Threading-followed-by-shrinking protocol for the synthesis of a [2]rotaxane incorporating a Pd(II)-salophen moiety

Article abstract of DOI:10.1021/ja0464490

This communication describes a new protocol for the construction of [2]rotaxanes: threading-followed-by-shrinking . This approach involves the threading of a rodlike unit through a crown ether-like macrocycle and then shrinking the size of the macrocycle's cavity through coordination of a transition-metal ion by a salophen moiety in the macrocycle. The self-assembly of the macrocycle and a thread, followed by addition of palladium acetate, afforded the [2]rotaxane, which contains a palladium(II)-salophen moiety, after counterion exchange. This [2]rotaxane was characterized fully by NMR and IR spectroscopic, mass spectrometric, and elemental and X-ray crystallographic analyses. Copyright

Full text of DOI:10.1021/ja0464490

Published on Web 12/07/2004
Threading-Followed-by-Shrinking Protocol for the Synthesis of a [2]Rotaxane
Incorporating a Pd(II)-Salophen Moiety
Il Yoon, Mamiko Narita,† Toshimi Shimizu, and Masumi Asakawa*
Nanoarchitectonics Research Center, National Institute of AdVanced Industrial Science and Technology (AIST),
Tsukuba Central 5, 1-1-1 Higashi, Tsukuba Ibaraki 305-8565, Japan
Received June 16, 2004; E-mail: masumi-asakawa@aist.go.jp
Scheme 1
Rotaxanes and catenanes have attracted a considerable amount
of interest in recent years because a number of them function as
molecular motors and molecular switches.1 Although rotaxanes have
been prepared from many different building blocks, the number of
synthetic methods for their construction remains limited. [2]-
Rotaxanes are most conveniently prepared using template-directed
syntheses such as clipping,2 threading-followed-by-stoppering,3 and
slipping4 methods. In this communication, we report a new synthetic
method (Figure 1), which we name “threading-followed-by-
Figure 1. Synthesis of a [2]rotaxane using a threading-followed-by-
shrinking method.
exchange (Scheme 1). We have characterized 3-H‚ClO4 fully
through NMR and IR spectroscopic, mass spectrometric, and
elemental and X-ray crystallographic analyses.
shrinking”, that involves threading a rodlike unit through a
macrocycle and then shrinking the free space within the macrocycle
through coordination between its salophen [N,N′-o-phenylenebis-
(salicylidene-iminato) dianion] moiety and a transition metal.
Recently, Leigh et al. reported the synthesis of [2]rotaxanes, based
on octahedral and square-planar metal complexes formed by thread-
macrocycle-metal assemblies incorporating transition-metal ions;
the metal coordination in these systems occurs through binding of
both the thread and macrocycle components to the metal ion, and
these rotaxanes are formed effectively upon mixing of the com-
ponents in what is, essentially, a threading-followed-by-stoppering
approach.5 Our protocol for [2]rotaxane formation differs conceptu-
ally in a number of areas: the metal ion is stabilized through square-
planar coordination, the shrinking process involves metal ion
coordination by the macrocycle only (i.e., the threadlike unit does
not coordinate to the metal ion), and the macrocycle is not
interlocked by the thread in the absence of the metal ion.
The 1H NMR spectrum of 3-H‚ClO4 (Figure 2c), together with
its 2D (ROESY and COSY) NMR spectra (Supporting Information),
provides good evidence for the formation of the rotaxane. Figure
2c indicates that the signal of the CH2N+ (A) protons in the thread
has shifted downfield significantly, relative to that of the free thread
(Figure 2a), as a result of the formation of [C-H‚‚‚O] hydrogen
bonds11 (Figure 3). In addition, the signal of one proton (k) of the
salophen unit in the macrocycle also underwent a significant
downfield shift relative to that of the free macrocycle (Figure 2b);
Recently, we synthesized the bis-compartmental sodium per-
chlorate-crown ether complex 1, which incorporates a salophen
moiety, and its transition-metal complex.6 Salophens are tetradentate
ligands that react with transition-metal ions to form square-planar
complexes7 whose versatile properties are of interest to applications
in areas such as molecular recognition,8 metallocatalysis,9 and
electron transfer.6,10 We introduced the salophen moiety as a unit
to control the size of the macrocycle within rotaxanes, which may,
in addition, have potential for use as catalysts.
