A study of C-F···M+ interaction: Alkali metal complexes of the fluorine-containing cage compound

Article abstract of DOI:10.1021/jo0016778

The C-F···M⁺ interaction was investigated by employing a cage compound 1 that has four fluorobenzene units. The NMR (¹H, ¹³C, and ¹⁹F) spectra and X-ray crystallographic analyses of 1 and its metal complexes showed clear evidence of the interaction. Short C-F···M⁺ distances (CF···K⁺, 2.755 and 2.727 A; C-F···Cs⁺ 2.944 and 2.954 A) were observed in the crystalline state of K⁺ ? 1 and Cs⁺ ? 1. Furthermore, the C-F bond lengths were elongated by the interaction with the metal cations. By calculating Brown's bond valence, it is shown that the contribution of the C-F unit to cation binding is comparable or greater than the ether oxygen in the crystalline state. Representative spectroscopic changes implying the C-F···M⁺ interaction were observed in the NMR (¹H, ¹³C, and ¹⁹F) spectra. In particular, ¹³³Cs-¹⁹F spin coupling (J = 54.9 Hz) was observed in the Cs⁺ complex.

Full text of DOI:10.1021/jo0016778

2778
J . Org. Chem. 2001, 66, 2778-2783
A Stu d y of C-F ···M+ In ter a ction : Alk a li Meta l Com p lexes of th e
F lu or in e-Con ta in in g Ca ge Com p ou n d
Hiroyuki Takemura,*,† Noriyoshi Kon,‡ Masayuki Kotoku,‡ Sachiko Nakashima,‡
Kazuhiro Otsuka,‡ Mikio Yasutake,§ Teruo Shinmyozu,§ and Takahiko Inazu‡
Department of Chemistry, Faculty of Science, Kyushu University, Ropponmatsu 4-2-1, Chuo-ku,
Fukuoka 810-8560, J apan, Department of Chemistry, Faculty of Science, Kyushu University,
Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, J apan, and Institute for Fundamental Research of
Organic Chemistry, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, J apan
takemura@rc.kyushu-u.ac.jp
Received November 29, 2000
The C-F‚‚‚M+ interaction was investigated by employing a cage compound 1 that has four
fluorobenzene units. The NMR (1H, 13C, and 19F) spectra and X-ray crystallographic analyses of 1
and its metal complexes showed clear evidence of the interaction. Short C-F‚‚‚M+ distances (C-
F‚‚‚K+, 2.755 and 2.727 Å; C-F‚‚‚Cs+, 2.944 and 2.954 Å) were observed in the crystalline state of
K+ ⊂ 1 and Cs+ ⊂ 1. Furthermore, the C-F bond lengths were elongated by the interaction with
the metal cations. By calculating Brown’s bond valence, it is shown that the contribution of the
C-F unit to cation binding is comparable or greater than the ether oxygen in the crystalline state.
Representative spectroscopic changes implying the C-F‚‚‚M+ interaction were observed in the NMR
(1H, 13C, and 19F) spectra. In particular, 133Cs-19F spin coupling (J ) 54.9 Hz) was observed in the
Cs+ complex.
In tr od u ction
On the basis of recent research, it has become apparent
that the fluorine atom covalently bonded to a carbon atom
acts as a donor unit to cations (Figure 1).1 In previous
papers, we revealed that the C-F unit binds alkali metal
cations, NH4+, and Ag+ by employing the hexafluoro cage
compound 4 (Figure 2).2 We showed the first example of
a host-guest complex system in which metal cations are
captured only by the C-F unit. As shown in the series
of fluorinated macrocyclic compounds, preorganization of
the C-F unit for cations is the most important factor for
capturing spherical metal cations.2b Characteristic NMR
spectroscopic changes (1H, 13C, and 19F) were observed
as a result of the C-F‚‚‚M+ interaction. We also con-
firmed that the C-F bond lengths of the complexes (K+
F igu r e 1. Schematic illustration of the C-F‚‚‚M+ interaction.
into the cavity. Therefore, by the replacement of four
pyridine rings with a fluorobenzene unit, we can expect
to observe the C-F‚‚‚M+ interaction by this new host
molecule. Furthermore, different from compound 4, we
can simultaneously compare the contribution of the
binding power of C-F‚‚‚M+, -O‚‚‚M+, and dN‚‚‚M+. In
this paper, estimation of the C-F‚‚‚M+ interaction is
described by measurement of the stability constants, the
1H, 13C, and 19F NMR spectral features, and X-ray
crystallographic analyses of M+ ⊂ 1.
