Anion-π interactions in salts with polyhalide anions: Trapping of I 42-

Article abstract of DOI:10.1002/chem.201001534

The directionality of interaction of electron-deficient π systems with spherical anions (e.g,. halides) can be controlled by secondary effects like NH or CH hydrogen bonding. In this study a series of pentafluorophenyl-substituted salts with polyhalide anions is investigated. The compounds are obtained by aerobic oxidation of the corresponding halide upon crystallization. Solid-state structures reveal that in bromide 2, directing NH-anion interactions position the bromide ion in an η¹-type fashion over but not in the center of the aromatic ring. The same directing forces are effective in corresponding tribromide salt 3. In the crystal, the bromide ion is paneled by four electron-deficient aromatic ring systems. In addition, compounds 4 and 6, which have triiodide and the rare tetraiodide dianion as anions, are described. Computational studies reveal that the latter is highly unstable. In the present case it is stabilized by the crystal lattice, for example, by interaction with electron-deficient π systems. Sheltered and tranquil: Br₃ ^-, I₃^-, and I₄^2- are incorporated into different ammonium and phosphonium salts, in which they show, for example, anion-π interactions with the electron-deficient C ₆F₅ groups of the cations. Theoretical calculations indicate that I₄^2- is highly unstable, but is stabilized in the obtained crystals. A bis-phosphonium salt incorporating I^- and I₄^2- (C gray, F green, H light blue, I purple, P orange) is shown here.

Full text of DOI:10.1002/chem.201001534

DOI: 10.1002/chem.201001534
2ꢀ
Anion–p Interactions in Salts with Polyhalide Anions: Trapping of I4
Michael Mꢀller,[a] Markus Albrecht,*[a] Verena Gossen,[a] Tanja Peters,[a]
Andreas Hoffmann,[a] Gerhard Raabe,[a] Arto Valkonen,[b] and Kari Rissanen*[b]
Dedicated to Professor Kazuhisa Hiratani on the occasion of his 65th birthday
Abstract: The directionality of interac-
tion of electron-deficient p systems
with spherical anions (e.g,. halides) can
be controlled by secondary effects like
NH or CH hydrogen bonding. In this
study a series of pentafluorophenyl-
substituted salts with polyhalide anions
is investigated. The compounds are ob-
tained by aerobic oxidation of the cor-
responding halide upon crystallization.
Solid-state structures reveal that in
bromide 2, directing NH–anion interac-
tions position the bromide ion in an h1-
type fashion over but not in the center
of the aromatic ring. The same direct-
ing forces are effective in correspond-
ing tribromide salt 3. In the crystal, the
bromide ion is paneled by four elec-
tron-deficient aromatic ring systems. In
addition, compounds 4 and 6, which
have triiodide and the rare tetraiodide
dianion as anions, are described. Com-
putational studies reveal that the latter
is highly unstable. In the present case it
is stabilized by the crystal lattice, for
example, by interaction with electron-
deficient p systems.
Keywords: computational chemis-
try · halogens · polyhalides · pi
interactions
chemistry
·
supramolecular
Introduction
perimental examples involve organometallic coordination
assemblies, whereas anion–p interactions in purely organic
compounds are only rarely described.[5]
Supramolecular chemistry is defined as the chemistry of
noncovalent interactions. The most prominent of such weak
interactions are hydrogen bonding, electrostatic attraction,
and metal coordination.[1] Aromatic units can be involved in
p–p stacking or cation–p interactions. Recently, an addition-
al type of weak interaction was reported, that is, the anion–
p interaction between electron-deficient aromatic rings and
anions. Theoretical investigations show that anion–p interac-
tions are attractive.[2,3] Experimental evidence is mainly
found in the crystal, but some observations indicate the rele-
vance of this interaction in solution.[4] A large number of ex-
Recently, we started systematic studies on anion–p inter-
actions of halide anions in pentafluorophenyl ammonium
and phosphonium salts.[6] Crystal structures show high struc-
tural versatility in the relative position of the anion to the
pentafluorophenyl moieties of the cations. The position of
the anion with respect to the p system can be best described
by the hapticity (h) nomenclature that was introduced for
the extensively investigated cation–p systems.[7] Because of
the weak nature of the anion–p interaction a strong direct-
ing influence by the substituents of the ammonium and
phosphonium cations (mainly NH··· or CH···anion interac-
tions) on the location of the anion was observed.[8] Thus, the
interaction between a spherical anion (halide) and an elec-
tron-deficient aromatic ring is controlled by 1) the electro-
static interaction between the anion and the aromatic unit,
and 2) by the substituents at the periphery of the aromatic
ring. With spherical anions, it is mainly the size and the po-
larizability of the anion that are important. Therefore, it is
of interest to investigate derivatives that contain electron-
deficient aromatic moieties in addition to linear anionic spe-
cies (e.g., polyhalide anions).
