Phenylacetylene macrocycles
[2 3 4 5 a priori . For example, tribenzo[14]annulene
(1 , Figure
[1 6 7 1 readily
undergoes 1,4-polymerization when heated or exposed to UV light.
[6 1 to be unique.
[8 w
1/2 ≈ 5-10 °C)
than normal (w
1/2 <1 °C)
DSC exotherms of the annulenes.
Figure 1 The structure
of tribenzo[14]annulene (1 )
A possible solution to the preorganization problem involves supramolecular
chemistry.
[9 10 11 12 2 )
in order to organize the DBA molecules. These systems can utilize
external forces such as the interpenetrating guest-host interaction
between secondary dialkylammonium ion centers in guests containing
one or more binding sites for crown ether hosts.
[13 2 and the mono- and dicationic hexafluorophosphate
salts 3 and 4 ,
respectively (Figure
[2
Figure 2 The structures
of crown ether-dehydrobenzoannulene hybrid 2 and
mono- and dicationic hexafluorophosphate salts 3 and 4
Hybrid 2 was assembled using the same
strategy as that reported previously for the construction of site-specifically
functionalized DBAs (Scheme
[1 8b f g 5
[14 15 6 ) in moderate yield. Cross-coupling 6 with two equivalents of 1-(4-trimethylsilylbuta-1,3-diynyl)-2-(triisopropylsilylethynyl)benzene
[8g 7 in 81% yield. Desilylation of 7 with Bu4 NF and subsequent
Cu-mediated intramolecular oxidative cyclization under pseudo-high
dilution conditions generated the benzo-24-crown-8-fused annulene 2 as a light yellow solid in 55% yield.
Scheme 1 (a) 4,5-diiodocatechol,
CsCO3 , MeCN; (b) 1-(4-trimethylsilylbuta-1,3-diynyl)-2-(triisopropylsilylethynyl)benzene,
aq KOH, PdCl2 (PPh3 )2 , CuI, Et3 N,
THF; (c) Bu4 NF, MeOH, THF; (d) Cu(OAc)2 , CuCl,
pyridine
Slow evaporation of a THF solution of 2 afforded
yellow blocks suitable for X-ray diffraction. The crystal structure of
macrocycle 2 is shown in Figure
[3 16 6 8
Figure 3 Molecular structure
of 2 (left); ellipsoids drawn at the 30% level.
Side view of two molecules (right). THF solvate molecules omitted
for clarity
Mixing equimolar amounts of hybrid 2 and
salt 3 in CD2 Cl2 at
room temperature resulted in a significant difference in the 1 H
NMR spectra (Figure
[4 2 ,
is relatively uncomplicated, reflecting the C2v symmetry
of the crown ether moiety. The bottom spectrum shows a number of ether
moiety. The bottom spectrum shows a number of changes upon addition
of an equimolar amount of 3 , all of which
support strong complexation. The most noticeable differences are
in the crown ether region, where the central ethylene protons (Hg )
change from a singlet in free 2 to two
multiplets in pseudorotaxane 2 ·3 (Figure
[5 e and Hf show
increased separations between the two sets of multiplets as well
as slight upfield shifts. The resonances in the aromatic region
also exhibit notable changes. The broad singlet attributable to
the four Hb protons in 2 splits into
the expected AA′BB′ multiplet
with an upfield shift of ca. 0.1 ppm once the complex is formed.
The singlet for Ha shifts upfield by 0.15 ppm. Resonances
of the ammonium ion were observed at δ = 7.57
(broad singlet), 7.32-7.13 (multiplets), and 4.74 (broad
triplet) representing H3 , H1 ,
and H2 , respectively. Based on the large number
of previous pseudorotaxane studies,
[13 2 , are consistent with strong complexation
between the host and guest molecules.
Figure 5 The structures
of 1:1 pseudorotaxane 2 ·3 and 2:1 pseudorotaxane 2
2
·4
The supramolecular complex 2 ·3 was also analyzed by FAB mass spectrometry.
Although the spectrum did not show the parent peak of m/z 1085, peaks corresponding
to M+ - PF6 and hybrid 2 were observed at 940 and 742 mass units,
respectively. Attempts to obtain single crystals suitable for X-ray
diffraction have been unsuccessful to date.
