CH-Anion versus anion-π interactions in the crystal and in solution of pentafluorobenzyl phosphonium salts

Article abstract of DOI:10.1039/c0dt00766h

A series of phosphonium salts with pentafluorobenzyl substituents have been synthesized and were investigated in the crystal as well as in solution. The solid state structures of 1a, 1b and 2d reveal the presence of anion-π as well as CH-anion interactions. The two attractive, yet competitive forces seem to act in concert and a directing effect of the CH interaction on the relative position between anion and π-system is observed. The search for anion-π interactions in solution failed. Only CH-anion interactions proved to be important in solution.

Full text of DOI:10.1039/c0dt00766h

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
CH-Anion versus anion-p interactions in the crystal and in solution of
pentafluorobenzyl phosphonium salts†
Michael Mu¨ller,a Markus Albrecht,*a Johannes Sackmann,a Andreas Hoffmann,a Fiete Dierkes,a Arto
Valkonenb and Kari Rissanenb
Received 1st July 2010, Accepted 23rd September 2010
DOI: 10.1039/c0dt00766h
A series of phosphonium salts with pentafluorobenzyl substituents have been synthesized and were
investigated in the crystal as well as in solution. The solid state structures of 1a, 1b and 2d reveal the
presence of anion-p as well as CH-anion interactions. The two attractive, yet competitive forces seem to
act in concert and a directing effect of the CH interaction on the relative position between anion and
p-system is observed. The search for anion-p interactions in solution failed. Only CH-anion
interactions proved to be important in solution.
Introduction
Supramolecular Chemistry is commonly defined as the chemistry
beyond the molecule. It deals with intermolecular interactions of
molecules and with the self-assembly of molecular multicompo-
nent aggregates.1 Just recently anion-p interaction was recognized
as an important weak force being present in ionic systems with
electron deficient aromatics. However, the literature reveals a
rapidly growing interest in anion-p interactions within the last
20 years.2
Fig. 1 Different views of the crystal structure of pentafluorobenzyl
triphenyl phosphonium bromide showing anion-p interaction (h ). One
of the protons of the water is disordered and was removed for clarity
(green: F, blue: H, black: C, yellow: P, brown: Br, red: O).6
2
In the early 1990s, Schneider et al. described some experimental
evidence for anion-p interactions by observing a weak attraction
between a negatively charged part of the molecule and a polarized
p-system.3 This early study was followed by theoretical investiga-
interactions in solution, but they did not reveal if they are relevant
tions by Mascal, Alkorta and De`ya. They explained the attractive
for binding.7
nature of the interaction of the p-cloud of an electron-deficient
In this manuscript, systematic investigations on anion-p interac-
tions in the crystals of pentafluorobenzyl phosphonium salts with
varying anions are described which are accompanied by NMR
spectroscopic studies in solution.
arene with an anion.4
Subsequently several groups reported on anion-p interactions,
mainly in the crystalline state.5
In 2008 we started systematic studies on anion-p interactions
of ammonium and phosphonium salts, utilizing the pentaflu-
orophenyl unit as an appropriate electron deficient aromatic
moiety.6 Initial results showed the versatility of the binding
motifs between anions and electron-deficient aromatics which
might be controlled by strong directing effects like CH- and
NH-anion interactions between the anion and hydrogen atoms at
the cation. An already reported example for a pentafluorophenyl
phosphonium salt exhibiting an anion-p interaction in the solid
phase is shown in Fig. 1. The CHphenyl-anion interaction fixes the
Results and discussion
Based on the observation of the directing effects of substituents on
the position of halide anions in the crystals of pentafluorobenzyl
phosphonium and ammonium salts, phosphonium salts with
different anions (halides, hexafluorophosphate, tetrafluoroborate
or tetraphenylborate) were synthesized. The solid phase structures
were investigated to show the presence of anion-p as well as
CH-anion interactions. In addition, titration experiments were
performed with the phosphonium salts of “noncoordinating”
anions by adding n-tetrabutyl ammonium halides.
2
ion above the pentafluorophenyl unit in a h type binding motif.
The role of anion-p interactions in solution is still an open
question. Early studies gave indications for the presence of anion-p
Synthesis of phosphonium compounds
aInstitut fu¨r Organische Chemie, RWTH Aachen, Landoltweg 1, 52074,
Aachen, Germany. E-mail: markus.albrecht@oc.rwth-aachen.de; Fax: +49
241 809 2385; Tel: +49 241 809 4678
The preparations of the phosphonium salts started from the
corresponding phosphanes, which were reacted in a nucleophilic
substitution with pentafluorobenzyl halides (1a,b, 2a, 3a). The
phosphonium compounds with hexafluorophosphate, tetrafluo-
roborate or tetraphenylborate as anions 2b–2d and 3b–3d were
obtained by salt metathesis from saturated, aqueous solutions.
bDepartment of Chemistry, Nanoscience Center, University of Jyva¨skyla¨,
Survontie 9, 40014, Jyva¨skyla¨, Finland. E-mail: kari.t.rissanen@jyu.fi;
Fax: +358 14 260 2672; Tel: +358 50 562 3721
† CCDC reference numbers 795076–795078. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00766h
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 11329–11334 | 11329
©

View Article Online
All compounds were characterized by standard analytical
techniques. Crystals suitable for X-ray analysis were obtained for
representative derivatives.
