Synthesis and electrochemistry of new tetrathiafulvalene (TTF) dendrimers: X-ray crystal structure of a tetrafunctionalised TTF core unit

Article abstract of DOI:10.1039/a607597e

A new synthetic approach to tetrathiafulvalene (TTF) dendrimers is reported. Tetrakis(4-chloromethylbenzylthio)tetra-thiafulvalene 7 is a functionalised core unit which reacts with four equivalents of the thiolate ion generated from compound 16 to afford

Full text of DOI:10.1039/a607597e

Synthesis and electrochemistry of new tetrathiafulvalene (TTF) dendrimers:
X-ray crystal structure of a tetrafunctionalised TTF core unit
Changsheng Wang, Martin R. Bryce,* Andrei S. Batsanov, Leonid M. Goldenberg and Judith A. K. Howard
Department of Chemistry, University of Durham, Durham DH1 3L E, UK
A new synthetic approach to tetrathiafulvalene (TTF) dendrimers is reported. Tetrakis(4-chloromethylbenzylthio)tetra-
thiafulvalene 7 is a functionalised core unit which reacts with four equivalents of the thiolate ion generated from compound 16 to
aÂord the trisdeca-TTF derivative 3. Compound 3 is a shelf-stable solid which has been characterised by elemental analysis,
MALDI-TOF mass spectrometry, 1H NMR spectroscopy and solution electrochemistry. Thin layer cyclic voltammetry studies on
pentakis-TTF and trisdeca-TTF derivatives 11 and 3 in dichloromethane solution in the presence of 2,3-dichloronaphthoquinone
as an internal reference, show that all the TTF units undergo two single-electron oxidations. The single crystal X-ray structure of
compound 7 is reported: the molecules have crystallographic C symmetry and form chair-like stacks parallel to the
i
crystallographic y axis.
A bourgeoning topic within the arena of nanochemistry1 is the
study of dendritic and hyperbranched macromolecules.2 Of
particular interest is the fact that these materials possess a
high degree of structural order, and their size and architecture
can be precisely controlled in their synthesis, providing unique
molecular scaÂolds for the emplacement of functional groups
in predetermined spatial arrangements.2d,3 A range of substitu-
ents (e.g. crown ethers,4 chiral units,5 polynuclear metal com-
plexes6 and liquid crystal groups7) have recently been appended
to, or embedded within, dendrimer frameworks to impart
special properties to these macromolecules.8,9 A variety of
redox-active organic and organometallic groups have been
incorporated into dendritic and hyperbranched systems10 with
several long-term aims in mind. These include: (i) new electron-
transfer catalysts; (ii) studies on the dynamics of electron
transport at surfaces and within restricted reaction spaces;
(iii) new materials for energy conversion; (iii) organic semi-
conductors; (iv) organic magnets; and (v) mimics of biological
redox processes.
tors,13 because of their propensity to form highly-ordered
stacks along which there is high electron mobility. The stacks
are stabilised by intermolecular p–p interactions and non-
bonded sulfur, sulfur interactions. Most multi-TTF deriva-
tives reported to date14 are dimers,15 although some trimers,16
pentamers,17 higher oligomers18 and main-chain and side-chain
polymeric TTFs19 are now known. A key feature of these
multi-TTF systems is that they generally yield multiply-charged
species upon electrochemical oxidation in solution.
In our initial work on TTF dendrimers, a convergent strategy
based on a repetitive coupling/deprotection sequence, using 4-
(hydroxymethyl)-TTF as the starting monomer, furnished den-
drimer 1 comprising a benzene-1,3,5-triester core, and surface-
functionalised with twelve TTF units.12 A conceptually similar
synthesis using a 4,4∞-biphenyl ether diester core gave the
octakis-TTF system 2 possessing a more open structure than
analogue 1.20 The solution electrochemical redox behaviour of
systems 1 and 2 was studied by classical cyclic voltammetry
(CV), cyclic voltammetry with ultramicroelectrodes (UME
CV) and chronoamperometry.12,20,21 For compound 1, the CV
waves were quasi-reversible, with slight broadening, which
became more noticable with repeated scans, when the second
TTF oxidation peak became irreversible and deposition of
material on the electrode surface was observed: each wave
represented a multi-electron transfer with essentially no inter-
action between the charged TTF units. We were unable to
establish unambiguously the number of electrons involved in
each redox wave for compounds 1 and 2: the diÂerent diÂusion
rates of the internal standard (2,3-dichloronaphthoquinone)
and the dendrimer could readily account for the apparent
incomplete oxidation of all the TTF units. (Scanning to higher
potentials showed no further oxidation waves, precluding the
presence of any TTF groups buried within the dendrimer
structure.)
Some dendrimer systems contain a single redox-active unit
(e.g. a metalloporphyrin)11 at the core, for which the key issue
is generally to observe how the redox behaviour of this central
‘encapsulated’ group is modulated by the shielding eÂect of
the rest of the dendrimer structure, which should provide a
more compact insulating layer than would an analogous linear
polymer. The majority of studies, however, concern multiple
redox units (e.g. polynuclear metal complexes)6 emplaced
within the branches and/or at peripheral sites, where the redox
groups may act independently in multi-electron processes (n
identical electroactive centres which undergo electron transfer
in a single n-electron wave) or they may interact intra- or
inter-molecularly (overlapping or closely-spaced redox waves
at diÂerent potentials).
