Synthesis and characterization of annulene-fused pseudorotaxanes

Article abstract of DOI:10.1055/s-2002-32536

A 24-crown-8 ether-fused dehydrobenzo[18]annulene has been prepared via a stepwise Pd/Cu-mediated strategy. This annulene-crown ether hybrid forms a pseudorotaxane complex in CD₂Cl₂ with dibenzylammonium hexafluorophosphate when they

Full text of DOI:10.1055/s-2002-32536

1256
PAPER
Synthesis and Characterization of Annulene-Fused Pseudorotaxanes
Synthesis
o
of
A
nnulene
-
Fused Pse
h
udorotaxane
u
s
a J. Pak,a,1 Timothy J. R. Weakley,a Michael M. Haley,*a Danny Y. K. Lau,b J. Fraser Stoddartb
a
Department of Chemistry, University of Oregon, Eugene, OR 97403-1253 USA
Fax +1(541)3460487; E-mail: haley@oregon.uoregon.edu
b
Department of Chemistry, University of California – Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095 USA
Fax +1(310)2061843; E-mail: stoddart@chem.ucla.edu
Received 1 April 2002
Abstract: A 24-crown-8 ether-fused dehydrobenzo[18]annulene
has been prepared via a stepwise Pd/Cu-mediated strategy. This an-
nulene-crown ether hybrid forms a pseudorotaxane complex in
CD2Cl2 with dibenzylammonium hexafluorophosphate when they
are combined in a 1:1 ratio, as indicated by 1H NMR spectroscopy
and mass spectrometry.
1
Key words: annulenes, crown compounds, macrocycles, pseudoro-
taxanes, supramolecular chemistry
Figure 1 The structure of tribenzo[14]annulene (1)
A possible solution to the preorganization problem in-
volves supramolecular chemistry.9 Over the last decade a
tremendous number of ordered arrays and assemblies
have been prepared utilizing various noncovalent bonding
interactions (hydrogen bonding, -stacking, dipole-dipole
interactions, etc.).10 One of the more interesting and rele-
vant examples was the recent use of supramolecular orga-
Phenylacetylene macrocycles2 and networks3 are poten-
tial building blocks for the assembly of tubular and/or po-
rous molecular crystals.4 Key to such a transformation is
preorganization of the precursor molecules so that they
may undergo controlled oligomerization/polymerization
to form ordered arrays. Unfortunately, such preorganiza-
tion in the solid state5 is often rare and impossible to pre-
dict a priori. For example, tribenzo[14]annulene (1,
Figure 1)6 packs in the solid state according to the param-
eters outlined by Enkelmann7 for a topochemical diacety-
lene polymerization. Indeed, 1 readily undergoes 1,4-
polymerization when heated or exposed to UV light.6
Subsequent studies of a number of other dehydrobenzoan-
nulenes (DBAs) show the reactivity displayed by 1 to be
unique.8 More often than not the packing of the macrocy-
cles in the crystal lattice precludes any type of ordered po-
lymerization, which is reflected in the broader (w1/2 5–
10 °C) than normal (w1/2 <1 °C) DSC exotherms of the an-
nulenes.
nization for the first 1,6-polymerization of
a
triacetylene.11 Similar preorganization has been success-
fully used for the polymerization of a number of other di-
acetylenes.12 Encouraged by these reports, we decided to
target a new class of pseudorotaxanes using crown ether-
dehydrobenzoannulene hybrids (e.g, 2) in order to orga-
nize the DBA molecules. These systems can utilize exter-
nal forces such as the interpenetrating guest-host
interaction between secondary dialkylammonium ion cen-
ters in guests containing one or more binding sites for
crown ether hosts.13 The resultant supramolecular com-
plexes might thermally generate dimer fragments, which
could provide insight into diacetylene polymerization for
DBA systems. We describe herein our initial work to-
NH2
O
O
O
O
O
O
O
O
2PF6
NH2
NH2
PF6
4
2
3
Figure 2 The structures of crown ether-dehydrobenzoannulene hybrid 2 and mono- and dicationic hexafluorophosphate salts 3 and 4
Synthesis 2002, No. 9, 01 07 2002. Article Identifier:
1437-210X,E;2002,0,09,1256,1260,ftx,en;C11602SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

