On the structure of cross-conjugated 2,3-diphenylbutadiene

Article abstract of DOI:10.1002/ejoc.200700410

The structure of the cross-conjugated compound 2,3-diphenylbutadiene was investigated by single-crystal X-ray diffraction and computational methods. In the crystal structure the central butadiene fragment adopts an s-gauche geometry [-55.6(2)° torsion angle φ around the essential single bond], whereas the styrene moieties are close to planarity. MP2/6-311G* calculations show that the s-gauche conformation represents the global minimum along the φ coordinate, but also revealed the existence of an s-trans local minimum. While the crystal structure seems to reflect dominance of styrene-like conjugation, the MP2/6-311G* calculations indicate that conjugation in both the styrene and butadiene π-systems is important. An NBO orbital deletion study shows that the structure is primarily determined by (hyper)conjugation and that steric effects play a minor role. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700410

FULL PAPER
DOI: 10.1002/ejoc.200700410
On the Structure of Cross-Conjugated 2,3-Diphenylbutadiene
Cornelis A. van Walree,*[a] Bas C. van der Wiel,[a] Leonardus W. Jenneskens,[a]
Martin Lutz,[b] Anthony L. Spek,[b] Remco W. A. Havenith,[c] and Joop H. van Lenthe[c]
Keywords: Conformation analysis / ab initio calculations / Conjugation / Hyperconjugation
The structure of the cross-conjugated compound 2,3-di-
phenylbutadiene was investigated by single-crystal X-ray
diffraction and computational methods. In the crystal struc-
ture the central butadiene fragment adopts an s-gauche ge-
ometry [–55.6(2)° torsion angle φ around the essential single
bond], whereas the styrene moieties are close to planarity.
MP2/6-311G* calculations show that the s-gauche conforma-
tion represents the global minimum along the φ coordinate,
but also revealed the existence of an s-trans local minimum.
While the crystal structure seems to reflect dominance of sty-
rene-like conjugation, the MP2/6-311G* calculations indi-
cate that conjugation in both the styrene and butadiene π-
systems is important. An NBO orbital deletion study shows
that the structure is primarily determined by (hyper)conjuga-
tion and that steric effects play a minor role.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
tion in a 2,3-diphenylbutadiene of which the phenyl groups
were functionalized with electron donor-acceptor groups
has been demonstrated, showing that charges can be trans-
ported over this cross-conjugated π-system.[15] In 2,3-di-
phenylbutadiene three potential linear π-paths, viz. a 1,3-
butadiene subsystem and two styrene subsystems, are dis-
tinguished (Figure 1, a). This brings about that 1 can be
regarded as a diphenyl-substituted butadiene, as α,α-bi-
styryl, or as somewhere in between these extremes. Which
linear conjugation path prevails depends strongly on the di-
hedral angles between the different unsaturated moieties,
and the other way around. It is known from work on related
branched π-compounds such as dendralenes[1,16] and phen-
ylenevinylidene oligomers[5] that steric interactions have a
large impact on the structure of these compounds. In 1,
twisting can occur along the essential single bond between
the double bonds (φ) or along the single bonds which con-
nect the phenyl groups to the double bond (θ, Figure 1, b).
When conjugation in the butadiene subsystem dominates,
rotation will occur along θ. Behavior as two α-bonded sty-
renes will be reflected by rotation along φ.
