The [Re(CO)6]+ cation as a ligand-transfer reagent with ferrocene derivatives

Article abstract of DOI:10.1002/1099-0682(200207)2002:7<1848::AID-EJIC1848>3.0.CO;2-G

The [Re(CO)₆]⁺ cation is a stable compound, soluble in aqueous media. We show that it can be used as a reagent in the synthesis of tricarbonyl(cyclopentadienyl)rhenium complexes. [Re(CO)₆]⁺ reacts with ferrocene derivatives, particularly acetylferrocene, in DMSO, DMF or a water/DMSO (1:1) mixture at 160 °C to give tricarbonyl(cyclopentadienyl)rhenium derivatives with high yields. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200207)2002:7<1848::AID-EJIC1848>3.0.CO;2-G

FULL PAPER
The [Re(CO)6]؉ Cation as a Ligand-Transfer Reagent with Ferrocene
Derivatives
[a]
[a]
[a]
´
´
Siden Top,* Stephane Masi, and Gerard Jaouen*
Keywords: Carbonyl(cyclopentadienyl)rhenium / Hexacarbonylrhenium / Ferrocene / Ligand transfer
The [Re(CO)6]+ cation is a stable compound, soluble in aque-
ous media. We show that it can be used as a reagent in the
synthesis of tricarbonyl(cyclopentadienyl)rhenium com-
plexes. [Re(CO)6]+ reacts with ferrocene derivatives, particu-
larly acetylferrocene, in DMSO, DMF or a water/DMSO (1:1)
mixture at 160 °C to give tricarbonyl(cyclopentadienyl)rhen-
ium derivatives with high yields.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
available in the form of the perrhenate.[8] It is for this reason
that rhenium-based radiopharmaceuticals have normally
been prepared as chelates of the N2S2 or N3S type.[9] The
need for new radiopharmaceuticals with good stability has
led us to consider the idea of using the tricarbonyl(cyclo-
pentadienyl)rhenium group in place of the chelates, since it
has the advantages of being lipophilic, less bulky and more
robust.[10] The concept of using carbonyl organometallic
compounds as radiopharmaceuticals is undergoing rapid
expansion.[11] However, syntheses of cyclopentadienyl com-
plexes of Re require multi-step reactions. The traditional
methods are not available for radionuclides of rhenium. The
search for an efficient preparation method has led us to
propose a new synthesis for certain rhenium compounds,
including Re2(CO)10 at normal atmospheric pressure,[12]
and (η5-C5H4COOH)Re(CO)3 by a simple thermal reaction
of Re2(CO)10.[13] Other synthetic advances have been made
by Katzenellenbogen et al.[14] and by Alberto et al.[15] Re-
cently, Alberto demonstrated the viability of preparing
cyclopentadienyltechnetium complexes in aqueous media
using the reagent [Tc(CO)3(H2O)3]ϩ obtained from radio-
active pertechnetate.[16] However, this synthesis is limited
for the moment to cyclopentadienyl compounds bearing a
carbonyl substituent. There is therefore a clear need for a
new source of radioactive rhenium to widen the range of
organometallic radiopharmaceuticals. With this aim in
mind, [188Re(CO)6]ϩ could be generated by the decay of
188W(CO)6, thus providing a solution to the problem and
The [Re(CO)6]ϩ cation is a robust compound insensitive
to air or moisture. It is normally prepared by one of two
different standard preparation methods, either by reaction
of Re(CO)5X with AlCl3 under high pressure of CO gas,[1]
or by treating ethyl chloroformate with Re(CO)5Na at nor-
mal atmospheric pressure, followed by addition of BF3.[2]
Unlike Re2(CO)10, Re(CO)5Br or [Re(CO)5]Ϫ, precursors
that are often used as reagents in the synthesis of carbonyl
complexes of Re, [Re(CO)6]ϩ is normally considered to be
a relatively inert compound. To the best of our knowledge
only a few rare studies have dealt with its reactivity. One
example is the nucleophilic reaction with the azide ion or
amines, leading to the formation of the isocyanate Re-