+
and NH4 ⊂ 4) were longer than that of the metal-free 4
in the crystalline structures.
Resu lts a n d Discu ssion
On the other hand, we reported the cation and anion
inclusion ability of the cage compound 3, which consists
of four pyridine rings and two ethyleneoxa units.3 This
compound has a strong cation affinity because it has eight
nitrogen atoms and two oxygen atoms as donors in its
cavity, and thus, a total of 20 electrons are converged
Coor d in a tion Str u ctu r es of K+ ⊂ 1 a n d Cs+ ⊂ 1.
The cage compounds described in this paper were syn-
thesized by the one-step coupling procedure previously
described (Figure 2).4 Compound 1 was obtained as a
potassium complex, K+ ⊂ 1, while the fluorine-free
compound 2 was obtained as the metal-free form. Since
basic molecular skeletons of both compounds are re-
garded as the same, it is obvious that the C-F unit has
a donor ability to metal cations. Here, we have to
remember that Plenio et al. reported a very similar
compound that consists of two diethyleneoxa units and
four fluorobenzene units. They reported very short C-F‚
‚‚Cs+ distances in the cesium complex and concluded that
* To whom correspondence should be addressed. Tel: +81-92-726-
4755. Fax: +81-92-726-4755.
† Kyushu University, Ropponmatsu.
‡ Kyushu University, Hakozaki.
§ Institute for Fundamental Research of Organic Chemistry.
(1) Plenio, H. Chem. Rev. 1997, 97, 3363-3384 and references
therein.
(2) (a) Takemura, H.; Kon, N.; Yasutake, M.; Kariyazono, H.;
Shinmyozu, T.; Inazu, T. Angew. Chem. 1999, 111, 1012-1014; Angew.
Chem., Int. Ed. Engl. 1999, 38, 959-961. (b) Takemura, H.; Kariya-
zono, H.; Yasutake, M.; Kon, N.; Tani, K.; Sako, K.; Shinmyozu, T.;
Inazu, T. Eur. J . Org. Chem. 2000, 141-148. (c) Takemura, H.; Kon,
N.; Yasutake, M.; Nakashima, S.; Shinmyozu, T.; Inazu, T. Chem. Eur.
J . 2000, 6, 2334-2337.
(4) (a) Kon, N.; Takemura, H.; Otsuka, K.; Tanoue, K.; Nakashima,
S.; Yasutake, M.; Tani, K.; Kimoto, J .; Shinmyozu, T.; Inazu, T. J . Org.
Chem. 2000, 65, 3708-3715. (b) Takemura, H.; Inazu, T. J . Synth.
Org. Chem. J pn. 1998, 56, 604-614. (c) Takemura, H.; Shinmyozu,
T.; Inazu, T. Coord. Chem. Rev. 1996, 156, 183-200.
(3) Takemura, H.; Otsuka, K.; Kon, N.; Yasutake, M.; Shinmyozu,
T.; Inazu, T. Tetrahedron Lett. 1999, 40, 5561-5564.
10.1021/jo0016778 CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/17/2001

Study of C-F···M+ Interaction
J . Org. Chem., Vol. 66, No. 8, 2001 2779
F igu r e 2. Structures of the tetrafluoro cage compound 1 and its derivatives.
F igu r e 3. X-ray crystallographic structure of 1 (H atoms are
omitted for clarity). Bond lengths (Å): C1-F1, 1.358(2); C12-
F2, 1.355(2); C18-F3, 1.355(2); C24-F4, 1.356(2).
F igu r e 4. X-ray crystallographic structure of K+ ⊂ 1 (H atoms
are omitted for clarity).
contribution of the C-F unit to stabilization of the cation
is superior to the ether oxygen in their complex.5
In this research, we chose alkali metal cations in order
to investigate the C-F‚‚‚M+ interaction. This is because
the cations have a wide range of ionic radii, and the effect
of the d electrons can be ignored when C-F units interact
with them. Therefore, these are suitable metal cations
for estimating the C-F‚‚‚M+ interaction on the basis of
charge and ionic radii.
X-ray crystallographic analysis plays an important role
in proving the interaction between C-F and cations.