A structure very similar to that of 1a is found for the
dimethylphenyl phosphonium iodide 1b. Here the solid phase
structure again reveals a h type binding motif for the iodide.
1
In contrast to 1a, structure 1b (Fig. 2b) shows no cocrystallisation
of water. The distances between the pentafluorophenyl group and
the anion are longer in 1b (two molecules in asymmetric unit,
Solid state studies
˚
˚
Weak interactions are dominant intermolecular forces in crystals.
They usually lead to well ordered arrays of molecules. In the
following not the overall packing of the crystals will be described,
but relevant anion-p and p–p interactions between neighbouring
species (especially anions and cations) will be the focus of
attention.
Cmeta ◊ ◊ ◊ I = 3.764(4) A, Cpara ◊ ◊ ◊ I = 4.044(5) A, Cortho ◊ ◊ ◊ I = 4.095(4)
˚
˚
˚
A and Cmeta ◊ ◊ ◊ I = 3.657(4) A, Cpara ◊ ◊ ◊ I = 3.675(5) A, Cortho ◊ ◊ ◊ I =
˚
4.322(4) A) due to the larger van der Waals radius of iodide
compared to bromide. The CH-anion interactions of the iodide
˚
1b (two molecules in asymmetric unit, CHmethyl ◊ ◊ ◊ I = 2.93(3) A
˚
˚
˚
and 3.10(3) A, CHphenyl ◊ ◊ ◊ I = 3.21(3) A and 3.28(4) A) are very
similar to those found in the bromide 1a.
Pentafluorobenzyl-dimethylphenyl phosphonium bromide and io-
The observation of very similar structures for 1a and 1b in the
solid state (despite the difference of cocrystallization of water in
the case of 1a) indicates that the cation-anion ensemble possessing
anion-p as well as CH-anion interactions is a discrete building
block in the crystal.
dide (1a,b). A part of the crystal structure of dimethylphenyl
1
2
phosphonium bromide 1a· H2O is shown in Fig. 2a. It reveals
an asymmetric anion-p interaction between bromide and the
1
pentafluorophenyl moiety which can be best described as “h ”
3
or maybe as “h ”. The closest anion-p contact is found between
In both structures 1a and 1b, the molecular packing reveals
face-to-face orientation of either two pentafluorophenyl or two
phenyl groups, respectively (e.g. Fig. 2c). The distances between the
centromers of the pentafluorophenyl groups (1a: c1-c2 = 3.829(7)
˚
bromide and the 3-position of the arene (Cmeta ◊ ◊ ◊ Br = 3.451(5) A,
˚
˚
Cpara ◊ ◊ ◊ Br = 3.696(5) A, Cortho ◊ ◊ ◊ Br = 3.895(5) A). Additionally the
anion forms CH-hydrogen bonds with the methyl (two molecules
˚
˚
˚
˚
in asymmetric unit, CHmethyl ◊ ◊ ◊ Br = 3.35(3) A and 2.93(3) A) and
A, 1b: c1-c2 = 3.611(6) A) are in both complexes a bit shorter than
the centromer distances in the electron-richer systems (1a: c3-c4 =
˚
phenyl group (CHphenyl ◊ ◊ ◊ Br = 2.92(3) A) and in every second case
with cocrystallized water (OH ◊ ◊ ◊ Br = 2.50(2) A). The different
˚
˚
˚
4.074(7) A, 1b: c3-c4 = 4.161(7) A).
types of CH-anion bonds determine the position of the bromide
on top of the pentafluorophenyl system and lead to the observed
asymmetric binding motif. The same structure controlling effect
was described before for the corresponding ammonium salt.6b The
cocrystallized water molecule forms a pair with another water
Pentafluorobenzyl triphenyl phosphonium tetraphenylborate 2d.
Crystals of the salt 2d were obtained from an aqueous solution of
2a by adding a saturated solution of sodium tetraphenylborate in
water. They formed within minutes. The analysis of 2d regarding
interactions between anion and cation is difficult due to the
geometric requirement of the anion. It reveals several edge-to-face
type orientations of the phenyl groups of the differently charged
ions. The observation of a phenylic hydrogen atom pointing
towards the center of the electron-deficient arene with a separation
˚
by OH ◊ ◊ ◊ O interaction (O ◊ ◊ ◊ O distance 2.929(9) A) leading
to disordered H-atom locations. One hydrogen of four of this
pair misses an H-bond acceptor, while another participates in an
OH ◊ ◊ ◊ O contact and the remaining two in OH ◊ ◊ ◊ Br contacts.6a
˚
of only 2.95(2) A is rather unexpected (Fig. 3b).
Fig. 3 X-ray structure of pentafluorobenzyl triphenyl phosphonium
tetraphenylborate 2d showing the anion cation pair (a) and CH-p
interactions (b) (green: F, blue: H, black: C, yellow: P, pink: B).
The earlier described crystal structure of 2a with the same
cation as in 2d but with bromide instead of tetraphenylborate
reveals anion-p interactions. The bromide is directed above two
1
2
1
Fig. 2 (a) Part of the crystal structure of 1a· H2O showing the h type
interaction between bromide and the pentafluorophenyl unit. One of the
disordered protons of the water is omitted for clarity. (b) Part of the crystal
structure of 1b. (c) Molecular packing in the structure of 1b showing the
face-to-face orientation of homologous arenes (green: F, blue: H, black:
C, yellow: P, brown: Br, magenta: I, red: O).
