Acetylenic dithiafulvene derived donor-π-acceptor dyads: Synthesis, electrochemistry and non-linear optical properties

Article abstract of DOI:10.1039/b504124d

A selection of donor-acceptor chromophores containing the redox-active dithiafulvene unit about acetylenic and aryl scaffolds has been synthesised. The molecules were studied for their optical, redox and structural properties. Moreover, third-order non-li

Full text of DOI:10.1039/b504124d

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Acetylenic dithiafulvene derived donor–p–acceptor dyads: synthesis,
electrochemistry and non-linear optical properties{
Mogens Brøndsted Nielsen,*a Jan Conrad Petersen,b Niels Thorup,c Mikkel Jessing,a
Asbjørn Sune Andersson,a Anne Sofie Jepsen,d Jean-Paul Gisselbrecht,e Corinne Boudone and Maurice Grosse
Received 21st March 2005, Accepted 11th May 2005
First published as an Advance Article on the web 27th May 2005
DOI: 10.1039/b504124d
A selection of donor–acceptor chromophores containing the redox-active dithiafulvene unit about
acetylenic and aryl scaffolds has been synthesised. The molecules were studied for their optical,
redox and structural properties. Moreover, third-order non-linear optical properties were
investigated as a function of molecular structure.
1. Introduction
2. Results and discussion
Synthesis
The design and synthesis of new organic materials with good
non-linear optical (NLO) properties has attracted considerable
attention in organic chemistry,1 since such materials are
important for the development of high performance electro-
optical switching elements for telecommunication and optical
information processing. One advantage of organic materials
over inorganic crystals is the possibility for fine-tuning the
NLO properties for the desired applications. The general
structural element for NLO chromophores is a conjugated
molecule with donor–acceptor (D–A) substitution.2 The
successful design of new NLO materials is promoted by
systematic investigations where structure–property relation-
ships are established by varying the D and A entities as well as
the conjugated spacer unit.
First, acetylene-spaced donor–acceptor dyads were prepared
from suitable starting materials, phosphonium salts 19 and 210
and the aldehyde 311 (Scheme 1). Thus, deprotonation of 1
and 2, respectively, followed by treatment of each phos-
phorous ylide with 3 afforded in a Wittig reaction the novel
chromophores 4 and 5.
Next, we decided to incorporate the D–p–A dyad 4 into
larger scaffolds. As precursors for such target molecules,
we chose benzene-extended TTFs with lateral acetylene
appendages. The acceptor functionalities are then to be
attached in a final step via a suitable cross-coupling reaction
at the terminal acetylene positions. The synthesis is depicted in
Scheme 2.8a In the first step, terephthalaldehyde 6 was treated
with lithium triisopropylsilylacetylide generated in situ. The
resulting diol 7 was oxidised by PCC to the diketone 8 that
was subsequently reacted with two equivalents of the ylide
of 1. The outcome of this two-fold Wittig reaction was the
benzene-extended TTF derivative 9. Trans-esterification (to
enhance solubility) under basic conditions was accomplished
by reacting 9 with 1-decanol and potassium carbonate, which
afforded the decyl ester 10. Both TTFs 9 and 10 are very stable
compounds that were subjected to normal chromatographic
work-up and stored at room temperature. Removal of the silyl
Tetrathiafulvalene (TTF) is a reversible two-electron donor
that has found applications in both materials and supra-
molecular chemistry on account of its unique redox pro-
perties.3 Yet the first NLO investigations on TTF D–p–A
dyads first appeared in 1997,4 focusing on second-order
optical non-linearities. We and others have investigated the
third-order NLO properties of different extended TTFs,
such as bis(1,3-dithiole) polymethine dyes,5 alkene- and
alkyne-extended TTFs6 and pyrrolo-annelated TTFs.7 As a
continuation of this work, we describe the syntheses
and characterisations of new extended TTFs and D–p–A
dyads based on acetylenic derivatives of the dithiafulvene
donor unit.8 These chromophores were investigated for
their linear and non-linear optical properties and redox
behaviour.
