A chiral pentadecanuclear metallamacrocycle with a sextuple twisted moebius topology

Article abstract of DOI:10.1021/ja075945w

A C₃ symmetric pentadecanuclear metallamacrocycle was obtained by the self-assembly of a pentadentate bridging ligand, N-phenylpropiolyl salicylhydrazide (H₃L), and a manganese ion. The combination of a narrow Cα-Cβ region near the b

Full text of DOI:10.1021/ja075945w

Published on Web 10/26/2007
A Chiral Pentadecanuclear Metallamacrocycle with a Sextuple Twisted
Mo1bius Topology
Rohith P. John,† Mira Park,† Dohyun Moon,† Kyungjin Lee,† Seunghee Hong,† Yang Zou,†
Chang Seop Hong,‡ and Myoung Soo Lah*,†
Department of Chemistry and Applied Chemistry, College of Science and Technology, Hanyang UniVersity, Ansan,
Kyunggi-Do 426-791, Korea, and Department of Chemistry, Korea UniVersity, Seoul 136-701, Korea
Received August 8, 2007; E-mail: mslah@hanyang.ac.kr
Scheme 1
Construction of cyclic molecules has received much attention
in recent years because of both scientific curiosity and their potential
use in applications such as magnetic materials, sensors for small
molecules, and new classes of catalysts.1 Although the possibility
of forming molecules with a twisted cyclic band structure (Mo¨bius
molecules) was predicted theoretically among organic molecules
such as polyenes and other conjugated aromatic systems,2 only a
few of such molecules have been realized experimentally.3 Recently,
an example of an inorganic Mo¨bius strip of NbSe3 crystal based
on the coordination chemistry of inorganic elements has been
reported.4 A suitable design of the ligands and an appropriate choice
of metal ions acting as connecting nodes can also lead to twisted
cyclic architectures with a Mo¨bius topology. The only metallamac-
rocycle of Mo¨bius topology was obtained from a self-assembly of
[Li2(pyridyl-2,6-diphenyl)(tmeda)2] (tmeda ) N,N,N′,N′-tetrameth-
ylethylene diamine) and a AuI-diphosphane complex.5 While
several strategies exist to introduce multiple twists in conjugated
cyclic polyenes or other aromatic systems,6 none of these exhibits
a twist greater than double twists (360° twists), which is probably
around the metal center. The occurrence of successive metal centers
due to the large strain that the cyclic system needs to accommodate.
of the same ∆ configuration produces double twists (360° twists)
in the metallamacrocycle along the direction of the propagation
Metallamacrocycles that may experience lower strains around the
metal centers due to the twist may be a convenient alternative for
(Figure 2 and Figure S3). To obtain an insight into the nature and
the generation of multiple twisted cyclic systems.
extent of the twist and its contribution to the overall geometry of
The pentadentate N-acylsalicylhydrazide can serve as an asym-
the metallamacrocycle, we calculated the twist resulting from the
metric ditopic bridging ligand between octahedral metal ions using
chiral configuration at each metal center with respect to the ligand
its tridentate and bidentate binding modes to form metallamacro-
orientation. The consecutive twist angles calculated using the
cycles (Scheme 1).7 Depending on the influence of the N-terminal
dihedral angle between the neighboring ligand planes were +90,
steric domain during self-assembly, the ligand chooses either Λ or
+81, +99, +82, and -92°, where the direction and the extent of
∆ configuration around each metal center (Figure S1). In addition,
an individual twist is determined by the chiral sequence of four
it is also possible to modify the nuclearity of the macrocycle8 and
consecutive metal centers (Table S1). The five consecutive (+ +
+ + -) twists contribute a net twist of 360° (double twist) along
the direction of propagation.11
the stereochemistry of the metal centers.9,10 A decrease in the steric
volume near the CR-Câ region may increase the possibility of
three or more successive metal centers having the same chiral con-
figuration in the macrocycle that can induce multiple twists in the
cycle.
Herein, we report on the self-assembly and characterization of a
unique manganese-based pentadecanuclear metallamacrocycle from
a manganese ion and a pentadentate ligand, N-phenylpropiolyl
salicylhydrazide (H3L), which has the smallest steric volume near
the CR-Câ region (Scheme 1).
X-ray quality single crystals of the complex were grown from a
DMF solution of the ligand, N-phenylpropiolyl salicylhydrazide,
and manganese acetate by layering with diethyl ether. The penta-
decanuclear metallamacrocycle with C3 symmetry, [Mn15L15S15] 1
(Figure 1), where S is either a DMF or a water molecule, crystallizes
in the chiral space group P63, and the asymmetric unit contains
five ligand units bound to five metal centers (Figure S2).
The steric requirements of the ethynyl phenyl group in the N-
terminal steric domain restrain the chiral sequence to ‚‚‚∆∆∆∆Λ‚‚‚
The macrocycle makes a sharp turn at the metal center with a Λ
configuration (Figure 2). Three such turns in the backbone lead to
a C3 symmetric pentadecanuclear metallamacrocycle. This results
in a sum of six 180° twists in the overall cycle, creating a sextuple
twisted metallamacrocycle (Figure S4).12
The double twist in the asymmetric unit orients the three salicyl
moieties toward the inner core of the macrocycle on one face of
the cycle (Figure S5). The chiral nature of the C3 symmetric
macrocycle13 is exemplified by the fact that the inner core of the
other face of the macrocycle has different residues, that is, three
ethynyl phenyl groups.
Depending on the nature of the N-acyl residue, the chiral
sequence of the metal centers is determined to minimize the
unfavorable steric repulsion and to maximize the favorable weak
interactions, such as the C-H‚‚‚π and π‚‚‚π stacking interactions.
The macrocyclic assembly has a total of nine intramolecular
C-H‚‚‚O interactions between the N-terminal aromatic C-H’s and
oxygen atoms in the bridging domains of the different ligand units
(Table S2). Three intramolecular C-H‚‚‚π interactions between
† Hanyang University.
‡ Korea University.
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10.1021/ja075945w CCC: $37.00 © 2007 American Chemical Society

