Conformational interconversions in [2]catenanes containing a wide rigid bis(p-benzyl)methyl spacer

Article abstract of DOI:10.1021/jo070809v

(Figure Presented) The conformational interconversions of four [2]catenanes (1-4) containing a dibenzo-34-crown-10 ether (BPP34C10) interlocked with rings containing two 4,4′-dipyridiniums tethered by 1,3-bis(ethyloxy)-phenyl and bis(p-benzyl)methyl spacers have been studied by VT ¹H NMR spectroscopy. Symmetrically placed blocking groups on thickened tethers enabled either pathway for circumrotation of the BPP34C10 between isoenergetic sites to be blocked. On the basis of chemical shifts of the BPP34C10, its internal p-hydroquinone forms π-π-stacking interactions with only one 4,4′-dipyridinium ring at a time. The activation barrier for migration along either open tether was approximately 11.5 kcal/mol. This study demonstrates an ability to select the pathway for conformational interconversions in these [2]catenanes containing the rigid bis(p-benzyl)methyl tether and the lowering the barrier for interconversion through destabilization of the ground state structures.

Full text of DOI:10.1021/jo070809v

Conformational Interconversions in [2]Catenanes Containing a Wide
Rigid Bis(p-benzyl)methyl Spacer
Ronald L. Halterman,* Xingang Pan, David E. Martyn, Jason L. Moore, and
Andrew T. Long†
Department of Chemistry and Biochemistry, UniVersity of Oklahoma,
620 Parrington OVal, Norman, Oklahoma 73019
rlhalterman@ou.edu
ReceiVed April 26, 2007
The conformational interconversions of four [2]catenanes (1-4) containing a dibenzo-34-crown-10 ether
(BPP34C10) interlocked with rings containing two 4,4′-dipyridiniums tethered by 1,3-bis(ethyloxy)-
phenyl and bis(p-benzyl)methyl spacers have been studied by VT 1H NMR spectroscopy. Symmetrically
placed blocking groups on thickened tethers enabled either pathway for circumrotation of the BPP34C10
between isoenergetic sites to be blocked. On the basis of chemical shifts of the BPP34C10, its internal
p-hydroquinone forms π-π-stacking interactions with only one 4,4′-dipyridinium ring at a time. The
activation barrier for migration along either open tether was approximately 11.5 kcal/mol. This study
demonstrates an ability to select the pathway for conformational interconversions in these [2]catenanes
containing the rigid bis(p-benzyl)methyl tether and the lowering the barrier for interconversion through
destabilization of the ground state structures.
Introduction
transition state energy. We have previously demonstrated the
ability through alterations in the required transition state energy
to select paths for the conformational interconversion of bistable
[2]catenanes containing a 1,3-bis(ethyloxyl)phenyl spacer and
a 1,3- or 1,4-xylyl spacer connecting two 4,4′-dipyridinium
groups and an interlocked BPP34C10 ring (Figure 1).3 Such
electron rich-electron poor [2]catenanes form bistable com-
Noncovalent interactions such as π-π-stacking, van der Waal
interactions, and hydrogen bonding are often crucial factors in
determining the molecular properties of compounds having
biological and materials relevance.1 The ability not only to
understand but also to control these interactions is especially
important in the preparation of mechanical-chemical molecular
machines and switches.2 Of particular interest is to alter the
activation barrier for interconversions in nanoscaled devices by
either changing the transition state energy relative to a ground
state energy or changing the ground state energy relative to a
(2) (a) Beckman, R.; Beverly, K.; Boukai, A.; Bunimovich, Y.; Choi, J.
W.; Delonno, E.; Green, J.; Johnston-Halperin, E.; Luo, Y.; Sheriff, B.;
Stoddart, J. F.; Heath, J. R. Faraday Discuss. 2006, 131, 9-22. (b) Balzani,
V.; Credi, A.; Ferrer, B.; Silvi, S.; Venturi, M. Top. Curr. Chem. 2005,
262, 1-27.
(3) (a) Halterman, R. L.; Martyn, D. E.; Pan, X.; Ha, D. B.; Frow, M.;
Haessig, K. Org. Lett. 2006, 8, 2119-2121. (b) Halterman, R. L.; Martyn,
D. E.; Pan, X. Abstracts of Papers, 230th National Meeting of the American
Chemical Society; American Chemical Society: Washington, DC, 2005;
ORGN-307.
† Undergraduate research participant.
