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Anion-Assisted Self-Assembly.

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Anion-Assisted Self-Assembly**
Matthew C. T. Fyfe, Peter T. Glink, Stephan Menzer,
J. Fraser Stoddart,* Andrew J. P. White, and
David J. Williams *
Dedicated to Professor Dieter Seebach
on the occasion of his 60th birthday
On account of its pivotal role in several essential chemical and
biological processes, anion binding and recognition['] is currently arousing considerable attention within the domain of
supramolecular chemistry.['] Traditionally, supramolecular
chemists have positioned anion recognition sites within covalent
macro(po1y)cyclic framework^^^] in a preorganizedL4]manner,
so as to achieve strong anion binding. However, the discovery of
self-a~sembled[~~
superniolecules that are capable of binding
anions has been accomplished,[61as supramolecular science has
developed. Nevertheless, to the best of our knowledge, there has
been no report to date of a self-assembled anion receptor whose
components are held together entirely by hydrogen bonds.
We describe here the discovery of two novel supermoleculesself-assembled utilizing only hydrogen bonds-which display
either partial or complete envelopment of PF, ions in the solid
state.
Recently, we reportedL7]that macrocyclic polyethers form
inclusion complexes, termed pseudorotaxanes,[*Iof varying stoichiometries with secondary dibenzylammonium ions. In these
pseudorotaxanes the ammonium ions are threaded through
the macrorings and are held in place by a combination of
[N+-H. . .01 and [C-H . . .O] hydrogen bonds, with occasional assistance from n-7~ stacking interactions. For instance, the
ditopic crown ether bis-p-phenylene[34]crown-l0 (BPP34C10)
has been shown[71to form complexes with the dibenzylammonium ion (1-H+), in which two of these threadlike cations interpenetrate the macroring's void simultaneously to form (Figure 1) a double-stranded [3]pseudorotaxane. While researching
these systems, we became intrigued by the possibility that higher
h o r n ~ l o g u e s [of
~ ~BPP34C10--specifically, the crown ethers
tris-p-phenylene[51]crown-15 (TPP51C15) and tetrakis-pphenylene[68]crown-20 (TPP68C20-ould
incorporate three
and four 1-H+ cations within their respective cavities. Moreover, on account of the increased dimensions of the circumferences of their crown ether precursors, the resultant [4]- and
[5]pseudorotaxanes should possess ammonium centers ideally
predisposed to associate with anions by means of hydrogen
bonding and anion-dipole interactions, that is, where the
macrocyclic polyethers effect supramolecular preorganization["] of the anion binding sites. Indeed, we have found (vide
infra) that the [TPP51C15.(1-H)J3+ and [TPP68C20.(1-H),I4+
[*I Prof. .I.
F. Stoddart,[+' M. C. T. Fyfe, Dr. P. T. Glink
School of Chemistry, University of Birmingham
Edgbaston, Birmingham B152TT (UK)
Prof. D. J. Williams, Dr. S. Menzer, Dr. A. J. P. White
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
South Kensington, London SW72AY (UK)
Fax: Int. code +(171)594-5804
['I Current address:
Department of Chemistry and Biochemistry
University of California at Los Angeles
405 Hilgard Avenue, Los Angeles, CA 90095 (USA)
Fax: Int. code +(310)206-1843
e-mail: stoddart@chem.ucla. edu
[**I This research was funded in the UK primarily by the ZENECA Strategic
Research Fund, and was supported additionally by the Biotechnology and
Biological Sciences Research Council and the Engineering and Physical Sciences Research Council.
2068
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
Figure 1. Complexation of thedibenzylammonium ion (1-H+)with the crown ether
BPP34C10 yields a double-stranded [3]pseudorotaxane. The question is: would
larger macrocycles such as TPP51C15 and TPP68C20 allow the concurrent threading of three and four 1-H+ ions through their respective cavities?