{ Electronic supplementary information (ESI) available: Full experi-
mental details and crystallographic data. See http://www.rsc.org/
suppdata/jm/b5/b504124d/
Scheme 1 Reagents and conditions: i, (1 + 3 A 4) BunLi, THF,
278 uC, 65%; ii, (2 + 3 A 5) NEt3, THF, MeCN, rt, 53%.
*mbn@kiku.dk
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Scheme 2 Reagents and conditions: i, triisopropylsilylacetylene, BunLi, THF, 278 uC, 55%; ii, PCC, CH2Cl2, rt, 77%; iii, 1, BunLi, THF, 278 uC,
66%; iv, 1-decanol, THF, K2CO3, rt, 55%; v, Bun4F, THF; rt, 76%; vi, (11 A 12) phenylacetylene, CuCl, TMEDA, CH2Cl2, air, rt, 60%; vii,
13) p-iodonitrobenzene, [PdCl2(PPh3)2], CuI, THF, Pri2NH, rt, 29%. PCC
(11 pyridinium chlorochromate; TMEDA 5
A
5
N,N,N9,N9-tetramethylethylenediamine.
protecting groups was accomplished with two equivalents of
tetrabutylammonium fluoride. This deprotection step was
very fast, and the mixture was worked up after only 15 min
of stirring at room temperature. After chromatographic
purification, TTF 11 containing two terminal acetylene units
was obtained. This desilylated compound was rather unstable
and decomposed after prolonged standing at room tempera-
ture. 1H NMR spectroscopy confirmed the presence of
terminal acetylene protons resonating as a singlet at dH
3.76 ppm. Moreover, IR spectroscopy revealed the C–H
stretching band at 3307 cm21
.
The compound 11 is a useful building block for further
scaffolding. Thus, 11 was treated with an excess of phenyl-
acetylene under oxidative Hay conditions12 (Scheme 2), i.e.
employing the CuCl, N,N,N9,N9-tetramethylethylenediamine
(TMEDA) catalyst system in the presence of oxygen (from the
air). This reaction afforded in good yield the extended TTF 12
in which each dithiole ring is in linear conjugation to a phenyl
ring via a buta-1,3-diynediyl spacer. The p-nitrophenyl electron
acceptor was incorporated by subjecting 11 to a Pd-catalysed
cross-coupling reaction with 4-iodonitrobenzene under
Sonogashira conditions13 (Scheme 2). This reaction gave
TTF 13 that corresponds structurally to two units of D–p–A
dyad 4 separated by a p-phenylene spacer, except for the
different peripheral ester groups.
Scheme 3 Reagents and conditions: i, [PdCl2(PPh3)2], CuI, THF,
Et3N, rt, 79%.
which afforded the decyl ester 18. Desilylation followed by
two-fold cross-coupling with two equivalents of 15 (present in
excess) gave 19. This diiodide was subsequently cross-coupled
with the acetylenic dithiafulvene 14, which provided the
extended tris-dithiafulvene 20. The reaction seemed to proceed
almost quantitatively as judged by 1H NMR spectroscopy
after a first crude column chromatographic work-up. However,
repeated chromatography to provide pure compound resulted
in almost complete decomposition. We managed nevertheless
The acetylenic dithiafulvene 14 (Scheme 3) was earlier
successfully employed for the construction of oligoyne-
extended TTFs via sequential Hay coupling reactions.6b–d
Subjecting instead 14 to a Sonogashira cross-coupling with
1,4-diiodobenzene (15) gave the p-diethynylbenzene-extended
TTF 16 in good yield.8b
1
to characterize the unstable compound 20 by H , 13C NMR
and high-resolution mass spectrometry.