The interaction of 1 with the secondary dialkylammonium salt
2-H‚PF64b forms a pseudorotaxane intermediate in a reversible self-
assembly process; the addition of palladium acetate afforded the
rotaxane 3-H‚ClO4 in reasonable yield (30%) after counterion
Figure 2. 1H NMR spectra of (a) 2-H‚PF6, (b) 1, and (c) 3-H‚ClO4 in
CDCl3/CD3CN (5:1) at 25 °C. The signal labeled with an asterisk represents
CHCl3.
† Current address: Toyota Central R&D Labs., Inc., 41-1, Aza Yokomichi, Oaza
Nagakute, Nagakute-cho, Aichi-gun, Aichi-Ken, 480-1192, Japan.
9
16740
J. AM. CHEM. SOC. 2004, 126, 16740-16741
10.1021/ja0464490 CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
followed-by-shrinking methodsthat we believe will be useful for
the construction of additional mechanically interlocked molecules.
Acknowledgment. I.Y. thanks the Japan Society for the
Promotion of Science (JSPS) for a postdoctoral fellowship. M.N.
thanks the New Energy and Industrial Technology Development
Organization (NEDO) of Japan for a grant from the Industrial
Technology Research Grant Program.
Supporting Information Available: Experimental procedures and
spectroscopic data for 3-H‚ClO4 (PDF, CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) (a) Hernandez, R.; Tseng, H.-R.; Wong, J. W.; Stoddart, J. F.; Zink, J. I.
J. Am. Chem. Soc. 2004, 126, 3370-3371. (b) Leigh, D. A.; Wong, J. K.
Y.; Dehez, F.; Zerbetto, F. Nature 2003, 424, 174-179. (c) Schalley, C.
A.; Beizai, K.; Vo¨gtle, F. Acc. Chem. Res. 2001, 34, 465-476. (d) Collin,
J.-P.; Dietrich-Buchecker, C.; Gavin˜a, P.; Jimenez-Molero, M. C.; Sauvage,
J.-P. Acc. Chem. Res. 2001, 34, 477-487. (e) Jun, S. I.; Lee, J. W.;
Sakamoto, S.; Yamaguchi, K.; Kim, K. Tetrahedron Lett. 2000, 41, 471-
475.
(2) (a) Asakawa, M.; Brancato, G.; Fanti, M.; Leigh, D. A.; Shimizu, T.;
Slawin, A. M. Z.; Wong, J. K. Y.; Zerbetto, F.; Zhang, S. J. Am. Chem.
Soc. 2002, 124, 2939-2950. (b) Wisner, J. A.; Beer, P. D.; Drew, M. G.
B.; Sambrook, M. R. J. Am. Chem. Soc. 2002, 124, 12469-12476. (c)
Glink, P. T.; Oliva, A. I.; Stoddart, J. F.; White, A. J. P.; Williams, D. J.
Angew. Chem., Int. Ed. 2001, 40, 1870-1875.
Figure 3. Molecular structure of 3-H‚ClO4 (ORTEP, 30% thermal
probability ellipsoids) displaying the intercomponent [N+-H‚‚‚O] and
[C-H‚‚‚O] hydrogen bonds. Hydrogen atoms, except for those involved
in H-bonds, have been omitted for clarity. Hydrogen bond geometries {-
[X‚‚‚O], [H‚‚‚O] distances (Å), and [X-H‚‚‚O] angles (deg)}: (a) 3.010,
2.187, 151.8; (b) 2.823, 2.120, 134.2; (c) 2.835, 2.015, 150.8; (d) 3.067,
2.346, 137.1; (e) 3.384, 2.476, 157.8.
