Synthesis of new ferrocenyl derivatives and their use in the first cyclopropanation of fullerene C60 with ferrocenes

Article abstract of DOI:10.1016/S0022-328X(03)00590-4

New ferrocenyl derivatives (a β-ketoester and a β-diester) were synthesised and linked to fullerene C₆₀, with the aim to elucidate factors involved in intramolecular electronic communication. These are the first examples of fullerene functionalised with ferrocenes via the cyclopropanation reaction. The resulting dyads were characterised.

Full text of DOI:10.1016/S0022-328X(03)00590-4

Journal of Organometallic Chemistry 679 (2003) 202Á207
/
www.elsevier.com/locate/jorganchem
Synthesis of new ferrocenyl derivatives and their use in the first
cyclopropanation of fullerene C60 with ferrocenes
Barbara Floris a,*, Pierluca Galloni a, Roberta Seraglia b, Pietro Tagliatesta a
a Dipartimento di Scienze e Tecnologie Chimiche, Universita` di Roma, ‘‘Tor Vergata’’, I-00133 Roma, Italy
b CNR, ISTM Sez. di Padova, Via Marzolo 1, I-35100 Padova, Italy
Received 1 May 2003; received in revised form 17 June 2003; accepted 18 June 2003
Abstract
New ferrocenyl derivatives (a b-ketoester and a b-diester) were synthesised and linked to fullerene C60, with the aim to elucidate
factors involved in intramolecular electronic communication. These are the first examples of fullerene functionalised with ferrocenes
via the cyclopropanation reaction. The resulting dyads were characterised.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Cyclopropanation; Ferrocenyl derivatives; Fullerene; Ferrocenes
1. Introduction
2. Results and discussion
Fullerene derivatives are being prepared in an in-
creasing number, because of their interesting applica-
tions, e.g. in modified biomolecules and medicinal
chemistry [1] or in material science [2]. In particular,
electron transfer systems are of interest, since they are
related to the problem of artificial photosynthesis [3]. In
this respect, the coupling of a strong electron-attracting
moiety, as C60, with a strong electron-donating species,
as the ferrocenyl group, is promising and a number of
dyads and triads containing both Fc (ferrocenyl) and
C60 moieties have been described [4]0. However, the
Ethyl 3-ferrocenyl-3-oxopropanoate, FcCOCH2-
CO2Et, was prepared in a 76% yield from ferrocene
and ethyl 2-chlorocarbonylethanoate, by a FriedelÁ
/
Crafts acylation. The b-ketoester, pure at the gas
chromatographic analysis, showed a mass spectrum
with Mꢀ ꢁ300 m/z (MF, 300.14) and a 1H-NMR
/
spectrum complicated by the presence of some amount
of the enol form (enolic OH at d 17 ppm), but in
agreement with what expected for a mono-substituted
ferrocene.
Ethyl ferrocenylmethyl propanedioate, FcCH2O-
COCH2CO2Et, was prepared in a 82% yield from
ferrocenylmethanol, FcCH2OH (that, in turn, was
obtained reducing with NaBH4 the commercially avail-
able ferrocenecarboxyaldehyde, FcCHO) and ethyl 2-
chlorocarbonylethanoate. The obtained b-diester, pure
ferrocenes used for the construction of ferroceneÁfull-
/
erene dyads were generally commercial compounds. We
report here the preparation of new ferrocenyl deriva-
tives, designed ad hoc, in order to obtain substrates
suitable for introduction in ferroceneÁfullerene dyads.
/
at the GC analysis, presented a mass spectrum with
Moreover, these compounds were used to prepare the
dyads, applying for the first time the Bingel [5]
cyclopropanation with ferrocenes.
1
330 m/z (MF, 330.16) and a H-NMR spectrum
M
ꢀ ꢁ
characteristic of a mono-substituted ferrocene.
/
Both ferrocenyl derivatives were reacted with full-
erene in anhydrous toluene, in the presence of I2 and
DBU (1,8-diazabicyclo[5.4.0]-7-undecene). Reagents,
conditions, and yields for all the reactions were reported
in Scheme 1. Dyads 1 (MF, 1018.78) and 2 (MF,
* Corresponding author. Tel.:
72594328.
E-mail address: floris@uniroma2.it (B. Floris).
ꢀ
/
390-6-72594351; fax:
ꢀ/390-6-
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00590-4

