Coordination-driven self-assembly of cavity-cored multiple crown ether derivatives and poly[2]pseudorotaxanes

Article abstract of DOI:10.1021/ja711502t

The synthesis of a new 120° diplatinum(II) acceptor unit and the self-assembly of a series of two-dimensional metallacyclic polypseudorotaxanes that utilize both metal-ligand and crown ether-dialkyl-ammonium noncovalent interactions are described. Judiciously combining complementary diplatinum(II) acceptors with bispyridyl donor building blocks, with an acceptor and/or donor possessing a pendant dibenzo[24]crown-8 (DB24C8) moiety, allows for the formation of three new rhomboidal bis-DB24C8, one new hexagonal tris-DB24C8, and four new hexakis-DB24C8 metallacyclic polygons in quantitative yields. The size and shape of each assembly, as well as the location and stoichiometry of the DB24C8 macrocycle, can be precisely controlled. Each polygon is able to complex two, three, or six dibenzylammonium ions without disrupting the underlying metallacyclic polygons, thus producing eight different poly[2]pseudorotaxanes and demonstrating the utility and scope of this orthogonal self-assembly technique. The assemblies are characterized with one-dimensional multinuclear (¹H and ³¹P) and two-dimensional (¹H- ¹H COSY and NOESY) NMR spectroscopy as well as mass spectrometry (ESI-MS). Further analysis of the size and shape of each assembly is obtained through molecular force-field simulations. ¹H NMR titration experiments are used to establish thermodynamic binding constants and poly[2]pseudorotaxane/dibenzylammonium stoichiometries. Factors influencing the efficiency of poly[2]pseudorotaxane formation are discussed.

Full text of DOI:10.1021/ja711502t

Published on Web 03/15/2008
Coordination-Driven Self-Assembly of Cavity-Cored Multiple
Crown Ether Derivatives and Poly[2]pseudorotaxanes
Koushik Ghosh,† Hai-Bo Yang,*,† Brian H. Northrop,† Matthew M. Lyndon,§
Yao-Rong Zheng,† David C. Muddiman,§ and Peter J. Stang*,†
Departments of Chemistry, UniVersity of Utah, 315 South 1400 East, Room 2020, Salt Lake City,
Utah 84112, and North Carolina State UniVersity, Raleigh, North Carolina 27695
Received December 31, 2007; E-mail: hbyang@chem.utah.edu; stang@chem.utah.edu
Abstract: The synthesis of a new 120° diplatinum(II) acceptor unit and the self-assembly of a series of
two-dimensional metallacyclic polypseudorotaxanes that utilize both metal–ligand and crown ether-dialkyl-
ammonium noncovalent interactions are described. Judiciously combining complementary diplatinum(II)
acceptors with bispyridyl donor building blocks, with an acceptor and/or donor possessing a pendant
dibenzo[24]crown-8 (DB24C8) moiety, allows for the formation of three new rhomboidal bis-DB24C8, one
new hexagonal tris-DB24C8, and four new hexakis-DB24C8 metallacyclic polygons in quantitative yields.
The size and shape of each assembly, as well as the location and stoichiometry of the DB24C8 macrocycle,
can be precisely controlled. Each polygon is able to complex two, three, or six dibenzylammonium ions
without disrupting the underlying metallacyclic polygons, thus producing eight different poly[2]pseudorotaxanes
and demonstrating the utility and scope of this orthogonal self-assembly technique. The assemblies are
characterized with one-dimensional multinuclear (1H and 31P) and two-dimensional (1H-1H COSY and
NOESY) NMR spectroscopy as well as mass spectrometry (ESI-MS). Further analysis of the size and
shape of each assembly is obtained through molecular force-field simulations. 1H NMR titration experiments
are used to establish thermodynamic binding constants and poly[2]pseudorotaxane/dibenzylammonium
stoichiometries. Factors influencing the efficiency of poly[2]pseudorotaxane formation are discussed.
The use of noncovalent interactions in modern synthetic
chemistry allows for the selective and spontaneous formation,
through the dynamic self-assembly of reversible yet robust
linkages, of stable, highly complex supramolecular structures
with specific functionalities, architectures, topologies, and/or
properties.1 One of the chief motivating factors for exploring
supramolecular chemistry is the desire to synthesize new robust,
functional, and technologically important materials. Many
examples2 from nature have demonstrated the power of self-
assembly in constructing biologically relevant materials in which
the self-assembled whole is greater than the sum of its parts. In
biological ensembles such as collagen and enzymes,3 for
example, the combination of the individual molecular compo-
nents is not solely responsible for their unique properties. Rather,
their unique properties depend heavily on the specific spatial
orientations of multicomponent structures that result from natural
self-assembly and molecular organization. With the aim of
obtaining a deeper understanding of the nature of such biological
processes, a great deal of effort has been put forth to investigate
artificial functional supramolecular systems.4 Although the
promise and potential of supramolecules that are obtained
through accurately controlling chemical structure and function-
ality at the macromolecular level is considerable, it should be
realized that this is not a simple process given the distinctive
features of macromolecules compared to small molecules (e.g.,
number of functional groups, molecular weight distribution,
purification techniques, etc.). Therefore, the elucidation of
nanoscale molecular synthetic protocols that proceed with
structural fidelity and a high level of functional group compat-
ibility remains a great challenge.
Coordination-driven self-assembly has proven to be a highly
efficient strategy for the construction of discrete two-dimensional
(2-D) and three-dimensional (3-D) architectures with well-
† University of Utah.
§ North Carolina State University.
(1) (a) Lehn, J.-M. Angew. Chem., Int. Ed. 1990, 29, 1304. (b) Philip,
D.; Stoddart, J. F. Angew. Chem., Int. Ed. 1996, 35, 1155. (c)
Whitesides, G. M.; Grzybowski, B. Science 2002, 295, 2418. (d) Lehn,
J. M. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4763. (e) Hori, A.;
Yamashita, K.-I.; Fujita, M. Angew. Chem., Int. Ed. 2004, 43, 5016.
(2) (a) Kushner, D. J. Bacteriol ReV. 1969, 33, 302. (b) Gellman, S. H.
Chem. ReV. 1997, 97, 1231. (c) Neidle, S. Oxford Handbook of Nucleic
Acid Structure; Oxford University Press: Oxford, 1999. (d) Jones,
M. N.; Chapman, D. Micelles, Monolayers, and Biomembranes;Wiley-
Liss: New York, 1995. (e) Kauffman, S. At Home in the UniVerse:
the Search for Laws of Self Organization and Complexity; Oxford
University Press: New York, 1995.
(4) (a) Ikkala, O.; Brinke, G. Science 2002, 295, 2407. (b) Fiedler, D.;
Bergman, R. G.; Raymond, K. N. Angew. Chem., Int. Ed. 2006, 45,
745. (c) Pluth, M. D.; Bergman, R. G.; Raymond, K. N. Science 2007,
316, 85. (d) Yoshizawa, M.; Tamura, M.; Fujita, M. Science 2006,
312, 251. (e) Nishioka, Y.; Yamaguchi, T.; Yoshizawa, M.; Fujita,
M. J. Am. Chem. Soc. 2007, 129, 7000. (f) Leung, D. H.; Bergman,
R. G.; Raymond, K. N. J. Am. Chem. Soc. 2007, 129, 2746. (g) Qin,
L.; Banholzer, M. J.; Xu, X.; Huang, L.; Mirkin, C. A. J. Am. Chem.
Soc. 2007, 129, 14870. (h) Masar, M. S., III; Gianneschi, N. C.; Oliveri,
C. G.; Stern, C. L.; Nguyen, S. T.; Mirkin, C. A. J. Am. Chem. Soc.
2007, 129, 10149. (i) Gianneschi, N. C.; Bertin, P. A.; Nguyen, S. T.;
Mirkin, C. A.; Zakharov, L. N.; Rheingold, A. L. J. Am. Chem. Soc.
2003, 125, 10508.
(3) (a) Horne, R. W. Virus Structure; Academic Press: New York, 1974.
(b) Groll, M.; Dizel, L.; Löwe, J.; Stock, D.; Bochter, M.; Bartunik,
H. D.; Huber, R. Nature 1997, 386, 463.
9
5320 J. AM. CHEM. SOC. 2008, 130, 5320–5334
10.1021/ja711502t CCC: $40.75
2008 American Chemical Society

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
defined shapes and sizes.5 However, many of the ensembles
prepared to date have been built from simple, fairly inert
building blocks that are often aliphatic or aromatic in nature.
Stimulated by the possibility of constructing artificial functional
nanoscale devices with predesigned shapes and sizes, recent
efforts have focused on incorporating functionality into the final
discrete assemblies.6,7 For example, we have previously reported
the facile synthesis of snowflake-shaped metallodendrimers with
hexagonal cavities as their cores.6c Fujita and co-workers have
prepared saccharide-coated M12L24 molecular spheres that form
aggregates through multiple interactions with proteins.7e En-
couraged by the power and versatility of coordination-driven
self-assembly in the design and synthesis of novel supramo-
lecular species with desired functionality, we envisioned that
the specific control over chemical structure and functionality
at the macromolecular level can be realized by employing the
coordination-driven strategy and can allow for the formation
of more complicated multiple functional architectures, such as
multiple crown ether derivatives and higher-order pseudo-
rotaxanes.
Figure 1. Molecular structures of 120° DB24C8-containing acceptor and
120° DB24C8-containing donor.
Since first introduced by Pedersen in 1967,8 crown ethers
and their structural analogues have attracted significant attention
from various fields of science, as can be illustrated by numerous
literature reports of their applications in host–guest chemistry
and the construction of structurally interesting molecular ar-
chitectures.9 During the past two decades, considerable research
interest has been devoted to the design of multiple crown ether
derivatives, which can be used in multicomponent host–guest
recognition or in the construction of higher-order complexes.10
However, considering the time-consuming procedures and low
yields generally achieved by traditional covalent synthetic
strategies, noncovalent synthetic methodologies may provide a
new path for the formation of such sophisticated compounds.
In addition, crown ethers, along with other macrocycles such
as cyclodextrins, cucurbiturils, and tetracationic cyclobis(par-
aquat-p-phenylene) cyclophanes, have been extensively used for
the construction of rotaxanes and pseudorotaxanes.11 As a
consequence of their structural properties and potential applica-
tions as nanoscale devices, chemists have been inspired to
prepare novel interwoven architectures based upon polyrotax-
anes and polypseudorotaxanes.12 Nevertheless, systematic in-
vestigations of the synthesis of polypseudorotaxanes, especially
higher-order polypseudorotaxanes, are still rare.
As indicated above, the incorporation of functionality into
well-defined 2-D and 3-D ensembles can be achieved by
coordination-driven self-assembly.6,7 More importantly, this
methodology allows for precise control over each parameter of
composition, structure, and overall macromolecular topology.
