Self-assembly of M24L48 polyhedra based on empirical prediction

Article abstract of DOI:10.1002/anie.201108731

Critical structural switch: A small initial difference in the angle within bidentate ligands (see scheme) is amplified into an incommensurable difference in the resultant structures (M₁₂L₂₄ or M ₂₄L₄₈). This molecular-level emergent behavior was predicted from the empirical threshold of the ligand bend angle, determined by a ligand mixing experiment, for the critical M₁₂L₂₄/M ₂₄L₄₈ switchover. Copyright

Full text of DOI:10.1002/anie.201108731

Angewandte
Chemie
DOI: 10.1002/anie.201108731
Self-Assembly
Self-Assembly of M L Polyhedra Based on Empirical Prediction**
2
4
48
Jens Bunzen, Junji Iwasa, Pia Bonakdarzadeh, Eri Numata, Kari Rissanen,* Sota Sato,* and
Makoto Fujita*
Self-assembly of giant coordination polyhedra from metal
ions and bridging ligands is one of the intriguing topics in
[
1–3]
current chemistry.
In theory, the structures of the poly-
hedra can be predicted based on the analysis of the
coordination geometry at the metal and the bridging angles
[4]
of the ligands. In reality, however, unpredicted structures
often appear because molecular components are much more
flexible than expected and metal centers can permit consid-
[
5,6]
erable deviation in their coordination angles.
when the number of the components is considerably large
more than about 50), the prediction of self-assembled
structures becomes increasingly difficult or impossible.
In particular,
(
[7]
Recently, an M L cuboctahedron and an M L
rhombicuboctahedron were constructed from very similar
ligands 1 and 5, respectively, upon complexation with Pd ions
1
2
[
24
8]
24 48
II
Figure 1. Self-assembly of M L and M24L48 polyhedra in which the
1
2 24
(
Figure 1). The prediction of these two structures by theory
metal centers define a cuboctahedron and a rhombicuboctahedron,
respectively. a) Representation. b) Structural formulae of ligands 1–5
with their bend angles. Angle spans used to predict the formation of
M L and M24L are indicated below the formulae.
was not possible, but when mixed ligands (1 + 5) were
subjected to metal complexation, we observed the critical
switch of the resultant structures from M L to M L at the
12 24
48
1
2
24
24 48
mixing ratios of 1:5 = 8:2 ꢀ 7:3, where the averaged ligand
[
8]
[9]
bend angle varies from 131 to 1348. We assumed that the
most important parameter that controls the resultant struc-
tures was the bend angle q of the ligands and predicted that
the critical structural switch would occur at around q = 131–
the values of 1358, 1438, and 1478, respectively. These values
fit nicely into the angle span that predicts the formation of
M L (Figure 1b). The larger bend angle in 4 than 2 is
2
4
48
probably due to the steric demand of the N-methyl substitu-
ent in 4 that pushes the two pyridyl groups apart. These
ligands could be easily prepared in relatively few steps by
using Suzuki cross-coupling (for 2 and 4) or [3+2] isocyanide–
olefin cycloaddition (for 3) as key reactions (for details, see
the Supporting Information).
1
348 if the bend angle was chemically modulated (Figure 1b).
Herein, we show that this simple empirical prediction is
applicable for self-assembly from ligands 2–4. By referring the
bend angles of these ligands to the empirical scale in
Figure 1b, we predicted the self-assembly of M L , the
2
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48
largest hitherto known coordination polyhedron, from these
ligands 2–4.