We first recognised12 that tetrathiafulvalene (TTF) units
oÂered considerable potential as components of novel redox-
active dendrimers. The incorporation of TTF into dendrimers
presents a fascinating prospect for the following reasons:
(i) oxidation of the TTF ring system to the cation radical and
dication species occurs sequentially and reversibly at very
accessible potentials in a range of organic solvents (for unsub-
stituted TTF, E 1/2=+0.34 and E 1/2=+0.78 V, vs. Ag/AgCl
Herein we report an entirely diÂerent approach to TTF
dendrimers which has culminated in the synthesis of macro-
molecule 3 comprising thirteen TTF units. There are several
novel features of this work: (i) TTF units are emplaced at all
layers of the structural hierarchy (unlike compounds 1 and 2);
(ii) compound 7 is presented as a new, versatile building
block for macromolecular TTF assemblies, and its single
crystal structure is described; (iii) thin layer cyclic
voltammetry (TLCV) has been applied to redox-active den-
drimer systems for the first time, and it is clear that all the
TTF groups of 3 are involved in the solution electrochemical
redox processes.
1
2
in acetonitrile); (ii) the oxidation potentials can be finely tuned
by the attachment of appropriate substituents; (iii) the TTF
cation radical is thermodynamically very stable; and (iv) oxi-
dised TTF units are key components of molecular conduc-
J. Mater. Chem., 1997, 7(7), 1189–1197
1189

Me
Me
S
S
S
S
Me
Me
S
S
S
S
S
S
SMe
MeS
S
S
S
S
Me
Me
S
S
S
S
S
S
S
S
S
S
SMe
MeS
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
SMe
MeS
Me
Me
S
S
S
S
S
S
S
S
Me
Me
SMe
S
MeS
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
SMe
MeS
S
S
S
S
S
S
S
S
S
S
Me
Me
S
S
S
S
S
S
SMe
MeS
S
S
S
S
S
S
Me
Me
S
S
3
Me
Me
1190
J. Mater. Chem., 1997, 7(7), 1189–1197

by a combination of elemental analysis, MALDI TOF mass
spectrometry and 1H NMR spectroscopy. In particular, the
MALDI TOF spectrum of 3, showed a parent ion peak at m/z
Results and Discussion
Synthesis
7377 (M+, calc. for C
H
S
, 7372) with several other
Zincate salt 422 reacted with a-chloro-p-xylene 5a or with
a,a∞-dichloro-p-xylene 5b to yield 4,5-disubstituted 1,3-dithi-
ole-2-thione derivatives 6a (90% yield) and 6b (60% yield),
respectively. The latter was converted to the ketone 6c (84%
yield) using the standard mercuric acetate procedure
(Scheme 1). Compound 7 was synthesised in 78% yield by
self-coupling of 6c in the presence of triethyl phosphite under
standard conditions,23 and isolated as orange crystals suitable
for X-ray analysis (see below). Compound 7 is our key core
unit and displacement of the benzylic chlorines by thiolate
anions proved to be a facile process. We identified 10 as a
promising building block from which a reactive thiolate anion
could be generated, following the protocol developed by
Becher and coworkers for related cyanoethyl-protected TTF-
thiolate systems.24 Accordingly, compound 6a was cross-
coupled with ketone 8 to furnish TTF derivative 9 in 67%
yield (Scheme 2). Sequential deprotection of 9 allowed unsym-
metrical substitution reactions. Initial treatment of 9 with
caesium hydroxide (1.05 equiv.), followed by methylation of
the resulting monothiolate anion, aÂorded 10 (96% yield)
which was deprotected using a second equivalent of caesium
hydroxide to yield the caesium salt of the thiolate anion of
10, four equivalents of which reacted with 7 to yield the
pentakis-TTF derivative 11 in almost quantitative yield.
Compound 11 was purified by column chromatography and
isolated as a yellow–brown solid. The parent molecular ion
of 11 was observed in the matrix-assisted laser desorption
time-of-flight (MALDI TOF) mass spectrum at m/z 2964
314 276 104
peaks observed in the spectrum due to fragmentation of the
parent molecule.
Solution electrochemistry
The solution redox properties of compounds 3,7,9–11,15 and
16 in benzonitrile are collated in Table 1, together with data
for TTF for comparison. All these new compounds exhibited
two redox couples typical of the TTF system25 and for the
multi-TTF derivatives there was no apparent interaction
between the diÂerent TTF units. The redox waves were revers-
ible, at least up to scan rates of 500 mV s−1: the criterion
applied for reversibility was a ratio of 1.0±0.5 for the intensities
of the cathodic and anodic currents I /I , and no shift of the
c
a
half wave potentials with varying scan rates. The attachment
of thioalkyl substituents to the TTF ring is known to raise the
oxidation potential25,26 (an additive eÂect has been noted for
one, two and four thioalkyl substituents)26 and the new com-
pounds in Table 1 follow this trend. It is notable that the
values of both the first and second redox potentials appear to
be further raised slightly by the presence of the cyanoethyl
groups (viz. compounds 9, 10 and 15), although for compound
16 inequivalence of the TTF groups (only one of which carries
a cyanoethyl group) was not observed.
