R. Rathore et al.
and evaporated under reduced pressure to afford a brown-colored syrup.
The crude material was purified by flash chromatography on silica gel
using hexanes as an eluent to afford 4b as a clear oil (10.2 g, 83%).
1H NMR (300 MHz, CDCl3): d=0.55 (m, 2H), 0.75 (t, 3H), 1.07 (m,
6H), 1.28 (t, 3H), 2.12 (m, 2H), 3.22 (s, 2H), 4.26 (q, 2H), 6.64 (d, 2H),
7.29 (m, 8H), 7.51 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d=14.50,
23.06, 26.03, 30.07, 32.06, 33.49, 46.98, 47.85, 51.75, 61.03, 120.13, 123.64,
127.04, 127.36, 128.22, 128.56, 130.19, 140.06, 143.06, 150.62, 166.80 ppm.
the guest silver cations during the emission measurements.
None the less, only a modest excess of Ag+ (i.e., 1.5 equiv)
was necessary to fully quench the entire emission of the flu-
orophores in various receptors (i.e., 1, 3b-X, and 3b-PS).
Conclusion
Preparation of 5b: Lithium aluminum hydride (1.3 g, 35 mmol) was
added carefully to a solution of ester 4b (9.0 g, 26.0 mmol) in THF
(75 mL). The resulting suspension was heated at reflux for 2 h and cooled
to room temperature. H2O (1.4 mL), 15% aqueous sodium hydroxide
(1.4 mL), and H2O (4.2 mL) were added successively and slowly to this
mixture to afford a white slurry, which upon stirring, separated the inor-
ganic component into a solid mass. The organic layer was separated by a
simple filtration and the solid mass was triturated with dichloromethane
(3100 mL). The combined organic layers were dried over anhydrous
magnesium sulfate and filtered. Evaporation of the solvent under re-
duced pressure afforded 5b as a colorless oil (8.0 g, 90%), which was
used in the next step without further purification. 1H NMR (300 MHz,
CDCl3): d=0.58 (m, 2H), 0.75 (t, 3H), 1.05 (m, 6H), 2.11 (m, 2H), 3.14
(s, 2H), 4.45 (d, 2H), 6.64 (d, 2H), 6.93 (d, 2H), 7.29 (m, 6H), 7.54 ppm
(m, 2H); 13C NMR (75 MHz, CDCl3): d=14.27, 22.83, 23.96, 29.95, 31.71,
39.26, 46.60, 56.08, 65.32, 119.94, 123.90, 126.06, 126.89, 127.12, 130.67,
137.06, 138.49, 141.16, 149.59 ppm.
In summary, we have designed and synthesized a conforma-
tionally adaptable silver receptor from readily available
starting materials and have shown that it can be easily
woven onto the backbone of polystyrene. The polymer-sup-
ported receptor 3b-PS binds quantitatively one equivalent
1
of Ag+ per receptor unit, as monitored by H NMR spec-
troscopy. Also, the Ag+ binding can be monitored by emis-
1
sion spectroscopy. Moreover, a comparison of the H NMR
spectral changes in 3b-PS to monomeric 1 and 3b-X sug-
gests that the receptor moieties undergo similar conforma-
tional changes into D-shaped cavities for efficient capture of
silver cations. We are presently exploring the solid-state
properties of these polymer-supported receptors for poten-
tial materials applications as well as their usage in organic
synthesis.[11]
Preparation of 6b: With the aid of a dropping funnel, a solution of thio-
nyl chloride (1.9 mL, 26 mmol) in chloroform (50 mL) was slowly added
to a cold (ꢀ08C) solution of alcohol 5b (8.0 g, 21.6 mmol) in chloroform
(100 mL). The resulting mixture was stirred for an additional 30 min at
08Cand at room temperature for 10 h. The reaction was quenched by a
slow addition of 5% aqueous NaHCO3 (150 mL). The organic layer was
separated and the aqueous layer was extracted with dichloromethane (3
100 mL). The combined organic extracts were dried over anhydrous mag-
nesium sulfate, filtered, and evaporated under reduced pressure to afford
6b as a white solid (6.1 g, 73%), which was sufficiently pure and was
used in the next step without further purification. M.p. 64–668C;
1H NMR (300 MHz, CDCl3): d=0.58 (m, 2H), 0.75 (t, 3H), 1.06 (m,
6H), 2.11 (m, 2H), 3.14 (s, 2H), 4.37 (s, 2H), 6.62 (d, 2H), 6.94 (d, 2H),
7.27 (m, 6H), 7.53 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d=14.34,
22.89, 24.03, 30.00, 31.79, 39.27, 46.50, 46.69, 56.09, 120.04, 123.90, 126.99,
127.24, 127.63, 130.85, 135.11, 138.02, 141.20, 149.50 ppm.
