Involvement of organic fluorine substitution in the crystalline packing structures of tricyclic Diels-Alder adducts derived from diarylfulvenes and N-arylimides

Article abstract of DOI:10.1016/j.jfluchem.2009.11.013

Fluorinated tricyclic Diels-Alder adducts derived from corresponding diarylfulvenes and N-arylmaleimides, each of different degree and positions of the fluorine substituents, and including the non-fluorinated parent compound, have been synthesized. Their X-ray crystal structures were determined in order to study the effect of fluorine substitution on the solid state organization in competition with other weak intermolecular interactions. A balanced interplay of C-H?O, C-H?F and especially C-H?π contacts is typical of the crystal packings while other potential interactions such as C-F?F, C-F?π^F, π^H?π^F and Br?Br are secondary or not to be found. Isostructurality calculations and comparison of molecular conformations have been performed in order to structurally classify the compounds depending on the number and mode of fluorination.

Full text of DOI:10.1016/j.jfluchem.2009.11.013

Journal of Fluorine Chemistry 131 (2010) 345–356
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Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Involvement of organic fluorine substitution in the crystalline packing structures
of tricyclic Diels–Alder adducts derived from diarylfulvenes and N-arylimides
Anke Schwarzer a, Petra Bombicz b, Edwin Weber a,
*
a Institute of Organic Chemistry, Technische Universita¨t Bergakademie Freiberg, Leipziger Straße 29, D-09596 Freiberg, Sachsen, Germany
b Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1525 Budapest, Hungary
A R T I C L E I N F O
A B S T R A C T
Article history:
Fluorinated tricyclic Diels–Alder adducts derived from corresponding diarylfulvenes and N-arylmalei-
mides, each of different degree and positions of the fluorine substituents, and including the non-
fluorinated parent compound, have been synthesized. Their X-ray crystal structures were determined in
order to study the effect of fluorine substitution on the solid state organization in competition with other
Received 28 August 2009
Received in revised form 16 November 2009
Accepted 18 November 2009
Available online 26 November 2009
weak intermolecular interactions. A balanced interplay of C–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀF and especially C–Hꢀ ꢀ ꢀ
p
,
contacts is typical of the crystal packings while other potential interactions such as C–Fꢀ ꢀ ꢀF, C–Fꢀ ꢀ ꢀpF
Keywords:
pHꢀ ꢀ ꢀpF and Brꢀ ꢀ ꢀBr are secondary or not to be found. Isostructurality calculations and comparison of
molecular conformations have been performed in order to structurally classify the compounds
depending on the number and mode of fluorination.
Fluorinated Diels–Alder adducts
X-ray crystal structures
Supramolecular interactions
Fluorine involved contacts
Isostructurality calculations
ß 2009 Elsevier B.V. All rights reserved.
1. Introduction
existence [6,10,19]. However, a particular problem arises if further
non-dominating interactions including weaker hydrogen bonds
Crystal engineering via the manipulation of intramolecular
interactions has become a major area of research in recent years
[1]. In the course of these studies, different types of packing motifs
in crystals including bonding potentials such as strong (O–Hꢀ ꢀ ꢀO,
(O–Hꢀ ꢀ ꢀ
p
, C–Hꢀ ꢀ ꢀ ) [3,4] or Xꢀ ꢀ ꢀX contacts between the higher
p
halogens [20] compete. This has prompted to systematically study
the crystal structures of properly fluorinated organic compounds
[10]. A new such testing system of fluoroorganic compounds is
provided with the present series of Diels–Alder adducts 1–18
(Scheme 1). Compared to the previously studied groups of
fluorinated N-phenylmaleimides and corresponding phthalimides
of different fluorine substitution [21], the tricyclic fulvene with
arylimide Diels–Alder adducts, discussed here, are more rigid and
bulky molecules containing additional aromatic rings.
O–Hꢀ ꢀ ꢀN, N–Hꢀ ꢀ ꢀO, N–Hꢀ ꢀ ꢀN) [2] and weaker (C–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀ
p)
[3,4] hydrogen bonding or
p-stacking interactions [5] have been
discussed in detail. Having a more profound understanding of the
nature and strength of organic fluorine involved non-covalent
interactions is another current challenge [6]. A motive for it is that
fluorinated organic compounds often show particular physical and
chemical behaviour [7] that can be utilized in pharmaceutics [8]
and materials science [9]. Replacement of hydrogen by fluorine in
organic molecules was also found to lead to distinct changes in
between crystal structure [10] or turned to good account in solid
state reactions [11] and crystalline inclusion chemistry [12]. As a
result, crystal engineering of fluoroorganic compounds has become
a very actual topic [13].
Within this frame, specific modes of organic fluorine involving
weak interactions are considered to be rather effective, first and
foremost applying to the Arꢀ ꢀ ꢀArF staking motif [5,14], while others
are rated less distinct in their effectiveness (C–Fꢀ ꢀ ꢀH, C–Fꢀ ꢀ ꢀF and
C–Fꢀ ꢀ ꢀpF) [15–18] thus causing sometimes a questioning of their
2. Results and discussion
2.1. Compounds studied
The compounds studied in this paper involve a systematic
series of fluorinated molecules 1–18 (Scheme 1) that feature a
tricyclic framework of N-arylimides. Compound 1 is the non-
fluorinated parent molecule. The compounds 2–6 represent
derivatives with different number and positions of fluorine atoms
substituted into the N-phenyl unit. In 7–12, the organic fluorine
substituents are included both in the N-phenyl unit and p-
positioned in the two phenyl rings attached to the methylidene
group. Hence the fluorine substituents are found either on one or
both sides of the molecule. Compounds 13–18 differ from 7 to 12 in
the replacement of the fluorine substituents of the methylidene
* Corresponding author. Tel.: +49 3731 392386; fax: +49 3731 393170.
E-mail address: edwin.weber@chemie.tu-freiberg.de (E. Weber).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.11.013

346
A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
Scheme 1. Formula structures of compounds studied with designation of ring
Scheme 2. Formula structures of imide and fulvene intermediates.
planes.
bound phenyl rings for bromine atoms. This opens the possibility
to explore the effect of bromine versus fluorine in the formation of
the crystal packing.
dimethylformamide, dimethylsulfoxide, dichloromethane, chloro-
form, tetrachloromethane, benzene, toluene, xylenes, and mesi-
tylene. Only in the case of 14 and benzene, a respective 1:1
crystalline solvent inclusion compound 14ꢀC6H6 was obtained. All
other compounds failed to form solvent inclusions. This suggests
almost non-existent clathrate behaviour of this compound family,
though potential molecular bulkiness is present, which has been
defined a favourable parameter of clathrate formation [28,29].
Apparently, with the exception of 14, the molecules offer good
opportunity to pack in a crystal lattice without making use of
solvent assistance.
Aside from 15 and 16, single crystals of the target compounds
suitable for X-ray structure analysis were obtained by isothermal
evaporation or cooling of a saturated solution from acetone or
benzene. Their crystal structures are comparatively discussed in
the following. Dependent on the mode of fluorine substitution, a
subdivision is made into different categories of compounds
including the non-fluorinated parent molecule 1, compounds with
the fluorine atoms attached to the N-phenyl unit (2–6), compounds
possessing fluorine atoms in the methylidene bound phenyl rings
(7–12) and compounds containing additional bromo substituents
(13, 14ꢀC6H6, 17, 18).
All the compounds 1–18 have been synthesized via Diels–Alder
reactions [22] using the respective N-arylimides 19a–f and the
corresponding diarylfulvenes 20a–c (Scheme 2). They are colour-
less solids that show high temperature melting points (>200 8C)
attended by decomposition. There is no report in the literature
with reference to these compounds, except for 1 giving, however, a
melting point that has not been approved [23]. The N-arylimides
19a–f were prepared from condensation reaction [24] of maleic
anhydride and the respective aniline [21], the fulvenes 20a–c [25]
from corresponding diaryl ketones and 1,3-cyclopentadiene [26].
All the compounds being 2,6-difluoro substituted in the N-
phenyl unit (4–6, 10–12 and 16–18) show a hindered conforma-
tional rotation around the N-aryl bond at T = 26 8C. This has been
proven by 19F NMR determination in CDCl3, giving rise to separate
signals for the 2- and 6-fluoro substituents (see Section 4). The
potential energy of the rotational barrier was calculated to be in
the range of 100 kJ/mol with the minimum of the potential energy
at an interplanar angle relating to the pyrrolidine and the aryl ring
of about 608. DFT calculations on 19d have been performed at the
B3LYP/6-311G(d) level of theory using GAUSSIAN 03 [27].
In order to probe the capacity of solvent inclusion [28], the
target compounds 1–18 were recrystallized from a wide range of
polar and apolar solvents including methanol, ethanol, n-butanol,
diethylamine, triethylamine, acetone, butanone, ethyl acetate,
2.2. X-ray single crystal structures
The crystallographic data and structure refinement parameters
for the studied compounds (1–13, 14ꢀC6H6, 17 and 18) are

