Towards to the trans-bromination of 2-styrylpyridine with a palladacycle intermediary and structure analysis for trans-1,2-dibromo-2-styrylpyridine

Article abstract of DOI:10.1016/j.molstruc.2010.12.029

The simple halogenation of alkynes in conventional organic reactions gives a blend of cis and trans isomers. It is proposed then, a synthesis of stereospecific halogenation of alkynes in trans position, using palladacycle as intermediaries. The recrystallization of the compound obtained by bromination of 2-Styrylpyridine, with cyclepalladium intermediary results in a single crystal, which is subjected to X-ray diffraction. The crystal packing is established through weak interactions of three types. The first one is of the type π × π interactions, from symmetry operation, between the centroids. The second one is of the type C-X?π interactions. And the last type is an anomalous intermolecular interaction between halogens, C-X?X-C, with bond distances smaller than the sum of the van der Waals radii. The conformation on the C=C bond is trans and the dihedral angle between the aromatic rings is (with esd approximate) 18.1(3)°.

Full text of DOI:10.1016/j.molstruc.2010.12.029

Journal of Molecular Structure 988 (2011) 87–90
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Towards to the trans-bromination of 2-styrylpyridine with a palladacycle
intermediary and structure analysis for trans-1,2-dibromo-2-styrylpyridine
a
b
Ana Carolina Mafud a, , Maria Teresa do Prado Gambardella , Antonio Carlos Fávero Caires
⇑
a Instituto de Química de São Carlos, Universidade de São Paulo, Brazil
b Centro Interdisciplinar de Investigação Bioquímica, Universidade de Mogi das Cruzes, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
The simple halogenation of alkynes in conventional organic reactions gives a blend of cis and trans isomers.
It is proposed then, a synthesis of stereospecific halogenation of alkynes in trans position, using palladacy-
cle as intermediaries. The recrystallization of the compound obtained by bromination of 2-Styrylpyridine,
with cyclepalladium intermediary results in a single crystal, which is subjected to X-ray diffraction.
The crystal packing is established through weak interactions of three types. The first one is of the type
Received 1 December 2010
Accepted 12 December 2010
Available online 21 December 2010
Keywords:
Trans-1,2-dibromo-2-styrylpyridine
X-ray diffraction
Stereospecificity
2-Styrylpyridine
p
Â
p
interactions, from symmetry operation, between the centroids. The second one is of the type CAXÁ Á Á
p
interactions. And the last type is an anomalous intermolecular interaction between halogens, CAXÁ Á ÁXAC,
with bond distances smaller than the sum of the van der Waals radii. The conformation on the C@C bond is
trans and the dihedral angle between the aromatic rings is (with esd approximate) 18.1(3)°.
Ó 2010 Elsevier B.V. All rights reserved.
Palladacycle complex
p
Ring interaction
1. Introduction
in [16,17] by changing the reaction’s temperature to 0 °C which in-
creases the yield of the reaction. The product characterization was
Textbook mechanism of the trans-bromination of alkynes via a
more or less symmetrically bridged bromonium ion does not al-
ways apply [1].
done by analyzing one single crystal of it through the X-ray
diffraction.
Therefore, studies for new routes of bromination have contin-
ued to attract the interest of researchers due to the difficulty of
controlling the product stereoselectivities [2–4]. The bromination
of alkynes through cyclepalladated includes the coordination of
the heteroatom to palladium followed by an interaction of the tri-
ple bond with the metal center [5]. The intermolecular nucleophilic
attack of bromide ion binding to CtripleC coordinated to atom of
palladium results in a palladacycle thermodynamically stable [6].
As a consequence of interactions palladium-alkyne, the formation
of a wide range of cyclopalladated derivatives of amines and thio-
ethers propargylic differently functionalized occurs [7]. The palla-
dacycles have been receiving closer attention lately because of
the possibility of its application in several areas [8]. As examples,
it can be cited: organic synthesis [9,10]. Development of new
materials to obtain liquid crystals [11]. Bio-organometallic chemis-
try and antitumor chemotherapeutic agent [12]. Photochemical
reactions of electron transfer [13]. In catalysis as catalyst precur-
sors in a wide range of reactions such as hydrogenation [14,15].
This work have proposed a new stereospecific synthesis, as a
reaction intermediate cyclepalladated. A departure complex cycle-
palladated was obtained and characterized as previously described
2. Methods
2.1. Synthesis of pyridinyl-phenyl-ethyne
The functionalized alkyne pyridinyl-phenyl-ethyne was ob-
tained by stoichiometric reaction between 2-bromo-pyridine and
phenylacetylene, using diethylamine as a solvent and 0.1 t% Pd
Cl2 (PPh3)2/CuI in equal proportions as a catalyst. The reaction
was performed during 3 h on constant agitation in argon atmo-
sphere and at a temperature of 0 °C, using an ice bath. The diethyl-
amine was then removed by distillation at reduced pressure. The
catalyst was removed by filtration on Celite (L = 3.0 cm,
Ø = 3.0 cm) and the product was purified by extraction with hex-
ane followed by micro distillation at reduced pressure (te = 74 °C,
P = 10À1 mm Hg) after hexane evaporation. The product, a brown
liquid with high boiling point, was isolated with 80% of yield.
The NMR spectra of 1H {13C} and 13C{1H} were performed on a
Brucker AC-200 spectrometer. 1H NMR (dppm, DCCl3): 8.60–8.56
(m, 2H, Py), 7.67–7.53 (m, 7H, Ar) 13C (1H) NMR (dppm, DCCl3):
90.0 (s, pyAÃC„CA), 90.6 (s,AC„C ÃAØ), 123.0(AÃC(phe)AC„).
The IR spectrum was measured on a spectrometer Perkin–Elmer,
mod. Spectrum-100 spectrophotometer, in the region 4000–
400 cmÀ1, using a resolution of 2 cmÀ1, using Nujol emulsion
⇑
Corresponding author.
E-mail address: mafud@iqsc.usp.br (A.C. Mafud).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.12.029

