Reversible formation of a [2]catenane through first- and second-sphere coordination

Article abstract of DOI:10.1002/anie.200604724

(Figure Presented) Reversible catenation: A remarkably stable [2]catenane (see picture; Pd turquoise, Cl green) is formed in one step through a combination of first- and second-sphere coordination of a bidentate ligand and the {PdCl₂} metal cen

Full text of DOI:10.1002/anie.200604724

Angewandte
Chemie
DOI: 10.1002/anie.200604724
Catenanes
Reversible Formation of a [2]Catenane through First- and Second-
Sphere Coordination**
Barry A. Blight, James A. Wisner,* and Michael C. Jennings
The synthesis of compounds containing catenated rings has
received increasing attention because of their aesthetic
appeal[1] as well as their potential in the areas of molecular
machines and switches.[2] A particularly facile synthetic
method in this context is the closure of one or more of the
rings in the final products by using labile metal–ligand
coordination as a linkage in the backbone under thermody-
namic control.[3] However, the template used to generate the
interlocked structures in the great majority of these cases
operates independently from the aforementioned ring-clo-
sure reaction. Examples in which these two functions are
associated with the same metal center(s) simultaneously are
rare and involve either bridging ligands[4] or metal–metal
interactions to achieve this result.[5] Herein, we report the
one-step, high-yield synthesis and characterization of a new
[2]catenane architecture that depends on the same metal
center for both the macrocyclization and templated catena-
tion stages of its self-assembly. The topology of the product is
dependent on solvent polarity, the character of which can be
used to switch reversibly between catenated and non-inter-
locked geometries.
macrocycles would further be templated through mutual
recognition of the {PdCl2L2} subunit in one ring by its
orthogonally disposed partner. Although we were reasonably
confident that the macrocyclization reaction would occur, the
viability of the catenation step was uncertain because of the
requirement of dissociated acyclic intermediates, which might
not conform to the intended template.
Bidentate ligand 2 was synthesized in 34% overall yield
from tert-butylisophthalic acid and readily available or
prepared starting materials[9] (Scheme 1; see also the Sup-
Recently, we described the formation of a series of
interpenetrated [2]pseudorotaxanes,[6] and
a subsequent
interlocked [2]rotaxane[7] from a known macrocyclic compo-
nent[8] and trans-palladium dihalide complexes. The driving
force for formation of the complexes rested mainly on the
hydrogen-bond-donating interaction of amide groups in the
macrocyclic framework with the residual hydrogen-bond-
acceptor character of the halide ligands of the preformed
metal complexes. The potential adaptation of this template to
the formation of a [2]catenane superstructure led us, through
examination of molecular models, to synthesize 2 as a
bidentate ligand that could chelate a palladium dichloride
metal center in a trans arrangement. Formation of the
resulting product would yield a macrocycle incorporating
both the desired metal center subunit (trans-{PdCl2L2}) in its
backbone as well as the components for recognition of the
subunit within the newly created cavity. Catenation of two
Scheme 1. Synthesis of 2. 1) MeOH/THF, H2SO4; 2) DCC, HOBT,
DMF; 3) 0.5m LiOH, THF; 4) DCC, HOBT, 3-aminopyridine, DMF.
DCC=N,N’-dicyclohexylcarbodiimide; HOBT=1-hydroxy-1H-benzotria-
zole.
porting Information). Partial esterification of the starting acid
and subsequent DCC-mediated coupling produced inter-
mediate diester 1. Hydrolysis of 1 and a second DCC-
mediated amide-forming reaction with 2 equivalents of 3-
aminopyridine yielded 2.
[*] B. A. Blight, Prof. J. A. Wisner, Dr. M. C. Jennings
Department of Chemistry
The University of Western Ontario
London, ON, N6G5B7 (Canada)
Fax: (+1)519-661-3022
Self-assembly of the [2]catenane target (3) was attempted
by combining equimolar amounts of [Pd(PhCN)2Cl2][10] and 2
in a solvent mixture of 3:1 CHCl3/MeCN and heating at reflux
for 8 h. TLC of the final reaction solution indicated a sole
product that did not match the Rf values of either starting
material. Removal of the solvent and precipitation from
dichloromethane with hexanes gave a pale yellow solid (87%
E-mail: jwisner@uwo.ca
Homepage: http://www.uwo.ca/chem/people/faculty/wisner.htm
[**] We thank the Natural Sciences and Engineering Research Council of
Canada for financial support of this research.