The complexation between DBA 2 and the
bis-ammonium salt 4 was also performed
in CD2 Cl2
by mixing a 2:1 ratio
of host and thread molecules (Figure
[5 1 H NMR
spectra indicated the presence of a mixture of pseudorotaxane complexes
and their free components in solution. The FAB mass spectrum showed
very small peaks of the 2:1 complex corresponding to M+ - PF6 ,
M+ - 2PF6 , and crown ether 2 containing a sodium ion. Further efforts to
decipher these results are in progress.
Figure 4
1 H
NMR (300 MHz, CD2 Cl2 ) spectra of the free
hybrid 2 (top) and of the 1:1 pseudorotaxane 2 ·3 (bottom)
In conclusion, we have demonstrated an efficient synthesis of
crown ether containing dehydrobenzoannulene 2 and
its ability to complex secondary dialkylammonium ions. The formation
of a pseudorotaxane from a 1:1 mixture of 2 and 3 is facile in CD2 Cl2 ,
according to 1 H NMR spectroscopic data. The
formation of the corresponding [3]pseudorotaxane
from a 2:1 mixture of 2 and 4 was
incomplete under analogous conditions. Synthetic efforts towards
making bis- and tris-crown ether-fused annulenes are underway and
experiments to probe the formation of more complicated supermolecules
will be reported in due course.
Reagents and instrumentation used have been described previously.
[8g
4,5-Diiododibenzo-24-crown-8
(6)
A suspension of CsCO3 (18.4 g, 56.5 mmol) in anhyd
MeCN (250 mL) was placed under N2 and brought to reflux.
To this was added ditosylate 5
[14 15 (4.09 g, 11.3 mmol)
dissolved in anhyd MeCN (250 mL) over a 24 h period. The mixture
was refluxed for an additional 48 h and then cooled. The suspension
was filtered and concentrated in vacuo. The residue was dissolved
in CH2 Cl2 (150 mL) and washed with aq sat. NaHCO3 solution
(150 mL). The aqueous layer was extracted with CH2 Cl2 (2 × 100
mL) and the combined organics were dried (MgSO4 ), filtered,
and concentrated. Chromatography on silica gel (hexanes-EtOAc,
1:1) gave 6 (3.09 g, 39%) as a
white solid; mp 91.7-93.6 °C.
IR (CDCl3 ): 3062, 2922, 2870, 1592, 1249, 1127 cm-1 .
1 H NMR (CDCl3 ): δ = 7.24
(s, 2 H), 6.92-6.84 (m, 4 H), 4.16-4.12 (m, 4
H), 4.10-4.06 (m, 4 H), 3.93-3.86 (m, 8 H), 3.84-3.77
(m, 8 H).
13 C NMR (CDCl3 ): δ = 149.44,
148.85, 123.89, 121.39, 113.97, 96.47, 71.35, 71.23, 69.91, 69.64,
69.56, 69.32.
MS (APCI): m /z (%) = 718 (100, M+ + H2 O),
701 (5, M+ + H).
Anal. Calcd for C24 H30 I2 O8 (700.30):
C, 41.16; H, 4.32. Found: C, 40.98; H, 4.23.
α,ω-Polyyne
7
The diiodide 6 (981 mg, 1.4 mmol) and
1-(4-trimethylsilylbuta-1,3-diynyl)-2-(triisopropylsilylethynyl)benzene
[8g 2 O-THF-Et3 N (0.01:1:5,
20 mL) in separate vessels. The solutions were degassed vigorously
by three freeze-pump-thaw cycles. The acetylene solution was added
via syringe pump to the solution of 6 charged
with PdCl2 (PPh3 )2 (35 mg, 0.05 mmol),
CuI (15 mg, 0.08 mmol), and KOH (2.36 g, 42 mmol) over 12 h at 50 °C
under N2 . Upon completion, the mixture was concentrated
in vacuo and redissolved in CH2 Cl2 . The dark
residue was filtered through a thin cake of silica gel using CH2 Cl2 and concentrated.
Chromatography on silica gel (hexanes-THF, 3:1) gave polyyne 7 (1.21 g, 81%) as a tan gum.
IR (neat): 2946, 2866, 2415, 2203 cm-1 .
