A triptycene-based bis(crown ether) host: Complexation with both paraquat derivatives and dibenzylammonium salts

Article abstract of DOI:10.1021/ol053008s

A novel triptycene-based bis(crown ether) host (1) incorporating two dibenzo-24-crown-8 ether moieties has been synthesized. It can form not only a new bis[2]pseudorotaxane with dibenzylammonium salts but also stable clip-shaped complexes with paraquat de

Full text of DOI:10.1021/ol053008s

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
ORGANIC
LETTERS
2006
Vol. 8, No. 6
1069-1072
A Triptycene-Based Bis(crown ether)
Host: Complexation with Both Paraquat
Derivatives and Dibenzylammonium
Salts
Tao Han†,‡ and Chuan-Feng Chen*,†
Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China, and Graduate School, Chinese Academy of Sciences,
Beijing 100049, China
cchen@iccas.ac.cn
Received December 12, 2005
ABSTRACT
A novel triptycene-based bis(crown ether) host (1) incorporating two dibenzo-24-crown-8 ether moieties has been synthesized. It can form not
only a new bis[2]pseudorotaxane with dibenzylammonium salts but also stable clip-shaped complexes with paraquat derivatives. Moreover,
the complexation process between 1 and the two classes of guests can be chemically controlled.
Since Stoddart et al. first reported the complexation of
paraquat by the bisparaphenylene-34-crown-10 in the late
1980s,1 paraquats (N,N′-dialkyl-4,4′-bipyridinium salts) have
been extensively studied as guests in host-guest chemistry.
In particular, a variety of interlocked molecules, such as
pseudorotaxanes, rotaxanes, and catenanes, have been con-
structed by the complexation of the paraquats with crown
ethers,2 cryptands,3 and other hosts.4
supramolecular systems with unique structures and proper-
ties.5 Inspired by the fact that dibenzo-24-crown-8 (DB24C8)
can be threaded by secondary ammonium ions to form [2]-
pseudorotaxanes,6 we recently reported that the complexation
of a triptycene-based homotritopic host with dibenzylam-
(3) For recent examples on cryptand/paraquat complexes, see: (a) Huang,
F.; Fronczek, F. R.; Gibson, H. W. J. Am. Chem. Soc. 2003, 125, 9272-
9273. (b) Huang, F.; Gibson, H. W.; Bryant, W. S.; Nagvekar, D. S.;
Fronczek, F. R. J. Am. Chem. Soc. 2003, 125, 9367-9371. (c) Huang, F.;
Switek, K. A.; Zakharov, L. N.; Fronczek, F. R.; Slebodnick, C.; Lam, M.;
Golen, J. A.; Bryant, W. S.; Mason, P. E.; Rheingold, A. L.; Ashraf-
Khorassani, M.; Gibson, H. W. J. Org. Chem. 2005, 70, 3231-3241.
(4) For some recent examples, see: (a) Huang, F.; Zakharov, L. N.;
Rheingold, A. L.; Ashraf-Khorassani, M.; Gibson, H. W. J. Org. Chem.
2005, 70, 809-813. (b) Huang, F.; Gibson, H. W. Chem. Commun. 2005,
1696-1698. (c) Kwangyul, M.; Grindstaff, J.; Sobransingh, D.; Kaifer, A.
E. Angew. Chem., Int. Ed. 2004, 43, 5496-5499. (d) Kwangyul, M.; Kaifer,
A. E. Org. Lett. 2004, 6, 185-188. (e) Arduini, A.; Calzavacca, F.; Pochini,
A.; Secchi, A. Chem. Eur. J. 2003, 9, 793-799. (f) Credi, A.; Dumas, S.;
Silvi, S.; Venturi, M.; Arduini, A.; Pochini, A.; Secchi, A. J. Org. Chem.
2004, 69, 5881-5887. (g) Arduini, A.; Ciesa, F.; Fragassi, M.; Pochini,
A.; Secchi, A. Angew. Chem., Int. Ed. 2005, 44, 278-281.
Triptycene, for its three-dimensional rigid structure, was
found to be a useful building block for the construction of
† Institute of Chemistry, Chinese Academy of Sciences.
‡ Graduate School, Chinese Academy of Sciences.
(1) Allwood, B. L.; Spencer, N.; Shahriari-Zavareh, H.; Stoddart, J. F.;
Williams, D. J. J. Chem. Soc., Chem. Commun. 1987, 1064-1066.
(2) For recent examples on crown ether/paraquat complexes, see: (a)
Badjic, J. D.; Balzani, V.; Credi, A.; Silvi, S.; Stoddart, J. F. Science 2004,
303, 1845-1849. (b) Badjic, J. D.; Cantrill, S. J.; Stoddart, J. F. J. Am.
Chem. Soc. 2004, 126, 2288-2289. (c) Huang, F.; Fronczek, F. R.; Gibson,
H. W. Chem. Commun. 2003, 1480-1481. (d) Long, B.; Nikitin, K.;
Fitzmaurice, D. J. Am. Chem. Soc. 2003, 125, 15490-15498.
10.1021/ol053008s CCC: $33.50
© 2006 American Chemical Society
Published on Web 02/24/2006

