Convergent Synthesis of Alternating
Fluorene-p-xylene Oligomers and
Delineation of the (Silver) CationInduced Folding
Vincent J. Chebny and Rajendra Rathore*
J. Am. Chem. Soc. 2007, 129, 8458-8465
1
The Biopolymers Permit Structure Modulation
by Difference Interaction
1. Hydrogen bonding
2. -stacking
3. Columbic interactions
4. Metal-ion binding
2
The Biopolymers Permit Structure Modulation
by -Stacking
NDI :1,4,5,8-naphthalenetetracarboxylic diimide
acceptor
DAN: 1,5-dialkoxynaphthalene
Donor
3
Zych, A. J.; Iverson, B. L. J. Am. Chem. Soc. 2000, 122, 8898
Artificial Polymeric Materials can be
Modulated by Light
Irradiation at 365 nm
4
Khan, A.; Kaiser, C.; Hecht, S. Angew. Chem., Int. Ed. 2006, 45, 1878.
Artificial Polymeric Materials can be
Modulated by Metal-ion Binding
5
Suzuki, Y. J. Phys. Chem. B 1998, 102, 7910
Selective Zinc Sensor Molecules
6
Kikuchi. K. J. Am. Chem. Soc. 2005, 127, 10197
Synthesis of Receptor (a) and
Its Model Compound (b)
b
a
7
Rathore, R. et. al J. Am. Chem. Soc. 2005, 127, 8012
Optimized Structures of
the Isoenergetic Conformers of 1
density functional theory (DFT) calculations at the B3LYP/6-31G* level
8
Rathore, R. et. al J. Am. Chem. Soc. 2005, 127, 8012
X-ray Structure of 1 Showing the
Extended Conformer
9
An Extended Conformer to an Delta Conformer
by Binding a Single Silver Cation
10
A Hitherto Unknown Polymeric Structure A
11
A Similar Mixture of Cyclic Oligomers
12
1H/13C
NMR Spectra of
the Mixture of Cyclic Oligomers
4
5
a
c
a
3
6
7,8
10
9
b
e
d
5
b
1
e
d
c
7,8
10
2
3
2
4
6
9
1
13
The Syntheses of Acyclic Oligomers
(a) n-BuLi/THF/-78 °C. (b) n-BuLi/-78 °C/ethyl-4-(bromomethyl)benzote.
(c) LiAIH4/THF/reflux. (d) SOCI2/CHCI3/0 °C
F: fluorenes group, H: hydrogens group, M: methyls group,
E: ester group, A: alcohol group, C: chloro group, X:xylyl group
14
The Syntheses of Acyclic Oligomers
(a) n-BuLi/THF/-78 °C. (b) n-BuLi/-78 °C/ethyl-4-(bromomethyl)benzote.
(c) LiAIH4/THF/reflux. (d) SOCI2/CHCI3/0 °C. (e) Fluorene/n-BuLi/THF/-78 °C.
F: fluorenes group, H: hydrogens group, M: methyls group,
E: ester group, A: alcohol group, C: chloro group, X:xylyl group
15
The Syntheses of Acyclic Oligomers
Z2-Z8
16
The Syntheses of Acyclic Oligomers
Z2-Z8
17
A Comparison of the 1H NMR Spectra
of Z1-Z9 Oligomers.
a:b:c= 6:4n+4:4n+4
18
1H
NMR Spectra of Z1 and Plot of Changes
in the Chemical Shifts of the Xylenic Protons
19
The Maximum Number of Ag+ Cations
Captured by Zn
Zn receptors
Max. number of Ag+ cation
Z1
Z3
Z5
Z7
Z9
1
2
3
4
5
20
The Maximum Number of Ag+ Cations
Captured by Z1
Joe’s plot
21
The Binding of multiple Silver Cations
to Representative Zn Receptors
Zn receptors
Max. number of Ag+ cation
Z1
Z2
Z3
Z4
Z5
Z6
Z7
Z8
Z9
1
1
2
2
3
3
4
4
5
22
It is important to note that the simplicity of the 1H NMR
spectra, obtained in the presence of varying equivalents
of Ag+, suggests the dynamic nature of the binding of Ag+
to the multiple receptor sites of Z2-Z9
23
The Formation of Multiple -prismand-like
Cavities for Binding of Ag+ Cations.
24
Benesi, H. A.; Hildebrand, J. J. J. Am. Chem. Soc. 1949, 71, 2703
25
Four Isoenergetic Conformers of
the Oligomer Z3
density functional theory (DFT) calculations at the B3LYP/6-31G* level
26
1H
NMR Spectra of Z3 and Plot of Changes
in the Chemical Shifts
27
Conclusions
1. They developed convergent syntheses of hitherto unknown
fluorene-p-xylene oligomers Z1-Z9 in excellent yields
with the aid of four repetitive sequences of reactions.
2. The binding of multiple silver cations to Z3-Z9 was possible
due to the folding of these oligomers, by simple C-C bond
rotations.
3. We are actively exploring the syntheses of the Zn analogues
containing different substituents to further modulate the binding
and selectivity of various metal cations.
28
2 eq. Ag+
29
Possible Structures of Z3 upon
Exposure to 1 and 2 Equiv of Silver Cations
30
Four Isoenergetic Conformers of
the Oligomer Z3
31
A313 : molar absorbance
ε313: extinction coefficient of the new absorption band
K : association constant
32
O
R C OR'
LiAlH4
H2O
RCH2OH + R'OH
SOCl2
RCH2Cl + SO2 + HCl
33
34
462 nm, typical of pyrene excimer fluorescence
35
J.Am. Chem. Soc. 2003, 125, 2884.