A binuclear CuII metallacycle capable of discerning between pyrazine and its different methyl-substituted derivatives based on reversible intracage metal-ligand binding

Article abstract of DOI:10.1002/chem.200802690

A report on the formation of Cu^II using self-assembly process for reversible encapsulation of pyrazine and its methyl-substituted derivatives through metal-ligand interactions was presented. It was observed that the reaction was capable of disc

Full text of DOI:10.1002/chem.200802690

COMMUNICATION
DOI: 10.1002/chem.200802690
A Binuclear CuII Metallacycle Capable of Discerning between Pyrazine and
Its Different Methyl-Substituted Derivatives Based on Reversible Intracage
Metal–Ligand Binding
Gui-Ge Hou, Jian-Ping Ma, Ting Sun, Yu-Bin Dong,* and Ru-Qi Huang[a]
Metal-mediated self-assembly is an excellent approach to
build up well-defined molecular containers with an isolated
functional cavity that provide various functions such as mo-
lecular recognition, separation, and chemical reactions.[1]
During recent decades, numerous self-assembled, metal-
mediated, discrete molecular containers—in particular met-
allamacrocycles—have been reported.[2] Coordination-driven
molecular containers with dynamically adjusting cavities in
which the metal center acts as a reversible substrate-binding
site, however, are rarely documented.[3] Metal-centered mo-
lecular containers with reversible binding sites for specific
organic substrates might be metallaenzyme mimics. We have
been interested in selective and reversible host–guest
chemistry of metal-centered containers based on bent five-
membered heteroatom ring-bridged organic ligands. Some
of them display interesting selective, molecular recognizing,
and tunable luminescent properties.[4] Herein, we present a
preliminary report on a CuII–macrocycle formed by a simple
self-assembly process working as a highly selective host cage
for reversible encapsulation of pyrazine and its different
methyl-substituted derivatives through metal–ligand interac-
tions. More importantly, it is capable of discerning between
pyrazine molecules that have different numbers of methyl
substituents.
an N2O2 donor environment (Scheme 1). The opposite
Cu···Cu and O···O distances in the Cu2L2 unit are 8.8 and
8.4 ꢀ, respectively. In addition, the four exocyclic pyridyls
surround the ring and spread effectively outside, thus
making a saddle-shaped cage. These Cu2L2 rings are weakly
À
linked together through four equivalent exocyclic Cu N
bonds into a 3D framework. The external pyridine–copper
À
distance is 2.376(5) ꢀ, which is longer than the Cu N
(apical pyridine) bond length of 2.10–2.20 ꢀ commonly ob-
served in CuII complexes. This makes the externally bound
pyridine donors particularly labile, especially in solution.[5]
Two such identical frameworks interpenetrate each other to
generate a high density structure (see the Supporting Infor-
mation).
The crystals of 1 are not soluble in DMSO or DMF, are
sparingly soluble in MeOH, but are soluble in CHCl3. The
ESIMS of 1 shows a prominent signal at m/z 1207 (see the
Supporting Information), indicating the formation of the
neutral, discrete Cu2L2 (2) molecular cage in solution. Cage
2 has two square-planar CuII centers separated by 8.8 ꢀ,
which hopefully form a perfect host pocket to trap pyrazine
(N···N separation of approximately 2.8 ꢀ) and its derivatives
by weakly coordinating interactions. This is because a CuII
ion can adopt a square-pyramidal coordination sphere and a
size matching between the pyrazine guest and the Cu2L2
host. Indeed, when 2 was treated with an excess of pyrazine
in CHCl3/DMF at room temperature, the new host–guest
Metalation of ligand LH with CuACTHNUTRGNENUG(OAc)2 in an EtOH/THF
mixed solvent system at room temperature afforded the
neutral metallamacrocyclic complex {Cu2L2}n. The coordina-
tion geometry around the CuII center is square planar with
system Cu2L2ACHTNUTRGNEUNG(pyrazine)·5CHCl3 (3) was generated in high
yield, and was confirmed by single-crystal X-ray analysis.