Supporting information (experimental details, including syntheses,
characterizations, and kinetic treatments) for this article is available
on the WWW under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2007, 46, 2835 –2838
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2835

Communications
Figure 1. Stick representation of [2]catenane 3 in the solid state. All
À
C H hydrogen atoms, methyl, cyclohexyl, and tert-butyl groups have
been removed for clarity. NH···Cl hydrogen bonds are indicated by
orange dashed lines; O red, N blue, H light purple, Cl light green.
based on [2]catenane). Cold-spray-ionization mass spectrom-
etry (CSI-MS)[11] of the product was consistent with the
formation of the catenane; the only high-mass (m/z > 300)
peaks observable were at m/z 1061.3 [Pd2(2)2Cl4 + 2H]2+ and
m/z 2121.8 [Pd2(2)2Cl4 + H]+. The isotopic ratios of the peaks
corresponding to [M+2H]2+ matched directly with those
calculated for the catenane product. Poor resolution of the
signals corresponding to the [M+H]+ ion prevented a similar
isotopic analysis. No peaks were observed in the regions in
which either the non-interlocked macrocycle or the starting
materials would be expected to appear.
in the backbones of the component macrocycles. As a
qualitative test of this stability, solutions of 3 (5 mmol) in
CDCl3 were diluted to 50% v/v with a number of more
competitive deuterated solvents ([D3]MeCN, [D3]MeNO2,
[D8]THF, [D6]acetone, [D4]methanol) and heated at reflux for
1
24 h. The H NMR spectra of the samples during dilution,
before, and after reflux indicated no change in the integrity of
the [2]catenane superstructure under these conditions. How-
ever, dissolution of 3 in a mixed solvent system of > 1m
[D6]DMSO/CDCl3 results in the gradual appearance of a
new set of resonances in the 1H NMR spectra, consistent with
the formation of free macrocycle 4, and the concomitant
Pale-yellow cube-shaped crystals of the putative [2]cate-
nane were grown by slow diffusion of diisopropyl ether into a
concentrated solution of 3 in 1,2-dichloroethane. Proof of the
anticipated interlocked topology in the solid-state was
obtained by single-crystal X-ray diffraction analysis
disappearance of those corresponding to
3 (Figure 2).
Although the number of protons and respective coupling
patterns are the same in both sets of peaks, all of the aromatic
and amide protons experience a change in chemical shift to
different degrees upon the loss of the topological bond. In
particular, the amide protons b and d are shifted downfield in
the free macrocycle as a result of their exposure to the
strongly hydrogen-bond-accepting solvent. The protons j at
the 6-position of the pyridyl rings are more shielded in the
(Figure 1).[12,13] 3 crystallized in space group P1 containing
¯
two catenated macrocyclic rings, which adopt a nearly
orthogonal orientation (848), as measured from their inter-
secting least-squares planes.[14] Although each of the macro-
cycles (containing either Pda or Pdb) adopt different gross
conformations, the intended template is manifested in the
interaction between both of the {PdCl2} subunits and their
opposing macrocyclic cavities. {PdaCl2} is hydrogen bonded to
the four amide nitrogen atoms of macrocycle b (N···Cl = 3.53
À
catenated structure owing to their involvement in C H···p
bonding to the aryl sidewalls of the opposing macrocycle.
Hence, they are shifted downfield in the non-interlocked
macrocycle. Conversely, the sidewall protons a are shifted
downfield in the catenane caused by their location within the
deshielding regions of the pyridyl rings in the opposing
macrocycle. CSI-MS of the NMR sample supported the
presence of macrocycle 4 with observable high-mass peaks at
m/z 1146.1 [Pd(2)Cl2 + [D6]DMSO + H]+ and m/z 1194.0
[Pd(2)Cl + 2[D6]DMSO]+, the isotopic ratios of which dis-
played a direct match to the calculated patterns. Notably, no
high-mass peaks that could be reasonably ascribed to 3 were
observed.