Figures 3-5 show the structures of the metal-free 1, K+
⊂ 1, and Cs+ ⊂ 1, respectively. In the metal-free 1, two
oxygen atoms are directed outward from the molecular
cavity, while the lone pairs of the oxygen in K+ ⊂ 1 and
Cs+ ⊂ 1 are directed to the metal cation center: struc-
tural changes occur so as to stabilize the cation-inclusion
form.
Here, three requirements are desired as proof of the
C-F‚‚‚M+ interaction: (1) the C-F bond length becomes
longer by the interaction, (2) a short C-F‚‚‚M+ distance
is observed, and the third requirement is described below.
F igu r e 5. X-ray crystallographic structure of Cs+ ⊂ 1 (H
atoms are omitted for clarity).
The average C-F bond lengths of metal-free 1 is 1.356
Å, while those of the K+ ⊂ 1 and Cs+ ⊂ 1 are 1.382 and
1.369 Å, respectively (Tables 1 and 2). Obviously, the
(5) Plenio, H.; Diodone, R.; Badura, D. Angew. Chem. 1997, 109,
130-132; Angew. Chem., Int. Ed. Engl. 1997, 36, 156-158.

2780 J . Org. Chem., Vol. 66, No. 8, 2001
Takemura et al.
) 0.395 (V ) 1.41) were obtained.10 In the case of Cs+
Ta ble 1. Rep r esen ta tive Bon d Len gth s, In ter a tom ic
⊂
Dista n ces, a n d Bon d An gles of K+ ⊂ 1
1, the sum of s values becomes considerably greater than
1.00. This is because the cavity size of 1 is not so variable
while cesium has a large ionic radius. Because the s value
is a function of r (ligand-cation distances), the s becomes
large when the relative distances between Cs+ and F, N,
and O are short. However, this deviation does not affect
the estimation of the bonding contribution of each ligand
to Cs+. On the basis of these values, it is concluded that
C-F‚‚‚M+ bonding is dominant (s ) 0.155 per one C-F‚
‚‚K+, 0.0890 per one O‚‚‚K+, and 0.0530 per one N‚‚‚K+)
in K+ ⊂ 1, and in the case of Cs+ ⊂ 1, contribution of
C-F‚‚‚Cs+ and O‚‚‚Cs+ is comparable (s ) 0.172 per one
C-F‚‚‚Cs +, 0.165 per one O‚‚‚Cs +, and 0.0988 per one
N‚‚‚Cs +).
interatomic
bond lengths (Å)
distances (Å)
bond angles (deg)
C1-F1 1.380(5) F1 ‚‚‚ K1 2.755(3) C1-F1 ‚‚‚ K1 108.8(2)
C7-F2 1.383(6) F2 ‚‚‚ K1 2.727(3) C7-F2 ‚‚‚ K1 107.4(2)
O1 ‚‚‚ K1 3.034(5) O1-K1 ‚‚‚ O2 180.0
O2 ‚‚‚ K1 3.081(4) F1-K1 ‚‚‚ F1* 134.8(1)
N1 ‚‚‚ K1 3.310(4) F2-K1 ‚‚‚ F2* 136.5(1)
N2 ‚‚‚ K1 3.370 (4)
Ta ble 2. Rep r esen ta tive Bon d Len gth s, In ter a tom ic
Dista n ces, a n d Bon d An gles of Cs+ ⊂ 1
interatomic
bond lengths (Å)
C6-F1
distances (Å)
bond angles (deg)
101.5(1)
1.369(3) F1 ‚‚‚ Cs1 2.944(2) C6-F1 ‚‚‚ Cs1
C14-F2 1.368(3) F2 ‚‚‚ Cs1 2.954(2) C14-F2 ‚‚‚ Cs1 101.8(1)
O1 ‚‚‚ Cs1 3.094(2) O1-Cs1 ‚‚‚ O2 180.0
O2 ‚‚‚ Cs1 3.075(2) F1-Cs1 ‚‚‚ F1* 132.12(6)
N1 ‚‚‚ Cs1 3.365(2) F2-Cs1 ‚‚‚ F2* 133.29(6)
N2 ‚‚‚ Cs1 3.344(2)
A dominant factor in the C-F‚‚‚M+ interaction can be
considered as a cation-dipole interaction rather than a
coordination bond. The dative bond of the F atom to
cation is considered to be smaller than that of the oxygen
or nitrogen atom because the ionization potential of the
F atom is larger than that of the O or N atom. The cation-
dipole interaction between fluorobenzene and M+ is
larger than that of the ether oxygen or amine nitrogen.
