Assembly of a twin-cage complex containing a linear array of Pd3

Article abstract of DOI:10.1039/b101691l

The M₃L₄ twin-cage complex [Pd₃(bitmb)₄Cl₄]Cl₂· 2H₂O·CH₃CN [bitmb = 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene] was obtained by assembly of three Pd(II) ions with four molecules of the new flexible ditoptic ligand bitmb; structural analysis showed that the complex contains two M₂L₂ cages with a cavity size of ca. 200 A³.

Full text of DOI:10.1039/b101691l

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Assembly of a twin-cage complex containing a linear array of
Pd †
3
ab
a
b
a
a
Hong-Ke Liu, Cheng-yong Su, Cheng-Ming Qian, Jun Liu, Hai-Yan Tan and
a
Bei-Sheng Kang*
a
School of Chemistry and Chemical Engineering, Zhongshan University, Guangzhou 510275,
China
b
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
Received 21st February 2001, Accepted 19th March 2001
First published as an Advance Article on the web 29th March 2001
The M L4 twin-cage complex [Pd (bitmb) Cl ]Cl ؒ2H Oؒ
3
3
4
4
2
2
CH CN
[bitmb = 1,3-bis(imidazol-1-ylmethyl)-2,4,6-tri-
3
methylbenzene] was obtained by assembly of three Pd(II)
ions with four molecules of the new flexible ditoptic ligand
bitmb; structural analysis showed that the complex
3
contains two M L cages with a cavity size of ca. 200 Å .
2
2
Assembly of complexes with inner cavities formed from metal
ions and multidentate organic ligands has been a high profile
1–3
topic in supramolecular chemistry in recent years. The form-
ation of such complexes has been successfully accomplished
4–6
in two extreme areas: discrete cage-like complexes with only
7–9
one cavity and complexes with extended porous frameworks
containing innumerable cavities. However, discrete multicage
or multicompartmental complexes are rare. It is important
therefore that the formation of these species, which exhibit an
abiological analogy to numerous biological processes mediated
by collective interactions and recognition events between large
10
molecules, be studied. Recently, Lehn reported two multi-
compartmental nanoarchitectural complexes assembled by
transition metal ions with two different multidentate ligands.
An M L cage can be assembled by combining two flexible
Fig. 1 Molecular structure of the twin-cage complex [Pd (bitmb) -
3
4
Cl ]Cl ؒ2H OؒCH CN. All the hydrogen atoms and solvate molecules
4
2
2
3
2
2
Ϫ
and the uncoordinated Cl anions are omitted for clarity. Selected bond
bidentate ligands L of cis conformation with two transition
11
distances (Å) and angles (Њ): Pd1–N 2.014(3) ∼2.021(3), N–Pd1–N
metal ions M. However, difficulty arises in how to combine
two or more M L cages. In order to achieve this the following
8
7.79(12) ∼92.21(12)/180.00(11), Pd2–N 2.005(3) ∼2.008(3), Pd2–Cl
2
2
2.2966(10) ∼2.3005(11); N–Pd2–N 179.30(12), Cl–Pd2–Cl 177.64(5),
N–Pd2–Cl 89.45(9) ∼ 90.65(10), Pd1 ؒ ؒ ؒ Pd2 5.19.
factors must be taken into consideration: (1) an adequately
flexible bidentate ligand; (2) a transition metal ion with
square-planar or octahedral geometry with a radius large
enough to accommodate four 5- or 6-membered heterocycles;
and (3) a counter-anion with moderate coordination capability
are required. Scheme 1 depicts the assembly strategy of discrete
multicage complexes. Herein we report the synthesis and
characterization of the twin-cage complex [Pd (bitmb) Cl ]Cl ؒ
2H OؒCH CN, where bitmb is a new ditoptic ligand 1,3-bis-
2
3
(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene.
