Sterically shielded pyramidal amino groups in two 4,4′-(aryl-methyl- ene)bis-(6-allyl-3-chloro-2-methyl-aniline) derivatives

Article abstract of DOI:10.1107/S0108270109031175

4,4′-(Phenyl-methyl-ene)bis-(6-allyl-3-chloro-2-methyl-aniline), C27H28Cl2N2, (I), and 4,4′-(2-thienylmethyl-ene)bis-(6-allyl-3-chloro-2- methyl-aniline), C25H26Cl2N2S, (II), adopt similar mol-ecular conformations, although the thienyl group in (II) exhib

Full text of DOI:10.1107/S0108270109031175

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
unexpected new compounds arising from the self-condensa-
tion of the aldimines, and these have been identified as 4,40-
(phenylmethylene)bis(6-allyl-3-chloro-2-methylaniline), (I),
and 4,40-(2-thienylmethylene)bis(6-allyl-3-chloro-2-methyl-
aniline), (II), and we report here their molecular and supra-
molecular structures (Figs. 1 and 2).
ISSN 0108-2701
Sterically shielded pyramidal amino
groups in two 4,40-(arylmethylene)-
bis(6-allyl-3-chloro-2-methylaniline)
derivatives
Maria C. Blanco,a Alirio Palma,a Ali Bahsas,b Michael B.
Hursthouse,c Justo Cobod and Christopher Glidewelle*
a
´
´
´
Laboratorio de Sıntesis Organica, Escuela de Quımica, Universidad Industrial de
Santander, AA 678 Bucaramanga, Colombia, bLaboratorio de RMN, Grupo de
´
´
Productos Naturales, Departamento de Quımica, Universidad de los Andes, Merida
5101, Venezuela, cSchool of Chemistry, University of Southampton, Highfield,
d
´
´
Southampton SO17 1BJ, England, Departamento de Quımica Inorganica y
Organica, Universidad de Jaen, 23071 Jaen, Spain, and eSchool of Chemistry,
´
´
´
University of St Andrews, Fife KY16 9ST, Scotland
Correspondence e-mail: cg@st-andrews.ac.uk
Received 28 July 2009
Accepted 6 August 2009
Online 26 August 2009
4,40-(Phenylmethylene)bis(6-allyl-3-chloro-2-methylaniline),
C27H28Cl2N2, (I), and 4,40-(2-thienylmethylene)bis(6-allyl-3-
chloro-2-methylaniline), C25H26Cl2N2S, (II), adopt similar
molecular conformations, although the thienyl group in (II)
exhibits orientational disorder over two sets of sites with
occupancies of 0.614 (3) and 0.386 (3). The amino groups in
both compounds are pyramidal. A single N—Hꢀ ꢀ ꢀN hydrogen
bond links the molecules of (I) into cyclic centrosymmetric
dimers. Molecules of (II) are linked by an ordered C—
Hꢀ ꢀ ꢀꢀ(arene) hydrogen bond to form cyclic centrosymmetric
dimers, and these dimers are linked into statistically inter-
rupted chains by a second C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bond
involving a donor in the minor component of the disordered
thienyl unit.
While the molecules of compound (I) are fully ordered
(Fig. 1), those of (II) exhibit orientational disorder of the
2-thienyl substituent, corresponding to a rotation about the
C1—C32 bond (Fig. 2), with unequal populations in the two
conformers with refined values of 0.614 (3) and 0.386 (3). With
the exception of the orientation of the unsubstituted phenyl
group in compound (I), as compared to that of the thienyl
group in compound (II), the rest of the skeletal conformation
is very similar in the two compounds, as indicated by the
leading torsion angles defining the orientation of the substi-
tuted aryl rings (Table 1). Thus, the torsion angles defining the
orientation of the C11–C16 ring are very similar in both
compounds; likewise the corresponding angles defining the
orientation of the C21–C26 ring are very similar in the two
compounds. However, while the C18—C19—C20 allyl group
adopts an almost identical conformation in each compound,
the torsion angles defining the orientation of the the C28—
C29—C30 allyl groups have opposite signs in the two
compounds. Thus, the Ar2C unit (where Ar represents the
substituted aryl ring) does not exhibit even approximate
internal symmetry.
Comment
We have recently investigated the synthetic utility of 2-allyl-
anilines as building blocks in heterocyclic synthesis (Palma et
´
´
al., 2004; Gomez Ayala et al., 2006; Yepez et al., 2006). On the
other hand, it is well known that condensation of substituted
anilines with aromatic or heteroaromatic aldehydes produces
aldimines. These in turn can react with thioglycollic acid to
give 4-thiazolidinones (Singh et al., 1981), which exhibit a wide
range of biological activities. Prompted by the possibility of
preparing new bioactive 4-thiazolidinone derivatives, we have
investigated the reactivity of aldimines with thioglycollic acid.
However, we found that under the reaction conditions
employed, these reactions did not produce the expected
4-thiazolidinones. Instead, we observed the formation of two
In each compound, the two amino N atoms, viz. N14 and
N24, have markedly pyramidal geometry and, consistent with
this, the C—N distances are close to the mean value for
˚
C(aryl)—NH2 bonds having a pyramidal N atom (1.394 A;
Allen et al., 1987), rather longer than the mean value for such
˚
bonds having a planar N atom (1.355 A). Despite this, the
orientation of the amino groups is such that the lone-pair
orbital on each N atom is approximately orthogonal to the
plane of the adjacent aryl ring. However, the shielding effect
Acta Cryst. (2009). C65, o479–o482
doi:10.1107/S0108270109031175
# 2009 International Union of Crystallography o479