Introduction
Molecules and polymers with a π-conjugated bonding
motif play a central role in the development of organic ma-
terials with advanced optic, electronic or electro-optic func-
tions. Their properties depend strongly on the type of un-
saturated units present (which can be double bonds, triple
bonds or various kinds of aromatic moieties), but another
factor of interest is the topology in which the unsaturated
building blocks are connected. These are usually arranged
in a linear fashion, but also a branched architecture is pos-
sible.[1–7] In branched π-systems, which are also referred to
as cross-conjugated systems,[8,9] several linear π-conjugation
paths are present. From a fundamental point of view it is
of interest to assess which conjugation path dominates in a
given cross-conjugated compound, and by which factors
this is controlled. Knowledge of these and other properties
of branched π-systems is important for the rational design
of 2-dimensional conjugated systems.[10] These hold a
promise as advanced switching and conducting systems,[3,11]
while radical cations derived from cross-conjugated systems
may form the foundation of high-spin magnetic materi-
als.[12–14]
A fundamental type of branched π-system is presented
by 2,3-diphenylbutadiene (1). Photoinduced charge separa-
[a] Organic Chemistry and Catalysis, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
E-mail: c.a.vanwalree@chem.uu.nl
[b] Bijvoet Center for Biomolecular Research, Crystal and Struc-
tural Chemistry, Utrecht University,
Figure 1. Possible conjugation paths (a) and designation of torsion
angles (b) in 2,3-diphenylbutadiene 1.
Padualaan 8, 3584 CH Utrecht, The Netherlands
[c] Theoretical Chemistry Group, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
In this contribution the molecular structure of 2,3-di-
phenylbutadiene is reported and interpreted in terms of
conjugation phenomena and steric interactions. This is
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4746–4751

Cross-Conjugated 2,3-Diphenylbutadiene
done by single-crystal X-ray diffraction, MP2/6-311G*
structural calculations and a natural bond orbital (NBO)
analysis.
Results and Discussion
Single Crystal X-ray Structure
To our surprise, the single-crystal X-ray structure of the
relatively simple compound 1 has, until recently, not been
published. The reason might be that, as we reported earlier,
the crystal structure is subject to reticular pseudomerohed-
ral twinning.[17] The molecular structure is depicted in Fig-
ure 2, while important bond lengths and torsion angles are
compiled in Tables 1 and 2, respectively. In the pseudo C2
symmetric structure the compound adopts a butterfly-like
geometry with a face-to-face like arrangement of the phenyl
Figure 2. Displacement ellipsoid plot of the 2,3-diphenylbutadiene
crystal structure, drawn at the 50% probability level, and adopted
groups. The angle between the normals to the phenyl numbering scheme.
groups is 73.10(8)°. A striking feature is that the C11–C12–
C22–C21 torsion angle φ is –55.6(2)°. Thus, the butadiene
Table 1. C–C bond lengths [Å] in the crystal structure of 1, along
with bond lengths in the MP2/6-311G* calculated s-gauche and s-
trans minima (C2 symmetry).
subsystem is in a gauche conformation and far from planar.
By analogy with butadiene,[18,19] one would be inclined to
think that 1 adopts an s-trans geometry. Torsion angles
around the C12–C13 and C22–C23 single bonds all lie in
Bond
X-ray
s-gauche s-trans
Bond
X-ray
the range –15.6(2) to –19.3(3)° or 160.50(18) to 164.92(15)°. C11–C12 1.329(3) 1.350
1.352
1.483
1.480
1.403
1.404
1.397
1.397
1.399
1.395
C21–C22 1.335(3)
C22–C23 1.486(2)
C12–C13 1.491(2)
C12–C22 1.492(2)
C13–C14 1.393(2)
C13–C18 1.397(3)
C14–C15 1.391(2)
C15–C16 1.386(3)
C16–C17 1.377(3)
C17–C18 1.383(3)
1.480
1.484
1.404
1.403
1.395
1.398
1.397
1.396
The near-planar geometry around these bonds corresponds
to the situation in styrene, for which torsion angles of the
same order of magnitude have been reported.[18,20] Both the
butadiene and the styrene substructures suggest that 1
should be regarded as being composed of two α,α-linked
styrene units, rather than as a disubstituted butadiene. This
is supported by the C12–C22 bond length of 1.492(2) Å.