C O M M U N I C A T I O N S
rigid ethynyl phenyl N-tail to the ligand minimized the steric
interaction in the CR-Câ region and provided a moderate steric
volume beyond this region. This led to the formation of four
successive metal centers of the same ∆ configuration, followed by
a Λ, which resulted in a sextuple twisted chiral macrocycle. To
the best of our knowledge, this is the first sextuple twisted high-
nuclearity metallamacrocycle that has a Mo¨bius topology.
Acknowledgment. This work was supported by KRF (KRF-
2005-070-C00068), KOSEF (R01-2007-000-10167-0), and CBMH.
The authors also acknowledge PAL for beamline use (2007-2041-
17).
Supporting Information Available: Synthesis of the ligand and
1, crystallographic details of 1. This material is available free of charge
via the Internet at http://pubs.acs.org.
References
(1) (a) Farrell, J. R.; Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.;
Rheingold, A. L. Angew. Chem., Int. Ed. 1998, 37, 465-467. (b) Holliday,
B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-2043. (c)
Szejtli, J. Chem. ReV. 1998, 98, 1743-1753. (d) Spitler, E. L.; Johnson,
C. A., II; Haley, M. M. Chem. ReV. 2006, 106, 5344-5386. (e) Leininger,
S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853-908. (f)
Tasiopoulos, A. J.; Vinslava, A.; Wernsdorfer, W.; Abboud, K. A.;
Christou, G. Angew. Chem., Int. Ed. 2004, 43, 2117-2121. (g) Fujita,
M. Chem. Soc. ReV. 1998, 27, 417-425. (h) Gianneschi, N. C.; Bertin,
P. A.; Nguyen, S. T.; Mirkin, C. A.; Zakharov, L. N.; Rheingold, A. L.
J. Am. Chem. Soc. 2003, 125, 10508-10509. (i) Yamanari, K.; Yamamoto,
S.; Ito, R.; Kushi, Y.; Fuyuhiro, A.; Kubota, N.; Fukuo, T.; Arakawa, R.
Angew. Chem., Int. Ed. 2001, 40, 2268-2271. (j) Mimassi, L.; Cordier,
C.; Guyard-Duhayon, C.; Mann, B. E.; Amouri, H. Organometallics 2007,
26, 860-864.
Figure 1. A stick diagram of chiral pentadecanuclear metallamacrocycle
1 with C3 symmetry. The -N-N- connectivities are shown in green. The
metal ions with ∆ configuration appear as blue spheres, and the metal ions
with Λ configuration appear as red spheres.
(2) (a) Heilbronner, E. Tetrahedron Lett. 1964, 5, 1923-1928. (b) Rzepa, H.
S. Chem. ReV. 2005, 105, 3697-3715.
(3) (a) Ajami, D.; Oeckler, O.; Simon, A.; Herges, R. Nature 2003, 426, 819-
821. (b) Herges, R. Chem. ReV. 2006, 106, 4820-4842. (c) Ajami, D.;
Hess, K.; Ko¨hler, F.; Na¨ther, C.; Oeckler, O.; Simon, A.; Yamamoto, C.;
Okamoto, Y.; Herges, R. Chem.sEur. J. 2006, 12, 5434-5445.
(4) Kui, S. C. F.; Huang, J.-S.; Sun, R. W.-Y.; Zhu, N.; Che, C.-M. Angew.
Chem., Int. Ed. 2006, 45, 4663-4666.
(5) (a) Tanda, S.; Tsuneta, T.; Okajima, Y.; Inagaki, K.; Yamaya, K.;
Hatakenaka, N. Nature 2002, 417, 397-398. (b) Patzke, G. R. Angew.
Chem., Int. Ed. 2003, 42, 972-974.
(6) (a) Rath, H.; Sankar, J.; PrabhuRaja, V.; Chandrashekar, T. K.; Joshi, B.
S.; Roy, R. Chem. Commun. 2005, 3343-3345. (b) Sprutta, N.; Latos-
Graz˘yn´ski, L. Chem.sEur. J. 2001, 7, 5099-5112. (c) Hinrichs, H.;
Boydston, A. J.; Jones, P. G.; Hess, K.; Herges, R.; Haley, M. M.; Hopf,
H. Chem.sEur. J. 2006, 12, 7103-7115. (d) Setsune, J.; Katakami, Y.;
Iizuna, N. J. Am. Chem. Soc. 1999, 121, 8957-8958. (e) Collins, S. K.;
Yap, G. P. A.; Fallis, A. G. Org. Lett. 2000, 2, 3189-3192.
(7) John, R. P.; Moon, D.; Lah, M. S. Supramol. Chem. 2007, 19, 295-308.
(8) (a) John, R. P.; Lee, K.; Kim, B. J.; Suh, B. J.; Rhee, H.; Lah, M. S.
Inorg. Chem. 2005, 44, 7109-7121. (b) Liu, S.-X.; Lin, S.; Lin, B.-Z.;
