M3L2 metallo-cryptophanes: [2]Catenane and simple cages

Article abstract of DOI:10.1039/c1cc10806a

Crystalline M₃L₂ complexes with either single cage or triply interlocking [2]catenane chiral structures are formed the self-assembly of host-like ligands with transition metals.

Full text of DOI:10.1039/c1cc10806a

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COMMUNICATION
M3L2 metallo-cryptophanes: [2]catenane and simple cageswz
James J. Henkelis,a Tanya K. Ronson,a Lindsay P. Hardingb and Michaele J. Hardie*a
Received 11th February 2011, Accepted 29th March 2011
DOI: 10.1039/c1cc10806a
Crystalline M3L2 complexes with either single cage or triply
interlocking [2]catenane chiral structures are formed the self-
assembly of host-like ligands with transition metals.
groups with the N-donor in a 3-position. One such complex
affords the second example of a triply interlocked [2]-catenane
based on metallo-cryptophanes. Different types of larger
CTV-based metallo-cages have also been reported.11
Tris(3-pyridylmethyl)cyclotriguaiacylene
1
and tris-
Cryptophanes are molecular 3D cage-like hosts where two
cyclotriveratrylene (CTV) fragments are linked together
via organic functional groups.1 Metallo-cryptophanes are
analogous species where the CTV moieties are linked via
metal–ligand coordination, and there have been few reported
[4-(5-pyrimidyl)benzoyl]cyclotriguaiacylene 2 were synthesised
as racemic mixtures in 44% and 81% yields respectively from
the CTV-analogue cyclotriguaiacylene (CTG), Scheme 1.z
Reaction of 1 with Ag(ClO4) in dimethylformamide (DMF)
gave a triply interlocked [2]catenane metallocryptophane
{[Ag3(1)2]}2.(ClO4)6.(solvent)n, as revealed by X-ray crystallo-
graphy.y Crystals with similar unit cell parameters were
obtained by use of Ag(BF4) or Ag(SbF6) in place of Ag(ClO4).
Reaction of 2 with [Ag(CH3CN)4]BF4 in DMSO or with
Cu(NO3)2 in DMF yields single-cage [M3(2)]2]n+ metallo-
cryptophanes in the solid state.
6+
examples.2–4 Our recently reported complex [M3(L)2(NO3)3]2
where M = Zn(II) or Co(II) and L = tris(40-methyl-2-20-
bipyridine-4-methyl)cyclotriguaiacylene is a highly unusual
metallo-cryptophane where two cages form a triply inter-
locked [2]catenane.4
In catenanes and other interlocked molecular species the
threading of one component through another, or coming
together of precursors in specific arrangements, are critical
steps in their formation. Templation and structure directing
supramolecular interactions such as p–p stacking or hydrogen
bonding are important strategies to induce molecular threading
or close association of components.5 Most catenanes are
essentially 2D. A handful of examples of [2]catenane structures
involving interlocked 3D cages have been reported,4,6–9 and a
3D coordination polymer comprised of catenated adamantane
cages has recently been reported by Lu.10 Beer, for example,
reports an anion templated assembly of a triply interlocked
organic cage;6 while examples of triply and quadruply inter-
locked metallo-cages where aromatic p–p stacking interactions
are observed between individual cage species have been
reported by Fujita,7 and Kuroda respectively.8 Cooper and
coworkers have recently reported a triply interlocked organic
cage where there is no template nor obvious structure-directing
supramolecular interactions between the components.9
We report herein M3L2 metallo-crytophanes involving
CTV-type ligands with monodentate pyridyl or pyrimidine
The crystal structure of the complex {[Ag3(1)2]}2.(ClO4)6ꢀ
(DMF)3 has an asymmetric unit comprising two inter-
locked [Ag3(1)2]3+ units, six perchlorate anions disordered
across seven molecular positions, and three DMF molecules.
Ag(I) cations have approximately linear coordination and
are coordinated by pyridyl groups from two different 1
ligands. Ag–N distances range from 2.107(6) to 2.311(10) A,
and N–Ag–N angles from 165.1(4) to 176.9(4)1. One Ag
also shows a long contact to a DMF at Ag–O separation
2.580(13) A.
One [Ag3(1)2]3+ metallo-cryptophane cage of the [2]catenane
is shown in Fig. 1a. The cage is composed of two 1 ligands,
both of the same enantiomer. Hence this metallo-cryptophane
is analogous to the chiral anti isomer cryptophanes.1 This is in
6+
contrast with the previously reported [Zn3(L)2(NO3)3]2
[2]catenane structure where a syn-type isomer containing both
enantiomers of the ligand was formed. The second [Ag3(1)2]3+
cage, while crystallographically distinct, is structurally very
similar to the first. It is oriented such that the host ligands of
the two cages form a bowl-in-bowl arrangement, and the two
form a triply interlocked [2]catenane, Fig. 1b. The [2]catenane
is chiral as all 1 ligands are the same enantiomer, although
each crystal is a racemate.
a School of Chemistry, University of Leeds, Leeds, UK.
E-mail: m.j.hardie@leeds.ac.uk; Fax: +44 113 343 6565;
Tel: +44 113 343 6458
b Department of Chemical and Biological Sciences,
University of Huddersfield, Huddersfield, UK
There are no significant intermolecular interactions between
the two cages of the [2]catenane. Despite the bowl-in-bowl
arrangement of the ligands, there are no p–p stacking inter-
actions between them, as indicated by the long aromatic ring
centroid separations ranging from 4.64 to 4.98 A. Further-
more, there are no Ag...Ag interactions (all separations 4 5.2 A).
While the Ag centres of one cage are positioned above the
w This article is part of a ChemComm ‘Supramolecular Chemistry’
web-based themed issue marking the International Year of Chemistry
2011.
z Electronic supplementary information (ESI) available: Synthesis and
additional details on crystallographic and NMR studies. CCDC
812988–812990. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1cc10806a
c
6560 Chem. Commun., 2011, 47, 6560–6562
This journal is The Royal Society of Chemistry 2011