Even for a C(sp2)–C(sp2) single bond in a twisted system
(i.e., with torsion angles larger than 20°; the average length
of such bonds is 1.478(12) Å][21] this is long. Somewhat in
disagreement with the above picture, the lengths of the
C12–C13 and C22–C23 single bonds do not match those in
other planar styrene moieties and are quite large for a
C(sp2)–C(aryl) single bond. The average length of C(sp2)–
C(aryl) bonds is 1.470(15) Å.[21] The C11–C12 and C21–
C22 distances do not lend themselves to discriminate
between butadiene or styrene conjugation, as they do
not deviate from the double bond length in both
butadienes (1.330(14) Å] and phenyl-substituted alkenes
(1.339(11) Å].[21] No sign of bond length alternation is de-
C23–C24 1.397(2)
C23–C28 1.399(3)
C24–C25 1.390(2)
C25–C26 1.381(3)
C26–C27 1.381(3)
C27–C28 1.380(2)
Table 2. Selected torsion angles in the crystal structure of 1.
C11–C12–C13–C14 162.49(18) C13–C12–C22–C21 122.5(2)
C11–C12–C13–C18 –17.0(3)
C22–C12–C13–C14 –15.6(2)
C22–C12–C13–C18 164.92(15) C12–C22–C23–C28 162.89(15)
C13–C12–C22–C23 –59.6(2)
C12–C22–C23–C24 –17.3(2)
C11–C12–C22–C21 –55.6(2)
C11–C12–C22–C23 122.3(2)
C21–C22–C23–C24 160.50(18)
C21–C22–C23–C28 –19.3(3)
Structural Calculations
To get a deeper understanding of its structure, 1 was sub-
tected within the phenyl groups. It is known that bond jected to MP2/6-311G* calculations. A free optimization in
length alternation phenomena are not particularly pro- the C2 point group gave an s-gauche structure with φ = 48.7°
nounced in cross-conjugated compounds.[22]
and θ = 37.3° (Figure 3) at an energy of –616.584103 a.u.
Short intramolecular contacts between the atoms or pair (–386912.42 kcalmol–1). As φ is close to the angle found in
of atoms C11/H11 and C18/H18, C21/H21 and C28/H28, the crystal, the calculated structure looks similar to the X-
C12 and H24, and C22 and H14 are observed. This suggests ray structure. However, since the phenyl-C=C torsion angle
that the region where the phenyl groups are linked to the θ is 37.3°, twisting about the C12–C13 bond is much more
butadiene moiety is crowded, and this may well be responsi- pronounced than in the crystal so that the calculated struc-
ble for the long C12–C13 and C22–C23 bonds. Steric con- ture reflects less styrene conjugation than the geometry in
gestion in the butadiene moiety itself does not occur. This the solid state. As can be seen in Table 1, the MP2 lengths
can be taken as another indication that conjugation within of the single bonds are on the short side, while the double
the butadiene moiety is more readily disrupted than conju- bonds are a fraction too long. This indicates that MP2
gation within the styrene moieties.
tends to overestimate the conjugation to some extent.
Eur. J. Org. Chem. 2007, 4746–4751
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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C. A. van Walree et al.
FULL PAPER
Table 3. 6-311G*/MP2 calculated torsion angles θ and ω as well as
energies of 2,3-diphenylbutadiene (1) as a function of torsion angle
φ.
φ[a]
θ[b]
ω[c]
E [a.u.]
0
15
30
45
60
75
90
105
120
135
150
165
180
56.4
49.2
43.5
38.4
34.4
32.0
31.5
151.2
143.7
138.4
131.7
123.5
113.2
51.9
43.3
39.4
37.4
36.7
37.3
39.1
150.7
142.7
135.5
130.1
124.4
115.9
–616.577043
–616.579999
–616.582762
–616.584059
–616.583606
–616.581725
–616.578882
–616.577466
–616.578775
–616.580662
–616.582118
–616.582279
–616.581056
[a] C11–C12–C22–C21 (see Figure 1). [b] C11–C12–C13–C18. [c]
C22–C12–C13–C14. Note that in contrast to the X-ray data in the
calculations φ was taken as positive.
Figure 3. MP2/6-311G* calculated s-gauche (top) and s-trans (bot-
tom) minima of 1.