¯
Compound 3 crystallizes in the triclinic space group P1. As
[a] G.-G. Hou, J.-P. Ma, T. Sun, Prof. Dr. Y.-B. Dong, Prof. R.-Q. Huang
College of Chemistry, Chemical Engineering and Materials Science
Key Lab of Molecular and Nano Probes
shown in Figure 1, the trapped pyrazine molecule is cen-
tered in the Cu2L2 pocket and weakly coordinates to the
CuII centers. The bond length between the copper and pyra-
Engineering Research Center of Pesticide and
Medicine Intermediate Clean Production
Ministry of Education, Shandong Normal University
Jinan, 250014 (P.R. China)
Fax : (+86)531-82615258
E-mail: yubindong@sdnu.edu.cn
À
zine nitrogen (Cu1 N3) is 2.409 ꢀ, even longer than that of
À
1, but within the range of 2.6–2.8 ꢀ for axial Cu N bond
lengths.[6] In the solid state, the Cu2L2 rings stack together
along the crystallographic c axis to generate columns with
squarelike channels in which the pyrazine guests arrange in
parallel (Figure 1). No intermolecular p–p interactions have
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802690.
Chem. Eur. J. 2009, 15, 2261 – 2265
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2261

Scheme 1. The synthesis of 1. The long external cage pyridine–copper distances are shown as dotted lines.
powder XRD pattern of the hollow cage has sharp diffrac-
tion peaks, indicating that the ring structure is maintained
without the pyrazine guest, but undergoes a slight change
compared with that of the initial framework of 3 (Figur-
e 2a,b). The ESIMS (see the Supporting Information) spec-
À
Figure 1. Top: molecular structures of 3; the weak Cu N coordination in-
teractions are shown as dotted lines. Bottom: crystal packing of 3; the
trapped pyrazine is shown in orange for clarity.
been found in 3. The CuII···CuII separation in 3 is 7.6 ꢀ,
which has contracted by 1.2 ꢀ compared with that of the
hollow cage, whereas the opposite oxadiazole O3···O3 dis-
tance is 8.8 ꢀ, which has expanded by 0.4 ꢀ compared with
that of the hollow cage.
Figure 2. a) The powder XRD pattern of 3 and the 1H NMR spectrum
obtained from the [D6]DMSO extract, b) the powder XRD pattern of the
hollow cage and the 1H NMR spectrum obtained from the [D6]DMSO
extract, and c) the powder XRD pattern of regenerated
3 and the
1H NMR spectrum obtained from the [D6]DMSO extract. The signals
A host cage that could bind a guest moiety in a reversible
fashion would lead to practical applications. As shown in
Figure 1, the effective pores in the extended structure, and
the weak CuII–pyrazine interaction, would allow easy mobi-
lity of the pyrazine guests through the crystal in a reversible
manner. Indeed, the pyrazine molecules included in the
pores could be readily removed by solid–liquid extractions.
When the crystalline solid of 3 was stirred in [D6]DMSO at
room temperature for approximately one day (monitored by
1H NMR spectroscopy), the weakly coordinated pyrazine
guests were removed by extraction with [D6]DMSO. The
marked by an asterisk correspond to the pyrazine protons (d=8.65 ppm).
trum, 1H NMR spectrum, and elemental analysis indicate
that the hollow cage of 2 was regenerated (see Figure 2b for
1
powder XRD pattern and H NMR spectrum of 2). Further-
more, when the regenerated 2 was suspended in a solution
of pyrazine (excess) in [D6]DMSO at room temperature, the
pyrazine guests are reincorporated into the cage. The
powder XRD pattern indicates that the pyrazineꢀCu2L2
species is completely reformed (Figure 2c). Compound 2 is
2262
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 2261 – 2265

A Flexible and Reversible Metal-Binding Cu2L2 Cage
COMMUNICATION
insoluble in DMSO, therefore, it is unlikely that a dissolu-
tion–recrystallization mechanism could explain the pyrazine
reabsorption.