pseudorotaxanes interact with PF, ions in the solid state. Furthermore, it appears that the bound anions can dictate the overall three-dimensional topology of the pseudorotaxane complexes, thus assisting the overall self-assembly processes.[111
TPP51C15 is capable of extracting three molar equivalents of
[1-HIPF, from a suspension of a large excess of the salt in
CD,Cl,. Since [1-H]PF, is practically insoluble in this solvent in
the absence of the crown ether, this observation provides a
semiquantitative guide to the likely stoichiometry of the complex. Analysis of the resulting CD,Cl, solution by 'HNMR
spectroscopy reveals[lZ1significant chemical shift changes for
the proton resonances associated with both species, indicative of
host-guest complex formation. An analysis of a single crystal
(obtained by liquid diffusion of n-hexane into a 1 :3 molar mixture of TPP51C15 and [1-H]PF, in CH,Cl,) by X-ray crystallography[13]revealed the solid-state structure depicted in Figure 2. The complex's supramolecular architecture corresponds
Figure 2. Space-fillingrepresentation of the [TPP51C15.(1-H),.PF6]'+ superstructure formed in the solid state, depicting both the threading of the three 1-H+ cations
(blue) through the cavity of the macrocyclic polyether TPP51C15 (red), and the
coordination of a PF; ion (phosphorus in purple, fluorines in green) within the cleft
formed by the [TPP5lCl5.(1-H)J3+ complex.
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Angew. Chem. Int. Ed. Engl. 19!J7,36, No. 19
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to a triple-stranded [4]pseudorotaxane, in which each of the
enthreaded 1-H ions is independently involved in stabilizing
[N’ -H . . ‘01and [C-H . . .O] hydrogen bonding interactions
with TPP51C15’s separate polyether loops. The macroring
adopts a folded conformation with approximate C, symmetry.
A closer investigation of the location of the three PF; ions
reveals that one of the three anions is located almost centrally
within a cleft generated by the saddlelike co-c~nformation[’~~
of
the 1:3 complex (Figure 2). Complexation of this anion is
achieved by a series of [C-H . . . F] hydrogen bonds to hydrogen
atoms on the hydroquinone rings of the crown ether and the
benzylic methylene groups of the bound 1-H+ ions. Hence, the
crown ether participates simultaneously in both of the anion’s
first and second coordination spheres.“ A noticeable feature
of this binding is the order bestowed upon the bound PF, ion.
This discovery of partial anion envelopment by the
[TPP51C15.(1-H),J3+ supermolecule led us to believe that the
total encapsulation of anions by self-assembled pseudorotaxane
superstructures of this type could be achieved with suitably expanded crown ethers. Four molar equivalents of the [I-HIPF,
salt are solubilized in a CD,Cl, solution containing one molar
equivalent of TPP68C20. Significant changes in the chemical
shifts of probe protons in both the salt and the crown ether are
observed[’61in the ’H NMR spectrum of this solution, suggesting that cation complexation is occurring in this solvent. Single
crystals were obtained when a 1:4 molar solution of TPP68C20
and [1-H]PF, in CH,Cl, was layered with n-hexane. The X-ray
analysis*131
of one of these crystals reveals that, when the macrocyclic polyether is extended by an additional hydroquinonespaced polyether loop, a crystalline aggregate results which
contains two independent quadruple-stranded [5]pseudorotaxane complexes (Figure 3). The asymmetric unit also
+
polyether’s oxygen atoms. On the other hand, the remaining
cations, which lie on the crystallographic C, plane, are not involved in any hydrogen bonding interactions. The most striking
feature of both independent [5]pseudorotaxane complexes is the
siting of a single PF; ion at each of their cores in ordered
arrangements (Figure 3). In this case, the anion is totally encaps ~ l a t e d [ ’by
~ ] both the four hydroquinone rings, which are oriented with their planes intersecting on the phosphorus center,
and the four tetrahedrally disposed, positively charged
CH,-NHl-CH,
regions of the four 1-Hf cations. The phosphorus atoms lie only about 0.3 8, from the complexes’ centroids. In view of the “spherical” shape of PF; ions, they tend
to assume random orientations in crystal lattices. However, in
this example, the anion is fully ordered-an ordering which is
undoubtedly a consequence of a series of [C-H . . . F] hydrogen
bonds, involving the cooperative action of hydroquinone methine and benzylic methylene hydrogen atoms which, in addition to coulombic forces, direct the physical envelopment of the
anion. Thus, the self-assembled [Slpseudorotaxanes provide elegant concentric spheres of cationic and neutral ligands for the
total encapsulation of the anions (Figure 4).
Figure 4. Cartoon representation of the [TPP68C20.(1-H), .PF,]-’+superstructure.
It is not unreasonable to conclude that the enfolded geometries of the l :4:l complexes-and, indeed, the l :3: l complex as well-have been programmed by the negatively charged
PF, ions; that is, the supramolecular system could be equally
well viewed as receiving its instructions from the anionic core,
which are then relayed through a four-component, tetracationic, first sphere to the neutral, second-sphere ligand.