X-Ray crystallography
Single crystals of 4 were grown by slow diffusion of hexane
into a CH2Cl2 solution and used for X-ray crystal structure
analysis (Fig. 1). This analysis revealed that the two halves
are both planar and almost co-planar (dihedral angle 8.5u,
cf. supplementary material). The bond length alternation in the
An extended TTF based on three dithiafulvene units was
prepared according to Scheme 4. The diacetylenic dithia-
fulvene 176b,c was subjected to a trans-esterification reaction
upon treatment with 1-decanol and potassium carbonate,
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˚
Fig. 1 X-Ray crystal structure of 4. Selected bond lengths (A) and
angles (u): C1–C2 1.382(4), C2–C3 1.368(4), C3–C4 1.407(3), C4–C7
1.427(4), C7–C8 1.198(4), C8–C9 1.402(4), C9–C10 1.352(3), C11–C12
1.346(3), N1–C1 1.462(3), N1–O5 1.226(3), N1–O6 1.234(3), S1–C10
1.747(3), S1–C12 1.748(2); C3–C4–C7 119.8(2), C4–C7–C8 177.6(3),
C7–C8–C9 176.1(3), C8–C9–C10 123.7(2).
Fig. 2 Definition of bond lengths for calculation of quinoid
character (dr).
Scheme 4 Reagents and conditions: i, 1-decanol, THF, K2CO3, rt,
85%; ii, Bun4NF, THF, 0 uC–rt; iii, 15 (excess), [PdCl2(PPh3)2], CuI,
THF, Et3N, rt, 24% (two steps); iv, 14, [PdCl2(PPh3)2], CuI, THF,
Et3N, rt, 97% (not isolated yield).
p-nitrophenyl ring can be expressed by the quinoid character
(dr) of the ring defined by14
dr 5 [(a 2 b) + (c 2 b)]/2 # [(a9 2 b9) + (c9 2 b9)]/2,
where a, b and c are defined according to Fig. 2. A relatively small
˚
value of dr 5 0.027 A is obtained, which indicates that little charge
transfer (CT) is present in the ground state of 4. Yet, the quinoid
character is more than twice than that of the p-NO2Ph ring of
14
˚
p-NO2C6H4–CMC–C6H4NH2 (dr 5 0.011 A).
Electronic absorption spectroscopy
Fig. 3 UV–vis absorption spectra in CHCl3.
The UV–vis spectral data of the compounds measured in
CHCl3 are listed in Table 1, and spectra of selected compounds
are displayed in Fig. 3. Compound 4 shows a strong CT
absorption band at lmax 414 nm. For 13, the absorption
maximum of this band is red-shifted to lmax 426 nm, and the
end-absorption (absorption onset) reaches ca. 550 nm (2.3 eV).
This red-shift indicates the existence of some electronic
communication across the phenylene spacer. The longest-
wavelength absorption maximum of 4 is close to that of the
known compound 2115 (lmax 412 nm), devoid of the acetylene
spacer. In contrast, the longest-wavelength absorption
a
Table 1 Absorption band maxima and molar extinction coefficients in the UV–vis spectra of compounds in CHCl3
Compound
l )
max/nm (e/M21cm21
4
9
292 (14000)
287 (15700)
287 (17100)
260 (sh, 56300)
289 (35500)
272 (16100)
250–270 (br)
256 (12600)
312 (sh, 11400)
352 (sh, 21700)
350 (sh, 22100)
295 (35000)
386 (42900)
396 (49400)
300 (br)
414 (22600)
393 (30900)
394 (32900)
326 (33500)
426 (38500)
415 (sh, 42900)
360 (br sh)
10
12
13
16
20
21
a
380 (43900)
394
397 (43600)
415 (sh)
412 (22100)
sh 5 shoulder; br 5 broad.
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maximum of TTF 16 (lmax 415 nm, shoulder) is significantly
red-shifted relative to that of 9 (lmax 393 nm) and 10 (lmax
394 nm). The p-systems in these three TTFs contain the
same number of atoms, but differ in their connectivity. The
acetylene moieties are linearly conjugated with the phenylene
group in 16 but cross-conjugated with respect hereto in 9 and
10. Bryce and co-workers16 have shown that cross-ethylenic
extended TTFs (dendralenes) are not planar, and UV–vis
absorption data revealed poor cross-conjugation in these
molecules. In order to elucidate the preferred conformations
of 9 and 16, semi-empirical PM3 geometry optimisations were
carried out using the Gaussian program package.17 The
conjugated moiety of 16 took a planar conformation whatever
the starting geometry for optimisation. In contrast, two energy
minima exist for the conjugated moiety of 9. One of these
minima corresponds to a planar conformation, whereas the
other corresponds to a conformation in which the phenylene
spacer is vertical to the two acetylenic dithiafulvene groups.
