Hexagon wreaths: Self-assembly of discrete supramolecular fractal architectures using multitopic terpyridine ligands

Article abstract of DOI:10.1021/ja501417g

In this study, we overcame a challenge in conventional self-assembly of macrocycles that uses ditopic 2,2:6,2-terpyridine (tpy) building blocks with a 120angle between two ligating moieties, which generally produces a mixture of multiple macrocycles instead of a single hexagon. Two supramolecular hexagon wreaths, [Zn₉LA₆] and [Zn₁₂LB₆], were designed and self-assembled from tritopic and tetratopic tpy ligands with Zn(II) ions, respectively. These multitopic ligands, bearing multiple binding sites, increased the total density of coordination sites and provided high geometric constraints to induce the formation of discrete structures. Such hexagon wreaths, which were constructed by simple recursion of small hexagons around a central hexagon, exhibit fractal geometry features with self-similarity at different levels. The shapes, sizes, and structures were fully characterized by NMR, ESI-MS, traveling-wave ion mobility mass spectrometry (TWIM-MS), and transmission electron microscopy. With diameters around 5.5 nm for [Zn ₉LA₆] and 5.8 nm for [Zn₁₂LB₆], the remarkable rigidity of these fractal architectures was supported by TWIM-MS, in contrast to the high flexibility of macrocycles assembled by ditopic tpy ligands.

Full text of DOI:10.1021/ja501417g

Article
pubs.acs.org/JACS
Hexagon Wreaths: Self-Assembly of Discrete Supramolecular Fractal
Architectures Using Multitopic Terpyridine Ligands
Ming Wang,†,§ Chao Wang,†,§ Xin-Qi Hao,‡ Jingjing Liu,⊥ Xiaohong Li,∥ Chenglong Xu,∥ Alberto Lopez,†
Luyi Sun,⊥ Mao-Ping Song,‡ Hai-Bo Yang,# and Xiaopeng Li*,†
†Department of Chemistry and Biochemistry, Texas State University, San Marcos, Texas 78666, United States
‡College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450052, P. R. China
⊥Department of Chemical & Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of
Connecticut, Storrs, Connecticut 06269, United States
∥College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
#Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University,
Shanghai 200062, P. R. China
S
* Supporting Information
ABSTRACT: In this study, we overcame a challenge in
conventional self-assembly of macrocycles that uses ditopic
2,2′:6′,2″-terpyridine (tpy) building blocks with a 120° angle
between two ligating moieties, which generally produces a
mixture of multiple macrocycles instead of a single hexagon.
Two supramolecular hexagon wreaths, [Zn9LA6] and
[Zn12LB6], were designed and self-assembled from tritopic
and tetratopic tpy ligands with Zn(II) ions, respectively. These
multitopic ligands, bearing multiple binding sites, increased the
total density of coordination sites and provided high geometric
constraints to induce the formation of discrete structures. Such
hexagon wreaths, which were constructed by simple recursion
of small hexagons around a central hexagon, exhibit fractal geometry features with self-similarity at different levels. The shapes,
sizes, and structures were fully characterized by NMR, ESI-MS, traveling-wave ion mobility mass spectrometry (TWIM-MS), and
transmission electron microscopy. With diameters around 5.5 nm for [Zn9LA6] and 5.8 nm for [Zn12LB6], the remarkable
rigidity of these fractal architectures was supported by TWIM-MS, in contrast to the high flexibility of macrocycles assembled by
ditopic tpy ligands.
The weak bonding strength of metal−ligand interactions helps
in modulating the coordination kinetics of self-assembly
processes by introducing rigidity and reversibility. However,
unpredicted macrocycles often appear because organic ligands
are much more flexible than expected and metal centers can
allow considerable deviation in their coordination geometry.