this shift may be attributable to the deshielding effect of the aromatic
rings of the thread in the rotaxane (Figure S4). In contrast, the signal
for proton f of the oligoether ring shifted relatively upfield, which
we attribute to the shielding effect of the aromatic units in the thread
that arises from the bent conformations of the components (Figure
3). In addition, the signals of some protons in the salophen (h, g,
j; Figure 2c) and aromatic units in the thread (B, C; Figure 2c)
have shifted upfield relative to those signals in the free components,
which suggests the existence of π-π stacking interactions.12
Moreover, the interlocked nature of 3-H‚ClO4 is suggested by the
ROESY spectrum (Supporting Information), which displays cross-
peaks between the signals of the protons of the ether linkages in
the macrocycle (c-f) and those of both the CH2N+ (A) and aromatic
(C) groups of the thread.
(3) (a) Cao, J.; Fyfe, M. C. T.; Stoddart, J. F.; Cousins, G. R. L.; Glink, P.
T. J. Org. Chem. 2000, 65, 1937-1946. (b) Tachibana, Y.; Kihara, N.;
Ohga, Y.; Takata, T. Chem. Lett. 2000, 806-807. (c) Cantrill, S. J.; Fulton,
D. A.; Heiss, A. M.; Pease, A. R.; Stoddart, J. F.; White, A. J. P.; Williams,
D. J. Chem.-Eur. J. 2000, 6, 2274-2287.
(4) (a) Cantrill, S. J.; Preece, J. A.; Stoddart, J. F.; Wang, Z.-H.; White, A.
J. P.; Williams, D. J. Tetrahedron 2000, 56, 6675-6681. (b) Ashton, P.
R.; Baxter, I.; Fyfe, M. C. T.; Raymo, F. M.; Spencer, N.; Stoddart, J. F.;
White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1998, 120, 2297-
2307. (c) Ha¨ndel, M.; Plevoets, M.; Gestermann, S.; Vo¨gtle, F. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1199-1201.
(5) (a) Hogg, L.; Leigh, D. A.; Lusby, P. J.; Morelli, A.; Parsons, S.; Wong,
J. K. Y. Angew. Chem., Int. Ed. 2004, 43, 1218-1221. (b) Fuller, A.-M.;
Leigh, D. A.; Lusby, P. J.; Oswald, I. D. H.; Parsons, S.; Walker, D. B.
Angew. Chem., Int. Ed. 2004, 43, 3914-3918.
(6) Yoon, I.; Goto, M.; Shimizu, T.; Lee, S. S.; Asakawa, M. J. Chem. Soc.,
Dalton Trans. 2004, 1513-1515.
(7) (a) Chichak, K.; Jacquemard, U.; Branda, N. R. Eur. J. Inorg. Chem. 2002,
357-368. (b) Rosa, D. T.; Coucouvanis, D. Inorg. Chem. 1998, 37, 2328-
2329.
We obtained orange-colored single crystals of 3-H‚ClO4 suitable
for X-ray analysis upon vapor diffusion of diethyl ether into an
acetonitrile solution of 3-H‚ClO4.13 The crystal structure of 3-H‚
ClO4 (Figure 3) confirms the encircling of the macrocycle about
the molecular axle of the thread. Stabilization of the [2]rotaxane is
achieved through a combination of (a) [N+-H‚‚‚O]14 and [C-H‚
‚‚O]14b,d hydrogen bonds between the oxygen atoms of the mac-
rocycle and the NH2+ and benzylic CH2N+ units of the secondary
dialkylammonium ion and (b) π-π stacking interactions14 between
aromatic rings (Supporting Information). The packing of the [2]-
rotaxane is stabilized by pairs of [C-H‚‚‚π] interactions14a,c (a and
b in Figure S4) between one proton of an aromatic ring of the
salophen unit in one rotaxane and an aromatic ring of the thread in
another and between one proton of a CH2O unit in one rotaxane
and an aromatic ring of the salophen in another. The [N+-H‚‚‚
O]14 and [C-H‚‚‚O]14b,d hydrogen bonding distances (2.823-3.384
Å) are comparable with those of related compounds.14 The
palladium atom exists in a distorted square-planar array that is very
similar to one that we have described previously6 (Figure S3). The
Pd(II)‚‚‚π distances (3.477 and 3.733 Å) are longer than the sum
of the van der Waals radii (3.25-3.30 Å).15 In summary, we have
successfully self-assembled and characterized the [2]rotaxane 3-H‚
ClO4 incorporating a crown ether-like macrocycle containing a
palladium(II)-salophen moiety. In particular, we have demonstrated
a new protocol for the synthesis of [2]rotaxanessthe threading-
(8) Cametti, M.; Nissinen, M.; Cort, A. D.; Mandolini, L.; Rissanen, K. Chem.