We have previously reported a highly efficient approach to
prepare tris(dibenzo[24]crown-8) derivatives and hexagonal
cavity-cored tris[2]pseudorotaxanes.6d Herein, we present a
much extended investigation of the self-assembly of different
sized and shaped multiple crown ether derivatives and
poly[2]pseudorotaxanes, from bis[2]pseudorotaxanes up to
hexakis[2]pseudorotaxanes, thus demonstrating the wide-ranging
efficiency and applicability of this approach.
(5) (a) Stang, P. J.; Olenyuk, B. Acc. Chem. Res. 1997, 30, 502. (b)
Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853.
(c) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972. (d)
Schwab, P. F. H.; Levin, M. D.; Michl, J. Chem. ReV. 1999, 99, 1863.
(e) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40,
2022. (f) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001,
34, 759. (g) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc.
Chem. Res. 2005, 38, 369. (h) Fiedler, D.; Leung, D. H.; Bergman,
R. G.; Raymond, K. N. Acc. Chem. Res. 2005, 38, 349. (i) Gianneschi,
N. C.; Masar, M. S., III.; Mirkin, C. A. Acc. Chem. Res. 2005, 38,
825.
(6) (a) Yang, H.-B.; Das, N.; Huang, F.; Hawkridge, A. M.; Diaz, D. D.;
Arif, A. M.; Finn, M. G.; Muddiman, D. C.; Stang, P. J. J. Org. Chem.
2006, 71, 6644. (b) Yang, H.-B.; Das, N.; Huang, F.; Hawkridge,
A. M.; Muddiman, D. C.; Stang, P. J. J. Am. Chem. Soc. 2006, 128,
10014. (c) Yang, H.-B.; Hawkridge, A. M.; Huang, S. D.; Das, N.;
Bunge, S. D.; Muddiman, D. C.; Stang, P. J. J. Am. Chem. Soc. 2007,
129, 2120. (d) Yang, H.-B.; Ghosh, K.; Northrop, B. H.; Zheng, Y.-
R.; Lyndon, M. M.; Muddiman, D. C.; Stang, P. J. J. Am. Chem. Soc.
2007, 129, 14187. (e) Yang, H.-B.; Ghosh, K.; Zhao, Y.; Northrop,
B. H.; Lyndon, M. M.; Muddiman, D. C.; White, H. S.; Stang, P. J.
J. Am. Chem. Soc. 2008, 130, 839.
A new novel dibenzo[24]crown-8 (DB24C8)-containing 120°
di-Pt(II) acceptor building block has been designed and prepared.
A series of different sized and shaped multiple crown ether
derivatives can be formed in nearly quantitative yield when this
new 120° DB24C8 di-Pt(II) acceptor and/or the known 120°
DB24C8 dipyridyl donor6d (Figure 1) are combined with
different complementary angle precursors (donors or acceptors)
via coordination-driven self-assembly in one single step. A
reasonable extension of these strategies is the utilization of
(7) (a) Merlau, M. L.; Del Pilar Mejia, M.; Nguyen, S. T.; Hupp, J. T.
Angew. Chem., Int. Ed. 2001, 40, 4239. (b) Sun, S.-S.; Stern, C. L.;
Nguyen, S. T.; Hupp, J. T. J. Am. Chem. Soc. 2004, 126, 6314. (c)
Murase, T.; Sato, S.; Fujita, M. Angew. Chem., Int. Ed. 2007, 46, 1083.
(d) Kawano, M.; Kawamichi, T.; Haneda, T.; Kojima, T.; Fujita, M.
J. Am. Chem. Soc. 2007, 129, 15418. (e) Kamiya, N.; Tominaga, M.;
Sato, S.; Fujita, M. J. Am. Chem. Soc. 2007, 129, 3816.
(10) (a) Sasaki, S.; Shionoya, M.; Koga, K. J. Am. Chem. Soc. 1985, 107,
3371. (b) Voyer, N. J. Am. Chem. Soc. 1991, 113, 1818. (c) Voyer,
N.; Roby, J.; Deschenes, D.; Bernier, J. Supramol. Chem. 1995, 5,
61. (d) Huang, Z. B.; Chang, S. H. Synlett 2005, 14, 2257. (e) Tanaka,
M.; Higuchi, Y.; Adachi, N.; Shibutani, Y.; Ahmed, S. A.; Kado, S.;
Nakamura, M.; Kimura, K. Tetrahedron 2005, 61, 8159. (f) Dykes,
G. M.; Smith, D. K. Tetrahedron 2003, 59, 3999. (g) Sathiyendiran,
M.; Liao, R.-T.; Thanasekaran, P.; Luo, T.-T.; Venkataramanan, N. S.;
Lee, G.-H.; Peng, S.-M.; Lu, K.-L. Inorg. Chem. 2006, 45, 10052.
(h) Li, C.; Law, G-L.; Wong, W.-T. Org. Lett. 2004, 6, 4841.
(8) Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 7017.
(9) For recent reviews on crown ether and its analogues, see: (a) Bradshaw,
J. S.; Izatt, R. M. Acc. Chem. Res. 1997, 30, 338. (b) Gokel, G. W.;
Leevy, W. M.; Weber, M. E. Chem. ReV. 2004, 104, 2723. (c) Jarosz,
S.; Listkowski, A. Curr. Org. Chem. 2006, 10, 643. (d) Steed, J. W.
Coord. Chem. ReV. 2001, 215, 171. (e) Ritch, J. S.; Chivers, T. Angew.
Chem., Int. Ed. 2007, 46, 4610. (f) Tsukube, H. Coord. Chem. ReV.
1996, 148, 1.
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5321

A R T I C L E S
Ghosh et al.
Scheme 1. Retrosynthetic Analysis of Multiple Crown Ether Derivatives with Cavities of Varying Size and Shape
multiple crown ethers to incorporate dialkylammonium ions
(R2NH2+) for the formation of poly[2]pseudorotaxanes. By
employing the non-interfering, orthogonal nature13 of weak
hydrogen bonding and electrostatic forces and relatively strong
metal–ligandcoordinationbonding,aseriesofpoly[2]pseudorotaxanes
with well-designed shapes and different sized cavities was
obtained. It is worth noting that, to the best of our knowledge,
this is the first report of the formation of discrete hexakis-
DB24C8 derivatives and hexakis[2]pesudorotaxanes, which
further enriches the library of higher-order supramolecular
host–guest architectures.
individual 2-D polygon is usually determined by the value of
the turning angle within its angular components. For example,
the combination of 60° units with complementary 120° linking
components will yield a molecular rhomboid. Planar hexagonal
structures can be self-assembled in two different ways based
on the above-mentioned models. Discrete hexagonal entities of
type A2 L2 can be self-assembled from a combination of six
6
6
shape-defining and directing corner units A2 (containing two
coordination sites which enclose a 120° angle) with six
appropriate linear linker units L2 (containing two coordination
sites oriented 180° from each other). An alternative route for
the assembly of hexagonal supramolecular systems involves the
combination of two complementary ditopic building blocks, A2
and X2, each incorporating 120° angles between the active
coordination sites, allowing for the formation of hexagonal
structures of type A2 X2 .5a
Results and Discussion
Retrosynthetic Analysis of Polygonal Multiple Crown
Ether Derivatives. According to the “directional bonding” model
and the “symmetry interaction” model,5 the shape of an
3
3
By synthesizing a diverse library of donor and acceptor
building blocks, two complementary strategies have been
devised in order to construct “isomeric” supramolecular struc-
tures possessing the same geometry, though the turning angle
of component donor and acceptor building blocks has been
reversed. An example of such self-assembled structures can be
found in the synthesis of cuboctahedra,14a where a pair of
matching cages was assembled from two complementary sets
of angular and tritopic building units. Similar reasoning has been
applied in other nanoscopic cages, such as truncated tetrahedra
and supramolecular M3L2prisms.14b,c
Complementary self-assembly strategies that utilize crown
ether-derivatized 120° donors and/or 120° acceptors are explored
herein to prepare bis-, tris-, and hexakis-DB24C8 derivatives
in one single step. Retrosynthetically, the concept used to
prepare multiple crown ether-derivitized molecular polygons is
summarized in Scheme 1. This coordination-driven self-as-
sembly strategy for introducing crown ether moieties on the
periphery of molecular polygons not only provides a strategy
that can be built upon to devise additional routes to function-
alized molecular polygons but also allows for a direct com-
parison of the properties of the multiple crown ether structures
obtained from complementary units.
(11) (a) Catenanes, Rotaxanes, and Knots; Schill, G., Ed.; Academic Press:
New York, 1971. (b) Molecular Catenanes, Rotaxanes and Knots;
Dietrich-Buchecker, C. O., Sauvage, J. P., Eds.; Wiley-VCH: New
York, 1999. (c) Sauvage, J. P. Acc. Chem. Res. 1990, 23, 319. (d)
Hoss, R.; Vögtle, F. Angew. Chem., Int. Ed. 1994, 33, 375. (e)
Amabilino, D. B.; Stoddart, J. F. Chem. ReV. 1995, 95, 2725. (f) Jäger,
R.; Vögtle, F. Angew. Chem., Int. Ed. 1997, 36, 930. (g) Nepogodiev,
S. A.; Stoddart, J. F. Chem. ReV. 1998, 98, 1959. (h) Sauvage, J. P.
Acc. Chem. Res. 1998, 31, 611. (i) Raymo, F. M.; Stoddart, J. F. Chem.
ReV. 1999, 99, 1643. (j) Tian, H.; Wang, Q.-C. Chem. Soc. ReV. 2006,
35, 361. (k) Wenz, G.; Han, B.-H.; Mueller, A. Chem. ReV. 2006,
106, 782. (l) Loethen, S.; Kim, J.-M.; Thompson, D. H. Polym. ReV.
2007, 47, 383.
(12) (a) Liu, Y.; Yu, L.; Chen, Y.; Zhao, Y.-L.; Yang, H. J. Am. Chem.
Soc. 2007, 129, 10656. (b) Park, C.; Oh, K.; Lee, S. C.; Kim, C. Angew.
Chem., Int. Ed. 2007, 46, 1455. (c) Hoffart, D. J.; Loeb, S. J. Angew.
Chem., Int. Ed. 2005, 44, 901. (d) Huang, F.; Nagvekar, D. S.;
Slebodnick, C.; Gibson, H. W. J. Am. Chem. Soc. 2005, 127, 484. (e)
Lo Nostro, P.; Lopes, J. R.; Cardelli, C. Langmuir 2001, 17, 4610. (f)
Yamaguchi, N.; Nagvekar, D. S.; Gibson, H. W. Angew. Chem., Int.
Ed. 1998, 37, 2361. (g) Gibson, H. W.; Yamaguchi, N.; Jones, J. W.
J. Am. Chem. Soc. 2003, 125, 3522. (h) ten Cate, A. T.; Kooijman,
H.; Spek, A. L.; Sijbesma, R. P.; Meijer, E. W. J. Am. Chem. Soc.