organic compounds
Figure 2
Figure 1
The molecular structure of compound (II), showing the two orientations
of the thienyl substituent, with occupancies of 0.614 (3) and 0.386 (3), and
the atom-labelling scheme. Displacement ellipsoids are drawn at the 30%
probability level and H atoms are shown as small spheres of arbitrary
radii.
The molecular structure of compound (I), showing the atom-labelling
scheme. Displacement ellipsoids are drawn at the 30% probability level
and H atoms are shown as small spheres of arbitrary radii.
of the two adjacent substituents, namely the methyl and allyl
groups, means that the participation of the amino groups in
intermolecular hydrogen-bond formation is restricted: only
one of the four N—H bonds in (I), and none of those in (II), is
involved in hydrogen-bond formation (Table 2).
Accordingly, the supramolecular aggregation in both
compounds is fairly simple. In compound (I), two molecules
related by inversion are linked by paired N—Hꢀ ꢀ ꢀN hydrogen
bonds (Table 2), in which atom N14 acts as hydrogen-bond
donor and atom N24 acts as hydrogen-bond acceptor, so
forming a centrosymmetric R22(24) (Bernstein et al., 1995)
motif centred at (12, 21, 21) (Fig. 3). There are no direction-specific
interactions between these dimers. In particular, N—Hꢀ ꢀ ꢀ
ꢀ(arene) and C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds and aromatic
ꢀ–ꢀ stacking interactions are all absent.
one or zero C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds, depending
upon the local orientation of the two thienyl groups con-
cerned. Hence, the resulting chain is best regarded as a
statistically interrupted chain running parallel to the [101]
direction, in that the likelihood that a continuous chain of
centrosymmetric rings will be formed must be extremely low.
There are no direction-specific interactions between adjacent
chains.
It is noteworthy that only one of the N—H bonds in (I)
participates in hydrogen-bond formation, while neither of the
amino N atoms in (II) is within hydrogen-bonding range
of any plausible donor or acceptor. The amino groups in
1,1-bis(4-amino-3,5-dimethylphenyl)cyclohexane, (III) [Cam-
bridge Structural Database (CSD; Allen, 2002) refcode
YAFNUO; Hanton et al., 1992] are similarly subject to steric
shielding. These groups are also markedly pyramidal, but only
one of the four N—H bonds participates in the formation of
N—Hꢀ ꢀ ꢀN hydrogen bonds, although two others form
N—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds. It was suggested (Hanton
et al., 1992) that the assumption of pyramidal geometry at the
amino N atoms in (III) was a response to the deficit of
conventional hydrogen-bond acceptors in this compound. The
behaviour of compound (II) reported here does not support
this suggestion.
There are no hydrogen bonds in compound (II) involving
the amino groups, either as donors or as acceptors. Instead,
the supramolecular aggregation depends upon two C—Hꢀ ꢀ ꢀ
ꢀ(arene) hydrogen bonds, one of which involves a C—H bond
in the minor component of the disordered thienyl group, so
adding an element of statistical uncertainty to the aggregation.
Fully ordered atom C20 in the molecule at (x, y, z) acts as
hydrogen-bond donor to the C11–C16 ring in the molecule at
(1 ꢁ x, 1 ꢁ y, 1 ꢁ z), so generating a cyclic centrosymmetric
dimer centred at (12, 21, 21) (Fig. 4). Partially occupied atom C44
forms a second hydrogen bond (Table 2), the role of which is
to link the ordered dimers stacked along (n + 12, 21, n + 21), where
n represents an integer. Atom C44 in the molecule at (x, y, z),
which is part of the dimer centred at (12, 1, 21), acts as donor to
the C21–C26 ring in the molecule at (ꢁ2x, 1 ꢁ y, ꢁz), which
When the flanking substituents have sufficient steric bulk,
for example tert-butyl groups, even fairly acidic phenolic
hydroxyl groups sometimes fail to participate in any
hydrogen-bond formation (Rezende et al., 2005; Lutz & Spek,
2005). Thus, a survey (Lutz & Spek, 2005) of the August 2005
release of the CSD identified 53 examples of 2,6-di-tert-
butylphenol derivatives for which H-atom coordinates had
been deposited for fully ordered structures, and in 29 of these
the shielded hydroxyl group formed no hydrogen bonds to any
1
1
itself forms part of the dimer centred at (ꢁ , 12, ꢁ ). Since atom
2
2
C44 lies in the minor component of the disordered thienyl
group, with occupancy 0.386 (3), then a pair of molecules such
as those at (x, y, z) and (ꢁx, 1 ꢁ y, ꢁz) could be linked by two,
ꢂ
o480 Blanco et al. C27H28Cl2N2 and C25H26Cl2N2S
Acta Cryst. (2009). C65, o479–o482

