Synthesis and structural investigations of derivatives of 5-ethyl-2-styryl-pyridine

Article abstract of DOI:10.1023/A:1009563518376

Because of their strongly delocalized π electronic systems, polymeric and non-polymeric aromatic compounds show high nonlinear optical properties. The present work deals with the synthesis and structural characterization (including X-ray single crystal st

Full text of DOI:10.1023/A:1009563518376

Journal of Chemical Crystallography, Vol. 29, No. 6, 1999
Synthesis and structural investigations of derivatives
of 5-ethyl-2-styryl-pyridine
Carolina Chavarin,(1) Sylvain Bernes,(2)* and Octavio Manero(1)
`
Received March 15, 1999
Because of their strongly delocalized ȏ electronic systems, polymeric and non-polymeric
aromatic compounds show high nonlinear optical properties. The present work deals with
the synthesis and structural characterization (including X-ray single crystal studies) of new
picoline derivatives, 5-ethyl-2-(4-nitro-styryl)-pyridine, space group P1, a ϭ 6.9505(7), b ϭ
˚
7.418(1), c ϭ 13.877(2) A, Ͱ ϭ 105.14(1), ͱ ϭ 93.88(1), Ͳ ϭ 105.89(1)Њ, and 5-ethyl-2-(4-
˚
nitro-7-ol-styryl)-pyridine, space group Pcab, a ϭ 8.628(2), b ϭ 10.405(2), and c ϭ 31.604(5) A.
KEY WORDS: Picoline derivative; X-ray structure; nonlinear optic.
Introduction
Experimental
Because of their strongly delocalized ȏ electronic
General
1H-NMR spectra were recorded on a Varian
systems, finite polyenes and polyynes are currently
of great interest1 for potential use as nonlinear optical
(NLO) organic materials. In this field, it is necessary
to carefully analyze the structural features of molecu-
lar organic solids in the hope to correlate geometric
characteristics, such as molecular chirality and optical
activity. During the investigation of model molecules,
i.e., 5-ethyl-2-styryl-pyridine2 in view to obtain distyr-
ylpyrazine, which is known3 to give crystalline poly-
mers upon UV irradiation, we obtained new deriva-
tives. The aim of the present work is the synthesis
of molecular organic solids using classical Wittig4 and
Knoevenagel5 condensation reactions starting from
the carefully chosen aldehyde and the X-ray charac-
terization of the products.
Gemini 300a spectrometer. Chemical shifts are rela-
tive to TMS. IR spectra were recorded on a Nicolet
FT-IR5-SX spectrometer using a dispersion of the
sample in CHCl3. For elemental analysis, a Carlo
Erba 1106 CHNϩO/S instrument was applied. Mass
spectra were measured on a Jeol JMS-AX505 HA
mass spectrometer operated in the positive ion mode
(70 eV). Thermal analyses (TGA) were carried out
on a Dupont 2100 HI-RES.
Syntheses
5-Ethyl-2-(4-nitro-styryl)-pyridine (1). Nine
grams (0.059 mole) of 4-nitrobenzaldehyde was dis-
solved in a mixture of DMF and THF. Benzoic anhy-
dride (12 g, 0.053 mol) was dissolved in 20 mL of
THF and both solutions were mixed with 5 mL (0.057
mole) of 5-ethyl-2-picoline under stirring and reflux
(180ЊC). Reactives and mixtures were prepared in-
(1) Instituto de Investigaciones en Materiales, Universidad Nacio-
nal Auto´noma de Me´xico, Apdo. Postal 70-360, Me´xico D.F.
04510, Me´xico.
(2) Facultad de Quı´mica, USAI, Universidad Nacional Auto´noma
de Me´xico, Coyoaca´n 04510, Me´xico D.F. Me´xico.
* To whom correspondence should be addressed.
653
1074-1542/99/0600-0653$16.00/0 1999 Plenum Publishing Corporation

654
Chavarin, Bernes, and Manero
`
side an anaerobic container under N2 atmosphere.