DFT single point energy calculations at the B3LYP/6-31G(d)
level reveal that the non-planar conformation is 23.8 kcal mol21
more stable than the planar conformation. This preferred non-
planar conformation of 9 does not allow for p-electron
delocalisation through the entire p-system, which explains
the lower wavelength of absorption for this compound as
compared to that of 16. The tris-dithiafulvene 20 (expanded
dendralene) exhibits almost the same longest-wavelength
absorption maxima (lmax 394 nm, followed by shoulder at
ca. 415 nm) as the related TTF 16. This result reflects again the
less efficient p-electron delocalisation via cross-conjugation,
here across the central dithiafulvene.
Table 2 Electrochemical data measured in CH2Cl2
Bun4NPF6. All potentials versus Fc +/Fc. Working electrode: glassy
carbon electrode; counter electrode: Pt; reference electrode: Ag/AgCl
+ 0.1 M
?
Rotating disk
voltammetry
Cyclic voltammetry
DEp/
mV
Slope /
E1/2/V mV
Compound Eu/Va
Ep/Vb
+0.40c
TTF
9
20.08 (1 e2)
+0.56 (1 e2) 80
+0.56
+0.68
60
60
+0.66 (1 e2) 70
21.83
21.95
22.28
21.87 150
10
13
+0.54 (1 e2) 70
+0.67 (1 e2) 75
+0.55
+0.71
75
70
22.03
21.98 100
+0.61 (1 e2) 60
+0.71 (1 e2) 60
21.42 (2 e2) 85
+0.61
+0.71
21.48
60
60
85
21.92
21.94 120
d
16
+0.65 (2 e2)
21.88 (2 e2)
e
a
Eu 5 (Epc + Epa)/2, where Epc and Epa 5 cathodic and anodic peak
potentials. Ep 5 irreversible peak potential. Precipitation on
b
c
d
e
electrode.
unresolved wave.
Electrode inhibition during oxidation.
Spread-out
further chemical reactions (oligomerization).3f,18 The oxida-
tions are shifted to more positive potentials for 13 relative to
9 and 10 owing to the electron-withdrawing properties of
the nitrophenyl moieties. The compounds were also reduced
electrochemically. Only irreversible electron transfers are
observed at any sweep rate, except for 13 which exhibits a
reversible two electron reduction centered on the two
+
?
p-C6H4NO2 moieties at a potential of 21.42 V versus Fc /
Fc. The position of this reduction is in agreement with
previously studied tetraethynylethene derivatives bearing
p-C6H4NO2 groups.19 Since both p-C6H4NO2 groups are
reduced in a single step, they behave as independent redox
centres. From the first oxidation and reduction potentials, an
electrochemical HOMO–LUMO gap of 2.0 eV is obtained,
while the optical gap is estimated to be 2.3 eV (vide supra).
Electrochemistry
The redox properties of the extended TTFs 9, 10, 13 and 16
Third-order NLO properties
were examined by cyclic voltammetry (CV) and rotating disk
+
?
voltammetry (RDV). The redox potentials versus Fc /Fc
The NLO properties of 4, 13 and 21 were investigated by third
harmonic generation (THG) measurements on thin films con-
taining the compounds in a matrix of poly(methyl methacryl-
ate) (PMMA). The Maker fringe patterns were measured at
1064 and 1907 nm. The second hyperpolarisabilities (c) are
listed in Table 3 together with the results published previously
(ferricinium/ferrocene couple) are listed in Table 2. The TTFs
9, 10 and 13 undergo two reversible one-electron oxidation
steps separated by 100 mV for 9, 130 mV for 10 and 100 mV
for 13, whereas 16 experiences an irreversible two electron
oxidation. The single two electron oxidation observed for 16,
compared to two well separated one electron transfers for 9, 10
and 13, results from an increasing distance between the two
redox centres and a decrease of the electrostatic repulsion
between the two generated cations as observed previously with
other extended TTFs.6 The lack of lateral appendages in 16
may decrease the stability of the generated radical cation and
dication. Therefore a fast follow-up chemical reaction occurs,
which explains the irreversible behaviour observed during
oxidation. Indeed, it has been observed for other benzene-
extended TTFs that the lack of substituents on the fulvene
double bonds generates rather active species which undergo
Table 3 Second hyperpolarisabilities (,c.) of compounds in
PMMA filmsa
Compound
,c.1064 nm /10236 esu
,c.1907 nm /10236 esu
4
13
21
22
23
a
265
550
195
135
160
1700b
500
1400b
1500c
THG measurements at two fundamental wavelengths (1064 and
b
1907 nm). Ref. 5. Ref. 7.