Therefore, assemblies with similar components resulting in an
equilibrating mixture of binary or multiple entities instead of
single discrete structures have been reported. Using binary
systems as an example, Stang,18 Fujita,19 Schalley,20 and
others21 reported cases of triangle−square equilibria with
Pd(II)- and Pt(II)-based self-assembly. In a study of multiple
entities, Lin and co-workers used stepwise directed assembly to
obtain a family of macrocycles with kinetically inert Pt−alkynyl
linkages11d,22 from a supramolecular library.11e
INTRODUCTION
■
Precise control over the shape and size of supramolecular
architectures through self-assembly has been a major driving
force for chemists over the past few decades.1,2 As supra-
molecular chemistry has become a highly diverse field, metallo-
macrocycles have been marked by the successful construction
of a wide array of two-dimensional (2D) geometries with
increasing complexity since the seminal work of Stang et al.3
and Fujita et al.,4 including triangles,5 squares,6 rectangles,7
rhomboids,8 pentagons,9 hexagons,10 and large ring systems.11
Such well-defined structures with high diversity and complexity
make metallo-macrocycles an ideal platform for scientists
seeking to design novel materials with molecular-level
precision.1c,h,12 Among the possible applications, metallo-
macrocycles are being investigated as new materials in a variety
of contexts with excellent sensing,13 magnetic,14 photonics,15
enantiomeric enrichment,16 and catalytic properties.17
Moving to the self-assembly of 2,2′:6′,2″-terpyridine (tpy),23
which has attracted considerable attention in supramolecular
In many cases, the success of such assemblies with precise
shapes and sizes mainly relies on the angles of the organic
ligands and the coordination geometry of the metal ions.1a,b
Received: February 10, 2014
Published: April 14, 2014
© 2014 American Chemical Society
6664
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
polymers,24 2D macrocycles,10b,25 three-dimensional (3D)
cages,26 and heteroleptic coordination-based self-assembly,27
Newkome and co-workers recently succeeded in isolating
unexpected pentameric, heptameric, octameric, nonameric, and
decameric macrocycles composed of rigid ditopic tpy ligands
with 120° orientation of their metal binding sites.28 Never-
theless, precise control over the self-assembly of metallo-
macrocycles toward discrete structures is still one of the
ultimate goals and challenges in the field of supramolecules,
recalling that many weak (noncovalent) interactions, acting
cooperatively, can yield stable supramolecular complexes.29 For
example, intramolecular noncovalent interactions are largely
responsible for the stable secondary and tertiary structures of
proteins and therefore the proteins’ functions in the
mechanisms of life.30 Therefore, we reason that a system with
a high density of noncovalent interactions is preferable to form
a discrete architecture. Accordingly, we herein designed two
hexagon wreath structures (Figure 1) assembled by tritopic
(LA, Scheme 1A) and tetratopic tpy ligands (LB, Scheme 2A).
Compared to ditopic ligands used in the self-assembly of
conventional macrocycles, our strategy increased the number of
coordination sites within the hexagon wreath, which was named
the “density of coordination sites” (DOCS), and thus provided
more constraints to form discrete and thermodynamically stable
structures. Remarkably, such hexagon wreaths, which were
constructed by simple recursion of small hexagons around the
center hexagon, exhibit fractal geometry features with self-
similarity at different levels.31
RESULTS AND DISCUSSION
■
A Sonogashira coupling reaction was used to synthesize ligand
LA (Scheme 1A) in a decent yield, purified by column
chromatography (Al2O3). LA and Zn(NO3)2·6H2O were mixed
in a stoichiometric ratio (2:3) in CHCl3/MeOH at 55 °C for
12 h, followed by addition of an excess of NH4PF6 salt to give a
white precipitate (complex [Zn9LA6], yield 88%) with nine
coordination sites.
1
The H NMR spectrum of complex [Zn9LA6] is shown in
Figure 2. There are 24 sets of aromatic protons from three sets
of tpy units and phenyl groups in the aromatic region of
1
[Zn9LA6]; only two sets of tpy units were found in the H
NMR spectrum of LA. Many proton signals of the pyridine
1
rings are overlapping in the H NMR spectrum of complex
[Zn9LA6]. According to 2D-COSY results (Figures S23−S25),
1
there are three groups of H signals from tpy, as expected.
Furthermore, the NMR spectrum of [Zn9LA6] shows broad 1H
signals, due to its slow tumbling motion on the NMR time
scale,32 suggesting a very large complex was obtained. We also
performed temperature-dependent NMR studies from 28 to 70
°C for [Zn9LA6].33 NMR signals became slightly sharper with
splitting between 50 and 70 °C rather than showing a
significant improvement (see Figure S27). However, this
complex could not tolerate temperatures higher than 70 °C
and immediately decomplexed into an unassignable mixture of
oligomers because of the labile nature of the Zn(II)−
terpyridine coordination (data not shown). Because electron
density was lower upon coordination with metal ions, both the
3′,5′-tpy and a3′,a5′-tpy protons were significantly shifted
downfield. For this complexation with Zn(II), all the 6-position
signals of pyridine shifted upfield (Δδ = 0.8 ppm) due to the
electron shielding effect.25b At the same time, almost all other
aromatic proton signals were shifted to downfield. There is only
one set of proton signals for methoxy (−OCH3) and alkyloxy
Figure 1. Structures of hexagon wreaths [Zn9LA6] and [Zn12LB6].
chains (−OCH2−), suggesting the possibility of a single
component in the product.
Electrospray ionization mass spectrometry (ESI-MS) and
traveling-wave ion mobility mass spectrometry (TWIM-MS)
have been recognized as effective methods to determine
molecular composition and provide shape and size informa-
tion.28c,34 In Figure 3A, only one prominent set of peaks with
different charge states (7+ to 12+) is observed (due to the loss
−
of a different number of PF6 ). Each isotope pattern of these
peaks agrees excellently with the corresponding simulated
isotope pattern of [Zn9LA6] (Figure S1) for the desired
hexagon wreath structure with molecular weight of 9793.4 Da.