The resulting black solid was treated with a 30%
NaHCO3 solution to induce the formation of the salt
of the p-nitrobenzoic acid. The product was passed
through a column packed with silica. The resulting
80 fractions yielded 8.0 g of solid by slow evaporation
(25 days) which was recrystallized from hexane–ethyl
acetate (7.5:2.5), yielding 5.0 g (34% yield from the
picoline derivative) of a solid of constant melting
point and R ϭ 0.78. Yellow plate crystals, m.p. 119–
120ЊC. Found: C 70.5; H 5.4; N 10.8. Calc. for
C15H14N2O2: C 70.8; H 5.5; N 11.0. IR (CHCl3): 3020
(ArUH), 2971 (CUH), 1596 (CuN), 1343 (CUN),
hexane (R ϭ 0.46). Colorless irregular crystals, m.p.
145–146ЊC; MS (EI), 272 (Mϩ, C15H16O3N2), 122 (Mϩ-
150, C6H4NO2), 106 (Mϩ-166, C7H8N). IR (CHCl3):
3411 (C-O), 3017 (ArUH.), 2923 (CUH), 1715
(CuN), 1450, 1217 (OUH), 1373 (NUH), 1071
(NuO) cmϪ1. 1H-NMR (CDCl3): ͳ1.26 (t, 3H, CH3),
2.65 (q, 2H, CH2), 3.09 (m, 2H, CH2-C(H)OH), 5.24
(dd, 1H, CH), 6.45 (broad band, 1H, OH, exchange-
able with D2O), 7.01 (d, 2H, Ar.), 7.59 (dd, 2H, Ar.),
8.20 (d, 2H, HCuCNO2), 8.38 (s, 1H, NuCH).
Crystallography. Suitable single crystals of 1 and
2 were obtained by slow evaporation of solutions
(methanol for 1 and hexane for 2). The diffraction
data were collected at 293 K on a Siemens P4 diffrac-
tometer using graphite monochromatic MoUKͰ radi-
1
1110 (NuO), 972 (CuC) cmϪ1. H-NMR (CDCl3):
ͳ 1.25 (t, 3H, CH3), 2.66 (q, 2H, CH2), 7.30 (m, 2H,
Ar.), 7.51 (dd, 2H, HCuCH), 7.66 (m, 2H, Ar.), 8.19
(d, 2H, HCuCNO2), 8.46 (d, 1H, NuCH). TGA:
decomposition observed at 180.8ЊC.
5-Ethyl-2-(4-nitro-7-ol-styryl)-pyridine (2). The
same procedure as for 1 was followed, but the separa-
tion was performed using an Ͱ-Al2O3 column, taking
advantage of the alcohol’s stability in basic media. A
white solid was obtained (1.0 g, yield 6.4% from the
picoline derivative), which was recrystallized from
˚
ation (␭ ϭ 0.71073 A) and ␪/2␪ scan mode with vari-
able scan speed. Pertinent crystal data and other
crystallographic parameters are listed in Table 1. In
the case of 2, the very thin plate habit of the crystal
prevented the collection of data at high resolution
˚
(␪max ϭ 21Њ, i.e., resolution of 1 A). In both cases, an
absorption correction was not considered necessary.
Data collection was carried out using XSCANS,6
while solution and refinements of the structures were
Table 1. Crystallographic data for 1 and 2
Compound
1
2
Chemical formula
CCDC deposit no.