2004, 126, 3801. (i) Yelamaggad, C. V.; Achalkumar, A. S.; Rao,
D. S. S.; Prasad, S. K. J. Am. Chem. Soc. 2004, 126, 6506. (j) Kim,
H. J.; Zin, W. C.; Lee, M. J. Am. Chem. Soc. 2004, 126, 7009.
(13) (a) Pollino, J. M.; Stubbs, L. P.; Weck, M. Polym. Prepr. 2003, 44,
730. (b) Pollino, J. M.; Stubbs, L. P.; Weck, M. J. Am. Chem. Soc.
2004, 126, 563. (c) Hofmeier, H.; El-ghayoury, A; Schenning,
A. P. H. J.; Schubert, U. S. Chem. Commun. 2004, 318. (d) Hofmeier,
H.; Hoogenboom, R.; Wouters, M. E. L.; Schubert, U. S. J. Am. Chem.
Soc. 2005, 127, 2913. (e) Kishore, R. S. K.; Paululat, T.; Schmittel,
M. Chem. Eur. J. 2006, 12, 8136. (f) Kishore, R. S. K.; Kalsani, V.;
Schmittel, M. Chem. Commun. 2006, 3690.
(14) (a) Olenyuk, B.; Whiteford, J. A.; Fechtenkotter, A.; Stang, P. J. Nature
1999, 398, 796. (b) Kryschenko, Y. K.; Seidel, S. R.; Muddiman, D. C.;
Nepomuceno, A. I.; Stang, P. J. J. Am. Chem. Soc. 2003, 125, 9647.
(c) Leininger, S.; Fan, J.; Schmitz, M.; Stang, P. J. Proc. Natl. Acad.
Sci. 2000, 97, 1380.
9
5322 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
Scheme 2. Synthesis of 120° Angular Di-Pt(II) Acceptor Subunit 5a
a Key: (a) (trimethylsilyl)acetylene, Pd(PPh3)4, CuI, Et3N, THF, room
temperature, 16 h (80%); (b) NaHCO3, methanol/THF/water, reflux, 12 h
(95%); (c) DB24C8 carboxylic acid, DCC, DMAP, CH2Cl2, room temper-
ature, 10 h (85%); (d) CuI, Et2NH, toluene, room temperature, 16 h (65%);
(e) AgOTf, CH2Cl2, room temperature, 4 h (90%).
Scheme 3. Two Complementary Ways To Self-Assemble
Rhomboidal Bis-DB24C8 Derivatives
Figure 2. Partial 1H NMR (500 MHz, CD2Cl2, 298 K) spectra of free
building blocks 5 (A), 6 (B), and 8 (D) and rhomboids 7 (C), 11 (E), and
12 (F).
C-H bonds in alkynes as the key step to the synthesis of a
novel 120° acceptor unit.
The 120° crown ether-containing di-Pt(II) acceptor 5 can be
easily synthesized as indicated in Scheme 2. 3,5-Diethynyl-
phenol (2) was prepared by palladium-mediated coupling of
acetic acid 3,5-dibromo-phenyl ester (1) with (trimethyl-
silyl)acetylene, followed by deprotection in a methanol/THF/
water solvent mixture. The crown ether moiety was introduced
by a coupling reaction of 2 with dibenzo[24]crown-8 carboxylic
acid. Compound 3 was then reacted with 4 equiv of trans-
PtI2(Et3)2 to give diiodometal complex 4 in accordance with a
similar procedure reported in the literature.17 Subsequent halogen
abstraction with AgOTf resulted in the isolation of bistriflate
salt 5 in reasonable yield (38% overall). In the 31P NMR
spectrum, the diplatinum acceptor 5 displayed a singlet at 22.7
ppm, accompanied by flanking 195Pt satellites. Attempts to grow
single crystals for X-ray diffraction studies of 5 failed; therefore,
(15) (a) Yang, H.-B.; Ghosh, K.; Arif, A. M.; Stang, P. J. J. Org. Chem.
2006, 71, 9464. (b) Yang, H.-B.; Ghosh, K.; Das, N.; Stang, P. J.
Org. Lett. 2006, 8, 3991. (c) Werner, H.; Bachmann, P.; Martin, M.
Can. J. Chem. 2001, 79, 519. (d) John, K. D.; Hopkins, M. D. Chem.
Commun. 1999, 589. (e) Werner, H.; Bachmann, P.; Laubender, M.;
Gevert, O. Eur. J. Inorg. Chem. 1998, 1217. (f) Wong, W.-Y.; Wong,
C.-K.; Lu, G.-L.; Lee, A. W.-M.; Cheah, K.-W.; Shi, J.-X. Macro-
molecules 2003, 36, 983. (g) Berenguer, J. R.; Bernechea, M.; Fornies,
J.; Lalinde, E.; Torroba, J. Organometallics 2005, 24, 431. (h) Vicente,
J.; Chicote, M.-T.; Alvarez-Falcon, M. M.; Jones, P. G. Organome-
tallics 2005, 24, 2764.
Synthesis of Angular 120° Crown Ether-Functionalized
Acceptor Unit. The acidity of C-H bonds in alkynes induced
by transition metals has received considerable attention in
organometallic chemistry.15 By taking advantage of the linear
geometry of the alkynyl unit and its π-unsaturated character,
the metal alkynyls have been extensively explored to prepare
molecular wires and polymeric organometallic materials, which
may possess interesting properties such as optical nonlinearity,
luminescence, liquid crystallinity, and electrical conductivity.16
Herein we utilize the coupling reaction of trans-PtI2(PEt3)2 with
(16) (a) Paul, F.; Lapinte, C. Coord. Chem. ReV. 1998, 178–180, 431. (b)
Ziessel, R.; Hissler, M.; El-ghayoury, A.; Harriman, A. Coord. Chem.
ReV. 1998, 178–180, 1251. (c) Nguyen, P.; Go´mez-Elipe, P.; Manners,
I. Chem. ReV. 1999, 99, 1515. (d) Dembinski, R.; Bartik, T.; Bartik,
B.; Jaeger, M.; Gladysz, J. A. J. Am. Chem. Soc. 2000, 122, 810. (e)
Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586.
(17) Leininger, S.; Stang, P. J.; Huang, S. Organometallics 1998, 17, 3981.
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5323

A R T I C L E S
Ghosh et al.
Figure 3. Calculated (top) and experimental (bottom) ESI-MS spectra of rhomboids 7 (A), 11 (B), and 12 (C).
Scheme 4. Two Complementary Ways To Self-Assemble
Hexagonal Tris-DB24C8 Derivatives
the distance between the two platinum centers was estimated
using molecular mechanics force-field (MMFF) simulations and
shown to be ∼1.0 nm (see Supporting Information). It is worth
noting that compound 5 is unique in the sense that it carries
sites for multiple recognition: the crown ether can recognize
cations or small organic compounds and the Pt(II) center can
act as an acceptor unit to a variety of ligands.
Self-Assembly of Rhomboidal Bis-DB24C8 Derivatives. With
the 120° crown ether-containing precursorssboth donor and
acceptorsin hand, the self-assembly of crown ether derivatives
with rhomboidal cavities was investigated. As discussed above,
the combination of 60° units with 120° linking components will
yield a molecular rhomboid. Upon mixing the newly designed
120° acceptor unit 5 and the 60° donor 6 in dichloromethane,
bis-DB24C8 rhomboid 7 was obtained (Scheme 3, Method I).
In a complementary manner (Scheme 3, Method II), stirring
the crown ether-containing 120° angular donor 8 with an
equimolar amount of the known 60° angular Pt(II) acceptor,
2,9-(trans-Pt(PEt3)2NO3)2-phenanthrene (9), in dichloromethane
resulted in the rhomboidal structure 11. By using different sized
60° angular Pt(II) acceptors, the size of the rhomboidal cavity
in the final assemblies can be controlled. For example, stirring
acceptor 10 with 120° donor unit 8 for 30 min in dichlo-
romethane gave bis-DB24C8 rhomboid 12, which possesses a
slightly larger rhomboidal cavity size compared to ensemble
11. Molecular modeling studies show an inner cavity diameter
of 1.6 nm for 11, whereas the cavity diameter of 12 is 2.0 nm
(see Supporting Information).
to be inequivalent, likely due to a slightly twisted structure
resulting from the flexibility of the triple bonds in both acceptor
and donor units. Moreover, in accordance with the previously
reported molecular rectangles and trigonal bipyramidal cages,
the inner and outer pyridyl protons of 11 are found to be
inequivalent because of restricted rotation around the Pt-pyridine
bond.6a,14a,18
Mass spectrometric studies of all three rhomboids were
performed using the electrospray ionization mass spectral (ESI-
MS) technique, which allows the assemblies to remain intact
during the ionization process while obtaining the high resolution
required for isotopic distribution. In the ESI-MS spectrum of
rhomboid 7 (Figure 3A), for example, peaks attributable to the
loss of triflate counterions, [M - 2OTf]2+ (m/z ) 2006.6) and
[M - 3OTf]3+ (m/z ) 1287.7), where M represents the intact
assembly, were observed and their isotopic resolutions are in
excellent agreement with the theoretical distributions. Similarly,
The self-assembly of rhomboids 7, 11, and 12 was monitored
by multinuclear NMR spectroscopy. Analysis of the 31P NMR
spectrum of each reaction solution is consistent with the
formation of highly symmetric species, by the appearance of a
sharp singlet (16.0 ppm for 7, 12.6 ppm for 11, and 16.1 ppm
for 12, each with concomitant 195Pt satellites), shifted by 6.7,
8.4, and 7.0 ppm upfield for 7, 11, and 12 relative to the signals
for the starting acceptor units 6, 9, and 10, respectively.
1
Examination of the H NMR spectra (Figure 2) also indicates
1
the existence of highly symmetric structures. The H NMR
spectra display significant downfield shifts of the pyridyl proton
signals (for R proton, ∆δ ) 0.02 ppm for 7, 0.11 ppm for 11,
and 0.10 ppm for 12; for ꢀ proton, ∆δ ) 0.41 ppm for 7, 0.20
ppm for 11, and 0.43 ppm for 12), associated with the loss of
electron density upon coordination by the nitrogen lone pair to
platinum metal centers. An interesting dynamic effect was
observed in rhomboid 7, where the H4 proton signals are found
(18) Tarkanyi, G.; Jude, H.; Palinkas, G.; Stang, P. J. Org. Lett. 2005, 7,
4971.
9
5324 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
Figure 4. Partial 1H NMR spectra of free building blocks 5 (A) and 13 (B) and hexagon 14 (C).