(CO)5(NCO) and of the amide Re(CO)5(CONRRЈ), re-
spectively.[3] The carbonyl ligands are labile in this cation,
and up to three CO groups can be substituted by two-elec-
tron donor ligands, such as triphenylphosphane.[4] It is also
known that [Re(CO)6]ϩ reacts with the metallate anions
[Fe(CO)4]2Ϫ, [Mn(CO)5]Ϫ, [W(CO)5Cl]Ϫ and [W(CO)5H]Ϫ
by an electron-transfer reaction to give [Re(CO)5]Ϫ,
(CO)5MnRe(CO)5, Re(CO)5Cl and HRe(CO)5, respect-
ively.[5] [Re(CO)6]ϩ possesses several properties that are
worth exploiting. Firstly, its solubility and stability allow it
to be used in aqueous media. Secondly, it has been shown
that hexacarbonyltungsten is accessible in its radioactive
form 188W(CO)6 and that its disintegration should lead to
the formation of [188Re(CO)6]ϩ and [188Re(CO)5]·.[6] This
transformation is an important one, since 186Re and 188Re
are now recognized as radionuclides with therapeutic ap-
plications.[7] At present, the radionuclide of rhenium is only
Ϫ
an interesting alternative to the 188ReO4 generator based
on 188WO3.[8] 188W(CO)6 decay should clearly be the most
direct route to the production of the carbonyl rhenium re-
agent. It has already been clearly established that
[
99mTc(CO)6]ϩ can be obtained from 99Mo(CO)6.[17] This β
decay of 99Mo is interesting owing to the imaging applica-
tion of 99mTc as well as the recognized similarity between
the chemistry of Re and Tc. We were therefore interested in
examining the potential of [Re(CO)6]ϩ in the synthesis of
[a]
´
Laboratoire de Chimie Organometallique, Ecole Nationale
´
Superieure de Chimie de Paris, UMR C.N.R.S. 7576,
11, rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
Fax: (internat.) ϩ 33-1/43260061
E-mail: Jaouen@ext.jussieu.fr
1848
 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0707Ϫ1848 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 1848Ϫ1853

The [Re(CO)6]ϩ Cation as a Ligand-Transfer Reagent with Ferrocene Derivatives
FULL PAPER
organometallic complexes. The double ligand-transfer reac- C5H4COMe)Re(CO)3 was isolated in 64% yield. The choice
tion was a particular object of study with a view to prepar- of solvent has a clear influence on the outcome of the reac-
ing radiopharmaceuticals. This reaction, first reported by tion. To elucidate this point, we carried out the experiments
Wenzel,[18] has recently been enhanced by Katzenellenbogen with other common solvents, such as acetonitrile, acetone,
et al.[14] We also showed that Re2(CO)10 can be used in li- ethanol as well as water. Experimental conditions and
gand-transfer reactions with cyclopentadienyl complexes.[19] yields obtained are summarized in Table 1.
It may therefore be possible to use the [Re(CO)6]ϩ cation
in this type of ligand transfer. We describe here the first
results obtained with this cation.
[Re(CO)6][BF4] is also soluble in acetonitrile. Heating a
solution of the cation in acetonitrile at 95 °C for 27 h gave
neither (η5-C5H4COMe)Re(CO)3 nor CpRe(CO)3. The ex-
periment was repeated using a maximum temperature of
160 °C in a sealed tube. Again, no cyclopentadienylated
complex was formed, and only [Re(CO)3(MeCN)3]ϩ was
isolated. Heating the solution to boiling point in acetone or
ethanol also failed to give (η5-C5H4COMe)Re(CO)3.
Results and Discussion
Acetylferrocene was chosen for our first experiments with
[Re(CO)6]ϩ since this complex has been found to give the
best results in ligand-exchange reactions.[14]
We also tried to conduct the reaction in aqueous media,
because this solvent is the most commonly used for radio-
pharmaceutical syntheses.[16] Heating a solution of the
[Re(CO)6]ϩ cation and acetylferrocene in water at 95 °C for
2 h gave neither (η5-C5H4COMe)Re(CO)3 nor CpRe(CO)3.