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
monium salts formed a tris[2]pseudorotaxane that could
further be transferred into [4]pseudocatenanes.7 Here, we
report a novel triptycene-based host 1 containing two
DB24C8 moieties, which show the complexation not only
with dibenzylammonium salts to result in a bis[2]pseudo-
rotaxane but also with paraquats8 to form stable clip-shaped
complexes in solution and in the solid state (Figure 1).
Moreover, the complexation process between 1 and guests
3 and 4 can be chemically controlled.
due to charge transfer between the electron-rich aromatic
rings of the host 1 and the electron-poor pyridinium rings
of the guest 2. Similarly, the mixed solution of 1 and 3 also
showed typical charge-transfer features but the color is
1
yellow. As shown in Figure 2, the H NMR spectrum of a
Figure 2. Partial 1H NMR spectra (300 MHz, CD3CN, 295 K) of
(a) free host 1, (b) free guest 2, and (c) 1 and 1.0 equiv of 2.
[1]0 ) 2 mM.
Figure 1. Structure and proton designations of the host 1 and guests
2-4.
1:1 mixture of 1 and 2 in CD3CN showed a great difference
with those for host 1 and guest 2. Consequently, the proton
H7 of paraquat ring showed a significant upfield shift
(∆δ ) 0.901 ppm), which may be due to the strong shielding
effect of the aromatic rings in 1. Similarly, the H1-H5 proton
signals of 1 also shifted upfield. In contrast, a considerable
downfield shift of the methyl protons in guest 2 was
observed, which is attributed to the hydrogen bond interac-
tions and its position in the deshielding region of the aromatic
rings of 1. These observations suggested that a stable
complex between 1 and guest 2 was formed. Furthermore,
1H NMR spectroscopic titrations afforded a quantitative
estimate for the complex of 1 and 2 by monitoring the
changes of the chemical shift of the proton H7 in the paraquat
ring. The results showed that a 1:1 complex 1‚2 was formed
by a mole ratio plot.10 Accordingly, the apparent association
constant between 1 and paraquat 2 was calculated to be
Ka,exp,1‚2 ) 1.63((0.3) × 104 M-1.11 Similarly, 1 and the
paraquat derivative 3 also formed a 1:1 complex, and the
apparent association constant (Ka,exp,1‚3) was determined to
be 136 ((22) M-1. The big Ka,exp difference between 1‚2
and 1‚3 presumably results from the different bonding
manner of host 1 with guests 2 and 3. For complex 1‚2, there
exist strong NOE effects between N-methyl protons, pyri-
dinium protons (H6) of the guest, and crown ether protons
Synthesis of host 1 is depicted in Scheme 1. Reaction of
the triptycene derivative 55d and 2 equiv of 1,2-bis[2-[2-(2-
Scheme 1. Synthesis of Host 1
tosyloxyethoxy)ethoxy]ethoxy]benzene 67 under high dilution
conditions afforded 1 in 46% yield. Host 1 was characterized
1
by H NMR, 13C NMR, MALDI-TOF MS, and elemental
analysis.9
When host 1 and paraquat 2 (2 mM each) were mixed in
acetonitrile, they gave a deep orange solution immediately
(5) (a) Ma, J. C.; Dougherty, D. A. Chem. ReV. 1997, 97, 1303-1324.
(b) Corbett, P. T.; Tong, L. H.; Sanders, J. K. M.; Otto, S. J. Am. Chem.
Soc. 2005, 127, 8902-8903. (c) Zhu, X. Z.; Chen, C. F. J. Org. Chem.
2005, 70, 917-924. (d) Zong, Q. S.; Chen, C. F. Org. Lett. 2006, 8, 211-
214.
(6) Ashton, P. R.; Campbell, P. J.; Chrystal, E. J. T.; Peter, T. G.; Menzer,
S.; Phlip, D.; Sepencer, N.; Stoddart, J. F.; Tasher, P. A.; Willams, D. J.
Angew. Chem., Int. Ed. 1995, 34, 1865-1869.
(10) Tsukube, H.; Furuta, H.; Odani, A.; Takeda, Y.; Kudo, Y.; Inoue,
Y.; Liu, Y.; Sakamoto, H.; Kimura, K. In ComprehensiVe Supramolecular
Chemistry; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Vogtleand,
F., Lehn, J. M., Eds.; Elsevier: New York, 1996.
(11) Complexation between 1 and 2 was determined to be non-
concentration dependent, which is in contrast with the complex formed by
DB24C8 and 2.8 This result indicated that complexation of 2 with the host
1 occurred in a way different from the complexation of DB24C8. For the
determination of the Ka,exp, see the Supporting Information.
(7) Zhu, X. Z.; Chen, C. F. J. Am. Chem. Soc. 2005, 127, 13158-13159.
(8) Gibson et al. recently mentioned in a paper that DB24C8 can form
a 1:1 complex with the paraquat in solution, but a 2:1 complex in the solid
state. Huang, F.; Jones, J. W.; Slebodnick, C.; Gibson, H. W. J. Am. Chem.
Soc. 2003, 125, 14458-14464.
(9) See the Supporting Information.
1070
Org. Lett., Vol. 8, No. 6, 2006