More significant are the results of thin layer cyclic voltam-
metric (TLCV) studies on compounds 11 and 3, which contain
five and thirteen TTF units, respectively. In contrast to conven-
tional cyclic voltammetry, in TLCV27 the current is not limited
by the kinetics of mass transfer to the electrode. TLCV has
been applied recently to the detection of mixed valence states
in TTF and its derivatives.28 However, we are not aware of
any reports of this technique being applied to multi-TTF
systems or to redox-active dendrimers. As mentioned above,
classical CV, UME CV and chronoamperometry had pre-
viously given inconclusive results concerning the number of
electrons involved in the redox waves of compounds 112,21 and
2.20,21 For other multi-TTF systems (e.g. pentamers) oxidation
of all the TTF units had been assumed, based on the shapes
of the CV waves, but not rigorously established.17 For other
dendrimers and branched systems containing multiples of
structurally very similar (or identical) redox groups (e.g. ferro-
cene29 and related iron sandwiches30) the extent of oxidation
of the system can be calculated using formulae which take into
(M+, calc. for C
H
S
; 2956).
130 116 40
An analogous synthetic protocol enabled assembly of the
trisdeca-TTF derivative 3, which can be viewed as a second
generation dendrimer. For this synthesis we needed the mono-
thiolate derivative of 16 as the reactive ‘wedge’ to undergo
four-fold reaction with core reagent 7. The synthesis of 3 is
shown in Scheme 3. Compound 13 was prepared in high yield
by the literature route from 12,24b and converted into ketone
14 (98% yield) using mercuric acetate. Cross-coupling of
equimolar amounts of thione 6b and ketone 14, in the presence
of triethyl phosphite, gave compound 15 in an optimised yield
of 45%. By direct analogy with the preparation of 11, com-
pound 15 was converted into 16 in 74% yield. The caesium
thiolate salt of 16 (4 equiv.) reacted cleanly with compound 7
to furnish compound 3 in 66% yield as an air-stable yellow–
brown solid. Compound 3 was characterised unambiguously
Y
Cl
S
S
S
S
S
S
2-
S
S
S
S
i
X
+
S
Zn
S
+
(NEt4
)
2
Y
S
S
5a Y = H
b Y = Cl
Y
4
6 a X = S Y = H
b X = S Y = Cl
ii
c X = O Y = Cl
Cl
Cl
Cl
iii
S
S
S
S
S
S
S
S
Cl
7
Scheme 1 Reagents and conditions: i, acetone, reflux; ii, Hg(OAc) , CHCl –MeCO H, 20 °C; iii, P(OEt) , 120°C
2
3
2
3
J. Mater. Chem., 1997, 7(7), 1189–1197
1191

CN
CN
S
S
S
S
O
6a
+
8
i
Me
Me
CN
CN
CN
S
S
S
S
S
S
S
S
S
S
S
S
S
S
ii
S
SMe
10
9
Me
Me
iii
Me
Me
S
S
S
S
S
S
S
S
SMe
MeS
Me
S
S
Me
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
Me
S
S
Me
SMe
MeS
S
S
S
S
S
S
S
S
11
Me
Me
Scheme 2 Reagents and conditions: i, P(OEt) , 120 °C; ii, CsOH.H O (1.05 equiv.) DMF–MeOH, 20 °C, followed by MeI; iii, CsOH·H O,
3
2
2
DMF–MeOH, then compound 7, 20–50°C
account the diÂerent diÂusion coeÃcients of a model com-
pound and the dendrimer.31 A very elegant alternative method
is provided by certain macromolecules which contain within
their structure two (or more) diÂerent redox units in a known
ratio, which are oxidised or reduced at diÂerent potentials,
thereby providing a covalently-bound internal reference.6,32
However, this is not the case with the compounds herein where
all the TTF units are tetrathio-substituted.
the voltammetric waves, the number of electrons exchanged
per oxidation wave was calculated to be five for compound 11
(which contains five TTF units) and 12–14 (E ) and 11–12
1
(E ) for compound 3 (which contains 13 TTF units). These
2
data clearly suggest that complete oxidation occurs for all the
TTF units in compounds 11 and 3. For compound 3, the small
variation in the number of electrons calculated for diÂerent
experiments is within reasonable experimental limits, given the
very small quantities of the compound used and the large
number of TTF groups present. We note that for both com-
pounds 11 and 3 the second TTF oxidation wave was slightly
narrower than the first wave, which was probably due to
TLCV studies were conducted on known concentrations of
compounds 11, 3 and 2,3-dichloronaphthoquinone (DCNQ)
in dichloromethane solution. The one-electron reduction peak
of DCNQ provided the internal reference, and by integrating
1192
J. Mater. Chem., 1997, 7(7), 1189–1197

Cl
Cl
CN
CN
CN
CN
S
S
S
S
S
S
S
S
S
S
S
S
S
S
i
iii
S
X
SMe
SMe
12
13 X = S
14 X = O
15
ii
iv
Me
S
S
SMe
S
S
S
S
S
CN
Me
Me
S
S
S
S
S
S
S
SMe
S
S
S
S
S
S
S
SMe
16
Me
v
3
Scheme 3 Reagents and conditions: i, CsOH.H O (1 equiv.), DMF–MeOH, 20°C, followed by MeI; ii, Hg(OAc) , CHCl –MeCO H, 20 °C;
2
2
3
2
iii, compound 6b, P(OEt) , 125 °C; iv, compound 10, CsOHΩH O (1 equiv.), DMF–MeOH, then compound 15, 20°C; v, CsOH.H O,
3
2
2
DMF–MeOH, then compound 7, 20–80°C
Table 1 Solution redox properties of compounds 3,7,9–11,15 and 16a
compound
E 1/2/V
E 1/2/V
1
2
TTF
7
0.34
0.57
0.58
0.67
0.63
0.56
0.64
0.57
0.78
0.90
0.92
1.01
0.97
0.89
0.98
0.90
3
9
10
11
15
16
aPlatinum electrodes, supporting electrolyte Bu NPF (0.1 ) in
Fig. 1 TLCV of dendrimer 3 (0.5×10−4 ) and 2,3-dichloronaphtho-
quinone (6.4×10−4 ) as internal reference, in Bu NClO
4
6
benzonitrile, scan rate 100 mV s−1 versus Ag/AgCl.
