Synthesis and IR spectroelectrochemical studies of a [60] fulleropyrrolidine-(tricarbonyl)chromium complex: Probing C60 redox states by IR spectroscopy

Article abstract of DOI:10.1002/ejic.201100011

The synthesis of a new fulleropyrrolidine-(tricarbonyl)chromium complex: 1-methyl-2-(4-methoxyphenyl)-3,4-[60]fulleropyrrolidine-(tricarbonyl)chromium is described together with its characterization by IR, NMR and cyclic voltammetry. IR spectro-electroche

Full text of DOI:10.1002/ejic.201100011

FULL PAPER
DOI: 10.1002/ejic.201100011
Synthesis and IR Spectroelectrochemical Studies of a [60]Fulleropyrrolidine-
(tricarbonyl)chromium Complex: Probing C60 Redox States by IR
Spectroscopy
Claes-Henrik Andersson,[a] Gustav Berggren,[b,c] Sascha Ott,[b] and Helena Grennberg*[a]
Keywords: Fullerenes / Chromium / IR spectroscopy / Cyclic voltammetry / Redox chemistry / Electrochemistry
The synthesis of a new fulleropyrrolidine-(tricarbonyl)chro- level of the fullerene derivative via the relative position of
mium complex: 1-methyl-2-(4-methoxyphenyl)-3,4-[60]full-
eropyrrolidine-(tricarbonyl)chromium is described together
with its characterization by IR, NMR and cyclic voltammetry.
IR spectro-electrochemistry has been used to probe the redox
the vibrational bands of the CO ligands, which are sensitive
to the electronic state of the complex. Other strategies to in-
corporate a tricarbonylchromium moiety to fullerene C60 are
also briefly discussed and evaluated.
charge-transfer complexes with acceptors such as 1,3,5-tri-
nitrobenzene and tetracyanoethylene.[5] These properties
make also this group of compounds interesting for the use
in combination with electron acceptors such as C60. Even
more interesting is the fact that the CO ligands may serve
as sensitive probes to electronic effects. This has been well
established throughout extensive studies by IR spec-
troscopy, which have shown that the frequency of the CO
bands is affected by the electron density on the ligating aro-
matic ring via back-bonding from chromium to the carbon
monoxide ligands.[5] While fullerene anions are generally
monitored by NIR spectroscopy via their absorption
Introduction
Fullerenes have emerged as widely used molecular build-
ing blocks in the field of artificial photosynthesis and light-
harvesting devices. In this regard, the general interest in
fullerenes originates from their rich redox chemistry and
low reorganization energy which, in combination, makes
them attractive as electron acceptors.[1] Since the discovery
of C60 in 1985, great advances in fullerene chemistry has
permitted the efficient preparation of numerous fullerene-
based donor-acceptor systems, many of which have been
studied in terms of photo-induced electron transfer.[2] Most
such assemblies have electron donors based on transition
metal complexes such as ruthenium complexes, metallo-
porphyrins, phthalocyanines and ferrocene,[2] and the
strong donor capability of bis(arene)chromium complexes
makes also this group of compounds interesting for the use
in donor–acceptor systems with C60 as acceptor.[3] The air
sensitivity of bis(arene)chromium compounds and compli-
cated preparation routes however limits the usefulness
in this context. In contrast, monoarene-(tricarbonyl)-
chromium complexes are relatively stable, and can be syn-
thesized and manipulated by regular “wet chemistry” meth-
ods.[4] Also arene-(tricarbonyl)chromium complexes are
electron donors and have, for instance, been shown to form
1–
around 1080 nm for C60 and 945 nm for C602–, we were
interested in whether IR spectroscopy could be a compli-
mentary technique where the carbonyl absorption fre-
quency could be used to probe different redox states of the
C60 part of the complex.[6]
There are in principle three different ways to link a tri-
carbonylchromium moiety to C60: i. Direct complexation of
Cr(CO)3 to pristine C60 to yield a fullerene η6 complex, ii.
direct complexation of Cr(CO)3 to a modified fullerene
that, in the carbon cage, possess a cyclopentadienyl or
phenyl unit isolated from the fullerene π system by sp3 car-
bons, i.e. C60R5 or C60R6, and iii. complexation of Cr-
(CO)3 to a phenyl unit attached as an addend to the fuller-
ene cage. To the best of our knowledge no η6-metal com-
plexes of pristine C60 (category i) has been reported so far.