guest molecules are located (Figure 3). However, the hollow
Cu2L2 cage does not respond to the other pyrazine deriva-
tives, such as 2,3-dimethylpyrazine, 2,6-dimethylpyrazine,
2,3,5,6-tetramethylpyridine, and benzo[a]-pyrazine, under
the experimental conditions, which is clearly caused by the
steric repulsion of the substituted groups adjacent to the ni-
trogen donors.
The major hurdle in molecular recognition is selectivity,
that is, preparing a host pocket that responds only to the
specific substrate in the presence of other different potential
competitors. To explore the molecular selectivity of the
hollow cage 2, its binding affinity for pyrazine, 2-methylpyr-
azine, and 2,5-dimethylpyrazine was examined. When 2 was
treated with a mixture of pyrazine, 2-methylpyrazine, and
2,5-dimethylpyrazine (molar ratio: 2-pyrazine/2-methylpyra-
It is also notable that the Cu2L2 hollow cage can reversi-
bly absorb and reabsorb 2-methylpyrazine and 2,5-dimethyl-
pyrazine guests under the same reaction conditions. The
crystal structures (Figure 3) revealed that compound 4
(Cu2L2(2-methylpyrazine)·2.5CHCl3) crystallizes in the tri-
¯
clinic system P1, whereas compound 5 (Cu2L2(2,5-dimethyl-
¯
pyrazine)·3CHCl3 crystallizes in the triclinic system P1 (5a,
major) and the monoclinic system P2(1) (5b, minor), respec-
tively. Notably, products 5a and 5b are the same 2,5-dime-
thylpyrazineꢀCu2L2 host–guest complexes and exhibit simi-
lar solid-state arrangements (see the Supporting Informa-
À
tion). The Cu N bond lengths in 4 and 5 are in the range of
2.496(4) to 2.665(6) ꢀ, which are significantly longer than
that of 3. The CuII···CuII distances in 4 and 5 are 7.8 and
7.9 ꢀ, respectively, whereas the distance between the two
opposite oxadiazole oxygen atoms are 8.7 and 8.9 ꢀ, respec-
tively. Compared with 3, all of the changes that occur in 4–5
are clearly because of the steric demands resulting from the
substituted methyl groups on the pyrazinyl ring. Thus, the
Cu2L2 cage in compounds 4 and 5 is a flexible, spongelike,
and dynamic framework that can adjust its internal space in
response to different guest molecules.[4a,7] It is different from
the Cu2L2 cage in 3 because the weak intermolecular p–p in-
teractions exist in 4 and 5 in the solid state. Each neutral
ring in 4 and 5 stacks on its neighbors through the central
oxadiazole moiety along the channel direction, which gener-
ates a p–p-sustained two-dimensional network containing
squarelike channels in which the methyl-substituted pyridine
zine/2,5-dimethylpyrazine 1:20:20:20) in a CHCl3/DMF
mixed solvent system at room temperature, only 3 was
formed, which is confirmed by single-crystal X-ray analysis
1
and H NMR spectroscopy of the [D6]DMSO extract of the
resulting crystals (see the Supporting Information). More-
over, when 2 was treated with 2-methylpyrazine and 2,5-di-
methylpyrazine in a molar ratio of 1:20:20, only compound
5 was obtained, which was confirmed by single-crystal X-ray
analysis and 1H NMR spectroscopy of the [D6]DMSO ex-
tract of the resulting crystals (see the Supporting Informa-
tion). Thus, of the three types of guests, guest 2 has the best
binding affinity for pyrazine and the poorest affinity for 2-
methylpyrazine under the experimental conditions. To date,
only a handful of metal-centered molecular containers with
reversible binding sites[3c] and dynamically adjustable cavi-
ties for specific organic substrates have been presented.