4
4
(1 )–CH Cl solution, reference vs. Ag/Ag+, scan rate 5 mV s−1
2
2
adsorption phenomena. Fig. 1 shows the TLCV of compound
3 in the presence of DCNQ.
mation of all the substituents in 7 is profoundly out-of-(the
TTF)plane. Thus the overall molecular conformation is similar
to those in other TTF derivatives with long linear-chain
substituents,33 and so is the crystal packing. The molecules
form a stair-like stack in the direction parallel to the crystallo-
graphic y axis, in which the TTF planes are parallel with
X-Ray crystal structure of compound 7
Compound 7 is a functionalised, four-directional core unit
which oÂers considerable potential for future studies. It was of
interest, therefore, to establish the structure of 7 in the solid
state. The single crystal X-ray structure reveals that the mol-
˚
interplanar separations of ca. 3.6 A. The adjacent TTF moieties
ecule has a crystallographic C symmetry (Fig. 2). The TTF
in the stack overlap through only one dithiole ring each.
Apparently, the more eÂective (and more common) ring-over-
bond (i.e. the central CNC bond) overlap is prevented by the
steric bulk of the substituents.
i
moiety displays a chair-like distortion, the dithiole rings folding
by 6.4° along the S, S vectors. One of the two independent 4-
(chloromethyl)benzyl substituents is ordered, while the other
one is disordered over two positions (A and B) with approxi-
mately equal occupancies, diÂering in the torsion angles around
the S(3)–C(2), S(3)–C(4), C(4)–C(5) and C(8)–C(11) bonds
(by 30, 27, 81 and 27°, respectively) and consequently in the
orientation of the benzene ring plane (by 44°), but basically
occupying the same area of space (the positions of the terminal
It is noteworthy that in the crystal the disordered side-chain
of 7 is surrounded by such chains of other molecules on three
sides (the ordered chain of the same molecule being on the
fourth side) viz. two parallel chains of the neighbours within
the stack and one antiparallel chain of the inversion-equivalent
molecule of another stack. Thus the structure contains a vast
˚
˚
chlorine atom diÂer by only 0.67 A). In any case, the confor-
area of disorder, in the form of a wide (ca. 10×10 A) infinite
J. Mater. Chem., 1997, 7(7), 1189–1197
1193

Fig. 2 Molecular structure of 7. Position A of the disordered chain is shown solid, position B dashed. Primed atoms are symmetry-related via
˚
the inversion centre. Selected bond distances (A): C(1)–S(1) 1.752(7), C(1)–S(2) 1.754(8), S(1)–C(2) 1.759(7), S(2)–C(3) 1.761(7), C(1)–C(1∞)
1.345(13), C(2)–C(3) 1.342(9), C(2)–S(3) 1.755(7), C(3)–S(4) 1.738(7).
channel parallel to the y axis. It is not clear whether the choice
between the A and B positions of a chain is aÂected by that
of the adjacent chains or can be independent from them. The
shortest intermolecular contacts between these positions,
irradiation from a nitrogen laser at 337 nm. The matrix was
2,5-dihydroxybenzoic acid and spectra were averaged over 100
pulses whilst scanning across the sample: peak half-widths
were between 6–10 amus. Melting points were obtained on a
Reichert hot-stage microscope apparatus and are uncorrected.
Electrochemical data were obtained on a BAS CV-50W
Voltammetric Analyser. The counter, working and reference
electrodes were Pt wire, Pt disc (1.6 mm diameter from BAS)
and Ag/AgCl, respectively. Cyclic voltammetry was performed
under argon using IR compensation. The thin layer cyclic
voltammetry cell used in this work was constructed as
described previously.27b
˚
interstack C(4A), C(6A) 3.43 and C(6A), C(6A) 3.36 A and
˚
intrastack C(7B), C(10B) 3.36 A, are not prohibitively short.
Conclusions
We have developed new expedient methodology for the syn-
thesis of TTF-based dendrimers which possess well-defined
redox activity, notably the trisdeca-TTF derivative 3. The
methodology should be applicable to higher generation TTF
systems. Thin layer cyclic voltammetry has demonstrated that
the electrochemical oxidation of these macromolecules involves
all of the TTF units, and in these experiments there was no
observable interaction between the redox sites. These data
support our earlier suggestion10 that the TLCV technique
should be well-suited to electrochemical studies on dendritic
macromolecules containing multiple redox centres. Several new
functionalised TTF and multi-TTF reagents, e.g. compounds
7 and 16, synthesised during the course of this work are now
readily-available in synthetically useful quantities, and they
oÂer great potential as reactive building blocks in the assembly
of supramolecular34 and polymeric TTF systems. In particular,
by virtue of the four reactive benzylic halide groups at the
periphery of 7 this molecule is a very attractive core unit for
future studies, and the facile deprotection of 16, to generate a
reactive thiolate anion, makes this system eminently suited to
a range of further synthetic transformations.
