Triptycene-derived macrotricyclic polyether containing an anthracene unit as a powerful host for 1,2-bis(pyridium)ethane, diquat and 2,7-diazapyrenium salt

Article abstract of DOI:10.1039/c4ob00310a

Triptycene-derived macrotricyclic polyether containing an anthracene unit is a powerful host for 1,2-bis(pyridium)ethane, diquat and 2,7-diazapyrenium salt with association constants of the 1:1 complexes at >10⁵ M^-1. Crystal structures showed that π-π stacking interactions between the host and the guests play an important role in the formation of the stable complexes. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00310a

Volume 12 Number 18 14 May 2014 Pages 2813–2980
Organic &
Biomolecular
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Chuan-Feng Chen et al.
Triptycene-derived macrotricyclic polyether containing an anthracene
unit as a powerful host for 1,2-bis(pyridium)ethane, diquat and
2,7-diazapyrenium salt

Organic &
Biomolecular Chemistry
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Triptycene-derived macrotricyclic polyether
containing an anthracene unit as a powerful
host for 1,2-bis(pyridium)ethane, diquat and
2,7-diazapyrenium salt†
Cite this: Org. Biomol. Chem., 2014,
12, 2850
Received 11th February 2014,
Accepted 25th February 2014
DOI: 10.1039/c4ob00310a
Ya-Kun Gu,a,b Fei Zeng,a,b Zheng Menga,b and Chuan-Feng Chen*a
www.rsc.org/obc
Triptycene-derived macrotricyclic polyether containing an anthra- complexes with these guests is theoretically and practically
cene unit is a powerful host for 1,2-bis(pyridium)ethane, diquat meaningful for their wide potential applications in supra-
and 2,7-diazapyrenium salt with association constants of the 1 : 1 molecular chemistry.
complexes at >105 M−1. Crystal structures showed that π–π stack-
Recently, we2c,8 have demonstrated that triptycene can be
ing interactions between the host and the guests play an important used as a useful building block for the construction of
role in the formation of the stable complexes.
different kinds of macrocyclic hosts with specific structures
and properties. As a result, we reported a triptycene-derived
macrotricyclic host 19 containing an anthracene unit, which
can form cascade complexes with pyromellitic diimide and
anthraquinone in the presence of lithium and potassium,
respectively. Herein, we report the complexation between host
1 and electron-deficient guests BPE2+ (2a), DQ2+ (2b) and
DPDAP2+ (2c) both in solution and in the solid state (Fig. 1). It
was found that macrocycle 1 proved to be a powerful host for
the three guests with association constants (Ka) of the 1 : 1
complexes at >105 M−1. Moreover, different binding modes
depending on the guests were also observed. Controllable
binding and release of the guests in the complexes were
further achieved by adding and removing the potassium ion.
Firstly, we tested the binding abilities of host 1 and guests
2a–2c in solution. Due to the charge transfer between the elec-
tron-rich host and the electron-poor guest, the colorless solu-
tion changed into a yellow one in a short period of time when
The development of efficient host–guest recognition systems
with controllable binding properties has been one of the
major goals in the areas of molecular switches, supramolecu-
lar assembly and supramolecular catalysis.1 Developing new
classes of hosts and selecting appropriate guests are two of the
permanent topics in host–guest chemistry.2 Special attention
has been devoted to the binding between supramolecular
hosts and electron-deficient cations through π–π stacking and
other noncovalent interactions.3
Guests including 1,2-bis(pyridium)ethane (BPE2+), diquat
(DQ2+) and 2,7-diazapyrenium (DAP2+) derivatives with
different structural features have been widely studied in host–
guest chemistry.4 BPE2+ can bind with simple crown ethers,
which has been used to construct different interlocked mole-
cules and MOF structures by Loeb, Liu and other groups.5 But
the binding constants of 1 : 1 complexes between BPE2+ and
crown ethers are only 102 M−1. DQ2+ as a guest can bind with a
variety of hosts including cryptands, calixarenes, pillararenes
and cucurbituril,6 and the binding constants of the complexes
vary from 102 to 105 M−1 in organic solvents. DAP2+ derivatives
with large π-electron systems could have effective binding abili-
ties with macrocyclic hosts; however, reports on the complexa-
tion related to this class of guests are still limited.7 Therefore,
exploring an appropriate host to construct highly stable
1
guest 2a was added into the solution of host 1. The H NMR
spectrum of an equimolar (3.0 mM) mixture of host 1 and
aBeijing National Laboratory for Molecular Sciences, CAS Key Laboratory of
Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, China. E-mail: cchen@iccas.ac.cn
bUniversity of Chinese Academy of Sciences, Beijing 100049, China
†Electronic supplementary information (ESI) available: Mole ratio plots,
1H–1H COSY, ESI-MS spectra, X-ray crystallographic files for 1·2a–1·2c. CCDC
979732–979734. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4ob00310a
Fig. 1 Chemical structures and proton designations of host 1 and
guests 2a–2c.