Figure 3. Molecular structures and solid-state packing of 4 (top) and 5 (bottom). Hydrogen atoms and solvent molecules of crystallization are omitted for
clarity. For 5, only the structure of major product 5a is shown. The molecular structure and solid-state packing of 5b are given in the Supporting Infor-
mation.
Chem. Eur. J. 2009, 15, 2261 – 2265
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2263

Y.-B. Dong et al.
methylpyrazine)]. Elemental analysis calcd (%) for C69H54Cu2N14O6: C
63.63, H 4.18, N 15.06; found: C 63.38, H 4.32, N 15.24.
More importantly, the study of the molecular-recognizing
ability of 2 was simultaneously performed in the presence of
the similar competitors instead of by a respective detection
observed in previous studies.[3c,8] To the best of our knowl-
edge, cage 2 is the first “breathing” discrete metallamacro-
cycle that is able to recognize specific substrates in the pres-
ence of other competitors by means of the internal space
based on its reversible metal-binding property.
In summary, a reversible spongelike M2L2 molecular cage
with extreme sensitivity and selectivity towards pyrazine
and different methyl-substituted derivatives has been report-
ed. Such materials may find applications in the fields of sep-
aration, sensors, and purification, and studies towards the
preparation of new discrete and polymeric “breathing” mo-
lecular cages based on other bent heterocycle-bridged or-
ganic ligands of this type. Heterometallic coordination com-
plexes based on these are currently under investigation.
Synthesis of [Cu2L2(2,5-dimethylpyrazine)]·3CHCl3 (5): DMF (2 mL)
was carefully layered onto a solution of 2 (6.0 mg, 0.005 mmol) and 2,5-
dimethylpyrazine (10 mg, 0.100 mmol) in CHCl3 (2 mL). The solutions
were left for approximately 7 days at room temperature, and deep-green
blocklike (5a; 4.2 mg, 50% yield) and platelike (5b; 0.06 mg, 7% yield)
crystals were obtained. Single-crystal X-ray analysis revealed that 5a and
5b are isomeric. IR (KBr): 3421 (m), 1588 (s), 1557 (s), 1508 (s), 1473 (s),
1445 (s), 1397 (s), 1294 (m), 1207 (m), 1123 (m), 1026 (m), 898 (m), 868
(m), 802 (m), 751 (m), 724 (m), 699 (m), 581 cmÀ1 (m). The crystals desol-
vate rapidly and lose crystallinity upon isolation. The elemental analysis
corresponds to the formula [Cu2L2(2,5-dimethylpyrazine)]. Elemental
analysis calcd (%) for C70H56Cu2N14O6: C 63.87, H 4.29, N 14.90; found:
C 63.68, H 4.36, N 14.72.
Crystal data for LH: C32H26N6O3; monoclinic; P2/n; Mr =542.59; a=
10.979(3),
1308.2(6) ꢀ3; Z=2; 1calcd =1.377 gcmÀ3; m
568; T=298(2) K; l(MoKa)=0.71073 ꢀ; qmax =25.038; reflections collect-
b=6.0754(17),
c=19.843(5) ꢀ;
b=98.732(4)8;
V=
A
ACHTUNGTRENNUNG(000)=
AHCTUNGTRENNUNG
ed/unique: 5001/2306 [Rint =0.0404]; R1 (I> 2s(I))=0.0482; wR2 (I>
2s(I))=0.1060.