Formula weight
Crystal size/mm
Crystal system
Space group
C15H14N2O2
CCDC-1003/5586
254.28
0.60, 0.20, 0.10
Triclinic
P1
6.9505(7)
7.418(1)
13.877(2)
105.14(1)
93.88(1)
105.89(1)
656.79(14)
2
C15H16N2O3
CCDC-1003/5587
272.30
0.60, 0.10, 0.05
Orthorhombic
Pcab
8.628(2)
10.405(2)
31.604(5)
90
˚
a/A
˚
b/A
˚
c/A
Ͱ/Њ
ͱ/Њ
Ͳ/Њ
90
90
3
˚
V/A
2837.3(11)
8
1.275
Z
Dcalc/g cmϪ3
1.286
0.09
Ȑ(Mo-KͰ)/mmϪ1
0.09
2␪ range for data collection/Њ
No. of collected data
No. of unique data
No. of data with F0 Ͼ 4␴(F0)
R1, wR2 [F0 Ͼ 4␴(F0)]/%
R1 , wR2 (all data)/%
S
3-56
3626
3-42
2098
2901 (Rint ϭ 1.81%)
1354
6.50, 16.49
13.94, 21.16
1.019
1528 (Rint ϭ 7.35%)
671
7.63, 15.73
19.47, 21.27
1.022
Data to parameters ratio
Largest and mean ⌬/␴
Largest peak and hole/e.A
2901/191
0.000, 0.000
0.13, Ϫ0.12
1528/185
0.000, 0.000
0.21, Ϫ0.16
3
˚

Derivatives of 5-ethyl-2-styryl-pyridine
655
performed using SHELX-97.7 Both structures were
resolved by direct methods followed by Fourier maps
and refined by full matrix least-squares, without re-
straints nor constraints for non-H-atoms. In the case
of 1, a disorder was observed for the vinylic double
bond: atoms C7 and C8 (site occupation factors 1/3)
are disordered with C7Ј and C8Ј (occupation 2/3). For
both compounds, H atoms were placed on idealized
positions and refined using a riding model with a
fixed isotropic U, except for the H atom of the OH
group in 2, which was found on a difference Fourier
map. The position of this atom was refined.
For the hydroxy derivative 2, a broad band (6.2–6.8
ppm) which disappears on D2O addition confirms the
presence of the OH group. For the IR spectra of
2, a broad band at 3412 cmϪ1 corresponding to the
stretching mode for CUO and two sharp bands at
1450 and 1217 cmϪ1, assigned to the stretching mode
of OUH, confirm the presence of the alcohol group.
On the other hand, the peak at m/z 255 in the mass
spectra (Mϩ-OH) is characteristic of an alcohol.
The structure of 1 (see Table 2 and Fig. 1)
bears similarities to that of a previously reported
compound, 5-ethyl-2-styryl-pyridine.2 Selected bond
lengths and angles are presented in Table 4. For
both disordered vinylic moieties, the double bond
displays a trans geometry. The molecule is almost
planar, since the torsion angle C1UC7ЈUC8ЈUC9
is Ϫ179.1(3)Њ. The largest deviation from the calcu-
lated mean plane (excluding the ethyl group) is
Results and discussion
Two picoline derivatives were obtained in mod-
erate yields by condensation reactions starting from
5-ethyl-2-methyl-pyridine and two aldehydes
(Scheme 1) and varying the conditions of separation
(see Experimental Section). The condensation be-
tween a disubstituded aromatic pyridine and benzyl
aldehyde in order to synthesize olefinic compounds
was first reported8 in 1953 by Katada. In the case of
the compounds treated here, the reaction is con-
trolled by the position of the methyl group in the
starting material: as it is well known, the N atom in
the pyridine ring induces an acid character for the
methyl protons and the reactivity increases for a Ͱ
substituted pyridine. On the other hand, the litera-
ture9 reports the reactions of styryl-pyridine deriva-
tives with 4-nitro-benzaldehyde using zinc chloride as
catalyst to obtain 5-ethyl-2-(4-nitro-styryl)-pyridine.
However, the crystal structure for the product was
not reported.