Because each donor unit of the compound 1 is regarded
as fluorobenzene, diethyl ether, and triethylamine, re-
spectively, this is recognized by the comparison of the
dipole moment, i.e., fluorobenzene, 1.61; diethyl ether,
1.15; and triethylamine, 0.77.11 The cation-dipole inter-
action is dominant especially in the binding of alkali
metal cations because they do not have d orbitals
available for the dative bond like transition metals.
The interaction is roughly estimated by a simple
equation as follows
C-F bonds are elongated by the interaction. The changes
of the lengths are small, but these are not caused by
experimental errors or by libration of thermal ellipsoids.
That was observed in every case of our complexes, i.e.,
+
NH4 ⊂ 4, K+ ⊂ 4,2 and other examples (Tl+ ⊂ 4 and La3+
⊂ 1) which were recently observed. The K+‚‚‚F distances
are 2.755 and 2.727 Å, which are the shortest next to
that of K+ ⊂ 4 (2.563 Å).1,2a On the other hand, the K+‚
‚‚O distances are 3.034 and 3.081 Å. Considering that
the K+‚‚‚O distances in K+ ⊂ 18-crown-6 are 2.77-2.83
Å,6 bonding of the oxygen to the cation center is weak in
K+ ⊂ 1. The K+‚‚‚N distances are also long (3.310 and
3.370 Å), and the contribution can also be regarded as
very small. Considering that the sum of the van der
Waals radii of the oxygen and nitrogen atoms and ionic
radius of K+ are 2.85 and 2.88 Å, respectively, the
interactions of K+‚‚‚O and K+‚‚‚N are weak in this case.
E ) -Qµ cos θ/4πꢀr2
where µ ) dipole moment, θ ) C-F‚‚‚M+ (O‚‚‚M+) angle,
ꢀ ) permittivity, and r ) interatomic distance. If we put
the data of X-ray analysis of Cs+ ⊂ 1 into the equation,
each stabilization energy E (sum of four C-F‚‚‚Cs+ and
two O‚‚‚Cs+) was obtained as follows. E(C-F‚‚‚Cs+) ) 1.9
kcal mol-1 and E(O‚‚‚Cs+) ) 3.1 kcal mol-1 in fluoroben-
zene, respectively. The sum of the stabilization energy
is 5.0 kcal mol-1, which is almost equal to the free energy,
∆G ) 3.7-4.3 kcal mol-1, estimated by the binding
constants Ks described below. Although the cation-dipole
interaction strongly depends on the angle, the C-F‚‚‚M+
interaction operates in enough strength even if the angles
are around 100° (Table 2).
In the case of Cs+ ⊂ 1, the interatomic distances Cs+‚
‚‚F ) 2.944 and 2.954 Å are the shortest next to the
example of Plenio et al. (2.843 and 3.047 Å).5 The Cs+‚‚
‚O distances of Cs+ ⊂ 1 are 3.094 and 3.075 Å, which are
longer than the Cs+‚‚‚F distances but shorter than that
of the Cs+ ⊂ 18-crown-6 complex (3.15 Å in average).7
The Cs+‚‚‚N distances are long (3.365 and 3.344 Å), and
thus, bonds between the N atoms and Cs+ can be
considered as weak. We have already shown that the
bridgehead nitrogen atoms are not a concern in the
binding of the metal cations in the case of analogues of
cage compound 1.2
The contribution of each ligand to cation bonding can
be estimated using Brown’s bond-valence calculation.8
Two research groups employed this method in order to
evaluate the C-F‚‚‚M+ bonding.5,9 Bond valences, s, of
K+ ⊂ 1 and Cs+ ⊂ 1 were calculated on the basis of their
X-ray crystallographic data. As a result, Σs(K‚‚‚F) )
0.620, Σs(K‚‚‚O) ) 0.178, Σs(K‚‚‚N) ) 0.212 (V ) ΣΣs )
1.01); Σs(Cs‚‚‚F) ) 0.689, Σs(Cs‚‚‚O) ) 0.329, Σs(Cs‚‚‚N)
Com p lexa tion Stu d ies. The stability constants of M+
⊂ 1 were estimated by employing metal-free 1 and alkali
metal picrates. Since compound 1 was obtained as a
potassium complex, K+ was removed by dissolving the
complex in aqueous HCl. The metal-free 1 was precipi-
tated from the aqueous solution of the hydrochloride by
aqueous Me4NOH treatment. The reactions between 1
and metal picrates were monitored by the 1H NMR
(10) Bond-valence sum was calculated according to ref 8a: s ) exp-
[(ro - r)/B], B ) 0.37. The value r0 was calculated using the equation,
r0 ) rc + A × ra + P - D - F. In the case of the K+ complex, the best
result (total sum of s approaches 1.00) was obtained by employing the
calculated r0 rather than the experimental one. The values r0 ) 2.051
for K-F, 2.161 for K-O, 2.251 for K-N were employed for the
calculation. In the case of the Cs+ complex, the experimental r0 value
was well reproduced by the calculation employing D ) 0.1. The values
r0 ) 2.298 for Cs-F, 2.417 for Cs-O, and 2.498 for Cs-N were
employed for the calculation.