4
˚
carbon atoms of the pentafluorophenyl unit (C ◊ ◊ ◊ Br = 3.70 A,
4
˚
C ◊ ◊ ◊ Br = 3.71 A) by CH-anion bonding to phenylic hydrogen
2
3
6a
˚
˚
atoms (C H ◊ ◊ ◊ Br = 2.92 A, C H ◊ ◊ ◊ Br = 3.14 A).
11330 | Dalton Trans., 2010, 39, 11329–11334
This journal is The Royal Society of Chemistry 2010
©

View Article Online
A literature search on the corresponding non-fluorinated benzyl
triphenylphosphonium compounds does not reveal any anion-
p interactions.8 The results described herein show in addition
to many reports in the literature9 that anion-p interactions are
commonplace in solids containing electron deficient aromatics as
well as anions. The question remains whether anion-p interactions
are important in solution as well.
Scheme 2 Anion-exchange equilibrium.
Solution studies
As already mentioned in the introduction, some attempts were
made to investigate anion-p interactions in solution.7 Evidence
was collected, but the existence of this weak interaction could not
be finally proven. Strong solvation of the anions competes with
the anion-p interaction and thus might suppress it.
In the present study we performed NMR titration experiments
with the hexafluorophosphate 2b and tetrafluoroborate 2c salts
and with the analogues 3b and 3c with phenyl instead of
the electron deficient unit. n-Tetrabutyl ammonium halides (Cl,
Br, I) were successively added to the PF6 and BF4 salts and
differential binding constants were determined. Additionally, n-
butylammonium hexafluorophosphate and tetrafluoroborate were
added for comparison to exclude effects due to polarity changes
of the medium and to show that no significant binding occurs
between those “less-coordinating” anions and the cationsScheme
1.
Fig. 4 (a) Representational Job-Plot for the titration of 2b with n-Bu4NCl.
(b) Selected NMR spectra for the corresponding anion receptor system.
n-Bu4NCl (0.04 M solution) was successively added to a 0.01 M solution
of 2b. (c) Resulting 1H NMR shift during the titration of 2b with different
tetrabutyl ammonium salts.
Scheme 1 Preparation of pentafluorobenzyl phosphonium salts 1–3.
The corresponding tetraphenylborate 2d could not be used in
this study due to its low solubility in chloroform.
Scheme 2 summarizes the solution equilibria, assuming that
contact ion pairs are present but solvent separated ion pairs are
not. Shifting of proton NMR signals of the phosphonium cation
during the titration reveals that some interactions between the
cation and anion occur. The benzylic CH2 group proved to be an
appropriate NMR probe to follow this cation-anion interaction.
Initially Jobs method of continuous variation was used to show
a 1 : 1 stoichiometry in the interaction of anions with cations (Fig.
4a).10
tetrabutylammonium halide was added as a solution in CDCl3
(0.04 M). Titration curves (Fig. 4c) were obtained by following the
abovementioned benzylic NMR signal (Fig. 4b) and were analyzed
by standard methods of nonlinear regression.10 The determined
differential binding constants are summarized in Table 1.
Reference experiments with n-Bu4NPF6 and n-Bu4NBF4 (Fig.
4c) did not show any significant shifting of the resonance of the
benzylic protons, indicating no pronounced interaction of the
complex anions with the CH2 group.
Following this, NMR-titrations were performed in CDCl3 with
a concentration of 0.01 M of 2b,c or 3b,c, respectively. The
All binding constants for halide anions are found in the range
of 960 to 1610 M-1. There is no significant preference of the
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 11329–11334 | 11331
©

View Article Online
Table 1 Differential binding constants Ka [M-1] for the 1 : 1 complex of
actions like CH-anion binding, solvent effects or electrostatic
effects. While this interaction can be observed in many crystal
structures, it is highly difficult to find clear evidence for it in
solution.
phosphonium salts with various anions (Cl, Br and I added as tetrabutyl
1
ammonium salts). The binding constants were determined by H NMR
titration experiments in CDCl3. The proton signal of the benzylic group
was observed. Errors are estimated to be lower than 20%
Cl
Br
I
Experimental
2b
2c
3b
3c
1610
1390
1120
1200
1050
1120
1140
960
1020
1240
1150
1180
Commercially available reagents were used as received. The
solvents were used after distillation without any further pu-
rification. NMR spectra were taken on a Varian Mercury 300
NMR spectrometer (1H: 300 MHz, 19F: 282 MHz) in deuteric
chloroform. For mass spectrometric data, Finnigan SSQ 7000 and
Thermo Deca XP were used as EI (70 eV) or ESI. IR spectra were
obtained via a PerkinElmer FTIR spectrometer Spektrum 100.
The samples were measured in KBr at 4000–650 cm-1. CHN–O-
Rapid Vario EL from Heraeus was used for elemental analysis.
Melting points were measured on a Bu¨chi B540 and are not
corrected. Single crystal X-ray data of 1a, 1b and 2d were collected
at 123(2) K using a Bruker-Nonius KappaCCD diffractometer
with APEX-II detector and graphite monochromatized Mo-Ka
cations for a specific anion and no preference of the anion for
either fluorinated or non-fluorinated cations. In addition to the
1H NMR spectra, a series of 19F NMR spectra was collected. For
significant interactions of the anions with the p-system a shifting
of the fluoride signal should be expected. This was not observed.
