An unusual C=C?C=O interaction in (Z)-3-[(4-halogenphenyl)amino]-2-cyanoprop-2-enoates

Article abstract of DOI:10.1039/c5nj01814e

An unusual C=C?C=O interaction has been discovered in (Z)-3-[(4-halogenphenyl)amino]-2-cyanoprop-2-enoates and rationalized by the density functional theory calculations. Second order perturbation theory analysis based on the NBO method and LMOEDA energy decomposition further reveals that the C=C?C=O interaction is mainly dominated by dispersion and electrostatic energies, and two orbital interactions.

Full text of DOI:10.1039/c5nj01814e

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LETTER
Q
Q
An unusual C Cꢀ ꢀ ꢀC O interaction in (Z)-3-[(4-
halogenphenyl)amino]-2-cyanoprop-2-enoates†
Cite this: New J. Chem., 2016,
40, 85
Zhenfeng Zhang,* Nana Ma and Xiaopeng Xuan
Received (in Montpellier, France)
12th July 2015,
Accepted 18th August 2015
DOI: 10.1039/c5nj01814e
www.rsc.org/njc
Q
Q
O
An unusual
C
Cꢀ ꢀ ꢀC
interaction has been discovered in
(Z)-3-[(4-halogenphenyl)amino]-2-cyanoprop-2-enoates and ratio-
nalized by the density functional theory calculations. Second order
perturbation theory analysis based on the NBO method and
LMOEDA energy decomposition further reveals that the
Q
Q
C
Cꢀ ꢀ ꢀC O interaction is mainly dominated by dispersion and
electrostatic energies, and two orbital interactions.
Fig. 1 The dimeric structure of ethyl (Z)-2-cyano-3-[(4-bromophenyl)-
amino]prop-2-enoate, 1, showing both experimentally and theoretically
the formation of the Cꢀ ꢀ ꢀC interaction between C3 and C1i; the distances
C3ꢀ ꢀ ꢀC1i from experimental and DFT calculations are 3.277 and 3.186 Å,
respectively. Symmetry code: (i) 1 ꢁ x, 1 ꢁ y, 2 ꢁ z.
Noncovalent interactions play a dominant role in chemical
interactions between a protein and a drug,1 or an enzyme and
its substrate,2 self-assembly of nanomaterials,3 and even some
chemical reactions.4,5 A complete understanding of these
chemical interactions will often demand a complete under-
standing of the noncovalent interactions too. Therefore, it is
not surprising that a great deal of interest has been generated
in the study of noncovalent interactions. Experimental and
theoretical results have shown that unsaturated carbon atoms
can act as an electron donors6–8 as well as an electron acceptors9
forming various kinds of noncovalent interactions, such as
Cꢀꢀꢀp, cationꢀꢀꢀp and anionꢀꢀꢀp, etc. Considering the complementary
roles of carbon atoms, Cꢀ ꢀ ꢀC interactions are expected to occur
between electron-rich vinyl and electron-poor carbonyl fragments.
Our interest in b-enamino esters, (Z)-3-[(4-halogenphenyl)amino]-
2-cyanoprop-2-enoates, mainly stems from this expectation. In this
context, we have prepared a series of such b-enamino esters and
studied their X-ray crystal structures.
between C3 and C1i is only 3.277(3) Å, which is significantly shorter
than the sum of van der Waals radii, 3.4 Å. The characteristic
geometry suggests a pair of CꢀꢀꢀC interactions between the vinyl
and carbonyl groups.
A recent study7 has shown the existence of CꢀꢀꢀC interactions.
However, the only work on this subject still remains theoretical.
A computational study shows that the CꢀꢀꢀC interactions exist
between electron-deficient molecules (CO2 or NCCN) and
electron-rich molecules, such as HCRCH and H2CQCH2, etc.,
and that all the dimers formed by this interaction show C2V
symmetry and correspond to energy minima. The CQCꢀꢀꢀCQO
interaction in 1, we believe, is very similar to the CH2QCH2ꢀꢀꢀCO2
interaction, though the formed dimers differ in parameters and
symmetry.
