toporcer, R.E. Dessy, S.I.E. Green, Inorg. Chem. 4 (1965)
649.
7] H. Bellut, R. K o¨ ster, K.L. Amen, W. Fenzl, Angew. Chem. 83
1971) 805.
1
[
(
[
[
8] R. K o¨ ster, H. Bellut, W. Fenzl, Liebigs Ann. Chem. (1974) 54.
9] E. Rothgery, R. K o¨ ster, Liebigs Ann. Chem. (1974) 101.
4
. Supplementary material
[
10] H. N o¨ th, B. Wrackmeyer, Nuclear Magnetic Resonance Spec-
troscopy of Boron Compounds, Springer-Verlag, Berlin, 1978, p.
Listings of bond length and angles anisotropic ther-
8
8.
mal parameters and hydrogen atom parameters, tables
of calculated and observed structure factors have been
deposited at the Cambridge Crystallographic Data Cen-
ter.
[11] M. Nardelli, PARST96, J. Appl. Cryst. 28 (1995) 659.
[
12] A.F. Wells, Structural Inorganic Chemistry, PWN Warszawa,
Poland, 1993, p. 316.
[
[
[
13] M. Yalpani, R. K o¨ ster, R. Boese, Chem. Ber. 122 (1989) 19.
14] H.S. Turner, R.J. Warne, J. Chem. Soc. (1965) 6421.
15] P. Idelmann, G. M u¨ ller, W. Scheidt, W Sch u¨ ßler, K. Seevogel,
R. K o¨ ster, Angew. Chem. 96 (1984) 145.
[
[
16] G.M. Sheldrick, SHELXS-86, Acta Crystallogr. Sect. A 46
References
(
1990) 467.
17] G.M. Sheldrick, SHELXL-93, Program for the Refinement of
Crystal Structures; University of G o¨ ttingen, Germany, 1993.
[
[
1] S. Trofimienko, J. Am. Chem. Soc. 89 (1967) 3165.
2] M. Yalpani, R. Boese, R. K o¨ ster, Chem. Ber. 123 (1990) 1285.
[18] M.N Burnet, C.K. Johnson, ORTEP-III, 2996.
.