Imino-pyrrole derivatives containing electron-withdrawing substituents: The formation of dimers and supra-molecular arrangements

Article abstract of DOI:10.1107/S0108270111027491

The crystal structures of two p-substituted phenylformiminopyrrole derivatives, namely 2-[(4-fluorophenyl)iminomethyl]- pyrrole, C ₁₁H₉FN₂, (1), and 2-[(1H-pyrrol-2- ylmethylidene)- amino]benzonitrile, C₁₂H

Full text of DOI:10.1107/S0108270111027491

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
al., 2010) and Zn (Gomes et al., 2009) complexes containing
2-(arylimino)pyrrolyl ligands, where the Ni derivatives were
active in the oligomerization of ethylene and the Zn deriva-
tives showed luminescent properties. In these publications, we
also reported the molecular structure of some ligand precur-
sors, namely 2-[1-(mesitylimino)ethyl]pyrrole, 2-[1-(2,6-di-
isopropylphenylimino)ethyl]pyrrole, two polymorphs of
2-[(phenylimino)methyl]pyrrole and 2-[(2,6-diisopropyl-
phenylimino)methyl]pyrrole, which can be found in the
Cambridge Structural Database (CSD, Version 5.32; Allen,
2002) with refcodes UMUKUI (Bellabarba et al., 2003),
LILYUB (Carabineiro et al., 2007), CUKHUM (Gomes et al.,
2010), CUKHUM01 (Gomes et al., 2010) and CUKJEY
(Gomes et al., 2010), respectively (see Scheme).
ISSN 0108-2701
Iminopyrrole derivatives containing
electron-withdrawing substituents:
the formation of dimers and supra-
molecular arrangements
´
´
Clara S. B. Gomes, Claudia A. Figueira, Patrıcia S. Lopes,
D. Suresh, Pedro T. Gomes* and M. Teresa Duarte*
´
´
´
Centro de Quımica Estrutural, Departamento de Engenharia Quımica e Biologica,
´
´
Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Avenida Rovisco Pais,
1049-001 Lisboa, Portugal
Correspondence e-mail: pedro.t.gomes@ist.utl.pt, teresa.duarte@ist.utl.pt
Received 3 June 2011
Accepted 8 July 2011
Online 14 July 2011
The crystal structures of two p-substituted phenylformimino-
pyrrole derivatives, namely 2-[(4-fluorophenyl)iminomethyl]-
pyrrole, C11H9FN2, (1), and 2-[(1H-pyrrol-2-ylmethylidene)-
amino]benzonitrile, C12H9N3, (2), bear F and C N electron-
withdrawing groups, respectively. Both structures feature two
independent molecules in the asymmetric unit forming dimers
via N—HÁ Á ÁN hydrogen bonds. In the case of (1), each dimer
interacts with two other dimers via C—HÁ Á ÁF contacts, thus
forming one-dimensional chains in the b direction, whereas in
the case of (2), a weak C—HÁ Á ÁN interaction connects the
dimers in one-dimensional chains in the (110) direction.
Comment
Pyrrole and its substituted derivatives are well known five-
membered heterocyclic compounds which are involved in a
wide range of applications, in areas such as natural products,
bioactive molecules, pharmaceuticals, anion-binding systems,
etc. (Rao & Jothilingam, 2001; Braun et al., 2001; Hewton et al.,
2002; Sessler et al., 2005). Moreover, 2-(N-aryl or N-alkyl)-
iminopyrroles, (I) (see Scheme), are usually employed as
ligand precursors in the preparation of coordination
compounds, generally after deprotonation of the pyrrole NH
group (Mashima & Tsurugi, 2005). The synthetic strategy for
the preparation of these iminopyrrole derivatives is very
straightforward, consisting of a Vilsmeier–Haack acylation
(Garrido et al., 1984) followed by a condensation reaction with
a suitable aliphatic or aromatic amine. The resulting
complexes are mostly used as precatalysts in polymerization
reactions (Mashima & Tsurugi, 2005; Matsugi & Fujita, 2008),
but they can also have applications, for example, in lumines-
cence (Wu et al., 2003, 2004).