À
(E), 3.41 (F), 3.44 (G), 3.36 Š (H), and N H···Cl = 160 (E),
160 (F), 156 (G), 1638 (H)). {PdbCl2} is hydrogen bonded to
the four amide nitrogen atoms of macrocycle a (N···Cl = 3.26
À
(A), 3.48 (B), 3.54 (C), 3.51 Š (D), and N H···Cl = 153 (A),
163 (B), 151 (C), 1568 (D)). The interlocked structure is
À
further stabilized by two C H···p interactions between a
proton at the 6-position of one pyridyl ring in each macro-
cycle, and the diphenyl cyclohexyl sidewalls of the opposing
cavity.
The [2]catenane is remarkably stable in view of the lability
of the palladium metal centers that form the reversible links
2836
www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 2835 –2838

Angewandte
Chemie
Figure 2. The aromatic region of 1H NMR spectra (600 MHz, 298 K)
monitoring the disassembly of [2]catenane 3 (top) into macrocycle 4
(bottom) in 4m [D6]DMSO/CDCl3. Illustrated are the observed pertur-
bations in chemical shift between interlocked and free components
(dashed lines). ROESY experiments were performed to verify individual
1H NMR assignments.
Diisopropyl ether was diffused into a two-week-old
solution of 4 in 2m DMSO/CHCl3 to produce pale-yellow
X-ray quality crystals. Single-crystal X-ray diffraction analysis
provided confirmation of the change in topology in the solid
state (Figure 3).[15] The disassembled material crystallizes in
Figure 3. Stick representation of macrocycle 4 in the solid state;
a) view in the plane of the dimer of macrocycles; b) view from above
¯
space group P1 as centrosymmetric pairs of mutually hydro-
gen bonded but non-interlocked macrocycles. The influence
of the DMSO cosolvent in nullifying the catenane template is
apparent in the structure, as one of the two amide groups in
each of the isophthalamide clefts is engaged in hydrogen
bonding with included solvent molecules (N···OS(CH3)2 =
À
the plane of the macrocycles. All C H hydrogen atoms, methyl,
cyclohexyl, and tert-butyl groups have been removed for clarity.
=
=
NH···Cl, NH···O S, and NH···O C hydrogen bonds are indicated by
orange dashed lines; S yellow.
À
2.83 (A), 2.98 Š (B), and N H···OS(CH3)2 = 160 (A), 1538
(B)). The two remaining amides of each ring participate as
intermacrocyclic hydrogen-bond donors with a chloride
ligand (N···Cl = 3.54 Š, N-H···Cl = 1678(C)) and the carbonyl
group of an amide in the opposing macrocycle (N···O =
À
2.93 Š, N H···O = 1428 (D)) acting as acceptors.
The reversible nature of the catenane-forming step is
revealed in the 1H NMR spectra of 4 over a period of a week
after dissolution in CDCl3 (Figure 4). The resonances corre-
sponding to the macrocycle are gradually replaced by those
matching a separately prepared solution of catenane 3 in
CDCl3 (Figure 4). The identity of 3 was further confirmed by
comparison with an authentic sample (TLC). The first-order
rate constant k for loss of 4 (assembly of 3) was determined to
be 1.56 ” 10À5 sÀ1 in CDCl3 at 298 K by the method of initial
rates. The rate of the re-formation of 3 may be increased
substantially by either heating, the addition of a more-polar
cosolvent (e.g. MeCN), or both, which nonetheless results in 3
being observed as the only product.
Figure 4. The aromatic region of 1H NMR spectra (600 MHz, 298 K)
monitoring the reassembly of macrocycle 4 (top) into [2]catenane 3
(bottom) in CDCl3. Illustrated are the observed perturbations in
chemical shift between free and interlocked components (dashed
lines).