Interestingly we have discovered a hitherto unreported
CQCꢀꢀꢀCQO interaction in the supramolecular structure of ethyl
(Z)-3-[(4-bromophenyl)amino]-2-cyanoprop-2-enoate, 1 (Fig. 1). As
shown in the figure, the vinyl atom C3 resides orthogonally above
the pseudotrigonal axis of the ester carbonyl group. The distance
School of Chemistry and Chemical Engineering, Henan Normal University,
Xinxiang 453007, P. R. China. E-mail: zzf5188@163.com; Fax: +86 373-3326336;
Tel: +86 373-3326335
To quantitatively evaluate the strength of the CQCꢀ ꢀ ꢀCQO
interactions, the density functional theory (DFT) calculations at the
WB97XD10/6-311+G(d,p) level were performed on compound 1.
† CCDC 952088. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c5nj01814e
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The monomer and the dimers formed by CQCꢀꢀꢀCQO interaction 1.36 kcal molꢁ1. The results have theoretically confirmed that
were studied. All the calculations were carried out using the the orbital interaction between the vinyl and carbonyl groups,
GAUSSIAN 0911 package. At this selected theoretical level, both though weak, can actually occur, and may be of vital importance
the monomer and dimer of 1 correspond to energy minima, and in controlling the directionality and geometrical details.
are in good agreement with the crystallographically determined
Here the CQCꢀꢀꢀCQO interaction, though being bidirectional
structure. The optimized dimer is also shown in Fig. 1. As charge-transfer, leads to a redistribution of charge within the
shown in the figure, the atom C3 approaches the atom C1i dimer. NBO calculations have revealed that during the formation
perpendicularly to the ester carbonyl plane, and the distance of the CQCꢀꢀꢀCQO bond, the positive charge on the carbonyl
between C3 and C1i is 3.186 Å. The total dimerization energy is atom C1i decreases from 0.821 to 0.810 e, the charge (0.182 e) on
ꢁ20.79 kcal molꢁ1, showing theoretically that the CQCꢀ ꢀ ꢀCQO the partner atom C3 is, however, nearly unchanged, thus reducing
interaction is thermodynamically most favorable.
the repulsion component between C3 and C1i. Conversely, the
It is widely accepted that the natural bond orbital (NBO) negative charges on atoms C2 and N2 increase from ꢁ0.384 and
theory12,13 is quite useful for analyzing intermolecular inter- ꢁ0.340 e to ꢁ0.397 and ꢁ0.363 e, respectively, the former favoring
actions.14 In order to further characterize the CQCꢀ ꢀ ꢀCQO to maintain the dimer in a lower electrostatic repulsion level due to
interaction via orbital interactions, we have also performed the longer distance between C2 and C2i, and the latter favoring to
NBO analysis on the CQCꢀ ꢀ ꢀCQO dimer with NBO version enhance the following C–HꢀꢀꢀNRC hydrogen bond.
3.115 incorporated in the G09 package using the optimized
In addition to the orbital interactions between the vinyl and
ground-state geometries. Interestingly, we have found that carbonyl groups, the CQCꢀꢀꢀCQO dimer should also be stabilized
there are four intermolecular orbital interactions corresponding by other standard energy contributions, such as dispersion,
to the CQCꢀ ꢀ ꢀCQO interaction, out of which only the strongest electrostatic, exchange-repulsion and polarization. To roundly
interactions (as well as strongest between the dimer), A and B, explore the source of dimerization energy (ꢁ20.79 kcal molꢁ1),
are shown in Table 1 and Fig. 2. As shown in the table and we employed the localized molecular orbital energy decomposition
figure, the p-orbital of the carbonyl O1iQC1i interacts with the analysis (LMOEDA) approach of Su and Li16 to decompose the
p*-antibonding orbital of the vinyl C3QC2, with a concomitant CQCꢀ ꢀ ꢀCQO interaction energy into electrostatic, exchange,
second-order stabilization energy of E(2) = 0.27 kcal molꢁ1, and repulsion, polarization, and dispersion components. The
on the other hand, the p-orbital of C2QC3 interplays with LMOEDA computations have been performed using the
the p*-antibonding orbital of the C1iQO1i bond, with a GAMESS package at the MP2/maug-cc-pVTZ level.17 The results
second-order energy of 0.26 kcal molꢁ1. The orbital interactions shows that the CQCꢀ ꢀ ꢀCQO interaction is mainly dominated by
involving atoms C1 and C3i are completely identical to the dispersion energy and electrostatic energy, which contribute
ones involving C1i and C3. The total stabilization energy that 66.6% and 25.4%, respectively, to the total dimerization energy.