Received: March 12, 1997 [Z10232IE]
German version: Angew. Chem. 1997, 109,2158-2160
Figure 3. Space-filling view of one of the [TPP68C20.(1-H);PFJ3+ supermolecules formed in the solid state, illustrating both the threading of the four 1-H+
ions (blue) through the cavity of the macrocyclic polyether TPP68C20 (red), and the
encapsulation of a PF,; ion (phosphorus in purple, fluorines in green) within the
cavity formed by the fl’PP68C20.(1-H)J4+ complex. The [H . . ‘ 9distances range
between 2.41 and 2.73 A; the associated [C. - . contacts are between 3.16 and
3.52 A.
Keywords: anion complexation * host-guest chemistry
noncovalent interactions
self-assembly * supramolecular
chemistry
accommodates a pair of unassociated C,-symmetric dibenzylammonium ions with their allied PF, counterions. The two
[5]pseudorotaxane complexes have essentially identical co-conformations[I4];the TPP68C20 macrocycle adopts a conformation that possesses local S, symmetry and resembles the seam of
a tennis ball. The four dibenzylammonium ions are clipped over
each of the macrocycle’s four polyether loops. The tetracationic
complex is stabilized by a combination of [N+-H.. ‘01and
[C-H . .O] hydrogen bonds between both the ammonium centers’ hydrogen atoms and their adjacent CH, groups and the
[l] Recent reviews: a) P. D. Beer, Chem. Commun. 1996, 689-696; b) J. L. Atwood, K. T. Holman, J. W. Steed, ibid. 1996, 1401-1407; c) J. Scheerder, J. F. J.
Engbersen, D. N. Reinhoudt, Recl. Trav. Chim. Pays-Bas 1996, ff5,307-320.
[2] J.-M. Lehn, Supramolecular Chemurry-Concepts and Perspectives, VCH,
Weinheim, 1995.
[3] For instance, see: a) B. Dietrich, J. Guilhem, J.-M. Lehn. C. Pascard, E. Sonveaux, Helv. Chim. Acta 1984, 67, 91-104; b) K. Worm, F. P. Schmidtchen,
A. Schier, A. Schafer, M. Hesse, Angew. Chem. 1994, IM, 360-362; Angew.
Chem. Int. Ed. Engr 1994,33,327-329; c) K. Ichikawa, M A. Hossain, Chem.
Commun. 1996, 1721- 1722.
[4] a) D. J. Cram, Angew. Chem. 1986,98,1041- 1060;Angew. Chem. I n / . Ed. Engl.
1986,25,1039-1057; h) D. J. Cram, hid. 1988, f00,1041--1052 and 1988,27,
1009- 1020.
Arzgew. Chem. hi.Ed. Etzgl. 1997.36, No. 19
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0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
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[5] a) D. S . Lawrence, T. Jiang, M. Levett, Chem. Rev. 1995,95,2229-2260; b) D.
Philp, J. F. Stoddart, Angew. Chem. 1996,108,1242-1286; Angew. Chem. In[.
Ed. Engl. 1996.35, 1154- 1196.
[6] a) D. M. Rudkevich, W. Verboom, Z. Brzozka, M. J. Palys, W. P. R. V. Stauthamer. G. J. vanHummel, S . M. Franken, S . Harkema, J. F. J. Engbersen,
D. N. Reinhoudt, J. Am. Chem. SOC.1994,116,4341-4351; b) B. Hasenknopf,
L M . Lehn, B. 0. Kneisel, G. Baum, D. Fenske, Angew. Chem. 1996, 108,
1987-1990; Angew. Chem. Int. Ed. Engl. 1996,35,1838-1840; c) R. W Saalfrank, S. Trummer, H. Krautscheid, V. Schiinemann, A. X. Trautwein, S Hien,
C. Stadler, J. Daub, ibid. 1996.108,2350-2352 and 1996,35,2206-2208; d) S.
Mann, G. Huttner, L. Zsolnai, K. Heinze, ibid. 1996, 108, 2983-2984 and
1996,35,2808-2809.
[7] a) P. R. Ashton, E. J. T. Chrystal, P. T. Glink, S. Menzer, C. Schiavo, N.
Spencer, J. F. Stoddart, P. A. Tasker, A. J. P. White, D. J. Williams, Chem. Eur.
J 1996, 2, 709-728; b) P. T. Glink, C. Schiavo, J. F. Stoddart, D. J. Williams,
Chem. Commun. 1996, 1483-1490; c) P. R. Ashton. P. T. Glink, M.-V. Martinez-Diaz, J. F. Stoddart, A. J. P. White, D. J. Williams, Angew. Chem. 1996,
108, 2058-2061; Angew. Chem. I n t . Ed. Engl. 1996,35, 1930-1933.
