Dynamic assembly of coordination boxes from (en)Pd(II) unit and a rectangular panel-like ligand: NMR, CSI-MS, and X-ray studies [3]

Full text of DOI:10.1021/ja003043o

980
J. Am. Chem. Soc. 2001, 123, 980-981
Dynamic Assembly of Coordination Boxes from
(en)Pd(II) Unit and a Rectangular Panel-Like
Ligand: NMR, CSI-MS, and X-ray Studies
Yoshinori Yamanoi,† Youichi Sakamoto,‡
Takahiro Kusukawa,† Makoto Fujita,*,†,§
Shigeru Sakamoto,| and Kentaro Yamaguchi*,|
Department of Applied Chemistry
Graduate School of Engineering
Nagoya UniVersity and
CREST, Japan Science and Technology Corporation (JST)
Chikusaku, Nagoya 454-8603, Japan
Coordination Chemistry Laboratories
Institute for Molecular Science
Myodaiji, Okazaki 444-8585, Japan
Chemical Analysis Center, Chiba UniVersity
Yayoicho, Inageku, Chiba 263-8522, Japan
ReceiVed August 15, 2000
Figure 1. (a) X-ray structure of coordination box 616+. (b) The linkage
connectivity in 616+ involving two conformations (A and B).
The simple combination of square planar coordination geometry
of Pd(II) or Pt(II) with pyridine-based ligands offers an efficient
method for the self-assembly of nanometer-sized frameworks such
as macrocycles, cages, catenanes, tubes, and capsules.1 To expand
the structures of pyridyl-coordinated Pd(II) complexes into more
rigid and bigger coordination frameworks, one can replace a
mono-coordinating 4-pyridyl group by a doubly ligating 3,5-bis-
(3-pyridyl)phenyl unit. According to this idea, 4,4′-bipyridine,
interconvertable. Coldspray ionization mass spectroscopy (CSI-
MS), which was developed recently by some of us,4 is found to
be very effective to study both kinetic and thermodynamic
products in the assembly process (Scheme 1).
Scheme 1
which is the simplest pyridine-based bridging ligand, is modified
into tetradentate ligand 1). This ligand is expected to take a panel-
like conformation and, on complexation with (en)Pd(NO3)2 (2),
assemble into large discrete box structures such as 312+ and 416+
in analogy to the assembly of trinuclear and tetranuclear cyclic
complexes from 2 and 4,4′-bipyridine.2,3 Here we report that these
expected box structures are efficiently formed in a dynamic
fashion. Namely, the boxes are in equilibrium and smoothly
† Department of Applied Chemistry, Graduate School of Engineering,
Nagoya University.
‡ Institute for Molecular Science.
§ CREST, Japan Science and Technology Corporation (JST).
| Chemical Analysis Center, Chiba University.
(1) Reviews: (a) Fujita, M. Chem. Soc. ReV. 1998, 27, 417. (b) Biradha,
K.; Fujita, M. In AdVances in Supramolecular Chemistry; Gokel, G. W., Ed.;
JAI Press Inc.: Connecticut, 2000; Vol. 6, p 1. (c) Leininger, S.; Olenyuk,
B.; Stang, P. J. Chem. ReV. 2000, 100, 853.
Treatment of 2 (1.25 × 10-2 mmol) with ligand 1 (0.62 ×
10-2 mmol) at 50 °C for 4 d in D2O-CD3OD (1:1, 0.5 mL) gave
rise to one major product, which was assigned as tetrameric box
416+ by CSI-MS after being isolated as PF6 salt in 88% yield
(prominent peaks at m/z ) 1688.8 [4‚13PF6]3+ and 1230.8 [4‚
(2) 4,4′-Bipyridine-based coordination boxes: (a) Fujita, M.; Yazaki, J.;
Ogura, K. J. Am. Chem. Soc. 1990, 112, 5645. (b) Stang, P. J.; Cao, D. H. J.
Am. Chem. Soc. 1994, 116, 4981. (c) Slone, R. V.; Hupp, J. T.; Stern, C. L.;
Albrecht-Schmitt, T. E. Inorg. Chem. 1996, 35, 4096.
(3) Coordination boxes with other ligands: (a) Stang, P. J.; Olenyuk, B.
Acc. Chem. Res. 1997, 30, 502. (b) Stang, P. J. Chem. Eur. J. 1998, 4, 19. (c)
Fujita, M.; Sasaki, O.; Mitsuhashi, T.; Fujita, T.; Yazaki, J.; Yamaguchi, K.;
Ogura, K. J. Chem. Soc., Chem. Commun. 1996, 1535. (d) Rauter, H.;
Mutikainen, I.; Blomberg, M.; Lock, C. J. L.; OmarOchoa, P.; Freisinger, E.;
Randaccio, L.; Chiarparin, E.; Lippert, B. Angew. Chem., Int. Ed. Engl. 1997,
36, 1296. (e) Hanan, G. S.; Volkmer, D.; Schubert, U. S.; Lehn, J.-M.; Baum,
G.; Fenske, D. Angew. Chem., Int. Ed. Engl. 1997, 36, 1843. (f) Duan, C.-Y.;
Liu, Z.-H.; You, X.-Z.; Xue, F.; Mak, T. C. W. Chem. Commun. 1997, 381.
(g) Li, J.; Zeng, H.; Chen, J.; Wang, Q.; Wu, X. Chem. Commun. 1997, 1213.
(h) Cotton, F. A.; Daniels, L. M.; Lin, C.; Murillo, C. A. J. Am. Chem. Soc.
1999, 121, 4538. (i) Bonar-Law, R. P.; McGrath, T. D.; Singh, N.; Bickley,
J. F.; Steiner, A. Chem. Commun. 1999, 2457. (j) Bu, X.-H.; Morishita, H.;
Tanaka, K.; Biradha, K.; Furusho, S.; Shionoya, M. Chem. Commun. 2000,
971.