[a] M. Mꢀller, Prof. Dr. M. Albrecht, V. Gossen, T. Peters, A. Hoffmann,
Prof. Dr. G. Raabe
Institut fꢀr Organische Chemie
RWTH Aachen University
Landoltweg 1, 52074 Aachen (Germany)
Fax : (+49)241-8092385
E-mail: markus.albrecht@oc.rwth-aachen.de
[b] Dr. A. Valkonen, Prof. K. Rissanen
Department of Chemistry, Nanoscience Center
University of Jyvꢁskylꢁ, Survontie 9
40014 Jyvꢁskylꢁ (Finland)
Fax : (+358)14-260-2672
By serendipity we obtained a series of crystal structures
involving linear polyhalide anions (tribromide anion, triio-
dide anion, and the rare tetraiodide dianion) in crystal latti-
E-mail: kari.t.rissanen@jyu.fi
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001534.
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FULL PAPER
ces containing electron-deficient pentafluorophenyl groups
as part of the cations. The crystals were obtained in addition
to those of the parent halide salts. The polyhalides are
formed by aerobic oxidation of the halide during the crystal-
lization process. The corresponding crystals are recognized
by their intense color.
Results and Discussion
Scheme 1. Synthesis of 8-pentafluorobenzyloxy quinoline (1) and the cor-
responding bromide (2) and tribromide (3) salts.
Polyhalide anions are charge-transfer adducts between a di-
halide and a halide anion. They are of interest due to their
reactivity in oxidation or addition reactions with organic
substrates[9] or as components for organic conductors.[10] The
polyhalide anions are formed by reaction of the dihalide
with a corresponding halide anion. This may happen in situ
by formation of the dihalide from two anions followed by
aggregation with an additional anion. Most common are the
trihalide anions (tribromide or triiodide), but higher-order
species are also observed. The tetraiodide dianion is a rare
and exotic dianion that common sense says should be unsta-
ble due to electrostatic repulsion between the two iodide
anions bound to a central diiodine moiety. However, this
species has been observed in some rare cases.[11] Herein, ex-
amples are described in which oligo-iodides formed in situ
and in the crystal interact with electron-deficient aromatic
units by anion–p interactions.
During the investigations, situations were found in which
the unstable tetraiodide dianion is stabilized either by direct
anion–p interaction or by anion–p complexes, which provide
an ideal cavity in the crystal lattice for the stabilization of
this rare dianion.
Figure 1. Structure of quinoline derivative 1 as observed in the crystal
(created with ORTEP III[12], ellipsiods drawn at the 50% probability
level).
Protonated quinoline as a directing group for anion–p inter-
actions in bromide and tribromide salts: Following earlier
studies on anion-directing influences of substituents at elec-
tron-deficient aromatics, derivatives of 8-pentafluorobenzyl-
A
tween the pentafluorophenyl plane and the quinoline plane
of 96.388 is found.
pentafluorophenyl moiety is attached to the 8-position of
the quinoline unit by a CH2O linker. Upon protonation of
the quinoline, a conformation can be adopted in which the
NH bond is directed on top of the center of the fluorinated
aromatics. This should be ideal to fix an anion in this posi-
tion.
Compound 1 was prepared by Williamson ether synthesis
in ethanol from pentafluorobenzyl bromide and 8-hydroxy-
quinoline in the presence of KOH as base (Scheme 1). Dif-
fusion of hydrogen bromide into a solution of compound 1
in toluene under air results in two kinds of crystals. Single
crystals suitable for solid-state measurements were obtained
for compounds 1–3.
Compound 1 crystallizes from dichloromethane on slow
evaporation of the solvent. The solid-state structure
(Figure 1) reveals p–p stacking of the pentafluorophenyl
ring and the phenol ring of the quinoline moiety of a second
molecule. The intermolecular distance between the stacked
ring systems is about 3.5 ꢃ. An intramolecular angle be-
Diffusion of hydrogen bromide into a solution of 1 in tol-
uene leads to two kinds of crystals. The expected hydrogen
bromide adduct 2 is obtained in form of yellow crystals con-
taining one cocrystallized molecule of toluene. The solid-
state structure of the salt (Figure 2) reveals that the NH···an-
ion interaction (NH···Br 2.298 ꢃ) is able to direct the anion
to the top of the pentafluorophenyl unit. However, in con-
trast to our expectations, the anion is not located above the
center of the electron-deficient ring. The distance analysis
revealed only one carbon–bromide distance shorter than
4.1 ꢃ. Therefore, the bromide shows only an h1-type interac-
tion (C···Br 3.876 ꢃ) to one ortho position of the pentafluor-
ophenyl unit. Bromide mainly interacts by CH–anion inter-
actions (not shown in Figure 2) with toluene (CH···Br 2.990–
3.126 ꢃ) and with the quinoline backbone (CH···Br 3.509–
3.624 ꢃ).
In addition to HBr adduct 2, hydrogen tribromide salt 3
could be obtained in the form of an orange solid by oxida-
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M. Albrecht, K. Rissanen et al.
Figure 2. Two different views of part of the crystal structure of 2 (created
with ORTEP III[11], ellipsiods drawn at the 50% probability level).
tion upon crystallization. The solid-state structure (Figure 3)
follows the perception that the NH···anion interaction is
able to fix the anion above the p system of the pentafluoro-
phenyl substituent. Tribromide is known in its symmetrical
ꢀ
ꢀ
[13]
ꢀ
ꢀ
ꢀ
([Br Br Br] ) and unsymmetrical ([Br Br···Br] ) forms.