A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
347
Table 1
Selected geometric features of compounds 1–13, 14ꢀC6H6, 17 and 18a.
1
2
3
4
5
6-1
6-2
20- and 60-substitution
H
H
H
F
F
F
F
M–A interplanar angle (8)
B–C interplanar angle (8)
M–B interplanar angle (8)
M–C interplanar angle (8)
74.79
87.39
66.86
47.66
1.4007
1.4013
1.441
82.45
81.03
49.85
54.04
1.389
1.398
1.442
75.81
85.51
45.27
72.30
1.404
1.405
1.442
68.81
87.73
72.71
44.69
1.4037
1.4039
1.423
76.48
81.02
51.28
51.73
1.4017
1.4031
1.424
75.93
77.56
53.30
54.32
1.411
1.413
1.413
65.12
78.61
66.42
41.93
1.414
1.445
1.445
˚
N–C(5O) (A)
˚
CAryl–N (A)
7
8
9
10
11
12
20- and 60-substitution
H
H
H
F
F
F
M–A interplanar angle (8)
B–C interplanar angle (8)
M–B interplanar angle (8)
M–C interplanar angle (8)
81.53
81.91
81.55
50.58
60.89
1.390
1.390
1.430
69.85
83.73
43.07
69.68
1.392
1.412
1.432
66.70
88.33
71.36
42.51
1.402
1.408
1.425
76.55
82.41
51.25
63.98
1.4017
1.4031
1.425
61.31
75.32
63.21
46.72
1.413
1.419
1.421
83.00
52.11
59.89
1.3889
1.3925
1.434
˚
N–C(5O) (A)
˚
CAryl–N (A)
13
14ꢀC6H6
17
18
20- and 60-substitution
H
H
F
F
M–A interplanar angle (8)
B–C interplanar angle (8)
M–B interplanar angle (8)
M–C interplanar angle (8)
77.28
73.59
49.60
61.09
1.393
1.393
1.436
51.36
60.25
43.06
46.16
1.400
1.412
1.436
80.85
75.10
56.91
47.33
1.401
1.403
1.423
81.22
72.53
54.69
51.85
1.405
1.414
1.414
˚
N–C(5O) (A)
˚
CAryl–N (A)
a
Designation of the ring mean planes in Scheme 1.
summarized in Table S1 (SI). For the description of the crystal
structures, intermolecular contacts within the sum of the van-der-
Waals radii [30] for the pair of interacting atoms (Oꢀ ꢀ ꢀH, Fꢀ ꢀ ꢀH and
Fꢀ ꢀ ꢀF) and an angular cut off of >110 8C have been used. Contacts
between the aryl units and the hydrogen or fluorine atoms are
based upon the centre of the ring. Selected geometric features of
the structures are presented in Table 1. Weak intermolecular
dominated by C–Hꢀ ꢀ ꢀ
p interactions [4] with distances that range
between 2.77 and 2.98 A, creating intermolecular zigzag chains
˚
˚
or dimers. Only one C–Hꢀ ꢀ ꢀO contact (C15–H15ꢀ ꢀ ꢀO1: 2.32 A,
163.88) is present, giving rise to intermolecular dimer formation
(Fig. 2).
2.2.2. Compounds fluorinated at the N-phenyl ring subunit (2–6)
The molecular structures of compounds 2–6 are comparable to
the parent molecule 1, showing also a distortion around the N–Caryl
bond to yield interplanar angles between the imide and N-aryl
rings that range from 658 to 828. However, a clear relation between
the interplanar angles and the mode of fluorine substitution is not
becoming evident. A similar situation is revealed for the N–C(55O)
bond lengths. On the other hand, an observed shortening of the N–
Caryl bond length in the compounds 4–6 seems to be correlated
with the fluorine substitution in the 2- and 6-positions of the aryl
ring (Fig. 3).
In the crystalline packings of compounds 2–6, C–Hꢀ ꢀ ꢀO contacts
[3] mainly including aliphatic and olefinic hydrogen atoms are
rather frequent. On the other hand, it is a reasonable consequence
that with increasing fluorine substitution in the molecule, the
intermolecular C–Hꢀ ꢀ ꢀF contacts [13] also increase. But these C–
Hꢀ ꢀ ꢀF contacts are rather weak and thus their impact on the crystal
structure is in question. Only in compounds 4 and 6, these contacts
seem to be of more significance due to a shortened distance
between the interacting atoms. In the 3,5-difluorinated derivative
hydrogen bond type (C–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀF, C–Hꢀ ꢀ ꢀ
p/
pF) as well as C–
Fꢀ ꢀ ꢀF and C–Brꢀ ꢀ ꢀO contacts are represented in Tables S2–S4 (SI),
respectively.
2.2.1. Non-fluorinated parent compound 1
The non-fluorinated parent compound
1 was found to
crystallize in the centrosymmetric space group P21/c with one
molecule in the asymmetric unit. Due to intramolecular steric
repulsion, the imide ring shows a distortion of 748 relative to the
phenyl unit, referring to non-existent conjugation between
these two moieties (Fig. 1). The crystal packing of compound 1 is
˚
4, the contact C11–H11ꢀ ꢀ ꢀF1 (2.46 A, 121.08) is involved in the
formation of molecular zigzag chains along the crystallographic b-
axis which, however, are possibly more a result of the higher
˚
effectiveness of the C–Hꢀ ꢀ ꢀO interaction (C8–H8ꢀ ꢀ ꢀO1: 2.49 A,
˚
116.78). By the way of contrast, the C55–H55ꢀ ꢀ ꢀF4 (2.49 A, 132.18)
˚
and C27–H27ꢀ ꢀ ꢀF7 (2.44 A, 139.98) contacts form dimers in the
crystal structure of the pentafluorinated compound 6, giving rise to
an intermolecular zigzag chain in the combination.
Interestingly, in all compounds 2–6 only one single fluorine–
fluorine contact is found, if at all, since this contact is a rather weak
Fig. 1. ORTEP-Plot of compound 1 including atom numbering scheme. Thermal
ellipsoids are at the 50% probability level, respectively.

348
A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
Fig. 2. Packing diagram of 1 along the crystallographic c-axis. Heteroatoms are shaded. The C–Hꢀ ꢀ ꢀO contacts are shown as broken lines. Non-relevant hydrogen atoms are
omitted for clarity.
˚
one (C2–F2ꢀ ꢀ ꢀF6–C29: 2.81 A, 173.08 and 145.78), and might
perhaps merely be a result of the interplay of more effective
interactions in the crystal packing. Moreover, in 6 a potential aryl-
perfluoroaryl interaction [13] is found in the asymmetric unit.
fluoroaryl units are far beyond being of any significance to the
packing structure.
On the other side, in the compounds 2–6, contacts of the C–
Hꢀ ꢀ ꢀ
p type [4] are more essential to the packing structures,
although in 2 only one rather weak contact with a hydrogen-centre
˚
However, considering the centre-to-centre distance of 3.9 A and
˚
the angle of 21.18 between the aryl planes, the presence of a
distance of 3.2 A is present. But in 3–6, the corresponding distances
˚
respective stacking motif is rather questionable. In the compounds
ranging from 2.7 to 2.9 A point to higher effectiveness. These
˚
2–5, the centre-to-centre-distances of 4.2–5.7 A between aryl-
contacts result in the formation of intermolecular zigzag chains of
molecules along the crystallographic b-axis. Logically, with an
increasing number of fluorine substituents in the phenyl unit, the
number of C–Hꢀ ꢀ ꢀ
p contacts decreases, while their geometric
parameters remain constant.
2.2.3. Compounds fluorinated on the methylidene bound phenyl
groups (7–12)
Substitution of the hydrogen atoms at the para-position of the
methylidene bound phenyl groups for fluorine atoms results in an
electron withdrawing effect on these phenyl rings and may thus
lead to a molecular system with electron withdrawing units at
both ends of the molecule. Nevertheless, this seems to be of no
relevance for the used crystal system, since no significant
differences between the compounds 7–12 and 1–6 are found in
this respect. They all crystallize in the monoclinic crystal system
with one molecule in the asymmetric unit. More strictly speaking,
except 9 which crystallizes in the space group P21, the other
compounds show the space group P21/c (P21/n). Moreover,
corresponding molecular structures of the compounds 7–12
(examples in Fig. 4) and 1–6 are almost the same. This includes
the interplanar angles between imide and N-aryl rings (range of
61–818) as well as the non-existing dependence between N–C(55O)
bond lengths and fluorine substitution. Also the N–Caryl bond
lengths are shortened in the cases of the 2,6-difluoro substituted
compounds 10–12 due to reduced electron density and the
resulting compensation of the charge distribution by the nitrogen
atom.
With regard to the crystalline packing structures of 7–12, it is
shown that the oxygen involved contacts outnumber the fluorine
contacts, similar to the behaviour which is found for the
compounds 2–6. This is even the case for the derivatives 11 and
12 being enriched with fluorine substituents. Remarkably, the
compounds 9 and 12, featuring fluorine atoms in the 3,5-position
˚
of the N-aryl ring, give rise to both the shortest (i.e. 2.43 A, 146.98
Fig. 3. ORTEP-Plots of compounds 2 (a) and 6 (b) including atom numbering
˚
scheme. Thermal ellipsoids are at the 50% probability level, respectively.
for 9 and 2.40 A, 165.38 for 12) and longest C–Hꢀ ꢀ ꢀO contacts [3]

