'Self-complexing' tetrathiafulvalene macrocycles; A tetrathiafulvalene switch

Article abstract of DOI:10.1039/a707026h

Two 'self-complexing' macrocycles based on the electron donor TTF and a cyclic bipyridinium acceptor are prepared.

Full text of DOI:10.1039/a707026h

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‘Self-complexing’ tetrathiafulvalene macrocycles; a tetrathiafulvalene switch
Mogens Brøndsted Nielsen, Steen Brøndsted Nielsen and Jan Becher*
Department of Chemistry, Odense University, DK-5230 Odense M, Denmark
Two ‘self-complexing’ macrocycles based on the electron
donor TTF and a cyclic bipyridinium acceptor are pre-
pared.
resulting monothiolate was treated in situ with 2 or 3 affording
5 and 6, respectively. The two ester groups were reduced with
LiAlH4 followed by mesylation in the presence of DBU. The
mesylated compounds were converted directly to the corre-
sponding chloro compounds by reaction with an excess of LiCl,
giving fair yields of 9 and 10. Subsequent Finkelstein reactions
with LiBr gave the TTF-linked m-xylene dibromides 11 and
12.†
The construction of molecular devices which can operate as
machines upon external energy transfer has been of high interest
recently, as such systems may be able to store and process
information at the molecular level.1,2 A recent example is
provided by a pseudorotaxane system in which a naphthalene or
hydroquinone p-donor and the p-acceptor cyclobis(paraquat-
p-phenylene) are covalently linked.3
We have prepared a number of donor–acceptor catenanes by
incorporating the p-donor tetrathiafulvalene (TTF) into macro-
cyclic systems,4 as well as systems in which the TTF unit and
the bipyridinium unit are linked, either in a rigid conformation,
e.g. as a donor–acceptor cyclophane, or in a noncyclic system.5
Here we have extended these concepts by incorporating TTF
into macrocycles which may self-complex in order to in-
vestigate their switching properties. For synthetic reasons we
attached the TTF unit to the unsymmetrical m-p linked
cyclophane of cyclobis(paraquat-p-phenylene).6 The corre-
sponding symmetric m-m linked cyclophane was discarded due
to its poor ability to act as a host, as reported by Stoddart.7
First, 2 and 3 were prepared by O-alkylations of dimethyl
5-hydroxyisophthalate 1 (Scheme 1). The TTF derivative 4 was
deprotected with CsOH (1 equiv.) (Scheme 2),8 and the
The new anchimeric-complexed‡ macrocycles 14a and 15a
were obtained by treating 11 and 12, respectively, with the
dipyridinium dication of 13 under ultra-high pressure (10 kbar)
for 6 days (Scheme 3). The crude green products were subjected
to column chromatography and ion exchange.4 During work-up
of 15a, partial isomerisation ‘decomplexation’ to the orange
coloured form 15b was observed. Repeated fractional crystal-
lization via slow evaporation of Pri2O into MeCN solutions of
14a and 15a resulted in removal of small amounts of impurities.
In this way it was possible to obtain 14b and 15b as orange
microcrystalline compounds, e.g. in the completely ‘decom-
plexed’ forms. Redissolution of 15b in MeCN initially gave an
orange solution which slowly turned greener on standing due to
partial anchimeric complexation. However, an MeCN solution
of ‘decomplexed’ 14 did not change colour, and according to
UV–VIS spectroscopy only a very small charge-transfer (CT)
absorption could be detected after several days. Thus, when first
‘decomplexed’, the short linker of 14b more or less prevents the
TTF unit from intramolecularly slipping back into the cyclic
acceptor. Besides, the persistent orange colour indicates the
absence of intermolecular complexation.
CO2Me
CO2Me
(
X
i
HO
O
)
n
The UV–VIS absorption of the initially orange crystals of
15b dissolved in MeCN was followed over time [Fig. 1(a)].
After about 20 h the equilibrium between 15a and 15b was
established, as seen from the constant CT absorption (lmax
~ 785 nm). The relatively weak CT absorption indicates that
only a small degree of anchimeric complexation occurs, which
was confirmed by 1H NMR spectroscopy (estimated ratio
15a:15b: 1:10). The anchimeric complexation results in a
complicated set of bipyridinium proton resonances and a
downfield shift of the SMe protons in agreement with
observations for comparable TTF-based catenanes.4d The
question is whether the complexation is truly of the auchimeric
CO2Me
CO2Me
1
2 X = Br, n = 1, 32%
3 X = I, n = 3, 65%
Scheme 1 Reagents and conditions: i, K2CO3, BrCH2CH2Br (n = 1) or
I(CH2CH2O)2CH2CH2I (n = 3), acetone, reflux, 16 h
CO2Me
(
R
R
CN
i
O )n
4
CO2Me
5 n = 1, 95%
6 n = 3, 88%
(a)
0.6
(b)
ii
CH2OH
0.10
CH2Cl
CH2Cl
0.5
(
R
(
R
iii
O )n
O )n
0.05
0.4
CH2OH
0.00
0.3
5
10
15
20
7 n = 1, 60%
8 n = 3, 79%
9 n = 1, 84%
10 n = 3, 58%
t / h
0.2
0.1
0.0
iv
(iii)
CH2Br
(ii)
(i)
(
R
O )n
SMe
S
MeS
S
S
S
S
R =
400
500
600
700
800
l / nm
900 1000 1100
CH2Br
MeS
11 n = 1, 90%
12 n = 3, 96%
Fig. 1 (a) The UV–VIS absorption spectrum of the initially decomplexed
15b in MeCN at (i) 0, (ii) 3 and (iii) 19 h. (b) The time variation of the
maximum absorbance (lmax ~ 785 nm) of initially decomplexed 15b. A
first-order fit matches the points very well. Concentration of
Scheme 2 Reagents and conditions: i, CsOH·H2O (1 equiv.), 2 or 3, DMF,
room temp., 3 h; ii, LiAlH4, THF, reflux, 2 h; iii, MsCl, DBU, LiCl,
CH2Cl2, room temp., 24 h; iv, LiBr, acetone, reflux, 24 h
compound = 0.26 mmol dm23
.
Chem. Commun., 1998
475