˚
0.12 A for the O atoms of the nitro group. The
donor effect of the NO2 group is evident from, for
instance, the comparison of the C7UC8 bond
2
˚
lengths for 5-ethyl-2-styryl-pyridine [1.206(8) A]
˚
and 1 [1.319(13) and 1.301(6)A], which evidences
the delocalization of ȏ electrons over all the mole-
Table 2. Atomic Coordinates (ϫ104) and Equivalent Iso-
2
3
˚
tropic Displacement Coefficients (A ϫ 10 ) for 1
Atom
x/a
y/b
z/c
U(eq)a
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
Ϫ1047(4)
Ϫ730(4)
Ϫ2279(4)
Ϫ4205(3)
Ϫ4614(4)
Ϫ3030(5)
43(14)
1820(4)
940(4)
Ϫ8(4)
Ϫ103(3)
745(4)
Ϫ641(2)
Ϫ1594(3)
Ϫ2370(2)
Ϫ2202(2)
Ϫ1272(2)
Ϫ493(2)
510(9)
85(1)
94(1)
82(1)
65(1)
79(1)
88(1)
65(2)
69(1)
61(2)
74(1)
93(1)
97(1)
94(1)
86(1)
102(1)
131(1)
137(1)
108(1)
86(1)
120(1)
128(1)
1710(4)
2938(13)
2783(6)
3440(12)
3437(7)
4457(4)
5214(4)
6223(4)
6488(4)
5619(5)
7661(5)
6632(5)
4627(4)
Ϫ1108(3)
Ϫ1414(3)
Ϫ1589(3)
C(7)b
C(7Ј)c
C(8)b
C(8Ј)c
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
N(1)
N(2)
O(1)
O(2)
The spectroscopic characterization for com-
1
868(9)
57(3)
637(7)
pounds 1 and 2 was carried out by H NMR, MS
1
2036(12)
907(10)
2893(6)
2587(4)
4173(5)
6111(4)
6309(5)
7942(5)
8481(6)
4754(6)
Ϫ5883(4)
Ϫ7604(3)
Ϫ5490(4)
and IR. H NMR spectra are very similar for both
1026(3)
1740(2)
2685(2)
3439(2)
3252(2)
2267(3)
4052(3)
4716(3)
1509(2)
Ϫ3037(2)
Ϫ2842(2)
Ϫ3882(2)
compounds. Vinylic protons appear for 1, as expected
in the range 7.0–7.6 ppm as doublets (J ϭ 15.9 Hz).
aU(eq) is defined as one-third of the trace of the orthogonalized
Uij tensor.
bSite occupation Factors for C(7) and C(8); 1/3.
cSite occupation Factors for C(7Ј) and C(8Ј): 2/3.
Scheme 1.

656
Chavarin, Bernes, and Manero
`
Fig. 1. Molecular structure for compound 1 including labelling
scheme. Thermal ellipsoids for non-H atoms are at 30% probability
level. Disorder for C7Ј and C8Ј is omitted for clarity.
Fig. 2. Molecular structure for compound 2 including labelling
scheme. Thermal ellipsoids for non-H atoms are at 30% probabil-
ity level.
cule in the case of 1. As expected, the packing of
1 results from van der Waals forces. Phenyl and
pyridine rings are found in alternate positions with
respect to the vinyl group, which favors highly
efficient packing. The shortest distance between
of the nitro group and the methyl group, with a inter-
molecular distance C15UH15 и и и O2 ϭ 2.557 A. In
spite of breaking the delocalization in 2, the efficiency
˚
of packing in both reported crystals are very similar,
3
˚
˚
with a non-H-atomic volume of 17.3 and 17.7 A for
1 and 2, respectively.
centroids of phenyl and pyridine rings is 3.88 A.