(6) Seiler, P.; Dobler, M.; Dunitz, J . D. Acta Crystallogr. 1974, B30,
2744-2745.
(7) Dobler, M.; Phizackerley, R. P. Acta Crystallogr. 1974, B30,
2748-2750.
(8) (a) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244-
247. (b) Brown, I. D.; Wu, K. K. Acta Crystallogr. 1976, B32, 1957-
1959. (c) Brown, I. D.; Shannon, R. D. Acta Crystallogr. 1973, A29,
266-282.
(9) Murray-Rust, P.; Stallings, W. C.; Monti, C. T.; Preston, R. K.;
Glusker, J . P. J . Am. Chem. Soc. 1983, 105, 3206-3214.
(11) Lange’s Handbook of Chemistry; McGraw-Hill: New York, 1985.

Study of C-F···M+ Interaction
J . Org. Chem., Vol. 66, No. 8, 2001 2781
Ta ble 3. Sta bility Con sta n ts of M+ ⊂ 1 a n d Th eir
Sp ectr a l F ea tu r es
a
M+ ⊂ 1
log Ks 1J C-F (Hz)
δF (ppm)
metal-free 1
256.6
-116.7
Li+
2.7
3.1
3.2
3.1
3.0
2.9
249.8
242.0
244.0
244.0
243.9
246.9
-112.5, -128.1
-130.2
Na+
K+
-123.5
-120.9
Rb+
Cs+
NH4
-117.4 (octet, J ) 54.9 Hz)
-119.3
+
a
Shift (ppm) from CFCl3.
spectra in CDCl3/CD3CN (1/1, v/v). As described below,
the spectra of the cation complexes are remarkably
different from that of the metal-free 1, and the aromatic
proton signals appear at lower fields than that of the
metal-free 1. Therefore, the stability constants were
easily obtained by observing the M+ ⊂ 1 /1 ratios. The
reaction was very slow at 25 °C, and 2 weeks were
necessary to achieve the equilibrium. The constants could
not be measured by other highly accurate methods like
titration because of the slow reaction rate. As shown in
Table 3, cation selectivity was very small compared to
the hexafluoro cage compound 4.2 This phenomenon
resulted from the introduction of flexible ethyleneoxa
units into the cage structure. Similar tendency was
observed in the pyridine-containing cage compound 3.3
The reactions of the fluorine-free compound 2 and metal
picrates were also investigated, however, complex forma-
tion was not observed in the 1H NMR spectra. Therefore,
cations could not be captured by the four N atoms and
two O atoms; four C-F units play a dominant role in the
complexation. Compound 2 reacts only with an am-
monium ion, but the complexation was weak. In this case,
inclusion occurs by weak hydrogen bonds, NH4+‚‚‚O and
NH4+‚‚‚N.
F igu r e 6. Plots of 19F NMR shift of the complexes, M+ ⊂ 1
vs. ionic radii (Å) (CDCl3/CD3CN ) 1/1, v/v, 25 °C).
Sp ectr oscop ic F ea tu r es in Com p lexa tion . The
remarkable NMR spectral features during the C-F‚‚‚M+
interaction are reported, that is, (1) the 19F signal shifts
to the upper field and (2) the J C-F coupling constant
decreases in the 13C NMR spectrum.2,12 The same phe-
nomena were observed in the alkali metal complexes of
1. The spectral features of the metal-free 1 and its
complexes are summarized in Table 3. The coupling
constants, J C-F, of the complexes M+ ⊂ 1 are reduced by
ca. 7-15 Hz, and the 19F signals shift to the upper fields
(∼13.5 ppm). Interestingly, the ionic radii of the cations
and the 19F NMR chemical shift of M+ ⊂ 1 are in a good
linear relationship except Li+. They are proportional to
the interatomic distances between F and M+ (Figure 6);
they shift to higher fields as the cations become smaller.