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
of the host. However, such short distance contacts were not
observed for complex 1‚3 under the same conditions.9
The electrospray ionization mass spectrum (ESI MS)
provided more evidence for the formation of complexes
1‚2 and 1‚3.9 As a result, a strong peak at m/z 604.8 for
[1‚2 - 2PF6-]2+ was observed, which indicated that the 1:1
stable complex between 1 and guest 2 formed. For 1‚3, the
relevant peak was observed at m/z 632.5, corresponding to
- 2+
[1‚3 - 2PF6 ] .
Further support for formation of the complex 1‚2 came
from its X-ray diffraction results.12 As shown in Figure 3,
Figure 4. Partial 1H NMR spectra (300 MHz, CD3CN, 295 K) of
(a) free host 1, (b) free guest 4, and (c) 1 and 2.0 equiv of 4.
[1]0 ) 5 mM.
acetonitrile solution were determined to be 720 ( 180 and
77 ( 22 M-1, respectively. These values suggested that 1
binds to the dibenzylammonium salts with a similar strength
as the DB24C8 does.14 Formation of the complex 1‚42 was
further confirmed by its ESI MS. As a result, two relevant
peaks were observed for 1‚42 at m/z 619.9 (100) for [1‚42 -
-
+
- 2+ 9
PF6 + H3 O]2+ and 709.7 (91%) for [1‚42 - 2PF6 ] .
It was known that the association and disassociation of
the complex between DB24C8 and secondary ammonium
salts could be chemically controlled by pH, which inspired
us to further examine the competitive bonding ability of the
host 1 toward different guests. Consequently, a series of 1H
NMR experiments were carried out. As shown in Figure 5b,
the host 1 and 1 equiv of the guest 3 formed a stable complex
1‚3. When 2 equiv of the guest 4 was added into the solution
of 1‚3 in CD3CN, proton H7 of guest 3 shifted downfield
almost to the original position (Figure 5c), which indicates
that the complex 1‚3 disassociated. Meanwhile, the more
stable complex 1‚42 formed. To the above solution was added
1.6 µL of tributylamine,15 and it was found that protons on
guest 4 were peeled off, which showed that the complex 1‚
42 disassociated while 1‚3 recovered (Figure 5d). Further-
more, when 1.0 µL of trifluoroacetic acid was added, the
complex 1‚3 disassociated while the complex 1‚42 formed
again (Figure 5e). These observations suggested that the host
1 exhibited a pH-controllable guest-exchange process.
In summary, we have synthesized a novel triptycene-based
bis(crown ether) and demonstrated that it could form not only
bis[2]pseudorotaxane-type complex with dibenzylammonium
Figure 3. Top view (a) and side view (b) of the crystal structure
of the complex 1‚2. Hydrogen atoms not involved in the interac-
tions, and counterions are omitted for clarity.
in the solid state the paraquat is included in the center of
the host 1 while the two N-methyl groups are positioned in
the two DB24C8 cavities, which results in a pseudorotaxane-
like structure. Due to multiple CH‚‚‚O hydrogen bonds
between the N-methyl protons and proton H6 of the paraquat
unit and ether oxygen atoms in 1, and the face to face
π-stacking interactions between paraquat ring and aromatic
rings of the crown units, the complex 1‚2 exhibits a high
stability. This result is consistent with that of 1‚2 in solution.
Complexation between host 1 and dibenzylammonium salt
1
4 was studied by H NMR spectroscopic titrations (Figure
4). As expected, the host 1 binds two of the guest 4 to form
a bis[2]pseudorotaxane-type complex 1‚42, and the com-
plexation of 4 with host 1 occurs under a slow exchange
process. When the ion-pairing effect was considered, the
association constants13 for 1‚42, Kap,1, and Kap,2 in an
(13) Elizarov, A. M.; Chiu, S. H.; Glink, P. T.; Stoddart, J. F. Org. Lett.
2002, 4, 679-682.
-
(14) When PF6 counterion was considered, the asscociation constant
for the 1:1 complex between DB24C8 and 4 was determined to be 560 (
60 M-1 in CDCl3/CD3CN (3/2).
(15) Tributylamine was usually used as a base to deprotonate the NH2
+
(12) Crystal data for complex 1‚2: C70H84F12N2‚O16P2, Mr ) 1499.33,
triclinic, space group P-1, a )15.069(3) Å, b )24.790(6) Å, c)25.460(6)
Å; R ) 114.553(4)°, â ) 91.187(4)°, γ ) 102.178 (5)°; V ) 8393 (3) Å3,
Z ) 4, T ) 294(2) K, R1 ) 0.2371, wR2 ) 0.3210 (all data); R1 ) 0.1056,
wR2 ) 0.2819 [I > 2σ(I)].
center. See: Ashton, P. R.; Ballardine, R.; Balzani, V.; Baxter, I.; Credi,
A.; Fyfe, M. C. T.; Gandolfi, M. T.; Go´mez-Lo´pez, M.; Mart´ınez-D´ıaz, M.
V.; Piersanti, A.; Spencer, N.; Stoddart, J. F.; Venturi, M.; White, A. J. P.;
Williams, D. J. J. Am. Chem. Soc. 1998, 120, 11932-11942.
Org. Lett., Vol. 8, No. 6, 2006
1071