In the present work, we report the crystal structures of
2-[(4-fluorophenyl)iminomethyl]pyrrole, (1), and 2-[(1H-pyr-
rol-2-ylmethylidene)amino]benzonitrile, (2), in which the para
positions of the benzene rings are substituted by the electron-
withdrawing F or C N (nitrile) groups. The corresponding
molecular structures are depicted in Figs. 1 and 2, respectively.
In both compounds, the asymmetric unit contains two inde-
pendent molecules, where the pyrrole moieties show planar
backbones with similar features. A brief analysis of the bond
distances and angles in these derivatives (Table 1) reveals that
Recently, we reported the synthesis of new Ni (Bellabarba
et al., 2003), Co (Carabineiro et al., 2007, 2008), Na (Gomes et
Acta Cryst. (2011). C67, o315–o318
doi:10.1107/S0108270111027491
# 2011 International Union of Crystallography o315

organic compounds
Figure 2
The two independent molecules in the asymmetric unit of (2).
Displacement ellipsoids are drawn at the 50% probability level.
Figure 1
The two independent molecules in the asymmetric unit of (1).
Displacement ellipsoids are drawn at the 50% probability level.
dimerization of the iminopyrrole molecules through an R22(10)
motif, as can be seen in Figs. 3 and 4. However, in contrast to
what is observed in the more hindered derivatives UMUKUI,
LILYUB or CUKJEY, in which the iminopyrrole molecules of
the dimer are coplanar, in (1) and (2), and also in CUKHUM,
both molecules composing each dimer are not coplanar, the
wings of the pyrrole moieties making angles of 150.55 (10),
138.77 (10) and 151.94 (8)ꢀ in the cases of (1), (2) and
CUKHUM, respectively.
In compound (1), the most important observed inter-
molecular interactions are the two complementary hydrogen
bonds N1A—H1AÁ Á ÁN2B and N1B—H1BÁ Á ÁN2A (Table 2).
However, a C—HÁ Á ÁF short contact is found with HÁ Á ÁF
distances and C—HÁ Á ÁF angles within the limits reported in
the literature for this type of contact (Shimoni & Glusker,
1994; Howard et al., 1996; Dunitz & Taylor, 1997). In fact,
these interactions, always involving molecule B, occur
between the F atom and the pyrrole NH group at position 3 of
the neighbouring dimer, forming one-dimensional chains in
the b direction (Fig. 3). Conversely, in derivative (2), in
addition to the N1A—H1AÁ Á ÁN2B and N1B—H1BÁ Á ÁN2A
the longest bond in the pyrrole ring is C3—C4, with values
˚
ranging from 1.390 (3) to 1.397 (2) A, and that the shortest
bond is N1—C5. The imine distance varies between
˚
1.2809 (19) and 1.290 (2) A (Table 1). The torsion angles N2—
C6—C2—N1 of À2.6 (3) and À2.4 (3)ꢀ [molecules A and B of
(1)], and À4.1 (2) and À0.3 (3)ꢀ [molecules A and B of (2)]
show that the pyrrole ring and the formimino group are nearly
coplanar. The C2—C6 distances in the range 1.416 (2)–
˚
1.426 (2) A are slightly shorter than the normal values for
2
2
˚
typical Csp —Csp single bonds (1.476 A; Allen et al., 1987),
indicating an extension of the pyrrole ring ꢀ-electron delo-
calization towards the formimino substituent. For both (1) and
(2), the benzene substituents of the iminic fragments adopt
dihedral angles of around 45ꢀ relative to the pyrrole ring
[49.08 (9), 45.33 (10), 52.05 (9) and 39.10 (10)ꢀ for molecules
A and B of (1) and (2), respectively]. In fact, this is also true
for CUKHUM [46.97 (7) and 45.31 (8)ꢀ] and CUKHUM01
[41.96 (12), 8.93 (12), 47.96 (13) and 41.28 (12)ꢀ] that do not
have any substituents on the benzene ring, but is not the case
for UMUKUI [85.66 (8)ꢀ], LILYUB [86.54 (9) and 83.48 (9)ꢀ]
and CUKJEY [83.84 (10) and 86.17 (9)ꢀ], in which the
benzene rings are rotated about the Nimine—Car bond, being
nearly perpendicular to the formiminopyrrole plane defined
by atoms N2—C6—C2—N1, owing to the high steric
hindrance exerted by the alkyl groups in the 2- and 6-positions
(Bellabarba et al., 2003; Carabineiro et al., 2007; Gomes et al.,
2010). The value of 8.93 (12)ꢀ found in one of the four mol-
ecules of polymorph CUKHUM01, which is substantially
different from all the others, making the benzene ring almost
coplanar with the iminopyrrole fragment, is due to the
supramolecular arrangement.