Crystal data for 1: C64H48Cu2N12O6; tetragonal; P4(2)/n; Mr =1208.22;
a=22.7841(16), b=22.7841(16), c=15.297(2) ꢀ; V=7940.7(13) ꢀ3; Z=4,
1calcd =1.011 gcmÀ3; m(MoKa)=0.582 mmÀ1; F
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
Experimental Section
lACHTUNGTRENNUNG
¯
Synthesis of LH: 2,5-Bis(3-aminobenzoyl)-1,3,4-oxadiazole (1.0 g,
3.97 mmol) and nicotinoylacetone (2.5 g, 15.34 mmol) in an EtOH/
HCOOH (30 mL/0.2 mL) system was heated to reflux for 30 h to gener-
ate LH as a yellow crystalline solid (1.1 g, 51% yield). M.p. 248–2508C;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=13.25 (s, 2H; -OH), 9.14 (s,
2H; -C5H4N), 8.71 (d, 2H; -C5H4N), 8.25 (d, 2H; -C5H4N), 8.04 (d, 2H;
-C6H4), 7.99 (s, 2H; -C5H4N), 7.59 (t, 2H; -C6H4), 7.42 (m, 4H; -C6H4),
5.95 (s, 2H; -CH=C-), 2.26 (s, 3H; -CH3), 1.43 ppm (s, 3H; -CH3); IR
(KBr): 3443 (s), 1584 (s), 1547 (s), 1472 (m), 1520 (m), 1410 (m), 1328
(s), 1297 (s), 1195 (s), 1095 (s), 1024 (s), 895 (m), 1024 (s), 768 (s),
687 cmÀ1 (m); elemental analysis calcd (%) for C32H26N6O3: C 70.85, H
4.80, N 15.50; found: C 70.92, H 4.75, N 15.45.
Crystal data for 3: C73H57Cl15Cu2N14O6; triclinic; P1; Mr =1885.16; a=
12.0892(19), b=12.875(2), c=13.976(2) ꢀ; a=71.030(2), b=77.030(2),
g=79.031(2)8; V=1988.3(5) ꢀ3; Z=1; 1calcd =1.574 gcmÀ3
; mACHTUNGTRENNUNG
1.100 mmÀ1
;
F
(000)=954; T=174(2) K;
l
U
=
25.508; reflections collected/unique: 9999/7255 [Rint =0.0220]; R1 (I>
2s(I))=0.0748; wR2 (I> 2s(I))=0.1848.
¯
Crystal data for 4: C71.50H56.50Cl7.50Cu2N14O6; triclinic; P1; Mr =1600.76;
a=12.2525(18), b=17.680(2), c=17.895(3) ꢀ; a=92.546(2), b=
91.384(2), g=108.507(2)8; V=3669.4(9) ꢀ3; Z=2; 1calcd =1.449 gcmÀ3; m-
(MoKa)=0.914 mmÀ1; F
AHCTUNGTRENUNGN ACHTUNRTGEG(NNNU 000)=1634; T=298(2) K; lCAHTNUGTRENN(UNG MoKa)=0.71073 ꢀ;
qmax =25.508; reflections collected/unique: 19286/13386 [Rint =0.0242]; R1
(I> 2s(I))=0.0644; wR2 (I> 2s(I))=0.1828.