Scheme 1 Synthesis of ligands 1 and 2, and cartoon schematic of [2]catenane and single cage formation.
ether groups of the ligands of the other cage, the Ag. . .O
metallated arm of a cage projects into a window of an adjacent
cage, forming triangular interstitial cavities within the layer,
Fig. 2c. In the crystal lattice, these layers pack such that a CTV
fragment of a cage of another layer sits above this cavity.
Hence the packing of the metallo-cryptophanes is reminiscent
of simple close packing of spheres but with six layers in the
repeat unit accounting for the very long c unit cell dimension
of ca. 105 A.
separations (average 3.13, closest 2.91 A) are considerably
greater than the sum of the ionic and van der Waals radii
(2.66 A).12 Hence the [2]catenane has formed without
a template and in the absence of any evident strong
structure-directing interactions that are maintained in the final
complex.
The solution-phase assembly of the [2]catenane was
investigated by NMR and electrospray mass spectrometry.
The 1H NMR spectrum of a mixture of Ag(ClO4) and 1 in
d7-DMF showed considerable broadening and changes to the
chemical shifts of the ligand, consistent with coordination
occurring in solution.z The ESI-MS gives excellent evidence
for the formation of the [2]catenane, in particular through
m/z peaks attributable to species with four ligands:
{[Ag5(1)4](ClO4)4}+, {[Ag4(1)4](ClO4)3}+. Other peaks in the
spectrum are assigned to species {[Ag4(1)3](ClO4)3}+,
{[Ag3(1)3](ClO4)2}+, {[Ag3(1)2](ClO4)2}+, and [Ag(1)]+.
The crystalline complexes [Ag3(2)2](BF4)3.(solvent)n and
[Cu3(2)2(H2O)6(NO3)3](NO3)3.(solvent)n are isomorphic,y
and only the [Cu3(2)2(H2O)6](NO3)6.(solvent)n complex will
be discussed in detail (see supplementary information for Ag(I)
complexz). The Cu(II) centres of [Cu3(2)2(H2O)6(NO3)3](NO3)3
have distorted square pyramidal coordination with two
pyrimidine groups in a trans arrangement at Cu–N distance
2.054(3) A and N–Cu–N angle 177.26(16)1; disordered trans
aquo ligands (Cu–O 2.020(10) and 2.105(10) A); and a long
contact to a disordered nitrate (Cu–O 2.446 A). Only one of
the nitrogen atoms of each pyrimidine group binds to
the metal. The [Cu3(2)2(H2O)6(NO3)3]3+ complex forms an
anti-metallocryptophane, Fig. 2a, of ca. 2 nm size and with
significant internal space.
The solution properties of [Ag3(2)2](BF4)3 and
[Cu3(2)2(H2O)6](NO3)6 were also investigated by NMR and
electrospray MS, however no evidence was seen for their
formation in solution. The 1H NMR spectrum of a 3 : 2
mixture of [Ag(MeCN)4])BF4 and 2 in d6-DMSO shows no
shifts compared to the spectrum of the free ligand. This is
further confirmed with the electrospray MS of a similar
solution which shows peaks at m/z 1063.2, 2017.5 and
2973.8 for the small fragments{Ag(2)}+, {Ag(2)2}+ and
{Ag(2)3}+. Likewise the electrospray MS of a DMF solution
of Cu(NO3)2 and 2 shows dominant peaks for the fragments
{Cu(2)(NO3)}+, {Cu(2)2(NO3)}+, {Cu(2)3(NO3)}+ and
at m/z 1079.2 and 2035.5 and 2989.8 respectively.
In both the [2]catenane and single cage metallocryptophanes
reported here, the anti-isomer was obtained. This is in contrast
to similar previously reported metallocryptophanes where a
mixture of isomers2 or the syn-isomer4 were obtained. Here,
formation of the anti-isomer is likely to be predetermined by
the nature of the ligand. Both 1 and 2 have coordinating
N-atoms in (effectively) the 3-position, and, with the metal
acting as a linear linker, only the anti-isomer can form on
steric grounds.
The second example of a non-templated [2]catenane metallo-
cryptophane reported here, together with other recently
reported 3D and non-templated catenanes, indicated that such
catenation of cage-like molecules may be more general, and
points to complex self-assembly processes.
The metallo-cryptophane can also be described as a trigonal
bipyramidal cage with the three metals forming the equatorial
plane. Viewed down the axial direction, the metallated
side-arms extend outwards. Flat layers of interdigitated
[Cu3(2)2(H2O)6(NO3)3]3+ cations are formed with each metallo-
cryptophane surrounded by six others, Fig. 2b. Each
We thank the ESPRC, the Brotherton Trust and the
University of Leeds for funding and Ian Blakeley for micro-
analytical measurements.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6560–6562 6561