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pyridinium rings is weak in 2a because of the long distance. In
2b, the distance between two pyridine rings was shorter than
in 2a, which augmented the π–π conjugation between the adja-
cent pyridine rings. Therefore, the electron densities in both
pyridine rings were reduced. This effect made 2b a more
effective π-electron acceptor than 2a.13 As a result, the reduced
π-electron in pyridine ring of 2b lowered the exchange-repul-
sion14 and enhanced the π–π stacking interaction with tripty-
cene and anthracene units of host 1. Consequently, host 1 had
a more efficient binding ability for 2b than for 2a. Further-
more, complex 1·2c with the largest association constant was
due to the larger number of π-electron systems within 2c than
those in 2a and 2b, which makes 2c form much stronger π–π
stacking interactions with host 1.
Formation of the stable 1 : 1 complexes between host 1 and
the three guests was also demonstrated by the electrospray
ionization mass spectrometry. Consequently, the strongest
peaks at m/z 1403.6 for [1·2a-PF6]+, 628.3 and 681.3 for
[1·2b-2PF6]2+ and [1·2c-2PF6]2+ in 1 : 1 (v/v) chloroform and
acetonitrile were observed.10
Furthermore, suitable single crystals of complex 1·2a for
X-ray diffraction were obtained by vapor diffusion of isopropyl
ether into a 1 : 1 (v/v) CHCl3–CH3CN solution containing a
mixture of the two components. The crystal structure revealed
formation of the 1 : 1 complex between 1 and 2a. As shown in
Fig. 4a, guest 2a was located in the center of the cavity of host
1, and the two pyridine rings of 2a exhibited a dihedral angle
of 11.79°. This binding mode is totally different from that of
the complex between guest 2a and the simple [24]-crown-8
ether,15 which might be attributed to that host 1 contains a
three-dimensional electron-rich cavity; thus guest 2a has a
greater tendency to be encapsulated inside the central cavity
rather than threading the cavity of lateral [24]-crown-8 ether. In
complex 1·2a, there existed not only multiple C–H⋯O hydro-
gen bonding interactions, but also π–π stacking interactions
between the two pyridinium rings of the guest and the aro-
matic rings of the anthracene (dπ–π = 3.52 Å for AC and 3.81 Å
for BD) and triptycene moieties (dπ–π = 3.82 Å for BF) (Fig. 4b).
Fig. 2 Partial 1H NMR spectra (300 MHz, CD3CN–CDCl3 = 1 : 1, v/v,
295 K) of (a) free guest 2a, (b) 1 and 1.0 equiv. of 2a, and (c) free host 1.
[1]0 = 3.0 mM.
aromatic cation 2a in CDCl3–CD3CN (1 : 1 v/v) showed only one
set of resonances, which suggested that a new stable complex
1·2a was formed, and the binding was a fast exchange process
(Fig. 2). The significant upfield shift (Δδ −0.95 ppm) of Ha
proton signal of guest 2a was observed, which could be attribu-
ted to the strong shielding effect of the aromatic rings of 1. A
similar effect of aromatic cation 2a also resulted in the upfield
shift of protons H1–H4 of host 1. Because of the strong shield-
ing effect of the aromatic rings of 1, upfield shifts of the aro-
matic protons for both 1·2b and 1·2c were also observed.10
Similar to the case of 1·2a, complexes 1·2b and 1·2c exhibited
typical charge transfer with the color of the final solutions in
green-brown and tan, respectively.
Furthermore, we quantitatively estimated the binding pro-
perties between host 1 and guests 2a–2c through 1H NMR
spectroscopic titrations. The results showed that host 1 could
form 1 : 1 complexes with guests 2a–2c by the mole ratio plot.
Correspondingly, association constants K1·2a, K1·2b and K1·2c
for the three complexes were further calculated to be 1.06
( 0.01) × 105, 6.37( 0.02) × 105 and 1.51( 0.01) × 106 M−1
,
respectively, by fitting the data using a nonlinear regression
algorithm.11 It was noteworthy that K1·2b was almost 200 times
larger than the association constant of a similar complex pre-
viously reported.12 Moreover, to our knowledge, these binding
constants are also the largest ones among the known com-
plexes based on guests 2a–2c in organic solvents.5–7
In order to analyze the binding constants of the three com-
plexes, we further analyzed the electron charge density of the
guests by DFT(B3LYP) calculations using the 6-31G* basis set.