On the other hand, the same reaction carried out in a pres-
sure tube gave rise to (η5-C5H4COMe)Re(CO)3 in 13%
yield. The result is even more promising in a pressure tube
with a water/DMSO (1:1) mixture: in this case a yield of
60% of (η5-C5H4COMe)Re(CO)3 was obtained. The use of
the [Re(CO)6]ϩ cation in a water-based mixture of solvents
could thus be envisaged. It is essential to consider this as-
pect when radioactive elements are handled.
Scheme 1. Ligand-transfer reaction between acetylferrocene and
hexacarbonylrhenium cation
Scheme 1 shows the synthetic route that was used.
Acetylferrocene, [Re(CO)6][BF4] and methanol were placed
in a sealed tube and heated to 170 °C. After heating for 1 h
and purification by chromatography, (η5-C5H4CO-
Me)Re(CO)3 was obtained in 30% yield. We note that
CpRe(CO)3 is not formed under these reaction conditions.
The low yield is probably due to the poor solubility of [Re(-
CO)6][BF4] in methanol. Since this compound is very sol-
The results reported below show that temperature also
has a significant effect on the reaction. To study this effect,
the exchange reaction was repeated using DMSO and DMF
as solvents at different temperatures. The results obtained
are listed in Table 2.
In DMSO, the yield of (η5-C5H4COMe)Re(CO)3 drops
uble in DMSO and DMF, the experiment was therefore re- from 70% to 58% and then to 16% when the temperature is
peated with DMSO in place of methanol as solvent. Owing lowered from 160 °C to 130 °C and then 90 °C, even when
to the high boiling point of DMSO, it was not necessary to the reaction is allowed to proceed for a longer time. The
use a sealed tube. A solution of acetylferrocene and [Re(- same pattern is observed with DMF, in which case the yield
CO)6][BF4] in commercial DMSO was heated in an oil bath drops from 64% to 23%, and finally to 0%. This result in-
at 160 °C for 30 min. In this case, a 70% yield of (η5- dicates that the reaction with [Re(CO)6][BF4] requires heat-
C5H4COMe)Re(CO)3 was obtained. DMSO was later re- ing to approximately 160 °C to obtain the rhenium tri-
placed with DMF. Under the same conditions (η5- carbonyl complex in good yield.
Table 1. Reaction of acetylferrocene with [Re(CO)6][BF4] in a variety of solvents
Entry
Solvent
Quantity of
acetylferrocene
Heating
time
Temperature
of heating bath
Yield of
(η5-C5H4COMe)Re(CO)3
1
2
3
4
5
6
7
6
7
8
DMSO
DMF
3.12 equiv.
3.12 equiv.
3.12 equiv.
3.12 equiv.
3.12 equiv.
3.12 equiv.
3.12 equiv.
1.05 equiv.
1.05 equiv.
3.12 equiv.
30 min
30 min
1 h
17 h
2 h
1 h
1 h
27 h
17 h
17 h
160 °C
70%
64%
30%
0%
160 °C
MeOH[a]
MeOH
170 °C
95 °C (reflux)
110 °C (reflux)
160 °C
H2O
0%
H2O[a]
13%
60%
0%
0%
0%
H2O/DMSO (1:1)[a]
MeCN
160 °C
95 °C (reflux)
75 °C (reflux)
95 °C (reflux)
acetone
EtOH
[a]
Reaction under pressure in a sealed tube.
Eur. J. Inorg. Chem. 2002, 1848Ϫ1853
1849

S. Top, S. Masi, G. Jaouen
FULL PAPER
Table 2. Reaction of acetylferrocene with [Re(CO)6][BF4] in DMSO and DMF
Entry
Solvent
Quantity of
acetylferrocene
Heating
time
Temperature
of heating bath
Yield of
(η5-C5H4COMe)Re(CO)3
1
2
3
4
5
6
7
8
DMSO
DMSO
DMSO
DMSO
DMF
DMF
DMF
3.12 equiv.
3.12 equiv.
1.05 equiv.
3.12 equiv.
3.12 equiv.