A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
349
Fig. 4. ORTEP-Plots of compounds 7 (a) and 12 (b) including atom numbering
scheme. Thermal ellipsoids are at the 50% probability level, respectively.
˚
˚
(2.71 A, 147.28 and 2.58 A, 131.98 for 9 and 12, respectively)
observed in this category of compounds. While these shortest
contacts create chains and zigzag chains along the crystallographic
b-axis, the long contacts lead mainly to chains and dimers.
Moreover, the findings suggest that the affinity to create dimers via
C–Hꢀ ꢀ ꢀO contacts decreases with increasing number of fluorine
atoms at the N-aryl ring. Therefore, dimers produced by strong C–
Hꢀ ꢀ ꢀO contacts can only be found in the cases of compounds 7, 8
and 10. As regards the derivatives 7 and 8, a combination of weak
C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀF contacts induces the formation of zigzag
chains along the crystallographic b-axis. On the other hand, in the
structures of 9, 11 and 12, the C–Hꢀ ꢀ ꢀO interactions cause
intermolecular chains as well as zigzag chains.
Fig. 5. ORTEP-Plots of compounds 13 (a), 14ꢀC6H6 (b) and 18 (c) including atom
numbering scheme. Thermal ellipsoids are at 50% probability level, respectively.
group C2/c, and the pentafluorinated compound 18 makes use of
the non-centrosymmetric space group C2.
˚
Considering the observed range of distances (2.41–2.66 A) for
the C–Hꢀ ꢀ ꢀF contacts, this type of interaction seems not to be of
high relevance to the crystal structures. Possibly more important
Fꢀ ꢀ ꢀF contacts were only detected for compound 12 with distances
The molecular geometries of the compounds 13, 14, 17 and 18
(examples in Fig. 5) are closely comparable to the corresponding
analogous compounds with (1, 2, 5, and 6) and without (7, 8, 11,
and 12) fluorine substitution of the N-phenyl ring, showing little
influencing control of the bromine atoms. In the structures of the
bromine substituted compounds, the interplanar angles between
imide and aryl rings range from 518 to 818 (average 738). The
smallest angle was observed for 14 in the corresponding benzene
solvate. As before, no interdependence involving either the
interplanar angle or the N–C(55O) bond length and the mode of
fluorine substitution is obvious. Moreover, in the case of the 2,6-
difluoro substituted derivatives 17 and 18 the N–Caryl bond lengths
are shortened, which is also a property similar to the bromine-free
analogues.
˚
˚
2.87 A (107.78 and 131.68) and 2.93 A (80.28 and 158.18) being
˚
slightly shorter than the sum of the van-der-Waals radii (F: 1.47 A
[30]).
2.2.4. Bromo substituted compounds (13, 14ꢀC6H6, 17 and 18)
As a preliminary note, these bromine substituted compounds
tend to give only crystals of moderate to poor quality. For this
reason, we were unable to study the crystal structures of the
difluorinated derivatives 15 and 16. Another general finding
observed for this series of compounds is the change from the
primitive to face-centred lattice with the increasing number of
fluorine atoms in the molecule. While the non-fluorinated
compound 13 crystallizes in the space group P21/c and the
benzene solvate of 14 (14ꢀC6H6) in P21/n, the trifluorinated
derivative 17 is found to crystallize in the centrosymmetric space
Among all compounds studied here, the bromofluoro derivative
14 is the only one which crystallized as a stoichiometric 1:1 solvate
(host–guest inclusion compound) with benzene. The packing
structure of 14ꢀC6H6 shows a remarkable feature by the formation

350
A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
Fig. 6. Packing diagram of compound 14ꢀC6H6 along the a-axis. Non-covalent interactions are represented as broken lines.
of intermolecular Oꢀ ꢀ ꢀBr contacts [31]. They give rise to the
generation of a ring system consisting of six molecules of 14. This
particular kind of halogen bonding where halogens (electron
acceptor site) contact to atoms containing lone pairs (electron
donor site) is currently a topic of great promise in crystal
engineering [32,33]. The parameters of the present Brꢀ ꢀ ꢀO contact
[35–38]. Within this frame, the effects of the different degree of
fluorination on the N-phenyl ring and the halogenation of the
methylidene bound phenyl groups on the packing arrangements of
the molecules were investigated. All compounds crystallize in the
monoclinic crystal system with both centrosymmetric (P21/c, P21/n,
C2/c) and chiral space groups (P21, C2). Systematics regarding
the effect of halogenation on the molecular conformation and as a
result from the packing arrangement are revealed.
˚
(3.23 A, 169.18 and 119.58) coincide with the modern theoretical
interpretation of this particular interaction (effect of the
s-hole)
[34]. Besides this specific Brꢀ ꢀ ꢀO interactions, different C–Hꢀ ꢀ ꢀO (F)
contacts determine the crystalline packing of 14ꢀC6H6 (Fig. 6).
Except the special bromo involved interaction, corresponding
C–Hꢀ ꢀ ꢀO(F) contacts are also typical of the packing structures of the
non-solvated compounds 13, 17 and 18. Remarkably, it is the
fluorine-free derivative 13 which exhibits the shortest distance of
The presence of H, F or Br in para-position of the methylidene
bound phenyl rings markedly influences the space group of the
crystal (Table S1, SI). The plain molecules 1–6 crystallize in the P21
space group, with two exceptions (1 and 4) where space group P21/
c appears. On the other hand, the F substituted molecules 7–12
prefer the P21/c (or P21/n) arrangement, excepting 9 which shows
the space group P21. The Br substitution seems to have the greatest
effect on the packing. Although the N-phenyl non-fluorinated
compound 13 shows the space group P21/c, those being fluorinated
crystallize in space groups C2/c (17), C2 (18), and enclathrate the
solvent molecule (14ꢀC6H6) or resist suitable crystal formation (15,
16). Moreover, influences of the placement and degree of fluorine
substitution of the N-phenyl subunit on the space group of the
crystal are observed. The P21 structures (Fig. 7) show two different
kinds of assemblies: (1) the para 2 and ortho–para 5, and (2) the
meta (3, 9) fluoro substituted crystals, which are the most similar.
The P21/c (P21/n) structures (Fig. S2, SI) can be divided into three
subgroups: (1) the non-substituted 1 and ortho 4, 10, (2) the non-
substituted 7, 13, the para 8, and the ortho–para substituted 11, as
well as (3) the ortho–meta–para derivative 12. However, the most
different compounds are the perfluorinated ones. The compound 6
contains two molecules in the asymmetric unit, 12 is distinctly
different but keeps the P21/n space group while 18 appears in the
C2 space group.
˚
the C–Hꢀ ꢀ ꢀO contacts (C14–H14ꢀ ꢀ ꢀO2, 2.31 A, 165.78), generating a
dimer that bridges zigzag chains caused by a weaker C–Hꢀ ꢀ ꢀO
˚
contact (C8–H8ꢀ ꢀ ꢀO1, 2.62 A, 107.28). From size consideration,
substitution of
a hydrogen for a fluorine atom does not
considerably enlarge the molecular volume. On the other hand,
the charge distribution in the molecule will change significantly by
this kind of modification and hence also the attractive and
repulsive forces between adjacent molecules. As a result of the
repulsive forces between fluorine atoms, creating dimers of
molecules is hampered in the case of a high fluorine substitution.
Moreover, with an increasing number of fluorine atoms, being
added to the large bromine substituents in the molecular structure,
it is an obvious conclusion that C–Hꢀ ꢀ ꢀ
p contacts [4] are
increasingly restraint. This behaviour is clearly manifested with
the structures of the compounds 13, 14ꢀC6H6, 17 and 18,
respectively. The minor role of C–Hꢀ ꢀ ꢀ
p-contacts in the crystal
structures of these compounds is also shown with the rather long
distances involving the hydrogen atom and the centre of the
˚
aromatic ring. While the mean distance is found as 2.93 A in the
The fluorination of the N-phenyl ring, the molecular conforma-
tion (Table 1) and the packing arrangements can be well correlated.
Four different types of molecular conformations can be distin-
guished characterized by the interplanar angles of the phenyl rings
˚
present compounds, the corresponding values for 1–6 (2.88 A) and
7–12 (2.79 A) are shorter. Furthermore, the present compounds are
˚
mainly incorporated into zigzag chains and chains, mostly
extended along the crystallographic b-axis and always being in
combination with C–Hꢀ ꢀ ꢀO(F)-contacts. Nevertheless, whether or
(Table 2). The para and ortho–para N-phenyl
F substituted
molecules with plain methylidene bound phenyl groups shows
the type I molecular conformation in space group P21. The meta N-
phenyl F substitution results in the type II molecular conformation
in space group P21. A fluorine-free N-phenyl subunit, independent
of the particular methylidene bound phenyl groups, leads to either
type III or IV conformation in space group P21/c. The ortho N-phenyl
F substituted molecules reveal type III conformation, while the
ortho and ortho–para N-phenyl F substitutions result in the type IV
conformation. The perfluorinated molecules 6 and 12 differ the
most from the other members of the series. There are two
not these contacts are more
a consequence of the other
supramolecular interactions or a result of close packing effects
in the crystal lattice remains a matter for discussion.
2.3. Isostructurality calculations
The cell similarity (p), the isostructurality [Is] as well as the
molecular isometricity indices [Im] were calculated for those
compounds making possible a reasonable numerical comparison