Also, the energy of 1 as a function of rotation along the
C12–C22 bond was evaluated. The C11–C12–C22–C21 tor-
sion angle φ was varied in 15° steps; at each point all other
coordinates were optimized within the C2 point group. The
only other coordinates for which large changes can occur
are the dihedral angles between the phenyl and butadienyl
moieties, C11–C12–C13–C18 (θ) and C22–C12–C13–C14
(ω). Obviously, these angles are of similar magnitude
(Table 3). As shown in Figure 4, two minima are found
along the φ coordinate. The point of lowest energy at this
grid is situated at φ = 45°, with θ = 38.4° (Table 3), essen-
tially the same geometry as obtained in the free optimiza-
tion. A second minimum is found at φ = 165°. Here 1
adopts an extended structure with an s-trans torsion angle
about the central single bond. A free optimization of this
conformer yielded a geometry with φ = 159.2° and θ =
126.8° at –616.582390 a.u. (–386911.34 kcalmol–1). Hence,
the butadiene part is quite planar, while the phenyl groups
Figure 4. MP2/6-311G* torsional potential along the C12-C22
bond (φ) in 2,3-diphenylbutadiene 1.
are rotated out of the plane by 53° (Figure 3). The energy parts, i.e. at the smallest values of θ and ω which occur
at this geometry is 1.08 kcalmol–1 higher than at φ = 48.7°. from φ = 60° to φ = 120°, the energy is however not at a
This implies that, although the calculations indicate that a minimum. Interestingly, the smallest torsion angle θ is even
s-gauche geometry such as found in the solid state is favored found at the saddle point at φ = 105°; the value 180–151.2°
indeed, in solution or in the gas phase the compound can is in agreement with the one typically calculated for styrene,
also occur in a stretched s-trans geometry. The barrier at φ which varies from 0–30°.[18] The transition state in butadi-
= 105°, which has a height of 4.14 kcalmol–1 from the s- ene is also found near φ = 105°.[18,19] It is common knowl-
gauche site, is easily crossed at ambient temperatures. A sec- edge that the energy is high at this point because the π-
ond maximum occurs at the s-cis geometry of the butadiene bond of butadiene is broken. These observations imply that
fragment (φ = 0°).
an (at least partially) intact butadiene π-system is important
There appears to be a delicate balance between planarity for the stability of 1, and that a planar styrene π-system is
of the butadiene subsystem and planarity of the styrene not of crucial importance. The calculated barrier height is
subsystems. At φ = 0° the butadiene π-system is intact, but about 2.0 kcalmol–1 lower than the MP2/6-311G** calcu-
the energy is high since the phenyl groups are forced to be lated barrier in butadiene.[18] This difference suggests that
rotated by some 55° because of steric interference between the stabilizing effect of the phenyl groups on the transition
the ortho hydrogen atoms. In this context it is noteworthy state is only slightly larger than the stabilizing effect of the
that in butadiene the energy of the s-cis geometry (φ = 0°) phenyl groups in the minima.
is not very different from that of the gauche local mini-
Hence, according to the MP2/6-311G* calculations nei-
mum.[18,19] In 1 some stabilisation must be absent owing to ther planarity of the butadiene nor of the styrene conjuga-
the relatively large θ. At maximum planarity of the styrene tion path dominates the structure of 2,3-diphenylbutadiene.
4748
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Eur. J. Org. Chem. 2007, 4746–4751

Cross-Conjugated 2,3-Diphenylbutadiene
Two minima are found; the s-gauche structure reflects sty-
rene conjugation, while the s-trans geometry is based on
butadiene conjugation. This is also suggested by the calcu-
lated bond lengths and the bond length alternation patterns
(Table 1). The C12–C13 bond is slightly shorter in the s-
gauche than in the s-trans geometry, whereas the C12–C22
distance is somewhat shorter in the s-trans minimum.