[V] Pseudorotaxanes have been defined as inclusion complexes in which one or
more threadlike molecules (or ions) are encircled by one or more macrocyclic
molecules (or ions) in the absence of an intercomponent mechanical or covalent
bond. Consequently, pseudorotaxanes are free to dissociate into their separate
components. The prefix [n] implies that an [n]pseudorotaxane is comprised of
n components. For instance, the 1:2 complex [BPP34ClO.(l-H),]*+ depicted
in Figure 1 is a double-stranded [3]pseudorotaxane.
[9] D. B. Amabilino, P. R. Ashton, C. L Brown, E. Cbrdova, L. A. Gbdinez, T. T.
Goodnow, A. E. Kaifer, S. P. Newton, M. Pietraszkiewicz, D. Philp, F. M.
Raymo, A. S. Reder, M. T. Rutland, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, C. Vicent, D. J. Williams, J. Am. Chem. SOC.1995, 117, 1271-1293.
[lo] P. R. Ashton, A. N. Collins, M. C. T. Fyfe, S. Menzer, J. F. Stoddart, D. J.
Williams, Angew. Chem. 1997, 109, 760-763; Angen. Chern. Inr. Ed. Engl.
1997,36, 735-739.
[ll] For other examples of anion-controlled self-assembly, see: J. L. Sessler, A.
Andrievsky, P. A. Gale, V. Lynch, Angew. Chem. 1996, 108, 2954-2957;
Angen,. Chem. Int. Ed. EngL 1996,35, 2782-2785, and references therein.
[12] Ah values for the resonances associated with the polyether's u-, 8.. 7-, 6-OCH,
and hydroquinone methine protons [solution of TPP51ClS (approximately
5 x 1 0 - 3 ~ and
) [1-HJPF, (approximately 1 . 5 1~0 - 2 ~in
) CD2CI, at 2O"Cl:
h = 0.00, -0.17, -0.29, -0.36, +0.13.
M , = 2004.5, or[13] Crystal data for [TPP51C15.(1-H),][PF61,-2CH,C1,,
thorhombic, a = 19.592(1), b = 25.240(1), c = 20.117(3) 8, V = 9948(2) A3,
space group PcaZ,, Z = 4, prnlcd=1 338 g ~ m - ~~(CU,,)
,
= 23.5 cm-I,
i. =1.54178 A,F(OOO) = 4176, T = 293K,6518uniquereflections(0<6O0), of
which 3846 were observed [ l o > 2 ~ ( l o ) ] .Final R-factors: R, = 0.103,
wR2 = 0.269 for 670 parameters. Crystal data for [TPP68C20.(1-H),]M, = 2766.4, monoclinic,
[PF,], -0.5 (C,H,CH,)2NH2.0.5PF6~1.7SCH,CI,,
a = 19.179(3), h =70.669(7), c = 19.993(2)A, 8 = 90.55(lp, V = 27096 A',
space group P2,/m, Z = 8 (two independent supermolecules), pCaIcd
=
1 . 3 5 6 g ~ m - ~ , p(CuK.)=20.8cm~', i=1.54178&
F(OOO)=11532,
T = 293 K, 34335 unique reflections (6155"), of which 20274 were observed
(I,,>2u(lo)). Final R-factors: R, = 0.100, n'R, = 0.269 for 3282 parameters.
Data for both structures were collected on a Siemens P4/RA diffractometer
with Cu,, radiation (graphite monochromated) using o scans. The data were
corrected for Lorentz and polarization factors, but not for absorption. The
structures were solved by direct methods and refined by least-squares based on
F2.TheN-H hydrogen atoms werelocated from AFmaps, theC-H hydrogen
atoms were placed in calculated positions. Both were allowed to ride on their
parent atoms. The polarity ofthe ~PP51C15~(l-H),][PF6],
superstructure was
determined using the Flack parameter, which refined to 0.2(2). All computations were carried out using the SHELXTL 5.03 package. 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-100264. Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CBZlEZ, UK (Fax: Int. code +(1223)336-033; e-mail: deposit@chemcrys.cam.ac.uk)
[I41 Strictly speaking, the term "conformation" refers only to discrete molecular
species. Consequently, we have used "co-conformation" to designate the different three-dimensional spatial arrangement of a) the constituent parts (e.g.,
host and guest) in supramolecular systems and of b) the components of interlocked molecular systems.