1
12PF6]4+). In H NMR, a set of six protons was observed in
consistent with the D4h structure of 416+
.
In addition to box 416+, uncharacterized minor products were
also detected in 1H NMR. Being in equilibrium, all of the products
constituted a dynamic library of box structures from a single
ligand.5 From the library, we found that two box structures, both
(4) Cold ESI-MS is a sort of electrospray ionization (ESI) MS operated
under low temperature: Sakamoto, S.; Fujita, M.; Kim, K.; Yamaguchi, K.
Tetrahedron 2000, 56, 955.
(5) Lehn, J.-M. Chem. Eur. J. 1999, 5, 2455.
10.1021/ja003043o CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/10/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 981
Figure 2. 1H NMR (500 MHz, CD3CN, aromatic region) and CSI-MS (CH3CN) showing the conversion of 312+ into 416+ at the concentration of 6.7
mg/mL. CSI-MS conditions: accel volt, 5.0 kV; needle volt, 2.2 kV; orifice volt, 150 V; spray temp, -20 °C.
of which were very minor products under normal conditions, were
quantitatively formed by the following two methods.
and 416+, the proposed planer conformation of ligand 1, shown
in Scheme 1, was supported by the observation of strong NOE
(PyHa-ArHf and PyHd-ArHe). However, the solid structure 616+
involved two conformations (Figure 1b). The formation of this
linkage is possibly ascribed to a packing effect and unknown
equilibrium brought by THF diffusion9.
The first method is to use an organic template. When biphenyl
(5) was added as a template, trimeric 312+ was formed quantita-
tively.6 Thus, template 5 (2.0 × 10-2 mmol) was suspended in
the reaction mixture of 2 (2.0 × 10-2 mmol) and 1 (1.0 × 10-2
mmol) in D2O (1.0 mL) at 80 °C. After 7 h, the mixture became
The dynamic behavior of the coordination boxes in solution
was simultaneously monitored by 1H NMR and CSI-MS.10
Combination of these two methods was shown to be quite
effective to study the dynamic assembly process. Thus, clathrate
complex 3‚12(PF6)‚2(5)‚2H2O was dissolved in CH3CN or CD3-
CN. In this media, guest 5 was immediately liberated, leaving
empty 312+. Interestingly, the analysis of the reorganizing process
from 312+ into 416+ showed the presence of pentamer 720+ as a
kinetic intermediate (Figure 2). After 0.5 h, trimeric prism 312+
was observed with some uncharacterized components by NMR,
whereas CSI-MS clearly showed the formation of 312+, 416+, and
pentamer 720+. After 2 h, components were hardly analyzed by
NMR, but CSI-MS showed the increase of 416+ and 720+ and the
decrease of 312+. After 5 h, both NMR and CSI-MS displayed
two major components, which were easily assigned as 416+ and
720+ by comparing the spectra. After 26 h, the only major
component is tetrameric box 416+ as confirmed by both methods.
1
an almost clear solution and, after filtration, H NMR spectrum
showed a set of six signals for trimeric complex 312+ and another
set of three signals for 5 in aromatic region (see Supplementary
Information). The biphenyl protons were significantly upfield
shifted probably due to inclusion in the deep cavity of 312+. The
structure was strongly supported by conventional ESI-MS mea-
surement which displayed five peaks at m/z ) 1502.9, 982.1,
720.8, 564.3, and 460.3 corresponding to the cations [3‚10NO3]2+,
[3‚9NO3]3+, [3‚8NO3]4+, [3‚7NO3]5+, and [3‚6NO3]6+. The inte-
1
gration of the H NMR signals showed the enclathration of two
biphenyl molecules in the cavity of trimeric prism 312+. The host-
guest complex was precipitated by adding an excess amount of
NH4PF6 to the reaction solution and was isolated as a pure PF6
salt in 53% yield. Elemental analysis agreed with the formula of
3‚12(PF6)‚2(5)‚2H2O.
The second method to select a single box structure from the
library is crystallization.7 When THF vapor was slowly diffused
into the H2O-CH3CN solution of 1 and 2 for a few weeks, a
single-crystal suitable for diffraction study was obtained. X-ray
diffraction experiments showed the formation of unexpected
tetrameric box 616+, which has the same composition as 416+ but
different linkage connectivity (Figure 1).8 In the 1H NMR of 312+
Supporting Information Available: Experimental procedures and
spectroscopic characterization of ligand 1, tetramer 416+, and trimer 312+
,
and the details of the X-ray diffraction study of 616+ (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
JA003043O
(8) Crystallographic data of 6: See Supporting Information.
(9) Attempts to obtain the NMR of pure 616+ were unsuccessful because
of its rapid isomerization in D2O-CD3OD into more stable solution structures.
(10) ESI-MS and 1H NMR observation of kinetic and thermodynamic
products in the metal-directed self-assembly: Hasenknopf, B.; Lehn, J.-M.;
Boumediene, N.; Leize, E.; Dorsselaer, A. V. Angew. Chem., Int. Ed. 1998,
37, 3265.
(6) Guest-templated assembly: (a) Anderson, S.; Anderson, H. L.; Sanders,
J. K. M. Acc. Chem. Res. 1993, 26, 469. (b) Fujita, M.; Nagao, S.; Ogura, K.
J. Am. Chem. Soc. 1995, 117, 1649. (c) Bilyk, A.; Harding, M. M. J. Chem.
Soc., Chem. Commun. 1995, 1697.
(7) Baxter, P. N. W.; Lehn, J.-M.; Rissanen, K. Chem. Commun. 1997,
1323.