(1) (a) Liu, Y.; Guo, D.-S.; Yang, E.-C.; Zhang, H.-Y.; Zhao, Y.-L. Eur.
J. Org. Chem 2005, 162-170. (b) Brunsveld, L.; Folmer, B. J. B.; Meijer,
E. W.; Sijbesma, R. P. Chem. ReV. 2001, 101, 4071-4097. (c) Keizer, H.
M.; Sijbesma, R. P. Chem. Soc. ReV. 2005, 34, 226-234.
10.1021/jo070809v CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/14/2007
6454
J. Org. Chem. 2007, 72, 6454-6458

Conformational InterconVersions in [2]Catenanes
FIGURE 1. BPP34C10 rotation in previous [2]catenanes 3a.
FIGURE 3. [2]Catenanes in this study.
SCHEME 1. Synthesis of Rigid Tethers
FIGURE 2. Cartoon representation of [2]catenanes.
plexes where the p-phenoxy rings of the crown ether prefer to
π-stack over either of the dipyridinium groups.4 Passage of the
BPP34C10 over the thin 1,4-xylyl spacer was established to be
approximately 1 kcal/mol more favorable than that over the 1,3-
xylyl spacer, while passage over the 1,3-bis(ethyloxy)phenyl
spacer was energetically similar to passage over the 1,3-xylyl
spacer.3a Since these xylyl groups functioned as fairly narrow
spacers with respect to the separation of the two dipyridinium
groups, they allowed the internal p-phenoxy ring of the crown
ether to π-stack simultaneously with both 4,4′-dipyridinium
moieties. We anticipated that changing to the wider, rigid bis-
(p-benzyl)methane spacer would disrupt one of these π-π-
stacking interactions and perhaps have energetic consequences
for the circumrotation of the BPP34C10 ring through changes
in the ground state energies. We report herein our ability to
prepare these wider [2]catenanes, evidence for invoking π-π-
stacking interactions with only a single dipyridinium group at
a time, and a determination of the lowered energy barriers for
the circumrotation of the BPP34C10 ring between the stable
π-π-stacked forms.
only along the thin Pathway B. With neither blocking group
present, passage along both tethers would be allowed. Extending
our earlier work3a and the work of Stoddart,5 we have prepared
[2]catenanes 1-4 having either the resorcinol-based tether
blocked or not blocked and the bis(p-benzyl)methane-based
tether blocked or not blocked (Figure 3).
The preparations of the two bis(4-bromomethylphenyl)-
methane bridging groups were accomplished through modifica-
tions of literature procedures and are shown in Scheme 1.
Diphenylmethane was conveniently bromomethylated by using
aqueous rather than gaseous HBr and paraformaldehyde to give
bis(4-bromomethylphenyl)methane (5),6 which was purified
through a trituration procedure. Triarylmethanol 6 was prepared
through a Grignard reaction in which p-bromotoluene was added
to a mixture of magnesium turnings and methyl 4-tert-
butylbenzoate. Radical bromination of the two benzylic methyl
groups by NBS in ethyl acetate gave bis(bromomethyl) adduct
Results and Discussion
To determine the energy barrier for a selected translation
along Path A in Figure 2, we attached a blocking group to tether
B to allow only circumrotation of the crown ether along thin
Pathway A. With Path A blocked, interconversion would occur
(4) (a) Amabilino, D. B.; Anelli, P. L.; Ashton, P. R.; Brown, G. R.;
Cordova, E.; Godinez, L. A.; Hayes, W.; Kaifer, A. E.; Philip, D.; Slawin,
A. M. Z.; Spencer, N.; Stoddart, J. F.; Tolley, M. S.; Williams, D. J. J. Am.
Chem. Soc. 1995, 117, 11142-11170. (b) Ashton, P. R.; Chemin, A.;
Claessens, C. G.; Menzer, S.; Stoddart, J. F.; White, A. J. P.; Williams, D.
J. Eur. J. Org. Chem. 1998, 969-981.
(5) Asakawa, M.; Dehaen, W.; L’abbe, G.; Menzer, S.; Nouwen, J.;
Raymo, F. M.; Stoddart, J. F.; Williams, D. J. J. Org. Chem. 1996, 61,
9591-9595.
(6) Steinberg, H.; Cram, D. J. J. Am. Chem. Soc. 1952, 74, 5388-5391.
J. Org. Chem, Vol. 72, No. 17, 2007 6455

Halterman et al.