This complex was further characterized by TWIM-MS to
separate any superimposed fragments and detect the possible
presence of overlapping isomers or conformers. As a variant of
conventional ion mobility MS,35 TWIM-MS has been used as a
6665
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
Scheme 1. (A) Synthetic Route to Ligand LA, (B) Self-Assembly of Discrete Hexagon Wreath [Zn9LA6], and (C)Self-Assembly
of Multiple Macrocycles (n = 5−9) by Ligand 8
powerful method to determine the ion’s mass, charge, and
shape via the drift time.25,34,35 As the TWIM-MS result shows
in Figure 3B, each charge state is detected with a narrow drift
time distribution, indicating this complex is a single-component
product without other isomers or structural conformers.
Compared to macrocycles assembled by 120° ditopic tpy
ligands, multiple isomers and conformers were observed in
TWIM-MS.28
In sharp contrast with the discrete hexagon wreath, self-
assembly of ditopic tpy compound 8 (Scheme 1) with Zn(II)
under the same conditions was observed as a mixture of
multiple macrocycles by ESI-MS, including pentamer to
nonamer (Figure 4). This is consistent with the previous self-
assembly study of ditopic tpy ligand with a 120° geometry
between metal binding sites.28 After three small hexagons were
introduced around the core hexagon, the self-assembly gave a
single structure of [Zn9LA6] instead of multiple macrocycles.
Therefore, we postulated that the self-assembly of discrete
hexagon wreath [Zn9LA6] was induced by these three small
hexagons around the outer rim. Such small hexagons possessing
a higher density of coordination sites provides the whole
supramolecular fractal with greater rigidity and geometric
constraints, forcing the internal ditopic moieties with 120°
angle into a single hexagon wreath structure.
In order to prove this assumption, we performed another
self-assembly using ligand LA with Zn(II) at a molar ratio of
6666
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
Figure 4. ESI-MS of multiple macrocycles assembled by ditopic tpy
ligand 8 with Zn(II). The m/z ratio and possible ion compositions are
marked above the peaks. Macrocycle complexes are named Mnx+,
where M designates the repeat unit <tpy-Zn-tpy>, n is the number of
repeat units, and x is the number of charges.
1
Figure 2. H NMR spectra (400 MHz) of ligand LA in CDCl3 and
complex [Zn9LA6] in CD3CN.
Figure 5. ESI-MS and isotope pattern of the hexagon-like dimer
obtained by self-assembly of LA with Zn(II) at a molar ratio of 1:1.
Following this result, a tetratopic ligand LB was designed and
synthesized to build a more-complicated hexagon wreath,
[Zn12LB6] (Figure 1), which possesses six small hexagons
around acentral hexagon. In this fractal architecture, the self-
similarity was realized by a simple recursion of small hexagons
around a central hexagon. The synthetic route to ligand LB is
shown in Scheme 2A. Long alkyl chains were incorporated
around the outer rim of the hexagon wreath to increase the
solubility of complex [Zn12LB6].
Furthermore, the highly symmetric structure of LB simplified
1
the H NMR spectra and facilitated characterization. Complex
[Zn12LB6] was successfully obtained in 91% yield by using the
same self-assembly procedure as for [Zn9LA6]. Compared to
the three sets of tpy signals in [Zn9LA6], the 1H NMR
spectrum of [Zn12LB6] shows only two sets of tpy signals,
indicating the formation of a highly symmetric architecture
(Figure 6). Except for the 6-position of pyridine, which was
shifted upfield (Δδ = 0.75 ppm), all other aromatic proton
peaks (tpy and phenyl) were shifted slightly downfield. Note
Figure 3. (A) ESI-MS and (B) 2D ESI-TWIM-MS plot (m/z vs drift
time) of hexagon wreath [Zn9LA6]. The charge states of intact
assemblies are marked.
1:1. According to the structure of ligand LA, if the ratio of
ligand and metal is 1:1, we should observe the formation of a
small hexagon-like dimer as a preferable structure with two LA
and two metals under entropy-driven conditions. As shown in
Figure 5, one main set of peaks at different charge states (Z =
2+ to 4+) is observed in ESI-MS, corresponding to the dimer
structure. The knowledge gained in this initial study inspired us
to design more-sophisticated structures by applying the small
hexagon-like dimer to induce the formation of discrete
architectures. Here this small dimer was utilized as the basic
subunit in the recursion process toward large fractal geometry.
1
that the full assignments of the H NMR spectra shown in
Figure 6 were based on 2D-COSY (see Figures S30−S32). 2D
NOESY and HSQC NMR are also consistent with this hexagon
wreath as the sole product (see Figures S33 and S34).
Temperature-dependent NMR analysis of complex [Zn12LB6]
was also performed, as for [Zn9LA6], showing a slight
improvement between 50 and 70 °C (Figure S35).
The ESI result of this complex is depicted in Figure 7A.
Different charge states of the complex (Z = 10+ to 19+) were
6667
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
Scheme 2. (A) Synthetic Route to Ligand LB and (B) Self-Assembly of Discrete Hexagon Wreath [Zn12LB6]
Figure 7. (A) ESI-MS and (B) 2D ESI-TWIM-MS plot (m/z vs drift
time) of hexagon wreath [Zn12LB6]. The charge states of intact
assemblies are marked.