NBO Deletion Studies
In order to find out to what extent conjugation and steric
factors are responsible for its structure, 1 was subjected to
a natural bond orbital (NBO) deletion study.[23,24] In this
analysis, canonical molecular orbitals are first transformed
into a set of localized NBOs comprising core orbitals, lone
pairs, Rydberg orbitals, and two center orbitals.[25] The sub-
sequent deletion of weakly occupied NBOs leads to energy
changes which can be regarded to represent the loss in delo-
calization energy. Here, the deletion energy Edel is evaluated
as a function of the central butadiene torsion angle φ. To
this end, the energy of a particular conformation was calcu-
lated upon simultaneous deletion of π* and σ* NBOs of
the butadiene system including the C12–C13 and C22–C23
bonds. This gives the contribution of the idealized Lewis
structure (EL) to the total energy (Etot) and represents a
fully localized description. The non-Lewis fraction of the
total energy ENL is given by the difference between the total
energy and the Lewis contribution and equals the deletion
energy (ENL = Edel = Etot – EL). This non-Lewis contri-
bution corresponds to the delocalization energy provided
that contributions from Rydberg orbitals are negligible and
steric repulsions are small.[24] Since the NBO analysis is not
feasible with the MP2 method, it was performed at the
SCF/6-311G* level of theory. The SCF/6-311G* torsional
potential around φ (∆Etot, Figure 5) is similar to the MP2/
6-311G* curve, albeit that the s-gauche minimum is situated
at 60 instead of 45°. The Edel data were set to zero at φ =
Figure 5. Effect of deletion of the butadiene σ* and π* NBOs
(∆Edel) as a function of φ. Differences in the total SCF/6-311G*
energy ∆Etot are also given. In order to facilitate comparison with
∆Etot, ∆Edel data were set to zero at 165°. As a consequence, verti-
cal distances between the curves are arbitrary. At minima in the
∆Edel curve the delocalisation energy is large. Drawn lines are
guides to the eye and have no physical significance.
The mutual interactions between the butadiene-type double
bonds, interactions between the butadiene double bond and
the phenyl groups, delocalization within the σ-framework,
and “σ-π mixing” (hyperconjugation) all play a role. Inspec-
tion of second-order interaction energies in the NBO basis
reveals that an important factor in the rotational behaviour
of 1 is the hyperconjugative interaction in which the C11–
C12 (or C21–C22) π-bond functions as donor and the C22–
C23 (or C12–C13) σ* NBO functions as acceptor. This in-
teraction is maximal (5.27 kcalmol–1 a piece) at φ = 90°,
while it is smaller than 0.5 kcalmol–1 at the extremes of φ.
It is noteworthy that the hyperconjugation has a opposite
nature from that in alkenes, which relies on electron do-
nation from saturated to unsaturated bonds.[26]
165° in order to compare them with the total energy (∆Edel
;
General Discussion and Conclusions
the minimum of the Edel curve is actually situated at
–167.01 kcalmol–1, at φ = 60°).
From the perspective of the structure of butadiene, which
It is evident from Figure 5 that the course of the total prefers to adopt an s-trans conformation around the central
energy closely follows the ∆Edel data. The location of the single bond,[18,19] the s-gauche crystal structure of 2,3-di-
two minima and the transition state coincide nicely, while phenylbutadiene is unexpected. The MP2/6-311G* calcula-
energy differences between stationary points do not differ tions show that the s-gauche conformation represents one
by more than about 1.5 kcalmol–1. This makes clear that of the two minima along the φ coordinate, the other one
the conformational behavior of 1 is almost entirely gov- being a structure with an s-trans butadiene geometry. The
erned by delocalization phenomena. Also the observation energy of the latter conformer is slightly higher. The two
that the s-gauche minimum has a lower energy than the s- minima are separated by a barrier at a geometry with a
trans minimum is a consequence of a different delocaliza- highly twisted butadiene π-system (φ = 105°). It is note-
tion energy. The good agreement between the ∆Etot and worthy that only one crystal structure of a related butadiene
∆Edel curves show that secondary effects like steric repul- is available in the literature, that of 2,3-di-tert-butyl-1,3-bu-
sion play only a minor role along the φ coordinate. Steric tadiene.[27] In this compound the torsion angle around the
crowding was seen to have a possible effect on the C12–C13 central single bond amounts to 96.62(14)°, which is close to
and C22–C23 bond lengths in the X-ray structure, but small the torsion angle at the transition state in 1 (for the gas
variations in bond lengths are not expected to have a signifi- phase, a similar torsional angle of 101.5° has been re-
cant bearing on the delocalization energy.
ported[28]).