[15] Simultaneous first- and second-sphere coordination by macrocyclic polyethers
has been noted previously in our Iaboratorles. See: H. M. Colquhoun, S . M.
Doughty, A. M. Z. Slawin, J. F. Stoddart, D. J. Williams, Angew. Chem. 1985,
97, 124-125; Angen,. Chem. Int. Ed. Engl. 1985,24, 135-136.
[16] Ah values for the resonances associated with the polyether's a-,8-, y-. 6-OCH,
and hydroquinone protons [solution of TPP68C20 (approximately S x 1 0 - 3 M )
and [1-HIPF, (approximately 2 . 0 lo-")
~
in CD,CI, at 20°C): 6 = - 0.03,
-0.15, -0.23, -0.38, +0.16.
[I71 For the encapsulation of neutral species by self-assembled hosts, see: J. Rebek, Jr., Chem. Sor. Rev. 1996, 25, 255-264, and references therein.
2070
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
The Five-Stage Self-Assembly of a Branched
Heptacatenane""
David B. Amabilino, Peter R. Ashton, Sue E. Boyd,
J u Young Lee, Stephan Menzer, J. Fraser Stoddart,* a n d
David J. Williams*
The controlled creation of macromolecular chain compounds-that is, oligo- and polycatenanes-comprising mechanically linked macrocycles, which recognize each other link
by link as a result of noncovalent bonding interactions is one of
the most intellectually appealing goals in synthetic polymer
chemistry today. Self-assembly processes['] provide versatile
means of achieving this objective, operating in the first instance
by thermodynamically controlled recognition between the appropriate acyclic and cyclic intermediates, followed by kinetically controlled[21 ring closures in which both covalent and mechanical bonds are formed. Clearly, the ease of construction of
the higher order catenanes becomes a function of just how efficiently additional rings can be clipped around existing 0nes.1~~
Previously we have reported(31the self-assembly (Scheme 1)
of a tricatenane 3.4PF6 incorporating two tris-1,s-naphtho[57]crown-l5 macrocycles linked by the large tetracationic
cyclophane, cyclobis(paraquat-4,4'-biphenylene). We have also
shown[41that 3.4PF6 can be employed as a template to clip on,
in a stepwise manner, smaller tetracationic cyclophanes like cyclobis(paraquat-p-phenylene) tetracations. This approach to the
construction of oligo- and polycatenanes has already yieldedr4.'] the pentacatenane 5 . 12PF6, dubbed olympiadane.[61
Here we report how subsequent repetitive self-assembly steps
have been rendered more efficient by the use of ultrahigh pressure, leading to the isolation of a branched heptacatenene
(7.20 PF,), and describe its solid-state molecular structure as
determined by X-ray diffraction analysis.
When 3-4PF614]was treated (Scheme 1) with 2.2PF6 and 1 in
N,N-dimethylformamide at 12 kbar for 6 days, the 17lcatenane
7.20PF6 was isolated after chromatography in 26% yield, together with 5-12PF6 (30%) and 6.16PF6 (28%). No 4.8PF6
was obtained and only traces of 5' .12PF6 were detected."' The
[7]catenane was characterized initially from its mass spectrum
(LSI-MS) and 'H NMR spectrum (see Experimental Section).
Subsequently, single crystals of 7.20PF6, suitable for X-ray
crystallography, were obtained by vapor diffusion of diisopropyl ether into an acetonitrile solution of the [7]catenane.
The X-ray analysis[*]of 7.20PF6 (Figure 1) reveals a moiecular structure that fulfills every one of the anticipated design
features of the interlocked molecule: all the recognition sites are
['I Prof. J. F. Stoddart,"] Dr. D. B. Amabilino, P. R. Ashton, Dr. S . E. Boyd,
Dr. J. Y.Lee
School of Chemistry, University of Birmingham
Edgbaston, Birmingham B15 2TT (UK)
Prof. D. J. Williams, Dr. S . Menzer
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
South Kensington, London SW7 2AY (UK)
Fax: Int. code +(171)594-5804
Current address:
Department of Chemistry and Biochemistry
University of California at Los Angeles
405 Hilgard Avenue, Los Angeles. CA90095 (USA)
Fax: Int. code +(310)206-1843
e-mail: stoddart@chem.ucla.edu
[**I This research was sponsored in the U K by the Brit~shCouncil and the Engineering and Physical Sciences Research Council, and the Biotechnology and
Biological Sciences Research Council. We would like to thank Dr. E. R. Hovestreydt and Siemens, Karlsruhe, for making available their charge-coupled
device (CCD) detector system and for assistance.
I'[
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