1
Figure 6. H NMR spectra (400 MHz) of ligand LB in CDCl3 and
complex [Zn12LB6] in CD3CN.
observed, and the corresponding isotope patterns are shown in
Figure S3. The molecular weight of this giant hexagon wreath
was measured as 13 262.1 Da. With further characterization by
TWIM-MS (Figure 7B), the narrow distribution of each charge
state confirms that no isomer or conformer was generated in
the self-assembly. It suggests the formation of the hexagon
wreath as a single, rigid structure. The self-assembly of such
discrete complexes indicates that increasing the density of
coordination sites by applying multitopic ligands is a feasible
approach toward single discrete structures instead of multiple
entities by ditopic build blocks.
To gain more information about the sizes and shapes of these
two complexes, collision cross sections (CCSs), which
correspond to the sizes of analytes, can be employed to
6668
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
provide further evidence.34,35 Experimental CCSs of the ions
were derived from the drift time of TWIM-MS data using
standard curves.36 Theoretical CCSs, which were calculated
from molecular modeling, were correlated with experimental
CCSs deduced for these two hexagon wreath complexes at
various charge states (Table 1). The trajectory (TJ), projection
Table 1. Experimental and Theoretical Collision Cross
Sections (Å2)
drift time (ms)
CCS
average CCS
[Zn9LA6]
calcd avg CCS
Figure 8. TEM image (left) and energy-minimized structures from
molecular modeling (right) of complex [Zn12LB6]. The long alkyl
chains are omitted for clarity in the molecular modeling.
6.62 (7+)
5.29 (8+)
4.41 (9+)
3.75 (1+0)
3.31 (11+)
2.87 (12+)
2.65 (13+)
1463.5
1457.3
1463.2
1467.3
1490.4
1482.4
1524.8
b
1472.2 74.4
1272.8 67.4
1542.8 76.3
a
c
1478.4(23.6)
d
5.8 nm for [Zn12LB6]). Besides the structural characterization,
the ultraviolet absorption and fluorescence spectra of the two
ligands and their complexes were also evaluated, showing
similar results (see Figure S10).
[Zn12LB6]
6.62 (9+)
1880.3
1890.0
1869.5
1887.3
1905.9
1894.8
1896.8
1924.8
1936.5
CONCLUSIONS
■
5.62 (10+)
4.74 (11+)
4.19 (12+)
3.75 (13+)
3.31 (14+)
2.98 (15+)
2.76 (16+)
2.54 (17+)
Instead of using ditopic building blocks in conventional self-
assembly of macrocycles, we employed multitopic terpyridine
ligands to precisely control the size and shape of 2D self-
assembly. These multitopic ligands provided more noncovalent
interactions and significantly increased the density of
coordination sites within 2D structures, thus inducing the
self-assembly of discrete architectures. In other words, the high
density of coordination generated more geometric constraints
to prevent the formation of multiple entities. Two hexagon
wreath structures with fractal features were designed by
introducing three and six small hexagons around the center
hexagon, respectively. The strategy used in this study will not
only refresh the interest in self-assembly of macrocycles but also
advance the design of more sophisticated 2D architectures.
Recall that fractal geometry is a recursive mathematical
derivation of a form that possesses self-similar structures at
various levels of scale or detail. The success of these two
discrete supramolecular fractals opens a new avenue facilitating
the construction of complicated fractal gemoetry with self-
similarity by a simple recursion process.
b
c
1946.7 40.7
1657.1 25.1
2038.9 29.9
a
1898.4(21.1)
d
a
b
Average of all CCS values. Trajectory (TJ) value obtained using
c
MOBCAL. Projection approximation (PA) value obtained using
d
MOBCAL. Exact hard-sphere scattering (EHSS) value obtained using
MOBCAL.
approximation (PA), and exact hard-sphere scattering (EHSS)
method were applied to calculate average theoretical CCSs for
70 candidate structures of [Zn9LA6] and [Zn12LB6] from
annealing using MOBCAL.37 The plots of relative energy and
CCSs are shown in Figures S4−S9. Note that these 70
candidate structures were weighted equally in their contribution
to the average theoretical CCS. As a result, the TJ method
closely matched the average experimental CCS results for
different charge states in these three methods (Table 1),
because the TJ method considers both long-range interactions
and momentum transfer between the ions and the gas in the
ion mobility region.37 As shown in Table 1, the experimental
CCS of [Zn9LA6] is 1478.4 23.6 Å2, in excellent agreement
ASSOCIATED CONTENT
* Supporting Information
Experimental procedures and characterization data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
with the theoretical CCS, i.e., 1472.2
74.4 Å2 by TJ. The
experimental and theoretical CCSs of [Zn9LA6] were also
found to be in good agreement, i.e., 1898.4 21.1 Å2 vs 1946.7
40.7 Å2. The slight difference in the CCSs at each charge
state quantitatively suggests the remarkable rigidity of these
species is due to their high geometric constraints from a high
density of coordination sites; in contrast, the CCSs of
macrocycles assembled from ditopic ligands were vastly
different at different charge states due to their high flexibility.28
Finally, the sizes and shapes of individual molecules for these
two hexagon wreath structures were characterized by trans-
mission electron microscopy (TEM) on a JEOL 2010
microscope (Figures 8 and S36). The sizes observed by TEM
were consistent with theoretical ones calculated from molecular
simulation using Materials Studio (5.5 nm for [Zn9LA6] and
AUTHOR INFORMATION
Corresponding Author
X_L8@txstate.edu
■
Author Contributions
§M.W. and C.W. contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Xiaopeng Li gratefully acknowledges the Research Enhance-
ment Program of Texas State University and the Welch
Foundation (AI-0045) for financial support.