A similar relationship was observed in the complexes,
M+ ⊂ 4.13 Furthermore, a linear relationship is also
observed between log Ks of the complexes and coupling
constants J C-F in the 13C NMR. The more stable com-
plexes have smaller J C-F values (Figure 7). In the 1H
NMR spectra, the methylene proton signal of 1 is sharp,
while the line shapes of those of the complexes strongly
depend on the included cation size (Figure 8). The
methylene signal coalesced by inclusion of the Li+ ion,
and the signals split as the cation size increased. Finally,
F igu r e 7. Plots of log Ks of M+ ⊂ 1 vs. J C-F (Hz).
a clear split in the methylene signal is observed in the
Cs+ complex. This phenomenon originated from the
suppression of the structural mobility of the complexes.
On the other hand, the spectral pattern of the aromatic
proton is unchanged, but it shifts to low field due to the
complexation.
Of particular interest was the 19F-133Cs spin coupling
observed in the 19F NMR spectrum. This is the third
requirement of the C-F‚‚‚M+ interaction. As shown in
Figure 9, an octet was observed in the spectrum of Cs+
⊂ 1 (I (133Cs) ) 7/2, J ) 54.9 Hz) at room temperature.
An octet of the 19F signal was also observed in Cs+ ⊂ 4
at low temperatures.13 Only two such other examples are
reported by Davidson et al., and they observed 19F-
133Cs spin coupling (J Cs-F ≈ 58 Hz) in their fluorine-
containing complexes.14 The Cs+ complex of the cryptand
(12) (a) Plenio, H.; Burth, D. J . Chem. Soc., Chem. Commun. 1994,
2297-2298. (b) Plenio, H.; Diodone, R. J . Am. Chem. Soc. 1996, 118,
356-367. (c) Plenio, H.; Diodone, R. Chem. Ber. 1997, 130, 963-968.
(13) Takemura, H.; Nakashima, S.; Kon, N.; Inazu, T. Tetrahedron
Lett. 2000, 41, 6105-6109.
(14) (a) Boyd, A. S. F.; Davidson, J . L.; McIntosh, C. H.; Leverd, P.
C.; Lindsell, W. E.; Simpson, N. J . J . Chem. Soc., Dalton Trans. 1992,
2531-2532. (b) Davidson, J . L.; McIntosh, C. H.; Leverd, P. C.; Lindsell,
W. E.; Simpson, N. J . J . Chem. Soc., Dalton Trans. 1994, 2423-2429.

2782 J . Org. Chem., Vol. 66, No. 8, 2001
Takemura et al.
F igu r e 8. 1H NMR spectra of the complexes, M+ ⊂ 1 (CDCl3/CD3CN ) 1/1, v/v, 25 °C).
reported by Plenio et al. did not show the spin coupling
despite the very similar structure to 1.5 The 19F NMR
signal of the other complexes, M+ ⊂ 1 (M ) Li+-Rb+,
NH4+), did not show this kind of spin coupling.
Exp er im en ta l Section
Gen er a l P r oced u r e. Melting points were measured in N2
1
sealed tubes and are uncorrected. The H, 13C, and 19F NMR
spectra were recorded at 400.1, 100.6, and 376.5 MHz, with
TMS and CFCl3 as internal references, respectively. FAB mass
spectra were obtained with m-NBA (3-nitrobenzyl alcohol) as
a matrix. Elemental analyses were performed at the Service
Centre of the Elementary Analysis of Organic Compounds
affiliated with the Faculty of Science, Kyushu University. All
solvents and reagents were of reagent quality and used
without further purification.
Con clu sion
The X-ray crystallographic analyses, complex forma-
tion, and spectral changes showed that the C-F‚‚‚M+
interaction is relatively strong. Under specific conditions
in which several C-F units are in an adequate arrange-
ment, the C-F unit strongly binds cations. The donor
ability of C-F is comparable to ether oxygen, or some-
times stronger. The specific spectral changes are observed
Ca tion -F r ee 1. The potassium complex, K+ ⊂ 1‚Br- (99.8
mg, 0.12 mmol) was dissolved in hot HCl (6 M, 15 mL) and
concentrated to dryness. The residual white powder was
dissolved in water, and the aqueous solution was treated with
aqueous tetramethylammonium hydroxide. The resultant
white precipitates were collected and recrystallized from
benzene to afford colorless prisms (65.8 mg, 77.3%): mp >
1
in the H, 13C, and 19F NMR spectra due to this interac-
tion, and these are very important probes to detect the
interaction. A dominant factor of the C-F‚‚‚M+ interac-
tion can be considered as a cation-dipole interaction.