4,5-Bis(4-methylbenzylthio)-1,3-dithiole-2-thione 6a†
A mixture of zincate salt 422 (7.2 g, 10 mmol) and a-chloro-p-
xylene 5a (11.25 g, 80 mmol) in acetone (60 ml) was refluxed
for 1 h. The red solid which precipitated during the reaction
was removed by filtration, then the filtrate was concentrated
in vacuo aÂording a bright yellow solid, recrystallisation of
which from ethanol yielded yellow needles of 6a (7.50 g, 90%),
mp 85–86 °C (Found: C, 55.85; H, 4.42. C H S requires C,
19 18 5
56.11; H, 4.46%); d (CDCl ) 2.33(s, 6H), 3.89 (s, 4H), 7.12
H
3
(s, 8H).
4,5-Bis(4-chloromethylbenzylthio)-1,3-dithiole-2-thione 6b
By analogy with 6a, compound 4 (3.6 g, 5 mmol) and a,a∞-
dichloro-p-xylene 5b (10.5 g, 60 mmol) in acetone (150 ml)
gave yellow needles of 6b (2.86 g, 60%) after purification by
column chromatography [silica, eluent: dichloromethane–light
petroleum (bp 40–60 °C), 151 (v/v)], mp 123.5–124.5°C
(Found: C, 48.03; H, 3.39; C H Cl S requires C, 48.00; H,
19 16 2 5
Experimental
3.39 d (CDCl ) 3.91 (s, 4H), 4.57 (s, 4H), 7.23 (d, 4H, J 8.2),
H
3
General
7.35 (d, 4H, J 8.2).
All reagents and solvents were of commercial quality and were
dried where necessary using standard procedures. 1H NMR
Spectra were obtained on a VXR 200 spectrometer operating
at 200.14 MHz. MALDI TOF Mass spectra were obtained on
a Kratos IV instrument in the reflection mode, operating with
† Compound 6a has recently been prepared independently in 75%
yield by a similar route in Professor Becher’s laboratory (R. P.
Clausen and J. Becher, T etrahedron, 1996, 52, 3171). We thank
Professor Becher for bringing this reference to our attention.
1194
J. Mater. Chem., 1997, 7(7), 1189–1197

4,5-Bis(4-chloromethylbenzylthio)-1,3-dithiol-2-one 6c
was stirred at 20 °C overnight to obtain a brown–red solution.
Compound 7 (130 mg, 0.146 mol) was then added in one
portion and the mixture was aggitated with ultrasound for
10 min, followed by stirring at 20 °C for 1 h and then at 50 °C
for 4 h, to aÂord a precipitate. The reaction mixture was
evaporated in vacuo and water (20 ml) was added to the
residue. A brown–yellow solid was collected by filtration and
washed with a large amount of methanol. Column chromatog-
raphy of the solid [silica, eluent: dichloromethane–light pet-
roleum (bp 40–60°C), 251 (v/v)] gave compound 11 (430 mg,
99.5%) as an amorphous yellow–brown solid, mp ca. 150 °C
To a solution of compound 6b (3.5 g, 7.36 mmol) in a mix-
ture of chloroform and acetic acid (80 ml; 351, v/v), mercuric
acetate (7.0 g, 22 mmol) was added and the mixture was stirred
at 20 °C overnight. Filtration of the product through Celite
and evaporation of the filtrate yielded a yellow oil, which was
washed with 5% aqueous NaHCO (100 ml) and filtered to
3
give a pale yellow solid, which was chromatographed on a
silica column [eluent: light petroleum (bp 40–60°C)–di-
chloromethane, 151 (v/v)] aÂording 6c as oÂ-white crystals
(2.85 g, 84%), mp 67–68.5 °C (Found: C, 49.59; H, 3.46;
C H Cl OS requires C, 49.66; H, 3.51%); d (CDCl ) 3.87
(Found: C, 52.45; H, 3.93. C
H
S
requires C, 52.73; H,
130 116 40
19 16
2
4
H
3
3.95%); m/z (MALDI-TOF) 2964 (M+ calc. 2956); d (CDCl )
H
3
(s, 4H), 4.56 (s, 4H), 7.22 (d, 4H, J 8.2), 7.34 (d, 4H, J 8.2).
2.22 (s, 12H), 2.31 (s, 24H), 3.81 (s, 8H), 3.83 (s, 8H), 3.85 (s,
8H), 3.97 (s, 8H), 7.1–7.3 (m, 48H).
Tetrakis(4-chloromethylbenzylthio)tetrathiafulvalene 7
Compound 6c (2.8 g, 6.09 mmol) in triethyl phosphite (25 ml)
was stirred under argon and heated at 120 °C for 1 h. The
mixture was cooled to 20°C and methanol (70 ml) was added.
The precipitate was collected by filtration and washed with a
large volume of methanol, followed by purification by column
chromatography (silica, eluent: dichloromethane), aÂording
compound 7 as orange crystals (2.1 g, 78%), mp 181–183 °C,
which after recrystallisation from carbon disulfide gave red
needles which were suitable for X-ray analysis (Found: C,
4-(2-Cyanoethylthio)-5-methylthio-1,3-dithiole-2-thione 13
Following the reported method,24b reaction of compound 1222b
(1.5 g, 4.93 mmol) in DMF (30 ml) with CsOH·H O (0.83 g,
2
4.94 mmol) in methanol (30 ml) at 20 °C followed by addition
of methyl iodide (1.5 ml) gave a product which was purified
by column chromatography (silica, eluent: dichloromethane)
to yield 13 as yellow crystals (1.2 g, 92%), mp 88–89 °C (Found:
C, 31.56; H, 2.62; N, 4.91. C H NS requires C, 31.67; H, 2.66;
7
7
5
N, 5.28%); d (CDCl ) 2.56 (s, 3H), 2.76 (t, 2H, J 7.0), 3.09 (t,
51.40; H, 3.63. C H Cl S requires C, 51.46; H, 3.64%);
38 32 4 8
H
3
2H, J 7.0).
d (CDCl ) 3.84 (s, 8H), 4.56 (s, 8H), 7.24 (d, 8H, J 8.2), 7.34
H
3
(d, 8H, J 8.2).