These results indicate that the detected 1H NMR shifting upon
addition of halides to the tetrafluoroborate or hexafluorophos-
phate salts is not caused by anion-p interactions but rather by
CH-anion interactions of the highly acidic benzyl phosphonium
protons.
11
˚
(l = 0.71073 A) radiation. COLLECT software was used for
the data collection (q and w scans) and DENZO-SMN12 for
the processing. The structures were solved by direct methods
with SIR200413 and refined by full-matrix least-squares methods
with WinGX-software,14 which utilizes the SHELXL-97 module.15
Lorentzian polarization correction was applied on all data and
multi-scan absorption correction (SADABS16) for 1a and 1b. All
C–H hydrogen positions were calculated and refined as riding
atom model with 1.2 and 1.5 times the thermal parameter of the C
atoms, respectively. Disordered H-atoms of the water molecule in
1a were found from the electron density map and fixed (by DFIX)
Conclusion
In conclusion, it was possible to observe anion-p interactions
between pentafluorobenzylphosphonium salts and different an-
ions in the solid phase. Hereby, directing influences of CH-anion
interactions control the position of the anions above the electron-
deficient systems. Anion-cation interactions in pentafluoroben-
zyltriphenyl phosphonium tetraphenylborate 2d rely mainly on
interactions between the p-systems of the aromatic groups.
NMR titrations give no indication of anion-p interactions
in chloroform solutions of the investigated cations. Interactions
appear to occur mainly between the most acidic benzylic protons
and the anions. No significant differences could be detected for
the benzylic or pentafluorobenzylic derivatives, which could be
indicative for anion-p interactions.
Fig. 5 shows as a representative example a part of the crystal
structure of 1b depicting the anion-p interaction between iodide
and the pentafluorophenyl moiety as well as CH-anion binding
of the benzylic group with a second iodide. In solution the latter
interaction seems to be dominant while the anion-p interactions
are of minor importance or maybe not present at all.
˚
˚
to a distance of 0.84 A from the O atom and 1.4 A from each
other. Thermal parameters were set to 1.5 times that of the O
atom parameter.
Synthesis of compounds
Synthesis of pentafluorobenzyl-dimethylphenyl phosphonium bro-
mide 1a. Equimolar amounts of dimethylphenylphosphane (53
mg, 0.38 mmol) and pentafluorobenzyl bromide (100 mg,
0.38 mmol) were added to a round bottom flask and stirred for
24 h at room temperature. The resulting white block of solid was
crushed and dried under vacuum.
Yield: 110 mg colorless solid (M = 397.99 g mol-1, 0.28 mmol,
◦
1
72%). - M.p.: 194 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
7.92–7.79 (m, 3H, Haryl), 7.70–7.62 (dt, 3J = 8.5/3.2 Hz, 2H, Haryl),
4.21 (d, 2J = 15.8 Hz, 2H, Hbenz), 2.39 (d, 2J = 14.8 Hz, 6H, CH3).
-
19F NMR (CDCl3, 300 MHz): d (ppm) = -139.3 (m, 2F, Fmeta),
-154.7 (m, 1F, Fpara), -161.8 (m, 2F, Fortho). - MS (EI): m/z (%) =
318.3 (63 M–H+, C15H13F5P+). - IR (KBr): n/cm-1 = 3054 (w), 2949
(m), 2915 (w), 2882 (m), 2803 (w), 2210 (w), 2165 (w), 2084 (w),
2034 (w), 1991 (w), 1952 (w), 1658 (w), 1588 (w), 1507 (vs), 1440
(m), 1412 (m), 1368 (w), 1346 (w), 1308 (m), 1243 (w), 1183 (w),
1121 (s), 1055 (w), 1034 (w), 994 (vs), 964 (vs), 948 (vs), 906 (m),
888 (m), 841 (w), 784 (m), 742 (s), 715 (m), 686 (s).- C25H17BrF5N:
C 45.14, H 3.28, found: C 45.33, H 3.30.
Fig. 5 Part of the crystal structure of 1b showing the anion-p interaction
between the cation and the anion as well as the competing CH-anion
interaction of the benzylic unit.
Synthesis of pentafluorobenzyl iodide. To a solution of
pentafluorobenzyl bromide (2.5 g, 9.62 mmol) in 20 ml acetone
was added sodium iodide (2.88 g, 19.24 mmol). The suspension
The present study shows that weak anion-p interactions can
be easily overridden in solution by other non-covalent inter-
11332 | Dalton Trans., 2010, 39, 11329–11334
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
was stirred for 48 h at room temperature in the dark. Then 5 mL
water was added. The organic layer was dried over sodium sulfate
and the solvent was removed under reduced pressure.
873 (m), 823 (w), 790 (m), 751 (s), 718 (s), 688 (vs).- C25H22P: C
69.29, H 5.12, found: C 69.13, H 5.45.
Yield: 1.70 g brown solid (M = 307.91 g mol-1, 5.52 mmol, 57%).