Nevertheless, the dative bond also cooperates in the
binding of the cations because we can see remarkable
NMR spectral changes and the 19F-133Cs spin coupling;
there is a bond via electrons.
1
294.4 °C (dec in an N2 sealed tube); H NMR (CDCl3) δ 7.08
(t, J ) 7 Hz, 8H), 6.91 (t, J ) 7 Hz, 4H), 3.72 (t, J ) 6 Hz,
8H), 3.45 (s, 16H), 2.62 (t, J ) 6 Hz, 8H); 13C NMR (CDCl3) δ
161.77, 159.22, 130.26, 130.21, 125.87, 125.72, 120.70, 120.65,
66.94, 52.62, 52.06; 19F NMR (CDCl3) δ -117.16, -117.18,
-117.20; MS (FAB, m/z) 689 ([M+ + 1], 46). Anal. Calcd for

Study of C-F···M+ Interaction
J . Org. Chem., Vol. 66, No. 8, 2001 2783
X-r a y Cr yst a llogr a p h ic Da t a . Crystal data for 1:
C49H53N4O2F4, Mr ) 805.98 g mo1-1, colorless prismatic crystal
(grown from CH2Cl2-C6H6 mixture), size 0.50 × 0.30 × 0.10
mm, monoclinic, space group C2/c (#15), a ) 37.9015(9) Å, b
) 11.6150(3) Å, c ) 19.6321(5) Å, â ) 102.1239(6)o, V ) 8449.7-
(4) Å3, Z ) 8, Fcalcd ) 1.267 g cm-3, µ(Mo KR) ) 0.89 cm-1
,
F(000) ) 3416.00, T ) -180 ( 1 °C using the ω - 2θ scan
technique to a maximum 2θ value of 55.0°. A total of 39 953
reflections were collected. The final cycle of the full-matrix
least-squares refinement was based on 7042 observed reflec-
tions (I > 3.00σ(I)) and 551 variable parameters and converged
with unweighted and weighted agreement factors of R ) 0.039,
Rw ) 0.062, and GOF ) 1.06. The maximum and minimum
peaks on the final difference Fourier map corresponded to 0.54
and -0.37 e-/Å3, respectively.
Crystal data for K+ ⊂ 1‚Br-: C42H50N4O4F4KBr, Mr ) 869.88
g mo1-1, colorless prismatic crystal (grown from CH2Cl2-
MeOH mixture), size 0.50 × 0.30 × 0.50 mm, monoclinic, space
group C2/c (#15), a ) 19.550(2) Å, b ) 20.356(1) Å, c ) 12.5090-
(7) Å, â ) 125.814(3)o, V ) 4036.8(5) Å3, Z ) 4, Fcalcd ) 1.431
g cm-3, µ(Mo KR) ) 11.90 cm-1, F(000) ) 1808.00, T ) -180
( 1 °C using the ω - 2θ scan technique to a maximum 2θ
value of 55.0°. A total of 18 274 reflections were collected. The
final cycle of the full-matrix least-squares refinement was
based on 2725 observed reflections (I > 3.30σ(I)) and 265
variable parameters and converged with unweighted and
weighted agreement factors of R ) 0.056, Rw ) 0.105, and GOF
) 1.42. The maximum and minimum peaks on the final
difference Fourier map corresponded to 0.75 and -0.57 e-/Å3,
respectively.
F igu r e 9. 19F NMR spectra of (a) Cs+ ⊂ 1 and (b) K+ ⊂ 1.
Crystal data for Cs+ ⊂ 1‚Pic-: C46H46N7O9F4Cs, Mr
)
1049.81 g mo1-1, yellow prismatic crystal (grown from CH2-
Cl2-CH3CN mixture), size 0.50 × 0.50 × 0.50 mm, monoclinic,
space group C2/c (#15), a ) 20.8442(7) Å, b ) 20.0963(5) Å, c
) 12.6628(4) Å, â ) 123.8475(7)o, V ) 4405.4(2) Å3, Z ) 4,
C40H44N4O2F4‚C6H6: C, 72.04; H, 6.57; N, 7.31. Found: C,
72.00; H, 6.62; N, 7.39. The quantity of the solvent included
1
in the analytical sample was confirmed on the basis of the H
NMR spectrum.