6669
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
(13) Lee, S. J.; Lin, W. J. Am. Chem. Soc. 2002, 124, 4554.
(14) (a) Kahn, O. Acc. Chem. Res. 2000, 33, 647. (b) Dul, M.-C.;
REFERENCES
■
(1) (a) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev.
2011, 111, 6810. (b) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev.
2000, 100, 853. (c) Lehn, J.-M. Chem. Soc. Rev. 2007, 36, 151.
(d) Pluth, M. D.; Raymond, K. N. Chem. Soc. Rev. 2007, 36, 161.
(e) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res.
2005, 38, 369. (f) Dalgarno, S. J.; Power, N. P.; Atwood, J. L. Coord.
Chem. Rev. 2008, 252, 825. (g) Seidel, S. R.; Stang, P. J. Acc. Chem. Res.
2002, 35, 972. (h) Wurthner, F.; You, C.-C.; Saha-Moller, C. R. Chem.
Soc. Rev. 2004, 33, 133. (i) Nitschke, J. R. Acc. Chem. Res. 2007, 40,
103. (j) Lee, S. J.; Lin, W. Acc. Chem. Res. 2008, 41, 521. (k) Forgan, R.
S.; Sauvage, J.-P.; Stoddart, J. F. Chem. Rev. 2011, 111, 5434.
(2) (a) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40,
2022. (b) Hof, F.; Craig, S. L.; Nuckolls, C.; Rebek, J. J. Angew. Chem.,
Int. Ed. 2002, 41, 1488. (c) Saalfrank, R. W.; Maid, H.; Scheurer, A.
Angew. Chem., Int. Ed. 2008, 47, 8794.
Pardo, E.; Lescouezec, R.; Journaux, Y.; Ferrando-Soria, J.; Ruiz-
̈
García, R.; Cano, J.; Julve, M.; Lloret, F.; Cangussu, D.; Pereira, C. L.
M.; Stumpf, H. O.; Pasan
254, 2281.
́ ́
, J.; Ruiz-Perez, C. Coord. Chem. Rev. 2010,
(15) (a) Flynn, D. C.; Ramakrishna, G.; Yang, H.-B.; Northrop, B.
H.; Stang, P. J.; Goodson, T. J. Am. Chem. Soc. 2010, 132, 1348.
(b) Pollock, J. B.; Schneider, G. L.; Cook, T. R.; Davies, A. S.; Stang, P.
J. J. Am. Chem. Soc. 2013, 135, 13676.
(16) (a) Yeh, R. M.; Raymond, K. N. Inorg. Chem. 2006, 45, 1130.
́
(b) Gregolinski, J.; Starynowicz, P.; Hua, K. T.; Lunkley, J. L.; Muller,
G.; Lisowski, J. J. Am. Chem. Soc. 2008, 130, 17761. (c) Heo, J.; Jeon,
Y.-M.; Mirkin, C. A. J. Am. Chem. Soc. 2007, 129, 7712.
(17) (a) Lee, S. J.; Hu, A.; Lin, W. J. Am. Chem. Soc. 2002, 124,
12948. (b) Huang, S.-L.; Lin, Y.-J.; Hor, T. S. A.; Jin, G.-X. J. Am.
Chem. Soc. 2013, 135, 8125. (c) Gadzikwa, T.; Bellini, R.; Dekker, H.
L.; Reek, J. N. H. J. Am. Chem. Soc. 2012, 134, 2860.
(3) (a) Stang, P. J.; Cao, D. H. J. Am. Chem. Soc. 1994, 116, 4981.
(b) Stang, P. J.; Chen, K. J. Am. Chem. Soc. 1995, 117, 1667. (c) Stang,
P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc. 1995, 117,
6273.
(18) Schweiger, M.; Seidel, S. R.; Arif, A. M.; Stang, P. J. Inorg. Chem.
2002, 41, 2556.
(4) (a) Fujita, M.; Yazaki, J.; Ogura, K. J. Am. Chem. Soc. 1990, 112,
5645. (b) Fujita, M.; Nagao, S.; Iida, M.; Ogata, K.; Ogura, K. J. Am.
Chem. Soc. 1993, 115, 1574. (c) Fujita, M.; Ibukuro, F.; Hagihara, H.;
Ogura, K. Nature 1994, 367, 720. (d) Fujita, M.; Ibukuro, F.;
Yamaguchi, K.; Ogura, K. J. Am. Chem. Soc. 1995, 117, 4175.