Figure 5. Calculated (top) and experimental (bottom) ESI-MS spectra of hexagonal tris-DB24C8 derivative 14 (A) and hexagonal hexakis-DB24C8 derivative
19 (B). ESI-TOF-MS spectrum of hexagonal hexakis-DB24C8 derivative 25 (C). The vertical arrows are the theoretical abundances.
the ESI-MS spectra of rhomboids 11 and 12 (Figure 3B,C),
exhibited two charged states at m/z ) 1857.7 and m/z ) 1218.1
satellites (∆1JPPt ) - 84.7 Hz), is consistent with back-donation
1
from complexed platinum atoms. In the H NMR spectrum
for 11, corresponding to [M - 2NO3]2+ and [M - 3NO3]3+
,
(Figure 4), the ꢀ protons displayed a dramatic downfield shift
(∆δ ) 0.65 ppm) with respect to those of free donor 13 and
the R protons shifted slightly as well (∆δ ) 0.10 ppm). ESI-
MS spectrometry provides further evidence for the formation
of the new hexagonal assembly 14. In the mass spectrum of 14
(Figure 5A), peaks at m/z ) 2790.3 and m/z ) 1320.4,
corresponding to [M - 2 OTf]2+ and [M - 3OTf]3+, respec-
tively, were observed, and their isotopic resolutions are all in
excellent agreement with their theoretical distributions. Molec-
ular modeling studies reveal a smaller internal diameter of 2.3
nm for 14 as compared to 3.2 and 2.9 nm for 17 and 18,
respectively (see Supporting Information).
Self-Assembly of Hexgonal Hexakis-DB24C8 Derivatives. A
more dramatic extension of functionalization by means of
coordination-driven self-assembly is manifested in the construc-
tion of molecular hexagons with six crown ethers, where each
crown ether moiety is on each of the vertices of the hexagon.
As indicated in Scheme 5, six crown ethers can be introduced
in molecular hexagons along three routes. The first method
investigated utilizes three 120° donor units and three 120°
acceptor units, each derivatized with one crown ether moiety,
from which the [3+3] hexagon 19 can be self-assembled
(Scheme 5, Method I).
and at m/z ) 1992.1 and m/z ) 1278.4 for 12, attributable to
[M - 2OTf]2+ and [M - 3OTf]3+, respectively. These peaks
were isotopically resolved, and they agree very well with their
theoretical distribution.
Self-Assembly of Hexgonal Tris-DB24C8 Derivatives. Re-
cently, in a preliminary communication, we have reported6d the
self-assembly of tris-DB24C8 derivatives with hexagonal cavi-
ties through the combination of the 120° DB24C8-derivatized
donor subunit 8 with 120° di-Pt(II) acceptor 15 or 16 in a 1:1
stoichiometric ratio (Scheme 4, Method II). An extended
investigation into the viability of preparing similar types of tris-
DB24C8 derivatives employing a complementary approach has
now been undertaken. As shown in Scheme 4 (Method I), the
hexagonal tris-DB24C8 derivative 14 can also be easily
synthesized by simply mixing the 120° DB24C8-containing
acceptor subunit 5 and di-2-pyridyl ketone (13) in a 1:1 ratio
in dichloromethane.
The 31P NMR spectrum of 14 displayed a sharp singlet (ca.
16.0 ppm) shifted upfield from the signal for the starting
platinum donor 5 by approximately 6.7 ppm, which suggests
the formation of a discrete, highly symmetric assembly. This
change, as well as the decrease in coupling of the flanking 195Pt
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5325

A R T I C L E S
Ghosh et al.
Scheme 5. Three Ways To Self-Assemble Hexagonal
Hexakis-DB24C8 Derivatives
180° linear 4,4′-bipyridyl donor 24 (Scheme 5, Method III),
demonstrating a complementary method for the preparation of
hexagonal hexakis-DB24C8 assembly 25. After 30 min of
continuous stirring at room temperature, initial visual evidence
of the completion of self-assembly processes was indicated by
the complete dissolution of starting materials and formation of
a homogeneous yellow solution. More quantitative evidence of
successful self-assembly was then obtained from characteristic
changes observed in each assembly’s NMR spectra. In all three
cases, the analysis of 31P NMR spectra of the reaction solution
is consistent with the formation of highly symmetric species,
as indicated by the appearance of one sharp singlet (-14.8 ppm
for 22, 14.1 ppm for 23, and 16.3 ppm for 25) with concomitant
195Pt satellites shifted upfield from the signals for their respective
acceptor building blocks (∆δ ) 8.5 ppm for 22, 8.1 ppm for
23, and 6.4 ppm for 25). As expected, a decrease in coupling
of the flanking 195Pt signals (∆1JPPt ) -130 Hz for 22, ∆1JPPt
) -155 Hz for 23, and ∆1JPPt ) -67 Hz for 25) was also
observed. Examination of the 1H NMR spectrum (Figure 6) of
each assembly is also indicative of highly symmetric structures.
Only one set of peaks in the final self-assembly, arising from
donor and acceptor units, and significant downfield shifts of
the pyridyl proton signals (for R proton, ∆δ ) 0.11 ppm for
22, 0.23 ppm for 23, and 0.10 ppm for 25; for ꢀ proton, ∆δ )
0.36 ppm for 22, 0.43 ppm for 23, and 0.93 ppm for 25),
associated with the loss of electron density on coordination of
the nitrogen lone pair to the platinum metal center, support the
efficient self-assembly of hexagons 22, 23, and 25. The sharp
nature of the peaks supports the formation of molecular
hexagons with six crown ethers as opposed to the formation of
oligmers, which would significantly broaden the proton signals.
Compared to the previous multiple crown ether derivatives
(7, 11, 12, 14, and 17–19), it has proven more difficult to get
strong mass signals for dodeca-cationic ensembles 22, 23, and
25, on account of their larger molecular weight, even under the
ESI-TOF-MS conditions. Hexagonal crown ether derivative 23,
as a representative example, has a molecular weight of 12411
Da (C498H672N12O90P24Pt12S12). With considerable effort, the
peak attributable to [M - 5OTf]5+ (m/z ) 2167.6) was observed
(Figure 5C) for 25 in the ESI-TOF-MS spectrum, along with
isotopically resolved peaks (i.e., direct charge state determina-
tion), allowing for the molecularity of the crown ether-
derivatized hexagon to be unambiguously established. For
assemblies 22 and 23, a peak corresponding to [M - 5OTf]5+
was also observed in each ESI-MS spectrum; however, neither
peak could be isotopically well resolved because of the high
molecular weight of assemblies 22 and 23 (see Supporting
Information).
Stirring a mixture of acceptor (5) and donor (8) precursors
in a 1:1 ratio in dichloromethane for 45 min results in a
homogeneous clear yellow-orange solution. The 31P NMR
spectrum of this solution displayed a sharp singlet (ca. 18.3 ppm)
shifted upfield from the signal for the starting platinum acceptor
5 by approximately 4.4 ppm. Moreover, a decrease in coupling
of the flanking 195Pt satellites (∆J ≈ -65 Hz) was observed.
In the 1H NMR spectrum (Figure 6C), the proton signals of the
pyridine ring hydrogen atoms exhibited downfield shifts (ca.
R-HPy, 0.1 ppm; ꢀ-HPy, 0.4 ppm) typically observed upon
coordination with Pt(II) complexes. ESI-MS spectrometry
provides further evidence for the formation of the new hexagonal
assembly 19. In the mass spectrum of 19, peaks at m/z ) 3649.2
and m/z ) 1750.3, corresponding to [M - 2 OTf]2+ and [M -
4 OTf]4+, respectively were observed, and their isotopic
resolutions are all in excellent agreement with their theoretical
distributions (Figure 5B).
As indicated in the retrosynthetic analysis (Scheme 1), the
synthesis of hexagonal hexakis-DB24C8 assemblies can also
be achieved according to two additional complementary pro-
tocols from the combination of six 180° building blocks and
six 120° angular subunits. The self-assembly of crown ether-
derivatized donor 8 with different sized 180° linear acceptors
21 and 22 (Scheme 5, Method II) was investigated in dichlo-
romethane, leading to the formation of crown ether-derivatized
hexagons 22 and 23, respectively. Along similar lines, crown
ether-derivatized acceptor 5 was combined in a 1:1 ratio with
All attempts to grow X-ray-quality single crystals of the
hexagonal hexakis-DB24C8 derivatives have so far proven
unsuccessful. Therefore, molecular force-field simulations were
used to gain further insight into the structural characteristics of
these assemblies (Figure 7, see also Supporting Information).
A 1.0 ns molecular dynamics simulation (MMFF) was used to
equilibrate each supramolecule, followed by energy minimiza-
tion of the resulting structures to full convergence. Simulations
reveal that the underlying hexagonal structuress“scaffolds”sall
retain their planar and rigid geometries, even when derivatized
with pendent crown ether units. Internal diameters of 3.0, 5.2,
6.2, and 4.5 nm for 19, 22, 23, and 25, respectively, were
observed. The methods outlined in Scheme 4 provide not only
three different means of installing six crown ether units onto
the periphery of molecular hexagons but also a direct, unam-
9
5326 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
Figure 6. Partial 1H NMR spectra (500 MHz, CD2Cl2, 298 K) of free building blocks 5 (A), 13 (B), and 24 (F) and hexagonal hexakis-DB24C8 assemblies
19 (C), 22 (D), 23 (E), and 25 (G).
Figure 7. Simulated molecular model of hexagonal hexakis-DB24C8 derivatives 19, 25, 22, and 23, optimized with the molecular mechanics force field.
Color scheme: C, gray; O, red; N, blue; P, purple; and Pt, yellow (hydrogen atoms have been removed for clarity).
biguous means of varying the cavity size of these cavity-cored
hexakis-crown ether derivatives while retaining the efficiency
(i.e., short reaction time and high yield) of coordination-driven
self-assembly. In all cases, the flexible nature of the pendent
crown ether moieties and the rigid nature of the hexagonal cavity
can be observed from modeling studies.
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5327

A R T I C L E S
Ghosh et al.
Scheme 6. Formation of Rhomboidal Cavity-Cored
Bis[2]pseudorotaxanes
Scheme 7. Formation of Hexagonal Cavity-Cored
Tris[2]pseudorotaxanes
carried out. For many years, crown ethers have been recognized
as exceptionally versatile hosts for a wide variety of cationic
guests, particularly for substituted ammonium ions. Although
initial studies focused primarily upon alkylammonium ions19
(RNH3+), more recently, secondary alkylammonium ions20
(R2NH2+) have received considerable attention. Numerous
experimental investigations have demonstrated that appropriately
+
All of the above collective analytical results indicate that
multiple crown ether derivatives with predesigned shape and
size can be easily prepared (>95% yields) through coordination-
driven self-assembly, which avoids the time-consuming proce-
dures and lower yields often encountered in covalent synthetic
protocols. Previous approaches to the construction of single-
molecule, non-polymeric multiple crown ether units have been
limited to either the attachment of crown ethers to a helical
peptide scaffold or dendritic construction of multiple crown ether
units.10 The approach outlined herein provides an alternative
route to multiple crown ether molecules with different topologies
and arrangements. Furthermore, the synthesis is straightforward
and the yield is quantitative, which eliminates the need for
purification. In particular, to the best of our knowledge, we have
presented the first example wherein six crown ethers are
uniquely and precisely positioned on the periphery of molecular
polygons.
sized crown ether macrocycles bind R2NH2 ions in solution,
in the solid state, and in the gas phase in a threaded rather than
face-to-face manner.21 Consequent to these myriad studies, the
high-affinity binding and molecular recognition motifs operative
in the complexation between dialkylammonium ion centers
(-CH2NH2+CH2-) and different crown ether macrocycles, e.g.,
DB24C8, are well established and understood. Mixing comple-
mentary host and guest components in a 1:1 molar ratio in low-
polarity, nonprotic solvents (e.g., CH2Cl2, CH3CN, etc.) results
in the formation of a pseudorotaxane complex held by strong
[NsH· · ·O] hydrogen bonds between the acidic NH2+ protons
and the oxygen atoms of the DB24C8 ring. Additional
[CsH· · ·O] hydrogen-bonding and π-π stacking interactions,
as well as electrostatic forces, further contribute to the stability
of the resultant pseudorotaxanes. By taking advantage of the
complexation of dibenzylammonium ions (C6H5CH2NH2+CH2-
C6H5) and DB24C8 derivatives as well as the orthogonal, non-
interacting nature of metal–ligand and hydrogen-bonding non-
covalent interactions in solution, we envisioned that a new class
of poly[2]pseudorotaxane complexes could be prepared from
Investigation of the Self-Assembly of Poly[2]pseudorotaxanes.