The bend angle of ligand 4 is 1478, which is close to that of
5. Therefore, formation of M L is expected from this ligand.
2
4
48
DFT calculations (B3LYP/6-31G*) revealed that the
angles between the pyridine rings of ligands 2, 3, and 4 have
When ligand 4 was treated with Pd(NO ) in [D ]DMSO
3 2 6
(708C for 3 h), the selective formation of M L complex 6
2
4
48
was indicated by NMR spectroscopy (Figure 2) and CSI-
[
10]
MS (Figure 3). The roughly spherical M L complex 6 has
2
4
48
[
*] Dr. J. Bunzen, P. Bonakdarzadeh, Prof. K. Rissanen
Department of Chemistry, NanoScience Center
University of Jyvꢀskylꢀ
P.O. Box 35, 40014 Jyvꢀskylꢀ (Finland)
E-mail: kari.t.rissanen@jyu.fi
a rhombicuboctahedral symmetry and offers the ligands two
different positions in the framework, which can be seen from
two sets of signals in the H NMR spectrum of the complex
1
(Figure 2a). The signals show downfield shifts (particularly
J. Iwasa, E. Numata, Dr. S. Sato, Prof. M. Fujita
Department of Applied Chemistry, School of Engineering
The University of Tokyo
Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
E-mail: ssato@appchem.t.u-tokyo.ac.jp
mfujita@appchem.t.u-tokyo.ac.jp
for pyridine a protons: Dd = 0.61 ppm), which is indicative
of the formation of Pd complexes. Furthermore, the signals
Pya
II
are broadened, indicating the successful formation of a huge
structure. In DOSY, the observation of a single band at
logD = ꢁ10.60 confirmed the single product formation (Fig-
ꢁ
ure 2d). Ultrahigh-resolution CSI-MS of 6 (BF4 salt) showed
[
**] This work was supported by KAKENHI (MEXT), the Strategic
Japanese–Finnish Cooperative Program (JST-Academy of Finland),
and The Academy of Finland. The synchrotron X-ray experiments
were performed at AS, KEK, and SPring-8.
n+
a series of prominent peaks for [Mꢁn(BF )] (n = 15–22),
4
with expected isotopic distributions, from which the molec-
ular weight of 6 (18027.21 Da) was determined (Figure 3).
Ligand 3 has a slightly smaller bend angle (1438), from
which M L formation is still predicted. A disadvantage
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201108731.
2
4
48
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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.
Angewandte
Communications
1
1
ꢁ
3
Figure 2. H NMR spectra of a) 6, b) 7, and c) 8, and H DOSY NMR spectra of e) 6, f) 7, and g) 8 (NO salt, 500 MHz, [D ]DMSO, 300 K).
6
II
Figure 4. X-ray crystal structure of M L complex 7. Ligands and Pd
2
4 48
ions are shown by stick and ball representations, respectively. Views
are shown looking down along the C (left) and C (right) axes.
Counterions and solvents are omitted for clarity. The unsymmetrical
pyrrole core of ligand 3 is disordered in two positions.
3
4
ꢁ
ꢁ
n+
Figure 3. CSI-MS of complex 6 (BF4 salt). A series of [M-n(BF4 )]
peaks are clearly observed. The inset shows the simulated (resolving
power: 25601) and observed isotopic patterns of the [Mꢁ17(BF )]
ꢁ
17+
4
ion.
details) were collected after several trials with three different
synchrotron X-ray sources, and the final dataset (to resolution
of 1.32 ꢀ) was obtained from the MX2 beamline at the
Australian Synchrotron facility. The unsymmetric ligand 3 is
disordered over two opposite orientations (50:50), showing its
pseudosymmetry. The crystal structure clearly shows the
roughly spherical rhombicuboctahedral framework of 7 with
accompanying the use of this lower-symmetry ligand is an
increase in the demands upon analysis. Fortunately, after
II
1
complexation with Pd ions, H NMR spectrometry revealed
that the lowered symmetry of ligand 3 was unimportant or
actually averaged out in the analysis owing to its pseudosym-
metry. As expected, two sets of broadened signals were
observed in a ratio of 1:1, reflecting the two ligand positions
3
a huge ca. 110000 ꢀ void space (ca. 82%) in the unit cell. The
3
cavity volume of the sphere itself is ca. 23000 ꢀ .
II
(
Figure 2b). A DOSY experiment again confirmed the
Finally, the Pd complexation was examined with ligand 2.
generation of only one species in solution (Figure 2e). The
logD value (ꢁ10.52) was nearly identical to that of 6.
