C O M M U N I C A T I O N S
1
(
K
1b) with NaI were determined by calibrated competitive H NMR
13
studies in CDCl
3
. As “calibrant” we chose the well-characterized
+
14
complex between Na and [18]crown-6 (log K ) 6.11).
K
1a is
5
4
approximately 20 times larger than K1b (2.6 × 10 and 1.3 × 10
-
1
-
mol , respectively), thus proving the boosting effect of I‚‚‚I XB
+
on the Na complexation ability of 1a.
In summary, the new heteroditopic ligand 1a has been demon-
strated to simultaneously bind both the counterions of alkali metal
halides thanks to the presence of both anion and cation binding
sites. 1a binds NaI more efficiently than the monotopic ligand 1b,
and it also effectively discriminates different halides in XB-driven
Figure 2. Crystal packing (Mercury 1.3.1. view) of the [NaI(1a)] complex
showing the homochiral helix formed by the rolled-up infinite chain where
-
exo recognition processes wherein I is coordinated preferentially
2
-
-
over Br and Cl . XB has already widely proven its strength and
directionality but, to the best of our knowledge, no precedents have
been reported prior to now where it was exploited as a specific in-
teraction for selective anion recognition processes within heterodi-
topic receptors. The described protocol might be a new design prin-
ciple for anion-sensing receptors. Considering the easy introduction
of the iodotetrafluorophenyl residue on any scaffold, and the effec-
tiveness of this moiety as anion recognition site, the design principle
described here may produce even more powerful heteroditopic re-
ceptors, provided size- and shape-optimized frameworks are chosen.
iodide anions and podate modules alternate. XBs are dashed lines. Color
code as in Figure 1; the violet of iodine atoms and I‚‚‚I interactions
becomes darker approaching the bottom of the perspective view.
-
Acknowledgment. We thank EU (COST WG D29/0011/03 and
COST WG D31/0017/05) and MIUR (PRIN 2003) for financial
support, and Mr. Pietro Orsini for technical assistance. Dedicated
to Prof. Darryl D. DesMarteau on the occasion of his 65th birthday.
Figure 3. ESI-MS spectrum of a competitive binding experiment wherein
Supporting Information Available: Synthetic procedures, spec-
troscopic and X-ray structural data (PDF, CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
-
-
1
a was dissolved in a solution containing equimolar amounts of I , Br ,
-
and Cl .
Additional (qualitative) evidence for the heteroditopic binding
was gained by using ESI-MS. When 1a was treated with alkali
metal chlorides in a 1:1:1:1 ratio (1a:Na :K :Cs ), the peaks
corresponding to [1a + H] , [1a + Na] , [1a + K] , and [1 +
Cs] were observed in the positive ion polarity mode, and that
corresponding to [1a + Cl] was observed in the negative ion
polarity mode. Solutions of 1a containing either I , Br , or Cl
References
+
+
+
(1) Cametti, M.; Nissinen, M.; Dalla Cort, A.; Mandolini, L.; Rissanen, K. J.
Am. Chem. Soc. 2005, 127, 3831-3837. Sessler, J. L.; An, D.; Cho, W.-
S.; Lynch, V.; Yoon, D.-W.; Hong, S.-J.; Lee, C.-H. J. Org. Chem. 2005,
+
+
+
+
70, 1511-1517. Mahoney, J. M.; Nawaratna, G. U.; Beatty, A. M.;
-
Duggan, P. J.; Smith, B. D. Inorg. Chem. 2004, 43, 5902-5907. Special
Issue: 35 Years of Synthetic Anion Receptor Chemistry. Coord. Chem.
ReV. 2003, 270, and references therein. Choi, K.; Hamilton, A. D. J. Am.
Chem. Soc. 2003, 125, 10241-10249. Yoon, D.-W.; Hwang, H.; Lee,
C.-H. Angew. Chem., Int. Ed. 2002, 41, 1757-1759. Beer, P. D.; Gale,
P. A. Angew. Chem., Int. Ed. 2001, 40, 486-516.
-
-
-
were analyzed in the negative ion polarity ESI-MS mode. The cor-
responding spectra showed as the only signals the peaks at m/z
1
230, 1182-1184, and 1138-1140, respectively, in turn assigned
(
2) Tobey, S. L.; Anslyn, E. V. J. Am. Chem. Soc. 2003, 125, 14807-14815.