88
A.C. Mafud et al. / Journal of Molecular Structure 988 (2011) 87–90
Table 2
Crystal data and structure refinaments for trans-1,2-dibromo-2-styril-pyridine.
Empirical formula
C13H9Br2N
Formula weight
339.03
Temperature
293(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Monoclinic
P 1 21/c 1
a
b
c
b
8.8465(9) Å
10.496(2) Å
13.309(2) Å
97.11(1)°
Volume
Z
Calculated density
Absorption coefficient
F(0 0 0)
1226.2(3) A3
4
Fig. 1. The perspective view [22] of the trans-1,2-dibromo-2-styrylpyridine.
1.836 Mg/mÀ3
6.581 mmÀ1
656
Crystal size
h
0.5 Â 0.4 Â 0.4 mm
2.32–28.04°
À11 < h < 11
À13 < k < 0
0 < l < 17
3100/2973
0.0303
Psi-scan
0.3522 and 0.3028
Full-matrix least-squares on F2
2973/0/145
1.030
0.0558, 0.1380
0.1700, 0.1709
1.142 and À0.676 e ÅÀ3
Table 1
Bond lengths (Å) and angles (°), with esd approximate.
Br1AC6
Br2AC7
NAC1
NAC5
C1AC2
C1AC6
C2AC3
C3AC4
C4AC5
C6AC7
C7AC8
C8AC9
C8AC13
C9–10
C10AC11
C11AC12
C12AC13
C1ANAC5
NAC1AC2
NAC1AC6
1.965(1)
2.025(1)
1.346(1)
1.348(9)
1.366(1)
1.499(1)
1.391(1)
1.340(1)
1.361(1)
1.167(1)
1.503(1)
1.379(1)
1.381(9)
1.365(1)
1.347(1)
1.344(1)
1.369(1)
116.6(7)
123.5(7)
116.8(7)
C2AC1AC6
C1AC2AC3
C4AC3AC2
C3AC4AC5
NAC5AC4
119.3(7)
117.5(8)
119.9(7)
119.6(8)
122.8(8)
132.6(1)
114.3(9)
113.1(7)
135.5(1)
113.6(9)
110.9(6)
119.1(7)
121.5(7)
119.4(7)
119.4(7)
122.1(8)
118.0(8)
122.9(8)
118.5(8)
Limiting indices
Reflections collected/unique
R (int)
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
R1, wR2 [I > 2
R1, wR2 (all data)
Largest diff. peak and hole
C7AC6AC1
C7AC6ABr1
C1AC6ABr1
C6AC7AC8
C6AC7ABr2
C8AC7ABr2
C9AC8AC13
C9AC8AC7
C13AC8AC7
C10AC9AC8
C11AC10AC9
C12AC11AC10
C12AC12AC13
C12AC13AC8
r(I)]
The complex {PdÃ[(Ph)AÃC@C(Cl))A(PyAÃN)]} (
l-Cl)}2 was then
recrystallized in toluene with 65% of yield. The symbol (Ã) indicates
pallacycle ring bonds. (C, H, N, % calc; % Enc) C (43.8, 43.7), H (2.5,
2.6), N (3.9, 4.0).
technique, where we observe the vibrational normal mode of the
2.3. Bromination of the palladacycle complex synthesis
stretching AC„CA at 2219 cmÀ1
.
The reaction of palladacycle complex {PdÃ[(Ph)AÃC@C(Cl))A
(PyAÃN)]} (
l-Cl)}2 and bromine was performed in a 1:2 stoichiom-
2.2. Palladacycle synthesis
etric amounts respectively in chloroform at room temperature on
constant stirring during 1 h. After the reaction, the solution ob-
tained was filtered on Celite to remove the metallic palladium
formed and the solvent slowly evaporate at room temperature.
The large, white, needle-shaped crystals obtained were then ana-
lyzed by X-ray diffraction and identified as a trans[PyAC(Br)
@C(Br)AØ].
A Li2PdCl4 solution was prepared by dissolution of PdCl2 and
LiCl, using a molar ratio of 1:2, respectively in heated methanol.
At the end of reaction, a reddish-brown solution was formed,
which was filtered to remove solid residues. After cooling the reac-
tional mixture to room temperature, the previously synthezised
pyridinyl-phenyl-ethyne, which had been previously dissolved in
methanol in a 1:1 stoichiometric ratio in relation to the Li2PdCl4,
as slowly added by using an addition funnel during 24 h on con-
stant stirring at room temperature and inert atmosphere. At the
end of the reaction, a yellow precipitate was isolated by filtration,
and washed with ethanol and acetone and dried under vacuum.
3. Results
A single crystal was sealed in a thin-walled glass capillary with
approximate dimensions of 0.5 mm along [1 0 0], 0.4 mm along
Fig. 2. Intermolecular interactions [23] of the types:
p  p interactions, from symmetry operation [x, ½ À y, À½ + z], and CAXÁ Á Áp interactions, from [À1 + x, y, z].