The rotational dependence of the delocalization and total
The crystal structure of 1 is similar to the electron dif-
energy arises from an interplay of a number of interactions. fraction structure of [4]dendralene (3,4-dimethylenehexa-
Eur. J. Org. Chem. 2007, 4746–4751
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4749

C. A. van Walree et al.
FULL PAPER
106 mmol) was added, upon which a clear, orange-red solution was
obtained. The temperature of the reaction mixture was gradually
allowed to reach room temperature. After 1 h stirring, a solution
of benzil (10.00 g, 47.57 mmol) in THF (70 mL) was added in
30 min. The reaction mixture was refluxed overnight, quenched
with water (250 mL) and extracted with diethyl ether (3ϫ250 mL).
The combined organic layers were dried on magnesium sulfate, fil-
tered and dried under reduced pressure. Crude 1 (16.09 g, purity Ͻ
76% according to GC) was obtained after flash chromatography
with chloroform on silica. Consecutive recrystallisations from hex-
1,5-diene). This compound adopts a C2 geometry with a
central torsion angle (compare to φ in 1) of 71.7° and a θ-
like torsion angle of –174.8°.[16] Ab initio calculations at
various levels of theory give a somewhat larger torsion an-
gle φ of 73.8–80.2° and θ values in the range 172.4–
174.8°.[16,30] According to the same calculations, a con-
former with φ and θ angles of 158.4 and –48.5°, respectively,
being reminiscent of the s-trans structure of 1, occurs as
well.[16] It is 2.1 kcalmol–1 higher in energy than the mini-
mum structure. In 1, the preference for the gauche geometry ane and ethanol gave 1.5 g (15%) of pure 1 (purity Ͼ 99.7% by
1
GC); m.p. 46 °C (ref.[36] 45–47 °C). H NMR (CDCl3): δ = 7.41–
is thus less pronounced. When interpreted in terms of con-
2
7.36 (m, 4 H, Ar-H), 7.29–7.20 (m, 6 H, Ar-H), 5.53 (d, JH,H
=
jugation, this suggests that in the s-gauche structure of 1
interaction between the double bonds and the phenyl
groups is relatively inefficient. This is rationalized by the
fact that stabilization by interactions between olefinic π-
levels, which are of similar energy, will be more favourable
than stabilization by an interaction between energetically
different phenyl and olefinic π-levels. It is further note-
worthy that in the prevailing structure of the simplest cross-
conjugated compound, [3]dendralene (3-methylenepenta-
1,4-diene), there is a slightly twisted anti-butadiene frag-
ment while the third vinyl group is rotated by 40–50° rela-
tive to the butadiene plane.[29,30]
2
1.65 Hz, 2 H, =CH2), 5.30 (d, JH,H = 1.65 Hz, 2 H, =CH2) ppm.
13C NMR (CDCl3): δ = 150.0 (C =CH2), 140.4, 128.3 (2ϫ), 127.7
(aromatic C), 116.5 (C=CH ) ppm. IR (neat): ν = 3032, 1608, 1574,
˜
2
1493, 1443, 1098, 1071, 1029, 902, 774, 705 cm–1. GC-MS: m/z =
206 [M+], 191, 178, 165, 152, 128, 115, 102, 91, 77, 51.
Supporting Information (see also the footnote on the first page of
this article): Cartesian coordinates of the MP2/6-311G* s-gauche
and s-trans geometries of 2,3-diphenylbutadiene.
Acknowledgments
By exhibiting small dihedral angles θ around the phenyl-
butadiene essential single bonds, the solid state geometry
suggests that occurrence of conjugation in the styrene parts
is more important than conjugation in the butadiene frag-
ment. The ab initio calculations refine this picture and show
that butadiene conjugation can certainly not be neglected.
This is indicated by the presence of a minimum with an
almost planar butadiene subsystem and large θ and by the
penalty that is paid on breaking the butadiene π-system in
the transition state. According to its structure, 1 should thus
neither be considered as a α,α-bistyryl nor as a 2,3-disubsti-
tuted butadiene. The actual situation lies somewhere in be-
tween. The NBO deletion studies show that this is predomi-
nantly dictated by delocalization effects, and that hypercon-
jugative interactions also play a role.