This is probably due to the curvature of the six-membered
rings which prevents efficient orbital overlap between the
metal and the π-system.[7] On the other hand, fullerene
metal complexes such as M(η5-C60R5)Ln have been success-
fully synthesized (category ii) with several group 6–10 met-
als including chromium.[3d,8] In these complexes the ligating
five-membered ring have similar properties as a regular cy-
clopentadienyl ligand since all five carbon atoms, are
[a] Uppsala University, Dept. of Biochemistry and Organic
Chemistry,
Box 576, 57123 Uppsala, Sweden
Fax: +46-18-4713818
E-mail: Helena.Grennberg@Biorg.uu.se
[b] Uppsala University, Dept. of Photochemistry and Molecular
Science,
Box 523, 75120 Uppsala, Sweden
[c] Laboratoire de Chimie et Biologie des Métaux; UMR5249
CNRS-CEA-UJF, CEA Grenoble,
17 rue des Martyrs, 38054 Grenoble Cedex 9, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100011.
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Probing C60 Redox States by IR Spectroscopy
bonded to sp3 carbons of the fulleride. The properties of the hand we decided to explore the new, more convergent ap-
fulleride parts in this group of complexes are significantly proach where a pre-formed tricarbonylchromium arene
different from pristine C60. In contrast, the properties of compound is coupled to the fullerene (Scheme 1, route B).
fullerene monoadducts moieties of complexes belonging to
category iii should be relatively similar to that of pristine
C60. Furthermore, this route may be less synthetically de-
manding. Already in 1995 Nefedova et al. reported the syn-
thesis of a tricarbonylchromium complex of diphenylmeth-
anofullerene, prepared by addition of an organometallic di-
azonium salt to C60.[3c] This is still, as far as we know, the
only example of this kind. In the current paper we give an
account of our synthetic studies towards category iii fuller-
ene-tricarbonylchromium complexes. In this study we have
evaluated the possibility to attach tricarbonylchromium
Scheme 1. General strategies to prepare fullerene-tricarbonylchro-
mium complexes Cr(1) to Cr(3).
units to C60 by adapting some recently reported derivati-
zation methods. One new fulleropyrrolidine tricarbonyl-
chromium complex was successfully prepared and charac-
terized spectroscopically as well as by electrochemical and
IR spectroelectrochemical methods.
Fulleropyrrolidine synthesis via a 1,3-dipolar cycload-
dition to C60 is among the most versatile fullerene function-
alization reactions, and the robustness of this reaction was
further proven by the successful preparation of Cr(1) in an
isolated yield of 27% from 4-methoxybenzaldehyde-(tricar-
bonyl)chromium, sarcosine and C60. Since tricarbonylchro-
mium complexes are most easily formed with electron-rich
aromatics, we chose an aldehyde component derived from
anisole. This allowed the preparation of 4-methoxybenzal-
dehyde-(tricarbonyl)chromium in a yield of 51% over three
steps, with hydrolysis of 2-(4-methoxyphenyl)-1,3-dioxol-
ane-(tricarbonyl)chromium[9] immediately before the pyr-
rolidination step (Scheme 2). Purification of Cr(1) was suc-
cessfully achieved by repeated column chromatography. The
purified product could be exposed to air for short periods
(hours) without any signs of decomposition. Furthermore,
the compound could be stored in a freezer for several weeks
under nitrogen atmosphere before decomposing into 1 by
dissociation of tricarbonylchromium.
Results and Discussion
Fullerene adducts Cr(1)–Cr(3) (Figure 1) were suggested
as suitable category iii targets, each with a slightly different
distance between the fullerene and the tricarbonylchro-
mium moiety.
Scheme 2. Synthesis of 1-methyl-2-(4-methoxyphenyl)-3,4-[60]full-
eropyrrolidine-(tricarbonyl)chromium [Cr(1)]; i. 1,2-ethanediol, p-
toluenesulfonic acid, yield 95%; ii. Cr(CO)6, n-butyl ether, THF,
reflux 12 h, yield 60%; iii. HCl, ethanol, room temp., 4 h, yield
90%; iv. C60, sarcosine, toluene, reflux 12 h, yield 27%.
Figure 1. Fullerene derivatives 1–3 and their tricarbonylchromium
complexes Cr(1) to Cr(3).