A.C. Mafud et al. / Journal of Molecular Structure 988 (2011) 87–90
89
Fig. 3. Intermolecular interactions of the type CAXÁ Á ÁXAC [22].
[0 1 0] and 0.4 mm along [0 0 1]. The reflexions in one quadrant for
reciprocal space were measured, by using graphite-monochromat-
method. The hydrogen atom positions were fixed geometrically
at calculated distances and allowed to ride on the parent carbon
atoms. The structural analysis was performed by the PLATON sys-
tem [21].
ed [
l (MoKa) = 0.71073] radiation with x-2h scan technique at
room temperature. Intensities were corrected for Lorentz and
polarization effects and semi-empirical absorption, and the data
reduction was carried out using PSI-SCAN [18], with Fourier
smoothing equal to 7.
4. Discussion
The structure was solved by direct methods using WINGX sys-
tem [19]. All the non-hydrogen atoms were refined by SHELXL97
program [20] on F2 anisotropically by full-matrix least-squares
The measuring has been made in a diffractometer CAD-4, the
radiation was MoK
a
0.71073 Å at 293 K. Crystallographic data:
13.309(2) Å, 97.11(1)°, V
a
8.847(1) Å, 10.496(2) Å,
b
c
b
Fig. 4. Crystalline packing [22].

90
A.C. Mafud et al. / Journal of Molecular Structure 988 (2011) 87–90
1226.2(2) Å3, D 1.84 Mg mÀ3, Z = 4, non-centrosymmetric. The sys-
tematic absences analysis indicated the presence of a rotation axis,
order 2, and a glide in direction, with a primitive cell: space group
P21/c. The perspective view [22] of the Trans-1,2-dibromo-2-sty-
ril-pyridine is shown in Fig. 1.
The 2973 reflections were held and the agreement between the
real and the obtained model was evaluated by the disagreement
factors R(F) and Rw(F2), which were 5.6% and 17.1% respectively,
and S 1.030. Selected bond distances and angles are given in Tables
1. Crystal data and structure refinaments are shown in Table 2.
The crystalline packing presents two types of intermolecular
5. Conclusions
The trans-1,2-dibromo-2-styrylpyridine molecular structure
shows the phenyl and the pyridinyl rings attached to the double
bond and located trans to the pyridine ring. The bromines present
in the molecule are in trans position, the torsion angle
Br1AC6@C7ABr2 is 178.8(4)° and the distances of halogens in rela-
tion to the best minimum square plane through the molecule is
2.05(1) and 1.82(1) Å to Br1 and Br2, respectively.
References
interactions is shown in Fig. 2. The first one is
p
Â
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from symmetry operation [x, ½ À y, À½ + z], between the centroids,
Cg1Á Á ÁCg2 (4.2362 Å) [where Cg1 is the centroid of the ring {N1, C1,
C2, C3, C4, C5} and Cg2 {C8, C9, C10, C11, C12, C13}]. The second one
is CAXÁ Á Á
p
interactions, from [À1 + x, y, z], C6ABr1Á Á ÁCg2
(3.5999 Å).
The delocalization of
p
electrons of the double bond can be
seen upon the C6, therefore, the bond distances and angles be-
tween the halogen and carbon are not equal (Table 1). This occur-
rence also implies in short contacts between halogens, in crystal
packing.
In the present case, the short anomalous intermolecular interac-
tion is smaller than the sum of the van der Waals radii,
{Br2Á Á ÁBr2AC7 equal 3.502 Å < 3.70 Å}, and they are coming an ste-
reospecific interaction between these atoms. Van der Waals radii
to Br is 1.86 Å [24]. This interaction is shown in Fig. 3, symmetry
operation [2 À x, 1 À y, Àz].
The merger of all these contacts gives rise to supramolecular
assembly, with parallel layers along the crystal lattice (Fig. 4).
The pyridine ring and the phenyl ring are all planar. The angle be-
tween the minimum square planes through the phenyl and the
pyridinyl is 18.1(3)°.
Crystallographic data for the structure reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-798560. Copies
of available material can be obtained, free of charge, on appli-
cation to the CCDC, 12 Union Road, Cambridge CB2 IEZ, UK
(fax: +44-(0)1223-762910 or via www.ccdc.cam.ac.uk/data-
request/cif.
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