Synthesis of Isomers of Calix[6]arene Bis-crown-4
J. Am. Chem. Soc., Vol. 122, No. 7, 2000 1491
1
of both isomers were studied in chloroform by H NMR titration
4H) 3.11 (m, 4H) 3.03 (m, 4H). 13C NMR (100 MHz, CDCl
1
1
3
) δ 156.47,
54.33, 134.70, 134.39, 133.97, 133.48, 130.17, 129.66, 126.66, 123.69,
23.37, 117.52, 74.43, 72.57, 70.78, 69.98, 31.61, 31.28. Anal. Calcd
10: C 76.25, H 6.83. Found: C 76.49, H 6.92.
experiments, liquid-liquid extraction, electrospray-ionization
mass spectroscopy, and X-ray crystallography. Both conformers
formed 1:1 complexes with all alkali metal ions. The 1:1
complex stoichiometries observed with 4 are most likely a
consequence of cooperative binding of one metal ion by the
two crown moieties. Alternatively, one metal ion guest may be
in rapid exchange between the two opposing crown straps in
the 1,2,3-alternate isomer 3. Even though 3 could potentially
accommodate an additional metal ion, it is prohibited via
electrostatic repulsion by the initially complexed cation. Both
for C60
Cone isomer 4: 0.3 g (11%), rf ) 0.6, mp ) 230-232 °C H NMR
400 MHz, CDCl ) δ 7.58-7.56 (d of d, J ) 6.8 Hz, 4H) 7.12-7.06
d of t, J ) 8H) 6.29 (t, J ) 7.6 Hz, 2H) 6.17 (m, 2H) 6.03 (d, J ) 7.6
64
H O
1
(
(
3
Hz, 4H) 5.65-5.61 (d of d, J ) 17.2 Hz, 2H) 5.30-5.27 (d of d, J )
1
4
1
0.4 Hz, 2H) 4.61 (d, J ) 16.4 Hz, 4H) 4.59 (d, J ) 13.2 Hz, 2H)
.51 (d, J ) 3.6 Hz, 4H) 4.02 (d, J ) 9.0 Hz, 4H) 3.85-3.72 (m,
2H) 3.54 (d, J ) 13.6 Hz, 4H) 3.46-3.43 (m, 6H) 3.13 (d, J ) 10.8
13
Hz, 4H). C NMR (100 MHz, CDCl
3
) δ 155.63, 154.21, 135.09,
3
and 4 displayed a strong preference for the larger cesium ion
134.29, 134.20, 133.25, 130.63, 129.46, 125.99, 123.76, 122.94, 116.29,
over the smaller alkali metal ions, with 4 being more selective
73.54, 72.52, 71.43, 70.66, 30.88, 27.09. Anal. Calcd for C60
C 76.25, H 6.83. Found: C 76.66, H 6.87.
64 10
H O :
+
+
than 3. The Cs /Na selectivity factor of 1500 observed with
host 4 is somewhat lower than those observed in some cesium-
NMR Experiments. In the titration experiments, solutions of the
hosts and metal picrate salts were prepared in 1 mL volumetric flasks.
The solid compounds were placed directly into the flask, and CDCl
3
was added to the mark. The solutions were stirred for several hours to
ensure that all components were dissolved. The solutions were then
transferred to NMR tubes, and their spectra were recorded at room
temperature. In the Job plot analysis, solutions of host:guest ratios
ranging from 80:20 to 20:80 were prepared in 1 mL volumetric flasks.
1
a-c
selective calix[4]arene crown-6 hosts,
but higher than that
1f
of a bis-crown host derived from calix[8]arene. The crystal
structure of the Cs complex of 4 indicated that the cesium ion
+
was coordinated to all eight oxygen atoms of the parallel
crown-4 rings to form a “deep-cavity” complex. There was also
evidence of π-metal interactions with two aromatic rings canted
over the cavity of the calixarene framework. This type of p-metal
interaction has been previously observed in calix[4]arenes but
not in calix[6]- or calix[8]arenes.
Aliquots of a 1 M NaSCN solution in CD
containing the hosts dissolved in CDCl . The total solvent composition
was then adjusted to be 90% CDCl and 10% CD OD. Spectra of the
hosts in the absence of added guest were obtained in the various CDCl
CD OD solutions so that shifts due to changes in the solvent
composition could be quantified.