A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
351
Table 3
Cell similarity (p), isostructurality [I(s)] and molecular isometricity indices [I(m)]
calculated within the group of conformational categories for 31 and 12 atoms,
respectively.
Space group
Structure
p
Is (31) %
Is (12) %
Im (31) %
P21
2/5
3/9
0.01434
0.00744
78.9
–
84.1
55.4
99.05
84.14
P21/c
1/4
0.00066
0.02518
0.02582
0.01432
0.00510
0.02408
0.00936
0.00990
0.01908
66.9
54.3
78.0
90.8
79.2
27.0
76.2
27.6
22.4
73.2
67.7
87.4
93.4
76.0
25.4
73.0
27.5
25.3
94.43
90.73
99.12
99.43
98.98
99.07
97.83
98.55
99.35
1/10
4/10
7/8
7/11
7/13
8/11
8/13
11/13
Cell similarity, isostructurality and molecular isometricity
calculations were carried out considering the conformational
categories (Table 3). Isostructurality calculations were performed
on two different levels. In one case, 31 heavy atoms including all C,
N and O atoms but excluding any halogen, were taken into account.
In the other case, a restriction was imposed using only the 12 core
atoms (N1, O1, O2, C7, C8, C9, C10, C11, C12, C13, C14, C15) since
the calculation with this rigid framework gives more information
on the positional differences and eliminates the effect of the
rotation of the phenyl rings. Molecular similarity is calculated with
the least squares fit of the 31 non-halogen heavy atoms. Within a
respective conformational category, the R4 substituents on the
methylidene bound phenyl rings exercise the most significant
effect: as the size of R4 increases, the similarity of I(s) and I(m)
considerably decreases (Fig. 7).
Fig. 7. Superimposed molecules (1–14, 17, 18) from different structures. Only rings
M are fitted in the figures to enhance the visualization of the conformational
differences.
3. Comparative reflection and conclusions
crystallographically independent molecules in the asymmetric
unit of 6 (Z0 = 2), one of them is close to the type III, the other one is
close to the type IV conformation. The unit cell of 12 is significantly
larger than for the other members in the series of the para F
substituted methylidene bound phenyl group containing com-
pounds 7–11 with a molecular conformation close to the type III.
Bromine substitution of the methylidene bound phenyl groups has
a substantial increased space requirement which gives more
freedom to the set of molecular conformations. Compound 13
belongs to the type IV conformation, although it is the most
deviating of this type class. The compound 14 enclathrates a
benzene solvent molecule, while it was not possible to grow single
crystals from 15 and 16, and 17 and 18 crystallize in the space
groups C2/c and C2, respectively. Thus these latter compounds can
hardly be categorized to the previous types of molecular
conformation.
The present series of systematically fluorine substituted
molecules show specific changes in the packing arrangements to
a substantial extent. The compounds with two plain phenyl rings
attached to the methylidene group crystallize mainly in the space
group P21, while the respective para-fluorinated phenyl deriva-
tives prefer the space group P21/c. Considering the series of
bromine substituted compounds, the most different space groups
are observed, if compounds yield suitable crystals at all.
The placement of the molecule in the unit cell is mainly
determined by the molecular conformation which is essentially
governed by the mode of fluorine substitution of the N-phenyl ring.
The packing arrangements can be classified into four categories.
They are similar in the cases of the ortho and the ortho–para
fluorine substituted molecules, and also in case of the meta
substitution, while the ortho–meta–para perfluorinated com-
pounds are the most different ones. Although the effects of
halogenation of the molecules on the crystal structures are not
strictly systematic, tendencies are revealed that may be useful in
crystal structure prediction.
Table 2
Types of molecular conformation observed in the investigated series of compounds.
Typical values of the interplanar angles in the different conformational types are
givena.
Rating the influence of the fluorine and bromine substitution in
regard of their competition with stronger hydrogen acceptors, such
Conformation type
I
II
III
IV
as oxygen, nitrogen and the
p system, provides the following facts.
Structures
B–C (8)
M–B (8)
M–C (8)
2, 5
81
3, 9
85
1, 4, 10
87
7, 8, 11, 13
Contrary to the prevailing opinion that the aryl-perfluoroaryl
intermolecular stacking arrangement behaves as a rather robust
synthon [5,14], an interaction of this type has not been determined
as a relevant binding motif in the present crystal structures. This
particular finding corresponds with a previous observation [21].
However, there is a distinct balance of hydrogen interactions to
82
54
60
50
44
70
53
71
44
M–B < M–C M–B ꢁ M–C M–B ꢂ M–C M–B < M–C
jM–B ꢃ M–Cj (8)
ꢄ3
ꢄ27
P21
ꢄ26
ꢄ9
Space group
P21
P21/c
-, o, o
P21/c
N-Phe substitution p, o-p
m, m
-, p, o-p, -
oxygen and fluorine atoms and significant C–Hꢀ ꢀ ꢀ
p contacts.
a
A more detailed comparison in this respect yields the following
The ring mean planes are labelled as M: N1/C7–C10; B: C17–C22; C: C23–C28
(Scheme 1).
data. As shown in Scheme 3, the ratio of C–Hꢀ ꢀ ꢀO interactions

352
A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
Scheme 3. Ratio of intermolecular contacts based on the crystal structures;
allocated to the compound classes.
increases only slightly with the introduction of fluorine in the
methylidene bound phenyl rings (7–12) but reaches almost half of
the number of all localized contacts with the corresponding
bromine substitution (13, 14ꢀC6H6, 17, 18). This increase of the
number of C–Hꢀ ꢀ ꢀO interactions goes with the decrease in the
Scheme 4. Diagram showing the relevant intermolecular C–Hꢀ ꢀ ꢀF (green) and
C–Hꢀ ꢀ ꢀO (red) contacts of the different compounds dependent on the hydrogen
atom position. (For interpretation of the references to color in this scheme, the
reader is referred to the web version of the article.)
number of C–H/Xꢀ ꢀ ꢀ
p
/
pF contacts. However, unlike the C–Hꢀ ꢀ ꢀO
visible in the present study. Actually, as can be taken from Scheme
4, there is no C–Hꢀ ꢀ ꢀF interaction with a hydrogen atom of a
fluorinated phenyl ring but only with aliphatic or olefinic
hydrogens and especially with hydrogen atoms of the methylidene
bound phenyl rings. The oxygen atoms show a less specific
behaviour but prefer aliphatic and olefinic H atoms.
Another point of interest relates to the particular modes of
interaction represented in Scheme 5. Hydrogen atoms of the N-
substituted phenyl ring prefer contacts in the kind of zigzag chains
interactions, the C–Hꢀ ꢀ ꢀ
p
contacts are rather constant in their
length and hence potentially also in their strength. As a result of
the fluorine substitution of the methylidene bound phenyl rings,
the number of C–Hꢀ ꢀ ꢀF interactions increases up to 44% but drops
down rapidly to 19% with the alternative bromine substitution. The
Fꢀ ꢀ ꢀF contacts observed in the crystal structures are rather
secondary and mostly determined by the packing, while C–Fꢀ ꢀ ꢀpF
F
are not present at all.
Additional information arises from a more specific comparison
of the C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀF contacts. These were previously found
to depend significantly on the position of the hydrogen atom in the
respective molecules of fluorinated maleimides and phthalimides
[21]. As a result, it was shown that the fluorine atom is more
specific than oxygen in making its choice to contact a hydrogen
atom. In particular, it appeared that hydrogen atoms bonded to the
already fluorinated aromatic ring are at a disadvantage with
reference to other hydrogen atoms, such as olefinic ones, in the
formation of C–Hꢀ ꢀ ꢀF contacts. This behaviour is also becoming
to oxygen atoms or the p system. The same behaviour is found for
the C–Hꢀ ꢀ ꢀO– and C–Hꢀ ꢀ ꢀF interactions involving the aliphatic H
atoms, while the corresponding contacts with olefinic and
aromatic hydrogen atoms do not demonstrate such a clear
specification of the interaction modes.
In summary, we conclude that even in the case of a systematic
substitution of hydrogen for fluorine atoms in a favourable model
compound, such as shown with the series of highly rigid Diels–
Alder adducts 1–18, it is presently not possible to accurately
correlate the crystallization outcome with the particular pattern of
Scheme 5. Diagram showing the motifs of intermolecular C–Hꢀ ꢀ ꢀF (green), C–Hꢀ ꢀ ꢀO (red) and C–Hꢀ ꢀ ꢀ
p (black) contacts dependent on the hydrogen atom position,
demonstrated with the parent model molecules irrespective of the fluorine substitution. Motifs are chains, zigzag chains and dimers. The digits depict the number of motifs
found in compounds 1–13, 14ꢀC6H6, 17 and 18. (For interpretation of the references to color in this scheme, the reader is referred to the web version of the article.)