Lin, C.-C.; Huang, J.-Q. Angew. Chem., Int. Ed. 2001, 40, 1084-1087.
(c) John, R. P.; Park, J.; Moon, D.; Lee, K.; Lah, M. S. Chem. Commun.
2006, 3699-3701.
Figure 2. A section of the macrocyclic backbone that shows the double
twist and the turn in the direction of propagation. The metal ions are shown
as spheres and the ligand binding moieties as planes. The blue spheres have
∆ configuration, and the red spheres have Λ configuration. The blue arrows
represent a clockwise (+) rotation, and the red arrows represent an
counterclockwise (-) turn for successive ligand planes.
the N-terminal phenyl groups and three other interactions between
the salicyl C-H’s and ethynyl phenyl groups are identified in the
assembly. In addition, three intramolecular π‚‚‚π stacking interac-
tions between the ethynyl phenyl ring and the salicyl ring of
neighboring ligand units, and extensive van der Waals interactions,
support the assembly (Figure S6). One coordinated DMF molecule
per crystallographic asymmetric unit is lodged in a small pocket
created between the ligand frames of D- and B-labeled residues
using van der Waals interactions (Figure S7 and Table S2). We
believe that a rigid steric domain of the ligand with a narrow CR-
Câ region near the bridging domain and a bulky aromatic phenyl
end located away from the bridging domain induces the four
consecutive ∆ configurations for a double twist and the final Λ
configuration for a turn in the propagation direction in the
asymmetric unit. The combination of weak interactions, such as
C-H‚‚‚π and π‚‚‚π stacking interactions, and extensive van der
Waals interactions may be the reason for the stabilization of the
sextuple twisted pentadecanuclear assembly forming.
(9) John, R. P.; Lee, K.; Lah, M. S. Chem. Commun. 2004, 2660-2661.
(10) Moon, D.; Lee, K.; John, R. P.; Kim, G. H.; Suh, B. J.; Lah, M. S. Inorg.
Chem. 2006, 45, 7991-7993.
(11) The total sum of the twist angles calculated from the dihedral angles
between the two consecutive ligand planes in one asymmetric unit (∼260°)
does not make up the 360° for double twist in the asymmetric unit along
the propagation direction, as shown in Figure 2. This discrepancy is from
the fact that the calculation was performed using the ligand planes that
were not parallel to the direction of the propagation of the macrocyclic
backbone. For a more accurate calculation, we need to calculate the best-
fit straight line representing the propagation direction and the normal vector
residing at the ligand planes, and the twist angles obtained using this
information will form the required 360° for a double twist comprising
four consecutive ∼120° clockwise twists and a ∼120° counterclockwise
twist.
(12) The Mo¨bius topology is only possible in a metallamacrocycle which does
not contain any Sn symmetry. The metallamacrocycle having the chiral
sequence related by an Sn symmetry leads to the same extent of twist but
in an opposite direction, hence the net twist in an achiral metallamacrocycle
is always zero regardless of the individual sequence.
(13) The Flack parameter of the crystal was found to be 0.20(3). However,
the bulk crystals dissolved in chloroform did not show any CD activity,
which suggests that metallamacrocycle 1 in bulk is not homochiral but
racemic.
In conclusion, we have constructed a unique C3 symmetric
pentadecanuclear metallamacrocycle using a pentadentate bridging
ligand, N-phenylpropiolyl salicylhydrazide. The introduction of a
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