An ion-pair template for rotaxane formation and its exploitation in an orthogonal interaction anion-switchable molecular shuttle

Article abstract of DOI:10.1002/anie.200802745

(Chemical Equation Presented) Chloride control: The serendipitous discovery of a molecular recognition motif that is triggered by the formation of an anion-palladium coordination bond is exploited as an efficient rotaxane-forming template and as the basis of a molecular shuttle. The macrocycle of this rotaxane moves between the two stations when the counterion is changed from chloride to hexafluorophosphate (see picture).

Full text of DOI:10.1002/anie.200802745

Communications
DOI: 10.1002/anie.200802745
Rotaxanes
An Ion-Pair Template for Rotaxane Formation and its Exploitation in
an Orthogonal Interaction Anion-Switchable Molecular Shuttle**
Michael J. Barrell, David A. Leigh,* Paul J. Lusby,* and Alexandra M. Z. Slawin
Despite significant advances[1] in anion-template methods for
the construction of mechanically interlocked molecules,[2] the
use of anions to induce changes in the relative positions of the
components of catenanes and rotaxanes has proved partic-
ularly challenging,[3] especially in comparison to the wide-
spread success achieved with other stimuli.[4–6] The few
examples of anion-switchable molecular shuttles developed
to date employ competition between the same types of weak
interaction in both states of the molecule to achieve switching
(solvation effects[3d,e] or the anion outcompeting hydrogen-
bonding acceptor groups of the macrocycle for donor groups
on the thread [3e,f]). Other features of anions, such as the
propensity of halides to form strong coordination bonds to
various transition metals, have yet to be exploited.[7] Herein
we report the serendipitous discovery of a new efficient
template for rotaxane formation and its use in the assembly of
a chloride-switchable molecular shuttle which exhibits excel-
lent positional integrity (> 98%) of the ring in both states that
arises from orthogonal binding modes: direct intercomponent
metal–ligand coordination in one state and a combination of
tight ion pairing, aromatic stacking interactions, and CH···O
and CH···Cl hydrogen bonding in the other.
The development of the new template for rotaxane
formation was prompted by the chance observation that
displacement of the acetonitrile ligand of [(L1)Pd(CH3CN)]
by the chloride ion of benzyl pyridinium chloride (1-Cl) was
Figure 1. An allosteric anion-activated template for threadingbased on
tight ion pairing reinforced through multiple other noncovalent inter-
actions. a) Synthesis of pseudorotaxane [(L1)PdCl·1]. Reaction condi-
accompanied by encapsulation of the organic cation by the
anionic PdCl-coordinated macrocycle [(L1)PdCl]À (Fig-
ure 1a).[8] The threaded nature of the complex [(L1)PdCl·1]
tions: CH2Cl2, 1 h, quantitative yield (use of 1-PF6 instead of 1-Cl, or
in CDCl3 was clearly apparent from 1H NMR spectroscopy (a
usingDMSO instead of CH Cl2, does not lead to pseudorotaxane
2
formation). b) Side-on and c) face-on views of the X-ray crystal
distinct upfield shift in the pyridinium resonances with respect
structure of [(L1)PdCl·1].[9] N blue, O red, Pd silver, Cl and the C atoms
of the macrocycle green, pyridinium purple, and other C atoms gray.
Selected bond lengths [Š] and angles [8]: N1–Pd 2.04, N2–Pd 1.93,
N3–Pd 2.03, Cl–Pd 2.32, O1–H3 2.47, O1–H1 2.57, O2–H1 2.37; N1-
Pd-N3 160.8, N2-Pd-Cl 176.4.
[*] M. J. Barrell, Prof. D. A. Leigh, Dr. P. J. Lusby
School of Chemistry, University of Edinburgh
The King’s Buildings, West Mains Road, Edinburgh EH9 3JJ (UK)
Fax: (+44)131-650-6453
E-mail: david.leigh@ed.ac.uk
paul.lusby@ed.ac.uk
Homepage: http://www.catenane.net
to those in 1-Cl caused by shielding by the benzylic groups of
the macrocycle, see the Supporting Information) and was also
found to persist in the solid state (Figure 1b and c) from the
X-ray crystal structure of single crystals grown from a
saturated CH2Cl2/EtOAc solution.[9]
Prof. A. M. Z. Slawin
School of Chemistry, University of St. Andrews
Purdie Building, St. Andrews, Fife KY16 9ST (UK)
[**] We thank Michael Hoffman and Dr. Anne-Marie Fuller for initial
work on ion-pair rotaxane templates in our group and the EPSRC
National Mass Spectrometry Service Centre (Swansea, U.K.) for
accurate mass data. This work was supported by the EPSRC. P.J.L. is
a Royal Society University Research Fellow. D.A.L. is an EPSRC
Senior Research Fellow and holds a Royal Society-Wolfson Research
Merit Award.