TABLE 1. Summary of Data and Calculation of Activation
Energy
SCHEME 2. [2]Catenane Synthesis
coalescence
temp (K)
freq difference
(Hz)
energy of activation
(kcal/mol)
catenane
1
2
3
4
228
238
248
79
79
166
84
10.8
11.4
11.5
>335
>15
both sets of signals are observed at room temperature for [2]-
catanenes of BPP34C10 and dipyridium-based rings; they
generally coalesce above 50 °C to give a single averaged signal
near 5 ppm. The energy barrier for the translocation or
circumrotation of the crown ether from near one dipyridinium
group to the other typically requires several kilocalories per mole
less energy.4
Given these prior findings, catenanes 1-4 exhibited quite
unusual 1H NMR spectra at room temperature in that only one
set of signals for the hydrogen atoms on the hydroquinone rings
were observed at about 6.1 ppm. These signals remained
unchanged in the temperature range -40 to +60 °C. Below
-40 °C the observed decoalescence of the BPP34C10 signals
was most likely due the freezing out of a known rocking motion
of the crown ether rather than its translocation.4 We ascribe
these findings to the presence of similar chemical shift environ-
ments for the two hydroquinone ringssinside and outside the
catenated dipyridinium ring both have only a single π-π-
stacking interaction with one dipyridinium group as they would
in a rotaxane complex.4a We conclude that the second dipyri-
dinium ring cannot interact with the internal hydroquinone due
to the spacing enforced by the wide, rigid bis(p-benzyl)methyl
tether (see depiction in Figure 3). Previous analogous catenations
involving the wide 4,4′-bis(methylene)-1,1-biphenyl tether
between 4,4′-dipyridinium groups led only to the formation of
[3]catenanes where two BPP34C10 rings were interlocked onto
either side of a single tetracationic ring.11 In our preparation of
catenanes 1-4, only [2]catenanes were observed despite
evidence for π-π-stacking with only one dipyridinium group
at a time.
The energy barriers for the translocation of the crown ether
in [2]catenanes 1-4 were determined by analyzing the desym-
metrization of the dipyridinium rings in VT 1H NMR spectros-
copy. At room temperature a single set of averaged signals was
observed for the protons at the 2 and 2′ dipyridyl positions for
catenanes 1-3. Below -40 °C, the 1:1 set of dipyridyl signals
indicated that both exchange processes were in the slow
exchange region. For catenane 4 containing blocking groups
on both thick tethers, the slow exchange spectrum was observed
up to 60 °C. The coalescence temperature and frequency
difference of exchanging sets of signals were used to calculate
the activation barrier for the translocation of the crown ether
between the bistable states.10 The data are summarized in Table
1.
7, which was reduced by sodium borohydride in trifluoroacetic
acid to give tethering group 8.7 The resorcinol-tethered bis-
(mono-pyridinium) salt 9 and 5-[bis(4-methylphenyl)methyl]-
resorcinol derivative 10 were prepared as previously reported.3a
Catenanes 1-4 were formed through three-component reac-
tions between 1 equiv of bis(pyridiniums) 9 or 10, 1.3 equiv of
bis(4-bromomethylphenyl)methane (5) or triaryl dibromide 8,
and 1.6 equiv of BPP34C10 in acetonitrile at room temperature
under 1 atm of nitrogen for 4 days (Scheme 2). After solvent
removal, the catenanes were isolated by preparative TLC on
silica, initially at 50 °C with 1:1 methanol-ethyl acetate, to
promote dethreading of any pseudorotaxanes and rapid elution
of the crown ether to the top of the plate. A second elution at
room temperature with 7:2:1 methanol-2 M aqueous am-
monium chloride-nitromethane8 moved the catenanes to about
0.3-0.4 Rf and left uncoordinated pyridinium salts near the
origin of the plate. The silica gel with the catenanes was
removed and extracted with the 7:2:1 solvent system. The filtrate
was concentrated and aqueous NH4PF6 was added to precipitate
the catenanes as orange to red solids in 18% to 24% yield. We
found that the yields of the [2]catenanes were significantly
improved by using very high purity BPP34C10. We have found
that the most convenient and reliable preparation of this crown
ether was a modification of a one-pot cyclization from hydro-
quinone and the ditosylate of tetraethylene glycol.9 As described
in the Experimental Section, suitable purity of the BPP34C10
was obtained by a series of extractions and column purifications.