Schmidtchen, F. P.; Berger, M. Chem. ReV. 1997, 97, 1609-1646. Worm,
K.; Schmidtchen, F. P. Angew. Chem., Int. Ed. Engl. 1995, 34, 65-66.
-
-
-
to [1a + I] , [1a + Br] , and [1a + Cl] . Isotopic cluster were
resolved in all cases. Interestingly, the ESI-MS spectrum of a mix-
-
-
-
(3) Steed, J. W.; Juneja, R. K.; Atwood, J. L. Angew. Chem., Int. Ed. Engl.
995, 33, 2456-2457.
ture containing 1a and equimolar amounts of I , Br , and Cl (com-
petitive experiment) afforded a strong signal at m/z 1230, consistent
1
(
4) Lee, H.; Knobler, C. B.; Hawthorne, M. F. Angew. Chem., Int. Ed. 2001,
-
with [1a + I] , with broad peaks of relative abundance <1% cen-
tered at m/z 1182-1184 (consistent with [1a + Br] with non-
resolved isotopic cluster), and m/z 1138 (consistent with [1a + Cl]
40, 2124-2126.
-
(5) Rosokha, Y. S.; Lindeman, S. V.; Rosokha, S. V.; Kochi, J. K. Angew.
Chem., Int. Ed. 2004, 43, 4650-4652. de Hoog, P.; Gamez, P.;
Mutikainen, I.; Turpeinen, U.; Reedijk, J. Angew. Chem., Int. Ed. 2004,
43, 5815-5817. Maeda, H.; Osuka, A.; Furuta, H. J. Inclusion Phenom.
Macrocycl. Chem. 2004, 49, 33-36.
-
with nonresolved isotopic cluster) (Figure 3). These findings show
the preferential binding of 1a to iodide anion and are consistent
with the scale of XBs established in solution, where the strength
(
6) Bowman-James, K. Acc. Chem. Res. 2005, 38, 671-678 and references
therein. Sessler, J. L.; Davis, J. M. Acc. Chem. Res. 2001, 34, 989-997.
-
-
-
of different XBs was decreasing in the order I > Br > Cl
>
(7) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc. Chem. Res. 2005,
38, 386-395.
-
10
F . This trend is opposite to that shown by most anion receptors
that function through hydrogen bonding. Further evidence of
stronger binding of 1a with I came from MS/MS experiments.
Isolation and collision-induced decomposition (CID) of [1a + Cl]
6
(8) Caronna, T.; Liantonio, R.; Logothetis, T. A.; Metrangolo, P.; Pilati, T.;
-
Resnati, G. J. Am. Chem. Soc. 2004, 126, 4500-4501.
-
(9) Liantonio, R.; Metrangolo, P.; Pilati, T.; Resnati, G. Cryst. Growth Des.
2003, 3, 355-361.
-
and [1a + Br] adducts gave m/z 291 as the only fragmentation
(
10) Weiss, R.; Schwab, O.; Hampel, F. Chem. Eur. J. 1999, 5, 968-974.
product, consistent with the decomposition of the podand and the
formation of the iodotetrafluorophenolate moiety. Conversely, CID
Grebe, J.; Geiseler, G.; Harms, K.; Dehnicke, K. Z. Naturforsch. B 1999,
54, 77-86.
-
-
(11) Results to be published.
of the parent ion [1a + I] at m/z 1230 gave I at m/z 127 as the
only fragment.
(
12) Neukirch, H.; Guido, E.; Liantonio, R.; Metrangolo, P.; Pilati, T.; Resnati,
G. Chem. Commun. 2005, 12, 1534-1536.
The complexation ability of 1a in solution was finally studied
by NMR (Supporting Information). In all the NMR experiments, a
single signal was observed corresponding to the average of the
complexed and free receptors. Clearly, the binding process is fast
on the NMR time scale. The binding constants of 1a (K1a) and 1b
(
13) Heath, E. H.; Dykes, G. M.; Fish, H.; Smith, D. K. Chem. Eur. J. 2003,
9, 850-855.
(14) Wilson, M. J.; Pethrik, R. A.; Pugh, D.; Saiful Islam, M. J. Chem. Soc.,
Faraday Trans. 1998, 94, 39-46.
JA054862H
J. AM. CHEM. SOC.
9
VOL. 127, NO. 43, 2005 14973