The solid-state structure of [(L1)PdCl·1] indicates that a
broad range of noncovalent interactions are responsible for
the assembly of the threaded architecture. In addition to the
tight ion pair[10] (the pyridinium nitrogen atom is within 4Š of
atoms in the first coordination sphere of the formally
negatively charged metal complex), aromatic stacking inter-
actions between the aromatic rings of the host and guest, aryl-
and alkyl-CH···O hydrogen bonding between the polyether
Supportinginformation for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200802745.
8036
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2008, 47, 8036 –8039

Angewandte
Chemie
oxygen atoms and protons on the carbon atoms adjacent to
À
the pyridinium nitrogen atom (C O distances 3.19–3.36 Š),
and CH···Cl(Pd) second coordination sphere interactions[7]
À
(C Cl distance 3.72 Š) all apparently contribute to the
stability of the interpenetrated structure. Many of these
primarily electrostatic interactions should be much weaker in
more polar environments and, indeed, the 1H NMR spectrum
of [(L1)PdCl·1] (see the Supporting Information) shows the
complex is largely unthreaded in [D6]DMSO. The chloride
anion is a vital component of the assembly process: [(L1)Pd-
(CH3CN)] did not form a threaded complex when treated
with 1-PF6 in CH2Cl2, a result which suggested that the
recognition motif could also be used as the basis of an anion-
selective trigger.
A pyridinium chloride salt suitable for rotaxane synthesis
(2-Cl) was prepared in four steps from 4-pyridinepropanol
(see the Supporting Information). Treatment of [(L1)Pd-
(CH3CN)] with 2-C1 in dichloromethane for one hour,
followed by reaction with 3 by a CuI-catalyzed azide–alkyne
1,3-cycloaddition (CuAAC)[11] in the presence of tris(benzyl-
triazolylmethyl)amine (TBTA)[12] and diisopropylethylamine
(DIPEA) led to [(L2)PdCl] in 64% yield (Scheme 1). The
mass spectrum of this product was strongly suggestive of a
rotaxane, as the major peak, which corresponds to [(L2)Pd]+,
does not fragment to the intact macrocycle and axle, as would
be expected for a non-interlocked salt. The irreversible
formation of a stoppered rotaxane was further confirmed
when removal of palladium did not cause separation of the
components (see the Supporting Information). Comparison
of the 1H NMR spectrum of [(L2)PdCl] (Figure 2b) with that
of the chloride salt of the thread (Figure 2a), shows significant
upfield shifts to the pyridinium resonances Hd , He , and Hf,
and adjacent protons (Ha and Hc).[13] Other signals of the
thread show little change, which indicates
Scheme 1. Synthesis and operation of chloride-switchable molecular
shuttle [(L2)Pd]+: a) CH2Cl2, 1 h; b) 3 (1.1 equiv), [Cu(CH3CN)4]PF6
(0.2 equiv), TBTA (0.25 equiv), DIPEA (1 equiv), CH2Cl2/CH3CN (7:1),
18 h, 64% (from 2-Cl); c) AgPF6 (1.1 equiv), acetone, 18 h, quantita-
tive; d) Bu4NCl (1.5 equiv), CHCl3, quantitative.
that the anionic PdCl–macrocycle is located
overwhelmingly over the pyridinium station,
that is, the structure is pyrdm[14]-[(L2)PdCl]
(Scheme 1).
The triazole group introduced by the
CuAAC reaction can also act as a ligating
station for the palladium–macrocycle.[15]
Treatment of pyrdm-[(L2)PdCl] with
AgPF6 (1.1 equiv; Scheme 1, step c)
smoothly precipitated AgCl and resulted in
quantitative conversion into a new rotaxane,
[(L2)Pd]PF6, in which the chloride ligand
had been replaced by the noncoordinating
À
PF6 counterion.