With these novel multiple crown ether derivatives in hand, an
investigation of the self-assembly of poly[2]pseudorotaxanes was
Figure 8. Calculated (top) and experimental (bottom) ESI-MS spectra of rhomboidal bis[2]pseudorotaxane 27 (A), rhomboidal bis[2]pseudorotaxane 28
(B), and hexagonal tris[2]pseudorotaxane 29 (C).
9
5328 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
Scheme 8. Formation of Hexagonal Cavity-Cored
Hexakis[6]pseudorotaxanes
was observed in both spectra, and protons HR, Hꢀ, and Hγ of
DB24C8 exhibited upfield shifts of 0.03, 0.08, and 0.25 ppm,
respectively. Further characterization with 2-D spectroscopic
techniques (1H-1H COSY and NOESY) are in agreement with
the formation of the rhomboidal cavity-cored bis[2]pseudorotaxanes.
For example, through-space interactions between the R-H proton
of the complexed crown ether and the benzylic methylene protons
were observed in the NOESY spectrum of each complex (see
Supporting Information).
In the 1H NMR spectrum of 28, the formation of bis[2]pseudo-
rotaxane as the prevailing product was supported by the
observation of one dominant set of proton signals (>90% by
integration) along with some signals for partially complexed
and uncomplexed species at equilibrium. In the 1H NMR
spectrum of 27, however, resonances attributable to uncom-
plexed glycol -OCH2CH2O- protons of the crown ether rings
and of free dibenzylammonium (26) were observed. The ratio
of the complexed and uncomplexed species is approximately
1:1, as established by integration. This observation suggests that
either (a) the kinetics of pseudorotaxane self-assembly is
considerably slower for bis[2]pseudorotaxane 27 than for
bis[2]pseudorotaxane 28 or (b) the binding constant of bis-
DB24C8 host 7 is lower than that of the related bis-macrocycle
12. The first of these two possibilities is easily ruled out both
intuitively (the kinetics of assembly should essentially be equal,
given that derivatized macrocycles 7 and 12 have nearly identical
size and structural characteristics) and experimentally (periodi-
molecular polygons functionalized with crown ether moieties
on their periphery. The generation, by three different methods,
of tris[2]pseudorotaxane structures via this orthogonal self-
assembly strategy has been recently reported by our group.6d
Herein we significantly expand upon these preliminary studies
and demonstrate the formation of multiple different shaped and
sized poly[2]pseudorotaxanes in a stepwise manner.
1
cally checking the H NMR spectrum of assembly 27 over
Within 15 min of adding 2 equiv of dibenzylammonium triflate
salt 26 to a solution of rhomboidal bis-DB24C8 derivatives 7 (2.25
mM) and 12 (2.33 mM) in dichloromethane, bis[2]pseudorotaxanes
27 and 28, respectively, with rhomboidal cavities were obtained
(Scheme 6). Compared to the spectra of free hosts 7 and 12, the
31P NMR spectrum of each complex does not exhibit any
significant change, indicating that the threading process of diben-
zylammonium ions does not substantially change the chemical
environment of the phosphorus atoms present in the rhomboids.
several days revealed no changes, indicating that equilibrium
had been reached). It is more likely that the electron-withdraw-
ing effects of the proximal Pt(II) centers of the derivatized crown
ether building block 5 decrease the binding ability of the crown
ether sites of bis-host 7, which in turn decrease the ratio of
complexed to uncomplexed species to 1:1 at equilibrium.
Further quantitative proof of the existence of rhomboidal
cavity-cored bis[2]pseudorotaxanes 27 and 28 is provided by
ESI-MS spectrometry. A peak at m/z ) 1519.5 was observed,
corresponding to [M - 3OTf]3+ for 27, as were peaks
attributable to [M - 2OTf]2+ and [M - 3OTf]3+ of 28 at m/z
) 2340.0 and m/z ) 1510.3, respectively. All peaks were
isotopically resolved, and they agree very well with their
theoretical distribution (Figure 8).
Hexagonal tris-DB24C8 derivatives 17 and 18 can be used
to prepare hexagonal tris[2]pseudorotaxanes 30 and 31 along
three different routes by the orthogonal self-assembly strategy,
as reported previously.6d New tris[2]pseudorotaxane 29, which
exhibits an architecture similar to those of 30 and 31, has been
obtained from the self-assembly of 14 and 26 in a 1:3 ratio
(Scheme 7). The crown ether moieties of tris-host 14 are directly
attached to di-Pt(II) acceptor building blocks rather than
bispyridyl donor building blocks as in 17 and 18, changing the
electronic environment of host 14. In the case of assembly 29,
the equilibrium ratio of complexed to uncomplexed species was
observed to be somewhat less than 1:1, indicating a slight excess
of uncomplexed species. This observation is analogous to the
comparison of rhomboid bis[2]pseudorotaxanes 27 and 28 and
further supports the conclusion that covalent attachment of the
crown ether derivatives to di-Pt(II) acceptors lowers the binding
abilities of the typically electron-rich macrocycles. Despite this
shift in equilibrium, positive assignment of tris[2]pseudorotaxane
29 was obtained through ESI-MS, which revealed a peak at
m/z ) 1580.9, corresponding to [M - 4OTf]4+. Two-
dimensional spectroscopic techniques (1H-1H COSY and
1
The H NMR spectra of 27 and 28, however, displayed charac-
teristic shifts associated with the complexation of dibenzylammo-
nium ion 26 by DB24C8. A 0.45 ppm downfield shift of the signal
+
for the benzylic methylene protons adjacent to the NH2 center
(19) (a) Cram, D. J.; Cram, J. M. Science 1974, 183, 803. (b) Cram, D. J.;
Cram, J. M. Acc. Chem. Res. 1978, 11, 8. (c) Jong, F. D.; Reinhoudt,
D. N. AdV. Phys. Org. Chem. 1980, 17, 279. (d) Cram, D. J.;
Trueblood, K. N. Top. Curr. Chem. 1981, 98, 43. (d) Sutherland, I. O.
Chem. Soc. ReV. 1986, 15, 63. (e) Stoddart, J. F. Top. Stereochem.
1987, 17, 205. (f) Izatt, R. M.; Wang, T.; Hathaway, J. K.; Zhang,
X. X.; Curtis, J. C.; Bradshaw, J. S.; Zhu, C. Y.; Huszthy, P.
J. Inclusion Phenom. 1994, 17, 157.
(20) (a) Yamaguchi, N.; Hamilton, L. M.; Gibson, H. W Angew. Chem.,
Int. Ed. 1998, 37, 3275. (b) Ishow, E.; Credi, A.; Balzani, V.; Spadola,
F.; Mandolini, L. Chem. Eur. J. 1999, 5, 984. (c) Bryant, W. S.; Guzei,
I. A.; Rheingold, A. L.; Gibson, H. W Org. Lett. 1999, 1, 47. (d)
Meillon, J. C.; Voyer, N.; Biron, E.; Sanschagrin, F.; Stoddart, J. F
Angew. Chem., Int. Ed. 2000, 39, 143. (e) Ashton, P. R.; Campbell,
P. J.; Chrystal, E. J. T.; Glink, P. T.; Menzer, S.; Philip, D.; Spencer,
N.; Stoddart, J. F.; Tasker, P. A.; Williams, D. J. Angew. Chem., Int.
Ed. 1995, 34, 1869. (f) Aricó, F.; Badjic´, J. D.; Cantrill, S. J.; Flood,
A. H.; Leung, K. C.-F.; Liu, Y.; Stoddart, J. F. Top. Curr. Chem.
2005, 279, 203.
(21) (a) Ashton, P. R.; Campbell, P. J.; Chrystal, E. J. T.; Glink, P. T.;
Menzer, S.; Philp, D.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.;
Williams, D. J. Angew. Chem., Int. Ed. 1995, 34, 1865. (b) Metcalfe,
J. C.; Stoddart, J. F.; Jones, G. J. Am. Chem. Soc. 1977, 99, 8317. (c)
Krane, J.; Aune, O. Acta Chem. Scand. Ser. B 1980, 34, 397. (d)
Metcalfe, J. C.; Stoddart, J. F.; Jones, G.; Atkinson, A.; Kerr, I. S.;
Williams, D. J. J. Chem. Soc., Chem. Commun. 1980, 540. (e) Abed-
Ali, S. S.; Brisdon, B. J.; England, R. J. Chem. Soc., Chem. Commun.
1987, 1565.
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5329

A R T I C L E S
Ghosh et al.
Figure 9. Partial 1H NMR spectra (500 MHz, CD2Cl2, 298 K) of free hosts 22 (A) and 25 (C) and hexagonal hexakis[2]pseudorotaxanes 32 (B) and 33 (D).
1
NOESY) provided further evidence for the formation of the new
hexagonal tris[2]pseudorotaxane in solution (see Supporting
Information).
that the collective H NMR spectroscopic results are able to
demonstrate the orthogonality of self-assembly along this
stepwise approach to 27–29, 32, and 33: only those signals
associated with the pyridyl functionalities of 7, 12, 14, 22, and
25 shift upon metal coordination, while only those signals
associated with the derivatized DB24C8 macrocycles shift upon
complexation of 26.
The highly efficient coordination-driven self-assembly of
multiple crown ether derivatives, particularly of hexakis-
DB24C8 derivatives, provides the possibility of forming higher-
order [2]pseudorotaxanes such as hexakis[2]pseudorotaxanes.
Reports of such well-defined higher-order pseudorotaxanes have,
to date, proven rare. Hexakis-DB24C8 derivatives 22 and 25
with different sized hexagonal cavities were selected as hosts
to incorporate six dibenzylammonium guests each, thus generat-
ing (Scheme 8) two different hexakis[2]pseudorotaxanes (32
and 33, respectively). The 1H NMR spectra of a 1:6 mixture of
host 22 (4.02 mmol) or 25 (4.13 mmol) and dibenzylammonium
salt 26 in dichloromethane exhibited characteristic shifts as-
sociated with the complexation of dibenzylammonium ions by
DB24C8, analogous to those that have previously been observed
in the 1H NMR spectra of poly[2]pseudorotaxanes 27–29.