Experimental Section
General: Fluorene, 1-bromohexane, n-butyllithium, silver trifluorometha-
nesulfonate, ethyl-4-(bromomethyl)benzoate, a-chloro-p-xylene, potassi-
um tert-butoxide, thionyl chloride, lithium aluminum hydride, chloroform,
hexanes, tetrahydrofuran, and ethyl acetate were commercially available
from Aldrich and were used as received unless otherwise specified.
Anhydrous tetrahydrofuran (THF) was prepared by refluxing the com-
mercial THF over lithium tetrahydroaluminate under an argon atmos-
phere for 24 h followed by distillation. The dry THF was then stored
under an argon atmosphere in a Schlenk flask equipped with a Teflon
valve fitted with Viton O-rings. Dichloromethane was repeatedly stirred
with fresh aliquots of concentrated sulfuric acid (ꢀ10% by volume) until
the acid layer remained colorless. After separation, the solution was
washed successively with water, aqueous sodium bicarbonate, water, and
saturated aqueous sodium chloride, and dried over anhydrous calcium
chloride. The dichloromethane was distilled twice from P2O5 under an
argon atmosphere and stored in a Schlenk flask equipped with a Teflon
valve fitted with Viton O-rings. The hexanes and toluene were distilled
from P2O5 under an argon atmosphere and then heated at reflux over cal-
cium hydride (ꢀ12 h). After distillation from CaH2, the solvents were
stored in Schlenk flasks under an argon atmosphere.
Preparation of 3b: nBuLi (2.5m in hexanes, 6.3 mL) was added dropwise
to a pre-chilled (À788C) solution of fluorene (2.6 g, 15.7 mmol) in anhy-
drous THF (75 mL). After 10 min of stirring, solid 6b (6.1 g, 15.7 mmol)
was added and the mixture was stirred for 15 min at À788C. The cooling
bath was removed and the reaction mixture was stirred for an additional
1 h. The resulting mixture was poured onto water (200 mL) and the aque-
ous layer was extracted with dichloromethane (3100 mL). The com-
bined dichloromethane extracts were dried over anhydrous magnesium
sulfate, filtered, and evaporated under reduced pressure to afford a color-
less solid. The crude material was purified by flash chromatography on
silica gel using hexanes as an eluent to afford 3b as a white solid (6.0 g,
1
73%). M.p. 54–568C; H NMR (300 MHz, CDCl3): d=0.58 (m, 2H), 0.74
Preparation of 4b: Under an argon atmosphere, nBuLi (2.5m in hexanes,
12 mL) was added dropwise to a cooled (À788C) solution of fluorene
(5.0 g, 30 mmol) in anhydrous THF (100 mL). After 10 min of stirring, 1-
bromohexane (4.2 mL, 30 mmol) was added and the mixture was stirred
for an additional 15 min before it was left to warm to room temperature.
[Note that it is critical to maintain the temperature at À788Cthroughout
the addition of 1-bromohexane and for an additional 15 min to avoid the
formation of 9,9-dihexylfluorene.] The resulting reaction solution was re-
cooled to À788C, and nBuLi (2.5m in hexanes, 12 mL) was added drop-
wise to afford a dark-orange mixture, which was stirred for an additional
10 min. Solid ethyl-4-(bromomethyl)benzoate (7.29 g, 30 mmol) was
added to this mixture and the cooling bath was removed. The resulting
mixture was stirred for 1 h and the reaction was quenched by pouring it
onto water (200 mL). The organic layer was separated and the aqueous
layer was extracted with dichloromethane (3100 mL). The combined or-
ganic extracts were dried over anhydrous magnesium sulfate, filtered,
(t, 3H), 1.07 (m, 6H), 2.14 (m, 2H), 2.84 (d, 2H), 3.18 (s, 2H), 4.00 (t,
1H), 6.50 (d, 2H), 6.76 (d, 2H), 6.86 (d, 2H), 7.27 (m, 10H), 7.57 (m,
2H), 7.69 ppm (d, 2H); 13C NMR (75 MHz, CDCl3): d=14.34, 22.91,
24.13, 30.04, 31.79, 39.34, 40.04, 46.85, 49.04, 56.40, 119.84, 119.97, 123.97,
125.37, 126.83, 126.95, 127.15, 127.25, 128.35, 130.26, 135.55, 137.43,
140.99, 141.43, 147.15, 149.71 ppm.
Preparation of 3b-X: Under an argon atmosphere, potassium tert-butox-
ide (0.9 g, 8.0 mmol) was added to a cold (ꢀ08C) solution of 3b (1.1 g,
2.0 mmol) in anhydrous THF (40 mL). After 10 min of stirring, a-chloro-
p-xylene (0.3 g, 2.0 mmol) was added and the mixture was stirred for
15 min at 08C. The cooling bath was removed and the reaction mixture
was stirred for an additional 8 h at room temperature. The resulting mix-
ture was poured onto water (50 mL) and the aqueous layer was extracted
with dichloromethane (350 mL). The combined dichloromethane ex-
tracts were dried over anhydrous magnesium sulfate, filtered, and evapo-
6512
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 6508 – 6513