B. Floris et al. / Journal of Organometallic Chemistry 679 (2003) 202Á
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Scheme 1. Synthesis of ferrocene precursors and of ferroceneÁfullerene dyads.
/
1048.79) were purified by column chromatography, with
purity checked via HPLC, and characterised by
MALDI-TOF mass spectrometry (Fig. 1). Attempts to
grow crystals for X-ray analysis failed. 1H-NMR spectra
in CDCl3 changed with concentration, probably as a
consequence of molecular stacking. Moreover, it was
very difficult to get completely rid of toluene from the
reaction. The signal of COCH2CO disappeared in the
spectra of both 1 and 2. The low solubility prevented the
possibility to obtain 13C-NMR spectra. IR spectra
cmꢂ1), [6]beside the CO absorption (1745 cmꢂ1).
Significant changes were observed in electronic spectra,
both in lmax and in molar extinction, o, as reported in
Table 1. In particular, in the range 280Á320 nm a large
/
variation of spectra was observed, as illustrated in Fig.
2, where the spectra of equimolar solutions of
FcCOCH2CO2Et, fullerene, and the dyad 1 are re-
ported.
Voltammetric measurements in anhydrous CH2Cl2
evidenced a shift in oxidation potential, from 0.79 V of
FcCOCH2CO2Et to 0.66 V of dyad 1. For the latter, two
maintained features typical of fullerene (720 cmꢂ1
and mono-substituted ferrocenes (1001 and 1105
)
reduction potentials were also recorded, at ꢂ0.59 and
/

204
B. Floris et al. / Journal of Organometallic Chemistry 679 (2003) 202Á207
/
Fig. 1. MALDI-TOF mass spectra of fullereneÁferrocene dyads 1 and 2.
/
oxidation potential at 0.39 V). In order to have better
data, better work is necessary to optimise the analysis
conditions, especially in view of the problems related to
the recently discussed retro-Bingel electrochemical reac-
tion [9].
Table 1
Electronic spectra of dyads 1 and 2, compared with those of ferrocene
precursors and fullerene
Compound
lmax
o
Concentration
(M)
These results are indicative of some electronic com-
munication within the molecule and work is in progress
to link other b-dicarbonyl derivatives of ferrocene to
fullerene, with the aim to fine-tuning the structure in
order to obtain better intramolecular electronic transfer.
Fullerene
FcCOCH2CO2Et
Dyad 1
329, 406 38100, 2200
322, 463 2100, 500
6.1ꢃ
/
10ꢂ5
10ꢂ4
10ꢂ5
3.3ꢃ
/
318, 426, 31600, 2000, 6.2ꢃ
468 1700
, 200
/
FcCH2OCOCH2CO2Et 320 (sh),
454
Á/
1.5ꢃ
/
10ꢂ3
10ꢂ5
Dyad 2
327, 428, 19200, 8300, 2.5ꢃ
/
456 11100
3. Experimental
Solvent, CH2Cl2.
Gas chromatographic analyses have been carried out
with a Varian CP3000 instrument, equipped with a 30
ꢂ
/
0.95 V, shifted from those of fullerene (ꢂ
/
0.44 and
ꢂ
/
0.82 V, respectively [7]). Although the variations may
mꢃ0.25 mm capillary column (methylsilicone). A
/
seem not very large, they are higher than those of other
examples in the literature [8].
As to dyad 2, only preliminary data are available (a
Bruker AM400 spectrometer was used to obtain 1H-
and 13C-NMR spectra, as CDCl3 solutions with Me4Si
as the internal standard. GasÁ
lyses have been performed with a GC/MS Shimadzu
CP6000 system (30 mꢃ0.25 mm capillary column).
/mass spectrometry ana-
reduction potential at ꢂ0.61 V and a very weak
/
/
Direct inlet (FAB) mass spectra were obtained with a
VG Quattro spectrometer. MALDI-MS measurements
were performed on a Reflex time-of-flight instrument
(Bruker-Franzen
Analytik,
Bremen,
equipped with an SCOUT ion source, operating in
Germany)
linear positive mode. Ions, formed by a pulsed laser
beam (nitrogen laser; lꢁ337 nm), were accelerated to
/
25 kV. Pulsed ion extraction (PIE) was done applying to
the second grid a voltage of 23 kV for 150 ns. 2,5-
Dihydroxybenzoic acid (DHB) was used as matrix (10
mg mlꢂ1 in acetone). About 0.5 mg of each sample was
dissolved in 1 ml of chloroform. 5 ml of sample solution
was added to the same volume of matrix solution. 1 ml of
the resulting mixture was deposited on the stainless steel
sample holder and allowed to dry before introduction
into the mass spectrometer. External mass calibration
Fig. 2. Comparison of the electronic spectra of ethyl 3-ferrocenyl-3-
oxopropanoate (dotted line), fullerene (dashed line), and dyad 1 (solid
line) at the same concentration (6.1ꢃ
10ꢂ5 M in CHCl3).
/