c
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for other dithiafulvene-containing compounds, methine salt
225 and pyrrolo-annelated TTF D–A dyad 23,7 investigated
under the same conditions. The more extended compound 13
exhibits roughly twice as high a c value as 4 at a fundamental
of 1064 nm. In contrast, however, c decreases at 1907 nm. The
optical third-order non-linearities for compounds 4, 13 and 21
are one order of magnitude smaller than those of 22 and 23.
aq. NH4Cl (200 mL) was added. Then Et2O (300 mL) was
added, and the organic phase was separated, dried (MgSO4)
and concentrated in vacuo. Column chromatography (SiO2,
CH2Cl2) afforded 9 (0.92 g, 64%) as an orange solid. m.p. 155–
156 uC; IR (KBr): n/cm21 5 2944 (s), 2890 (m), 2864 (s), 2126
(m), 1734 (s), 1584 (s), 1518 (m), 1462 (m), 1434 (s), 1403 (w),
1365 (w), 1259 (s), 1096 (m), 1028 (m), 997 (m), 918 (w), 883
1
(m), 837 (w), 802 (w), 772 (w), 679 (m), 560 (w), 468 (w); H
NMR (300 MHz, CDCl3): d/ppm 5 1.14 (s, 42 H), 3.84 (s,
6 H), 3.89 (s, 6 H), 7.55 (s, 4 H); 13C NMR (75 MHz, CDCl3):
d/ppm 5 11.3, 18.7, 53.3, 53.5, 101.6, 104.8, 107.7, 126.5,
129.6, 133.0, 135.4, 141.2, 159.4, 160.2; MALDI-TOF-MS
(matrix: 2,5-dihydroxybenzoic acid, DHB): m/z 5 898 (M+).
Anal. calc. for C44H58O8S4Si2 (899.35): C 58.76, H 6.50, S
14.26; found: C 58.94, H 6.38, S 14.38.
1,4-Bis[1-{4,5-bis(decyloxycarbonyl)-1,3-dithiol-2-ylidene}-3-
triisopropylsilyl-2-propynyl]benzene 10. A mixture of 9 (260 mg,
0.29 mmol) and K2CO3 (1.379 g) in 1-decanol (10 mL) and
THF (5 mL) was stirred at rt for 17 h. Then Et2O (250 mL)
was added, and the mixture was washed with H2O (200 mL),
dried (MgSO4) and concentrated in vacuo. The residue was
passed through a short column (SiO2, cyclohexane) in order to
remove most of the 1-decanol. A second column chromato-
graphic purification (SiO2, cyclohexane–CH2Cl2 2 : 1 to 1 : 1)
3. Conclusions
With the objective to establish structure–property relation-
ships for acetylenic dithiafulvenes, we have prepared a
selection of D–p–A dyads and extended TTFs and elucidated
their optical and electrochemical properties. The dyads are
interesting building blocks for future construction of larger
opto-electronic materials.
gave 10 (224 mg, 55%) as an orange oil. IR (KBr): n/cm21
5
2924 (s), 2853 (s), 2128 (w), 1736 (s), 1703 (s), 1575 (s), 1514 (s),
1491 (s), 1466 (s), 1442 (w), 1402 (m), 1277 (s), 1233 (s), 1098
(m), 1000 (m), 966 (m), 914 (w), 838 (w), 792 (m), 755 (s), 722
4. Experimental
1
(m), 689 (s), 618 (w), 525 (w), 481 (m); H NMR (300 MHz,
For full experimental details, including synthetic procedures
for all new compounds, see the Electronic Supplementary
Information(ESI){.