organic compounds
6-allyl-3-chloro-2-methyl-N-(aryl-2-ylmethylene)aniline (1 mmol) in
toluene (10 ml). The reaction mixtures were heated under reflux, with
stirring, for 6–8 h. Each mixture was brought to pH = 8 using aqueous
sodium carbonate solution, and then extracted with ethyl acetate (2 ꢃ
50 ml). The organic extracts were dried over anhydrous sodium
sulfate and then concentrated under reduced pressure to give the
crude products, which were purified by column chromatography on
silica gel using heptane–ethyl acetate (5:1 to 1:1 v/v) as eluent.
Crystallization from heptane gave crystals suitable for single-crystal
X-ray diffraction. Compound (I): yellow crystals, yield 33%, m.p.
405–406 K; MS (70 eV) m/z (%): 450 (M+, 100), 415 (24), 409 (34),
373 (79), 270 (31), 234 (23); analysis found: C 71.9, H 6.2, N 6.3%;
C27H28Cl2N2 requires: C 71.8, H 6.3, N 6.2%. Compound (II):
colourless crystals, yield 25%, m.p. 412–413 K; MS (70 eV) (m/z (%):
456 (M+, 100), 421 (28), 415 (30), 379 (20), 373 (6), 339 (9), 276 (64),
240 (18); analysis found: C 65.6, H 5.8, N 6.2%; C25H26Cl2N2S
requires: C 65.6, H 5.7, N 6.1%.
Figure 3
Compound (I)
Part of the crystal structure of compound (I), showing the formation of a
centrosymmetric R22(24) dimer. For the sake of clarity, H atoms bonded to
C atoms have been omitted, as has the unit-cell outline. Atoms marked
with an asterisk (*) are at the symmetry position (1 ꢁ x, 1 ꢁ y, 1 ꢁ z).
Crystal data
C27H28Cl2N2
Mr = 451.41
Triclinic, P1
a = 8.9868 (2) A
b = 10.8718 (4) A
˚
c = 12.4359 (4) A
ꢁ = 94.333 (2)ꢄ
ꢂ = 93.634 (3)ꢄ
ꢃ = 102.490 (2)ꢄ
3
˚
V = 1178.90 (6) A
Z = 2
˚
Mo Kꢁ radiation
ꢄ = 0.29 mmꢁ1
T = 120 K
0.08 ꢃ 0.08 ꢃ 0.06 mm
˚
Data collection
Bruker–Nonius APEXII
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.971, Tmax = 0.983
15045 measured reflections
4344 independent reflections
3431 reflections with I > 2ꢅ(I)
Rint = 0.059
Refinement
R[F2 > 2ꢅ(F2)] = 0.061
wR(F2) = 0.128
S = 1.08
4344 reflections
294 parameters
4 restraints
H atoms treated by a mixture of
independent and constrained
refinement
ꢁ3
˚
Áꢆmax = 0.28 e A
ꢁ3
˚
Áꢆmin = ꢁ0.31 e A
Figure 4
Compound (II)
A stereoview of part of the crystal structure of compound (II), showing
the formation of a statistically interrupted chain of rings along [101]. For
the sake of clarity, H atoms bonded to C or N atoms which are not
involved in the motifs shown have been omitted, and all possible
C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds involving atom C44 have been
included.
Crystal data
C25H26Cl2N2S
Mr = 457.44
Triclinic, P1
a = 8.7263 (2) A
b = 10.6766 (2) A
ꢃ = 82.367 (2)ꢄ
V = 1104.35 (4) A
Z = 2
3
˚
˚
Mo Kꢁ radiation
ꢄ = 0.40 mmꢁ1
T = 120 K
0.08 ꢃ 0.06 ꢃ 0.05 mm
˚
˚
acceptor. In a total of 90 structures containing 2,6-di-tert-
butylphenol units, none contained Oꢀ ꢀ ꢀO distances consistent
with the formation of hydrogen bonds between pairs of
shielded hydroxyl groups.
c = 12.2691 (3) A
ꢁ = 77.1100 (10)ꢄ
ꢂ = 87.7930 (10)ꢄ
Data collection
Bruker–Nonius APEXII
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.959, Tmax = 0.980
16485 measured reflections
5043 independent reflections
4375 reflections with I > 2ꢅ(I)
Rint = 0.030
Experimental
Thioglycollic acid (2 mmol) and a catalytic quantity of boron tri-
fluoride etherate were added to a solution of the corresponding (E)-
ꢂ
Acta Cryst. (2009). C65, o479–o482
Blanco et al.
C27H28Cl2N2 and C25H26Cl2N2S o481