It is known from the literature (Bellabarba et al., 2003;
Munro et al., 2006; Carabineiro et al., 2007; Gomes et al., 2010)
that these types of organic derivatives assemble as
formiminopyrrole dimers through the formation of two
complementary hydrogen bonds between a pyrrole NH group
and the imine N atom belonging to the other molecule of the
pair. In agreement with this, compounds (1) and (2) both show
Figure 3
The packing of (1), showing the one-dimensional zigzag chains in the b
direction and the R22(10) motifs forming the dimers. Donor and acceptor
atoms are identified. Dashed lines represent N—HÁ Á ÁN and C—HÁ Á ÁF
interactions (blue and red, respectively, in the electronic version of the
paper). [Symmetry code: (i) 1 À x, À + y, 32 À z.]
1
2
ꢁ
o316 Gomes et al. C11H9FN2 and C12H9N3
Acta Cryst. (2011). C67, o315–o318

organic compounds
Figure 4
The packing of (2), showing a chain of dimers along the (110) direction and the R22(10) motifs forming the dimers. Donor and acceptor atoms are
identified. Dashed lines represent N—HÁ Á ÁN and C—HÁ Á ÁN interactions (blue and red, respectively, in the electronic version of the paper). [Symmetry
code: (ii) x + 1, y À 1, z.]
product was dissolved in refluxing n-hexane. In the case of (1), the
resulting solution was stored at 253 K, yielding yellow prismatic
crystals (yield 54%). However, in the case of (2), the product, which
was an oil, was insoluble in n-hexane and partially soluble in diethyl
ether. After evaporation of these solvents, the initial oil was trans-
formed into a brown solid, which was purified by sublimation at a
temperature of 353 K and a pressure of 10 Pa (yield 49%). Yellow
crystals of (2) suitable for X-ray diffraction were obtained by
recrystallization from diethyl ether at 253 K.
NMR data for (1): 1H (300 MHz, CDCl3): ꢁH 9.98 (br s, 1H, NH),
8.25 (s, 1H, CH N), 7.19–7.13 (m, 2H, m-phenyl), 7.10–7.02 (m, 2H,
o-phenyl), 6.86 (br s, 1H, H5), 6.69 (dd, JHH = 1.38 Hz, 1H, H3), 6.29
(dd, JHH = 2.49 Hz, 1H, H4). 13C{1H} (75 MHz, CDCl3): ꢁC 160.9 (d,
1JCF = 242 Hz, p-phenyl), 149.8 (CH N), 147.8 (ipso-phenyl), 130.7
(C2), 123.3 (C3), 122.2 (d, 3JCF = 8 Hz, o-phenyl), 116.8 (C4), 115.9 (d,
2JCF = 22 Hz, m-phenyl), 110.5 (C5).