For compound 2 (see Table 3 and Fig. 2), bond
lengths C1UC7, C7UC8 and C8UC9 [1.497(9),
In relation with potential NLO properties, it
˚
should be mentioned that unexpectedly, 1 and 2 crys-
1.517(9), and 1.498(9) A respectively, see Table 4]
are in agreement with formally sp3 hybridized C7 and
C8 atoms. This is confirmed by angles around C7 and
C8, in the range 109.7(6) to 113.3(6)Њ. The crystal
structure is stabilized by a network of virtually linear
intermolecular hydrogen bonds involving the hy-
droxy group, with a distance O3UH3 и и и N1 of 2.023
¯
tallize in centrosymmetric space groups, P1 and Pcab,
while 5-ethyl-2-styryl-pyridine crystallizes in the non
centrosymmetric space group P21.2 The introduction
of the nitro group may increase the molecular polariz-
ability, but crystals are not good candidates for NLO
applications. On the other hand, in the case of 2 that
contains a chiral center, C7, the centric character
of the space group indicates that a racemic mixture
was crystallized.
˚
A. A weaker interaction is noted between an O atom
Table 3. Atomic Coordinates (ϫ104) and Equivalent Isotropic
2
3
˚
Displacement Coefficients (A ϫ 10 ) for 2
Atom
x/a
y/b
z/c
U(eq)a
˙
Table 4. Selected Bond Lengths (A) and Angles (Њ) for 1 and 2
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
N(1)
N(2)
O(1)
O(2)
O(3)
2691(8)
3515(10)
3513(10)
2650(11)
1827(8)
1854(8)
2718(8)
4054(9)
4267(9)
3648(10)
3879(11)
4653(11)
5224(10)
4921(14)
5824(14)
5073(8)
2569(12)
1796(10)
3326(11)
1281(6)
6527(7)
7336(7)
7246(9)
6280(9)
5420(7)
5563(7)
6627(7)
5863(7)
6070(9)
5241(8)
5488(9)
6546(9)
7331(8)
6904(9)
5974(10)
7108(7)
6187(9)
5336(9)
6942(8)
6207(5)
4827(2)
4574(3)
4144(3)
3961(3)
4195(3)
4630(2)
5300(2)
5485(2)
5950(2)
6249(3)
6670(3)
6806(3)
6483(3)
7276(2)
7494(3)
6069(2)
3497(3)
3343(2)
3289(2)
5468(2)
49(2)
72(2)
78(3)
77(3)
62(2)
57(2)
53(2)
66(2)
60(2)
78(2)
87(3)
78(3)
81(3)
120(4)
161(5)
69(2)
107(3)
146(4)
155(4)
73(2)
Length/angle
Compound 1
Length/angle
Compound 2
C1UC7Ј
C1UC7
C4UN2
C7UC8
C7ЈUC8Ј
—
C8UC9
C8ЈUC9
C9UN1
C13UN1
N2UO1
N2UO2
1.471(6)
1.616(12)
1.465(3)
1.319(13)
1.301(6)
—
1.515(10)
1.520(6)
1.334(4)
1.350(4)
1.218(3)
1.206(3)
114.9(11)
—
C1UC7
1.497(9)
—
1.473(11)
1.517(9)
—
1.418(8)
1.498(9)
—
1.338(9)
1.333(9)
1.211(9)
1.214(10)
111.1(6)
111.0(6)
109.7(6)
—
113.3(6)
—
117.9(7)
123.5(10)
118.1(10)
118.3(10)
—
C4UN2
C7UC8
—
C7UO3
C8UC9
—
C9UN1
C13UN1
N2UO1
N2UO2
C8UC7UC1
O3UC7UC8
O3UC7UC1
—
C7UC8UC9
—
C9UN1UC13
O1UN2UO2
O2UN2UC4
O1UN2UC4
C8UC7UC1
—
—
—
C8ЈUC7ЈUC1
C7UC8UC9
C7ЈUC8ЈUC9
C9UN1UC13
O1UN2UO2
O2UN2UC4
O1UN2UC4
121.7(7)
110.4(11)
121.4(7)
116.9(3)
123.3(3)
118.4(3)
118.3(2)
aU(eq) is defined as one-third of the trace of the orthogonalized
Uij tensor.

Derivatives of 5-ethyl-2-styryl-pyridine
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