As shown in Fig. 3, these cationic guests have similar electron-
deficient distributions. The interaction between the two
Fig. 4 (a, b) Crystal structure of 1·2a, the dash lines denote the non-
covalent interactions between 1 and 2a. (c) Packing of 1·2a with a 3D
microporous structure. Solvent molecules, PF6− counterions, and hydro-
gen atoms were omitted for clarity.
Fig. 3 DFT calculated electron charge distributions (Å−3) of 2a–2c.
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Fig. 5 Crystal structures of (a) 1·2b and (b) 1·2c. The distances (Å) for
the π–π stacking interactions: AC = 3.55, BD = 3.53, AE = 3.92. UX =
3.58, UY = 3.89, VX = 3.88, WY = 3.62. Solvent molecules, PF6− counter-
ions, and hydrogen atoms were omitted for clarity.
These multiple non-covalent interactions play an important
role in the formation of stable complex 1·2a. Moreover, the
crystal packing of the complex also showed a 3D microporous
supramolecular structure (Fig. 4c) with solvent molecules and
PF6− anions situated inside the channels.
Fig. 6 Partial 1H NMR spectra (300 MHz, CD3CN–CDCl3 = 1 : 1, v/v,
295 K) of (a) free host 1, (b) free guest 2a, (c) 1 and 1.0 equiv. of 2a, (d) to
the solution of (c) was added 4.0 equiv. of KPF6, and (e) to the solution
of (d) was added 6.0 equiv. of [18]-crown-6. [1]0 = 3.0 mM.
Formation of 1 : 1 complexes of 1·2b and 1·2c was also con-
firmed by their X-ray crystal structures (Fig. 5). Similar to the
structure of complex 1·2a, guest 2b was also located at the
center of the host cavity, and π–π stacking interactions between
the host and the guest were observed. For complex 1·2c, it was
found that guest 2c threaded the central cavity of host 1 to
form a [2]pseudorotaxane-type complex, which is different
from the complex modes of 1·2a and 1·2b. Because of the
strong electron-deficient properties of guest 2c, it could form
the most stable complex with host 1 compared with two other
complexes. These results are consistent with those of the
theoretical evaluation.
It has been proved that host 1 could form a 1 : 2 stable
complex with K+ ions by complexation with two dibenzo[24]-
crown-8,9 which could introduce electrostatic repulsion into
the organic guest to dissociate the previously formed complex.
Therefore, we further investigate the ion-controlled binding
and release of the guests in the complexes. When 4.0 equiva-
lents of KPF6 were added into the solution of 1·2a, the color of
the solution turned from yellow to colorless immediately.
Meanwhile, the 1H NMR spectrum showed that the aromatic
proton signals in 1·2a shifted downfield to almost the original
positions of free host 1 and guest 2a (Fig. 6d), suggesting that
decomplexation of 1·2a occurred while the crown cavities co-
ordinate with potassium ions. When 6.0 equivalents of KPF6
were added into the above system, the yellow solution re-
appeared. Correspondingly, the 1H NMR spectrum displayed the
proton signals of 1·2a. Thus, the binding and release of 2a in
the complex could be easily induced by adding and removing
the potassium ion. Similarly, K+-ion-controlled binding and
release of 2b and 2c in their host–guest complexes could also
be achieved.10
2,7-diazapyrenium salt. The host and the guests could form
1 : 1 stable complexes in CHCl3–CH3CN (1 : 1, v/v) solution with
association constants of more than 105
M
−1, which repre-
sented the largest ones among the known complexes based
on these three guests in organic solvents. Crystal structures
showed that different binding modes depending on the guests
with different structural features were observed, and multiple
non-covalent interactions, especially the strong π–π stacking
interactions between the host and the guests, play an impor-
tant role in the formation of the stable complexes. Moreover,
the binding and release of the guests in the complexes could
also be controlled by the addition and removal of potassium
ions.
We thank the National Natural Science Foundation of
China (91127009 and 21332008), and the National Basic
Research Program (2011CB932501) for financial support.
Notes and references
1 (a) J. W. Steed and J. L. Atwood, Supramolecular Chemistry,
John Wiley & Sons Ltd, Chichester, 2009; (b) P. W. N. M. van
Leeuwen, Supramolecular Catalysis, Wiley-VCH, 2008.
2 (a) F.-H. Huang, L. N. Zakharov, A. L. Rheingold, M. Ashraf-
Khorassani and H. W. Gibson, J. Org. Chem., 2005, 70, 809;
(b) F. P. Schmidtchen and M. Berger, Chem. Rev., 1997, 97,
1609; (c) C.-F. Chen, Chem. Commun., 2011, 47, 1674;
(d) M. Xue, Y. Yang, X.-D. Chi, Z.-B. Zhang and
F.-H. Huang, Acc. Chem. Res., 2012, 45, 1294; (e) C.-J. Li,
K. Han, J. Li, Y.-Y. Zhang, W. Chen, Y.-H. Yu and X.-S. Jia,
Chem.–Eur. J., 2013, 19, 11892.