- M.p.: 58 ◦C. - 1H NMR (CDCl3, 300 MHz): d (ppm) = 4.36 (t,
J (HF) = 1.5 Hz, 2H, Hbenz). - 19F NMR (CDCl3, 300 MHz): d
(ppm) = -142.25 (m, 2F, Fortho), -154.05 (m, 1F, Fpara), -161.4 (m,
2F, Fmeta). - MS (EI): m/z (%) = 307.9 (5 M+, C7H2F5I+), 181.0
Synthesis of the phosphonium hexafluorophosphates 2b, 3b,
tetrafluoroborates 2c, 3c and tetraphenylborates 2d, 3d. To sat-
urated solutions of the phosphonium bromides, solutions of am-
monium hexafluorophosphate, ammonium tetrafluoroborate or
sodium tetrafluoroborate were added dropwise until precipitation
stopped. The white solids were filtered off and dried under reduced
pressure.
(100, C7H2F5 ). - IR (KBr): n/cm-1 = 3043 (w), 2962 (w), 2655
+
(w), 2325 (w), 2087 (w), 1713 (w), 1656 (m), 1589 (w), 1569 (w),
1500 (vs), 1425 (m), 1389 (w), 1313 (w), 1286 (w), 1260 (w), 1159
(m), 1130 (m), 1116 (s), 1045 (w), 1021 (w), 963 (vs), 842 (w), 800
(w), 736 (w), 660 (w).- C7H2F5I: C 27.30, H 0.65, found: C 27.18,
H 0.70.
2b: Yield: 743 mg colorless solid (M = 588.33 g mol-1, 1.26 mmol,
◦
1
74%). - M.p.: 215 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
2
7.90–7.83 (m, 3H, Haryl), 7.74–7.59 (m, 12H, Haryl), 4.78 (d, J =
13.6 Hz, 2H, Hbenz). - 19F NMR (CDCl3, 300 MHz): d (ppm) =
2
2
Synthesis of pentafluorobenzyl-dimethylphenyl phosphonium io-
dide 1b. To a solution of dimethylphenyl phosphine (90 mg,
0.65 mmol) in 15 mL of toluene a solution of pentafluorobenzyl
iodide (200 mg, 0.65 mmol) in 5 mL of toluene was added dropwise.
The mixture was heated to 120 ◦C for 3 h. The solvent was removed
under reduced pressure and the light-yellow solid was dried.
Yield: 150 mg light yellow solid (M = 445.97 g mol-1, 0.24 mmol,
-72.91 (d, J = 756 Hz, 6F, PF6), -137.14 (d, J = 18.13 Hz,
2 2
2F, Fmeta), -150.18 (t, J = 21.151 Hz, F, Fpara), -159.52 (t, J =
18.130 Hz, 2F, Fortho). - MS (ESI): m/z (%) = 443.2 (100 M+,
C25H16P+). - IR (KBr): n/cm-1 = 2928 (w), 1660 (w), 1588 (w),
1507 (m), 1440 (m), 1403 (w), 1310 (w), 1195 (w), 1112 (m), 974
(s), 830 (vs), 749 (m), 724 (m), 686 (m).- C25H17F5PPF6: C 51.04,
H 2.91, found: C 50.95, H 2.82.
◦
1
52%). - M.p.: 254 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
3b: Yield: 685 mg colorless solid (M = 498.38 g mol-1, 1.36 mmol,
◦
2
1
7.85–7.63 (m, 5H, Haryl), 2.77 (d, J = 13.2 Hz, 2H, Hbenz), 1.75
69%). - M.p.: 234 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
7.83–7.76 (m, 3H, Haryl), 7.68–7.61 (m, 6H, Haryl), 7.55–7.47 (m,
6H, Haryl), 7.28–7.26 (m, 1H, Haryl), 7.16 (t, 3J = 7.8 Hz, 2H, Haryl),
6.91 (d, 3J = 7.8 Hz, 2H, Haryl), 4.58 (d, 2J = 13.8 Hz, 2H, Hbenz). -
19F NMR (CDCl3, 300 MHz): d (ppm) = -72.61 (d, 2J = 759 Hz,
6F, PF6). - MS (EI): m/z (%) = 353.17 (14 M+, C22H22P). - IR
(KBr): n/cm-1 = 3066 (w), 1590 (w), 1489 (w), 1440 (m), 1413 (w),
1337 (w), 1238 (w), 1191 (w), 1164 (w), 1143 (w), 1113 (m), 1069
(w), 1033 (w), 998 (w), 925 (w), 876 (w), 824 (vs), 785, (m), 747 (m),
720 (m), 700 (m), 686 (s).- C25H22PPF6: C 60.25, H 4.45, found: C
60.15, H 4.41.
(d, J = 13.2 Hz, 6H, CH3). - 19F NMR (CDCl3, 300 MHz): d
2
(ppm) = -137.2 (m, 2F, Fmeta), -150.0 (m, 1F, Fpara), -158.8 (m,
2F, Fortho). - MS (EI): m/z (%%) = 318.2 (3 M–H+, C15H13F5P+). -
IR (KBr): n/cm-1 = 3058 (w), 2952 (m), 2883 (m), 2801 (w), 2257
(w), 2084 (w), 1902 (w), 1658 (w), 1588 (w), 1508 (vs), 1440 (m),
1409 (m), 1346 (w), 1309 (m), 1244 (w), 1182 (w), 1121 (s), 1034
(w), 994 (vs), 964 (vs), 946 (s), 886 (m), 837 (w), 784 (w), 742 (s),
715 (m), 685 (s).- C25H17BrF5P: C 40.38, H 2.94, found: C 40.39,
H 3.00.