A comparison of the
1H NMR spectrum of [(L2)Pd]PF6 (Fig-
ure 2c) with that of the PF6 salt of the
thread (Figure 2d) shows that the signals of
the pyridinium station (Hd-f) appear at
similar chemical shifts in the thread and
rotaxane, while the triazole resonance (Hj)
and adjacent protons (e.g., Hi) are shifted
upfield in the rotaxane, which indicates that
removal of the chloride ion from the palla-
dium center is accompanied by translocation
of the palladium–macrocycle component to
Figure 2. Partial 1H NMR (400 MHz, CDCl3, 298 K) spectra of a)Àchloride salt of the
thread,[13] b) pyrdm-[(L2)PdCl], c) triazole-[(L2)Pd]PF6, and d) PF6 salt of the thread. The
assignments correspond to the lettering shown in Scheme 1. Signals shown in gray arise
from impurities and residual solvents.
Angew. Chem. Int. Ed. 2008, 47, 8036 –8039
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
8037

Communications
switching induced by anion solvation effects, see: d) B. W.
Laursen, S. Nygaard, J. O. Jeppesen, J. F. Stoddart, Org. Lett.
2004, 6, 4167 – 4170; e) C.-F. Lin, C.-C. Lai, Y.-H. Liu, S.-M.
Peng, S.-H. Chiu, Chem. Eur. J. 2007, 13, 4350 – 4355. For co-
conformational switching induced by intermolecular anion-
hydrogen bonding, see: Ref. [3e] and f) Y.-L. Huang, W.-C.
Hung, C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H. Chiu, Angew.
Chem. 2007, 119, 6749 – 6753; Angew. Chem. Int. Ed. 2007, 46,
6629 – 6633.
give triazole-[(L2)Pd]PF6. Simple addition of tetrabutylam-
monium chloride to triazole-[(L2)Pd]PF6 in chloroform
(Scheme 1, step d) reverses this process to afford a product
with identical physical and spectroscopic properties to the
original rotaxane, pyrdm-[(L2)PdCl].
The chance discovery of a molecular recognition motif
that is triggered by the formation of an anion–palladium
coordination bond has been exploited as both an efficient
rotaxane-forming template and as the basis for a chloride-
switchable molecular shuttle. The use of wholly different and
orthogonal binding modes in the two states of the shuttle
leads to exceptional positional integrity of the ring in both
forms. Anion-activated allosteric templates could lead to new
developments in sensors, logic gates, transport agents, and
molecular machines.
[4] For examples of light-switchable molecular shuttles, see: a) A. C.
Benniston, A. Harriman, Angew. Chem. 1993, 105, 1553 – 1555;
Angew. Chem. Int. Ed. Engl. 1993, 32, 1459 – 1461; b) H.
Murakami, A. Kawabuchi, K. Kotoo, M. Kunitake, N. Naka-
shima, J. Am. Chem. Soc. 1997, 119, 7605 – 7606; c) A. M.
Brouwer, C. Frochot, F. G. Gatti, D. A. Leigh, L. Mottier, F.
Paolucci, S. Roffia, G. W. H. Wurpel, Science 2001, 291, 2124–
2128; d) C. A. Stanier, S. J. Alderman, T. D. W. Claridge, H. L.
Anderson, Angew. Chem. 2002, 114, 1847 – 1850; Angew. Chem.
Int. Ed. 2002, 41, 1769 – 1772; e) A. Altieri, G. Bottari, F. Dehez,
D. A. Leigh, J. K. Y. Wong, F. Zerbetto, Angew. Chem. 2003,
115, 2398–2402; Angew. Chem. Int. Ed. 2003, 42, 2296–2300;
Angew. Chem. Int. Ed. 2003, 42, 2296–2300; f) G. Bottari, D. A.
Leigh, E. M. PØrez, J. Am. Chem. Soc. 2003, 125, 13360 – 13361;
g) E. M. PØrez, D. T. F. Dryden, D. A. Leigh, G. Teobaldi, F.
Zerbetto, J. Am. Chem. Soc. 2004, 126, 12210 – 12211; h) H.
Murakami, A. Kawabuchi, R. Matsumoto, T. Ido, N. Nakashima,
J. Am. Chem. Soc. 2005, 127, 15891 – 15899; i) J.-P. Collin, D.
Jouvenot, M. Koizumi, J.-P. Sauvage, Eur. J. Inorg. Chem. 2005,
1850 – 1855; j) D.-H. Qu, Q.-C. Wang, H. Tian, Angew. Chem.