1.05 equiv.
1.05 equiv.
1.05 equiv.
30 min
3 h
4 h 30
5 h 30
30 min
3 h
160 °C
130 °C
130 °C
90 °C
160 °C
160 °C
130 °C
90 °C
70%
62%
58%
16%
64%
71%
23%
0%
3 h
4 h 30
DMF
Table 3. Reaction of (η5-C5H4R)FeCp with [Re(CO)6][BF4] in DMSO
Entry
R
Quantity of
Heating
time
Temperature
of heating bath
Yield of
(η5-C5H4R)FeCp
(η5-C5H4R)Re(CO)3
1
2
3
4
5
6
COMe
H
COH
COH
COOEt
CϵCH
1.05 equiv.
3.56 equiv.
1.05 equiv.
1.05 equiv.
1.05 equiv.
1.05 equiv.
4 h 30
5 h
30 min
3 h 20
2 h 30
1 h 30
130 °C
180 °C
160 °C
130 °C
160 °C
160 °C
58%
18%
12%
33%
34%
0%
We also assessed how the nature of the ferrocene sub- one-pot reaction between ReO4Ϫ and acetylferrocene in the
stituent might influence the reaction. Ferrocene, formylfer- presence of Cr(CO)6 and CrCl2 does not lead to the ex-
rocene, ethyl ferrocenecarboxylate and ethynylferrocene pected product in DMSO or in DMF. For this double li-
were all tested in reactions in DMSO. Yields and experi- gand-transfer reaction, methanol was the only solvent that
mental conditions are shown in Table 3.
provided (η5-C5H4COMe)Re(CO)3 in acceptable yield
Ferrocene gives 18% CpRe(CO)3 after 5 h of heating at (65%). This difference might be attributed to the fact that
180 °C. Formylferrocene and ethyl ferrocenecarboxylate the reduction or the carbonyl transfer did not seem to pro-
give 33% and 34%, respectively of tricarbonyl(cyclopentadi- ceed very well in DMSO or in DMF. By contrast, in our
enyl)rhenium derivatives. Ethynylferrocene, however, gives case, the best yields were obtained with DMSO or DMF,
(η5-C5H4COMe)Re(CO)3 in 48% yield instead of the ex- while methanol gave only mediocre results. It should be
pected (η5-C5H4CϵCH)Re(CO)3. This type of transforma- noted that [Re(CO)6][BF4] is the only reagent that can react
tion was also observed in the reaction with the perrhen- with ferrocene itself, while the perrhenate[14] and Re2(CO)10
ate.[14] The reaction with [Re(CO)6][BF4] was also tested [13] are inactive. To identify the real intermediate of the reac-
with a fairly complex molecule such as N-phenylferrocene- tion, the [Re(CO)6][BF4] solution in DMSO was heated to
carboxamide (Scheme 2).
80 °C for 3 h. The progress of the reaction was monitored
using IR spectroscopy. A progressive disappearance of the
peak at 2071 cmϪ1 of [Re(CO)6][BF4] and concomitant pro-
gressive formation of two peaks at 2021 cmϪ1 and 1893
cmϪ1 were observed, characteristic of a molecule possessing
C3v symmetry. We postulate the formation of
[Re(CO)3(DMSO)3]ϩ. The same transformation was also
noted when [Re(CO)6][BF4] was heated in DMF or aceton-
itrile under pressure. In this last case, it was possible to
isolate the [Re(CO)3(MeCN3)]ϩ cation which was identified
Scheme 2. Ligand-transfer reaction between N-phenylferrocenecar- by IR data.[20] Consequently, we propose that our reaction
boxamide and hexacarbonylrhenium cation
occurs in two stages (Scheme 3).
The first is the replacement of the three CO groups with
solvent molecules. This exchange occurs at around 80 °C.