(5) (a) Rasika Dias, H. V.; Palehepitiya Gamage, C. S. Angew. Chem.,
(19) Fujita, M.; Sasaki, O.; Mitsuhashi, T.; Fujita, T.; Yazaki, J.;
Yamaguchi, K.; Ogura, K. Chem. Commun. 1996, 1535.
(20) Weilandt, T.; Troff, R. W.; Saxell, H.; Rissanen, K.; Schalley, C.
A. Inorg. Chem. 2008, 47, 7588.
(21) (a) Lee, S. B.; Hwang, S.; Chung, D. S.; Yun, H.; Hong, J.-I.
Tetrahedron Lett. 1998, 39, 873. (b) Sautter, A.; Schmid, D. G.; Jung,
́
Int. Ed. 2007, 46, 2192. (b) Schnebeck, R.-D.; Freisinger, E.; Glahe, F.;
G.; Wurthner, F. J. Am. Chem. Soc. 2001, 123, 5424. (c) Zhang, L.;
̈
Lippert, B. J. Am. Chem. Soc. 2000, 122, 1381. (c) Hwang, S.-H.;
Moorefield, C. N.; Fronczek, F. R.; Lukoyanova, O.; Echegoyen, L.;
Newkome, G. R. Chem. Commun. 2005, 713. (d) Kryschenko, Y. K.;
Seidel, S. R.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2003, 125, 5193.
(e) Schmittel, M.; Mahata, K. Chem. Commun. 2008, 2550.
(f) Schmittel, M.; Mahata, K. Inorg. Chem. 2009, 48, 822. (g) Mahata,
K.; Saha, M. L.; Schmittel, M. J. Am. Chem. Soc. 2010, 132, 15933.
(6) (a) Whiteford, J. A.; Lu, C. V.; Stang, P. J. J. Am. Chem. Soc. 1997,
119, 2524. (b) Stang, P. J.; Cao, D. H.; Chen, K.; Gray, G. M.;
Muddiman, D. C.; Smith, R. D. J. Am. Chem. Soc. 1997, 119, 5163.
Niu, Y.-H.; Jen, A. K.-Y.; Lin, W. Chem. Commun. 2005, 1002.
(d) Uehara, K.; Kasai, K.; Mizuno, N. Inorg. Chem. 2007, 46, 2563.
(e) Uehara, K.; Kasai, K.; Mizuno, N. Inorg. Chem. 2010, 49, 2008.
(22) Jiang, H.; Lin, W. J. Am. Chem. Soc. 2006, 128, 11286.
(23) (a) Schubert, U. S.; Eschbaumer, C. Angew. Chem., Int. Ed. 2002,
41, 2892. (b) Hofmeier, H.; Schubert, U. S. Chem. Soc. Rev. 2004, 33,
373. (c) Wild, A.; Winter, A.; Schlutter, F.; Schubert, U. S. Chem. Soc.
Rev. 2011, 40, 1459. (d) Constable, E. C. Coord. Chem. Rev. 2008, 252,
842. (e) De, S.; Mahata, K.; Schmittel, M. Chem. Soc. Rev. 2010, 39,
1555.
(c) You, C.-C.; Wurthner, F. J. Am. Chem. Soc. 2003, 125, 9716.
̈
(24) (a) Whittell, G. R.; Hager, M. D.; Schubert, U. S.; Manners, I.
Nat. Mater. 2011, 10, 176. (b) Mansfeld, U.; Hager, M. D.;
Hoogenboom, R.; Ott, C.; Winter, A.; Schubert, U. S. Chem. Commun.
2009, 3386. (c) Mansfeld, U.; Winter, A.; Hager, M. D.;
Hoogenboom, R.; Gunther, W.; Schubert, U. S. Polym. Chem. 2013,
4, 113. (d) Mansfeld, U.; Winter, A.; Hager, M. D.; Festag, G.;
Hoeppener, S.; Schubert, U. S. Polym. Chem. 2013, 4, 3177.
(25) (a) Chan, Y.-T.; Li, X.; Soler, M.; Wang, J.-L.; Wesdemiotis, C.;
Newkome, G. R. J. Am. Chem. Soc. 2009, 131, 16395. (b) Wang, J.-L.;
Li, X.; Lu, X.; Hsieh, I. F.; Cao, Y.; Moorefield, C. N.; Wesdemiotis,
C.; Cheng, S. Z. D.; Newkome, G. R. J. Am. Chem. Soc. 2011, 133,
11450. (c) Schultz, A.; Li, X.; Barkakaty, B.; Moorefield, C. N.;
Wesdemiotis, C.; Newkome, G. R. J. Am. Chem. Soc. 2012, 134, 7672.
(d) Sautter, A.; Kaletas,
̧ B. K.; Schmid, D. G.; Dobrawa, R.; Zimine,
M.; Jung, G.; van Stokkum, I. H. M.; De Cola, L.; Williams, R. M.;
Wurthner, F. J. Am. Chem. Soc. 2005, 127, 6719.
̈
(7) Saha, M. L.; Schmittel, M. J. Am. Chem. Soc. 2013, 135, 17743.