NMR data for (2): 1H (300 MHz, CDCl3): ꢁH 9.53 (br s, 1H, NH),
8.21 (s, 1H, CH = N), 7.67–7.63 (m, 2H, m-phenyl), 7.22–7.18 (m, 2H,
o-phenyl), 7.03 (d, JHH = 10.8 Hz, 1H, H5), 6.76 (dd, JHH = 1.2 Hz, 1H,
H3), 6.34 (m, 1H, H4). 13C{1H} (75 MHz, CDCl3): ꢁC 155.7 (ipso-
phenyl), 151.1 (CH = N), 133.4 (m-phenyl), 130.4 (C2), 124.2 (C3),
121.7 (o-phenyl), 119.2 (C4), 118.2 (C N), 111.1 (p-phenyl), 108.4
(C5).
hydrogen bonds, one can also notice the existence of a weak
intermolecular C—HÁ Á ÁN hydrogen bond, forming chains in
the (110) direction, in which the nitrile group interacts weakly
with an aromatic meta-H atom of the neighbouring dimer
(Fig. 4), the latter having a more electropositive character than
the corresponding H atom of derivative (1), owing to the
proximity of the more powerful electron-withdrawing nitrile
group. This is in agreement with the 1H and 13C NMR data for
the corresponding meta-H and meta-C nuclei that are clearly
more deshielded in compound (2) than in (1) [ꢁ 1H 7.67–7.63
versus 7.19–7.13 and ꢁ 13C 133.4 versus 116.8 p.p.m. for (2) and
(1), respectively] (Figs. 3 and 4).
Moreover, comparing these two crystal structures with
VIYWUW (Heinze et al., 2008), an iminopyrrole derivative
containing a hydroxy substituent in the para position of the
benzene ring (see Scheme), it is possible to notice that the
benzene substituent of the iminic fragment also lies around
45ꢀ relative to the pyrrole ring [dihedral angle = 49.59 (5)ꢀ],
and that all the distances within the molecule are in agreement
with those observed for the derivatives discussed above. On
the other hand, the formation of dimers through the estab-
lishment of complementary N—HÁ Á ÁN hydrogen bonds is
disabled in this compound, because of the presence of the
para-hydroxy substituent, which is involved in three different
interactions, viz. O—HÁ Á ÁN, N—HÁ Á ÁO and C—HÁ Á ÁO. Simi-
larly to derivative (2), this compound also forms an extended
one-dimensional chain.
Compound (1)
Crystal data
3
˚
C11H9FN2
Mr = 188.20
Orthorhombic, Pbca
V = 3782.9 (3) A
Z = 16
Mo Kꢂ radiation
ꢃ = 0.09 mmÀ1
T = 150 K
0.60 Â 0.60 Â 0.30 mm
˚
a = 9.5542 (5) A
˚
b = 18.7198 (9) A
˚
c = 21.1509 (12) A
Experimental
n-Hexane, diethyl ether and absolute ethanol were predried over
˚
activated 4 A molecular sieves and then distilled from sodium and
Data collection
kept under a nitrogen atmosphere. The synthetic procedure followed
for the syntheses of (1) and (2) was that used previously by our group
(Bellabarba et al., 2003; Carabineiro et al., 2007, 2008; Gomes et al.,
2010). 2-Formylpyrrole [10.5 mmol in the case of (1) and 14.4 mmol
in the case of (2)], aniline (1 equivalent), a catalytic amount of
p-toluenesulfonic acid and MgSO4 (to remove the water formed in
the reaction mixture) were suspended in absolute ethanol in a round-
bottomed flask fitted with a condenser and a CaCl2 guard tube. The
mixture was refluxed overnight. After cooling to room temperature,
CH2Cl2 was added and the suspension filtered through Celite and
washed through with more CH2Cl2. After removal of all volatiles, the
Bruker APEXII CCD
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.946, Tmax = 0.972
21637 measured reflections
3605 independent reflections
2479 reflections with I > 2ꢄ(I)
Rint = 0.040
Refinement
R[F2 > 2ꢄ(F2)] = 0.038
wR(F2) = 0.100
S = 1.03
3605 reflections
261 parameters
H atoms treated by a mixture of
independent and constrained
refinement
À3
˚
Áꢅmax = 0.14 e A
À3
˚
Áꢅmin = À0.26 e A
ꢁ
Acta Cryst. (2011). C67, o315–o318
Gomes et al. C11H9FN2 and C12H9N3 o317

organic compounds
Table 1
Selected bond distances and angles (A, ) for compounds (1) and (2).