Heating a solution of [Re(CO)6][BF4] and N-phenylferro- The second step is the reaction between [Re(CO)3(L)3]ϩ and
cenecarboxamide to 160 °C for 3 h gives tricarbonyl(N- the ferrocene derivative. This final reaction only begins
phenylcyclopentadienylcarboxamide)rhenium in 43% yield. around 130 °C and reaches full efficiency at 160 °C. Based
The results obtained clearly show that [Re(CO)6][BF4] on literature work, it has been suggested that the η5Ϫη3
does not react in the same way as the perrhenate.[14] The slippage of the FeϪcyclopentadienyl bond of the ferrocene
1850
Eur. J. Inorg. Chem. 2002, 1848Ϫ1853

The [Re(CO)6]ϩ Cation as a Ligand-Transfer Reagent with Ferrocene Derivatives
FULL PAPER
complexes. The reaction is rapid and in certain cases gives
good yields. Due to its reactivity in water and its potential
availability in a radioactive form, this reagent could be used
for synthesis in water, and also in radiopharmaceutical syn-
theses. The reaction with [Re(CO)6]ϩ is both simpler and
cleaner than that with the perrhenate, which requires a CO
source and high pressure. We are continuing to study other
types of reactions with this cation.
Experimental Section
General: The synthesis of all the compounds was performed under
ambient atmospheric conditions. DMSO was used without any
purification. TLC chromatography was performed on silica gel 60
GF254. Infrared spectra were obtained with an IR-FT BOMEM
Michelson-100 spectrometer. 1H and 13C NMR spectra were re-
corded with 200 MHz and 400 MHz Bruker spectrometers. Mass
spectrometry was performed with a Nermag R 10-10C spectro-
meter. Melting points were measured with a Kofler device. Ele-
mental analyses were performed by the regional microanalysis de-
Scheme 3. Possible mechanism of cyclopentadienyl transfer reac-
tion
derivative is responsible for its reaction with [Re(CO)3-
(MeO)(MeOH)2].[14] It has also been observed that
the ferrocene derivative reacts with [(naphthalene)-
´
partment of the Universite Pierre et Marie Curie.
Hexacarbonylrhenium: [Re(CO)6][BF4] was prepared according to
the procedure described in the literature.[2] IR (CH3CN): ν˜ ϭ 2085
Mn(CO)3]BF4
via
the
dimetallic
intermediate
(νCO) cmϪ1
.
[CpϪFeϪCpЈϪMn(CO)3]ϩ.[21] Two mechanistic possibil-
ities thus spring to mind for the reaction with Synthesis of (Acetylcyclopentadienyl)tricarbonylrhenium in DMSO
[Re(CO)3(L)3]ϩ. The first is the η5Ϫη3 slippage of the
and in DMF: [Re(CO)6][BF4] (0.073 g, 0.166 mmol) was dissolved
in DMSO (1 mL) in a 5-mL round-bottom flask equipped with a
magnetic stirrer bar. Acetylferrocene (0.040 g, 0.175 mmol) was ad-
ded and the solution heated for 4 h 30 min at 130 °C. The mixture
was allowed to warm to room temperature and then 10 mL of water
was added. The product was extracted with dichloromethane (2 ϫ
50 mL). The organic phase was washed, dried (MgSO4), filtered
and concentrated. The mixture was purified by chromatography on
FeϪcyclopentadienyl bond, allowing the formation of the
intermediate I which is converted into the tricarbonylrhen-
ium compound. The second possibility is formation of the
dimetallic intermediate II, followed by breaking of the
FeϪCpЈ bond. Sweigart has shown that heating to 40 °C in
dichloromethane is sufficient to cause [(naphtha-
lene)Mn(CO)3]BF4 to react with a ferrocene derivative,
leading to formation of tricarbonyl(cyclopentadienyl)man-
a silica gel plate (petroleum ether/ethyl acetate, 7:1) to give (acetyl-
cyclopentadienyl)tricarbonylrhenium (0.036 g, 58%). 1H NMR
ganese. Heating [Re(CO)3(L)3]ϩ with the ferrocene com- (200 MHz, CDCl3): δ ϭ 2.34 (s, 3 H, CH3), 5.40 (t, J ϭ 2.2 Hz, 2
H, 3,4-H of C5H4), 5.98 (t, J ϭ 2.2 Hz, 2 H, 2,5-H of C5H4) ppm.