4-(2-Cyanoethylthio)-5-methylthio-1,3-dithiol-2-one 14
4,5-Bis(2-cyanoethylthio)-4∞,5∞-bis(4-methylbenzylthio)tetrathia-
To the solution of 13 (1.2 g, 4.52 mmol) in a mixture of
chloroform and acetic acid [351 (v/v), 40 ml], mercuric acetate
(4.0 g, 12.6 mmol) was added and the mixture was stirred at
20°C overnight. Filtration of the product mixture through
Celite and evaporation of the filtrate yielded a yellow residue,
which was dissolved in dichloromethane and washed with
fulvalene 9
A mixture of compound 822b (2.88 g, 10 mmol), compound 6a
(6.10 g, 15 mmol) and triethyl phosphite (50 ml) was heated
with stirring at 120 °C for 75 min under argon. Ethanol (50 ml)
was added to the reaction mixture which was then cooled to
20 °C. The orange solid which precipitated was collected by
filtration, washed with a large volume of ethanol and then
chromatographed (silica column, eluent: dichloromethane) to
aÂord compound 9 (4.36 g, 67%) as orange needles, mp
142–143.5 °C (from ethanol–dichloromethane) (Found: C,
saturated NaHCO solution. The organic phase was separated,
3
dried over MgSO , concentrated and chromatographed (silica
4
column, eluent: dichloromethane), aÂording white needles of
14 (1.1 g, 98%), mp 57.5–58.5°C (Found: C, 33.42; H, 2.78; N,
5.24. C H NOS requires C, 33.71; H, 2.83; N, 5.62%); d
7
7
4
H
(CDCl ) 2.52 (s, 3H), 2.75 (t, 2H, J 7.0), 3.08 (t, 2H, J 7.0).
52.05; H, 3.99; N, 4.37. C H N S requires C, 51.98; H, 4.05;
28 26 2 8
3
N, 4.33%); d (CDCl ) 2.32 (s, 6H), 2.75 (t, 4H, J 7.0), 3.09 (t,
H
3
4H, J 7.0), 3.85 (s, 4H), 7.13 (s, 8H).
4-(2-Cyanoethylthio)-5-methylthio-4∞,5∞-bis(4-chloromethyl-
benzylthio)tetrathiafulvalene 15
4-(2-Cyanoethylthio)-5-methylthio-4∞,5∞-bis(4-methylbenzyl-
A mixture of 14 (125 mg, 0.5 mmol) and 6b (238 mg, 0.5 mmol)
in triethyl phosphite (5 ml) was heated to 125 °C and stirred
under argon for 1.5 h. The mixture was evaporated in vacuo
and the orange oily residue was chromatographed on a silica
column (eluent: dichloromethane), aÂording 15 as an orange
solid (153 mg, 45%), mp 146.5–148.5 °C (Found: C, 46.15; H,
3.38; N, 1.64. C H Cl NS requires C, 46.13; H, 3.42; N,
thio)tetrathiafulvalene 10
To a stirred solution of compound 9 (3.0 g, 4.64 mmol) in
dimethylformamide (30 ml) under argon at 20 °C, a solution
of CsOH·H O (0.82 g, 4.88 mmol) in methanol (25 ml) was
2
added dropwise over 2 h. Stirring was continued for 1 h at
20 °C, then methyl iodide (4.5 ml) was added and the mixture
was stirred for a further 1 h. Evaporation of the reaction
mixture in vacuo gave an orange residue, which was dissolved
in dichloromethane (50 ml) and washed with water, then the
26 23
2
8
2.07%); d (CDCl ) 2.48 (s, 3H), 2.72 (t, 2H, J 7.0), 3.04 (t, 2H,
H
3
J 7.0 ), 3.85 (s, 4H), 4.57 (s, 4H), 7.25 (d, 4H, J 8.2), 7.34 (d,
4H, J 8.2).
organic layer was separated and dried over MgSO . Column
4
chromatography of the concentrated solution (silica, eluent:
4,5-Bis(4-{[4∞,5∞-bis(4-methylbenzylthio)-5-methylthiotetrathia-
fulvalen-4-yl]thiomethyl}benzylthio)-4∞-(2-cyanoethylthio)-5’-
methylthiotetrathiafulvalene 16
dichloromethane) yielded an orange solid which crystallised
from ethanol–chloroform as orange needles (2.24 g, 92%) mp
135–136.5 °C (Found: C, 51.15; H, 4.07; N, 2.08. C H NS
26 25
8
By analogy with the preparation of compound 11, compound
requires C, 51.36; H, 4.14; N, 2.03%); d (CDCl ) 2.32 (s, 6H),
H
3
16 was synthesized from 10 (277 mg, 0.456 mmol) in DMF
2.48 (s, 3H), 2.71 (t, 2H, J 7.2), 3.03 (t, 2H, J 7.2), 3.84 (s, 4H),
(20 ml), CsOHΩH O (76.5 mg, 0.456 mmol) in methanol (4 ml)
7.13 (s, 8H).