In the solid-state structure of 3, an unsymmetrical structure
ꢀ
ꢀ
ꢀ
is found (Br1 Br2 2.644, Br2 Br3 2.469 ꢃ). The Br3 anion
undergoes anion–p interactions. Analysis of the distances re-
veals a h3-type interaction between Br1 and the 1-, 2-, and
ꢀ
3-positions of a C6F5 unit (C Br1 3.596-3.917 ꢃ). One termi-
nus is fixed by an NH hydrogen-bonding interaction with
the quinolinium moiety (NH···Br1 2.465 ꢃ). The second ter-
minus (Br3) interacts with the C6F5 moiety of another
cation, which can be described as slightly shifted from h6
(C···Br3 3.430-4.015 ꢃ). In addition anion–p contacts are ob-
served with the electron-deficient pyridinium unit of the
quinoline. Here the electrostatic attraction between pyridini-
um and the anion seems to be an important contribution to
the binding (C···Br2 3.671, N···Br1 3.624 ꢃ).
Figure 3. Different views of the solid-state structure of compound 3 (el-
lipsiods drawn at the 50% probability level).
In compound 4 we observed oxidation of iodide to triio-
dide and to the tetraiodide dianion. Both anions are linear
and interact with the lattice by CH···anion hydrogen bonds
In the crystal of 3, the tribromide is located in an elec-
tron-deficient box, surrounded by aromatic p acceptors. The
ꢀ
termini of the Br3 anion are capped by two pentafluoro-
phenyl rings, and two parallel quinoline units flank the sides.
An additional quinolinium group is involved in CH···anion
bonds (Figure 3c, the parallel quinolinium moiety at the
front is omitted for clarity). Figure 4 shows the p boxes
formed in the crystal by two pentafluorophenyl and two qui-
nolinium units, which include the tribromide anion.
A triiodide anion and a tetraiodide dianion in the crystal of
a pentafluorobenzyl ammonium salt: Pentafluorobenzyldi-
benzylamine was obtained by treatment of dibenzyl amine
with pentafluorobenzyl bromide in the presence of potassi-
um carbonate. Crystals of 4 were obtained by diffusion of
HI into a solution of the amine in toluene.
Figure 4. Part of the crystal lattice of 3 showing the inclusion of tribro-
mide anions in boxes paneled by four p acceptors.
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Anion–p Interactions in Polyhalide Salts
FULL PAPER
ꢀ
(Figure 5). The I I bond lengths of the triiodide ion are
2.896 and 2.921 ꢃ. For the tetraiodide ion, we observed
The tetraiodide dianion is encompassed by four ammoni-
um cations and is stabilized by CH and NH hydrogen bonds
(Figure 7). Two of the four electron-poor phenyl rings show
an anion–p interaction (C···I 3.661, 4.068 ꢃ).
ꢀ
ꢀ
bonds of I Iinternal 2.762 ꢃ and I Iterminal =3.363 ꢃ. In addi-
tion to anion binding through CH hydrogen bonds, close
contact of both anions to the pentafluorophenyl moiety is
found, manifested in an anion–p interaction.
ꢀ
2ꢀ
Figure 5. Pentafluorobenzyldibenzylamonium salt 4 with I3 and I4 as
anions.
In compound 4, two triiodide anions are surrounded by
four ammonium cations (Figure 6) and are stabilized by CH
hydrogen bonds of the benzylic and phenylic substituents
(and additional CH hydrogen bonds from cocrystallized tol-
uene). Each anion is flanked by two pentafluorophenyl moi-
eties (C···I 3.804-4.082 ꢃ) with the central iodine atom locat-
ed over the center of the p system. The axis of the triiodide
ion is orientated in parallel to the F-C3-C6-F-axis of the per-
fluorinated phenyl ring.
Figure 7. Two different views of the tetraiodide anion in part of the crys-
tal structure of 4. The termini of the linear anion are in close contact
with the pentafluorophenyl units (ellipsiods drawn at the 50% probabili-
ty level).
1,3-Bis(diphenylpentafluorobenzylphosphonium)propane
1
2ꢀ
salts with two Iꢀ or with Iꢀ and = I4 as anions: Reaction of
2
1,3-propanylbis(diphenylphosphane) and pentafluorobenzyl
iodide results in the formation of the bis-phosphonium salt,
with traces of an oxidized side product as impurity. During
crystallization of this salt from ethanol, colorless and red
crystals were obtained.
The structural investigation of colorless crystals
5
(Figure 8) reveals that one of the two iodide anions is locat-
ed nearly in the center between the planes of the
pentafluoroACTHNUGTRNEUNGphenyl rings. This iodide ion exhibits contacts
which are indicative for anion–p interactions (C···I 4.000–
5.110 ꢃ; only two interactions are shorter than 4.1 ꢃ). It fur-
ther interacts through CH···anion bonds with the alkyl chain
(CH···I 2.964, 2.984 ꢃ). The iodine···CC F distances seem to
6
5
be quite long, but an electron-poor cavity is provided by the
C6F5 units to host the iodide ion. The second anion shows
short contacts to alkyl and phenyl hydrogen atoms.