IR (CH2Cl2): ν˜ ϭ 2032 s, 1939 s (νCO), 1688 w (COCH3) cmϪ1. By
using DMF as solvent and by applying the same procedure (heating
time: 3 h), 23% yield of (acetylcyclopentadienyl)tricarbonylrhenium
was obtained.
pound to a high temperature is thus necessary to change
the hapticity of the cyclopentadienyl ligand (intermediate
I), or to drive off the three solvent molecules (intermediate
II). Without proof of the formation of intermediates I and
II, it is difficult at this stage to suggest a precise mechanism.
However, the acetyl group on the cyclopentadienyl ring,
acting as an electron-withdrawing group, should minimize
the formation of the intermediate II. It is noteworthy that
the reaction under pressure, using acetonitrile as the sol-
vent, stops only at the point where [Re(CO)3(Me3CN)3]ϩ is
formed indicating that this intermediate is not sufficiently
reactive in the ligand-transfer reaction. To summarize,
[Re(CO)3(Me3CN)3]ϩ is not an efficient intermediate, but
its existence is a valuable mechanistic indicator suggesting
future directions in the use of [Re(CO)6]ϩ.
Synthesis of (Acetylcyclopentadienyl)tricarbonylrhenium under Pres-
sure: [Re(CO)6][BF4] (0.073 g, 0.166 mmol) and acetylferrocene
(0.118 g, 0.519 mmol) were combined in a 20-mL pressure tube
containing a magnetic stirrer bar. Methanol (1 mL) was added, and
the tube was sealed and heated to 170 °C. After the heating period,
the tube was cooled to room temperature. The solvent was evapor-
ated, the mixture was dissolved in a minimum volume of CH2Cl2
and purified by chromatography on a silica gel plate (petroleum
ether/ethyl acetate, 7:1) to give (acetylcyclopentadienyl)tricarbon-
ylrhenium (0.020 g, 30%).
Ethyl Ferrocenecarboxylate: Ferrocenecarboxylic acid (0.500 g,
2.17 mmol) was dissolved in ethanol (12 mL) in a 25-mL round-
bottom flask equipped with
a magnetic stirrer bar. H2SO4
Conclusion
(0.15 mL) was added, and the solution heated under reflux for 12 h.
The mixture was allowed to cool to room temperature and the solv-
ent was partially evaporated. Cold water (10 mL) was added and
the product was extracted with diethyl ether (3 ϫ 100 mL). The
We have shown for the first time that the [Re(CO)6]ϩ cat-
ion reacts with ferrocene derivatives through a ligand-trans-
fer reaction to give tricarbonyl(cyclopentadienyl)rhenium organic phase was washed first with saturated K2CO3 solution, to
Eur. J. Inorg. Chem. 2002, 1848Ϫ1853 1851

S. Top, S. Masi, G. Jaouen
FULL PAPER
eliminate the excess acid, and then with water. The organic phase
was dried (MgSO4), filtered and concentrated. The mixture was
Reaction with (N-Phenyl)ferrocenecarboxamide: The procedure is
similar to that of the synthesis of (acetylcyclopentadienyl)tricar-
purified by chromatography on a silica gel plate (petroleum ether/ bonylrhenium in DMSO. N-phenylferrocenecarboxamide (0.054 g,
ethyl ether, 4:1) to give ethyl ferrocenecarboxylate (0.108 g, 19%).