In conclusion, we have prepared a new [2]catenane by
using first-and second-sphere coordination of the same metal
center to form the interlocked topology. The catenation of the
two rings is a fully reversible process and is dependent on the
Angew. Chem. Int. Ed. 2007, 46, 2835 –2838
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
2837

Communications
2001, 40, 4235 – 4239; ; W. W. H. Wong, J. Cookson, A. A. L.
Evans, E. J. L. McInnes, J. Wolowska, J. P. Maher, P. Bishop, P. D.
Beer, Chem. Commun. 2005, 2214 – 2216.
solvent used to dissolve the component macrocycle. We are
currently exploring methods to expand this template further
for the reversible formation of functional molecules such as
molecular shuttles and switches.
[5] N. C. Habermehl, F. Mohr, D. J. Eisler, M. C. Jennings, R. J.
Puddephatt, Can. J. Chem. 2006, 84, 111 – 123.
[6] B. A. Blight, K. A. Van Noortwyk, J. A. Wisner, M. C. Jennings,
Angew. Chem. 2005, 117, 1523 – 1528; Angew. Chem. Int. Ed.
2005, 44, 1499.
Received: November 20, 2006
Published online: March 12, 2007
[7] B. A. Blight, J. A. Wisner, M. C. Jennings, Chem. Commun. 2006,
4593.
[8] C. Fischer, M. Nieger, O. Mogck, V. Böhmer, R. Ungaro, F.
Vögtle, Eur. J. Org. Chem. 1998, 155.
[9] For the synthesis of 1,1-bis(4-amino-3,5-dimethylphenyl)cyclo-
hexane, see: C. A. Hunter, J. Am. Chem. Soc. 1992, 114, 5303.
[10] P. Braunstein, R. Bender, J. Jud, Inorg. Synth. 1989, 26, 341.
[11] S. Sakamoto, M. Fujita, K. Kim, K. Yamaguchi, Tetrahedron
2000, 56, 955.
Keywords: catenanes · hydrogen bonds · palladium ·
self-assembly · template synthesis
.
[1] P. D. Beer, M. R. Sambrook, D. Curiel, Chem. Commun. 2006,
2105 – 2117; C. A. Schalley, W. Reckien, S. Peyerimhoff, B.
Baytekin, F. Voegtle, Chem. Eur. J. 2004, 10, 4777 – 4789; Z. Cao,
A. W. Roszak, L. J. Gourlay, G. J. Lindsay, N. W. Isaacs, Structure
2005, 13, 1661 – 1664; A. Hori, T. Sawada, K.-i. Yamashita, M.
Fujita, Angew. Chem. 2005, 117, 4974 – 4977; Angew. Chem. Int.
Ed. 2005, 44, 4896 – 4899; ; A.-M. Fuller, D. A. Leigh, P. J. Lusby,
A. M. Z. Slawin, D. B. Walker, J. Am. Chem. Soc. 2005, 127,
12612 – 12619; Y. Liu, P. A. Bonvallet, S. A. Vignon, S. I. Khan,
J. F. Stoddart, Angew. Chem. 2005, 117, 3110 – 3115; Angew.
Chem. Int. Ed. 2005, 44, 3050 – 3055; ; E. N. Guidry, S. J. Cantrill,
J. F. Stoddart, R. H. Grubbs, Org. Lett. 2005, 7, 2129 – 2132;
R. T. S. Lam, A. Belenguer, S. L. Roberts, C. Naumann, T.
Jarrosson, S. Otto, J. K. M. Sanders, Science 2005, 308, 667 – 669;
L. Raehm, J.-M. Kern, J.-P. Sauvage, C. Hamann, S. Palacin, J.-P.
Bourgoin, Chem. Eur. J. 2002, 8, 2153 – 2162; A. L. Hubbard,
G. J. E. Davidson, R. H. Patel, J. A. Wisner, S. J. Loeb, Chem.
Commun. 2004, 138 – 139.
[2] J.-C. Chambron, J.-P. Collin, V. Heitz, D. Jouvenot, J.-M. Kern, P.
Mobian, D. Pomeranc, J.-P. Sauvage, Eur. J. Org. Chem. 2004,
1627 – 1638; W.-Q. Deng, A. H. Flood, J. F. Stoddart, W. A.