Synthesis of pentafluorobenzyl 2a and benzyl triphenylphospho-
nium bromide 3a. Equimolar amounts of triphenyl phosphane
and pentafluorobenzyl bromide were dissolved in toluene. The
mixture was heated to 120 ◦C for 3h. Then the precipitate was
filtered off and dried in vacuum.
2c: Yield: 608 mg colorless solid (M = 530.17 g mol-1, 1.15 mmol,
◦
1
61%). - M.p.: 198 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
2
7.88–7.83 (m, 3H, Haryl), 7.72–7.65 (m, 12H, Haryl), 4.95 (d, J =
13.8 Hz, 2H, Hbenz). - 19F NMR (CDCl3, 300 MHz): d (ppm) =
2
-136.80 (m, 2F, Fmeta), -150.50 (m, 1F, Fpara), -152.23 (m, J =
2a: Yield: 0.9 g colorless solid (M = 522.02 g mol-1, 1.70 mmol,
12.1 Hz, 4F, BF4), -159.66 (m, 2F, Fortho). - MS (ESI): m/z (%) =
443.25 (100 M+, C25H16F5P+). - IR (KBr): n/cm-1 = 3642 (w), 3556
(w), 3070 (w), 2975 (w), 2909 (w), 2079 (w), 1987 (w), 1937 (w),
1656 (w), 1619 (w), 1587 (w), 1506 (s), 1439 (m), 1403 (m), 1371
(w), 1322 (w), 1286 (w), 1248 (w), 1194 (w), 1111 (s), 1054 (vs), 980
(vs), 968 (vs), 850 (m), 754 (s), 726 (s), 691 (s).- C25H17F5PBF4: C
55.63, H 3.31, found: C 55.42, H 3.36.
◦
1
45%). - M.p.: 244 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
7.99–7.95 (m, 3H, Haryl), 7.84–7.76 (m, 12H, Haryl), 5.30 (d,2J =
14.1 Hz, 2H, Hbenz). - 19F NMR (CDCl3, 300 MHz): d (ppm) =
-137.9 (m, 2F, Fortho), -152.3 (m, 1F, Fpara), -161.4 (m, 2F, Fmeta). -
MS (EI): m/z (%) = 442.3 (80, C25H16F5P+). - IR (KBr): n/cm-1
=
3061 (m), 3009 (w), 2952 (w), 2849 (w), 2764 (w), 2212 (w), 2108
(w), 2006 (w), 1813 (w), 1656 (w), 1586 (w), 1520 (m), 1503 (s),
1435 (m), 1392 (w), 1309 (w), 1251 (w), 1191 (w), 1160 (w), 1110
(s), 1033 (w), 973 (vs), 865 (w), 838 (w), 753 (s), 725 (s), 686 (s).-
C25H17BrF5P: C 57.38, H 3.26, found: C 58.11, H 3.59.
3c: Yield: 853 mg colorless solid (M = 440.22 g mol-1, 1.94 mmol,
◦
1
85%). - M.p.: 215 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
3
7.88 (t, J = 8.3, 3H, Haryl), 7.68–7.50 (m, 12H, Haryl), 7.25–7.20
(m, 1H, Haryl), 7.14 (t, 3J = 7.9 Hz, 2H, Haryl), 6.93 (d, 3J =
3a: Yield: 953 mg colorless solid (M = 434.33 g mol-1, 2.19 mmol,
7.9 Hz, 2H, Haryl), 4.77 (d, J = 14.3 Hz, 2H, Hbenz). - 19F NMR
2
◦
1
95%). - M.p.: 241 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
(CDCl3, 300 MHz): d (ppm) = -151.99 (d, 2J = 12.1 Hz, 4F, BF4).
- MS (ESI): m/z (%) = 353.84 (14 M+, C25H22P+). - IR (KBr):
n/cm-1 = 3068 (w), 3030 (w), 2973 (w), 2931 (w), 2219 (w), 2084
(w), 1982 (w), 1740 (m), 1587 (w), 1487 (w), 1455 (w), 1438 (s),
1418 (w), 1367 (w), 1286 (w), 1230 (w), 1216 (w), 1193 (w), 1166
(w), 1110 (s), 1058 (vs), 925 (w), 857 (m), 821 (w), 788 (m), 749 (s),
719 (s), 688 (vs).- C25H22PBF4: C 68.21, H 5.04, found: C 67.89,
H 4.68.