0.175 mmol)was used and the reaction mixture was heated for 3 h
1H NMR (200 MHz, CDCl3): δ ϭ 1.37 (t, J ϭ 7.1 Hz, 3 H, CH3), at 160 °C. The compound was purified by chromatography on a
4.21 (s, 5 H, Cp), 4.29 (q, J ϭ 7.1 Hz, 2 H, OϪCH2Ϫ), 4.40 (t, J ϭ silica gel plate (ethyl acetate/petroleum ether, 2:1) to give tricarbon-
1.9 Hz, 2 H, 3,4-H of C5H4), 4.82 (t, J ϭ 1.9 Hz, 2 H, 2,5-H of yl(N-phenylcyclopentadienylcarboxamide)rhenium (0.032 g, 43%),
C5H4) ppm. MS (EI): m/z ϭ 258 [M]ϩ, 230 [M Ϫ C2H4]ϩ, 138,
m.p. 179 °C. 1H NMR (200 MHz, (CD3)2CO): δ ϭ 5.72 (t, J ϭ
2.3 Hz, 2 H, 3,4-H of C5H4), 6.41 (t, J ϭ 2.3 Hz, 2 H, 2,5-H of
C5H4), 7.10 (m, 1 H, Ph), 7.32 (m, 2 H, Ph), 7.67 (m, 2 H, Ph),
9.25 (s, 1 H, ϪNHϪCO) ppm. 13C NMR (100 MHz, (CD3)2CO):
δ ϭ 86.6 (CCp), 88.1 (CCp), 96.5 (CCp), 120.9 (CAr), 124.7 (CAr),
129.4 (CAr), 139.3 (CAr), 161.0 (NHCϭO), 194.1 (CO) ppm. IR
(CH2Cl2): ν˜ ϭ 2033 s, 1945 s (νCO) cmϪ1. MS (EI): m/z ϭ 455
[M]ϩ, 427 [M Ϫ CO]ϩ, 371 [M Ϫ 3CO]ϩ. C15H10NO4Re (454.45):
calcd. C 39.64, H 2.22, N 3.08; found. C 40.05, H 2.00, N 3.00.
121, 56 [Fe]ϩ.
N-Phenylferrocenecarboxamide: The reaction was carried out under
argon in a Schlenk tube equipped with a reflux condenser. Ferro-
cenecarboxylic acid (0.152 g, 0.66 mmol) was placed into the
Schlenk tube and cooled with an ice bath. Oxalyl chloride (3 mL,
34 mmol) was then added and the solution was kept at room tem-
perature for 2 h. The oxalyl chloride was evaporated. The acyl
chloride formed was dissolved in anhydrous THF (4 mL), and anil-
ine (0.186 g, 2 mmol) was added dropwise. The mixture was stirred
for 3 h then separated by chromatography on a silica gel plate (pet-
roleum ether/dichloromethane, 1:1) to give N-phenylferrocenecar-
boxamide (0.114 g, 57%) m.p. 211 °C. 1H NMR (200 MHz,
(CD3)2CO): δ ϭ 4.24 (s, 5 H, Cp), 4.42 (dd, J ϭ 1.9 Hz, 2 H, 3,4-
H of C5H4), 4.97 (dd, J ϭ 1.9 Hz, 2 H, 2,5-H of C5H4), 7.05 (m, 1
H, Ph), 7.31 (m, 2 H, Ph), 7.76 (m, 2 H, Ph), 8.84 (s, 1 H, NH)
ppm. 13C NMR (50 MHz, (CD3)2CO): δ ϭ 73.7, 74.6, 75.5, 77.8,
120.8, 123.9, 129.4, 140.5, 168.9 (CO) ppm. MS (EI): m/z ϭ 305
[M]ϩ, 213 [CpFeC5H4CO]ϩ, 185 [FeCp2]ϩ, 65 [Cp]ϩ. C17H15FeNO
(305.16): calcd. C 66.91, H 4.95, N 4.59; found. C 66.70, H 5.27,
N 4.39.