This work was supported in part (M. L., A. L. S.) by the Neder-
landse Organisatie voor Wetenschappelijk Onderzoek, Chemische
Wetenschappen (NWO-CW). R. W. A. H. acknowledges financial
support from Nederlandse Organisatie voor Wetenschappelijk On-
derzoek (NWO), grant 700.53.401. The authors thank NWO/NCF
for the use of supercomputer time on TERAS/ASTER, SARA
(project number SG-032).
[1] H. Hopf, Angew. Chem. 1984, 96, 947–958.
[2] P. W. Fowler, P. Hansen, G. Caporossi, A. Soncini, Chem. Phys.
Lett. 2001, 342, 105–112.
[3] M. R. Bryce, M. A. Coffin, P. J. Skabara, A. J. Moore, A. S.
Batsanov, J. A. K. Howard, Chem. Eur. J. 2000, 6, 1955–1962.
[4] J. P. Gisselbrecht, N. N. P. Moonen, C. Boudon, M.
Brøndsted Nielsen, F. Diederich, M. Gross, Eur. J. Org. Chem.
2004, 2959–2972.
[5] M. Klokkenburg, M. Lutz, A. L. Spek, J. H. van der Maas,
C. A. van Walree, Chem. Eur. J. 2003, 9, 3544–3554.
[6] C. A. van Walree, V. E. M. Kaats-Richters, S. J. Veen, B. Wiec-
zorek, J. H. van der Wiel, B. C. van der Wiel, Eur. J. Org.
Chem. 2004, 3046–3056.
Experimental Section
[7] K. Itami, Y. Ohashi, J. Yoshida, J. Org. Chem. 2005, 70, 2778–
2792.
[8] N. F. Phelan, M. Orchin, J. Chem. Educ. 1968, 45, 633–637.
[9] M. Gholami, R. R. Tykwinski, Chem. Rev. 2006, 106, 4997–
5027.
[10] M. H. van der Veen, M. T. Rispens, H. T. Jonkman, J. C. Hum-
melen, Adv. Funct. Mater. 2004, 14, 215–223.
[11] R. Baer, D. Neuhauser, J. Am. Chem. Soc. 2002, 124, 4200–
4201.
[12] M. Mizouchi, A. Ikawa, H. Fukutome, J. Am. Chem. Soc.
1995, 117, 3260–3269.
[13] M. Iyoda, S. Sasaki, M. Miura, M. Fukuda, J. Yamauchi, Tet-
rahedron Lett. 1999, 40, 2807–2810.
[14] N. Tyutyulkov, F. Dietz, K. Müllen, M. Baumgarten, S. Kara-
bunarliev, Chem. Phys. 1994, 189, 83–97.
[15] B. C. van der Wiel, R. M. Williams, C. A. van Walree, Org. Bi-
omol. Chem. 2004, 2, 3432–3433.
[16] P. T. Brain, B. A. Smart, H. E. Robertson, M. J. Davis,
D. W. H. Rankin, W. J. Henry, I. Gosney, J. Org. Chem. 1997,
62, 2767–2773.
General: Details of the crystal structure determination can be
found elsewhere.[17]
Computational Methods: Both MP2 and SCF calculations were per-
formed with GAMESS-UK version 7.0,[31] employing the 6-311G*
basis set. The minima were characterized by a Hessian calculation;
no imaginary frequencies were found. NBO deletion studies[24] were
conducted with the NBO module implemented in Gaussian 98[32]
on the SCF/6-311G* geometries taken from the GAMESS outputs.
Cartesian coordinates of MP2/6-311G* calculated minima of 1 are
to be found in the Supporting Information.