Goddard, J. Am. Chem. Soc. 2005, 127, 15994 – 15995; A. H.
Flood, A. J. Peters, S. A. Vignon, D. W. Steuerman, H.-R. Tseng,
S. Kang, J. R. Heath, J. F. Stoddart, Chem. Eur. J. 2004, 10, 6558 –
6564; D. A. Leigh, P. J. Lusby, A. M. Z. Slawin, D. B. Walker,
Chem. Commun. 2005, 4919 – 4921; J. V. Hernandez, E. R. Kay,
D. A. Leigh, Science 2004, 306, 1532 – 1537.
[12] The multiple conditions used in attaining X-ray diffraction
quality crystals of 3 are listed in the Supporting Information.
[13] Crystal-structure data for [2]catenane 3: [(C56H62N6O4)Pd-
Cl2]2·2.5(diisopropyl ether), M = 2120.83, triclinic, space group
¯
P1, a = 16.6067(5), b = 20.0933(5), c = 20.9225(6) Š, a =
96.87(0), b = 109.83(0), g = 92.81(0)8, V= 6490.43(346) Š3, Z =
2, 1calcd = 1.08514 gcmÀ3, 2qmax = 50.068, MoKa radiation (l =
0.71073 Š), T= 123 K. Pale-yellow crystal with dimensions
0.458 ” 0.33 ” 0.30 mm3. 50966 total reflections, 22750 unique
reflections [Rint = 0.044], R1 = 0.0992, wR2 = 0.2920[I>2sI], R1 =
0.1404, wR2 = 0.3295, GOF(F2) = 1.174, No/Nv = 22750/1228 with
I > 2s(I). Please refer to the Supporting Information for a full
description of the collection and refinement processes. CCDC-
627518 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.
[14] The least-squares planes were defined by the four carbonyl
carbon atoms of each macrocyclic unit.
[15] Crystal structure data for macrocycle 4: [(C56H62N6O4)Pd-
Cl2]·2CHCl3·2.8DMSO·0.6(diisopropyl ether), M = 1565.91, tri-
¯
clinic, space group P1, a = 12.3343(4), b = 17.5097(8), c =
18.9205(9) Š, a = 90.6(0), b = 107.29(0), g = 104.19(0)8, V=
3767.25(341) Š3, Z = 2, 1calcd = 1.38037 gcmÀ3
, 2qmax = 50.068,
[3] M. Fujita, Acc. Chem. Res. 1999, 32, 53 – 61; M. Fujita, M.
Tominaga, A. Hori, B. Therrien, Acc. Chem. Res. 2005, 38, 369 –
378; T. S. M. Abedin, L. K. Thompson, D. O. Miller, Chem.
Commun. 2005, 5512 – 5514; N. C. Habermehl, D. J. Eisler, C. W.
Kirby, N. L.-S. Yue, R. J. Puddephatt, Organometallics 2006, 25,
2921 – 2928; M. Chas, E. Pia, R. Toba, C. Peinador, J. M.
Quintela, Inorg. Chem. 2006, 8, 6117 – 6119; C. Dietrich-
Buchecker, B. Colasson, M. Fujita, A. Hori, N. Geum, S.
Sakamoto, K. Yamaguchi, J.-P. Sauvage, J. Am. Chem. Soc. 2003,
125, 5717 – 5725.
MoKa radiation (l = 0.71073 Š), T= 123 K. Pale-yellow crystal
with dimensions 0.50 ” 0.13 ” 0.05 mm3. 31282 total reflections,
13238 unique reflections [Rint = 0.051], R1 = 0.0762, wR2 =
0.2018[I>2sI], R1 = 0.1128, wR2 = 0.2277, GOF(F2) = 1.046, No/
Nv = 13230/893 with I > 2s(I). Please refer to the Supporting
Information for a full description of the collection and refine-
ment processes. CCDC-627517 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.
[4] M. E. Padilla-Tosta, O. D. Fox, M. G. B. Drew, P. D. Beer,
Angew. Chem. 2001, 113, 4365 – 4369; Angew. Chem. Int. Ed.
2838
www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 2835 –2838