B. Floris et al. / Journal of Organometallic Chemistry 679 (2003) 202Á
/207
205
was made using the [Mꢀ
/
H]ꢀ ions of DHB (m/z 155),
Angiotensin II (m/z 1047) and bovine insulin (m/z
5734).
2H, b-protons of the substituted Cp ring), 4.70 (com-
plex, 2H, a-protons of the substituted Cp ring) ppm.
Resonances (d) of 13C-NMR spectra (CDCl3) are
reported in Scheme 2.
Infrared spectra were recorded with a PerkinÁElmer
/
IR783 spectrophotometer, in Nujol (NaCl disks). UV
measurements were carried out with a Hewlett-Packard
8452A diode array spectrophotometer. HPLC analyses
were performed with a Shimadzu LC-10 AD instrument,
equipped with a 5 mm MetaPhor ODS-2 column (reverse
Ethyl ferrocenylmethyl propanedioate, FcCH2O-
COCH2CO2Et. FcCH2OH (1.1 g, 5.1 mmol) and
ClCOCH2CO2Et (0.7 g 5.1 mmol) in 15 ml anhydrous
THF was added dropwise to a suspension of NaHCO3
in 20 ml anhydrous THF containing 1 ml 2,2-dimethox-
ypropane, as a water scavenger. The mixture was stirred
12 h at room temperature, then poured into water and
extracted with diethyl ether. By evaporation of the
solvent, the diester was obtained as the sole product
(GC analysis). Recrystallisation from pentane and cool-
ing afforded 1.38 g of the diester, as a yellow solid that
melted out of the refrigerator; yield, 82%.
phase) as an UVÁVis diode array SPD-M10A detector.
/
Voltammetric measurements were carried out with a
Solatron 1285 instrument, equipped with software Corr
Ware, electrochemical cell with nitrogen inlet and outlet,
and Pt electrodes. The measurements were performed in
0.1 M tetrabutylammonium perchlorate in anhydrous
CH2Cl2, using SCE as the reference electrode.
These reaction conditions gave a result better than
that from a previous run, performed with DBU as the
base, at 0 8C. 2 mmol FcCH2OH and 2 mmol DBU in
50 ml anhydrous THF were added dropwise to 3.4 mmol
ClCOCH2CO2Et in 20 ml anhydrous THF at 0 8C and
then reacted 10 h at room temperature, under inert
atmosphere. After usual work-up, FcCH2OCOCH2-
CO2Et (1.4 mmol; yield, 70%) was obtained as the
only product.
3.1. Synthesis of ferrocenes
All the syntheses required dried glassware, dry
solvents, and inert atmosphere.
Ethyl
3-ferrocenyl-3-oxopropanoate,
FcCOCH2-
CO2Et. 5.6 g ferrocene (30 mmol) and 4 ml ClCOCH2-
CO2Et (4.5 g, 30 mmol) in 150 ml CH2Cl2 were added
dropwise to a suspension of 6.0 g AlCl3 in 70 ml of the
same solvent. After 24 h stirring, the solution was
poured into 250 ml of aqueous 5% ammonium chloride
and extracted with dichloromethane. The organic layer
was washed with water, dried over anhydrous sodium
sulphate, and evaporated. The crude mixture was
purified by column chromatography (silica gel, chloro-
form). The product, eluted as the second fraction, was
recrystallised from pentane, to give 6.84 g of a red solid
MS (EI, 70 eV): m/z, 330 [Mꢀ], 199 (FcCH2ꢀ). MS
(FAB, 3-nitrobenzyl alcohol): m/z, 331 [Mꢀꢀ
/
H]. IR
1002, 1105 cmꢂ1
7 Hz, 3H, CH2CH3),
(Nujol) nCO
ꢁ
/
1725, 1745 cmꢂ1; nCp
ꢁ
/
.
1H-NMR (CDCl3) d 1.22 (t, Jꢁ
/
3.35 (s, 2H, COCH2CO), 4.15 (complex, 9H, super-
position of unsubstituted Cp ring, b-protons of the
substituted Cp ring and CH2CH3), 4.25 (complex, 2H,
a-protons of the substituted Cp ring), 4.92 (s, 2H,
FcCH2O) ppm. Resonances (d) of 13C-NMR spectra
(CDCl3) are reported in Scheme 2.
(yield, 76%): m.p., 36Á37 8C.
/
These reaction conditions gave a result better than
that from a previous run, performed at the reflux
temperature for 10 h. Although the compound from
the column chromatography is pure, it is liquid and
decomposes, even if stored in the refrigerator. There-
fore, the recrystallisation is necessary in order to obtain
the ketoester as a solid, that is more stable.
3.2. Synthesis of dyads
Equivalent amounts (0.1 mmol) of the ferrocenyl
derivative, fullerene C60, and iodine in anhydrous
toluene were reacted with DBU (0.3 mmol) for 16Á18
h, at room temperature, under inert atmosphere. The
dyads were purified by column chromatography (silica
/
GC/MS: m/z, 213 [Mꢀ Ã
/
CO2Et], 185 (Fcꢀ). MS
1
(FAB, 3-nitrobenzyl alcohol): m/z, 301 [Mꢀꢀ
/
H]. H-
NMR (CDCl3) d 1.21 (t, Jꢁ/6.7 Hz, 3H, CH2CH3), 3.65
gel, 1:1 (v/v) tolueneÁhexane to recover unreacted
/
(s, 2H, COCH2CO), 4.14 (complex, 7H, superposition of
unsubstituted Cp ring and CH2CH3), 4.47 (complex,
fullerene, then toluene to elute the dyad). The purity
was checked by HPLC (reverse phase column, toluene).
Scheme 2. 13C-NMR chemical shifts of ferrocene derivatives.