2005, 117, 5430 – 5433; Angew. Chem. Int. Ed. 2005, 44, 5296 –
5299; k) S. Schmidt-Schäffer, L. Grubert, U. W. Grummt, K.
Buck, W. Abraham, Eur. J. Org. Chem. 2006, 378 – 398; l) V.
Balzani, M. Clemente-León, A. Credi, B. Ferrer, M. Venturi,
A. H. Flood, J. F. Stoddart, Proc. Natl. Acad. Sci. USA 2006, 103,
1178 – 1183; m) W. Abraham, K. Buck, M. Orda-Zgadzaj, S.
Schmidt-Schäffer, U.-W. Grummt, Chem. Commun. 2007, 3094–
3096; n) V. Serreli, C.-F. Lee, E. R. Kay, D. A. Leigh, Nature
2007, 445, 523 – 527; o) W. Zhou, D. Chen, J. Li, J. Xu, J. Lv, H.
Liu, Y. Li, Org. Lett. 2007, 9, 3929 – 3932; For a recent review,
see: p) S. Saha, J. F. Stoddart, Chem. Soc. Rev. 2007, 36, 77 – 92.
[5] For examples of pH-switchable molecular shuttles, see: a) R. A.
Bissell, E. Córdova, A. E. Kaifer, J. F. Stoddart, Nature 1994,
369, 133 – 137; b) M.-V. Martínez-Díaz, N. Spencer, J. F. Stod-
dart, Angew. Chem. 1997, 109, 1991 – 1994; Angew. Chem. Int.
Ed. Engl. 1997, 36, 1904– 1907; c) P. R. Ashton, R. Ballardini, V.
Balzani, I. Baxter, A. Credi, M. C. T. Fyfe, M. T. Gandolfi, M.
Gómez-López, M.-V. Martinez-Díaz, A. Piersanti, N. Spencer,
J. F. Stoddart, M. Venturi, A. J. P. White, D. J. Williams, J. Am.
Chem. Soc. 1998, 120, 11932 – 11942; d) A. M. Elizarov, S.-H.
Chiu, J. F. Stoddart, J. Org. Chem. 2002, 67, 9175 – 9181; e) K.-W.
Cheng, C.-C. Lai, P.-T. Chianga, S.-H. Chiu, Chem. Commun.
2006, 2854– 2856; f) Y. Tokunaga, T. Nakamura, M. Yoshioka, Y.
Shimomura, Tetrahedron Lett. 2006, 47, 5901 – 5904; g) D. A.
Leigh, A. R. Thomson, Org. Lett. 2006, 8, 5377 – 5379; h) J. D.
Crowley, D. A. Leigh, P. J. Lusby, R. T. McBurney, L.-E. Perret-
Aebi, C. Petzold, A. M. Z. Slawin, M. D. Symes, J. Am. Chem.
Soc. 2007, 129, 15085 – 15090; i) S. J. Vella, J. Tiburcio, S. J. Loeb,
Chem. Commun. 2007, 4752 – 4754; j) D. Tuncel, Ö. Özsar, H. B.
Tiftika , B. Salih, Chem. Commun. 2007, 1369 – 1371; k) W. Zhou,
J. Li, X. He, C. Li, J. Lv, Y. Li, S. Wang, H. Liu, D. Zhu, Chem.
Eur. J. 2008, 14, 754– 763; l) J. Bernµ, S. M. Goldup, A.-L. Lee,
D. A. Leigh, M. D. Symes, G. Teobaldi, F. Zerbetto, Angew.
Chem. 2008, 120, 4464 – 4468; Angew. Chem. Int. Ed. 2008, 47,
4392 – 4396.
Experimental Section
Experimental procedure for the preparation of pyrdm-[(L2)PdCl]: 2-
Cl (59 mg, 0.066 mmol) and [(L1)Pd(CH3CN)] (50 mg, 0.073 mmol)
were stirred for 1 h in CH2Cl2 (7 mL) prior to the addition of 3 (43 mg,
0.073 mmol) and DIPEA (11 mL, 0.066 mmol). A solution of TBTA
(9 mg, 0.017 mmol) and [Cu(CH3CN)4]PF6 (6 mg, 0.0147 mmol) in
CH3CN (1 mL) was added and the reaction mixture allowed to stir for
a further 18 h. After this time the volatile compounds were removed
under reduced pressure and the residue taken up in CH2Cl2 (10 mL).