Hexakis[2]pseudorotaxane 32 was found to be the main species
in solution, as indicated (Figure 9B) by one dominant set of
Pseudorotaxane Stoichiometry and Thermodynamics. The
host:guest stoichiometry for supramolecular assemblies 27-29,
32, and 33 was established using the nonlinear least-squares fit
1
method22 based on H NMR titration experiments (Figure 10,
also see Supporting Information). Results of these studies
indicate a 1:2 host:guest stoichiometry for both rhomboidal bis-
DB24C8 hosts 7 and 12; a 1:3 host:guest stoichiometry for
hexagonal tris-DB24C8 host 14; and a 1:6 host:guest stoichi-
ometry for both hexakis-DB24C8 hosts 22 and 25, with the
guest in each case being dibenzylammonium salt 26. The
stoichiometric calculations further support the formation of
rhomboidal bis[2]pseudorotaxanes 27 and 28, hexagonal
tris[2]pseudorotaxane 29, and hexagonal hexakis[2]pseudo-
rotaxanes 32 and 33. Fitting the data to a 1:2 binding mode for
hosts 7 and 12, a 1:3 binding mode for host 14, and a 1:6 binding
model for hosts 22 and 25 gave rise to host–guest association
constants based on the 1H NMR titration experiments (see Table
1). These values suggest that all multiple crown ether derivatives
have an ability to bind dibenzylammonium guest(s) similar to
that of DB24C8 in a nonpolar solvent such as dichloromethane.
The difference of the binding ability of each polygonal host
could be determined from these values as well. In all cases, the
covalent attachment of derivatized crown ether macrocycles to
1
proton signals observed in the H NMR spectrum. Similar to
pseudorotaxanes 27 and 29, the generation of hexakis[2]pseudo-
rotaxane 33 results in a nearly 1:1 equilibrium mixture of
complexed and uncomplexed species (Figure 9D) because of
the electron-deficient nature of di-Pt(II)-linked DB24C8 rings.
Further characterization with 2-D spectroscopic techniques
(1H-1H COSY and NOESY) supports the formation of hex-
agonal cavity-cored hexakis[2]pseudorotaxanes 32 and 33. The
NOESY spectrum of each complex, for example, clearly showed
through-space interactions between the R-H protons of the
complexed crown ether derivatives and the benzylic methylene
protons (see Supporting Information). It is important to note
(22) Bourson, J.; Pouget, J.; Valeur, B. J. Phys. Chem. 1993, 97, 4552.
9
5330 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
Figure 10. 1H NMR titration isotherms of 27 (A), 28 (B), 29 (C), 32 (D), and 33 (E), recorded at 500 MHz in CD2Cl2 at 298 K (9 indicates the change
in chemical shift of the proton signal corresponding to the γ-H of the crown ether).
Table 1. Thermodynamic Binding Constants (CD2Cl2, 298 K) of
Poly[2]pseudorotaxanes 27-29, 32, and 33
Ks.1 (M-1
)
Ks.2 (M-1
)
Ks.3 (M-1
)
27 (1.09 ( 0.17) × 104 (4.55 ( 0.04) × 102
28 (2.52 ( 0.24) × 104 (2.62 ( 0.00) × 103
29 (4.89 ( 0.63) × 103 (1.76 ( 0.05) × 103 (1.06 ( 0.01) × 103
32a (1.81 ( 0.34) × 104 (1.20 ( 0.13) × 103 (5.66 ( 0.32) × 102
33a (2.06 ( 0.10) × 103 (9.03 ( 0.23) × 102 (5.39 ( 0.03) × 102
a As a result of limitations in the method of analysis used to evaluate
the data obtained from 1H NMR titration experiments, only Ks.1, Ks.2
and Ks.3 of 32 and 33 could be established.
,
di-Pt(II) building blocks results in a decreased binding ability
of the resultant rhomboidal and hexagonal multi-crown ether
hosts (Table 1). The decrease in Ks.1 ranges from roughly one-
half in the comparison of bis-DB24C8 rhomboids 27 and 28
up to an order of magnitude in the case of hexakis-DB24C8
hosts 32 and 33. These findings support the conclusion that
placement of the derivatized crown ether macrocycles on
acceptor building blocks results in a loss of electron density
and, thus, binding ability. It can also be observed from Table 1
that, in all cases, binding constants get progressively smaller
with each successive complexation of a dibenzylammonium
guest. From the ratios of binding constants, it is clear that the
crown ether sites act more or less independent of each other
and pseudorotaxane formation is not influenced by any sort of
cooperative effects.23 Rather, the decrease in efficiency of the
threading process may be attributed to the entropic cost of
forming higher-order pseudorotaxanes.
Figure 11. Simulated molecular model of hexagonal hexakis-DB24C8
derivative 32, optimized with the molecular mechanics force field. Color
scheme: C, gray; O, red; N, blue; P, purple; Pt, yellow; and R2NH2
hydrogen atoms, white (all other hydrogen atoms have been removed for
clarity).
+
Conclusions
The work presented here provides a simple, yet highly
efficient approach to the construction, via coordination-driven
self-assembly, of crown ether-derivatized 2-D polygons pos-
sessing structurally well-defined cavities of varying diameter
and shape. The covalent attachment of a DB24C8 macrocycle
to both 120° di-Pt(II) acceptor and 120° bispyridyl donor units
allows for a series of rhomboidal bis-, hexagonal tris-, and
hexagonal hexakis-DB24C8 derivatives to be self-assembled
under mild conditions and in quantitative yields when combined
with complementary 60°, 120°, and 180° building blocks,
respectively. The resultant multi-crown ether assemblies are
unique in that the number and arrangement of their pendant
macrocycles can be precisely controlled owing to the conserved
rigidity of their core 2-D polygonal scaffolds. Furthermore, the
orthogonal, non-interacting nature of coordination-driven self-
assembly of the underlying polygons and the hydrogen-bonding/
electrostatic/π-π stacking-promoted self-assembly of crown
ether-dialkylammonium pseudorotaxanes allows for rhomboidal
and hexagonal poly[2]pseudorotaxanes to be prepared.
The facile construction of rhomboidal bis[2]pseudorotaxanes
and hexagonal tris- and hexakis[2]pseudorotaxanes by this
orthogonal approach not only expands upon the traditional
techniques of supramolecular chemistry, where the majority of
known supramolecular structures have been prepared using a
single recognition motif, but also provides a new methodology
to build supramolecular structures in which a variety of
noncovalent interactions allow for multiple complementary
components to self-assemble into supramolecular species with
complex functional architectures. The demonstration of the
power and scope of the orthogonal approach to supramolecular
Molecular force-field simulations were used to gain further
insight into the structural characteristics of cavity-cored
poly[2]pseudorotaxanes 27–29, 32, and 33. A 1.0 ns molecular
dynamics simulation (MMFF) was used to equilibrate each
supramolecule 27–29, 32, and 33, followed by energy minimi-
zation of the resulting structures to full convergence. The
modeled structure of hexakis[2]pseudorotaxane 32, for example,
is shown in Figure 11 (for compounds 27–29 and 33, see
Supporting Information). Molecular simulations reveal that the
addition of dibenzylammonium to DB24C8 hosts does not
disrupt the underlying polygonal scaffolds, as ammonium salts
are complexed by their pendant DB24C8 macrocycles, further
illustrating the orthogonality of the noncovalent interactions
involved in self-assembly. In all cases, the underlying rigid
nature of the 2-D polygonal cavity is retained, while the
flexibility of each crown ether is reduced as a result of
host–guest complexation.
(23) Gibson, H. W.; Yamaguchi, N.; Hamilton, L.; Jones, J. W. J. Am.
Chem. Soc. 2002, 124, 4653.
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5331

A R T I C L E S
Ghosh et al.
diethyl ether. Drying the ether phase over magnesium sulfate and
subsequent filtration resulted in a slightly yellow oil after removal
of the solvent. Column chromatography on silica gel with a solvent
mixture (hexane/acetone: 3/1) yielded 2 as a white powder. Yield:
assemblies provides a solid foundation upon which to extend
these studies. It quickly becomes apparent that there are many
avenues to be explored by expanding upon the orthogonal self-
assembly approach, given the many 2-D and 3-D supramolecular
assemblies that can be prepared, the variety of orthogonal
noncovalent interactions that can be combined, and the pos-
sibility of using three or more independent, non-interacting self-
assembly protocols as opposed to only two. Investigations aimed
at expanding the orthogonal approach along these lines are
currently underway.
1
0.17 g, 95%. Mp: 88–89 °C. Rf ) 0.40 (hexane/acetone: 3/1). H
NMR (CDCl3, 300 MHz): δ 7.21 (s, 1H), 6.94 (s, 2H), 3.07 (s,
2H). 13C NMR (CDCl3, 75 MHz): δ 155.3, 128.8, 123.9, 119.8,
82.4, 78.2. MS (CI): m/z 142.0 (M+).
Synthesis of Compound 3. To a solution of dibenzo[24]crown-
8 carboxylic acid27 (172 mg, 0.35 mmol) in 5 mL of anhydrous
dichloromethane were added a catalytic amount (10%) of DMAP
and 3,5-diethynyl-phenol (2, 50 mg, 0.35 mmol). DCC was then
added to the reaction mixture at 0 °C, followed by stirring for 5
min at 0 °C and 10 h at room temperature. Precipitated urea was
then filtered off, and the filtrate was evaporated under vacuum. The
residue was taken up in 25 mL of CH2Cl2, washed twice with 0.5
N HCl and with saturated NaHCO3 solution, and then dried over
MgSO4. The residue was purified by column chromatography on
silica gel (DCM/hexane: 1/1) to give compound 3. Yield: 183 mg,
85%. Mp: 70–71 °C. Rf ) 0.45 (DCM/hexane: 1/1). 1H NMR
(CD2Cl2, 300 MHz): δ 7.80 (dd, J ) 6.3 Hz, J ) 2.1 Hz, 1H),
7.63 (d, J ) 2.1 Hz, 1H), 7.51 (s, 1H), 7.34 (s, 2H), 6.89–6.94 (m,
5H), 4.18–4.22 (m, 4H, R-CH2), 4.09–4.13 (m, 4H, R-CH2),
3.84–3.93 (m, 8H, ꢀ-CH2), 3.77–3.78 (br, 8H, γ-CH2), 3.21 (s, 2H).
13C NMR (CD2Cl2, 75 MHz): δ 164.8, 154.4, 151.4, 149.6, 149.1,
133.4, 126.7, 125.3, 124.1, 121.9, 121.8, 115.3, 114.7, 114.6, 112.7,
82.0, 79.3, 71.8, 71.7, 71.6, 70.4, 70.2, 70.0, 69.7, 69.8 MS (ESI):
m/z 639.3 (M + Na+).