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
that the complex processes between host 1 and the guests 3
and 4 could be controlled by changing the solution pH, which
would be useful for the design of chemically controlled
molecular machines, such as molecular muscles.16 Further
work on the fabrication of a rotaxane-based molecular muscle
is being done.
Acknowledgment. We thank the Chinese Academy of
Sciences and the National Natural Science Foundation of
China for financial support. We also thank Dr. H. B. Song
for determining the crystal structure of the complex.
Supporting Information Available: Experimental pro-
cedure and characterization for the host and the complexes.
Determination of the association constants for the complexes.
The crystal structure for 1‚2 and its CIF data. This material
is available free of charge via the Internet at http://pubs.acs.org.
Figure 5. Partial 1H NMR spectra (300 MHz, CD3CN, 295 K) of
(a) [3]0 (5 mM), (b) [1]0/[3]0 ) 5 mM/5 mM, (c) [1]0/[4]0/[3]0 )
5 mM/10 mM/5 mM, (d) to the solution of c was added 1.6 µL of
tributylamine, and (e) to the solution of d was added 1 µL of
trifluoroacetic acid.
OL053008S
(16) (a) Jime´nez, M. C.; Dietrich-Buchecker, C.; Sauvage, J. P. Angew.
Chem., Int. Ed. 2000, 39, 3284-3287. (b) Yi, L.; Flood, A. H.; Bonvallet,
P. A.; Vignon, S. A.; Northrop, B. H.; Tseng, H. R.; Jeppesen, J. O.; Huang,
T. J.; Brough, B.; Baller, M.; Magonov, S.; Solares, S. D.; Goddard, W.
A.; Ho, C. M.; Stoddart, J. F. J. Am. Chem. Soc. 2005, 127, 9745-9759.
salts but also clip-shaped complexes with paraquat deriva-
tives in solution and in the solid state. Moreover, we found
1072
Org. Lett., Vol. 8, No. 6, 2006