Synthesis of 2,3-Diphenyl-1,3-butadiene (1): From the methods
available for the synthesis of 1,[33–35] we chose the double Wittig
reaction of benzil with triphenylmethylphosphonium bromide,[36]
albeit with another solvent. Thus, in a nitrogen atmosphere, a sus-
pension of triphenylmethylphosphonium bromide (37.40 g,
104.7 mmol) in THF (250 mL) was stirred and cooled to 0 °C. In
30 min n-butyllithium in hexanes (66 mL of a 1.6  solution,
4750
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Eur. J. Org. Chem. 2007, 4746–4751

Cross-Conjugated 2,3-Diphenylbutadiene
[17] M. Lutz, A. L. Spek, B. C. van der Wiel, C. A. van Walree,
Acta Crystallogr., Sect. C 2005, 61, o300–o302.
[18] A. Karpfen, C. H. Choi, M. Kertesz, J. Phys. Chem. A 1997,
101, 7426–7433.
[19] M. A. Murcko, H. Castejon, K. B. Wiberg, J. Phys. Chem.
1996, 100, 16162–16168.
[20] J. C. Cochran, K. Hagen, G. Paulen, Q. Shen, S. Tom, M.
Traetteberg, C. Wells, J. Mol. Struct. 1997, 413–414, 313–326.
[21] Handbook of Chemistry and Physics, 82nd ed. (Ed.: D. R. Lide),
CRC, Boca Raton, 2001, pp. 9–1 to 9–14.
[22] M. Bruschi, M. G. Giuffreda, H. P. Lüthi, ChemPhysChem
2005, 6, 511–519.
[31] M. F. Guest, I. J. Bush, H. J. J. van Dam, P. Sherwood, J. M. H.
Thomas, J. H. van Lenthe, R. W. A. Havenith, J. Kendrick,
Mol. Phys. 2005, 103, 719–747.
[32] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Mont-
gomery Jr, R. E. Stratmann, J. C. Burant, S. Dapprich, J. M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas,
J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C.
Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson,
P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D. Rab-
uck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Or-
tiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko, P. Pis-
korz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gon-
zalez, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon,
E. S. Replogle, J. A. Pople, Gaussian 98, Version A.7, Gaussian,
Inc., Pittsburgh PA, 1998.
[23] M. Bruschi, M. G. Giuffreda, H. P. Lüthi, Chem. Eur. J. 2002,
8, 4216–4227.
[24] M. G. Giuffredda, M. Bruschi, H. P. Lüthi, Chem. Eur. J. 2004,
10, 5671–5680.
[25] A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev. 1988, 88,
899–926.
[26] D. Cappel, S. Tüllmann, A. Krapp, G. Frenking, Angew. Chem.
Int. Ed. 2005, 44, 3617–3620.
[27] W. R. Roth, O. Adamczak, R. Breuckmann, H.-W. Lennartz,
R. Boese, Chem. Ber. 1991, 124, 2499–2521.
[28] M. Traetteberg, H. Hopf, H. Lipka, R. Haenel, Chem. Ber.
1994, 127, 1459–1467.
[29] A. Almenningen, A. Gatial, D. S. B. Grace, H. Hopf, P. Kla-
eboe, F. Lehrich, C. J. Nielsen, D. J. Powel, M. Traetteberg,
Acta Chem. Scand. Ser. A 1988, 42, 634–650.
[30] M. H. Palmer, J. A. Blair-Fish, P. Sherwood, J. Mol. Struct.
1997, 412, 1–18.
[33] A. Hirao, Y. Sakano, K. Takenaka, S. Nakahama, Macromole-
cules 1998, 31, 9141–9145.
[34] R. A. Wagner, U. H. Brinker, Synthesis 2001, 376–378.
[35] T. Yamamoto, T. Yasuda, K. Kobayashi, I. Yamaguchi, T. Ko-
izumi, D. Ishii, M. Nakagawa, Y. Mashiko, N. Shimizu, Bull.
Chem. Soc. Jpn. 2006, 79, 498–500.
[36] Æ. de Groot, B. Evenhuis, H. Wynberg, J. Org. Chem. 1968,
33, 2214–2217.
Received: May 7, 2007
Published Online: July 25, 2007
Eur. J. Org. Chem. 2007, 4746–4751
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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