attributed to the CQCꢀ ꢀ ꢀCQO interactions is approximately
Given that the CQCꢀ ꢀ ꢀCQO interactions occur in ethyl
(Z)-3-[(4-bromophenyl)amino]-2-cyanoprop-2-enoate, 1, it is very
probable to find this kind of interactions in ethyl (Z)-3-[(4-
chlorophenyl)amino]-2-cyanoprop-2-enoate, 2 and methyl (Z)-3-[(4-
Table 1 Stabilization energies for selected NBO pairs in 1, as given by
second order perturbation theory analysis of the Fock Matrix in the NBO bromophenyl)amino]-2-cyanoprop-2-enoate, 3.
basis, obtained from WB97XD10/6-311+G(d,p)
Keeping our motivation in mind, we replace the Br1 atom
(Fig. 1) with a Cl1 atom and the O2-ethyl with methyl to build
the monomer and dimer of 2 and 3, respectively, for the
evaluation of CQCꢀ ꢀ ꢀCQO interactions. The DFT calculations
were performed for geometry optimization using the same
methods as for 1. Interestingly, in the optimized dimers 2
and 3, the main geometry parameters are in perfect accordance
with those found in 1 (Fig. 1); the atom C3 approaches the atom
C1i perpendicularly to the ester carbonyl plane; the distances
between C3 and C1i are 3.188 and 3.218 Å, respectively. The
corresponding total dimerization energies are ꢁ20.76 and
19.18 kcal molꢁ1, respectively. The main orbital interactions
involved in the CQCꢀ ꢀ ꢀCQO interaction are A, p(O1iQC1i) -
p*(C3QC2), and B, p(C2QC3) - p*(C1iQO1i) (Fig. 3), which
are shown by the second-order perturbation theory analysis of
the Fock Matrix. The results reveals that the CQCꢀ ꢀ ꢀCQO
interactions do exist universally in (Z)-3-[(4-halogenphenyl)amino]-
2-cyanoprop-2-enoates.
Pair name
Donor NBO
Acceptor NBO
E(2) energy (kcal molꢁ1
)
A
p(O1iQCi)
p(C2QC3)
p(O1QC1)
p(C2iQC3i)
p*(C3QC2)
p*(C1iQO1i)
p*(C3iQC2i)
p*(C1QO1)
0.27
0.26
0.27
0.26
B
A0
B0
The CQCꢀ ꢀ ꢀCQO interaction is very scarce. Searches of the
i
Fig. 2 Dominant orbital interactions A, p(O1QC1i) - p*(C3QC2), and B,
p(C2QC3) - p* (C1QO1i), showing the nature of the CQCꢀꢀꢀCQO in 1. For
i
Cambridge Structural Database (CSD) showed that no such
the sake of clarity, the same orbital interactions A0 and B0 have been omitted. interaction occurred between the vinyl and carbonyl groups
86 | New J. Chem., 2016, 40, 85--88
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i
Fig. 3 The dominant NBO orbital interactions A, p(O1QC1i) - p*(C3QC2),
and B, p(C2QC3) - p*(C1QO1i) corresponding to the CꢀꢀꢀC interaction
i
between vinyl atom C1 and carbonyl atom C3i in 2 (left) and 3 (right). For the
sake of clarity, the same orbital interactions between atoms C3 and C1i have
been omitted.
Fig. 5 Part of the crystal structure of 1, showing the formation of a
two-dimensional sheet via Cꢀ ꢀ ꢀC, Nꢀ ꢀ ꢀBr and C–Hꢀ ꢀ ꢀN interactions. For
the sake of clarity, H atoms not involved in the motif shown have been
omitted. Symmetry codes: (ii) ꢁx, 1 ꢁ y, 2 ꢁ z; (iii) x, y + 1, z ꢁ 1.
despite the abundance of vinyl and carbonyl groups existing in
crystal structures deposited so far in the CCDC. However, this
interaction exists predominantly in (Z)-3-[(4-halogenphenyl)amino]-
2-cyanoprop-2-enoates.