A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
353
fluorine substitution and the influence of a few selected other
4.2.2. N-(4-Fluorophenyl)-
heteroatoms. Owing to the rather weak interactions emanating
from the fluorine contacts, different modes of fluorine interactions
compete between each other and are also in a competition with the
interaction sites of the other potential acceptor groups. Thus the
finding of a predetermined pattern of fluorine involved supramo-
lecular interactions remains still a difficult problem. Nevertheless,
the crystalline packing structures of the organic fluorine com-
pounds, studied here, indicate some trends in the observed
interaction modes as specified above. In particular it should be
pointed out that although potential opportunities to form pHꢀ ꢀ ꢀpF
interactions between some of the molecules (e.g. 5, 6) are given,
they are not realized in the corresponding structures. This is in
contradiction to the generally held view on the pHꢀ ꢀ ꢀpF stacking
interaction, being understood as a so-called robust supramolecular
synthon [5,14]. Obviously, this kind of interaction requires in
addition to the mere presence of pH and pF involved subunits a
more planar overall structure of the molecule to become effective,
which is not fulfilled here. A further remarkable fact is that the
bromine atoms, although being easy to access due to their
peripheral location, are no effective competitors with the other
heteroatoms giving rise to Brꢀ ꢀ ꢀX (N, O [33,34] or Brꢀ ꢀ ꢀBr contacts
[20c]).
7(diphenylmethylidene)bicyclo[2.2.1]hept-2-ene-5,6-dicarboximide
(2)
N-(4-Fluorophenyl)maleimide (19b) (1.91 g, 10 mmol) and
diphenylfulvene (20a) (2.30 g, 10 mmol) were used. Yield 1.49 g
(35%); mp: 215 8C (dec.). Anal. Calcd. for C28H20FNO2: C, 79.79; H,
4.78; N, 3.32; Found: C, 79.95; H, 4.80; N, 3.11%. IR (KBr): nmax
(cmꢃ1) 3089 (CHAr), 3022 (CHC5C), 1773, 1708 (C55O), 1627 (C55C),
1601, 1512 (C55CAr), 1387, 1181 (C–N–C). 1H NMR (CDCl3): dH
7.35–7.08 (m, 14H, Ar–H), 6.48 (s, 2H, HC55CH), 4.02 (s, 2H, H-6),
3.59 (s, 2H, H-5); 13C NMR (CDCl3):
dC 175.6 (C55O); 162.2 (d, C-1,
1JCF = ꢃ249.5 Hz), 151.3 (C-7), 140.0 (C-9), 135.1 (HC55CH), 129.4
(C-10), 128.37 (C-3), 128.2 (C-11), 127.3 (C-12), 127.7 (C-4), 124.0
(C-8), 116.1 (d, C2, 2JCF = 23.0 Hz), 46.7 (C-6), 44.8 (C-5); 19F NMR
(CDCl3): dF ꢃ112.8 (m, F-1). MS (ESI) m/z: 422 [M+H]+ 100%.
4.2.3. N-(3,5-Difluorophenyl)-7-
(diphenylmethylidene)bicyclo[2.2.1]hept-2-ene-5,6-dicarboximide
(3)
N-(3,5-Difluorophenyl)maleimide (19c) (2.09 g, 10 mmol) and
diphenylfulvene (20a) (2.30 g, 10 mmol) were used. Yield: 1.74 g
(40%);mp: 225–226 8C(dec.). Anal. Calcd. forC28H19F2NO2: C, 76.53;
H, 4.36; N, 3.19; Found: C, 76.57; H, 4.40; N, 3.01%. IR (KBr): nmax
(cmꢃ1) 3084 (CHAr), 3022 (CHC5C), 1775, 1712 (C55O), 1620 (C55C),
4. Experimental
1607, 1475 (C55CAr). 1H NMR (CDCl3):
dH 7.35–6.81 (m, 13H, Ar–H),
6.48 (s, 2H, HC55CH), 4.02 (s, 2H, H-6), 3.60 (s, 2H, H-5); 13C NMR
4.1. General
(CDCl3):
d
C 174.9 (C55O), 162.8 (d, C-2, 1JCF = ꢃ249.5 Hz), 151.0 (C-7),
139.9 (C-9), 135.2 (HC55CH), 133.7 (C-4), 129.3 (C-10), 128.3 (C-11),
127.4 (C-12), 124.2 (C-8), 110.1 (d, C-3, 2JCF = 27.9 Hz), 104.2 (t, C-1,
2JCF = 25.2 Hz), 46.9 (C-6), 44.9 (C-5); 19F NMR (CDCl3):dF ꢃ108.9 (m,
F-2). MS (ESI) m/z: 440 [M+H]+ 100%.
Melting points were determined using a microscope heating
stage PHMK Rapido (VEB Wa¨getechnik). IR spectra were measured
on FT-IR 510 Nicolet as KBr pellets. 1H, 13C and 19F NMR spectra
were measured in chloroform solution at room temperature on a
Bruker Avance DPX 400 at 400, 100 and 376 MHz, respectively.
Elemental analyses were performed on a Heraeus CHN rapid
analyzer. Mass spectra were recorded with ESQUIRE-LC ion trap,
4.2.4. N-(2,6-Difluorophenyl)-7-
(diphenylmethylidene)bicyclo[2.2.1]hept-2-ene-5,6-dicarboximide
(4)
solvent: acetonitrile/water/0.1% formic acid; flow rate 3
ion polarity: positive.
All N-phenylmaleimides 19a–f (Scheme 2) were prepared from
the corresponding aniline and maleic anhydride according to the
literature [20]. The diarylfulvenes 20a–c (Scheme 2) were obtained
following reported procedures [24].
m
L/min;
N-(2,6-Difluorophenyl)maleimide (19d) (2.09 g, 10 mmol) and
diphenylfulvene (20a) (2.30 g, 10 mmol) were used. Yield: 1.64 g
(37%); mp: 234–236 8C (dec.). Anal. Calcd. for C28H19F2NO2: C,
76.53; H, 4.36; N, 3.19; Found: C, 76.67; H, 4.37; N, 3.03%. IR (KBr):
nmax (cmꢃ1) 3080 (CHAr), 3023 (CHC5C), 1782, 1717 (C55O), 1622
(C55C), 1598, 1477 (C55CAr). 1H NMR (CDCl3):
dH 7.39–6.81 (m, 13H,
Ar–H), 6.52 (s, 2H, HC55CH), 4.00 (s, 2H, H-6), 3.67 (s, 2H, H-5); 13
C
1
4.2. Syntheses of compounds 1–18
NMR (CDCl3): dC 174.1 (C55O), 158.33 (d, C-3, JCF = ꢃ256.5 Hz),
151.2 (C-7), 140.0 (C-9), 135.2 (HC55CH), 131.0 (C-1), 129.4 (C–10),
128.2 (C-11), 127.3 (C-12), 124.1 (C-8), 112.1 (d, C-2,
2JCF = 19.6 Hz), 109.2 (C-4), 46.7 (C-6), 45.7 (C-5); 19F NMR (CDCl3):
dF ꢃ115.4 (m, F-3-syn), ꢃ117.55 (m, F-3-anti). MS (ESI) m/z: 440
[M+H]+ 100%.
To a stirred solution of the respective N-phenylmaleimide
(10 mmol) in benzene (25 mL), a solution of the corresponding
diarylfulvene (10 mmol) in benzene (25 mL) was added. The
mixture was heated to reflux for 5 h and allowed to cool down to
room temperature. The solid precipitate which has formed was
collected and dried in vacuum. Recrystallization of the crude
product from acetone yielded the pure compounds as colourless
solids. Specific details for each compound are given below.
4.2.5. N-(2,4,6-Trifluorophenyl)-7-
(diphenylmethylidene)bicyclo[2.2.1]hept-2-ene-5,6-dicarboximide
(5)
N-(2,4,6-Trifluorophenyl)maleimide (19e) (2.27 g, 10 mmol)
and diphenylfulvene (20a) (2.30 g, 10 mmol) were used. Yield:
2.19 g (48%); mp: 246–247 8C (dec.). Anal. Calcd. for C28H18F3NO2:
C, 73.52; H, 3.97; N, 3.06; Found: C, 73.69; H, 4.01; N, 2.90%. IR
(KBr): nmax (cmꢃ1) 3079 (CHAr), 3022 (CHC5C), 1790, 1724 (C55O),
4.2.1. N-Phenyl-7-(diphenylmethylidene)bicyclo[2.2.1]hept-2-ene-
5,6-dicarboximide (1)
N-Phenylmaleimide (19a) (1.73 g, 10 mmol) and diphenylful-
vene (20a) (2.30 g, 10 mmol) were used. Yield 1.30 g (32%); mp:
236 8C (dec.), lit. [22] mp: 123 8C. Anal. Calcd. for C28H21NO2: C,
83.35; H, 5.25; N, 3.47; Found: C, 83.43; H, 5.28; N, 3.29%. IR (KBr):
nmax (cmꢃ1) 3074 (CHAr), 3022 (CHC5C), 1776, 1704 (C55O), 1621
1632 (C55C), 1608, 1518 (C55CAr). 1H NMR (CDCl3):
dH 7.41–7.32 (m,
6H, H-11, H-12), 7.17–7.15 (m, 4H, H10), 6.85 (m, 2H, H-2), 6.55 (s,
2H, HC55CH), 4.07 (s, 2H, H-6), 3.74 (s, 2H, H-5); 13C NMR (CDCl3):
(C55C), 1598, 1497 (C55CAr). 1H NMR (CDCl3):
Ar–H), 6.50 (s, 2H, HC55CH), 4.03 (s, 2H, H-6), 3.61 (s, 2H, H-5); 13
d
H 7.44–7.09 (m, 15H,
d
C 174.0 (C55O), 164.3, 161.7 (d, C-1, 1JCF = ꢃ253.0 Hz), 158.7 (d, C-
C
3, 1JCF = ꢃ255.7 Hz), 151.1 (C-7), 140.0 (C-9), 135.3 (HC55CH), 129.4
NMR (CDCl3) dC 175.73 (C55O), 151.4 (C-7), 140.0 (C-9), 135.2
(HC55CH), 131.8 (C-4), 129.4 (C-10), 129.1 (C-3), 128.7 (C-1), 128.2
(C-11), 127.3 (C-12), 126.6 (C-2), 123.9 (C-8), 46.8 (C-6), 44.9 (C-5).
MS (ESI) m/z: 404 [M+H]+ 100%.
(C-10), 128.3 (C-11), 127.4 (C-12), 124.3 (C-8), 105.9 (C-4), 101.1 (t,
C-2, JCF = 25.2 Hz), 46.7 (C-6), 45.7 (C-5); 19F NMR (CDCl3): dF
2
ꢃ104.9 (m, F-1), ꢃ112.1 (m, F-3-syn), ꢃ114.9 (m, F-3-anti). MS
(ESI) m/z: 458 [M+H]+ 100%.