The resulting solution was washed with saturated NH4Cl (3 ” 10 mL)
and the aqueous phase re-extracted with CH2Cl2 (3 ” 5 mL). The
combined organic extracts were concentrated under reduced pressure
and subjected to flash chromatography on silica gel (0–3% MeOH in
CH2Cl2 as eluent) to give pyrdm-[(L2)PdCl] as a bright yellow solid
(89 mg, 64%). For compound characterization, full synthetic details
for all precursors, and the switching experiments, see the Supporting
Information.
Received: June 11, 2008
Published online: September 15, 2008
Keywords: anion recognition · molecular shuttles · palladium ·
.
rotaxanes · template synthesis
[1] For a recent review on the anion-template synthesis of inter-
locked molecules, see: M. S. Vickers, P. D. Beer, Chem. Soc. Rev.
2007, 36, 211 – 225.
[2] a) G. M. Hübner, J. Gläser, C. Seel, F. Vögtle, Angew. Chem.
1999, 111, 395 – 398; Angew. Chem. Int. Ed. 1999, 38, 383 – 386;
b) J. A. Wisner, P. D. Beer, M. G. B. Drew, Angew. Chem. 2001,
113, 3718 – 3721; Angew. Chem. Int. Ed. 2001, 40, 3606 – 3609;
c) J. A. Wisner, P. D. Beer, M. G. B. Drew, M. R. Sambrook, J.
Am. Chem. Soc. 2002, 124, 12469 – 12476; d) M. R. Sambrook,
P. D. Beer, J. A. Wisner, R. L. Paul, A. R. Cowley, J. Am. Chem.
Soc. 2004, 126, 15364– 15365; e) K.-Y. Ng, A. R. Cowley, P. D.
Beer, Chem. Commun. 2006, 3676 – 3678; f) B. Huang, S. M.
Santos, V. Felix, P. D. Beer, Chem. Commun. 2008, DOI:
10.1039/b808094a.
[3] For co-conformational switching induced by intramolecular
anion–hydrogen bonding (which involves deprotonation of a
phenol group), see: a) C. M. Keaveney, D. A. Leigh, Angew.
Chem. 2004, 116, 1242 – 1244; Angew. Chem. Int. Ed. 2004, 43,
1222 – 1224; b) J. Bernµ, A. M. Brouwer, S. M. Fazio, N. Har-
aszkiewicz, D. A. Leigh, C. M. Lennon, Chem. Commun. 2007,
1910 – 1912; c) K.-Y. Ng, V. Felix, S. M. Santos, N. H. Reesa, P. D.
Beer, Chem. Commun. 2008, 1281 – 1283. For co-conformational
[6] For examples of redox-switchable molecular shuttles, see: a) N.
Armaroli, V. Balzani, J.-P. Collin, P. Gaviæa, J.-P. Sauvage, B.
Ventura, J. Am. Chem. Soc. 1999, 121, 4397 – 4408; b) A. Altieri,
8038 www.angewandte.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2008, 47, 8036 –8039

Angewandte
Chemie
F. G. Gatti, E. R. Kay, D. A. Leigh, D. Martel, F. Paolucci,
A. M. Z. Slawin, J. K. Y. Wong, J. Am. Chem. Soc. 2003, 125,
8644 – 8654; c) G. Cooke, J. F. Garety, B. Jordan, N. Kryvo-
khyzha, A. Parkin, G. Rabani, V. M. Rotello, Org. Lett. 2006, 8,
2297 – 2300; d) T. D. Nguyen, Y. Liu, S. Saha, K. C.-F. Leung, J. F.
Stoddart, J. I. Zink, J. Am. Chem. Soc. 2007, 129, 626 – 634; e) S.
Nygaard, K. C.-F. Leung, I. Aprahamian, T. Ikeda, S. Saha, B. W.
Laursen, S.-Y. Kim, S. W. Hansen, P. C. Stein, A. H. Flood, J. F.
Stoddart, J. O. Jeppesen, J. Am. Chem. Soc. 2007, 129, 960 – 970;
f) S. Saha, A. H. Flood, J. F. Stoddart, S. Impellizzeri, S. Silvi, M.