The solid-state structure of red crystals 6 (Figure 9) shows
that during the crystallization process iodine is partially oxi-
Figure 6. Part of the crystal structure of 4. a) Top and b) side view of two
triiodide anions surrounded by four cations. Each triiodide ion interacts
with two electron-poor phenyl rings (ellipsiods drawn at the 50% proba-
bility level).
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M. Albrecht, K. Rissanen et al.
Figure 8. Bis-phosphonium salts with two iodide (5) or iodide and the tet-
raiodide dianion (6) or dibromide 7.
Figure 10. Different views of the dianion in the crystal of 6, which show
the linear tetraiodide anion stabilized by multiple CH hydrogen-bonding
interactions (ellipsiods drawn at the 50% probability level).
Figure 9. Part of the crystal structure of 6 showing one iodide ion cen-
tered between the two pentafluorophenyl moieties (ellipsiods drawn at
the 50% probability level).
orientation of the two C6F5 rings, creating an electron-defi-
cient cleft to capture an Iꢀ anion. The modulation of the
crystal lattice results in an apolar tubular cavity, which in
concert with CH hydrogen bonds stabilizes the tetraiodide
dianion.
dized and the bis-phosphonium cation with one iodide and
half a tetraiodide dianion is obtained. As in compound 5,
the iodide anion is located between the planes of the penta-
fluorophenyl rings and exhibits weak anion–p interactions
(C···I 3.725–5.220 ꢃ; only two interactions are shorter than
4.1 ꢃ). CH bonds of the alkyl chains and one OH of a coc-
rystallized water molecule are directed towards this anion
(CH···I 2.890, 2.990 ꢃ).
Computational study of I42ꢀ: The rarely observed halogen-
2ꢀ
bonded I4 anion in the crystal structures of 4 and 6 in-
spired us to perform computational studies on this species.
Sæthre et al.[14] already performed some calculations on the
structure and bonding of linear polyiodide compounds,
which showed that the dominant intramolecular interaction
2ꢀ
2ꢀ
However, the tetraiodide dianion I4 is the most remark-
in the I4 anion is electrostatic repulsion between the termi-
able feature of the crystal structure of 6[8] (Figure 10). The
nal iodides. However, the correlation energy was omitted in
their calculations[14] and, therefore, we performed additional
calculations employing effective core potentials and includ-
ing correlation energy by means of Møller–Plesset perturba-
tion theory[15] to the second order (MP2).
2ꢀ
I4 anion is positioned in a cavity, which stabilizes it
through CH hydrogen bonds from the benzylic and phenylic
substituents to the terminal I atoms (CH···Iterminal 2.943–
3.308 ꢃ) and between the alkyl spacer and the internal I
atoms (CH···Iinternal 3.251–3.271 ꢃ).[9] The termini of the dia-
nion are capped by pentafluorophenyl units with I···CF sep-
arations of 3.927–4.125 ꢃ. Within I42ꢀ, lengths of 2.826 (cen-
tral bond) and 3.403 ꢃ (terminal bonds) are observed.
The calculations were performed with the Gaussian 09[16]
suite of programs. At the MP2/LANL2DZ[17] level of theory
the molecule is very slightly bent (C2v, aI-I-I =179.28) and
ꢀ
the lengths of the terminal and the central I I bonds are
For comparison, compound 7 with two bromide anions
was prepared. Only one of the anions shows an h2 anion···p
interaction (C···Br 3.815, 3.970 ꢃ). In contrast to 5 or 6, the
two C6F5 units are orientated to opposite sides of the central
diphosphonium propane moiety. Comparing 5, 6, and 7 re-
veals that the weak interactions of the diphenylpropylenedi-
phosphonium cation with the Iꢀ anion influence the relative
3.094 and 3.608 ꢃ, respectively. A second local minimum of
D1h symmetry is located only 0.03 kcalmolꢀ1 above the C2
structure. The geometries obtained at different levels of
theory together with the experimental values in the solid
state are listed in Table 2 of the Supporting Information,
and the total energies are compiled in Table 1. Possible reac-
2ꢀ
tion paths giving I4 are shown in Scheme 2.
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Anion–p Interactions in Polyhalide Salts
FULL PAPER
Table 1. Total energies [Hartree] at the MP2/LANL2DZ level. Values in
italics are those of the less stable linear structure; e0 is the zero-point
energy.
The presented studies and the cited references show that
anion–p interaction is a dominant intermolecular force in
crystals of salts with electron-deficient p systems. A chal-
lenge is to use this for host–guest interactions in solution.
However, no indications were found for anion–p interac-
tions between the ions in solution in the present case. Corre-
sponding solution studies with related systems are currently
being performed.