Experimental Section
Triethylamine was distilled from sodium hydroxide, and tet-
rahydrofuran (THF) was distilled from K(s)/benzophenone. Deu-
terated solvents were purchased from Cambridge Isotope Laboratory
(Andover, MA). All other reagents were purchased (Aldrich or
Acros) and used without further purification. NMR spectra were
recorded on a Varian Unity instrument (300 and 500 MHz). The
1H and 13C NMR chemical shifts are reported relative to residual
solvent signals, and 31P NMR resonances are referenced to an
external unlocked sample of 85% H3PO4 (δ 0.0). Element analysis
was performed in Atlantic Microlab (Norcross, GA). Mass spectra
were recorded on a Micromass Quattro II triple-quadrupole mass
spectrometer using electrospray ionization with a MassLynx operat-
ing system or on an ESI-TOF mass spectrometer (Agilent Tech-
nologies, Santa Clara, CA). The solvent for ESI-TOF mass spectra
is dichloromethane.
Titration experiments were carried out by the addition of a
concentrated CD2Cl2 solution of the ammonium triflate salt 26 to
solutions of multiple crown ether derivative hosts 7, 12, 14, 22,
and 25 in CD2Cl2, respectively. In order to account for dilution
effects, these ammonium triflate salt solutions also contained host
at its initial concentration. The association constants were calculated
by the Hyperquad2003 program using changes in the chemical shift
of the γ-proton resonance of crown ether in the 1H NMR spectra.24
The molecular structures of all multiple crown ether derivatives
as well as all poly[2]pseudorotaxanes were each constructed within
the input mode of the program Maestro v8.0.11025 with the
MMFF.26 A 1.0 ns molecular dynamics simulation (0.05 fs time
step) at a simulation temperature of 300 K was used to equilibrate
each structure. Following each molecular dynamics simulation, a
full energy minimization was used to obtain the final optimized
structures.
Synthesis of Diiodometal Complex 4. To a 50 mL round-bottom
Schlenk flask were added trans-diiodobis(triethylphosphine-
)platinum (0.80 g, 1.17 mmol) and 3 (181 mg, 0.29 mmol). Then
15 mL of toluene and 7 mL of dry diethylamine were added under
nitrogen. The solution was stirred for 10 min at room temperature
before 15 mg of cuprous iodide was added in one portion. After
16 h at room temperature, a small amount of diethylammonium
iodide started precipitating out of solution. The solvent was removed
under vacuum, the resulting yellow residue was separated by column
chromatography on silica gel with a solvent mixture (DCM/acetone:
5/1), and 4 was isolated. Yield: 326 mg, 65%. Mp: 172–173 °C. Rf
) 0.35 (DCM/acetone: 5/1). 1H NMR (CD2Cl2, 300 MHz): δ 7.81
(s, 1H), 7.79 (s, 1H), 7.64 (s, 2H), 7.08 (s, 2H), 6.87–6.96 (m,
5H), 4.20 (br, 4H, R-CH2), 4.09–4.12 (m, 4H, R-CH2), 3.86–3.97
(m, 8H, ꢀ-CH2), 3.77–3.78 (m, 8H, γ-CH2), 2.17–2.23 (m, 24H,
PCH2CH3), 1.10–1.21 (m, 36H, PCH2CH3). 31P{1H} NMR (CD2Cl2,
1
121.4 MHz): δ 9.25 (s, JPt-P ) 2312.5 Hz). 13C NMR (CD2Cl2,
Synthesis of 3,5-Diethynyl-phenol (2). In a 50 mL round-bottom
Schlenk flask, 3,5-dibromo-phenyl ester (1, 0.42 g, 1.43 mmol) and
0.83 mL of (trimethylsilyl)acetylene (11.7 mmol) were dissolved
in 20 mL of freshly distilled THF and 5 mL of dry triethylamine.
A mixture of 0.172 g of tetrakis(triphenylphosphine)palladium
(0.149 mmol) and 53 mg of cuprous iodide (0.12 mmol) was added,
and the suspension was stirred for 16 h at room temperature in the
absence of light. After removal of the solvent, the residue was
suspended in 50 mL of diethyl ether and washed twice with 50
mL of water, and the organic phase was dried over magnesium
sulfate. After filtration, the solvents were removed, and the residue
was separated by column chromatography on silica gel. With a
solvent mixture (hexane/acetone: 8/1), 0.43 g (80%, Rf ) 0.40,
hexane/acetone: 8/1) of 1a was isolated as a white solid.
75 MHz): δ 165.3, 154.2, 151.4, 149.6, 149.0, 130.9, 130.0, 125.0,
122.6, 121.9, 121.6, 115.3, 114.7, 114.6, 112.7, 99.6, 91.9, 71.8,
71.7, 71.6, 70.4, 70.2, 70.1, 69.8, 17.6, 17.4, 17.1, 16.9, 16.7, 8.7,
8.6, 8.4. MS (ESI): m/z 1752.7 (M + Na+). Anal. Calcd for
C59H94I2O10P4Pt2: C, 40.93; H, 5.47. Found: C, 41.24; H, 5.51.
Synthesis of Bistriflate Salt 5. A 50 mL round-bottom Schlenk
flask was charged with 0.30 g (0.173 mmol) of 4 and 15 mL of
dichloromethane. To the solution was added 98 mg (0.381 mmol)
of AgOTf at once, resulting in a yellowish precipitate of AgI. After
4 h at room temperature, the suspension was filtered through a glass
fiber and the volume of the solution reduced to 5 mL. Subsequent
addition of diethyl ether resulted in the precipitation of the bistriflate
salt 5 as a slightly yellow crystalline powder. Yield: 276 mg, 90%.
Mp: 70–71 °C. 1H NMR (CD2Cl2, 500 MHz): δ 7.83 (s, 1H), 7.81
(s, 1H), 7.66 (s, 2H), 6.81–7.00 (m, 7H), 4.23 (br, 4H, R-CH2),
4.15 (br, 4H, R-CH2), 3.86–3.92 (m, 8H, ꢀ-CH2), 3.77 (br, 8H,
γ-CH2), 2.02–2.07 (m, 24H, PCH2CH3), 1.16–1.27 (m, 36H,
PCH2CH3). 31P{1H} NMR (CD2Cl2, 121.4 MHz): δ 22.7 (s, 1JPt-P
) 2374.2 Hz). 13C NMR (CD2Cl2, 75 MHz): δ 165.3, 154.2, 151.4,
149.6, 149.0, 130.9, 130.0, 125.0, 122.6, 121.9, 121.6, 115.3, 114.7,
114.6, 112.7, 99.6, 91.9, 71.8, 71.7, 71.6, 70.4, 70.2, 70.1, 69.8,
17.6, 17.4, 17.1, 16.9, 16.7, 8.7, 8.6, 8.4. MS (ESI): m/z 1624.9
Desilylation of 1a (0.43 g, 1.31 mmol) was achieved by stirring
the compound in a NaHCO3 suspension of methanol/THF/water
(0.5 g of NaHCO3 in 5 mL of methanol, 5 mL of THF, and 7 mL
of water) for 12 h at 55 °C. The solution was carefully diluted
with 20 mL of water, and the organic product was extracted with
(24) Hyperquad2003; Protonic Software, http://www.hyperquad.co.uk.
(25) Mohamadi, F.; Richards, N. G. J.; Guida, W. C.; Liskamp, R.; Lipton,
M.; Caufield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J. Comput.
Chem. 1990, 11, 440.
(27) Feng, D.-J.; Li, X.-Q.; Wang, X.-Z.; Jiang, X.-K.; Li, Z.-T. Tetrahedron
2004, 60, 6137.
(26) Halgren, T. A. J. Comput. Chem. 1996, 17, 490.
9
5332 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008

Self-Assembly and Study of Poly[2]pseudorotaxanes
A R T I C L E S
(M - OTf). Anal. Calcd for C61H94F6O16P4Pt2S2: C, 41.26; H, 5.34.
Found: C, 40.95; H, 5.12.
added a 0.40 mL CD2Cl2 solution of 120° crown ether-containing
donor 8 (1.71 mg, 0.00225 mmol) drop by drop with continuous
stirring (10 min). The reaction mixture was stirred for 30 min at
room temperature. The solution was evaporated to dryness, and
the product of hexakis-DB24C8 derivative 19 was collected as a
Preparation of Rhomboidal Bis-DB24C8 Derivatives 7, 11,
and 12. Method I: To a 0.4 mL dichloromethane-d2 solution of
120° crown ether containing di-Pt(II) acceptor 5 (5.01 mg, 0.00282
mmol) was added a 0.4 mL dichloromethane-d2 solution of 60°
donor 6 (1.07 mg, 0.00282 mmol) drop by drop with continuous
stirring (10 min). The reaction mixture was stirred for another 20
min at room temperature. The solution was evaporated to dryness,
and the product of bis-DB24C8 derivative 7 was collected as a
1
pale yellow solid. Yield: 5.60 mg, 98%. H NMR (CD2Cl2, 500
MHz): δ 8.63 (d, J ) 5.5 Hz, 12H, HR-Py), 7.81–7.82 (m, 15H,
Hꢀ-Py and ArH), 7.65 (s, 6H, ArH), 7.56 (s, 3H, ArH), 7.33 (br,
9H, ArH and PhH), 6.89–7.06 (m, 18H, PhH), 5.07 (s, 6H,
PhCH2O), 4.22 (br, 12H, R-CH2), 4.17 (br, 12H, R-CH2), 4.12 (br,
24H, R-CH2), 3.86–3.92 (m, 48H, ꢀ-CH2), 3.78 (br, 24H, γ-CH2),
3.76 (br, 24H, γ-CH2), 1.80–1.83 (m, 72H, PCH2CH3), 1.15–1.22
(m, 108H, PCH2CH3). 31P{1H} NMR (CD2Cl2, 121.4 MHz): δ 18.3
1
pale yellow solid. Yield: 5.84 mg, 96%. H NMR (CD2Cl2, 500
MHz): δ 9.05–9.18 (m, 4H, H4), 8.65 (d, J ) 5.4 Hz, 8H, HR-Py),
7.83–7.99 (m, 22H, H1, H2, H10, ArH, and Hꢀ-Py), 7.66 (s, 4H,
ArH), 6.89–7.07 (m, 14H, PhH), 4.22 (br, 8H, R-CH2), 4.12 (br,
8H, R-CH2), 3.85–3.90 (m, 16H, ꢀ-CH2), 3.76 (br, 16H, γ-CH2),
1.83 (br, 48H, PCH2CH3), 1.19 (br, 72H, PCH2CH3). 31P{1H} NMR
(CD2Cl2, 121.4 MHz): δ 16.0 (s, 1JPt-P ) 2307.8 Hz). Anal. Calcd
for C178H224F12N4O30P8Pt4S4: C, 49.90; H, 5.27; N, 1.31. Found:
C, 49.59; H, 5.03; N, 1.22.