Fig. 2 From the crystal structure of [Cu3(2)2(H2O)6](NO3)6.n(solvent).
(a) the metallo-cryptophane; (b) packing in layers in the ab plane.
Disordered aquo and nitrate ligands are shown in a single averaged
position.
4 A. Westcott, J. Fisher, L. P. Harding, P. Rizkallah and
M. J. Hardie, J. Am. Chem. Soc., 2008, 130, 2950.
5 Molecular Catenanes, Rotaxanes and Knots, ed. J. -P. Sauvage and
C. Dietrich-Buchecker, 1999, Wiley-VCH, Weinheim, Germany,
1999.
6 Y. Li, K. M. Mullen, T. D. W. Claridge, P. J. Costa, V. Felix and
P. D. Beer, Chem. Commun., 2009, 7134.
7 M. Fujita, N. Fujita, K. Ogura and K. Yamaguchi, Nature, 1999,
400, 52.
8 M. Fukuda, R. Sekiya and R. Kuroda, Angew. Chem., Int. Ed.,
2008, 47, 706.
9 T. Hasell, X. Wu, T. A. Jones, J. Basca, A. Steiner, T. Mitra,
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11 For example B. F. Abrahams, N. J. FitzGerald and R. Robson,
Angew. Chem., Int. Ed., 2010, 49, 2896; T. K. Ronson, J. Fisher,
L. P. Harding, P. J. Rizkallah, J. E. Warren and M. J. Hardie, Nat.
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¨
M. Piel, Inorg. Chim. Acta, 1993, 207, 31.
13 A. L. Spek, Acta Cryst., 1990, A46, C34.
Fig. 1 From the crystal structure of {[Ag3(1)2]}2.(ClO4)6ꢀ(DMF)3.
(a) A single [Ag3(1)2]3+ metallo-cryptophane; (b) two metallocrypto-
phanes (shown in different colours) interlocking to form a [2]catenane.
Notes and references
y The SQUEEZE routine of PLATON13 was employed on all
structures.
Crystal
data.
{[Ag3(1)2]}2.(ClO4)6ꢀ(DMF)3.(solvent)n:
C177H177Ag6Cl6N15O51, Mr = 4190.26, monoclinic, a = 33.352(3),
b = 19.288(2), c = 40.328(3) A, b = 104.583(4), V = 25107(4) A3,
space group Cc, Z = 4, ymax = 22.501, T = 150(1) K, 1774
parameters, 124 restraints, R1 = 0.1037 (for 15793 data I 4 2s(I)),
wR2 = 0.2617 (all 27816 data). CCDC 812990.
[Cu3(2)2(H2O)6](NO3)6.(solvent)n: C114H96Cu3N18O45, Mr = 2628.71,
trigonal, a = 16.6949(7), c = 105.524(9) A, V = 25471(3) A3, space
ꢀ
group R3c, Z = 6, ymax = 25.991, 245 parameters, R1 = 0.0927 (for 4514
data I 4 2s(I)), wR2 = 0.3215 (all 5563 data). CCDC 812988.
1 T. Brotin and J.-P. Dutasta, Chem. Rev., 2009, 109, 88.
2 Z. Zhong, A. Ikeda, S. Shinkai, S. Sakamoto and K. Yamaguchi,
Org. Lett., 2001, 3, 1085.
3 T. K. Ronson, H. Nowell, A. Westcott and M. J. Hardie, Chem.
Commun., 2011, 47, 176.
c
6562 Chem. Commun., 2011, 47, 6560–6562
This journal is The Royal Society of Chemistry 2011