Etot
e0
Etot +e0
2ꢀ
I4
44.831645
44.831656
33.655768
22.354634
11.247857
0.000727
0.000778
0.000798
0.000407
44.830918
44.830878
33.654970
22.354227
ꢀ
I3
I2
Iꢀ
The energy changes associat-
ed with reactions a) and b) at
the MP2/LANL2DZ level of
Experimental Section
All solvents were used after distillation without further purification. All
reagents were used as received. NMR spectra were recorded in deutero-
chloroform by using a Varian Mercury 300 (1H: 300 MHz; 19F: 282 MHz),
and the mass spectrometric data were taken by using a Thermo Deca XP
in ESI mode. The infrared spectra were obtained in KBr by using a
Perkin–Elmer FTIR spectrometer Spektrum 100 in the range of 4000–
650 cmꢀ1. Elemental analyses were performed by using a CHN-O-Rapid
Vario EL from Heraeus, and the melting points were measured by using
a Bꢀchi B540. XRD data were collected by using a Bruker-Nonius Kap-
paCCD diffractometer with Apex-II detector at T=123 K with graphite-
monochromatized MoKa radiation (l=0.71073 ꢃ). Collect software[19]
was used for data measurement, and DENZO-SMN[20] was used for proc-
essing. The structures were solved by direct methods with SIR2004[21] and
refined by full-matrix least-squares methods using WinGX software,[22]
which utilizes the SHELXL-97 module.[23] Multiscan absorption correc-
tion (SADABS[24]) was applied on all data (except for 1). Some geometri-
cal (DFIX and SADI) and thermal (SIMU, ISOR) parameter restraints
were used to fix severely disordered molecules to be chemically reasona-
ble in the structures. The CH hydrogen positions were calculated and re-
fined as riding atom models with 1.2 or 1.5 times the thermal parameter
of the corresponding carbon atoms. All NH and OH positions were
found in the electron-density maps, and the bonds to parent atoms were
fixed as idealized lengths (0.91 ꢃ for NH, 0.84 for OH) and refined with
isotropic temperature factors of 1.2 (NH) or 1.5 (OH) times the parent-
atom factor.
theory
are
ꢀ33.2
and
+45.1 kcalmolꢀ1, respectively.
ꢀ
Thus, although formation of I3
Scheme 2. Reaction paths to
2ꢀ
from I2 and Iꢀ is exoenergetic,
I4
.
2ꢀ
ꢀ
that of I4 from I3 and Iꢀ is
significantly
endoenergetic.
2ꢀ
Therefore, I4 resides in a shallow local minimum 45.1 kcal
molꢀ1 above its starting materials and is separated from
them by a barrier of only 0.013 kcalmolꢀ1. The weakly
2ꢀ
bonded character of I4 is not only reflected in the low bar-
ꢀ
rier to fragmentation and the long terminal I I bonds of
3.608 ꢃ, but also by the results of an NBO analysis. Within
the framework of this method there is neither a s nor a p
bond between the terminal iodine atoms and the central I2
unit. Each of the terminal iodine atoms carries four lone
pairs, and the only stabilization comes from an interaction
of one lone pair per atom (degenerate HOMO) with the s*
ꢀ
orbital of the central I I bond (LUMO). Consequently, the
occupation numbers of these lone pairs are reduced to
about 1.86e whereas those of the others are essentially 2.0e
and the s* orbital is populated by 0.28e. This result supports
Synthesis of 8-pentafluorobenzyloxyquinoline (1): Potassium hydroxide
(108 mg, 1 equiv, 1.92 mmol) was dissolved in warm ethanol (10 mL) and
hydroxyquinoline (1 equiv, 1.92 mmol, 279 mg) was added. The yellow
mixture was stirred until the quinoline was completely dissolved, then
pentafluorobenzyl bromide (500 mg, 1 equiv, 1.92 mmol, 290 mL) was
added to give an orange mixture that turned red after 15 min. Heating to
reflux for 6 h changed the color back to yellow. The mixture was cooled
to RT and the white precipitate was filtered off. The colorless solid was
extracted with chloroform. Crystals of 1 were grown from dichlorome-
thane by slow evaporation of the solvent (yield: 500 mg of colorless solid,
2ꢀ
Hasselꢄs interpretation of the I4 dianion as a charge-trans-
fer complex of two donating iodide anions and an accepting
iodine molecule.[18]
Conclusion
M=325.05 gmolꢀ1
,
1.5 mmol, 81%). M.p. 1928C; 1H NMR (CDCl3,
This crystallographic study has revealed attractive interac-
300 MHz): d=8.90 (dd, 3J=4.2/1.7 Hz, 1H; Haryl), 8.10 (dd, 3J=8.4/
ꢀ
ꢀ
2ꢀ
tions between Brꢀ, Br3 , Iꢀ, I3 and I4 and electron-defi-
3
1.7 Hz, 1H; Haryl), 7.45–7,35 (m, 3H; Haryl), 7.14 (t, J=4.4 Hz, 1H; Haryl),
cient aromatics. In 3, the packing of the cations provides
cavities for Br3 , which is paneled by four aromatics (termi-
5.35 ppm (s, 2H; CH2C6F5); 19F NMR (CDCl3, 300 MHz): d=ꢀ141.49
(m, 2F; Fortho), ꢀ152.87 (m, 1F; Fpara), ꢀ161.78 ppm (m, 2F; Fmeta); IR
(KBr): n˜ =3430 (w), 3366 (w), 2998 (w), 1943 (w), 2906 (w), 2803 (w),
2163 (w), 2011 (w), 1973 (w), 1710 (w), 1658 (m), 1617 (w), 1565 (m),
1521 (s), 1501 (s), 1466 (m), 1433 (m), 1373 (s), 1319 (s), 1269 (s), 1212
(m), 1180 (m), 1135 (s), 1103 (vs), 1077 (s), 1058 (s), 979 (s), 938 (vs), 884
(m), 822 (s), 799 (s), 768 (vs), 715 (s), 669 cmꢀ1 (m); MS (ESI): m/z (%):
326.1 (100) [M+H]+ (C16H9F5NO+); elemental analysis calcd (%) for
C16H8F5NO: C 59.09, H 2.48, N 4.31; found: C 58.71, H 2.52, N 4.27.