Furthermore, CSI-MS confirmed the molecular weight of
M L complex 7 (17354.45 Da; see the Supporting Informa-
The empirical prediction of the self-assembled structure from
this ligand is a borderline case because its bend angle (q =
1358) is only slightly larger than the threshold (131–1348) for
the M L /M L critical switch (Figure 1b). When ligand 2
2
4
48
12 24
24 48
tion).
Further to these satisfactory NMR and MS data, the
structure of 7 was fully confirmed by X-ray crystallographic
analysis (Figure 4). Single crystals of 7 were obtained by slow
was complexed with Pd(NO ) , we were surprised to observe
3 2
the selective formation of expected M L complex 8 by
2
4
48
1
NMR and MS analyses. The H NMR spectrum showed the
two sets of broadened signals (1:1 ratio), which is typical for
the M L rhombicuboctahdron formation. The close coinci-
vapor diffusion of ethyl acetate into a DMSO solution of 7
2
4
48
ꢁ
(
BF4 salt) over 6 weeks. Owing to the slight positional
dence of logD value (ꢁ10.50) with those of 6 and 7 also
disorder of the sphere itself and the severe disorder of the
anions and solvent molecules, the diffraction power of the
crystals remained very low and no decent data were obtained
with the in-house diffractometer. However satisfactory dif-
fraction data (see the Supporting Information for further
supported the formation of 8. CSI-MS revealed a typical
ꢁ
n+
pattern for the series of [Mꢁn(OTf )] multiply charged ions
ꢁ
from 8 (OTf salt).
More importantly, neither DOSY nor CSI-MS measure-
ment revealed the concomitant formation of an M L
24
1
2
3
162
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Angewandte
Chemie
[
11]
cuboctahedron
assembly of 8. Considering the very similar structures of
and 2, we thus confirmed the critical M L /M L
or any other by-products in the self-
Chem. 1998, 110, 1940 – 1943; Angew. Chem. Int. Ed. 1998, 37,
840 – 1842; c) B. F. Abrahams, S. J. Egan, R. Robson, J. Am.
Chem. Soc. 1999, 121, 3535 – 3536; d) A. Mꢂller, V. P. Fedin, C.
Kuhlmann, H. Bçgge, M. Schmidtmann, Chem. Commun. 1999,
1
1
1
2
24
24 48
structural switch in a chemically well-defined system.
In summary, we succeeded in the self-assembly of three
M L rhombicuboctahedral complexes 6–8, the largest
927 – 928; e) B. Olenyuk, M. D. Levin, J. A. Whiteford, J. E.
Shield, P. J. Stang, Nature 1999, 398, 796 – 799; f) M. Ni, A.
Tassar, T. Antoun, O. M. Yaghi, J. Am. Chem. Soc. 2005, 127,
12752 – 12753.
2
4
48
hitherto known coordination polyhedra, from pyrrole-cored
ligands 2–4. Most importantly, the formation of the M L , at
[2] Recent examples: a) S. Hiraoka, K. Harano, M. Shiro, Y. Ozawa,
N. Yasuda, K. Toriumi, M. Shionoya, Angew. Chem. 2006, 118,
2
4
48
the exclusion of entropically more favored M L , is predict-
1
2
24
6638 – 6641; Angew. Chem. Int. Ed. 2006, 45, 6488 – 6491;
able from an empirical scale that is readily available from
ligand-mixing experiments (1 + 5). It is particularly note-
b) N. K. Al-Rasbi, I. S. Tidmarsh, S. P. Argent, H. Adams, L. P.
Harding, M. D. Ward, J. Am. Chem. Soc. 2008, 130, 11641 –
11649; c) R. W. Saalfrank, H. Maid, A. Scheurer, F. W. Heine-
mann, R. Puchta, W. Bauer, D. Stern, D. Stalke, Angew. Chem.