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Synthesis of Annulene-Fused Pseudorotaxanes
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wards the assembly of novel supramolecular architectures Slow evaporation of a THF solution of 2 afforded yellow
containing hybrid 2 and the mono- and dicationic hexaflu- blocks suitable for X-ray diffraction. The crystal structure
orophosphate salts 3 and 4, respectively (Figure 2).
of macrocycle 2 is shown in Figure 3.16 The annulenic
core is essentially planar with a mean deviation less than
0.07 Å. The bond lengths and bond angles are typical for
those found in other dehydrobenzoannulenes.6,8 Interest-
ingly, the crown ether curves around the end of a second
annulene. Although there are no -stacking interactions in
the crystal lattice, there are short CH...O hydrogen bonds
that help dictate the crystal packing. With such a curved
arrangement, it might be possible to thread both the crown
ether and annulene, a motif we are actively pursuing.
Hybrid 2 was assembled using the same strategy as that
reported previously for the construction of site-specifical-
ly functionalized DBAs (Scheme 1).8b,f,g Cyclization of
ditosylate 514 with 4,5-diiodocatechol15 using high dilu-
tion conditions gave diiododibenzo-24-crown-8 (6) in
moderate yield. Cross-coupling 6 with two equivalents of
1-(4-trimethylsilylbuta-1,3-diynyl)-2-(triisopropylsilyl-
ethynyl)benzene8g using in situ desilylation/coupling con-
ditions furnished the , -polyyne 7 in 81% yield.
Desilylation of 7 with Bu4NF and subsequent Cu-mediat- Mixing equimolar amounts of hybrid 2 and salt 3 in
ed intramolecular oxidative cyclization under pseudo- CD2Cl2 at room temperature resulted in a significant dif-
high dilution conditions generated the benzo-24-crown-8- ference in the 1H NMR spectra (Figure 4), thus indicating
fused annulene 2 as a light yellow solid in 55% yield.
formation of the pseudorotaxane host-guest complex. The
top spectrum, which represents free 2, is relatively un-
complicated, reflecting the C2v symmetry of the crown
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OTs
OTs
O
O
O
O
I
I
Sii-Pr3
Sii-Pr3
a
b
c,d
2
55%
39%
81%
5
6
7
Scheme 1 (a) 4,5-diiodocatechol, CsCO3, MeCN; (b) 1-(4-trimethylsilylbuta-1,3-diynyl)-2-(triisopropylsilylethynyl)benzene, aq KOH,
PdCl2(PPh3)2, CuI, Et3N, THF; (c) Bu4NF, MeOH, THF; (d) Cu(OAc)2, CuCl, pyridine
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
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J. J. Pak et al.
PAPER
1
Figure 4 H NMR (300 MHz, CD2Cl2) spectra of the free hybrid 2 (top) and of the 1:1 pseudorotaxane 2 3 (bottom)
ether moiety. The bottom spectrum shows a number of Ha shifts upfield by 0.15 ppm. Resonances of the ammo-
changes upon addition of an equimolar amount of 3, all of nium ion were observed at = 7.57 (broad singlet), 7.32–
which support strong complexation. The most noticeable 7.13 (multiplets), and 4.74 (broad triplet) representing H3,
differences are in the crown ether region, where the cen- H1, and H2, respectively. Based on the large number of
tral ethylene protons (Hg) change from a singlet in free 2 previous pseudorotaxane studies,13 the observed chemical
to two multiplets in pseudorotaxane 2 3 (Figure 5) with an shift changes, as well as there being no indication of free
upfield shift of ca. 0.25 ppm. Crown ether protons He and 2, are consistent with strong complexation between the
Hf show increased separations between the two sets of host and guest molecules.
multiplets as well as slight upfield shifts. The resonances
The supramolecular complex 2 3 was also analyzed by
in the aromatic region also exhibit notable changes. The
FAB mass spectrometry. Although the spectrum did not
broad singlet attributable to the four Hb protons in 2 splits
show the parent peak of m/z 1085, peaks corresponding to
into the expected AA BB multiplet with an upfield shift
of ca. 0.1 ppm once the complex is formed. The singlet for
M+ – PF6 and hybrid 2 were observed at 940 and 742 mass
O
O
O
O
PF6
H2N
O
O
O
O
O
O
2PF6
O
O
H2N
O
O
O
O
O
O
O
O
H2N
O
O
O
O
2•3
22•4
Figure 5 The structures of 1:1 pseudorotaxane 2 3 and 2:1 pseudorotaxane 2 4
Synthesis 2002, No. 9, 1256–1260 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Annulene-Fused Pseudorotaxanes
1259
trated in vacuo and redissolved in CH2Cl2. The dark residue was fil-