program(s) used to refine structure: SHELXL97 (Sheldrick, 2008);
molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae
et al., 2006); software used to prepare material for publication:
enCIFer (Allen et al., 2004), PLATON (Spek, 2009) and publCIF
(Westrip, 2010).
ꢀ
˚
(1A)
(1B)
(2A)
(2B)
N1—C2
C2—C3
1.371 (2)
1.381 (2)
1.370 (2)
1.382 (2)
1.364 (2)
1.382 (2)
1.365 (2)
1.388 (2)
C3—C4
C4—C5
1.395 (3)
1.363 (3)
1.393 (3)
1.365 (2)
1.397 (2)
1.367 (2)
1.390 (3)
1.366 (2)
ˆ
The authors thank the Fundac¸a˜o para a Ciencia e Tecno-
N1—C5
C2—C6
N2—C6
N2—C7
C5—N1—C2
N1—C2—C3
C2—C3—C4
C3—C4—C5
C4—C5—N1
N1—C2—C6
C2—C6—N2
1.357 (2)
1.423 (2)
1.284 (2)
1.418 (2)
108.94 (15)
107.28 (15)
107.63 (16)
107.37 (15)
108.77 (16)
123.21 (15)
123.62 (16)
1.356 (2)
1.426 (2)
1.281 (2)
1.422 (2)
108.98 (15)
107.20 (16)
107.80 (16)
107.19 (16)
108.82 (17)
123.74 (15)
124.17 (16)
1.356 (2)
1.422 (2)
1.2809 (19)
1.416 (2)
109.27 (15)
107.45 (14)
107.48 (15)
107.24 (15)
108.55 (16)
123.23 (15)
123.42 (16)
1.362 (2)
1.416 (2)
1.290 (2)
1.414 (2)
109.20 (15)
106.99 (16)
107.91 (17)
107.27 (16)
108.63 (17)
123.42 (15)
124.13 (16)
logia, Portugal, for financial support (project No. PEst-OE/
QUI/UI0100/2011, project Nos. PTDC/QUI/65474/2006 and
PTDC/EQU-EQU/110313/2009, co-financed by FEDER) and
for fellowship Nos. SFRH/BPD/64423/2009, SFRH/BD/47730/
2008 and SFRH/BPD/47853/2008 to CSBG, CAF and DS,
respectively.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: LG3062). Services for accessing these data are
described at the back of the journal.
Table 2
Hydrogen-bond geometry (A, ) for compounds (1) and (2).
ꢀ
˚
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D—H
HÁ Á ÁA
DÁ Á ÁA
D—HÁ Á ÁA
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159.0 (16)
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3
˚
V = 2072.6 (4) A
Z = 8
C12H9N3
Mr = 195.22
Monoclinic, P21=n
a = 12.5935 (13) A
˚
b = 10.1843 (11) A
Mo Kꢂ radiation
ꢃ = 0.08 mmÀ1
T = 150 K
0.30 Â 0.22 Â 0.20 mm
˚
˚
c = 16.901 (2) A
ꢆ = 107.035 (5)ꢀ
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ꢁ
o318 Gomes et al. C11H9FN2 and C12H9N3
Acta Cryst. (2011). C67, o315–o318