2
and compound 15 (154 mg, 0.227 mmol) at 20°C with stirring
for 6 h. Purification was achieved by vacuum evaporation,
washing with water and chromatography on a silica column
(eluent: chloroform) to yield 16 (298 mg, 74%) as an orange
4,4∞,5,5∞-Tetrakis(4-{[4∞,5∞-bis(4-methylbenzylthio)-5-methylthio-
tetrathiafulvalen-4-yl]thiomethyl}benzylthio)tetrathiafulvalene 11
To the stirred solution of 10 (358 mg, 0.589 mmol) in degassed
solid, mp 55 °C (Found: C, 49.77; H, 3.77; N, 0.72. C H NS
72 65 24
DMF (20 ml) under argon, CsOHΩH O (99.4 mg, 0.59 mmol)
requires C, 50.46; H, 3.83; N, 0.82%); m/z 1710.84200 (M+
2
in methanol (2 ml) was added in one portion. The mixture
calc. 1710.84142); d (CDCl ) 2.22 (s, 6H), 2.30 (s, 12H), 2.44
H
3
J. Mater. Chem., 1997, 7(7), 1189–1197
1195

3
4
5
P. Hodge, Nature, 1993, 362, 18.
(s, 3H), 2.56 (t, 2H, J 6.7), 2.97 (t, 2H, J 6.7), 3.81 (s, 4H), 3.83
T. Nagasaki, O. Kimura, M. Ukon, S. Arimori, I. Hamachi and
S. Shinkai, J. Chem. Soc., Perkin T rans 1, 1994, 75.
(s, 4H), 3.85 (s, 4H), 3.96 (s, 4H), 7.1–7.3 (m, 24H).
(a) G. R. Newkome, X. Liu and C. D. Weis, T etrahedron:
Asymmetry, 1991, 2, 957; (b) J. F. G. A. Jansen, H. W. I. Peerlings,
E. M. M. de Brabander-Van den Berg and E. W. Meijer, Angew.
Chem., Int. Ed. Engl., 1995, 34, 1206.
4,4∞,5,5∞-Tetrakis(4-{[4∞,5∞-bis(4-{[4∞,5∞-bis(4-methylbenzylthio)-
5-methylthiotetrathiafulvalen-4-yl]thiomethyl}benzylthio)-5-
methylthiotetrathiafulvalen-4-yl]thiomethyl}benzylthio)tetra-
thiafulvalene 3
6
7
S. Campagne, G. Denti, S. Serroni, A. Juris, M. Venturi,
V. Ricevuto and V. Balzani, Chem. Eur. J., 1995, 1, 211.
(a) V. Percec, P. Chu and M. Kawasumi, Macromolecules, 1994, 27,
By analogy with the synthesis of compound 11, compound 3
was synthesized from compound 16 (178 mg, 0.104 mmol) in
4441; (b) K. Lorenz, D. Holter, B. Stuhn, R. Mulhaupt and H. Frey,
¨
¨
¨
Adv. Mater., 1996, 8, 414.
DMF (10 ml), CsOHΩH O (20 mg, 119 mmol) in methanol
2
8
For reviews which emphasise the functional properties of dendri-
(1.5 ml) and compound 7 (23 mg, 0.0259 mmol) with stirring
mers see: (a) J. Issberner, R. Moors and F. Vogtle, Angew. Chem.,
¨
for 3 h, both at 20°C and at 80 °C. After work-up, the dark
yellow filtrate was filtered through alumina 90 using a short
column (eluent: chloroform). The resultant solid was then
triturated with DMF (2×10 ml) to give compound 3 as a light
brown tar, which solidified into an amorphous solid (126 mg,
66%), mp ca. 75 °C, upon trituration with a large amount of
Int. Ed. Engl., 1994, 33, 2413; (b) R. Moors and F. Vogtle, in
¨
Advances in Dendritic Macromolecules, ed. G. R. Newkome, JAI
Press, London, 1996, vol. 2, p.41.
9
For an article summarising recent publications on functional den-
drimers, see R. Dagani, Chem. Eng. News, June 3, 1996, 30.
10 For a review of redox-active dendrimers, see M. R. Bryce and
W. Devonport, in Advances in Dendritic Macromolecules, ed.
G. R. Newkome, JAI Press, London, 1996, vol. 3, p.115.
methanol (Found: C, 50.81; H, 3.79. C
H
S
requires C,
314 276 104
51.07; H, 3.77%); m/z (MALDI-TOF) 7377 (M+ calc. 7372);
11 (a) P. J. Dandliker, F. Diederich, M. Gross, C. B. Knobler,
A. Louati and E. M. Sanford, Angew. Chem., Int. Ed. Engl., 1993,
33, 1739; (b) P. J. Dandliker, F. Diederich, J-P. Gisselbrecht, A
Louati and M. Gross, Angew. Chem., Int. Ed. Engl., 1994, 34, 2725.
12 M. R. Bryce, W. Devonport and A. J. Moore, Angew. Chem., Int.
Edn. Engl., 1994, 33, 1761.
d (CDCl ) 2.21 (s, 36H), 2.30 (s, 48H), 3.82 (s, 56H), 3.95 (s,
H
3
24H), 7.11(s) and 7.21 (m, 112H).