Two rotational temperature-dependent isomerizations of
related [2]catenanes have been established by Stoddart.4 Typi-
cally, the rotation of a BPP34C10 about a single dipyridinium
group has an energy barrier of approximately 16 kcal/mol
determined by using established NMR techniques.10 In such
cases, the internal hydroquinone ring exhibited a very high field
1H NMR resonance near 3.8 ppm due to π-π-stacking with
both dipyridinium moieties as depicted in Figure 1.3a The
external hydroquinone ring could only interact with a single
dipyridinium unit and can be found around 6.1 ppm. Typically
Catenane 1 having thin unsubstituted resorcinol and bis(p-
benzyl)methyl linkers gave an activation barrier of 10.8 kcal/
mol. When both the resorcinol and bis(p-benzyl)methyl tethers
were thickened in catenane 4, both pathways were blocked.
Since no line broadening was observed in the 1H NMR spectra
up to 60 °C the activation barrier for passing over either of
(7) Staab, H. A.; Ruland, A.; Chi, K. C. Chem. Ber. 1982, 115, 1755-
1764.
(8) Anelli, P. L.; Ashton, P. R.; Balardini, R.; Delgado, M.; Gandolfi,
M. T.; Goodnow, T. T.; Kaifer, A. E.; Philip, D.; Pietraszkiewicz, M.; Prodi,
L.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.;
Christina, V.; Williams, D. J. J. Am. Chem. Soc. 1992, 114, 193-218.
(9) Helgeson, R. C.; Tarnowski, T. L.; Timko, J. M.; Cram, D. J. J. Am.
Chem. Soc. 1977, 99, 6411-6418.
(11) Ashton, P. R.; Baldoni, V.; Balzani, V.; Claessens, C. G.; Credi,
A.; Hoffmann, H. D. A.; Raymo, F. M.; Stoddart, J. F.; Venturi, M.; White,
A. J. P.; Williams, D. J. Eur. J. Org. Chem. 2000, 1121-1130.
(10) Friebolin, H. P. Basic 1D and 2D NMR Spectroscopy; VCH
Publishers: New York, 1991; Chapter 11, pp 271-272.
6456 J. Org. Chem., Vol. 72, No. 17, 2007

Conformational InterconVersions in [2]Catenanes
The yellow semisolid was dissolved in hot ethyl acetate (10 mL)
and triturated with petroleum ether (approximately 200 mL) to give
an off-white solid. The off-white solid was collected via vacuum
filtration, washed with diethyl ether, and allowed to air-dry to give
an off-white powder (1.2 g). A portion of the off-white powder
(300 mg) was purified via column chromatography [SiO2-CH2-
Cl2-Et2O (3:7), v/v] as previously reported13 to give pure BPP34C10
(150 mg). The 1H NMR spectrum of the purified product was
consistent with literature data.9,13 The melting point of the purified
product was 93-94 °C, which was also consistent with literature
data.9
these blocking groups should be higher than the 15 kcal/mol
calculated from the observed chemical shift difference and 335
K as a minimum temperature of coalescence. When only the
resorcinol-based tether was blocked in 3, passage over the thin
bis(p-benzyl)methyl required 11.5 kcal/mol, and a similar 11.4
kcal/mol barrier was measured for passage over the thin 1,3-
bis(ethyloxy)benzene tether in 2.
We note that the energy barriers for passage along either the
rigid thin bis(p-benzyl)methane and the flexible thin 1,3-bis-
(ethyloxy)phenyl tethers are nearly identical (11.4-11.5 kcal/
mol). In catenane 1 where both paths are available, the lowered
activation barrier of 10.8 kcal/mol nicely reflects the entropic
contribution of two accessible paths. Interestingly, circumrota-
tion of the crown ether along the same thin resorcinol tether in
2 is about 1.5 kcal/mol lower in activation energy than in our
previous 1,3-bis(ethyloxy)phenyl-tethered catenanes shown in
Figure 1.3a This lowering of the barrier is unlikely to be due to
a lowering of the unfavorable energetic interactions in the
transition state structures since the interactions in the transition
state structure as the crown ether passes along these same tethers
should be about the same in the two catenanes. Given our NMR
spectroscopic evidence for the presence of just a single π-π-
stacking interaction in catenanes 1-4 and the typical double
π-π-stacking interactions seen in previous [2]catenanes, it
seems most likely that the activation barrier differences are due
to ground state destabilization in 1-4.