3
OD were added to the flask
3
3
3
3
/
Experimental Section
3
All chemical reactions were performed under inert nitrogen or argon
atmospheres. Tetrahydrofuran (THF) was freshly distilled from sodium
benzophenone ketyl. All other solvents and reagents were used as
Extraction Experiments. Extractions were done according to the
procedure described by Arduini where equal volumes (2 mL) of
chloroform containing host and an aqueous solution of metal picrates
were thoroughly shaken in 8 mL glass vials.19 Aliquots were taken
from each phase, and the picrate concentration in the organic phase
1
13
received. H and C NMR spectra were obtained in CDCl
referenced to the residual CHCl or to CDCl . Melting points were
obtained in unsealed capillary tubes and are uncorrected. Metal picrates
3
and were
3
3
1
8
were prepared according to known procedures. Solutions of the salts
were prepared with deionized water. The parent compound, 5,11,17,-
was determined from the decrease in the aqueous phase (ꢀ354 nm
)
-
1
-1
14 500 cm
M
) and reconfirmed by the increase in the chloroform
-
1
-1
2
3,29,35-hexa-tert-butylcalix[6]arene was prepared according to known
procedures and the de-tert-butylated compound, 1, was obtained by
treatment of the parent compound with AlCl
and phenol.19
7,40-Diallyloxy-(38-42),(39-41)-bis-crown-4-calix[6]arenes 3
layer (ꢀ380 nm ) 18 000 cm
M
). The concentrations of hosts 3 and
-3
4 were fixed at 1.0 × 10 M. The picrate concentrations of the original
-4
+
3
aqueous phases were 9.4, 9.1, 8.1, 9.6, and 9.4 × 10 M for Li ,
+ + + +
3
Na , K , Rb , and Cs , respectively.
4
and 4. The diallyl compound 2 (2.0 g, 2.8 mmol) was dissolved in
00 mL of THF-DMF (10:1). To this was added 0.68 g (17 mmol) of
Host 4/Cs+ complex. Approximately 100 mg of 4 was dissolved
1
in 2 mL of CHCl
borate dissolved in 0.5 mL of CH
3
. To this was added 2 mol equiv of cesium tetraphenyl
OH. The solution was mixed well
NaH, and the mixture was stirred for 30 min at room temperature.
Triethylene glycol di-p-tosylate (3.2 g, 6.8 mmol) dissolved in 50 mL
of THF was added via syringe, and the reaction was heated to reflux
for 12 h. The solvent was removed under reduced pressure, and the
3
and allowed to stand at room temperature for several day. The clear
crystals were then transferred to a clean vial.
residue was redissolved in CHCl
N HCl and 100 mL of brine. The organic solution was dried over
MgSO , filtered, and concentrated. Separation of 3 and 4 was effected
by column chromatography on silica gel (90% CHCl -10% EtOAc).
,2,3-Alternate isomer 3: 0.4 g (15%), rf ) 0.7, mp ) 235-240
3
and washed with 2 × 100 mL of 1
Acknowledgment. We thank the Robert A. Welch Founda-
tion for financial support (Grant No. AI-1240). We also thank
Professor Carl Carrano and Dr. Norman Dean (SWT) for the
X-ray crystallographic structural determination and helpful
discussions. Financial support for the X-ray facilities was
obtained from NSF Grant No. USE-9151286.
4
3
1
1
°
C H NMR (400 MHz, CDCl
3
) δ 7.18-7.15 (d of d, J ) 7.2 Hz, 4H)
7
.13-7.11 (d of d, J ) 7.6 Hz, 4H) 6.99 (t, J ) 7.6 Hz, 4H) 6.66 (t,
J ) 8.0 Hz, 2H) 6.51 (d, J ) 7.6 Hz, 4H) 6.19-6.13 (m, 2H) 5.41 (d,
J ) 16.0 Hz, 2H) 5.23 (d, J ) 10.4 Hz, 2H) 4.55 (d, J ) 15.2 Hz, 4H)
Supporting Information Available: Tables of crystal data
and structure refinement (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
4
.36 (d, J ) 5.6 Hz, 4H) 3.99 (s, 4H) 3.54-3.38 (m, 16H) 3.24 (m,
(18) Arduini, A.; Pochini, A.; Reverberi, S.; Ungaro, R.; Andreeti, G.
D.; Ugozzoli, F.; Tetrahedron 1986, 42, 2089-2100.
(19) Gutsche, C. D.; Lin, L. Tetrahedron 1986, 42, 1633-1640.
JA991810H