ꢀ
nal pentafluorophenyl and parallel quinolinium) involved in
anion–p interactions. To the best of our knowledge this is
the first observation of anion–p interactions involving the
tribromide anion.
Salts 4 and 6 have the rare tetraiodo dianion as a compo-
nent. Theoretical considerations show that the tetraiodide
itself should be rather unstable towards decomposition to
triiodide and iodide. In the crystal this dianion is stabilized
by attractive interactions with the crystal lattice, including
anion–p interactions. Thus, a first example is presented in
which anion–p interactions contribute to the stabilization of
an otherwise unstable species.
Synthesis of 8-pentafluorobenzyloxy quinoline hydrobromide (2): 8-Pen-
tafluorobenzyloxyquinoline (200 mg, 1 equiv, 0.62 mmol) was dissolved in
THF (10 mL), and hydrobromic acid (150 mL, 48%, 1.4 equiv, 0.89 mmol)
was added to the solution. The mixture was stirred for 1 h and then the
solvent was removed under reduced pressure. The yellow solid was dried
under vacuum (yield: 245 mg of yellow solid, M=404.98 gmolꢀ1
0.62 mmol, quant.). 1H NMR (CDCl3, 300 MHz): d=16.68 (brs, 1H;
,
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ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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12451

M. Albrecht, K. Rissanen et al.
NH), 9.46 (brs, 1H; Haryl), 8.95 (brd, 3J=7.8 Hz, 1H; Haryl), 8.12 (brs,
1H; Haryl), 7.89 (t, 3J=7.8 Hz, 1H; Haryl), 7.81 (d, 3J=7.8 Hz, 1H; Haryl),
7.59 (d, 3J=7.8 Hz, 1H; Haryl), 5.52 ppm (s, 2H; CH2C6F5); 19F NMR
(CDCl3, 300 MHz): d=ꢀ141.12 (m, 2F; Fortho), ꢀ151.26 (m, 1F; Fpara),
ꢀ161.03 ppm (m, 2F; Fmeta); IR (KBr): n˜ =3393 (w), 3061 (w), 2995 (w),
2899 (w), 2613 (w), 2037 (w), 1936 (w), 1855 (w), 1747 (w), 1703 (w),
1662 (m), 1629 (w), 1596 (m), 1544 (s), 1507 (vs), 1387 (s), 1296 (vs),
1201 (m), 1131 (s), 1113 (s), 1055 (s), 972 (s), 937 (s), 876 (s), 821 (s), 770
(s), 751 (s), 751 (s), 666 cmꢀ1 (m); MS (EI): m/z (%): 325.1 (100) [M]+
(C16H9F5NO+); elemental analysis calcd (%) for C16H8F5NOHBr·2H2O:
C 43.46, H 2.96, N 3.17; found: C 43.26, H 3.04, N 3.13.
Crystal data for 1: C16H8NOF5; Mr =325.23 gmolꢀ1; tetragonal; space
group P43; a=7.5204(1), b=7.5204(1), c=23.5049(4) ꢃ; V=
1329.35(3) ꢃ3; Z=4; 1calcd =1.625 gcmꢀ3; m=0.150 mmꢀ1; F
ACTHUNRTGNE(GNU 000)=656;
crystal size 0.20ꢅ0.12ꢅ0.09 mm; qmax =25.008; 2297 reflections collected,
1196 unique (Rint =0.0230), 1 restraint, 208 parameters, GOF on F2 =
1.089, final R indices for I>2s(I) were R1 =0.0332, wR2 =0.0657. Friedel
pairs merged.
Crystal data for 2: C16H9NOF5+·Brꢀ·C7H8; Mr =498.29 gmolꢀ1; triclinic;
¯
space group P1; a=7.4444(2), b=8.7250(3), c=16.9105(5) ꢃ; a=
96.918(2), b=93.800(2), g=109.434(10)8; V=1021.60(5) ꢃ3; Z=2;
1calcd =1.620 gcmꢀ3; m=2.072 mmꢀ1; F
ACTHNUTRGNEU(GN 000)=500; crystal size 0.25ꢅ0.20ꢅ
0.16 mm; qmax =25.028; 6088 reflections collected, 3607 unique (Rint
=
Synthesis of pentafluorobenzyldibenzylamine: Potassium carbonate
(1.02 g, 2 equiv, 6.14 mmol) and pentafluorobenzylbromide (470 mL,
0.800 g, 1 equiv, 3.07 mmol) were added to a solution of dibenzylamine
(0.605 g, 1 equiv, 3.07 mmol) in acetonitrile (10 mL). The mixture was
stirred for 24 h at RT, then the solvent was removed under reduced pres-
sure, and the white precipitate extracted with chloroform. The solvent
was removed and the white solid was recrystallized from ethanol and
0.0286), 1 restraint, 284 parameters, GOF on F2 =1.025, final R indices
for I>2s(I) were R1 =0.0398, wR2 =0.0894.