CDCl3): d/ppm 5 0.85–0.88 (m, 12 H), 1.14 (s, 42 H), 1.28 (br
m, 56 H), 1.68 (m, 8 H), 4.22 (t, 6.8 Hz, 4 H), 4.25 (t, 6.8 Hz,
4 H), 7.55 (s, 4 H); 13C NMR (75 MHz, CDCl3): d/ppm 5 11.3,
14.1, 18.7, 22.7, 25.7, 25.8, 28.3 (6 2), 29.1, 29.2, 29.3, 29.5(6
2), 29.6, 31.9, 66.9, 101.4, 105.0, 107.4, 126.5, 130.5, 132.4,
135.3, 141.6, 159.2, 159.6; MALDI-TOF-MS (DHB): m/z 5
1402 (M+). Anal. calc. for C80H130O8S4Si2 (1404.31): C 68.42,
H 9.33, S 9.13; found: C 68.61, H 9.48, S 9.15.
Third harmonic generation
The experimental set-up for thin-film THG Maker fringe
measurements has previously been described.20
Electrochemistry
1,4-Bis[1-{4,5-bis(decyloxycarbonyl)-1,3-dithiol-2-ylidene}-2-
The electrochemical experiments were carried out at 20 ¡ 2 uC
in CH2Cl2 containing 0.1 M Bun NPF6 in a classical three
propynyl]benzene 11. A mixture of 10 (361 mg, 0.25 mmol) and
Bun NF (1 M in THF, 0.50 mL) in THF (25 mL) was stirred at
4
4
electrode cell. The working electrode was a glassy carbon disk
electrode (3 mm in diameter) used either motionless for CV
(0.1 to 10 V s21) or as rotating-disk electrode for RDV. The
counter electrode was a platinum wire and the reference
electrode either an aqueous Ag/AgCl electrode or a platinum
wire used as pseudo-reference. All potentials are referenced to
rt for 15 min, whereupon Et2O (300 mL) was added. The
mixture was washed with H2O (2 6 200 mL), dried (MgSO4)
and concentrated in vacuo. Column chromatography (SiO2,
CH2Cl2–cyclohexane 1 : 1) afforded 11 (204 mg, 73%) as a red
unstable oil that turned greenish after prolonged standing at
rt. IR (KBr): n/cm21 5 3307 (m), 2924 (s), 2854 (s), 2085 (w),
1724 (s), 1582 (s), 1519 (s), 1466 (s), 1403 (w), 1386 (w), 1249
+
?
the ferricinium/ferrocene (Fc /Fc) couple used as an internal
standard.
1
(s), 1098 (m), 1017 (m), 836 (w), 798 (w), 761 (w), 724 (w); H
NMR (300 MHz, CDCl3): d/ppm 5 0.88 (m, 8 H), 1.26 (br s,
56 H), 1.56–1.70 (m, 8 H), 3.76 (s, 2 H), 4.21 (t, 6.8 Hz, 4 H),
4.25 (t, 6.5 Hz, 4 H), 7.54 (s, 4 H); 13C NMR (75 MHz,
CDCl3): d/ppm 5 14.1, 22.7, 25.7, 25.8, 26.9, 28.3, 28.5, 29.2 (x
2), 29.3, 29.5, 31.9, 67.0, 67.1, 82.3, 86.8, 105.6, 126.6, 126.7,
130.2, 132.4, 135.4, 142.8, 159.1, 159.6; MALDI-TOF-MS
(DHB): m/z 5 1091 (M+); HR-FT-MALDI-MS (DHB): m/z 5
1090.5474 (M+, calc. for C62H90O8S4: 1090.5519), 1113.5374
([M+Na]+, calc. for C62H90NaO8S4: 1113.5416).
Selected syntheses
1,4-Bis[1-{4,5-bis(methoxycarbonyl)-1,3-dithiol-2-ylidene}-
3-triisopropylsilyl-2-propynyl]benzene 9. To a solution of 1
(1.79 g, 3.52 mmol) in dry THF (55 mL) at 278 uC was slowly
added BunLi (1.6 M in hexane, 2.2 mL, 3.5 mmol) under an
atmosphere of argon, which resulted in a red solution. Then 8
(789 mg, 1.59 mmol) in dry THF (25 mL) was slowly added.