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+
N
+
N
MeS
SMe
SMe
MeS
MeS
SMe
S
S
S
S
S
S
S
S
S
ii
+
+
i (11)
N
N
N
15%
S
+
O
N
N
+
+
+
N
–
4 PF6
+
+
N
N
N
N
–
4 PF6
O
14b
14a
+
N
+
–
N
2 PF6
13
MeS
MeS
SMe
MeS
i (12)
12%
SMe
SMe
S
S
S
S
S
S
S
S
+
+
+
ii
N
N
N
iii
S
(
S
O
)
n
N
O
+
N
O
+
N
–
4 PF6
+
–
4 PF6
O
15a
15b
Scheme 3 Reagents and conditions: i, DMF, 10 kbar, room temp., 6 d; ii, fractional crystallization; iii, equilibrium in MeCN
(M+). For 14b: dH(CD3CN) 2.40–2.41 (2 s, 9 H, SCH3), 3.28 (t, J 5.9, 2 H,
SCH2), 4.34 (t, J 6.0, 2 H, OCH2), 5.69 (s, 4 H, NCH2), 5.76 (s, 4 H, NCH2),
6.89 (s, 1 H, Ar), 7.30 (d, J 1.3, 2 H, Ar), 7.60 (s, 4 H, Ar), 8.05 (d, J 6.8,
type. The formation of an intramolecular ‘complex’ by
anchimeric complexation would be expected to follow a first-
order rate equation. In Fig. 1(b) the observed absorption
4 H, b-H), 8.07 (d, J 6.9, 4 H, b-H), 8.74 (d, J 6.9, 4 H, a-H), 8.85 (d, J 7.1,
maxima are plotted against time, and a curve fitted using eqn.
4 H, a-H).
(1)§ confirms that the data are in good agreement with first-
‡ Anchimeric assistance is normally used to describe neighbouring group
order conditions. Of course this is not a final proof for exclusive
participation in a reaction. The expression ‘complexation’ is incorrect when
anchimeric complexation. Nevertheless, since 14b did not
readily undergo intermolecular slipping in dilute solution, we
would not expect this to be likely for 15b either.
used to describe an intramolecular reaction. We suggest using the
expression ‘anchimeric complexation’ to describe the present type of
isomerisation (‘self-complexation’) taking place between two covalently
linked groups.
§ The time-dependence of the absorbance (A) for first-order recomplexa-
tions with rate constant k+ is shown by eqn. (1),
Refluxing the equilibrium solution of 15a,b in MeCN for 45
min caused almost complete conversion to 15b. However, the
next day a CT absorption close to the starting equilibrium
absorption at room temperature was reestablished. This anchi-
meric decomplexation/recomplexation could be repeated.¶
Thus, 15 behaves as a thermal molecular switch, the state of
which is determined by both thermodynamics and kinetics. The
solution of 15a,b was subjected to 10 kbars of pressure (room
temp., 4 days); however, this caused no significant change in
absorption, i.e. in no displacement of the equilibrium.
A = A0 exp[2(k+ + k2)t] + constant·{1 2 exp[2(k+ + k2)t]
where k2 is the rate constant for the decomplexation reaction.
(1)
¶ A small decrease of the equilibrium CT absorption (ca. 5%) was observed
after each experiment, which may be due to a chemical decomposition upon
refluxing.
1 J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1988, 27, 89; 1990, 29,
1304.
2 R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi, S. J. Langford,
S. Menzer, L. Prodi, J. F. Stoddart, M. Venturi and D. J. Williams,
Angew. Chem., Int. Ed. Engl., 1996, 35, 978 and references therein.
3 P. R. Ashton, R. Ballardini, V. Balzani, S. E. Boyd, A. Credi,
M. T. Gandolfi, M. Go´mez-Lo´pez, S. Iqbal, D. Philp, J. A. Preece,