Synthesis of Cu2L2 (1) and (2): CuACTHNUGRTNEG(UN AcO)2·6H2O (8.0 mg, 0.04 mmol) in
¯
Crystal data for 5: 5a: C73H59Cl9Cu2N14O6; triclinic; P1; Mr =1674.47; a=
EtOH (8 mL) was layered onto a solution of L (22 mg, 0.04 mmol) in
THF (8 mL). The solutions were left for approximately one week at
room temperature, and green/black crystals were obtained (21.8 mg, 78%
12.316(5), b=12.411(5), c=13.015(5) ꢀ; a=91.797(5), b=103.385(5), g=
104.398(5)8; V=1866.2(12) ꢀ3; Z=1; 1calcd =1.490 gcmÀ3
; mACHTUNGTRENNUNG
0.954 mmÀ1
;
F
(000)=854; T=173(2) K;
l
U
=
yield; based on CuACHTUNGTRENNUNG(AcO)2·6H2O). IR (KBr): 3441 (s), 1588 (s), 1556 (m),
25.358; reflections collected/unique: 9492/6650 [Rint =0.0426]; R1 (I>
2s(I))=0.0927; wR2 (I> 2s(I))=0.2380. 5b: C73H59Cl9Cu2N14O6; mono-
clinic; P2(1); Mr =1674.47; a=12.227(3), b=24.892(6), c=12.577(3) ꢀ;
1507 (s), 1474 (s), 1446 (s), 1397 (s), 1293 (m), 1207 (m), 1025 (m), 869
(m), 728 cmÀ1 (m); elemental analysis calcd (%) for C64H48Cu2N12O6: C
63.58, H 3.97, N 13.91; found: C 63.65, H 3.85, N 13.76. When 1 was dis-
b=105.640(5)8; V=3686.1(15) ꢀ3; Z=1; 1calcd =1.509 gcmÀ3; m
ACHTUNGTRENNUNG
0.966 mmÀ1
;
F
(000)=1708; T=173(2) K;
l
N
=
solved in CHCl3, the discrete Cu2L2 compound of
2 was obtained.
ESIMS: m/z 1207 [C64H48Cu2N12O6 +1]+.
25.018; reflections collected/unique: 18721/12578 [Rint =0.0811]; R1 (I>
2s(I))=0.0878; wR2 (I> 2s(I))=0.1439.
Synthesis of [Cu2L2ACHTUNGTRENNUNG(pyrazine)]·5CHCl3 (3): DMF (2 mL) was carefully
layered onto a solution of 2 (6.0 mg, 0.005 mmol) and pyrazine (8 mg,
0.100 mmol) in CHCl3 (2 mL). The solutions were left for approximately
3 days at room temperature, and deep-green crystals were obtained
(5.2 mg, 70% yield; based on 2). IR (KBr): 3441 (m), 1588 (s), 1555 (s),
1516 (s), 1472 (s), 1448 (s), 1400 (s), 1293 (m), 1206 (m), 1027 (m), 866
(m), 747 (m), 698 cmÀ1 (m). The crystals obtained desolvate rapidly and
lose crystallinity upon isolation. The elemental analysis corresponds to
CCDC-693335 (1), 693336 (3), 693337 (4), 693338 (5a), 700878 (5b),
700879 (3’), 700880 (5a’), and 700881 (5b’) contain 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
the formula [Cu2L2ACHTUNGTRENNUNG(pyrazine)]. Elemental analysis calcd (%) for
C68H52Cu2N14O6: C 63.39, H 4.07, N 15.22; found: C 63.16, H 4.15, N
15.44.
Synthesis of [Cu2L2(2-methylpyrazine)]·2.5CHCl3 (4): DMF (2 mL) was
carefully layered onto a solution of 2 (6.0 mg, 0.005 mmol) and 2-methyl-
pyrazine (9 mg, 0.100 mmol) in CHCl3 (2 mL). The solutions were left for
approximately 7 days at room temperature, and deep-green crystals were
obtained (4.8 mg, 60% yield; based on 2). IR (KBr): 3445 (m), 1587 (s),
1555 (s), 1505 (s), 1446 (s), 1293 (m), 1207 (m), 1122 (m), 1064 (m), 1024
(m), 901 (m), 866 (m), 849 (m), 798 (m), 751 (m), 721 (m), 699 (m),
577 cmÀ1 (m). The crystals desolvate rapidly and lose crystallinity upon
isolation. The elemental analysis corresponds to the formula [Cu2L2(2-
Acknowledgements
We are grateful for financial support from the National Natural Science
Foundation of China (grant nos. 20871076 and 20671060), Shangdong
Natural Science Foundation (grant no. JQ200803), and the Ph.D. Pro-
grams Foundation of the Ministry of Education of China (grant
no. 200804450001).