206
B. Floris et al. / Journal of Organometallic Chemistry 679 (2003) 202Á207
/
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Dyad 1, from ethyl 3-ferrocenyl-3-oxopropanoate. MS
(MALDI-TOF): m/z 1018 [Mꢀ]. IR (Nujol) nCO
1700, 1745 cmꢂ1; nCp 1002, 1105 cmꢂ1; nC60
720
cmꢂ1 1H-NMR (CDCl3) d 1.20 (t, Jꢁ
6.7 Hz, 3H,
ꢁ
/
(d) S. Fukuzumi, J. Phys. Org. Chem. 15 (2002) 448;
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Angew. Chem. Int. Ed. 41 (2002) 2344;
ꢁ
/
ꢁ
/
.
/
CH2CH3), 4.35 (s, 2H, CH2CH3) partially superimposed
with 4.40 (s, 5H, unsubstituted Cp ring), 4.60 (complex,
2H, b-protons of the substituted Cp ring), 4.70 (com-
plex, 2H, a-protons of the substituted Cp ring) ppm.
Dyad 2, from ethyl ferrocenylmethyl propanedioate.
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H]. IR (Nujol),
/
1
nCO
ꢁ
/
1745 cmꢂ1; nC60
ꢁ
/
720 cmꢂ1. H-NMR (CDCl3)
7 Hz, 3H, CH2CH3), 4.45 (complex, 9H,
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d 1.3 (t, Jꢁ
/
superposition of unsubstituted Cp ring, b-protons of the
substituted Cp ring, and CH2CH3), 4.70 (complex, 2H,
a-protons of the substituted Cp ring), 5.00 (s, 2H,
FcCH2O) ppm.
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Acknowledgements
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We wish to thank Prof. Michele Maggini for helpful
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