Angewandte
Chemie
pseudo-square-planar geometry (the N3 bite angle is 160.08)
around the palladium center. The p stacking between the
macrocycle and the pyridine ring of the thread so apparent in
hydrogen-bonding interactions between the thread and the
macrocycle are “switched on”by the demetalation/protona-
tion procedure. It appears that the amide groups of H2L6
simultaneously hydrogen bond to the pyridine groups in both
the macrocycle and thread.
1
solution from the H NMR shifts is significantly offset in the
solid state (see the side-on view, Figure 3b). The co-con-
formation adopted by the macrocycle and thread in the crystal
structure of the rotaxane clearly illustrates why RCM of the
complexes formed with the 3,5-disubstituted threads
([Pd(L1)(L3)] and [Pd(L1)(L5)]) can lead to uninterlocked
products; even with both fragments attached to the metal,
cyclization of L1 can readily occur without encircling a 3,5-
substituted pyridine thread. Similarly, the conformation of the
thread suggests a possible reason for the lack of reactivity of
the 2,6-bis-ester thread L4 towards [Pd(L1)(CH3CN)]. In the
crystal structure the electron density of the ether oxygen
atoms of the thread is directed away from the occupied dz2
orbital lobes which lie above and below the plane of the
square-planar geometry at the d8 palladium center. Chelation
of L4 to [Pd(L1)] has to occur orthogonally for steric reasons.
Such an arrangement would force electron density from the
ester carbonyl groups into this high-energy space.
In conclusion, we have described methodology for assem-
bling a three-dimensional interlocked molecular architecture
from a two-dimensional metal template. A combination of
steric and electronic factors direct the synthesis in the third
dimension, either promoting or preventing interlocking. The
resulting [2]rotaxane is the first example derived from a
square-planar-coordinated metal center and completes the
series of mechanically interlocked ligands for common
transition-metal geometries initiated by Sauvage and co-
workers in 1983.
Received: December 29, 2003 [Z53622]
Keywords: coordination modes · palladium · rotaxanes ·
.
template synthesis
Demetalation of [Pd(L6)] with potassium cyanide
(Scheme 1, step d) generates the free [2]rotaxane H2(L6) in
97% yield, thus confiming that the coordination bonds are
not required to stabilize the interlocked architecture once it is
[1] C. O. Dietrich-Buchecker, J.-P. Sauvage, J.-P. Kintzinger, Tetra-
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1
formed. The H NMR spectrum of H2(L6) and its uninter-
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locked components in CDCl3 are shown in Figure 4. The
shielding of the benzyl groups in the rotaxane relative to the
free macrocycle, together with the large (d = 1.7 ppm) down-
field shift of the amide protons (HC), indicate that specific
[4] a) D. Pomeranc, D. Jouvenot, J.-C. Chambron, J.-P. Collin, V.
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Chang, H.-Y. Chang, Angew. Chem. 2000, 112, 1758 – 1761;
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Choi, K.-S. Jeong, Chem. Eur. J. 2001, 7, 2687 – 2697; c) S.-Y.
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1541; for complexes in which metal coordination forms part of
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Heo, K. Kim, Chem. Eur. J. 2002, 8, 498 – 508; for complexes in
which metal coordination forms the stoppers in a rotaxane, see
f) R. B. Hannak, G. Färber, R. Konrat, B. Kräutler, J. Am. Chem.
Soc. 1997, 119, 2313 – 2314; g) J.-C. Chambron, J.-P. Collin, J.-O.
Dalbavie, C. O. Dietrich-Buchecker, V. Heitz, F. Odobel, N.
SolladiØ, J.-P. Sauvage, Coord. Chem. Rev. 1998, 178–180, 1299 –
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polyrotaxanes based on metal-coordination polymers, see
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ersby, M. Schröder, Coord. Chem. Rev. 1999, 183, 117 – 138; l) K.
Kim, Chem. Soc. Rev. 2002, 31, 96 – 107.
Figure 4. 1H NMR spectra (400 MHz, CDCl3, 298 K) of a) macrocycle;
b) demetalated [2]rotaxane H2L6; c) thread L2. The lettering refers to
the assignments in Scheme 1.
Angew. Chem. Int. Ed. 2004, 43, 3914 –3918
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