The most straightforward synthesis of any of these com-
The synthesis of hydroarylated fullerene adducts such as
pounds would be by direct complexation of tricarbonyl- 2 was recently reported by Itami et al. The reaction is a
chromium to the parent compounds 1–3 (Scheme 1, route palladium or rhodium mediated coupling between an aro-
A). The established procedure to prepare tricarbonylchro- matic boronic acid and C60.[10] With this procedure in mind
mium arene derivatives is based on refluxing the arene with we attempted the complexation of tricarbonylchromium to
Cr(CO)6 in Bu2O/THF or decalin for several hours. While 4-methoxyphenyl boronic acid with the intention to obtain
this works well for small electron-rich aromatic compounds a chromium complex possible to couple to C60 (Scheme 3).
such as anisole, we were unsuccessful in preparing any of However, the isolated product was the tricarbonylchromium
the target compounds by this method despite numerous complex of anisole, formed by protodeboronation, a reac-
attempts and various modifications of the reaction condi- tion that has previously been described for similar sys-
tions. All attempts to prepare Cr(1) directly from com- tems.[11] In contrast, we were successful in preparing the
pound 1 resulted in decomposition of the fulleropyrrolidine, tricarbonylchromium complexes of the pinacol-protected
while the attempted synthesis of Cr(2) from compound 2 boronic acid and of 4-methoxyphenyl trifluoroborate. Un-
did not result in any reaction at all. With these results in fortunately, all attempts of rhodium- or palladium-medi-
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C.-H. Andersson, G. Berggren, S. Ott, H. Grennberg
FULL PAPER
ated coupling of these compounds to C60 only gave the par-
An obvious conclusion from these attempts is that the
ent fulleropyrrolidine adduct 2 and the protodeboronation tricarbonylchromium arene components are not compatible
product anisole-(tricarbonyl)chromium.
with the conditions for palladium and rhodium mediated
arene-C60 couplings used in our attempted synthesis of
compounds Cr(2) and Cr(3), whereas the cycloaddition
route to Cr(1) was successful.
Characterization
The IR spectrum of Cr(1) in its solid state shows two
strong bands for the CO groups at 1957 and 1876 cm–1,
typical of a tricarbonylchromium complex (Figure 2). As a
comparison, the CO bands of anisole-(tricarbonyl)chro-
mium are positioned at 1940 and 1837 cm–1.
Scheme 3. i. Cr(CO)6, decalin or n-butyl ether, THF, reflux 12 h,
yield 0%; ii. a) pinacol, MgSO4, CH2Cl2, reflux 12 h, yield 95%.
b) Cr(CO)6, n-butyl ether, THF, reflux 12 h, yield 85%; iii) KHF2,
methanol, H2O, stirring 2 h, yield 75%; iv) C60, Rh(cod)2BF4 or
Pd catalyst,[10] 1,2-dichlorobenzene, H2O, 80 °C, 12 h, yield of
Cr(2): 0%.
The synthesis of fulleroindolines via palladium-mediated
coupling of anilines and o-iodoanilines to C60 was very re-
cently reported by Zhu and Wang.[12] In an attempt towards
Cr(3), N-phenylacetamide-(tricarbonyl)chromium was pre-
pared by acylation of aniline-(tricarbonyl)chromium
(Scheme 4). The reported palladium-assisted procedure for
coupling of N-phenylacetamide to C60 did for our chro-
mium complex not give the desired product. Also 2-iodo-
N-phenylacetamide-(tricarbonyl)chromium, prepared via
ortholithiation and a potentially better starting material[12a]
did not yield the desired Cr(3), but the metal-free parent
compound 3.
Figure 2. IR spectra (neat) of compound 1 (upper), compound
Cr(1) (middle), and anisole-(tricarbonyl)chromium (lower).
The 1H NMR spectrum of Cr(1) in CDCl3/CS2 (Fig-
ure 3) display chemical shifts in the aromatic region typical
of aromatic tricarbonylchromium complexes.[13] In 1-
methyl-2-(4-methoxyphenyl)-3,4-[60]fulleropyrrolidine
(compound 1) the aromatic proton signals are at δ = 7.95
and 7.70 ppm, whereas in Cr(1), the signals appears at 6.2–
5.1 ppm. Moreover, all four aromatic protons in Cr(1) are
chemically non-equivalent and have different chemical
shifts, suggesting hindered rotation of the aromatic ring.
Scheme 4. i. Acetic anhydride, pyridine, stirring 12 h, yield 85%. ii.
n-butyllithium (2.5 m), 1,2-diiodoethane, THF, –79 °C Ǟ r.t., yield
46%. iii. C60, Pd(OAc)2, DABCO, PPh3, 130 °C, 12 h, yield of
Cr(3): 0%.