The solution was stirred at 278 uC for 2.5 h, whereupon sat.
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1,4-Bis[1-{4,5-bis(decyloxycarbonyl)-1,3-dithiol-2-ylidene}-3-
(4-nitrophenyl)-2-propynyl]benzene 13. A mixture of 11 (209 mg,
0.16 mmol) and 4-iodonitrobenzene (490 mg, 1.97 mmol)
in THF (10 mL) was Ar-degassed thoroughly. Then
[PdCl2(PPh3)2] (10 mg, 0.014 mmol) and diisopropylamine
(1.5 mL) were added under Ar-degassing. Finally, CuI (3 mg,
0.02 mmol) was added, and the mixture was stirred at rt for 3 h.
Then Et2O (300 mL) was added and the organic phase was
washed with H2O (250 mL) and sat. aq. NH4Cl (250 mL),
dried (MgSO4) and concentrated in vacuo. Column chromato-
graphy (SiO2, CH2Cl2–cyclohexane 2 : 1) afforded 13 (74 mg,
29%) as an oily orange solid. IR (KBr): n/cm21 5 2924 (s),
2854 (s), 2183 (m), 1737 (s), 1714 (s), 1590 (s), 1517 (s), 1469
(m), 1403 (w), 1377 (w), 1339 (s), 1253 (s), 1107 (m), 1013 (w),
973 (w), 855 (m) 802 (w), 749 (m), 722 (w), 687 (w), 622 (w); 1H
NMR (300 MHz, CDCl3): d/ppm 5 0.88 (m, 12 H), 1.27 (br s,
56 H), 1.70–1.76 (m, 8 H), 4.24 (t, 6.8 Hz, 4 H), 4.29 (t, 6.5 Hz,
4 H), 7.62 (s, 4 H), 7.63 (d, 8.8 Hz, 4 H), 8.21 (d, 8.8 Hz,
4 H); 13C NMR (75 MHz, CDCl3): d/ppm 5 14.1, 22.7,
25.7, 25.8, 28.3, 29.2 (6 2), 29.3, 29.5 (6 3), 31.9, 67.1,
67.3, 93.4, 97.3, 105.8, 123.7, 126.9, 129.8, 130.6, 131.6,
132.7, 135.5, 144.3, 146.9, 158.9, 159.5; HR-FT-MALDI-MS
(DHB): m/z 5 1332.5833 (M+, calc. for C74H96N20O12S4:
1332.5846), 1355.5634 ([M+Na]+, calc. for C74H96N2NaO12S4:
1355.5744). Anal. calc. for C74H96N20O12S4 (1333.82): C
66.64, H 7.25, N 2.10, S 9.61; found: C 66.84, H 7.33, N
2.15, S 9.55.
Acknowledgements
The Danish Technical Research Council (STVF, Research
project # 26-01-0033) and Carlsbergfondet are gratefully
acknowledged for financial support. A. S. Andersson acknowl-
edges The University of Copenhagen for a PhD scholarship.
Mogens Brøndsted Nielsen,*a Jan Conrad Petersen,b Niels Thorup,c
Mikkel Jessing,a Asbjørn Sune Andersson,a Anne Sofie Jepsen,d
Jean-Paul Gisselbrecht,e Corinne Boudone and Maurice Grosse
aDepartment of Chemistry, University of Copenhagen, DK-2100
Copenhagen Ø, Denmark. E-mail: mbn@kiku.dk
bDanish Institute of Fundamental Metrology, Bldg. 307,
Matematiktorvet, DK-2800 Lyngby, Denmark
cDepartment of Chemistry, Technical University of Denmark, DK-2800
Lyngby, Denmark
dDepartment of Chemistry, University of Southern Denmark, Campusvej
55, DK-5230 Odense M, Denmark
eLaboratoire d’Electrochimie et de Chimie Physique du Corps Solide,
UMR 7512, CNRS, Universite´ Louis Pasteur, F-67000 Strasbourg,
France
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