(8) (a) Yang, H.-B.; Das, N.; Huang, F.; Hawkridge, A. M.; Díaz, D.
D.; Arif, A. M.; Finn, M. G.; Muddiman, D. C.; Stang, P. J. J. Org.
Chem. 2006, 71, 6644. (b) Lu, J.; Turner, D. R.; Harding, L. P.; Byrne,
L. T.; Baker, M. V.; Batten, S. R. J. Am. Chem. Soc. 2009, 131, 10372.
(c) Lu, X.; Li, X.; Wang, J.-L.; Moorefield, C. N.; Wesdemiotis, C.;
Newkome, G. R. Chem. Commun. 2012, 48, 9873.
(9) (a) Zhao, L.; Ghosh, K.; Zheng, Y.; Lyndon, M. M.; Williams, T.
I.; Stang, P. J. Inorg. Chem. 2009, 48, 5590. (b) Campos-Fernandez, C.
́
S.; Schottel, B. L.; Chifotides, H. T.; Bera, J. K.; Bacsa, J.; Koomen, J.
M.; Russell, D. H.; Dunbar, K. R. J. Am. Chem. Soc. 2005, 127, 12909.
(c) Hwang, S.-H.; Wang, P.; Moorefield, C. N.; Godinez, L. A.;
Manriquez, J.; Bustos, E.; Newkome, G. R. Chem. Commun. 2005,
4672.
(10) (a) Stang, P. J.; Persky, N. E.; Manna, J. J. Am. Chem. Soc. 1997,
119, 4777. (b) Newkome, G. R.; Cho, T. J.; Moorefield, C. N.; Baker,
G. R.; Cush, R.; Russo, P. S. Angew. Chem., Int. Ed. 1999, 38, 3717.
(c) Wang, G.-L.; Lin, Y.-J.; Jin, G.-X. Chem.Eur. J. 2011, 17, 5578.
(11) (a) Hasenknopf, B.; Lehn, J.-M.; Kneisel, B. O.; Baum, G.;
Fenske, D. Angew. Chem., Int. Ed. 1996, 35, 1838. (b) Hasenknopf, B.;
Lehn, J.-M.; Boumediene, N.; Dupont-Gervais, A.; Van Dorsselaer, A.;
Kneisel, B.; Fenske, D. J. Am. Chem. Soc. 1997, 119, 10956.
(c) Newkome, G. R.; Wang, P.; Moorefield, C. N.; Cho, T. J.;
Mohapatra, P. P.; Li, S.; Hwang, S.-H.; Lukoyanova, O.; Echegoyen, L.;
Palagallo, J. A.; Iancu, V.; Hla, S.-W. Science 2006, 312, 1782. (d) Jiang,
H.; Lin, W. J. Am. Chem. Soc. 2004, 126, 7426. (e) Jiang, H.; Lin, W. J.
Am. Chem. Soc. 2003, 125, 8084.
(26) (a) Schroder, T.; Brodbeck, R.; Letzel, M. C.; Mix, A.;
̈
Schnatwinkel, B.; Tonigold, M.; Volkmer, D.; Mattay, J. Tetrahedron
Lett. 2008, 49, 5939. (b) Wang, C.; Hao, X.-Q.; Wang, M.; Guo, C.;
Xu, B.; Tan, E. N.; Zhang, Y.; Yu, Y.; Li, Z.-Y.; Yang, H.-B.; Song, M.-
P.; Li, X. Chem. Sci. 2014, 5, 1221.
(27) (a) Schmittel, M.; He, B. Chem. Commun. 2008, 4723.
(b) Schmittel, M.; He, B.; Mal, P. Org. Lett. 2008, 10, 2513.
(c) Cardona-Serra, S.; Coronado, E.; Gavina, P.; Ponce, J.; Tatay, S.
Chem. Commun. 2011, 47, 8235.
(28) (a) Chan, Y.-T.; Li, X.; Moorefield, C. N.; Wesdemiotis, C.;
Newkome, G. R. Chem.Eur. J. 2011, 17, 7750. (b) Chan, Y.-T.; Li,
X.; Yu, J.; Carri, G. A.; Moorefield, C. N.; Newkome, G. R.;
Wesdemiotis, C. J. Am. Chem. Soc. 2011, 133, 11967. (c) Wang, J.-L.;
Li, X.; Lu, X.; Chan, Y.-T.; Moorefield, C. N.; Wesdemiotis, C.;
Newkome, G. R. Chem.Eur. J. 2011, 17, 4830. (d) Li, X.; Chan, Y.-
T.; Casiano-Maldonad, M.; Yu, J.; Carri, G. A.; Newkome, G. R.;
Wesdemiotis, C. Anal. Chem. 2011, 83, 6667.
(12) Lehn, J.-M. Science 2002, 295, 2400.
6670
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671

Journal of the American Chemical Society
Article
(29) Fasting, C.; Schalley, C. A.; Weber, M.; Seitz, O.; Hecht, S.;
Koksch, B.; Dernedde, J.; Graf, C.; Knapp, E.-W.; Haag, R. Angew.