1
Figure 3. H NMR spectrum (500 MHz, CDCl3/CS2, 25 °C) of Cr(1).
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Probing C60 Redox States by IR Spectroscopy
The 13C NMR spectrum of the compound (see Support-
ing Information) shows a large shift to lower frequencies of
between 30–45 ppm for the aromatic CH carbons in Cr(1)
as compared to the corresponding atoms in 1. As expected,
only one signal for the three carbon monoxide ligands
could be observed at δ = 232.4 ppm at room temperature,
suggesting a low energy barrier for rotation about the
metal-arene bond, despite the relatively close proximity to
C
60 in the molecule. This low barrier was confirmed by low-
temperature 13C NMR measurements which showed a sin-
gle (broad) carbonylic signal at temperatures as low as
–95 °C, indicating a very low energy barrier of rotation, and
thus, a fast equilibrium exist between the different conform-
ers.
Figure 5. Voltammogram of compound Cr(1) (0.3 mm). Reduction
scan showing the two first reductions of Cr(1).
Electrochemistry
Cyclic voltammetry of Cr(1) (0.3 mm) carried out in
CH2Cl2 shows one irreversible oxidation taking place at
0.40 V vs. Fc/Fc+, which can be assigned to the one-electron
oxidation of the Cr(CO)3 unit (Figure 4). This is confirmed
by the reference voltammogram of 2-(4-methoxyphenyl)-
1,3-dioxolane-(tricarbonyl)chromium which shows one
irreversible oxidation at the same potential.
number of IR spectroelectrochemical measurements were
carried out, in which the various anions of Cr(1) were gen-
erated stepwise by controlled potential bulk electrolysis in
CH2Cl2 under inert conditions, and monitored by IR spec-
troscopy. Figure 6 shows the carbonylic region of the IR
spectra of compound Cr(1) at different redox states. The
frequencies of the two carbonylic bands in the neutral com-
plex are found at 1965 and 1888 cm–1. Upon reducing the
complex to its anionic state [Cr(1)]1–, these bands are red
shifted to 1962 and 1883 cm–1. Further reduction of the
complex to its dianionic state [Cr(1)]2– leads to an ad-
ditional shift of the bands to 1961 and 1880 cm–1, respec-
tively.
Figure 4. Voltammograms (oxidation scan) for Cr(1) (0.3 mm) (so-
lid line) and 2-(4-methoxyphenyl)-1,3-dioxolane-(tricarbonyl)chro-
mium (dashed line).
The reduction scan of compound Cr(1) on the other
hand shows several reductions, where at least the first two
reductions at –1.14 and –1.54 V vs. Fc/Fc+ are electrochem-
ically reversible (Figure 5 and Supporting Information).
Unfortunately, we were unable to determine the electro-
Figure 6. Expansion of the carbonylic region of the IR spectra of
compound Cr(1) at different redox states: neutral complex (solid),
[Cr(1)]1– (dashed), [Cr(1)]2– (dotted).
Importantly, reoxidation of the complex from both the
chemical reversibility of the later C60 reductions due to the anion and dianion to its neutral state is accompanied by a
instability of fullerene-trianions in CH2Cl2,[14] which among blue shift of the bands to their original position indicating
the solvents tried out was the one where all compounds further the electrochemical reversibility of these processes.
were soluble enough.
Furthermore, bulk electrolysis provided additional infor-
With the reduction potentials known, we were interested mation about the electrochemical processes and showed, in
in if we could use IR spectroscopy to probe the redox states agreement with the results from cyclic voltammetry and IR
of the fullerene in Cr(1) by monitoring the vibrational fre- spectroelectrochemistry, a high electrochemical reversibility
quency of the CO ligands. This would then also give infor- for the first two redox events (see Supporting Information).