354
A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
2
2
4.2.6. N-(2,3,4,5,6-Pentafluorophenyl)-7-
(C-8), 115.4 (d, C–11, JCF = 21.5 Hz), 110.0 (d, C-3, JCF = 27.8 Hz),
2
(diphenylmethylidene)bicyclo[2.2.1]hept-2-ene-5,6-dicarboximide
104.3 (t, C-1, JCF = 25.2 Hz), 46.8 (C-6), 44.8 (C-5); 19F NMR
(6)
(CDCl3): dF ꢃ108.8 (m, F-2), ꢃ114.8 (m, F-12). MS (ESI) m/z: 476
N-2,3,4,5,6-(Pentafluorophenyl)maleimide
(20f)
(2.63 g,
[M+H]+ 100%.
10 mmol) and diphenylfulvene (20a) (2.30 g, 10 mmol) were used.
Yield: 1.79 g (36%); mp: 211–216 8C (dec.). Anal. Calcd. for
4.2.10. N-(2,6-Difluorophenyl)-7-[bis(4-
C
28H16F5NO2: C, 68.16; H 3.27; N, 2.84; Found: C, 68.16; H,
fluorophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (10)
3.28; N, 2.70%. IR (KBr): nmax (cmꢃ1) 3081 (CHAr), 3024 (CHC5C),
1789, 1729 (C55O), 1627 (C55C), 1522, 1492 (C55CAr). 1H NMR
N-(2,6-Difluorophenyl)maleimide (19d) (2.09 g, 10 mmol) and
bis(4-fluorophenyl)fulvene (20b) (2.66 g, 10 mmol) were used.
Yield: 2.85 g (60%); mp: 237 8C (dec.). Anal. Calcd. for C28H17F4NO2:
C, 70.74; H, 3.60; N, 2.95; Found: C, 70.88; H, 3.59; N, 3.01%. IR
(KBr): nmax (cmꢃ1) 3063 (CHAr), 3017 (CHC5C), 1781, 1721 (C55O),
1600, 1505 (C55CAr), 1374, 1198 (C–N–C). 1H NMR (CDCl3): dH
7.43–7.00 (m, 11H, Ar–H), 6.52 (s, 2H, HC55CH), 3.99 (s, 2H, H-6),
(CDCl3): dH 7.35–7.27 (m, 6H, H-11, H-12), 7.10–7.08 (m, 4H, H10),
6.49 (s, 2H, HC55CH), 4.02 (s, 2H, H-6), 3.72 (s, 2H, H-5); 13C NMR
(CDCl3): dC 173.3 (C55O), 150.7 (C-7), 143.5 (d, C-3,
1JCF = ꢃ255.5 Hz), 142.2 (d, C-1, JCF = ꢃ257.5 Hz), 139.9 (C-9),
1
1
137.9 (d, C-2, JCF = ꢃ255.5 Hz), 135.3 (HC55CH), 129.3 (C-10),
128.3 (C-11), 127.5 (C-12), 124.6 (C-8), 107.0 (C-4), 46.8 (C-6), 45.9
(C-5); 19F NMR (CDCl3): dF ꢃ141.5 (m, F-3-syn), ꢃ143.5 (m, F-3-
anti), ꢃ151.7 (m, F-1), ꢃ161.5 (m, F-2). MS (ESI) m/z: 494 [M+H]+
100%.
3.69 (s, 2H, H-5); 13C NMR (CDCl3):
dC 173.9 (C55O), 162.1 (d, C-12,
1
1JCF = ꢃ247.5 Hz), 158.5 (d, C-3, d, JCF = ꢃ241.4 Hz), 151.5 (C-7),
135.8 (C-9), 135.2 (HC55CH); 131.2 (C-1), 130.9 (C-10), 122.2 (C-8),
2
2
115.3 (d, C-11, JCF = 21.5 Hz), 112.1 (d, C-2, JCF = 19.9 Hz), 109.2
(C-4), 46.6 (C-6), 45.6 (C-5); 19F NMR (CDCl3): dF ꢃ114.9 (m, F-12),
ꢃ115.5 (m, F-3-syn), ꢃ117.7 (m, F-3-anti). MS (ESI) m/z: 476
[M+H]+ 100%.
4.2.7. N-Phenyl-7-[bis(4-
fluorophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (7)
N-Phenylmaleimide (19a) (1.73 g, 10 mmol) and bis(4-fluor-
ophenyl)fulvene (20b) (2.66 g, 10 mmol) were used. Yield: 1.40 g
(32%); mp: 239 8C (dec.). Anal. Calcd. for C28H19F2NO2: C, 76.53; H,
4.36; N, 3.19; Found: C, 76.64; H, 4.32; N, 2.97%. IR (KBr): nmax
(cmꢃ1) 3058 (CHAr), 1771, 1708 (C55O), 1599, 1507 (C55CAr), 1382,
4.2.11. N-(2,4,6-Trifluorophenyl)-7-[bis(4-
fluorophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (11)
N-(2,4,6-Trifluorophenyl)maleimide (19e) (2.27 g, 10 mmol)
and bis(4-fluorophenyl)fulvene (20b) (2.66 g, 10 mmol) were
used. Yield: 1.91 g (39%); mp: 205–207 8C (dec.). Anal. Calcd. for
1187 (C–N–C). 1H NMR (CDCl3):
dH 7.45–7.02 (m, 13H, Ar–H), 6.50
(s, 2H, HC55CH), 3.97 (s, 2H, H-6), 3.58 (s, 2H, H-5); 13C NMR
(CDCl3):
d
C 175.5 (C55O), 162.1 (d, C-12, 1JCF = ꢃ247.5 Hz), 151.6 (C-
C
28H16F5NO2: C, 68.16; H, 3.27; N, 2.84; Found: C, 68.24; H, 3.27; N,
2.93%. IR (KBr):
max (cmꢃ1) 3048 (CHAr), 1782, 1724 (C55O), 1610,
1507 (C55CAr), 1393, 1184 (C–N–C). 1H NMR (CDCl3):
H 7.08–7.00
(m, 8H, H10, H-11), 6.79 (m, 2H, H-2), 6.48 (s, 2H, HC55CH), 3.97 (s,
2H, H-6), 3.66 (s, 2H, H-5); 13C NMR (CDCl3):
C 173.8 (C55O), 163.0
7), 135.8 (C-9), 135.1 (HC55CH), 131.7 (C-4), 130.9 (C-10), 129.2 (C-