The ligand bitmb was prepared from 1,3-bis(bromomethyl)-
2,4,6-trimethylbenzene and imidazole in a 1 : 2 molar ratio
in DMSO under strong alkali (KOH) conditions.‡ This ligand
is a derivation of 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimeth-
3
4
4
2
7
ylbenzene but lacks an imidazol-1-ylmethyl group. Crystals
of bitmb suitable for X-ray structural analysis§ (Fig. 1S) were
obtained from a water solution containing ammonium hexa-
fluorophosphate, which shows that the ligand in the solid state
is in a cis conformation with two disordered hexafluorophos-
phate anions for each bitmb (omitted from Fig. 1S for clarity).
Reaction of Pd(CH CN) Cl with bitmb in an M : L ratio of
3
2
2
1
: 1 resulted in a pale yellow powder which was preliminarily
identified as an M L2 cage complex with the formulation
2
[
Pd (bitmb) Cl ]ؒ3.5H O (1)¶ which was confirmed by elem-
2 2 4 2
ental analyses and FAB mass spectra. In order to obtain an
M L twin-cage complex, an M : L ratio of 1 : 2 was used. Pale
3
4
yellow sheet-like crystals of solvated [Pd (bitmb) Cl ]Cl
2
suitable for X-ray structural analysis§ were obtained directly
3
4
4
Scheme 1 Assembly strategy of discrete multicage complexes.
from the diffusion of diethyl ether into an acetonitrile–aqueous
solution containing bitmb and Pd(CH CN) Cl . The formula
†
Electronic supplementary information (ESI) available: structure of
3
2
2
[
Pd (bitmb) Cl ]Cl ؒ2H OؒCH CN (2) was confirmed by
3 4 4 2 2 3
ϩ
bitmb and view of a 1D chain of [Pd (bitmb) Cl ]Cl along the x-axis
showing C–H ؒ ؒ ؒ Cl hydrogen bonding. See http://www.rsc.org/
3
4
4
2
MALDI-TOF-MS measurements (m/z: 1619 [M Ϫ Cl] ) and
suppdata/dt/b1/b101691l/
elemental analyses.||
DOI: 10.1039/b101691l
J. Chem. Soc., Dalton Trans., 2001, 1167–1168
This journal is © The Royal Society of Chemistry 2001
1167

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Guangdong province for financial support of this work (to
H.-K. Lin).
Notes and references
‡
The ligand bitmb was prepared from 1,3-bis(bromomethyl)-2,4,6-
trimethylbenzene and imidazole in a 1 : 2 molar ratio in dimethyl
sulfoxide under strong alkaline (KOH) conditions in 70% yield.
Found: C, 72.80; H, 7.16; N, 19.97. Calc. for C H N : C, 72.82;
1
7
20
4
1
H, 7.19; N, 19.98%. H NMR(CDCl , ppm): δ 2.19(6H, s, CH ),
3
3
4
5
2
7
.33(3H, s, CH ), 5.15(4H, s, CH ), 6.74(2H, s, H ), 7.02(2H, s, H ),
3 2 im im
2
.04(1H, s, H ), 7.30(2H, s, H ). H refers to imidazole protons and
bz
im
im
Hbz refers to phenyl ring protons.
Crystallography. The intensity data were collected on a Bruker CCD
§
diffractometer with graphite-monochromated Mo-Kα (λ = 0.71073 Å)
radiation at room temperature. All absorption corrections were
performed using the SADABS program. The structures were solved
by direct methods and refined by full matrix least squares against F
1
2
Fig. 2 Stacking of the one-dimensional chains of the title complex in
the yz plane with only skeleton atoms retained for clarity, the hydrogen
bonds are indicated by dashed lines.
2
1
3
of all data using SHELXTL software.