Compound 6.7 Magnesium turnings (2.2 g, 0.091 mol) were
added to a three-necked flask. The ports of the three-neck flask
were affixed with a reflux condenser, addition funnel, and rubber
septa. The flask was purged with nitrogen and dry THF (50 mL)
was added to the flask under nitrogen via a syringe. Approximately
6-10 drops of 1,2-dibromoethane were added to the reaction flask
under nitrogen via a syringe to activate the magnesium. The
magnesium/THF mixture was heated to approximately 50 °C via
an oil bath. THF (50 mL) and 4-bromotoluene (8 mL, 0.065 mol)
were sequentially added to the addition funnel under nitrogen.
Methyl-4-tertbutylbenzoate (5.0 mL, 0.026 mol) was added to the
reaction flask under nitrogen via a syringe. The 4-bromotoluene/
THF mixture was added to the mixture dropwise and the reaction
mixture was refluxed at 70-80 °C for 20-24 h. The reaction
mixture was cooled to room temperature and poured into a solution
of ice (100 mL) and concentrated H2SO4 (3.3 mL) followed by the
addition of NH4Cl (3.3 g) to the aqueous mixture. The aqueous
mixture was extracted with diethyl ether (3 × 100 mL). The
combined organic fractions were washed with 5 wt % NaHCO3 (3
× 100 mL) and water (3 × 100 mL), dried (MgSO4), and
concentrated under reduced pressure (9.0 g, quantitative crude
yield). The crude product was purified via column chromatography
[SiO2-petroleum ether-CH2Cl2 (2:1), v/v] to give pure compound
6 (3.4 g, 38% yield). The 1H NMR spectrum of the purified product
was consistent with the chemical structure and that reported in the
literature.5
Conclusion
In summary, through the appropriate incorporation of block-
ing groups on one or both of the tethers it was possible to block
one or both of the two pathways for circumrotation in bistable
catenanes 1-4. The wide rigid bis(p-benzyl)methyl tether allows
π-π-stacking interactions with only one dipyridinium moiety
at a time. This destabilization of the ground state led to lowered
energy barriers for passage along a thin 1,3-bis(ethyloxyl)-
benzene tether of 11.5 kcal/mol. Passage of BPP34C10 over a
thin but wider bis(p-benzyl)methane tether was 11.4 kcal/mol.
This study demonstrates an ability to alter the activation barriers
through ground state destabilization and to choose different
pathways for circumrotation in these noncovalently linked
compounds.
Compound 7.14a-c NBS (1.8 g, 0.01 mol) and benzoyl peroxide
(0.1 g, 0.0005 mol) were added to a 50 mL sealed round-bottomed
flask and purged with nitrogen for 30 min. Compound 6 (1.7 g,
0.005 mol) and ethyl acetate (17 mL) were added to a separate 50
mL sealed round-bottomed flask and purged with nitrogen for 10
min. The solution of compound 6 and ethyl acetate was transferred
via syringe to the sealed flask containing NBS and benzoyl peroxide
at room temperature under nitrogen. The reaction mixture was
refluxed via a heat lamp (250 W) for 24 h under a nitrogen
atmosphere, cooled to room temperature, and extracted with ethyl
acetate (40 mL). The organic fraction was washed with aqueous
saturated NaHCO3 (3 × 25 mL) and H2O (3 × 25 mL), dried
(MgSO4), and concentrated under reduced pressure (1.8 g, 73%
Experimental Section
BPP34C10 Synthesis.9 Tetraethylene glycol bis(toluene-p-
sulfonate)12 (50.2 g, 0.134 mol) was added to 2-propanol (450 mL)
containing p-hydroxyquinone (14.7 g, 0.134 mol) and sodium
hydroxide (9.1 g, 0.228 mol) predissolved in water (10 mL). The
mixture was refluxed for approximately 24 h under nitrogen. The
reaction mixture was cooled to room temperature, then filtered via
vacuum filtration, and the insoluble solids were washed with
2-propanol. The liquid filtrate was collected and concentrated under
reduced pressure (6.1 g of crude product).
BPP34C10 Purification. Crude bis(p-phenylene)-34-crown-10
(BPP34C10) (21.6 g, brown solid) was dissolved in hot ethyl acetate
(500 mL) and the insoluble solids were removed via vacuum
filtration. The liquid filtrate was collected, concentrated under
reduced pressure, and purified via flash column chromatography
(neutral Al2O3; ethyl acetate) to give a viscous yellow oil (2.8 g)
that solidified at room temperature to give a waxy yellow semisolid.