Commun. 2003, 2420-2421.
(9) Castelli, V. van A.; Cort, A. D.; Mandolini, L.; Reinhoudt, D. N.;
Schiaffino, L. Eur. J. Org. Chem. 2003, 627-633.
(10) Franceschi, F.; Solari, E.; Scopelliti, R.; Floriani, C. Angew. Chem., Int.
Ed. 2000, 39, 1685-1687.
(11) (a) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48-76. (b) Raymo, F.
M.; Bartberger, M. D.; Houk, K. N.; Stoddart, J. F. J. Am. Chem. Soc.
2001, 123, 9264-9267. (c) Desiraju, G. R. Acc. Chem. Res. 1991, 24,
290-296.
(12) (a) Adams, H.; Hunter, C. A.; Lawson, K. R.; Perkins, J.; Spey, S. E.;
Urch, C. J.; Sanderson, J. M. Chem.-Eur. J. 2001, 7, 4863-4877. (b)
Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525-
5534.
(13) Crystallographic data for 3-H‚ClO4: [Pd(C34H32N2O8)C22H32N]ClO4,
C
56H64ClN3O12Pd, Mr ) 1112.95, triclinic, space group P1h, a ) 12.5559-
(7), b ) 14.3901(9), c ) 15.6599(9) Å, R ) 104.2930(10), â ) 96.2350-
(10), γ ) 102.1140(10)°, V ) 2642.1(3) Å3, Z ) 2, Fcalcd ) 1.399 g cm-3
,
µ(Mo KR) ) 4.67 cm-1, T ) 203(2) K, orange plate, 0.35 × 0.30 × 0.20
mm3, R1 ) 0.0357 [I > 2 σ(I)], wR2 ) 0.0993 (all data), GOF ) 1.029.
(14) (a) Cantrill, S. J.; Fyfe, M. C. T.; Heiss, A. M.; Stoddart, J. F.; White, A.
J. P.; Williams, D. J. Org. Lett. 2000, 2, 61-64. (b) Cantrill, S. J.; Fyfe,
M. C. T.; Heiss, A. M.; Stoddart, J. F.; White, A. J. P.; Williams, D. J.
Chem. Commun. 1999, 1251-1252. (c) Ashton, P. R.; Ballardini, R.;
Balzani, V.; Go´mez-Lo´pez, M.; Lawrence, S. E.; Mart´ınez-D´ıaz, M. V.;
Montalti, M.; Piersanti, A.; Prodi, L.; Stoddart, J. F.; Williams, D. J. J.
Am. Chem. Soc. 1997, 119, 10641-10651. (d) Ashton, P. R.; Glink, P.
T.; Stoddart, J. F.; Menzer, S.; Tasker, P. A.; White, A. J. P.; Williams,
D. J. Tetrahedron Lett. 1996, 37, 6217-6220.
(15) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry, 4th ed.;
Harper Collins College Publishers: New York, 1993; Table 8.1, p 292.
JA0464490
9
J. AM. CHEM. SOC. VOL. 126, NO. 51, 2004 16741