For bitmb: formula
C H N ؒ2HPF , M = 572.33, monoclinic, P2 /c, a = 8.556(3), b =
1
7
20
4
6
1
3
2
4.493(8), c = 11.792(4) Å, β = 110.170(5)Њ, U = 2319.5(14) Å , Z = 4,
Ϫ1
As shown in Fig. 1, the bitmb ligands in the structure of 2
are in a cis conformation and each is attached to two palladium
atoms by a nitrogen atom of each imidazolyl groups. There are
two different coordination environments for the three linearly
arranged palladium ions: the central Pd(1) is coordinated by
four N atoms from four bitmb ligands giving a distorted
square-planar N4 geometry; while the terminal Pd(2) is
coordinated by two N atoms from two bitmb and two Cl
anions, obtaining a distorted square-planar N Cl geometry.
µ(Mo-Kα) = 0.298 mm , R
(wR ) = 0.0827(0.1856). 8570 reflections
1 2
collected, 2763 [I > 2σ(I)] observed; for [Pd (bitmb) Cl ]Cl ؒ
3
4
4
2
¯
H OؒCH CN, C H N Cl O Pd , triclinic, P1, a = 10.9169(14),
2 3 70 87 17 6 2 3
2
b = 13.9121(17), c = 14.0065(18) Å, α = 69.913(2), β = 86.460(3),
3
Ϫ1
γ = 86.165(2)Њ, U = 1991.7(4) Å , Z = 4, µ(Mo-Kα) = 0.924 mm , R1
wR ) = 0.0409(0.1008). 13337 reflections collected, 6114 [I > 2σ(I)]
(
2
observed. CCDC reference numbers 154825 and 158770. See http://
www.rsc.org/suppdata/dt/b1/b101691l/ for crystallographic data in CIF
or other electronic format.
2
2
¶ A solution of bitmb (28 mg, 0.1 mmol) in acetonitrile–aqueous
solution (10 ml) was added to an acetonitrile solution (10 ml) of
Pd(CH CN) Cl (26 mg, 0.1 mmol) at room temperature with stirring.
The two square planes form a dihedral angle of 26.7Њ. The two
cis bitmb ligands adopt a face-to-face orientation and are
joined together by Pd(1) and Pd(2) to generate one M L cage,
3
2
2
Standing the filtrate at room temperature results in a pale yellow
2
2
powder, yield 10 mg (20%). Found: C, 41.51; H, 4.60; N, 11.25%. Calcd
whilst another two bitmb are similarly oriented and generate
another cage, and the two M L cages are linked together by
1
for [Pd (bitmb) Cl ]ؒ3.5H O: C, 41.73; H, 4.84; N, 11.45%. H NMR
2
2
4
2
2
2
(
5
CD SOCD , 293 K, ppm): δ 2.17(s, 6H, CH ), 2.50(3H, s, CH ),
3
3
3
3
Pd(1). Thus, the three linearly arranged metal atoms with a
Pd(1) ؒ ؒ ؒ Pd(2) distance of 5.19 Å together with the two pairs
of ligands generate a discrete M L twin-cage. In each M L
.31(4H, s, CH ), 6.90 ≈ 7.69(7H, s, H and H ), M = 915.4, FAB-
2
im
bz
calcd
ϩ
MS: m/z: 916 [M ϩ H ].
3
4
2
2
|| A solution of bitmb (56 mg, 0.2 mmol) in acetonitrile–aqueous
cage, the two phenyl planes of bitmb are tilted with an angle of
0Њ, with a closest distance between the two ligands of 7.7 Å.
The volume of the void space inside each cavity of an M L
cage is estimated to be ca. 200 Å , sufficient in principle to
accommodate a guest molecule, like toluene.