3 (a) S. T. Schneebeli, M. Frasconi, Z.-C. Liu, Y.-L. Wu,
D. M. Gardner, N. L. Strutt, C.-Y. Cheng, R. Carmieli,
M. R. Wasielewski and J. F. Stoddart, Angew. Chem., Int. Ed.,
2013, 52, 13100; (b) C.-F. Lin, Y.-H. Liu, C.-C. Lai,
S.-M. Peng and S.-H. Chiu, Angew. Chem., Int. Ed., 2006, 45,
3176; (c) C.-J. Li, X.-Y. Shu, J. Li, J.-Z. Fan, Z.-X. Chen,
Conclusions
In conclusion, we have demonstrated that the triptycene-
derived macrotricyclic polyether containing an anthracene
unit is a powerful host for 1,2-bis(pyridium)ethane, diquat and
2852 | Org. Biomol. Chem., 2014, 12, 2850–2853
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L.-H. Weng and X.-S. Jia, Org. Lett., 2012, 14, 4126;
(d) A. N. Basuray, H. J. Rouville, K. J. Hartlieb, T. Kikuchi,
N. L. Strutt, C. J. Bruns, M. W. Ambrogio, A. J. Avestro,
S. T. Schneebeli, A. C. Fahrenbach and J. F. Stoddart,
Angew. Chem., Int. Ed., 2012, 51, 11872; (e) Y.-F. Guan,
M.-F. Ni, X.-Y. Hu, T.-X. Xiao, S.-H. Xiong, C. Lin and
L.-Y. Wang, Chem. Commun., 2012, 48, 8529.
4 (a) X.-Z. Yan, X.-J. Wu, P.-F. Wei, M.-M. Zhang and
F.-H. Huang, Chem. Commun., 2012, 48, 8201; (b) S. J. Loeb,
Chem. Soc. Rev., 2007, 36, 226; (c) C.-F. Lin, Y.-H. Liu,
C.-C. Lai, S.-M. Peng and S.-H. Chiu, Chem.–Eur. J., 2006,
12, 4594.
7 (a) Y. Han, J. Cao, P.-F. Li, Q.-S. Zong, J.-M. Zhao, J.-B. Guo,
J.-F. Xiang and C.-F. Chen, J. Org. Chem., 2013, 78, 3235;
(b) V. Sindelar, M. A. Cejas, F. M. Raymo, W.-Z. Chen,
S. E. Parker and A. E. Kaifer, Chem.–Eur. J., 2005, 11,
7054; (c) M.-J. Li, C.-C. Lai, Y.-H. Liu, S.-M. Peng and
S.-H. Chiu, Chem. Commun., 2009, 5814; (d) L. Chen,
Y.-M. Zhang, L.-H. Wang and Y. Liu, J. Org. Chem., 2013, 78,
5357.
8 C.-F. Chen and Y.-X. Ma, Iptycene Chemistry: from Syn-
thesis to Applications, Springer-Verlag, Berlin, Heidelberg,
2013.
9 T. Han and C.-F. Chen, J. Org. Chem., 2007, 72, 7287.
5 (a) Y. Liu, C.-J. Li, H.-Y. Zhang, L.-H. Wang and X.-Y. Li, 10 See ESI.†
Eur. J. Org. Chem., 2007, 4510; (b) S. J. Loeb, J. Tiburcio, 11 P. Thordarson, Chem. Soc. Rev., 2011, 40, 1305.
S. J. Vella and J. A. Wisner, Org. Biomol. Chem., 2006, 4, 12 T. Han, Q.-S. Zong and C.-F. Chen, J. Org. Chem., 2007, 72,
667; (c) L. Chen, Y.-M. Zhang and Y. Liu, J. Phys. Chem. B,
2012, 116, 9500.
6 (a) X.-Z. Yan, Z.-Z. Li, P.-F. Wei and F.-H. Huang, Org. Lett.,
3108.
13 J. V. Sarah, T. Jorge, W. G. James and J. L. Stephen, Org.
Lett., 2006, 8, 3421.
2013, 15, 536; (b) F.-H. Huang, C. Slebodnick, K. A. Switek 14 E. G. Hohenstein and C.-D. Sherrill, J. Phy. Chem. A, 2009,
and H. W. Gibson, Tetrahedron, 2007, 63, 2829; (c) Y.-J. Ma, 113, 878.
X.-D. Chi, X.-Z. Yan, J.-Y. Liu, Y. Yao, W.-X. Chen, 15 S. J. Loeb and J.-A. Wisner, Angew. Chem., Int. Ed., 1998, 37,
F.-H. Huang and J.-L. Hou, Org. Lett., 2012, 14, 1532.
2838.
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