Crystal data for 3: C16H9NOF5+·Br3ꢀ; Mr =565.97 gmolꢀ1; triclinic; space
group P21/c; a=10.5370(4), b=7.0193(2), c=24.4694(8) ꢃ; b=
98.550(2)8;
V=1789.70(10) ꢃ3;
Z=4;
1calcd =2.101 gcmꢀ3
;
m=
6.817 mmꢀ1
;
F
A
=
dried under vacuum (yield: 290 mg of white solid, M=377.35 gmolꢀ1
,
25.008; 21647 reflections collected, 3154 unique (Rint =0.0514), 2 re-
straints, 238 parameters, GOF on F2 =1.037, final R indices for I>2s(I)
were R1 =0.0347, wR2 =0.0593.
0.77 mmol, 25%). M.p. 808C; 1H NMR (CDCl3, 300 MHz): d=7.40–7.20
(m, 10H; Haryl), 3.73 (s, 2H; CH2C6F5), 3.61 ppm (s, 4H; CH2C6H5);
19F NMR (CDCl3, 300 MHz): d=ꢀ141.31 (m, 2F; Fortho), ꢀ155.57 (m, 1F;
Crystal data for 4: 2(C21H17NF5+)·0.5I42ꢀ·I3ꢀ·C7H8; Mr =1483.35 gmolꢀ1
monoclinic; space group C2/c; a=19.3209(3), b=18.2036(3), c=
29.1411(4) ꢃ; b=93.6711(6); Z=8; 1calcd
V=10228.2(3) ꢃ3;
1.927 gcmꢀ3 m=3.112 mmꢀ1
(000)=5640; crystal size 0.30ꢅ0.20ꢅ
;
F
para), ꢀ162.77 ppm (m, 2F; Fmeta); IR (KBr): n˜ =3085 (w); 3061 (w);
=
3031 (w); 2948 (w); 2928 (w); 2886 (w); 2811 (w); 2715 (w); 2408 (w);
2321 (w); 2060 (w); 1982 (w); 1712 (w); 1656 (w); 1600 (w); 1521 (s);
1492 (vs); 1452 (m); 1403 (w); 1377 (w); 1366 (w); 1334 (m); 1294 (m);
1271 (w); 1242 (m); 1211 (w); 1179 (w); 1161 (w); 1126 (m); 1109 (vs);
1075 (m); 1009 (vs); 975 (m); 936 (m); 913 (s); 856 (w); 832 (m); 815
(m); 745 (vs); 730 (s); 695 cmꢀ1 (vs); MS (EI): m/z (%): 377.1 (59) [M]+
(C21H16F5N+); elemental analysis calcd (%) for C21H16F5N: C 66.84, H
4.27, N 3.71; found: C 66.83, H 4.32, N 3.74.
;
; FACHTUTGNENRNUG
0.16 mm; qmax =25.028; 25655 reflections collected, 9021 unique (Rint
=
0.0431), 162 restraints, 657 parameters, GOF on F2 =1.203, final R indices
for I>2s(I) were R1 =0.0489, wR2 =0.1016.
Crystal data for 5: 2(C41H30F10P22+)·4Iꢀ·H2O; Mr =2074.80 gmolꢀ1; tri-
¯
clinic; space group P1; a=13.4320(2), b=17.6232(3), c=27.6470(5) ꢃ;
a=87.1980(10), b=83.628(2), g=70.4250(10)8; V=6127.6(2) ꢃ3; Z=3
(Z’=1.5); 1calcd =1.687 gcmꢀ3; m=1.694 mmꢀ1; F
ACTHNUTRGNE(UNG 000)=3042; crystal size
Synthesis of bis(phosphonium iodide) 5: 1,3-Propanylbis(diphenylphos-
phane) (200 mg, 1 equiv, 0.49 mmol) was dissolved in pentane (10 mL),
and a solution of pentafluorobenzyl iodide (149 mg, 2 equiv, 0.98 mmol)
dissolved in pentane (2 mL) was added. The mixture was stirred for 2 h
at RT. The light yellow precipitate was filtered off and dried in vacuum
(yield: 280 mg of white solid, M=1027.98 gmolꢀ1, 0.27 mmol, 55%).
1H NMR (CDCl3, 300 MHz): d=7.96–7.59 (m, 10H; Haryl), 4.98 (d, 3J=
13.8 Hz, 4H; CH2C6F5), 3.81 (brs, 4H; CH2); 2.36 ppm (brs, 4H; CH2);
19F NMR (CDCl3, 300 MHz): d=ꢀ137.29 (m, 2F; Fortho), ꢀ149.98 (m, 1F;
0.25ꢅ0.20ꢅ0.13 mm; qmax =25.028; 39384 reflections collected, 21307
unique (Rint =0.0532), 316 restraints, 1602 parameters, GOF on F2 =1.044,
final R indices for I>2s(I) were R1 =0.0563, wR2 =0.1016.