Furthermore, an intriguing feature shown unambiguously
by the crystallographic analysis of 2 is the packing arrangement
of the twin-cages illustrated in Fig. 2 and Fig. 2S. As shown
in Fig. 2S, each molecule encapsulates two phenyl rings of the
bitmb ligands from neighboring molecules on two sides in
opposite directions. Each encapsulated phenyl ring is parallel to
one of the host phenyl rings with a center-to-center distance of
solution (15 ml) was added to an acetonitrile solution (10 ml)
3
of Pd(CH CN) Cl (26 mg, 0.1 mmol) at room temperature with
3 2 2
stirring. Diffusion of diethyl ether into the filtrate results in the form-
ation of pale yellow crystals of the title complex, yield 15 mg
2
2
3
(
(
20%). Found: C, 48.28; H, 5.22; N, 13.20%. Calcd for [Pd -
3
1
bitmb) Cl ]Cl ؒ2H O: C, 48.34; H, 5.01; N, 13.26%. H NMR
4
4
2
2
(
5
CD SOCD , 315 K, ppm): δ 2.26(6H, s, CH ), 2.49(3H, s, CH ),
.21(2H, s, CH ), 5.30(2H, s, CH ), 6.87–7.96(7H, H and H );
2 2 im bz
3
3
3
3
Mcalcd = 1653.4, MALDI-TOF-MS(DMSO): m/z: 1619 [[Pd (bitmb) -
3
4
ϩ
Cl ]Cl Ϫ Cl] .
4
2
1 R. W. Saalfrank and B. Demleitner, Transition Metals in Supra-
molecular Chemistry, in Series Perspectives in Supramolecular
Chemistry, ed. J. P. Sauvage, Wiley-VHC, Weinheim, 1999, vol. 5,
pp. 1–51.
6
.3 Å, but tilted from the other host phenyl ring, with an angle
of 30Њ and a center-to-center distance of 5.8 Å. In addition,
C–H ؒ ؒ ؒ Cl hydrogen bonds are formed between the methyl CH
of one molecule and one of the coordinated chloride anions
of a neighboring molecule with a C(25) ؒ ؒ ؒ Cl(2) distance of
2
M. Albrecht, Angew. Chem., Int. Ed., 1999, 38, 3463; L. R.
MacGillivray and J. L. Atwood, Angew. Chem., Int. Ed., 1999, 38,
1018; D. L. Caulder and K. N. Raymond, Acc. Chem. Res., 1999, 32,
975.
3
.39 Å (shown in Fig. 2S). Thus, the twin-cage molecules are
3
O. M. Yaghi, H. Li, C. Davis, D. Richardson and T. L. Groy,
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the x-axis and the stacking sequence is shown in Fig. 2, with
all of the solvent molecules (water and acetonitrile) in the
interspaces of the chains.
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5
6
7
The results described here represent a new way to assemble
twin-cage complexes from only one type of organic ligand,
which largely simplifies current synthetic processes. It is also the
first discrete M L twin-cage determined by X-ray crystallo-
B. F. Abrahams, S. J. Egan and R. Robson, J. Am. Chem. Soc., 1999,
1
21, 3535.
3
4
H. K. Liu, W. Y. Sun, W.-X. Tang, T. Yamamoto and N. Ueyama,
graphic analyses to show a one-dimensional chain. The inner
cavities of the two cages should be able to encapsulate one guest
molecule each when the complex is dissolved in appropriate
solvents. The encapsulation reactions and assembly of other
discrete multicages (such as M L triplet-cage) are now being
Inorg. Chem., 1999, 38, 6313.
8 D. D. L. Goodgame, D. A. Grachvogel and D. J. Williams, Angew.
Chem., Int. Ed., 1999, 38, 153.
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L. D. Williams, Science, 1999, 283, 1148.
4
6
1
1
1
0 P. N. W. Baxter, J.-M. Lehn, B. O. Kneisel, G. Baum and D. Fenske,
studied.
Chem. Eur. J., 1999, 5, 1213.
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2 R. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
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Acknowledgements
The authors are grateful for funding from the NNSF and
the FRDP of China, and the postdoctoral fund of
1985.
1
168
J. Chem. Soc., Dalton Trans., 2001, 1167–1168