1
crude yield). The H NMR spectrum of crude compound 7 was
consistent with the chemical structure and that reported in the
literature. A small amount of the over-brominated product was also
1
observed in the H NMR spectrum.
Compound 8.15 A mixture of compound 7 (2.4 g, 4.8 mmol)
and trifluoroacetic acid (72 mL) was cooled to 0 °C in an ice bath
under nitrogen. NaBH4 (1.8 g, 47.8 mmol) was slowly added to
the reaction mixture under nitrogen and the reaction mixture was
stirred for 5 min at 0 °C. The reaction mixture was concentrated
under reduced pressure and the residue was dissolved in water (50
mL) followed by the addition of NaHCO3 (50 mL). The aqueous
(13) Allwood, B. L.; Spencer, N.; Shahriari-Zavareh, H.; Stoddart, J.
F.; Williams, D. J. J. Chem. Soc., Chem. Commun. 1987, 1061-1064.
(14) (a) Gruetzmacher, H. F.; Husemann, W. Tetrahedron 1987, 43,
3205-3211. (b) Curran, D. P.; Yang, F.; Cheong, J.-h. J. Am. Chem. Soc.
2002, 124, 14993-15000. (c) Amijs, C. H. M.; van Klink, G. P. M.; van
Koten, G. Green Chem. 2003, 5, 470-474.
(12) (a) Fear, E. J. P.; Thrower, J.; Veitch, J. J. Chem. Soc. 1958, 1322-
1325. (b) Sekera, V. C.; Marvel, C. S. J. Am. Chem. Soc. 1933, 55, 345-
349.
(15) Gribble, G. W.; Leese, R. M.; Evans, B. E. Synthesis 1977, 3, 172-
176.
J. Org. Chem, Vol. 72, No. 17, 2007 6457

Halterman et al.
mixture was extracted with CH2Cl2 (3 × 50 mL). The combined
organic fractions were dried (Na2SO4) and concentrated under
reduced pressure (1.5 g, 65% crude yield). The 1H NMR spectrum
of crude compound 8 was consistent with the chemical structure
and that reported in the literature.
8.2 Hz, 4H), 7.44 (d, J ) 8.5 Hz, 2H), 7.39 (d, J ) 8.0 Hz, 4H),
7.28 (t, J ) 8.5 Hz, 1H), 7.17 (d, J ) 8.2 Hz, 2H), 6.94 (t, J ) 2.3
Hz, 1H), 6.72 (dd, J ) 8.5, 2.3 Hz, 2H), 6.13 (s, 12H), 5.77 (s,
1H), 5.44 (t, J ) 3.8 Hz, 4H), 4.76 (t, J ) 4.1 Hz, 4H), 3.85-3.47
(m, 32H), 1.32 (s, 9H). 13C NMR (C3D6O, 100 MHz): δ (ppm)
145.7, 130.3, 130.2, 129.1, 128.7, 126.3, 125.7, 125.2, 114.7, 106.4,
103.4, 70.4, 70.0, 69.6, 67.4, 65.8, 64.0, 60.8, 55.35, 30.6. MS
(ESI): m/z 494.9 (M4+PF6-), 814.3 (M4+2PF6-) (M4+ ) C83H94-
Bis(4-bromomethylphenyl)methane.6 A mixture of diphenyl-
methane (42 g, 0.25 mol), paraformaldehyde (32.5 g, 1.08 mol),
phosphoric acid (61.5 mL), 48% aqueous hydrobromic acid (82.5
mL), and glacial acetic acid (102 mL) was stirred under nitrogen
at 100 °C for 24 h. The reaction mixture was cooled to 0 °C in an
ice bath and the aqueous phase was separated from the organic
layer. Reagent grade acetone (0 °C) was added to the organic phase
and the mixture was placed in the laboratory refrigerator at 4 °C.
The off-white solid product was collected via vacuum filtration
(0.5442 g). The yellow liquid filtrate was concentrated under
reduced pressure, then triturated with methanol (0 °C), and more
off-white solid was isolated via vacuum filtration to yield additional
product (1.1254 g). The overall combined product yield was 2%.
4+
N4O12 requires 1338.68).