3), 128.8 (C-1), 126.5 (C-2), 121.9 (C-8), 115.4 (d, C-11,
2JCF = 21.5 Hz), 46.7 (C-6), 44.8 (C-5); 19F NMR (CDCl3): dF
ꢃ115.0 (m, F-12). MS (ESI) m/z: 440 [M+H]+ 100%.
n
d
d
1
1
(d, C-1, JCF = ꢃ252.5 Hz), 162.1 (d, C-12, JCF = ꢃ248.5 Hz), 158.7
(d, C-3, 1JCF = ꢃ255.5 Hz), 151.3 (C-7), 135.8 (C-9), 135.2 (HC55CH),
130.9 (C-10), 122.2 (C-8), 115.3 (d, C-11, 2JCF = 21.5 Hz), 105.8 (t, C-
4.2.8. N-(4-Fluorophenyl)-7-[bis(4-
fluorophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (8)
N-(4-Fluorophenyl)maleimide (19b) (1.91 g, 10 mmol) and
bis(4-fluorophenyl)fulvene (20b) (2.66 g, 10 mmol) were used.
Yield: 2.38 g (52%); mp: 211 8C (dec.). Anal. Calcd. for
2
2
4, JCF = 17.6 Hz), 101.1 (t, C-2, JCF = 25.7 Hz), 46.6 (C-6), 45.6 (C-
5); 19F NMR (CDCl3): dF ꢃ104.7 (m, F-1), ꢃ112.2 (m, F-3-syn),
ꢃ114.2 (m, F-3-anti), ꢃ114.9 (m, F-12). MS (ESI) m/z: 494 [M+H]+
100%.
C
28H18F3NO2: C, 73.52; H, 3.97; N, 3.06; Found: C, 73.40; H,
3.98; N, 2.92%. IR (KBr): nmax (cmꢃ1) 3068 (CHAr), 3012 (CHC5C),
1775, 1714 (C55O), 1601, 1508 (C55CAr), 1383, 1184 (C–N–C). 1H
NMR (CDCl3): dH 7.27–7.00 (m, 8H, Ar–H), 6.49 (s, 2H, HC55CH),
3.98 (s, 2H, H-6), 3.58 (s, 2H, H-5); 13C NMR (CDCl3): dC 175.4
4.2.12. N-(2,3,4,5,6-Pentafluorophenyl)-7-[bis(4-
fluorophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (12)
N-(2,3,4,5,6-Pentafluorophenyl)maleimide
(19f)
(2.63 g,
1
(C55O), 162.2 (d, C-1, JCF = ꢃ248.5 Hz), 162.1 (d, C-12,
10 mmol) and bis(4-fluorophenyl)fulvene (20b) (2.66, 10 mmol)
were used. Yield: 4.39 g (83%); mp: 188 8C (dec.). Anal. Calcd. for
1JCF = ꢃ247.5 Hz), 151.5 (C-7), 135.7 (C-9), 135.09 (HC55CH),
130.9 (C-10), 128.3 (C-3), 127.6 (C-4), 122.0 (C-8), 116.1 (d, C-2,
2JCF = 22.9 Hz), 115.3 (d, C-11, 2JCF = 21.5 Hz), 46.7 (C-6), 44.7 (C-5);
19F NMR (CDCl3): dF ꢃ112.7 (m, F-1), ꢃ114.9 (m, F-12). MS (ESI) m/
z: 458 [M+H]+ 100%.
C
28H14F7NO2: C, 63.52; H, 2.67; N, 2.65; Found: C, 63.61; H, 2.64; N,
2.71%. IR (KBr):
max (cmꢃ1) 3053 (CHAr), 3012 (CHC5C), 1781, 1731
(C55O), 1601, 1523 (C55CAr), 1361, 1178 (C–N–C). 1H NMR (CDCl3):
H 7.12–7.03 (m, 8H, Ar–H), 6.50 (s, 2H, HC55CH), 3.98 (s, 2H, H-6),
n
d
3.70 (s, 2H, H-5); 13C NMR (CDCl3):
dC 173.1 (C55O), 162.2 (d, C-12,
1
4.2.9. N-(3,5-Difluorophenyl)-7-[bis(4-
1JCF = ꢃ247.7 Hz), 151.0 (C-7), 143.5 (d, C-3, JCF = ꢃ254.5 Hz),
1
1
fluorophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (9)
142.2 (d, C-1, JCF = ꢃ257.5 Hz), 137.9 (d, C-2, JCF = ꢃ253.5 Hz),
135.6 (C-9), 135.3 (HC55CH), 130.9 (C-10), 122.6 (C-8), 115.4 (d, C-
N-(3,5-Difluorophenyl)maleimide (19c) (2.09 g, 10 mmol) and
bis(4-fluorophenyl)fulvene (20b) (2.66 g, 10 mmol) were used.
Yield: 2.20 g (46%); mp: 224 8C (dec.). Anal. Calcd. for C28H17F4NO2:
C, 70.74; H, 3.60; N, 2.95; Found: C, 70.81; H, 3.76; N, 2.89%. IR
(KBr): nmax (cmꢃ1) 3094 (CHAr), 1776, 1712 (C55O), 1621 (C55C),
11, JCF = 21.5 Hz), 107.0 (C-4), 46.7 (C-6), 45.8 (C-5); 19F NMR
2
(CDCl3): dF ꢃ114.7 (m, F-12), ꢃ141.6 (m, F-3-syn), ꢃ143.5 (m, F-3-
anti), ꢃ151.5 (m, F-1), ꢃ161.4 (m, F-2). MS (ESI) m/z: 530 [M+H]+
100%.
1604, 1507 (C55CAr), 1397, 1181 (C–N–C). 1H NMR (CDCl3):
(2H, H-3, s), 7.05–7.03 (m, 7H, Ar–H), 6.49 (s, 2H, HC55CH), 3.99 (s,
2H, H-6), 3.59 (s, 2H, H-5); 13C NMR (CDCl3):
C 174.7 (C55O), 162.8
d
H 8.12
4.2.13. N-Phenyl-7-[bis(4-
bromophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (13)
N-Phenylmaleimide (19a) (1.73 g, 10 mmol) and bis (4-
bromophenyl)fulvene (20c) (3.90 g, 10 mmol) were used. Yield:
d
1
1
(d, C-2, JCF = ꢃ249.5 Hz), 162.2 (d, C-12, JCF = ꢃ247.5 Hz), 151.3
(C-7), 135.7 (C-9), 135.2 (HC55CH), 133.6 (C-4), 130.9 (C-10), 122.2