tered through a thin cake of silica gel using CH2Cl2 and
concentrated. Chromatography on silica gel (hexanes–THF, 3:1)
gave polyyne 7 (1.21 g, 81%) as a tan gum.
units, respectively. Attempts to obtain single crystals suit-
able for X-ray diffraction have been unsuccessful to date.
The complexation between DBA 2 and the bis-ammoni-
um salt 4 was also performed in CD2Cl2 by mixing a 2:1
ratio of host and thread molecules (Figure 5). The results
of this experiment are considerably more complicated. 1H
NMR spectra indicated the presence of a mixture of pseu-
dorotaxane complexes and their free components in solu-
tion. 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.
IR (neat): 2946, 2866, 2415, 2203 cm–1.
1H NMR (CDCl3): = 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).
13C NMR (CDCl3): = 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 C66H80O8Si2 (M+): 1056.5392. Found:
1056.5386.
In conclusion, we have demonstrated an efficient synthe-
sis of crown ether containing dehydrobenzoannulene 2
and its ability to complex secondary dialkylammonium
ions. The formation of a pseudorotaxane from a 1:1 mix-
ture of 2 and 3 is facile in CD2Cl2, according to 1H NMR
spectroscopic data. The formation of the corresponding
[3]pseudorotaxane from a 2:1 mixture of 2 and 4 was in-
complete 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.
Crown Ether/Annulene Hybrid 2
Polyyne 7 (850 mg, 0.78 mmol) was dissolved in THF–MeOH (3:1,
20 mL) and treated with Bu4NF (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 Et2O (30 mL), washed
with H2O (3 20 mL) and brine (2 20 mL), and then dried
(MgSO4). The organic layer was concentrated in vacuo and the re-
sultant oil was redissolved in pyridine (10 mL). The pyridine solu-
tion 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 py-
ridine (200 mL) at 60 °C. The addition was done under house air
and stirred further for 8 h. Upon completion, the mixture was con-
centrated in vacuo and then redissolved in CH2Cl2. The mixture was
filtered through a thin cake of silica gel using CH2Cl2 and concen-
trated. Chromatography on silica gel (hexanes–THF, 3:1) afforded
2 (320 mg, 55%) as a light yellow solid; mp 230 °C (dec.).
Reagents and instrumentation used have been described previous-
ly.8g
4,5-Diiododibenzo-24-crown-8 (6)
IR (KBr): 2926, 2866, 2211, 2192, 2140 cm–1.
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 514 (7.72 g, 11.3 mmol) and 4,5-diiodocatechol15 (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 CH2Cl2 (150 mL) and washed with aq sat.
NaHCO3 solution (150 mL). The aqueous layer was extracted with
1H NMR (CD2Cl2): = 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).
13C NMR (CD2Cl2): = 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+).
CH2Cl2 (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.
Anal. Calcd for C48H38O8 C4H8O (814.93): C, 76.64; H, 5.69.
Found: C 76.54, H 5.65.
IR (CDCl3): 3062, 2922, 2870, 1592, 1249, 1127 cm–1.
Pseudorotaxane 2 3
1H NMR (CDCl3): = 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).
13C NMR (CDCl3): = 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+ + H2O), 701 (5, M+ + H).
CD2Cl2 (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.
1H NMR (CD2Cl2): = 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).
Anal. Calcd for C24H30I2O8 (700.30): C, 41.16; H, 4.32. Found: C,
40.98; H, 4.23.
MS (FAB): m/z = 940.3 (82, M+ - PF6), 742.2 (13, M+ - Bz2NH2PF6).
, -Polyyne 7
The diiodide 6 (981 mg, 1.4 mmol) and 1-(4-trimethylsilylbuta-1,3-
diynyl)-2-(triisopropylsilylethynyl)benzene8g (1.59 g, 4.2 mmol)
were dissolved in H2O–THF–Et3N (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 concen-
Acknowledgements
We thank the National Science Foundation (CHE-0104854 to
M.M.H. and CHE-9910199 to J.F.S.) for support of this research.
J.J.P. acknowledges the ACS Division of Organic Chemistry for a
DOC Graduate Fellowship (1998-1999). We thank A. J. Boydston
for his help with the acquisition of some characterization data.
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MoK radiation ( = 0.71073 Å), = 0.82 cm–1,
F(000) = 3440, T = 23 °C, 2 max = 23.5°, 13240
independent reflections scanned, 6623 independent
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Synthesis 2002, No. 9, 1256–1260 ISSN 0039-7881 © Thieme Stuttgart · New York