mation about the electronic coupling between the tri-
Together, the results suggest a certain degree of com-
carbonylchromium and the fullerene moiety. Therefore, a munication between C60 and the tricarbonylchromium moi-
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C.-H. Andersson, G. Berggren, S. Ott, H. Grennberg
FULL PAPER
a condenser. The solution was heated to 145 °C and refluxed over-
night. The solution was washed with NaOH (0.1 m), and the or-
ganic phase was collected. Toluene was removed in vacuo and the
crude product was purified by distillation. Purified yield 6.2 g,
95%, white solid. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 7.41
(AAЈ, 2 H), 6.90 (BBЈ, 2 H), 5.76 (s, 1 H), 4.13 (m, 2 H), 4.02 (m,
2 H), 3.81 (s, 3 H) ppm.
ety. The red shift of the CO frequencies upon reduction of
the complex is caused by increased back-bonding from the
chromium to the carbon monoxide, which results in a slight
decrease in C–O bond strength for the three carbon mon-
oxide ligands. It is noteworthy that the lower frequency IR
band around 1880 cm–1 is more sensitive to electronic ef-
fects than the band around 1965 cm–1 suggesting a prefer-
ential use of this band to probe redox processes going on
in the system. In this sense, the redox level of compound
Cr(1) can be determined via the relative position of the vi-
brational frequencies, v(CO), in the complex. According to
our measurements this is manifested by v(CO) = 1888 cm–1
for the neutral complex, v(CO) = 1883 cm–1 for [Cr(1)]1–
and v(CO) = 1880 cm–1 for the dianion, [Cr(1)]2–. It is
furthermore possible that this methodology could be used
to probe higher fullerene anions, but in that case another
solvent than CH2Cl2 has to be used.[14]
2-(4-Methoxyphenyl)-1,3-dioxolane-(tricarbonyl)chromium:
2-(4-
Methoxyphenyl)-1,3-dioxolane (0.8 g, 4.4 mmol), Cr(CO)6 (1.4 g,
6.4 mmol) was added to a three-necked flask equipped with a con-
denser and the flask was flushed with nitrogen. Degassed n-butyl
ether (20 mL) was added to the flask via syringe through a septum
and the solution was then heated to 160 °C and refluxed for one
hour. Degassed dry THF (6 mL) was added and also used to flush
sublimed Cr(CO)6 back down into the solution. The solution was
refluxed at 160 °C overnight. The yellow solution was then evapo-
rated and the residue was redissolved in ethyl acetate. The hetero-
geneous solution was filtered through a plug of silica to remove
green chromium by-products. The crude product was then sub-
jected to column chromatography (pentane/EtOAc, 10:1) giving
pure 2-(4-methoxyphenyl)-1,3-dioxolane chromium tricarbonyl as
yellow solid, yield 0.9 g, 65%. 1H NMR (500 MHz, CDCl3, 25 °C):
δ = 5.75 (AAЈ, 2 H), 5.49 (s, 1 H), 5.08 (BBЈ, 2 H), 4.12 (m, 2 H),
3.99 (m, 2 H), 3.72 (s, 3 H) ppm.
Conclusions
We have evaluated some methods to attach arene-(tri-
carbonyl)chromium units to fullerene C60 and successfully
prepared a new fulleropyrrolidine-(tricarbonyl)chromium
4-Methoxybenzaldehyde-(tricarbonyl)chromium:
2-(4-Methoxy-
complex via a 1,3-dipolar cycloaddition involving a tri- phenyl)-1,3-dioxolane-(tricarbonyl)chromium (218 mg, 0.7 mmol),
HCl (37%, 1 mL) and ethanol (99%, 15 mL) was added to a round-
bottomed flask and the mixture was stirred at room temp. under
nitrogen atmosphere for 4 h after which TLC showed that all start-
ing material had been consumed. The solvent was evaporated and
the crude product was chromatographed on basic Al2O3 (pentane/
EtOAc) to yield the pure product as an orange solid; yield 173 mg,
carbonylchromium arene aldehyde as one of the reactants.
In contrast, we were unable to prepare tricarbonylchro-
mium arene complexes of C60 by direct complexation to
arene-functionalized C60 or by adapting reported transi-
tion-metal mediated arene-C60 coupling methods. The suc-
cessfully prepared fulleropyrrolidine-(tricarbonyl)chromium
complex has been characterized by 1H NMR and 13C
NMR, cyclic voltammetry, bulk electrolysis and IR spec-
troscopy and was found to be chemically and electrochemi-
cally stable. IR spectroelectrochemistry revealed a clear de-
pendence of the CO frequencies on the redox state of the
1
92%. H NMR (500 MHz, CDCl3, 25 °C): δ = 9.39 (s, 1 H), 6.06
(AAЈ, 2 H), 5.19 (BBЈ, 2 H), 3.80 (s, 3 H) ppm.