7.81–7.71 (m, 9H, Haryl), 7.67–7.61 (m, 6H, Haryl), 7.25–7.19 (m,
2
1H. Haryl), 7.16–7.08 (m, 4H, Haryl) 5.42 (d, J = 13.7 Hz, 2H,
Hbenz). - MS (ESI): m/z (%) = 353.17 (100 M+, C25H22P+). - IR
(KBr): n/cm-1 = 3662 (w), 3374 (w), 3051 (w), 2984 (w), 2853 (m),
2774 (w), 2260 (w), 2103 (w), 1986 (w), 1907 (w), 1602 (w), 1585
(w), 1484 (m), 1455 (w), 1435 (s), 1333 (w), 1316 (w), 1250 (w),
1187 (w), 1162 (m), 1109 (s), 1072 (m), 1030 (w), 994 (m), 921 (w),
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 11329–11334 | 11333
©

View Article Online
2d: Yield: 120 mg colorless solid (M = 762.59 g mol-1, 0.16 mmol,
Acknowledgements
◦
1
60%). - M.p.: 183 C. - H NMR (CDCl3, 300 MHz): d (ppm) =
7.74–7.69 (m, 3H, Haryl), 7.52–7.43 (m, 6H, Haryl, cation), 7.30–7.23
(m, 6H, Haryl), 7.06–6.97 (m, 4H, Haryl), 6.83–6.73 (m, 16H, Haryl),
3.32 (d, 2J = 13.1 Hz, 2H, Hbenz). - 19F NMR (CDCl3, 300 MHz): d
(ppm) = -135.88 (m, 2F, Fmeta), -150.38 (m, 2F, Fpara), -159.52 (m,
2F, Fortho). - MS (ESI): m/z (%) = 443.1 (100 M+, C25H16F5P). - IR
(KBr): n/cm-1 = 3620 (w), 3371 (w), 3201 (w), 3053 (w), 2932 (w),
2869 (w), 2784 (w), 2210 (w), 2095 (w), 1994 (w), 1940 (w), 1828
(w), 1656 (w), 1583 (w), 1505 (vs), 1437 (s), 1314 (w), 1262 (w),
1197 (w), 1110 (s), 1032 (w), 976 (vs), 847 (m), 751 (s), 725 (vs), 690
(vs)- C25H17F5PBC24H20: C 77.17, H 4.89, found: C 77.05, H 4.76.
3d: Yield: 90 mg colorless solid (M = 672.64 g mol-1, 0.13 mmol,
45%). - M.p.: 231.2 ◦C. - 1H NMR (DMSO, 300 MHz): d (ppm) =
7.94–7.86 (m, 3H, Haryl), 7.78–7.61 (m, 12H, Haryl), 7.32–7.12 (m,
12H, Haryl), 7.00–6.88 (m, 10H, Haryl), 6.82–6.74 (m, 3H, Haryl),
5.13 (d, 2J = 15.9 Hz, 2H, Hbenz). - MS (ESI): m/z (%) = 353.2 (100
M+, C25H22P+). - IR (KBr): n/cm-1 = 3053 (m), 3001 (w), 2941 (w),
2899 (w), 2165 (w), 1949 (w), 1582 (m), 1480 (m), 1437 (m), 1401
(w), 1339 (w), 1269 (w) 1184 (w), 1146 (w), 1111 (m), 1068 (w),
1031 (m), 997 (w), 922 (w), 849 (m), 833 (m), 786 (m), 732 (s), 704
(vs).- C25H22PBC24H20: C 87.49, H 6.29, found: C 87.07, H 6.27.
This work was supported by the Fonds der Chemischen Industrie
(MA) and The Academy of Finland (KR, prof. no. 212588 and
218325).
Notes and References
1 (a) J.-M. Lehn, Supramolecular Chemistry – Concepts and Perspectives,
VCH: Weinheim, 1995; (b) J. Steed, J. L. Atwood, Supramolecular
Chemistry, John Wiley: New York, 2009.
2 P. de Hoog, P. Gamez, H. Mutikainen, U. Turpeinen and J. Reedijk,
Angew. Chem., 2004, 116, 5939, (Angew. Chem., Int. Ed., 2004, 43,
5815).
3 (a) H.-J. Schneider, F. Werner and T. Blatter, J. Phys. Org. Chem., 1993,
6, 590; (b) for some earlier studies in the gas phase see: K. Hiraoka, S.
Mizuse and S. Yamabe, J. Phys. Chem., 1987, 91, 5294.
4 (a) I. Alkorta, I. Rozas and J. Elguero, J. Am. Chem. Soc., 2002, 124,
8593; (b) M. Mascal, A. Armstrong and M. D. Bartberger, J. Am. Chem.
Soc., 2002, 124, 6274; (c) A. Frontera, F. Saczewski, M. Gdaniec, E.
Dziemidowicz-Borys, A. Kurland, P. M. Deya, D. Quinonero and C.
Garau, Chem.–Eur. J., 2005, 11, 6560; (d) C. Garau, D. Quinonero,
A. Frontera, P. Ballester, A. Costa and P. M. Deya, J. Phys. Chem. A,
2005, 109, 9341; (e) D. Quinonero, C. Garau, A. Frontera, P. Ballester,
A. Costa and P. M. Deya, Chem. Phys. Lett., 2002, 359, 486; (f) C.
Garau, A. Frontera, D. Quinonero, P. Ballester, A. Costa and P. M.
Deya, J. Phys. Chem. A, 2004, 108, 9423; (g) C. Garau, A. Frontera, P.
Ballester, D. Quinonera, A. Costa and P. M. Deya, Eur. J. Org. Chem.,
2005, 179.
5 (a) A. Bianchi, K. Bowman-James and E. Garcia-Espana, Supramolec-
ular Chemistry of Anions, Wiley-VCH: New York, 1997; (b) B. L.
Schottel, H. T. Chifotides and K. R. Dunbar, Chem. Soc. Rev., 2008,
37, 68; (c) B. P. Hay and V. S. Bryantsev, Chem. Commun., 2008, 2417.
6 (a) M. Albrecht, C. Wessel, M. de Groot, K. Rissanen and A. Lu¨chow,
J. Am. Chem. Soc., 2008, 130, 4600; (b) M. Albrecht, M. Mu¨ller, O.
Mergel, A. Valkonen and K. Rissanen, Chem.–Eur. J., 2010, 16, 5062.