2008, 120, 9073 – 9077; Angew. Chem. Int. Ed. 2008, 47, 8941 –
worthy that a mixture of M L and M L has never been
1
2
24
24 48
obtained from any of ligands 1–5, and, as a result, a small
initial difference (particularly, q values of 127 and 1358 for
8945; d) T. K. Ronson, J. Fisher, L. P. Harding, P. J. Rizkallah,
1
and 2) was amplified into an incommensurable difference in
J. E. Warren, M. J. Hardie, Nat. Chem. 2009, 1, 212 – 216; e) J.-R.
Li, H.-C. Zhou, Nat. Chem. 2010, 2, 893 – 898.
the resultant structures (M L or M L ), referable as
1
2
24
24 48
12,13]
[
a molecular-level emergent behavior.
[
3] Reviews: a) M. Fujita, M. Tominaga, A. Hori, B. Therrien, Acc.
Chem. Res. 2005, 38, 369 – 378; b) S. R. Seidel, P. J. Stang, Acc.
Chem. Res. 2002, 35, 972 – 983; c) A. Mꢂller, P. Kçgerler,
A. W. M. Dress, Coord. Chem. Rev. 2001, 222, 193 – 218;
d) D. L. Caulder, K. N. Raymond, Acc. Chem. Res. 1999, 32,
975 – 982.
Experimental Section
Preparation of M L complexes 6, 7, and 8: Ligand 4 (0.020 mmol)
2
4
48
was treated with Pd(NO ) (0.010 mmol) in DMSO (1.00 mL) at 708C
3
2
1
for 3 h. H NMR confirmed the quantitative formation of an M L
[4] S. Leininger, B. Olenyuk, P. J. Stang, Chem. Rev. 2000, 100, 853 –
908.
2
4
48
spherical complex 6. In a similar way, M L spherical complexes 7
2
4
48
ꢁ
and 8 were obtained from ligands 3 and 2, respectively. The BF or
[5] The simplest example is given by the formation of molecular
triangles from 908 metal ion hinges and linear bridging ligands:
a) M. Fujita, O. Sasaki, T. Mistuhashi, T. Fujita, J. Yazaki, K.
Yamaguchi, K. Ogura, Chem. Commun. 1996, 1535 – 1536;
b) S. B. Lee, S. Hwang, D. S. Chung, H. Yun, J.-I. Hong,
Tetrahedron Lett. 1998, 39, 873 – 876.
4
ꢁ
TfO salts were prepared using Pd(BF ) or Pd(OTf)2 instead of
4
2
1
ꢁ
Pd(NO ) . Complex 6: H NMR (500 MHz, [D ]DMSO, 300 K, NO
3
3
2
6
salt): d = 9.35 (br, 96H), 9.25 (br, 96H), 7.82 (br, 96H), 7.74 (br, 96H),
.75 (br, 48H), 6.66 (br, 48H), 3.70 (br, 72H), 3.54 ppm (br, 72H);
6
1
ꢁ
3
Complex 7: H NMR (500 MHz, [D ]DMSO, 300 K, NO salt): d =
6
9
2
8
1
.58–8.95 (br, 192H), 8.70 (br, 24H), 8.60 (br, 24H), 8.19–7.45 (br,
40H), 7.74 (br, 96H), 6.99 (br, 24H), 6.90 ppm (br, 24H); Complex
[6] M L vs. M L formation from the same ligand: D. Fujita, A.
1
2
24
6
12
Takahashi, S. Sato, M. Fujita, J. Am. Chem. Soc. 2011, 133,
13317 – 13319.
1
ꢁ
:
H NMR (500 MHz, [D ]DMSO, 300 K, NO salt): d = 12.20–
6
3
1.60 (br, 48H), 9.23 (br, 96H), 9.15 (br, 96H), 8.08 (br, 96H), 7.98
[7] a) M. Tominaga, K. Suzuki, M. Kawano, T. Kusukawa, T. Ozeki,
S. Sakamoto, K. Yamaguchi, M. Fujita, Angew. Chem. 2004, 116,
5739 – 5743; Angew. Chem. Int. Ed. 2004, 43, 5621 – 5625; b) S.
Sato, J. Iida, K. Suzuki, M. Kawano, T. Ozeki, M. Fujita, Science
2006, 313, 1273 – 1276; c) K. Suzuki, S. Sato, M. Fujita, Nat.