1-Methyl-2-(4-methoxyphenyl)-3,4-[60]fulleropyrrolidine-(tri-
carbonyl)chromium [Cr(1)]: C60 (80 mg, 0.1 mmol), 4-methoxybenz-
aldehyde-(tricarbonyl)chromium (30 mg, 0.1 mmol) and sarcosine
(18 mg, 0.2 mmol) was added to a round-bottomed flask equipped
with a condenser. Degassed toluene (60 mL) was added and the
solution was refluxed at 130 °C overnight under nitrogen atmo-
sphere. The solvent was evaporated and the residue was chromato-
graphed on silica using dichloromethane as eluent. The product
was obtained as a brown solid, yield 30 mg, 27%. 1H NMR
(500 MHz, CS2/CDCl3, 25 °C): δ = 6.18 (dd, J = 7.2, 1.9 Hz, 1 H,
HD), 5.78 (dd, J = 7.2, 1.9 Hz, 1 H, HE), 5.22 (dd, J = 7.1, 2.3 Hz,
1 H, HG), 5.09 (dd, J = 7.1, 2.3 Hz, 1 H, HF), 4.96 (d, J = 9.7 Hz,
2 H, HA), 4.64 (s, 1 H, HC), 4.31 (d, J = 9.7 Hz, 2 H, HB), 3.73 (s,
3 H, O-CH3), 3.15 (s, 3 H, N-CH3) ppm. 13C NMR (125 MHz,
CS2/CDCl3, 25 °C): δ = 232.4, 155.6, 153.4, 151.8, 147.4, 147.3,
146.34, 146.30, 146.25, 146.20, 146.12, 146.10, 146.0, 145.7, 145.6,
145.55, 145.4, 145.37, 145.30, 145.27, 145.18, 145.15, 144.7, 144.5,
144.4, 144.2, 143.1, 143.05, 142.8, 142.66, 142.61, 142.4, 142.20,
142.14, 142.12, 142.05, 141.9, 141.7, 141.67, 141.62, 140.4, 139.9,
139.4, 136.9, 136.3, 136.1, 135.4, 128.3, 101.3, 93.3, 91.7, 79.1, 78.1,
C
60 part of the complex and hence communication between
the C60 and the tricarbonylchromium moiety is proven. It
was further found that IR spectroscopy can be efficiently
used to probe the redox states of the fulleropyrrolidine via
the relative frequencies of the carbon monoxide ligands in
the complex, which red-shifts as the complex is reduced.
Experimental Section
General: Thin-layer chromatography analyses were performed on
pre-coated Merck silica gel plates (60 F254) and visualized with UV
light. 1H and 13C NMR spectra were recorded on a Varian
500 MHz spectrometer and chemical shifts are given in ppm (δ)
using the residual CHCl3 peak as internal standard. Solid state
IR spectra were recorded on a Perkin–Elmer Spectrum-100 FT-IR
spectrometer with an ATR accessory. The samples were analyzed
by placing neat samples directly on the ATR crystal. Solution state
IR was performed using a Perkin–Elmer FT-IR spectrometer. UV
spectra were recorded on a Varian Cary 3 Bio UV/Vis spectrometer.
71.2, 67.7, 55.5, 41.0 ppm. FT-IR (neat): ν = 2952, 2916, 2848,
˜
2783 (C–H), 1960, 1877 (CϵO), 1538, 1482, 1461, 1430, 1252,
1178, 1020, 904, 768, 731, 666 cm–1. C73H13CrNO4·H2O (1037.04):
calcd. C 84.48, H 1.44, N 1.35; found C 84.29, H 1.49, N 1.37.
2-(4-Methoxyphenyl)-1,3-dioxolane: 4-Methoxybenzaldehyde (5 g,
36 mmol), ethylene glycol (5 g, 80 mmol), p-toluenesulfonic acid
monohydrate (50 mg, 0.26 mmol) and toluene (50 mL) was added
to a round-bottomed flask equipped with a Dean–Stark trap with
Electrochemistry: Cyclic voltammetry and controlled potential elec-
trolysis were carried out in an inert atmosphere in a glovebox by
using an Autolab potentiostat with a GPES electrochemical inter-
face (Eco Chemie). Sample solutions (4 mL) were prepared from
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Probing C60 Redox States by IR Spectroscopy
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an argon-flushed IR-cell with CaF2 windows which was sealed in-
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Acknowledgments
This work was financially supported by the Swedish Research
Council and Uppsala University Priority Program for Molecular
Electronics.
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Received: January 5, 2011
Published Online: March 4, 2011
Eur. J. Inorg. Chem. 2011, 1744–1749
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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