Method II: To a 0.5 mL dichloromethane-d2 solution of small
60° angular Pt(II) acceptor 9 (4.50 mg, 0.00387 mmol) or large
60° angular Pt(II) acceptor 10 (5.36 mg, 0.00387 mmol), respec-
tively was added a 0.5 mL dichloromethane-d2 solution of 120°
crown ether containing donor 8 (2.93 mg, 0.00387 mmol) drop by
drop with continuous stirring (10 min). The reaction mixture was
stirred overnight (for 9) or for another 20 min (for 10) at room
temperature. The solution was evaporated to dryness, and the
product of bis-DB24C8 derivative 11 (white solid) or 12 (pale
yellow solid) was collected, respectively.
(s,
1JPt-P
)
2309.5
Hz).
Anal.
Calcd
for
C318H414F18N6O75P12Pt6S6 ·CH2Cl2: C, 49.87; H, 5.46; N, 1.09.
Found: C, 49.51; H, 5.33; N, 1.11.
Method II: To a 0.5 mL dichloromethane-d2 solution of small
180° angular Pt(II) acceptor 20 (3.53 mg, 0.0033 mmol) or large
180° angular Pt(II) acceptor 21 (4.33 mg, 0.0033 mmol) was added
a 0.5 mL dichloromethane-d2 solution of 120° crown ether-
containing donor 8 (2.50 mg, 0.0033 mmol) drop by drop with
continuous stirring (10 min). The reaction mixture was stirred for
another 20 min at room temperature. The solution was evaporated
to dryness, and the product of hexakis-DB24C8 derivative 22 (pale
yellow solid) or 23 (pale yellow solid) was collected, respectively.
22. Yield: 5.85 mg, 97%. 1H NMR (CD2Cl2, 500 MHz): δ 8.82
(d, J ) 6.0 Hz, 24H, HR-Py), 7.75 (d, J ) 6.5 Hz, 24H, Hꢀ-Py),
7.51 (s, 6H, ArH), 7.29 (s, 12H, ArH), 7.06 (s, 24H, ArH), 6.99 (s,
12H, PhH), 6.89–6.92 (m, 30H, PhH), 5.05 (s, 12H, PhCH2O),
4.11–4.16 (m, 48H, R-CH2), 3.84–3.87 (m, 48H, ꢀ-CH2), 3.76 (br,
48H, γ-CH2), 1.10–1.17 (m, 216H, PCH3). 31P{1H} NMR (CD2Cl2,
11. Yield: 7.13 mg, 96%. 1H NMR (CD2Cl2, 500 MHz): δ 9.33
(d, J ) 6.0 Hz, 4H, HR-Py), 8.82 (s, 4H, H4), 8.70 (d, J ) 6.0 Hz,
4H, HR-Py), 7.96 (d, J ) 5.7 Hz, 4H, Hꢀ-Py), 7.79 (d, J ) 5.7 Hz,
4H, Hꢀ-Py), 7.65 (s, 2H, ArH), 7.58–7.60 (m, 12H, H1, H2, and
H10), 7.37 (s, 4H, ArH), 7.02–7.04 (m, 4H, PhH), 6.90–6.94 (m,
10H, PhH), 5.09 (s, 4H, PhCH2O), 4.11–4.19 (m, 16H, R-CH2),
3.85–3.91 (m, 16H, ꢀ-CH2), 3.76–3.78 (m, 16H, γ-CH2), 1.36–1.41
(m, 48H, PCH2CH3), 1.05–1.20 (m, 72H, PCH2CH3). 31P{1H}
NMR (CD2Cl2, 121.4 MHz): δ 12.6 (s, 1JPt-P ) 2707.3 Hz). Anal.
Calcd for C166H224N8O30P8Pt4: C, 51.93; H, 5.88; N, 2.92. Found:
C, 51.63; H, 5.78; N, 2.96.
1
121.4 MHz): δ 14.8 (s, JPt-P ) 2731.7 Hz). Anal. Calcd for
C390H504F36N12O90P24Pt12S12: C, 42.77; H, 4.64; N, 1.53. Found:
C, 42.43; H, 4.93; N, 1.46.
23. Yield: 6.49 mg, 95%. 1H NMR (CD2Cl2, 500 MHz): δ 8.69
(d, J ) 5.5 Hz, 24H, HR-Py), 7.82 (d, J ) 6.6 Hz, 24H, Hꢀ-Py),
7.61 (s, 6H, ArH), 7.41 (br, 48H, ArH), 7.33 (s, 12H, ArH), 7.01
(s, 12H, PhH), 6.89–6.93 (m, 30H, PhH), 5.07 (s, 12H, PhCH2O),
4.11–4.17 (m, 48H, R-CH2), 3.85–3.89 (m, 48H, ꢀ-CH2), 3.77–3.78
(m, 48H, γ-CH2), 1.36–1.41 (m, 144H, PCH2CH3), 1.13–1.17 (m,
216H, PCH2CH3). 31P{1H} NMR (CD2Cl2, 121.4 MHz): δ 14.1
12. Yield: 7.79 mg, 94%. 1H NMR (CD2Cl2, 500 MHz): δ 8.69
(d, J ) 5.4 Hz, 8H, HR-Py), 8.51 (s, 4H, H4), 7.80–7.84 (m, 12H,
Hb-Py and H1), 7.68 (s, 4H, H10), 7.50–7.60 (m, 6H, H2 and ArH),
7.34 (s, 4H, ArH), 7.01 (d, 4H, PhH), 6.89–6.90 (m, 10H, PhH),
5.07 (s, 4H, PhCH2O), 4.12–4.14 (m, 16H, R-CH2), 3.85 (br, 16H,
ꢀ-CH2), 3.75–3.76 (m, 16H, γ-CH2), 1.87 (br, 48H, PCH2CH3),
1.21–1.26 (m, 72H, PCH2CH3). 31P{1H} NMR (CD2Cl2, 121.4
1
(s, JPt-P ) 2684.0 Hz). Anal. Calcd for C490H672F36N12O90-
P24Pt12S12: C, 48.16; H, 5.45; N, 1.35. Found: C, 48.14; H, 5.66;
N, 1.28.
Method III: To a 0.60 mL CD2Cl2 solution of 120° crown ether-
containing di-Pt(II) acceptor 5 (7.95 mg, 0.00448 mmol) was added
a 0.60 mL CD2Cl2 solution of linear 4,4′-bipyridyl donor 24 (0.70
mg, 0.00225 mmol) drop by drop with continuous stirring (10 min).
The reaction mixture was stirred for 30 min at room temperature.
The solution was evaporated to dryness, and the product of hexakis-
DB24C8 derivative 25 was collected as a pale yellow solid. Yield:
1
MHz): δ 16.1 (s, JPt-P ) 2319.2 Hz). Anal. Calcd for
C
178H224F12N4O30P8Pt4S·CH2Cl2: C, 49.21; H, 5.21; N, 1.28. Found:
C, 49.01; H, 5.18; N, 1.31.
Preparation of Tris-DB24C8 Derivative 14. To a 0.65 mL
CD2Cl2 solution of 120° crown ether-containing di-Pt(II) acceptor
5 (9.03 mg, 0.00509 mmol) was added a 0.65 mL CD2Cl2 solution
of di-2-pyridyl ketone 13 (0.94 mg, 0.00509 mmol) drop by drop
with continuous stirring (15 min). The reaction mixture was stirred
for 30 min at room temperature. The solution was evaporated to
dryness, and the product of tris-DB24C8 derivative 14 was collected
1
8.30 mg, 96%. H NMR (CD2Cl2, 500 MHz): δ 8.82 (d, J ) 5.5
Hz, 24H, HR-Py), 8.48 (d, J ) 6.0 Hz, 24H, Hꢀ-Py), 7.83 (s, 6H,
ArH), 7.81 (s, 6H, PhH), 7.66 (s, 12H, ArH), 7.07 (s, 12H, PhH),
6.90–6.98 (m, 24H, PhH), 4.22 (br, 24H, R-CH2), 4.13 (br, 24H,
R-CH2), 3.86–3.92 (m, 48H, ꢀ-CH2), 3.78 (br, 48H, γ-CH2),
1.82–1.85 (m, 144H, PCH2CH3), 1.18–1.23 (m, 216H, PCH2CH3).
1
as a pale yellow solid. Yield: 9.57 mg, 96%. H NMR (CD2Cl2,
1
31P{1H} NMR (CD2Cl2, 121.4 MHz): δ 16.3 (s, JPt-P ) 2307.7
500 MHz): δ 8.93 (d, J ) 5.7 Hz, 12H, HR-Py), 8.20 (d, J ) 6.0
Hz, 12H, Hꢀ-Py), 7.84 (s, 3H, ArH), 7.81 (s, 3H, PhH), 7.66 (s,
6H, ArH), 6.91–7.01 (m, 18H, PhH), 4.23 (br, 12H, R-CH2),
4.12–4.15 (m, 12H, R-CH2), 3.86–3.91 (m, 24H, ꢀ-CH2), 3.78 (br,
24H, γ-CH2), 1.83–1.85 (m, 72H, PCH2CH3), 1.14–1.26 (m, 108H,
PCH2CH3). 31P{1H} NMR (CD2Cl2, 121.4 MHz): δ 16.0 (s, 1JPt-P
) 2289.5 Hz). Anal. Calcd for C216H306F18N6O51P12Pt6S6: C, 44.13;
H, 5.25; N, 1.43. Found: C, 43.88; H, 5.03; N, 1,35.
Hz). Anal. Calcd for C426H612F36N12O96P24Pt12S12: C, 44.14; H, 5.32;
N, 1.45. Found: C, 44.02; H, 5.21; N, 1.36.
Acknowledgment. P.J.S. thanks the NIH (Grant GM-057052)
and the NSF (Grant CHE-0306720) for financial support. B.H.N.
thanks the NIH (Grant GM-080820) for financial support. We
thank Prof. Mei-Xiang Wang and Dr. Han-Yuan Gong for their
help with the calculation of thermodynamic binding constants.
D.C.M. and M.M.L. thank NCBC and NCSU for generous
financial support.
Preparation of Hexakis-DB24C8 Derivatives 19, 22, 23,
and 25. Method I: To a 0.40 mL CD2Cl2 solution of 120° crown
ether-containing di-Pt(II) acceptor 5 (4.0 mg, 0.00225 mmol) was
9
J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008 5333

A R T I C L E S
Ghosh et al.
Supporting Information Available: 1H and 13C NMR spectra
computational procedures and structures for all self-assemblies
obtained from modeling. This material is available free of charge
via the Internet at http://pubs.acs.org.
1
of compounds 2–4, H and 31P NMR spectra of 5, 7, 11, 12,
14, 19, 22, 23, 25, 27–29, 32, and 33, and two-dimensional
spectra (1H-1H COSY and NOESY) of 27–29, 32, and 33;
experimental data for 1H NMR titration experiments; and
JA711502T
9
5334 J. AM. CHEM. SOC. VOL. 130, NO. 15, 2008