C–Hꢀ ꢀ ꢀN hydrogen bonds (Fig. 4); chains of this type are laterally
linked to a sheet by Nꢀ ꢀ ꢀBr interactions (Fig. 5).
In conclusion, the detailed structural analysis has revealed
an unusual CQCꢀ ꢀ ꢀCQO interaction existing predominantly in
(Z)-3-[(4-halogenphenyl)amino]-2-cyanoprop-2-enoates. The DFT
computations and second order perturbation theory analysis of
the Fock Matrix on the NBO basis at the WB97XD/6-311+G(d,p)
level provided effective support to the interaction. The present
work, we believe, may be the first systematic study on CꢀꢀꢀC
interactions occurring between the vinyl and carbonyl fragments.
The crystal structure of 1 also exhibits strong intramolecular
N–Hꢀ ꢀ ꢀO hydrogen bonding and strong Hꢀ ꢀ ꢀH van der Waals
repulsion (Fig. 1). The distance of N1–H1ꢀ ꢀ ꢀO1 is 2.01 Å and
the associated angle is 1331. The H3ꢀ ꢀ ꢀH6 distance and the
C3–N1–C5–C6 torsion angle are 2.25 Å and 211, respectively,
suggesting strong van der Waals repulsion between C3–H and
C6–H. A combination of these two interactions leads to a nearly
planar conformation on the molecule’s main skeleton. This
conformation sets the stage for the CQCꢀ ꢀ ꢀCQO interactions
observed within the crystal lattice.
In addition to the CQCꢀ ꢀ ꢀCQO interactions, there are
two intermolecular noncovalent interactions in 1, one is of
vinyl C–Hꢀ ꢀ ꢀNRC type (Fig. 4), and the other is of CRNꢀ ꢀ ꢀBr
type (Fig. 5). The distances of H3ꢀ ꢀ ꢀN2ii and N2iiiꢀ ꢀ ꢀBr1 are 2.47
and 3.36 Å, respectively, and the bond angle of C3–H3ꢀ ꢀ ꢀN2ii is
1681. These noncovalent interactions synergistically constitute
a stepped (011) sheet, the formation of which can be understood
in the following way: the inversion-related molecules form a
dimer via a pair of CQCꢀ ꢀ ꢀCQO interactions (Fig. 1 and 4); such
dimers related by translation are further linked to a stepped
molecular chain parallel to [100] via a pair of equivalent
Experimental
Synthesis of ethyl (Z)-3-[(4-bromophenyl)amino]-2-cyanoprop-2-
enoate, 1
A mixture of 4-bromoaniline (0.02 mol) and ethyl-2-cyano-3-
ethoxyacrylate (0.02 mol) in toluene (10 ml) was refluxed for ca.
10 min. The reaction mixture was then cooled to room temperature.
The precipitate was collected by filtration and washed with
ethanol. Crystals suitable for X-ray analysis were obtained by
slow cooling of a hot toluene solution of the crude product.
X-Ray structure determination
The selected crystal was mounted with inert oil on glass fibers.
Data were measured using Mo-Ka radiation on a Bruker SMART
1000 CCD diffractometer. Data collection at 296 K and reduction
were performed using the SMART and SAINT software.18
Absorption correction was applied using the multi-scan
method (SADABS).19 The crystal structure of 1 was solved by
direct methods and refined by full matrix least-squares on F2
using the SHELXTL program package.20 All non-hydrogen
atoms were subjected to anisotropic refinement, and all H atoms
were placed in geometrically idealized positions and constrained
to ride on their parent atoms.
Crystal data
%
C
12H11BrN2O2, M = 295.13, triclinic, P1, a = 7.495 (1) Å, b = 7.525
Fig. 4 Packing diagram of 1, showing the formation of the stepped
hydrogen-bonded chain along the [100] direction. For the sake of clarity,
H atoms not involved in the motif shown have been omitted. Symmetry
transformations: (i) 1 ꢁ x, 1 ꢁ y, 2 ꢁ z; (ii) ꢁx, 1 ꢁ y, 2 ꢁ z.
(1) Å, c = 12.065(1) Å, a = 80.285(2)1, b = 86.767(2)1,
g = 67.729(2)1, V = 620.7(2) Å3, Z = 2, T = 293(2) K,
Dc = 1.579 g cmꢁ3; 6597 reflections collected, 2189 unique
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