Crystal data for 6: 2(C41H30F10P22+)·I42ꢀ·2Iꢀ·2H2O; Mr =2346.61 gmolꢀ1
;
¯
triclinic; space group P1; a=9.46480(10), b=13.1523(3), c=
18.7539(3) ꢃ; a=104.6900(10), b=94.888(2), g=105.873(2)8; V=
2141.96(6) ꢃ3; Z=1 (Z’=0.5); 1calcd =1.819 gcmꢀ3; m=2.339 mmꢀ1; F-
AHCTUNGRTENNG(NU 000)=1130; crystal size 0.50ꢅ0.10ꢅ0.07 mm; qmax =25.028; 12658 reflec-
tions collected, 7547 unique (Rint =0.0284), 2 restraints, 521 parameters,
GOF on F2 =1.075, final R indices for I>2s(I) were R1 =0.0363, wR2 =
0.0693.
F
para), ꢀ158.68 ppm (m, 2F; Fmeta); additional NMR signals arising from a
minor side product were observed.
Synthesis of bis(phosphonium bromide) 7: 1,3-Propanylbis(diphenylphos-
phane) (100 mg, 1 equiv, 0.24 mmol) was dissolved in toluene and penta-
fluorobenzyl bromide (126 mg 2 equiv, 0.49 mmol) was added. The mix-
ture was stirred for 3 h at 1208C. The white precipitate was filtered off
Crystal data for 7: 2(C41H30F10P22+)·4Brꢀ·1.2
ACHTNUGTRENN(UG C3H7NO)·0.8ACHTUNTGRNE(NUGN C4H10O)·3O;
Mr =2063.83 gmolꢀ1; monoclinic; space group P21/c; a=9.7141(2), b=
16.7628(2), c=28.9239(4) ꢃ; b=91.0920(10); V=4708.98(13) ꢃ3; Z=2
(Z’=2); 1calcd =1.456 gcmꢀ3; m=1.866 mmꢀ1; F
ACTHNUTRGNE(UNG 000)=2075; crystal size
and dried in vacuum (yield: 195 mg of white solid, M=932.00 gmolꢀ1
,
0.22ꢅ0.20ꢅ0.14 mm; qmax =25.028; 37233 reflections collected, 8294
unique (Rint =0.0717), 7 restraints, 590 parameters, GOF on F2 =1.025,
final R indices for I>2s(I) were R1 =0.0560, wR2 =0.1036.
0.21 mmol, 86%). M.p. 2388C; 1H NMR (CDCl3, 300 MHz): d=7.86 (m,
3
2
8H; Haryl), 7.68 (t, J=7.3 Hz, 4H; Haryl), 7.55 (m, 8H; Haryl), 5.05 (d, J=
13.6 Hz, 4H; CH2C6F5), 3.70 (br. S, 4H; CH2), 2.45 ppm (br. S, 2H;
CH2); 19F NMR (CDCl3, 300 MHz): d=ꢀ137.32 (m, 4F; Fortho), ꢀ150.33
(m, 2F; Fpara), ꢀ159.12 ppm (m, 2F; Fmeta); IR (KBr): n˜ =3411 (w), 3085
(w), 3019 (w), 2843 (w), 2777 (w), 2324 (w), 2167 (w), 2108 (w), 1993 (w),
1906 (w), 1657 (w), 1616 (w), 1586 (w), 1505 (vs), 1437 (m), 1396 (w),
1308 (w), 1260 (w), 1197 (w), 1163 (w), 1114 (s), 1027 (w), 976 (vs), 866
(w), 829 (w), 801 (w), 737 (s), 687 cmꢀ1 (s); MS (ESI): m/z (%): 1014.47
(100) [MBr3]ꢀ (C41H30Br3F10P2ꢀ); elemental analysis calcd (%) for
C25H17BrF5P·H2O: C 51.70, H 3.39; found: C 51.48, H 3.35.
CCDC-779159 (1), CCDC-779160 (2), CCDC-779161 (3), CCDC-774615
(4), CCDC-774616 (5), CCDC-774617 (6), and CCDC-774614 (7) contain
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data request/cif.
Preparation of crystals of 2–7: Compound 1 was dissolved in toluene
(1 mL) in a test tube and the solution was placed in a beaker containing
approximately 5 mL of hydrobromic acid (48%). Crystals were grown
over three weeks under air. Crystals of 4 were grown from a solution of
the free amine in toluene by diffusing hydroiodic acid into the solution.
Crystals were grown from a solution of 5 in ethanol. Two kinds of crystals
were obtained (colorless crystals of iodide 5 and red crystals of salt 6
with the tetraiodide dianion). Crystals of 7 were obtained by diffusion of
diethyl ether into a solution in dimethylformamide.
Acknowledgements
This work was supported by the Fonds der Chemischen Industrie and the
Academy of Finland (KR, proj. no. 212588 and 218325).
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12452
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Chem. Eur. J. 2010, 16, 12446 – 12453

Anion–p Interactions in Polyhalide Salts
FULL PAPER
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Received: June 2, 2010
Published online: September 15, 2010
Chem. Eur. J. 2010, 16, 12446 – 12453
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
12453