Venturi, A. Credi, J. Am. Chem. Soc. 2007, 129, 12159 – 12171;
g) I. Aprahamian, W. R. Dichtel, T. Ikeda, J. R. Heath, J. F.
Stoddart, Org. Lett. 2007, 9, 1287 – 1290; h) F. Durola, J.-P.
Sauvage, Angew. Chem. 2007, 119, 3607 – 3610; Angew. Chem.
Int. Ed. 2007, 46, 3537 – 3540; i) G. Fioravanti, N. Haraszkiewicz,
E. R. Kay, S. M. Mendoza, C. Bruno, M. Marcaccio, P. G.
Wiering, F. Paolucci, P. Rudolf, A. M. Brouwer, D. A. Leigh, J.
Am. Chem. Soc. 2008, 130, 2593 – 2601; j) Y.-L. Zhao, I.
Aprahamian, A. Trabolsi, N. Erina, J. F. Stoddart, J. Am.
Chem. Soc. 2008, 130, 6348 – 6350.
a “weak-link approach” macrocycle, which thereby promotes
subsequent pseudorotaxane formation with viologens, see: J.
Kuwabara, C. L. Stern, C. A. Mirkin, J. Am. Chem. Soc. 2007,
129, 10074– 10075.
[9] The X-ray crystal data and experimental details of the structural
refinement for [(L1)PdCl·1] are provided in the Supporting
Information. CCDC 689628 contains the supplementary crystal-
lographic 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.
[10] For other examples of rotaxane formation aided by ion-pairing,
see: a) D. J. Hoffart, J. Tiburcio, A. de La Torre, L. K. Knight,
S. J. Loeb, Angew. Chem. 2008, 120, 103 – 107; Angew. Chem. Int.
Ed. 2008, 47, 97 – 101; b) E. Lestini, K. Nikitin, H. Müller-Bunz,
D. Fitzmaurice, Chem. Eur. J. 2008, 14, 1095 – 1106.
[11] a) C. W. Tornøe, C. Christensen, M. Meldal, J. Org. Chem. 2002,
67, 3057 – 3064; b) V. V. Rostovtsev, L. G. Green, V. V. Fokin,
K. B. Sharpless, Angew. Chem. 2002, 114, 2708 – 2711; Angew.
Chem. Int. Ed. 2002, 41, 2596 – 2599.
[12] T. R. Chan, R. Hilgraf, K. B. Sharpless, V. V. Fokin, Org. Lett.
2004, 6, 2853 – 2855.
[7] For the exploitation of second-sphere coordination of metal–
halide and thiocyanate bonds in rotaxane and catenane assem-
bly, see: a) B. A. Blight, K. A. Van Noortwyk, J. A. Wisner,
M. C. Jennings, Angew. Chem. 2005, 117, 1523 – 1528; Angew.
Chem. Int. Ed. 2005, 44, 1499 – 1504; b) B. A. Blight, J. A.
Wisner, M. C. Jennings, Chem. Commun. 2006, 4593 – 4595;
c) B. A. Blight, J. A. Wisner, M. C. Jennings, Angew. Chem. 2007,
119, 2893 – 2896; Angew. Chem. Int. Ed. 2007, 46, 2835 – 2838;
d) B. A. Blight, X. Wei, J. A. Wisner, M. C. Jennings, Inorg.
Chem. 2007, 46, 8445 – 8447.
[13] The broad appearance of the Hd , He , and Hf resonances of the
chloride salt of the thread (Figure 2a) is probably a result of
multiple chloride positions within the tight ion pair.
[14] The prefix indicates the position of the macrocycle on the
thread: pyrdm- noncovalent bonding to the pyridinium group;
triazole- coordinated through the palladium ion to the triazole
ring.
[15] V. Aucagne, J. Bernµ, J. D. Crowley, S. M. Goldup, K. D. Hänni,
D. A. Leigh, P. J. Lusby, V. E. Ronaldson, A. M. Z. Slawin, A.
Viterisi, D. B. Walker, J. Am. Chem. Soc. 2007, 129, 11950 –
11963.
[8] In a two-step process, carbon monoxide and chloride coordina-
tion to rhodium has been used to change the shape and charge of
Angew. Chem. Int. Ed. 2008, 47, 8036 –8039
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 8039