Chem., Int. Ed. 2012, 51, 10472.
(30) (a) Breuker, K.; McLafferty, F. W. Proc. Natl. Acad. Sci. U.S.A.
2008, 105, 18145. (b) Rappas, M.; Schumacher, J.; Beuron, F.; Niwa,
H.; Bordes, P.; Wigneshweraraj, S.; Keetch, C. A.; Robinson, C. V.;
Buck, M.; Zhang, X. Science 2005, 307, 1972. (c) Ruotolo, B. T.; Giles,
K.; Campuzano, I.; Sandercock, A. M.; Bateman, R. H.; Robinson, C.
V. Science 2005, 310, 1658.
(31) (a) Barnsley, M. F. Fractals Everywhere; Morgan Kaufmann
Publishers: Burlington, MA, 1993. (b) Mandelbrot, B. Fractals: form,
chance and dimension; W. H. Freeman and Co.: New York, 1977.
(32) (a) Sun, Q.-F.; Iwasa, J.; Ogawa, D.; Ishido, Y.; Sato, S.; Ozeki,
T.; Sei, Y.; Yamaguchi, K.; Fujita, M. Science 2010, 328, 1144. (b) Sun,
Q.-F.; Sato, S.; Fujita, M. Nat. Chem. 2012, 4, 330. (c) Black, S. P.;
Stefankiewicz, A. R.; Smulders, M. M. J.; Sattler, D.; Schalley, C. A.;
Nitschke, J. R.; Sanders, J. K. M. Angew. Chem., Int. Ed. 2013, 52, 5749.
(d) Mahata, K.; Frischmann, P. D.; Wurthner, F. J. Am. Chem. Soc.
̈
2013, 135, 15656.
(33) (a) Saalfrank, R. W.; Maid, H.; Scheurer, A.; Puchta, R.; Bauer,
W. Eur. J. Inorg. Chem. 2010, 2010, 2903. (b) Saalfrank, R. W.;
Deutscher, C.; Maid, H.; Ako, A. M.; Sperner, S.; Nakajima, T.; Bauer,
W.; Hampel, F.; Heß, B. A.; van Eikema Hommes, N. J. R.; Puchta, R.;
Heinemann, F. W. Chem.Eur. J. 2004, 10, 1899.
(34) (a) Perera, S.; Li, X.; Soler, M.; Schultz, A.; Wesdemiotis, C.;
Moorefield, C. N.; Newkome, G. R. Angew. Chem., Int. Ed. 2010, 49,
6539. (b) Ujma, J.; De Cecco, M.; Chepelin, O.; Levene, H.; Moffat,
C.; Pike, S. J.; Lusby, P. J.; Barran, P. E. Chem. Commun. 2012, 48,
4423. (c) Thiel, J.; Yang, D.; Rosnes, M. H.; Liu, X.; Yvon, C.; Kelly, S.
E.; Song, Y.-F.; Long, D.-L.; Cronin, L. Angew. Chem., Int. Ed. 2011, 50,
8871. (d) Scarff, C. A.; Snelling, J. R.; Knust, M. M.; Wilkins, C. L.;
Scrivens, J. H. J. Am. Chem. Soc. 2012, 134, 9193. (e) Ruotolo, B. T.;
Benesch, J. L. P.; Sandercock, A. M.; Hyung, S. J.; Robinson, C. V. Nat.
Protoc. 2008, 3, 1139.
(35) (a) Brocker, E. R.; Anderson, S. E.; Northrop, B. H.; Stang, P. J.;
Bowers, M. T. J. Am. Chem. Soc. 2010, 132, 13486. (b) Bowers, M. T.;
Kemper, P. R.; von Helden, G.; Koppen, P. A. M. Science 1993, 260,
1446. (c) Clemmer, D. E.; Jarrold, M. F. J. Mass Spectrom. 1997, 32,
577. (d) Trimpin, S.; Plasencia, M.; Isailovic, D.; Clemmer, D. E. Anal.
Chem. 2007, 79, 7965. (e) Fenn, L. S.; McLean, J. A. Anal. Bioanal.
Chem. 2008, 391, 905. (f) Silveira, J. A.; Fort, K. L.; Kim, D.; Servage,
K. A.; Pierson, N. A.; Clemmer, D. E.; Russell, D. H. J. Am. Chem. Soc.
2013, 135, 19147.
(36) Thalassinos, K.; Grabenauer, M.; Slade, S. E.; Hilton, G. R.;
Bowers, M. T.; Scrivens, J. H. Anal. Chem. 2008, 81, 248.
(37) (a) Shvartsburg, A. A.; Jarrold, M. F. Chem. Phys. Lett. 1996,
261, 86. (b) Shvartsburg, A. A.; Liu, B.; Siu, K. W. M.; Ho, K.-M. J.
Phys. Chem. A 2000, 104, 6152. (c) Jarrold, M. F. Annu. Rev. Phys.
Chem. 2000, 51, 179.
6671
dx.doi.org/10.1021/ja501417g | J. Am. Chem. Soc. 2014, 136, 6664−6671