Crystal structure determination of compound 7
The X-ray diÂraction experiment was performed on a Siemens
3-circle diÂractometer with a CCD area detector, using graph-
13 (a) J. R. Ferraro and J. M. Williams, Introduction to Synthetic
Electrical Conductors, Academic Press, London, 1987;
(b) M. R. Bryce, Chem. Soc. Rev., 1991, 20, 355; (c) A. E. Underhill,
J. Mater. Chem., 1992, 2, 1; (d) J. Mater. Chem., Special Issue on
Molecular Conductors, 1995, 5, 1469.
˚
ite-monochromated Mo-Ka radiation, l =0.71073 A. Crystal
data: C H Cl S , M=886.9, monoclinic, space group P2 /c
38 32 4 8
1
˚
(No.14), a=12.706(2), b=5.789(1), c=28.159(3) A, b=
14 Review: M. Adam and K. Mu¨llen, Adv. Mater., 1994, 6, 439.
15 (a) M. Jørgensen, K. A. Lerstrup and K. Bechgaard, J. Org. Chem.,
1991, 56, 5684; (b) M. R. Bryce, G. J. Marshallsay and A. J. Moore,
J. Org. Chem., 1992, 57, 4859; (c) I. V. Sudmale, G. V. Tormos,
V. Yu. Khodorkovsky, A. S. Edzina, O. J. Neilands and
M. P. Cava, J. Org. Chem., 1993, 58, 1355; (d) L. M. Goldenberg,
V. Yu. Khodorkovsky, J. Y. Becker, M. R. Bryce and M. C. Petty,
J. Mater. Chem., 1995, 5, 191; (e) J. Y. Becher, J. Bernstein,
A. Ellern, H. Gershenman and V. Khodorkovsky, J. Mater. Chem.,
1995, 5, 1557; ( f ) Review: T. Otsubo, Y. Aso and K. Takimiya, Adv.
Mater., 1996, 8, 203.
˚
99.69(1)°, V=2041.7(5) A3, Z=2, D =1.44 g cm−3, F(000)=
c
912, m=7.3 cm−1, crystal size 0.32×0.18×0.08 mm, v scan
mode, 2h≤52°, 10429 total, 3515 unique, 1978 observed
[|F|>4s (F)] data, R (F2)=0.060. The structure was solved
int
by direct methods and refined by full-matrix least squares
against F2 of all data, using SHELXTL software.35 The C(4)
to C(11) and Cl(1) atoms were refined as disordered over two
positions (A and B) with equal occupancies and their geo-
metries restrained to similarity. The refinement (ordered non-
H atoms anisotropic, disordered ones isotropic, H atoms
‘riding’, 217 variables, 145 restraints) converged at wR(F2, all
data)=0.247, R(F, obs. data)=0.079, goodness-of-fit 1.07.
16 (a) F. Gerson, A. Lamprecht and M. Fourmigue, J. Chem. Soc.,
´
Perkin T rans. 2, 1996, 1409; (b) M. Adam, E. Fanghanel, K. Mullen,
¨
¨
Y-J. Shen and R. Wegner, Synth. Met., 1994, 66, 275; (c) R. P. Parg,
J. D. Kilburn, M. C. Petty, C. Pearson and T. G. Ryan, J. Mater.
Chem., 1995, 5, 1609; (d) Z-T. Li and J. Becher, Chem. Commun,
1996, 639.
Residual electron density features: Dr
=0.64, Dr
=
max
min
˚
−0.74 eA−3.
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge
Crystallographic Data Centre (CCDC). See Information for
Authors, J. Mater. Chem., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 1145/30.
17 (a) G. J. Marshallsay, T. K. Hansen, A. J. Moore, M. R. Bryce and
J. Becher, Synthesis, 1994, 926; (b) J. Lau, O. Simonsen and
J. Becher, Synthesis, 1995, 521.
18 M. A. Blower, M. R. Bryce and W. Devonport, Adv. Mater., 1996,
8, 63.
19 S. Frenzel, S. Arndt, R. Ma. Gregoroius and K. Mullen, J. Mater.
¨
Chem., 1995, 5, 1529.
20 M. R. Bryce and W. Devonport, Synth. Met., 1996, 76, 305.
21 W. Devonport, Ph.D. Thesis, University of Durham, 1995.
22 (a) G. Steimecke, H-J. Sieler, R. Kirmse and E. Hoyer, Phosphorus
Sulfur, 1979, 7, 49; (b) Review: N. Svenstrup and J. Becher,
Synthesis, 1995, 215.
We thank the EPSRC for funding (to C. S .W.). L. M. G.
thanks the University of Durham and the Royal Society for
financial support. A. S. B. thanks the EPSRC. M. R. B. thanks
the University of Durham for the award of the Sir Derman
Christopherson Research Fellowship.
23 A. Krief, Tetrahedron, 1986, 42, 1209.
24 (a) N. Svenstrup, K. M. Rasmussen, T. K. Hansen and J. Becher,
Synthesis, 1994, 809; (b) J. Becher, J. Lau, P. Leriche, P. Mørk and
N. Svenstrup, J. Chem. Soc., Chem. Commun., 1994, 2715.
25 (a) D. L. Lichtenberger, R. L. Johnston, K. Hinkelmann, T. Suzuki
and F. Wudl, J. Am. Chem. Soc., 1990, 112, 3302 and references
cited therein.
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Paper 6/07597E; Received 7th November, 1996
J. Mater. Chem., 1997, 7(7), 1189–1197
1197