7 For example: (a) H. Maeda, A. Osuka and H. Furuta, J. Inclusion
Phenom. Macrocyclic Chem., 2004, 49, 33; (b) H. Maeda and H. Furuta,
J. Porphyrins Phthalocyanines, 2004, 8, 67; (c) Y. S. Rosokha, S. V.
Lindeman, S. V. Rosokha and J. K. Kochi, Angew. Chem., 2004, 116,
4750, (Angew. Chem., Int. Ed., 2004, 43, 4650); (d) O. B. Berryman,
F. Hof, M. J. Hynes and D. W. Johnson, Chem. Commun., 2006, 506;
(e) M. Staffilani, K. S. B. Hancock, J. W. Steed, K. T. Holman, J. L.
Atwood, R. K. Juneja and R. S. Burkhalter, J. Am. Chem. Soc., 1997,
119, 6324; (f) R. M. Fairchild and K. T. Holman, J. Am. Chem. Soc.,
2005, 127, 16364.
X-ray structural analysis
Crystaldata
1a: Colorless rods from MeOH, (C15H13F5P)2Br2·H2O, F.W. =
816.28, crystal size 0.17 ¥ 0.07 ¥ 0.06 mm, triclinic, space group
¯
˚
P1(no. 2), a = 11.8147(4), b = 12.0612(3), ◦c = 14.5634(5) A, a =
3
˚
94.048(2), b = 110.887(2), g = 118.155(2) , V = 1636.05(9) A ,
Z = 2, Dc = 1.657 Mg m-3, m = 2.656 mm-1, F(000) = 812, 19069
collected reflections (qmax = 25.00◦) of which 5722 independent
[Rint = 0.0611], Tmax = 0.8569, Tmin = 0.6609, full-matrix least-
squares on F2 with 8 restraints and 415 parameters, GOF = 1.062,
R1 = 0.0481 [I > 2s(I)], wR2 (all data) = 0.0947, largest peak/hole =
-
-3
˚
0.509/-0.383 e A .
8 (a) A. C. Skapski and F. A. Stephens, J. Cryst. Mol. Struct., 1974, 4,
77; (b) S. J. Archer, T. A. Modro and L. R. Nassimbeni, Phosphorus
Sulfur Relat. Elem., 1981, 11, 101; (c) M. N. Ponnuswamy and E. W.
Czerwinski, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1986,
42, 1019.
9 Structural Database analysis: D. Quinonero, C. Garau, C. Rotger, A.
Frontera, P. Ballester, A. Costa and P. M. Deya`, Angew. Chem., 2002,
114, 3539, (Angew. Chem., Int. Ed., 2002, 41, 3389).
10 (a) K. A. Connors, Bindung Constants: The measurement of Molecular
Complex Stability, Wiley, New York, 1987; (b) C. S. Wilcox, in Frontiers
in Supramolecular Chemistry and Photochemistry (ed.: H.-J. Schneider
and H. Du¨rr), Wiley-VCH, Weinheim, 1991, p. 123.
11 COLLECT, Bruker AXS, Inc., Madison, Wisconsin, USA, 2008.
12 Z. Otwinowski, W. Minor, in Methods in Enzymology 1997, 276,
Macromolecular Crystallography, Part A, 307–326.
13 M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G. L. Cascarano,
L. De Caro, C. Giacovazzo, G. Polidori and R. Spagna, J. Appl.
Crystallogr., 2005, 38, 381–388.
14 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
15 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112–122.
1b: Colorless plates from CH3CN, (C15H13F5P)I, F.W. = 446.12,
crystal size 0.20 ¥ 0.18 ¥ 0.05 mm, monoclinic, space group P21/c
˚
(no. 14), ◦a = 12.6682(3), b = 18.0617(4), c = 14.3740(3) A, b =
3
-3
˚
90.972(2) , V = 3288.43(13) A , Z = 8 (Z¢ = 2), Dc = 1.802 Mg m ,
m = 2.087 mm-1, F(000) = 1728, 41227 collected reflections (qmax
=
25.02◦) of which 5799 independent [Rint = 0.0653], Tmax = 0.9028,
Tmin = 0.6803, full-matrix least-squares on F2 with 0 restraints and
397 parameters, GOF = 1.094, R1 = 0.0343 [I > 2s(I)], wR2 (all
-
-3
˚
data) = 0.0670, largest peak/hole = 0.480/-0.461 e A .
2d: Colourless blocks from MeOH–EtOH, (C25H17F5P)-
(C24H20B), F.W. = 762.57, crystal size 0.25 ¥ 0.25 ¥ 0.14 mm,
monoclinic, space group C2/c (no. 15), a ◦= 32.7210(7), b =
3
˚
˚
14.0835(3), c = 17.1709(3) A, b = 102.5470(10) , V = 7723.8(3) A ,
Z = 8, Dc = 1.312 Mg m-3, m = 0.131 mm-1, F(000) = 3168, 13235
collected reflections (qmax = 25.00◦) of which 6792 independent
[Rint = 0.0435], full-matrix least-squares on F2 with 0 restraints
and 505 parameters, GOF = 1.031, R1 = 0.0511 [I > 2s(I)], wR2
16 G. M. Sheldrick, SADABS, University of Go¨ttingen, Germany,
1996.
-
-3
˚
(all data) = 0.1110, largest peak/hole = 0.443/-0.434 e A .
11334 | Dalton Trans., 2010, 39, 11329–11334
This journal is
The Royal Society of Chemistry 2010
©