Catenane 3. 1,3-Bis-(2-(4,4′-dipyridinium)ethoxy)-5-di-p-tolyl-
methylbenzene dihexafluorophosphate (10) (0.158 g, 0.164 mmol),
bis(4-bromomethylphenyl)methane (5) (0.075 g, 0.213 mmol), and
BPP34C10 (0.141 g, 0.263mmol) were combined and dissolved in
CH3CN (20 mL). The reaction vessel was sealed with a septum.
This red solution was stirred 4 days under ambient conditions after
which time the solvent was removed in vacuo. The catenane was
purified and after removal of solvent in vacuo, 0.058 g (18%) of
1
red solid was obtained. H NMR (C3D6O, 300 MHz at 20 °C): δ
1
The H NMR spectrum of compound 5 was consistent with the
(ppm) 9.36 (d, J ) 7.0 Hz, 4H), 9.23 (d, J ) 6.7 Hz, 4H), 8.34 (m,
J ) 6.5, 5.3 Hz, 8H), 7.61 (d, J ) 8.5 Hz, 4H), 7.52 (d, J ) 8.2
Hz, 4H), 7.10 (d, J ) 8.5 Hz, 4H), 7.01 (d, J ) 8.2 Hz, 4H), 6.80
(t, J ) 2.1 Hz, 1H), 6.47 (d, J ) 2.1 Hz, 2H), 6.10 (s, 12H), 5.51
(s, 1H), 5.37 (t, J ) 4.1 Hz, 4H), 4.61 (t, J ) 4.1 Hz, 4H), 4.12 (s,
2H), 3.76-3.39 (m, 32H), 2.30 (s, 6H). 13C NMR (C3D6O, 100
MHz): δ (ppm) 146.2, 146.0, 129.5, 129.2, 128.9, 128.8, 125.9,
chemical structure.
Purification of Catenanes. After being stirred for 3 to 4 days
the catenane solutions were purified and isolated according to the
following method. The dark red solid was dissolved in ap-
proximately 10 mL of CH3OH/EtOAc/CH3COCH3 (1:1:1) and
loaded onto a 2 mm preparative TLC plate. After drying, the plate
was eluted twice with CH3OH/EtOAc (1:1) at 35 °C (Rf 0.1) and
finally with CH3OH/2 M NH4Cl/CH3NO2 (7:2:1) at room temper-
ature (Rf 0.3-0.4). The product was washed from the silica gel
with the final eluant and NH4PF6 (0.300 g) was added to the red
solution. Solvents CH3OH and CH3NO2 were removed via rotary
evaporator leaving a red solid suspended in water. This red product
was filtered, washed with distilled water, and allowed to dry.
Catenane 1. 1,3-Di(2-(4,4′-dipyridinium)ethoxy)benzene di-
hexafluorophosphate (9) (0.123 g, 0.16 mmol), bis(4-bromometh-
ylphenyl)methane (5) (0.068 g, 0.192 mmol), and BPP34C10 (0.223
g, 0.416 mmol) were combined and dissolved in CH3CN (20 mL).
The reaction vessel was sealed with a septum. This red solution
was stirred 4 days under ambient conditions after which time the
solvent was removed in vacuo. The catenane was purified and after
removal of solvent in vacuo, 0.063 g (22%) of red solid was
114.6, 107.6, 101.3, 70.3, 69.9, 69.5, 67.1, 65.8, 64.1, 61.0, 55.9,
-
40.9, 27.5. MS (ESI): m/z 515.2 (M4+PF6-), 845.8(M4+2PF6
)
4+
(M4+ ) C88H96N4O12 requires 1400.70).