1 H NMR (CDCl3 ): δ = 7.54-7.45
(m, 4 H), 7.33-7.21 (m, 4 H), 6.92 (s, 2 H), 6.89 (br s,
4 H), 4.19-4.11 (m, 8 H), 3.96-3.91 (m, 8 H), 3.84
(br s, 8 H), 1.16 (s, 42 H).
13 C NMR (CDCl3 ): δ = 149.39,
148.84, 132.66, 132.28, 128.53, 127.86, 127.18, 124.91, 121.37,
118.56, 116.85, 113.91, 104.56, 96.06, 81.31, 80.55, 78.06, 77.11,
71.47, 71.29, 69.94, 69.52, 69.43, 69.36, 18.70, 11.30.
HRMS: m /z Calcd
for C66 H80 O8 Si2 (M+ ):
1056.5392. Found: 1056.5386.
Crown Ether/Annulene
Hybrid 2
Polyyne 7 (850 mg, 0.78 mmol) was dissolved
in THF-MeOH (3:1, 20 mL) and treated with Bu4 NF
(2 mL, 1 M THF solution, 2.0 mmol) at r.t. The reaction was monitored
by TLC and was complete within 30 min. The mixture was diluted with
Et2 O (30 mL), washed with H2 O (3 × 20
mL) and brine (2 × 20 mL), and then dried (MgSO4 ).
The organic layer was concentrated in vacuo and the resultant oil
was redissolved in pyridine (10 mL). The pyridine solution was added
over 12 h via syringe pump to a flask charged with Cu(OAc)2 (3.54
g, 19.5 mmol), CuCl (2.10 g, 15.6 mmol), and pyridine (200 mL) at
60 °C. The addition was done under house air and
stirred further for 8 h. Upon completion, the mixture was concentrated
in vacuo and then redissolved in CH2 Cl2 . The
mixture was filtered through a thin cake of silica gel using CH2 Cl2 and
concentrated. Chromatography on silica gel (hexanes-THF,
3:1) afforded 2 (320 mg, 55%)
as a light yellow solid; mp 230 °C (dec.).
IR (KBr): 2926, 2866, 2211, 2192, 2140 cm-1 .
1 H NMR (CD2 Cl2 ): δ = 7.74-7.66
(m, 4 H), 7.49-7.42 (m, 4 H), 7.13 (s, 2 H), 6.89 (br s,
4 H), 4.19-4.15 (m, 4 H), 4.12-4.08 (m, 4 H),
3.92-3.82 (m, 8 H), 3.77 (br s, 8 H).
13 C NMR (CD2 Cl2 ): δ = 150.47,
129.54, 133.35, 133.15, 129.61, 129.40, 125.63, 125.29, 121.89,
118.97, 116.84, 114.69, 81.76, 81.32, 80.96, 78.49, 78.16, 77.00,
71.83, 71.63, 70.41, 70.00, 69.97, 69.76.
MS (FAB):
m /z = 742.2 (100, M+ ).
Anal. Calcd for C48 H38 O8 ·C4 H8 O
(814.93): C, 76.64; H, 5.69. Found: C 76.54, H 5.65.
Pseudorotaxane 2 ·3
CD2 Cl2 (0.7 mL) was added to hybrid 2 (11 mg, 0.015 mmol) and dibenzylammonium
hexafluorophosphate (4.8 mg, 0.014 mmol). The reaction mixture was
sonicated for 3 min and then filtered through a plug of glass wool
into an NMR tube.
1 H NMR (CD2 Cl2 ): δ = 7.76-7.69
(m, 4 H), 7.58 (br s, 2 H), 7.50-7.44 (m, 4 H), 7.36-7.27
(m, 4 H), 7.25-7.17 (m, 6 H), 6.88 (BB′m, 2 H),
6.72 (AA′m, 2 H), 4.68-4.62 (m, 2 H), 4.16-4.13
(m, 2 H), 4.05-4.02 (m, 2 H), 3.89-3.86 (m, 2
H), 3.74-3.71 (m, 2 H), 3.60-3.55 (m, 2 H), 3.53-3.49
(m, 2 H).
MS (FAB):
m /z = 940.3 (82, M+ -
PF6 ), 742.2 (13, M+ - Bz2 NH2 PF6 ).