A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
355
2.25 g (40%); mp: 229 8C (dec.). Anal. Calcd. for C28H19Br2NO2: C,
59.92; H, 3.41; N, 2.50; Found: C, 59.97; H, 3.40; N, 2.36%. IR (KBr):
nmax (cmꢃ1) 3068 (CHAr), 3017 (CHC5C), 1775, 1713 (C55O), 1595,
used. Yield: 3.60 g (59%); mp: 238–239 8C (dec.). Anal. Calcd. for
C
28H16Br2F3NO2: C, 54.66; H, 2.62; N, 2.28; Found: C, 54.76; H,
2.67; N, 2.29%. IR (KBr): nmax (cmꢃ1) 3079 (CHAr), 3022 (CHC5C),
1782, 1725 (C55O), 1609, 1516, 1488 (C55CAr), 1391, 1172 (C–N–C).
1488 (C55CAr), 1387, 1184 (C–N–C). 1H NMR (CDCl3):
dH 7.51–6.93
(m, 13H, Ar–H), 6.48 (s, 2H, HC55CH), 3.96 (s, 2H, H-6), 3.55 (s, 2H,
H-5); 13C NMR (CDCl3) dC 175.3 (C55O), 152.3 (C-7), 138.3 (C-9),
135.0 (HC55CH), 131.6 (C-10), 131.0 (C-11), 129.1 (C-3), 128.8 (C-
1), 128.3 (C-4), 126.50 (C-2), 121.8, 121.7 (C-8, C12), 46.7 (C-6),
44.6 (C-5). MS (ESI) m/z: 562 [M+H]+ 100%.
1H NMR (CDCl3):
dH 7.48–7.46 (m, 4H, Ar–H), 6.90–6.79 (m, 6H, Ar–
H), 6.48 (s, 2H, HC55CH), 3.96 (s, 2H, H-6), 3.65 (s, 2H, H-5); 13C
1
NMR (CDCl3): dC 173.6 (C55O), 163.0 (d, C-1, JCF = ꢃ253.5 Hz),
1
158.6 (d, C-3, JCF = ꢃ256.5 Hz), 152.0 (C-7), 138.3 (C-9), 135.1
(HC55CH), 131.6 (C-10), 130.9 (C-11), 122.2, 121.8 (C-8, C-12),
105.8 (t, C-4, 2JCF = 11.5 Hz), 101.4 (t, C-2, 2JCF = 27.2 Hz), 46.6 (C-6),
45.4 (C-5); 19F NMR (CDCl3): dF ꢃ104.7 (m, F-1), ꢃ112.2 (m, F-3-
syn), ꢃ114.2 (m, F-3-anti). MS (ESI) m/z: 616 [M+H]+ 100%.
4.2.14. N-(4-Fluorophenyl)-7-[bis(4-
bromophenyl)methylidene]bicycle[2.2.1]hept-2-ene-5,6-
dicarboximide (14)
N-(4-Fluorophenyl)maleimide (19b) (1.91 g, 10 mmol) and
bis(4-bromophenyl)fulvene (20c) (3.90 g, 10 mmol) were used.
Yield: 2.55 g (44%); mp: 219 8C (dec.). Anal. Calcd. for
4.2.18. N-(2,3,4,5,6-Pentafluorophenyl)-7-[bis(4-
bromophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (18)
C
28H18Br2FNO2: C, 58.06; H, 3.13; N, 2.42; Found: C, 57.98; H,
N-(2,3,4,5,6-Pentafluorophenyl)maleimide
10 mmol) and bis(4-bromophenyl)fulvene (20c) (3.90 g, 10 mmol)
were used. Yield: 3.10 g (48%); mp: 237 8C (dec.). Anal. Calcd. for
(19f)
(2.63 g,
3.01; N, 2.31%. IR (KBr): nmax (cmꢃ1) 3067 (CHAr), 3013 (CHC5C),
1774, 1709 (C55O), 1510, 1487 (C55CAr), 1384, 1182 (C–N–C). 1H
NMR (CDCl3): dH 7.55–6.89 (m, 12H, Ar–H), 6.48 (s, 2H, HC55CH),
3.97 (s, 2H, H-6), 3.56 (s, 2H, H-5); 13C NMR (CDCl3): dC 175.2
C
28H14Br2F5NO2: C, 51.64; H, 2.17; N, 2.15; Found: C, 51.84; H,
2.21; N, 2.16%. IR (KBr): nmax (cmꢃ1) 3048 (CHAr), 3022 (CHC5C),
1796, 1729 (C55O), 1517, 1487 (C55CAr), 1359, 1168 (C–N–C). 1H
1
(C55O), 162.3 (d, C-1, JCF = ꢃ249.5 Hz), 152.2 (C-7), 138.0 (C-9),
135.0 (HC55CH), 131.6 (C-10), 130.9 (C-11), 128.3 (C-3), 127.5 (C-
4), 121.9, 121.8 (C-8, C12), 116.2 (d, C-2, 2JCF = 22.9 Hz), 46.7 (C-6),
44.7 (C-5); 19F NMR (CDCl3): dF ꢃ112.7 (m, F-1). MS (ESI) m/z: 580
[M+H]+ 100%.
NMR (CDCl3): dH 7.48 (m, 4H, H-11), 6.95 (m, 4H, H-10), 6.49 (s, 2H,
HC55CH), 3.98 (s, 2H, H-6), 3.69 (s, 2H, H-5); 13C NMR (CDCl3): dC
172.9 (C55O), 151.6 (C-7), 143.7 (d, C-3, 1JCF = ꢃ250.4 Hz), 142.2 (d,
C-1, 1JCF = ꢃ258.3 Hz), 137.9 (d, C-2, 1JCF = ꢃ256.5 Hz), 138.2 (C-9),
135.3 (HC55CH), 131.7 (C-10), 130.9 (C-11), 122.5, 121.9 (C-8, C-
12), 106.9 (C-4), 46.7 (C-6), 45.6 (C-5); 19F NMR (CDCl3): dF ꢃ141.6
(m, F-3-syn), ꢃ143.6 (m, F-3-anti), ꢃ151.4 (m, F-2), ꢃ161.3 (m, F-
1). MS (ESI) m/z: 652 [M+H]+ 100%.
4.2.15. N-(3,5-Difluorophenyl)-7-[bis(4-
bromophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (15)
N-(3,5-Difluorophenyl)maleimide (19c) (2.09 g, 10 mmol) and
bis (4-bromophenyl)fulvene (20c) (3.90 g, 10 mmol) were used.
Yield: 4.30 g (72%); mp: 229–230 8C (dec.). Anal. Calcd. for
4.3. X-ray structure determination
C
28H17Br2F2NO2: C, 56.31; H, 2.87; N, 2.35; Found: C, 56.35; H,
Single crystals of the reported compounds were obtained by
isothermal evaporation or cooling of a saturated solution from
acetone or benzene. All crystals were measured on a Bruker Kappa
2.90; N, 2.24%. IR (KBr): nmax (cmꢃ1) 3094 (CHAr), 1775, 1714
(C55O), 1607, 1488 (C55CAr), 1393, 1171 (C–N–C). 1H NMR (CDCl3):
dH 7.49 (m, 4H, Ar–H), 6.79–6.99 (m, 7H, Ar–H), 6.49 (s, 2H,
HC55CH), 3.98 (s, 2H, H-6), 3.58 (s, 2H, H-5); 13C NMR (CDCl3): dC
174.5 (C55O), 162.8 (d, C-2, 1JCF = ꢃ250.5 Hz), 151.9 (C-7), 138.2 (C-
9), 135.1 (HC55CH), 133.5 (t, C-4, 2JCF = 12.7 Hz), 131.6 (C-10), 130.9
(C-11), 122.1, 121.8 (C-8, C-12), 110.0 (d, C-3, 2JCF = 27.9 Hz), 104.3
Apex II using graphite-monochromated Mo
˚
(l = 0.71073 A). Data collection: SMART; cell refinement: SMART;
Ka radiation
data reduction: SAINT [39]. Preliminary structure models were
derived by Direct Methods [40] and were refined by full-matrix
least squares calculation based on F2 for all reflections [41]. All
non-hydrogen atoms were refined anisotropically. Compounds 13,
14ꢀC6H6, 17, and 18 were scaled in multi-scan-mode using SADABS
[42]. The hydrogen atoms were included in the models in
calculated positions. For the compounds 6 and 14ꢀC6H6, a special
treatment is required due to structural disorder.
The structure of compound 6, involves two independent
disorders and hence the molecule was refined in two positions:
(1) the main position of the imide unit and pentafluoro substituted
phenyl group with 81.4%, and an additional but independent
position of the methylidene bonded phenyl ring with 35.1%; (2) the
secondary position of the imide unit and fluorinated phenyl ring
with 18.6%, and the independent position of the methylidene
bounded phenyl ring with 64.9%.
Compound 14 was also refined in two positions: the main
position with 84.2% and the secondary position with 15.8%. Due to
the remaining electron density and the shape of the ellipsoids of
the benzene it can be concluded that the benzene molecule itself is
probably disordered four times since it has more than two adjacent
molecules existing in two different shapes in space. On the other
hand, a continuous transition and an electron density maximum
cannot be detected. Therefore, a refinement of all possible
positions of the guest molecule was omitted.
(t, C-1, JCF = 25.2 Hz), 46.8 (C-6), 44.6 (C-5); 19F NMR (CDCl3): dF
2
ꢃ108.3 (1F, F-2, m). MS (ESI) m/z: 598 [M+H]+ 100%.
4.2.16. N-(2,6-Difluorophenyl)-7-[bis(4-
bromophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (16)
N-(2,6-Difluorophenyl)maleimide (19d) (2.09 g, 10 mmol) and
bis(4-bromophenyl)fulvene (20c) (3.90 g, 10 mmol) were used.
Yield: 2.75 g (46%); mp: 235–236 8C (dec.). Anal. Calcd. for
C
28H17Br2F2NO2: C, 56.31; H, 2.87; N, 2.35; Found: C, 56.45; H,
2.92;N, 2.22%. IR(KBr):
max (cmꢃ1)3079(CHAr), 3022(CHC5C), 1784,
1719 (C55O), 1596, 1505 (C55CAr), 1369, 1168 (C–N–C). 1H NMR
(CDCl3): H 7.48–7.46 (m, 5H, Ar–H), 7.01–6.94 (m, 6H, Ar–H), 6.49
n
d
(s, 2H, HC55CH), 3.97 (s, 2H, H-6), 3.66 (s, 2H, H-5); 13C NMR (CDCl3):
d
C 173.7 (C55O), 158.2 (d, C-3, 1JCF = ꢃ256.5 Hz), 151.1 (C-7), 138.3
(C-9), 135.1 (HC55CH), 131.5 (C-10), 131.1 (C-1), 130.9 (C-11), 122.0,
2
121.7 (C-8, C-12), 112.1 (d, C-2, JCF = 19.6 Hz), 110.0 (t, C-4,
2JCF = 17.6 Hz), 46.5(C-6), 45.4(C-5);19F NMR (CDCl3):dF ꢃ115.5 (m,
F-3-syn), ꢃ117.7 (m, F-3-anti). MS (ESI) m/z: 598 [M+H]+ 100%.
4.2.17. N-(2,4,6-Trifluorophenyl)-7-[bis(4-
bromophenyl)methylidene]bicyclo[2.2.1]hept-2-ene-5,6-
dicarboximide (17)
N-(2,4,6-Trifluorophenyl)maleimide (19e) (2.27 g, 10 mmol)
and bis(4-bromophenyl)fulvene (20c) (3.90 g, 10 mmol) were
All crystal data and experimental parameters are summarized
in Table S1 (SI). Crystallographic data (excluding structure factors)
for the structures in this paper have been deposited with the

356
A. Schwarzer et al. / Journal of Fluorine Chemistry 131 (2010) 345–356
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Cambridge Crystallographic Data Centre as supplementary publi-
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obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, (fax: +44 1223 336033 or e-mail:
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Acknowledgements
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Financial support from the Hungarian Research Fund (OTKA,
Grant T049712) is gratefully acknowledged. The authors thank
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