Catenane 4. 1,3-Bis(2-(4,4′-dipyridinium)ethoxy)-5-di-p-tolyl-
methylbenzene dihexafluorophosphate (10) (0.140 g, 0.146 mmol),
1,1′-[[4-(1,1-dimethylethyl)phenyl]methylene]bis[4-(bromomethyl)-
benzene] (8) (0.092 g, 0.190 mmol), and BPP34C10 (0.125 g,
0.233mmol) were combined and dissolved in CH3CN (20 mL). The
reaction vessel was sealed with a septum. This red solution was
stirred 4 days under ambient conditions after which time the solvent
was removed in vacuo. The catenane was purified and after removal
1
of solvent in vacuo, 0.057 g (19%) of red solid was obtained. H
NMR (C3D6O, 300 MHz at 20 °C): δ (ppm) 9.38 (m, J ) 6.7, 5.6
Hz, 4H), 9.32 (d, J ) 7.0 Hz, 2H), 9.07 (d, J ) 6.7 Hz, 2H), 8.49
(m, J ) 6.8, 6.5 Hz, 4H), 8.21 (dd, J ) 6.7, 2.1 Hz, 4H), 7.66 (d,
J ) 8.2 Hz, 2H), 7.60 (d, J ) 8.2 Hz, 2H), 7.44 (d, J ) 8.5 Hz,
2H), 7.40 (d, J ) 7.9 Hz, 2H), 7.38 (d, J ) 8.2 Hz, 2H), 7.17 (d,
J ) 8.2 Hz, 2H), 7.11 (d, J ) 7.9 Hz, 4H), 7.03 (d, J ) 8.2 Hz,
4H), 6.79 (t, J ) 2.1 Hz, 1H), 6.48 (dd, J ) 10.9, 2.1 Hz, 2H),
6.14-6.10 (m, 12H), 5.77 (s, 1H), 5.52 (s, 1H), 5.36 (m, 4H), 4.62
(m, 4H), 3.79-3.41 (m, 32H), 2.31 (s, 6H), 1.35 (s, 9H). 13C NMR
(C3D6O, 100 MHz): δ (ppm) 146.3, 146.2, 145.6, 130.4, 130.0,
129.3, 129.0, 128.9, 128.7, 126.7, 125.3, 125.0, 114.7, 108.3, 106.6,
101.2, 70.3, 70.0, 69.5, 67.3, 67.2, 68.9, 64.3, 63.8, 61.5, 60.4, 55.9,
1
obtained. H NMR (C3D6O, 300 MHz at 20 °C): δ (ppm) 9.25
(m, J ) 6.1, 6.5 Hz, 8H), 8.29 (d, J ) 6.4 Hz, 4H), 8.23 (d, J )
6.3 Hz, 4H), 7.58 (d, J ) 7.8 Hz, 4H), 7.48 (d, J ) 8.0 Hz, 4H),
7.24 (t, J ) 8.4, 1H), 6.87 (t, J ) 2.1 Hz, 1H), 6.67 (dd, J ) 8.4,
2.1 Hz, 2H), 6.07 (s, 8H), 6.02 (s, 4H), 5.36 (t, J ) 4.1 Hz, 4H),
4.76 (t, J ) 4.1 Hz, 4H), 4.07 (s, 2H), 3.76∼3.35 (m, 32H). 13C
NMR (C3D6O, 100 MHz): δ (ppm) 145.9, 130.5, 129.9, 129.5,
126.3, 125.9, 11.8, 106.6, 103.5, 70.3, 69.9, 69.4, 67.2, 65.8, 63.9,
-
60.9, 40.8. MS (ESI): m/z 450.5 (M4+PF6-), 748.3 (M4+ 2PF6
)
4+
(M4+ ) C73H82N4O12 requires 1206.59).
55.4, 30.7.20.0. MS (ESI): m/z 911.9(M4+2PF6-) (M4+
)
4+
Catenane 2. 1,3-Di(2-(4,4′-dipyridinium)ethoxy)benzene di-
hexafluorophosphate (9) (0.092 g, 0.120 mmol), 1,1′-[[4-(1,1-
dimethylethyl)phenyl]methylene]bis[4-(bromomethyl)benzene] (8)
(0.076 g, 0.156 mmol), and BPP34C10 (0.103 g, 0.192 mmol) were
combined and dissolved in CH3CN (20 mL). The reaction vessel
was sealed with a septum. This red solution was stirred 4 days
under ambient conditions after which time the solvent was removed
in vacuo. The catenane was purified and after removal of solvent
in vacuo, 0.055 g (24%) of red solid was obtained. 1H NMR
(C3D6O, 300 MHz at 20 °C): δ (ppm) 9.31 (d, J ) 5.9 Hz, 8H),
8.37 (d, J ) 6.7 Hz, 4H), 8.31 (d, J ) 6.7 Hz, 4H), 7.66 (d, J )
C98H108N4O12 requires 1532.79).
Acknowledgment. The support for R.L.H. as a DAAD guest
professor at TU-Berlin and the University of Oklahoma
Research Council is appreciated. J.L.M. acknowledges the
DOEd for a GAANN Fellowship.
Supporting Information Available: NMR spectra for com-
1
pounds 1-8 and VT H NMR spectra of 1-4. This material is
available free of charge via the Internet at http://pubs.acs.org.
JO070809V
6458 J. Org. Chem., Vol. 72, No. 17, 2007