L. Prodi, H. G. Ricketts, J. F. Stoddart, M. S. Tolley, M. Venturi,
A. J. P. White and D. J. Williams, Chem. Eur. J., 1997, 3, 152.
4 (a) Z.-T. Li, P. C. Stein, N. Svenstrup, K. H. Lund and J. Becher, Angew.
Chem., Int. Ed. Engl., 1995, 34, 2524; (b) Z.-T. Li, P. C. Stein, J. Becher,
D. Jensen, P. Mørk and N. Svenstrup, Chem. Eur. J., 1996, 2, 624; (c)
Z.-T. Li and J. Becher, Chem. Commun., 1996, 639; (d) M. B. Nielsen,
Z.-T. Li and J. Becher, J. Mater. Chem., 1997, 7, 1175.
Compounds 14 and 15 were characterized by electrospray
mass spectrometry (ESMS) showing peaks assignable to [M 2
nPF6]n+ (n = 1–4), [M 2 nPF6](n+1)+ (n = 1–3) and [M 2
nPF6](n21)+ (14, n = 3,4). Furthermore, a [2M 2 3PF6]3+ ion
was observed in the gas phase, but whether this is a real dimer
or a dimeric cluster ion cannot be concluded. Collisional
activation (MS/MS) of the mass selected [M 2 4PF6]4+ ions
caused similar fragmentations of the cyclic acceptor, as already
observed for related TTF based catenanes.4d
Notes and References
5 K. B. Simonsen, K. Zong, R. D. Rogers, M. P. Cava and J. Becher, J. Org.
Chem., 1997, 62, 679.
* E-mail: jbe@chem.ou.dk
6 D. Philp, A. M. Z. Slawin, N. Spencer, J. F. Stoddart and D. J. Williams,
J. Chem. Soc., Chem. Commun., 1991, 1584; P. R. Ashton, R. A. Bissel,
R. A. Spencer, J. F. Stoddart and M. S. Tolley, Synlett, 1992, 923;
W. Devonport, M. A. Blower, M. R. Bryce and L. M. Goldenberg, J. Org.
Chem., 1997, 62, 885; P.-L. Anelli, M. Asakawa, P. R. Ashton,
R. A. Bissel, G. Clavier, R. Go´rski, A. E. Kaifer, S. J. Langford,
G. Mattersteig, S. Menzer, D. Philp, A. M. Z. Slawin, N. Spencer,
J. F. Stoddart, M. S. Tolley and D. J. Williams, Chem. Eur. J., 1997, 3,
1113.
7 D. B. Amabilino, P. R. Ashton, M. S. Tolley, J. F. Stoddart and
D. J. Williams, Angew. Chem., Int. Ed. Engl., 1993, 32, 1297.
8 J. Becher, Z.-T. Li, P. Blanchard, N. Svenstrup, J. Lau, M. B. Nielsen and
P. Leriche, Pure Appl. Chem., 1997, 69, 465 and references therein.
† According to plasma desorption mass spectrometry (PDMS), 11 and 12
could not be separated by chromatography from a small amount of the
monobrominated compounds (Cl, Br). All other compounds were obtained
pure and gave satisfactory elemental analyses. Selected data for 5:
dH(CDCl3) 2.41–2.43 (3 s, 9 H, SCH3), 3.21 (t, J 6.4, 2 H, SCH2), 3.95 (s,
6 H, CO2CH3), 4.26 (t, J 6.4, 2 H, OCH2), 7.77 (d, J 1.4, 2 H, Ar.), 8.30 (t,
J 1.4, 1 H, Ar.); PDMS: m/z 610.1 (M+). For 7: dH(CDCl3) 2.40–2.44 (3 s,
9 H, SCH3), 3.18 (t, J 6.5, 2 H, SCH2), 4.21 (t, J 6.7, 2 H, OCH2), 4.68 (d,
J 5.2, 4 H, CH2OH), 6.85 (s, 2H, Ar), 6.97 (s, 1 H, Ar); PDMS: m/z 554.2
(M+). For 9: dH(CDCl3) 2.39–2.45 (3 s, 9 H, SCH3), 3.17 (t, J 4.9, 2 H,
SCH2), 4.21 (m, 2 H, OCH2), 4.55 (s, 4 H, ClCH2), 6.89 (d, J 1.2, 2 H, Ar),
7.02 (s, 1 H, Ar); PDMS: m/z 590.4 (M+). For 11: dH(CDCl3) 2.39–2.44 (3
s, 9 H, SCH3), 3.17 (t, J 6.5, 2 H, SCH2), 4.20 (t, J 6.5, 2 H, OCH2), 4.43
(s, 4 H, BrCH2), 6.86 (d, J 1.1, 2 H, Ar), 7.02 (s, 1 H, Ar); PDMS: m/z 680.2
Received in Liverpool, UK, 29th September 1997; 7/07026H
476
Chem. Commun., 1998