Chem. 2010, 2, 25 – 29; d) T. Kikuchi, S. Sato, M. Fujita, J. Am.
Chem. Soc. 2010, 132, 15930 – 15932.
1
3
1
(br, 96H), 7.16 (br, 48H), 7.03 (br, 48H), 3.70 ppm. C NMR, H
DOSY NMR and ultrahigh-resolution CSI-TOF-MS were also
measured for 6–8 (see the Supporting Information).
X-ray crystallographic analysis of 7: X-ray-quality single crystals
were obtained by the slow diffusion of ethyl acetate vapor into
ꢁ
a DMSO solution of 7 (BF4 salt). After several preliminary
synchrotron X-ray diffraction studies at KEK and Spring-8 (both in
Japan), the final diffraction data was collected at the MX2 beamline
[8] Q.-F. Sun, J. Iwasa, D. Ogawa, Y. Ishido, S. Sato, T. Ozeki, Y. Sei,
K. Yamaguchi, M. Fujita, Science 2010, 328, 1144 – 1147.
[9] The bend angle q was calculated by the following equation:
cosq = (ab)/(jajjbj)
in AS (in Australia). Crystal data: M = 16742, colorless prism, 0.12 ꢁ
r
3
0
6
1
.12 ꢁ 0.03 mm , tetragonal, space group I4m, a = b = 43.756(1), c =
9.505(2) ꢀ, V= 133073(2) ꢀ , Z = 1, 1
6904, m = 0.179 mm , T= 100(2) K, 2qmax = 31.68, 15157 unique
3
ꢁ3
= 0.418 gcm , F(000) =
where a and b are the vectors of the pyridyl lone pairs defined by
the coordinates of the pyridyl nitrogen and the ipso carbon atom.
[10] K. Yamaguchi, J. Mass Spectrom. 2003, 38, 473 – 490.
calcd
ꢁ
1
reflections used, 8767 with I > 2s(I ), R = 0.1565, 1394 parameters,
o
o
int
1
241 restraints, GoF = 1.45, R = 0.1565 [I > 2s(I )], wR = 0.419 (all
[11] The M L cuboctahedron from 1 has a logD value of ꢁ10.30,
o
o
12 24
3
reflections), 0.56 < D1 < ꢁ0.276 eꢀ . CCDC 860617 contains the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
which is clearly distinguishable from M L complexes 6–8.
2
4
48
[12] a) P. L. Luisi, The Emergence of Life: From Chemical Origins to
Synthetic Biology, Cambrige University Press, Cambridge, 2010;
b) “System self-assembly”: Studies in Multidisciplinary Series,
Vol. 5 (Eds.: N. Krasnogor, S. Gustafson, D. A. Pelta, J. L.
Verdegay), Elsevier, Dordrecht, 2008; c) H. J. Jensen, Self-
organized criticality: emergent complex behavior in physical
and biological systems, Cambridge Lecture Notes in Physics,
Cambridge Univ. Press, Cambridge, 2003; d) P. Bak, C. Tang, K.
Wiesenfeld, Phys. Rev. Lett. 1987, 59, 381 – 384.
[13] This is reminiscent of remarkable biological activity enhance-
ment by the subtle structure changes of the five-membered rings
of ligands in protein – ligand interactions: L. M. Salonen, M. C.
Holland, P. S. J. Kaib, W. Haap, J. Benz, J.-L. Mary, O. Kuster,
W. B. Schweizer, D. W. Banner, F. Diederich, Chem. Eur. J. 2012,
Received: December 12, 2011
Revised: January 5, 2012
Published online: February 10, 2012
Keywords: palladium · pyrroles · self-assembly ·
.
spherical structures
[
1] Earlier examples: a) M. Fujita, D. Oguro, M. Miyazawa, H. Oka,
K. Yamaguchi, K. Ogura, Nature 1995, 378, 469 – 471; b) D. L.
Caulder, R. E. Powers, T. N. Parac, K. N. Raymond, Angew.
18, 213 – 222.
Angew. Chem. Int. Ed. 2012, 51, 3161 –3163
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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