organic compounds
Table 1
Selected geometric parameters (A, ) for (I) and (II).
kUeq(C), where k = 1.5 for the methyl groups, which were permitted
to rotate but not to tilt, and k = 1.2 for all other H atoms bonded to C
atoms. The coordinates of the H atoms bonded to N atoms were
˚
refined subject to a distance restraint of 0.86 (1) A and with Uiso(H) =
1.2Ueq(N).
ꢄ
˚
Parameter
(I)
(II)
C14—N14
C24—N24
1.390 (4)
1.408 (4)
ꢁ145.7 (3)
ꢁ149.5 (3)
ꢁ128.9 (4)
73.4 (3)
76.8 (4)
10.7 (5)
50.7 (4)
ꢁ76.2 (4)
1.396 (2)
1.400 (2)
For both compounds, data collection: COLLECT (Nonius, 1999);
cell refinement: DENZO (Otwinowski
C21—C1—C11—C12
C14—C15—C18—C19
C15—C18—C19—C20
C11—C1—C21—C22
C24—C25—C28—C29
C25—C28—C29—C30
C11—C1—C31—C32
C21—C1—C31—C32
C11—C1—C32—S31
C11—C1—C32—S41
ꢁ145.13 (15)
ꢁ161.73 (16)
ꢁ130.1 (2)
77.66 (19)
ꢁ78.3 (2)
& Minor, 1997) and
COLLECT; data reduction: DENZO and COLLECT; program(s)
used to solve structure: SIR2004 (Burla et al., 2005); program(s) used
to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
PLATON (Spek, 2009); software used to prepare material for
publication: SHELXL97 and PLATON.
ꢁ12.8 (2)
ꢁ173.47 (12)
ꢁ5.5 (2)
´
JC thanks the Consejerıa de Innovacion, Ciencia y Empresa
(Junta de Andalucıa, Spain), the Universidad de Jaen (project
´
´
´
No. UJA_07_16_33) and the Ministerio de Ciencia e Innova-
´
Table 2
Hydrogen-bond parameters (A, ) for (I) and (II).
ꢄ
˚
cion (project No. SAF2008-04685-C02-02) for financial
support. MCB and AP thank COLCIENCIAS for financial
support (grant No. 1102-405-20350).
Cg1 is the centroid of the C11–C16 ring and Cg2 is the centroid of the
C21–C26 ring.
Compound D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GG3211). Services for accessing these data are
described at the back of the journal.
(I)
(II)
N14—H14Aꢀ ꢀ ꢀN24i 0.86 (3) 2.79 (2) 3.186 (4)(3) 155 (3)
C44—H44ꢀ ꢀ ꢀCg2ii
C20—H20Aꢀ ꢀ ꢀCg1i 0.95
2.90
2.88
3.718 (2)
3.772 (18)
145
156
0.95
Symmetry codes: (i) 1 ꢁ x; 1 ꢁ y; 1 ꢁ z; (ii) ꢁx; 1 ꢁ y; ꢁz.
References
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5043 reflections
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˚
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ꢁ3
˚
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´
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o482 Blanco et al. C27H28Cl2N2 and C25H26Cl2N2S
Acta Cryst. (2009). C65, o479–o482