F
calc. ) 1.583 g cm-3, µ(Mo KR) ) 9.24 cm-1, F(000) ) 2136.00,
K+ ⊂ 1‚Br -. The data of this compound were described in
T ) -180 ( 1 °C using the ω - 2θ scan technique to a
maximum 2θ value of 55.0°. A total of 20 332 reflections were
collected. The final cycle of the full-matrix least-squares
refinement (SHELXL-97) was based on 4873 observed reflec-
tions (I > 2.00σ(I)) and 442 variable parameters and converged
with unweighted and weighted agreement factors of R ) 0.027,
Rw ) 0.082, and GOF ) 1.23. The maximum and minimum
peaks on the final difference Fourier map corresponded to 0.57
and -0.82 e-/Å3, respectively.
ref 4a.
Cs+ ⊂ 1‚P ic-. Compound 1 (51.4 mg, 0.067 mmol) and
cesium picrate (40.2 mg, 0.11 mmol) were dissolved in 4 mL
of mixed solvent (CH2Cl2/CH3CN ) 1/1, v/v), and the solution
was stirred overnight at room temperature. After removal of
the solvent, the residual yellow powder was washed with a
small amount of water. Recrystallization of the powder from
CH2Cl2-CH3CN afforded yellow prisms (47.8 mg, 68.0%): mp
1
> 279.7 °C (dec in an N2 sealed tube); H NMR (CDCl3/CH3-
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC 149141 for 1, 149142 for K+ ⊂ 1, and
CCDC 149143 for Cs+ ⊂ 1. Copies of the data can be obtained
free of charge upon application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. [Fax: +44(1223)336-033; E-mail:
deposit@ccdc.cam.ac.uk].
CN, 1/1, v/v) δ 7.33-7.27 (m, 8H), 7.18 (t, J ) 7 Hz, 4H), 4.16
(d, J ) 12 Hz, 4H), 4.09 (d, J ) 12 Hz, 4H), 3.87 (t, J ) 11 Hz,
4H), 3.21 (d, J ) 12 Hz, 4H), 2.94 (t, J ) 11 Hz, 4H), 2.77 (d,
J ) 11 Hz, 8H), 2.28 (d, J ) 14 Hz, 4H); 13C NMR (CDCl3/
CH3CN, 1/1, v/v) δ 158.90, 156.48, 132.21, 132.17, 131.69,
131.65, 125.34, 125.19, 124.95, 124.20, 124.05, 123.05, 123.02,
67.74, 54.17, 52.19, 50.63; 19F NMR (CDCl3/CH3CN, 1/1, v/v)
δ -117.92, -117.77, -117.63, -117.49, -117.34, -117.18,
-117.04, -116.90; MS (FAB, m/z) 821 ([M + Cs]+, 62). Anal.
Calcd for C46H46N7O9F4Cs: C, 52.63; H, 4.42; N, 9.34. Found:
C, 52.90; H, 4.49; N, 9.31.
Ack n ow led gm en t. This research was supported by
a Grant-in-Aid for Developmental Scientific Research
provided by the Ministry of Education, Science, Sports
and Culture, J apan (No. 12640522) and for COE Re-
search “Design and Control of Advanced Molecular
Assembly Systems” from the Ministry of Education,
Science, Sports and Culture, J apan (No. 08CE2005). The
author thanks Professor Emeritus I. D. Brown for his
kind comments on the discussion of bond-valence sum.
Mea su r em en ts of Sta bility Con sta n ts. A solution of 1
in a mixture of CDCl3/CD3CN (1/1, v/v) at a concentration of
1.05 × 10-3 M was added to the alkali metal picrates (0.51-
0.77 equiv). Each mixture was allowed to stand for 2 weeks
1
at 25 ( 0.5 °C. After the equilibrium was established, the H
NMR spectra were recorded and the ratios of the metal-free
1, its complex, and picrate were calculated. The stability
constants were determined on the basis of the calculated
concentrations of the species using the following equation: K
) [M+ ⊂ 1]/[1][M+Pic].
J O0016778