2264
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 2261 – 2265

A Flexible and Reversible Metal-Binding Cu2L2 Cage
COMMUNICATION
2007, 119, 8755; Angew. Chem. Int. Ed. 2007, 46, 8601; c) K.-H. Kim,
R. Song, K. M. Kim, J. Am. Chem. Soc. 2003, 125, 7170.
[4] a) Y.-B. Dong, Q. Zhang, L.-L. Liu, J.-P. Ma, B. Tang, R.-Q. Huang, J.
Am. Chem. Soc. 2007, 129, 1514; b) Y.-B. Dong, P. Wang, J.-P. Ma,
X.-X. Zhao, B. Tang, R.-Q. Huang, J. Am. Chem. Soc. 2007, 129,
4872; c) P. Wang, J.-P. Ma, Y.-B. Dong, R.-Q. Huang, J. Am. Chem.
Soc. 2007, 129, 10620.
Keywords: copper
recognition · oxadiazole · pyrazine
·
host–guest systems
·
molecular
[1] a) S. Leininger, B. Olenyuk, P. J. Stang, Chem. Rev. 2000, 100, 853;
b) M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusukawa, K.
Biradha, Chem. Commun. 2001, 509; c) D. L. Caulder, K. N. Ray-
mond, Acc. Chem. Res. 1999, 32, 975.
[5] M. A. Alam, M. Nethaji, M. Ray, Angew. Chem. 2003, 115, 1984;
Angew. Chem. Int. Ed. 2003, 42, 1940.
[2] For some examples of metallacycles, see: a) S. Masaoka, S. Furukawa,
H.-C. Chang, T. Mizutani, S. Kitagawa, Angew. Chem. 2001, 113,
3933; Angew. Chem. Int. Ed. 2001, 40, 3817; b) V. C. Lau, L. A.
Berben, J. R. Long, J. Am. Chem. Soc. 2002, 124, 9042; c) S. J. Lee,
W. Lin, J. Am. Chem. Soc. 2002, 124, 4554; d) A. Hori, K. Yamashita,
M. Fujita, Angew. Chem. 2004, 116, 5126; Angew. Chem. Int. Ed.
2004, 43, 5016; e) P. H. Dinolfo, M. E. Williams, C. L. Stern, J. T.
Hupp, J. Am. Chem. Soc. 2004, 126, 12989; f) S. B. Zhao, R. Y. Wang,
S. Wang, J. Am. Chem. Soc. 2007, 129, 3092; g) R. W. Saalfrank, A.
Scheurer, R. Puchta, F. Hampel, H. Maid, F. W. Heinemann, Angew.
Chem. 2007, 119, 269; Angew. Chem. Int. Ed. 2007, 46, 265.
[6] Tables of Interatomic Distances and Configuration in Molecules and
Ions, Chem. Soc., Special Publ. No. 11, 1958.
[7] a) S. Kitagawa, K. Uemura, Chem. Soc. Rev. 2005, 34, 109; b) F. Mill-
ange, C. Serre, N. Fꢂrey, G. Guillou, R. I. Walton, Angew. Chem.
2008, 120, 4168; Angew. Chem. Int. Ed. 2008, 47, 4100; c) P. L. Lle-
wellyn, G. Maurin, T. Devic, S. Loera-Serna, N. Rosenbach, C. Serre,
S. Bourelly, P. Horcajada, Y. Filinchuk, G. Fꢂrey, J. Am. Chem. Soc.
2008, 130, 12808.
[8] A. W. Maverick, M. L. Ivie, J. H. Waggenspack, F. R. Fronczek, Inorg.
Chem. 1990, 29, 2403.
[3] a) K.-H. Kim, R. Song, K. M. Kim, J. Am. Chem. Soc. 2003, 125,
7170; b) N. P. Power, S. J. Dalgarno, J. L. Atwood, Angew. Chem.
Received: December 19, 2008
Published online: January 29, 2009
Chem. Eur. J. 2009, 15, 2261 – 2265
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2265