Reaction with Formylferrocene: The procedure is similar to that of
the synthesis of (acetylcyclopentadienyl)tricarbonylrhenium in
DMSO. Formylferrocene (0.038 g, 0.175 mmol) was used in a reac-
tion that underwent 3 h 20 min of heating at 130 °C. The com-
pound was purified by chromatography on a silica gel plate (petro-
leum ether/ethyl acetate, 5:1) to give tricarbonyl(formylcyclopenta-
1
dienyl)rhenium (0.020 g, 33%). H NMR (200 MHz, CDCl3): δ ϭ
5.5 (t, J ϭ 2.4 Hz, 2 H, 3,4-H of C5H4), 6.0 (t, J ϭ 2.4 Hz, 2 H,
2,5-H of C5H4), 9.59 (s, 1 H, ϪCOH) ppm. IR (CHCl3): ν˜ ϭ 2036
s, 1945 s (νCO), 1693 w (ϪCHO) cmϪ1. IR (KBr): ν˜ ϭ 2031 s, 1920
s (νCO), 1690 w (ϪCHO) cmϪ1. MS (EI): m/z ϭ 364 [M]ϩ, 336 [M
Ϫ CO]ϩ, 308 [M Ϫ 2 CO]ϩ, 280 [M Ϫ 3 CO]ϩ. Also isolated was
Re2(CO)10 (0.005 g, 4%). IR (CHCl3): ν˜ ϭ 2071 w, 2014 vs (νCO),
1971 w cmϪ1
.
Reaction in Water and in Water/DMSO: [Re(CO)6][BF4] (0.073 g,
0.166 mmol) and acetylferrocene (0.118 g, 0.519 mmol) were com-
bined in a 20-mL pressure tube containing a magnetic stirrer bar.
Water (1 mL) was added, then the tube was sealed and heated to
160 °C. After heating for 1 h, the tube was cooled to room temper-
ature. 10 mL of water was added. The product was extracted with
dichloromethane (2 ϫ 50 mL). The organic phase was dried
(MgSO4), filtered and concentrated. The mixture was purified by
chromatography on a silica gel plate (petroleum ether/ethyl acetate,
7:1) to give (acetylcyclopentadienyl)tricarbonylrhenium (0.008 g,
13%). By using a water/DMSO mixture (0.5 mL/0.5 mL) as solvent
and by applying the same procedure, 60% yield of (acetylcyclo-
pentadienyl)tricarbonylrhenium was obtained.
Reaction with Ethyl Ferrocenecarboxylate: The procedure is similar
to that of the synthesis of (acetylcyclopentadienyl)tricarbonylrhen-
ium in DMSO. Ethyl ferrocenecarboxylate (0.045 g, 0.175 mmol)
was used in a reaction that underwent 2 h 30 min of heating at 160
°C. The compound was purified by chromatography on a silica gel
plate (petroleum ether/ethyl ether, 4:1) to give tricarbonyl(ethoxyca-
bonylcyclopentadienyl)rhenium (0.023 g, 34%). 1H NMR
(200 MHz, CDCl3): δ ϭ 1.32 (t, J ϭ 7.1 Hz, 2 H, CH3), 4.28 (q,
J ϭ 7.1 Hz, 2 H, OCH2), 5.37 (t, J ϭ 2.3 Hz, 2 H, 3,4-H of C5H4),
6.02 (t, J ϭ 2.3 Hz, 2 H, 2,5-H of C5H4) ppm. IR (CHCl3): ν˜ ϭ
2033 s, 1945 s (νCO), 1722 w (ϪCOϪOEt) cmϪ1. MS (EI): m/z ϭ
408 [M]ϩ, 380 [M Ϫ CO]ϩ, 352 [M Ϫ 2 CO]ϩ, 324 [M Ϫ 3 CO]ϩ,
308, 268, 225.
Reaction in Acetonitrile: [Re(CO)6][BF4] (0.073 g, 0.166 mmol) and
acetylferrocene (0.040 g, 0.175 mmol) were combined in a 20-mL
pressure tube containing a magnetic stirrer bar. Acetonitrile (1 mL)
was added, then the tube was sealed and heated to 170 °C. After
the heating period, the tube was cooled to room temperature. The
solvent was evaporated, the mixture was dissolved in a minimum
volume of CH2Cl2 and purified by chromatography on a silica gel
Acknowledgments
Financial support from the Centre National de la Recherche Scien-
tifique is gratefully acknowledged. We thank Barbara McGlinchey
for the manuscript translation.
plate
[Re(CO)3(CH3CN)3]ϩ (0.042 g). IR (CH2Cl2): ν˜ ϭ 2053 s, 1953 s
(νCO) cmϪ1
(petroleum
ether/ethyl
acetate,
7:1)
to
give
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The [Re(CO)6]ϩ Cation as a Ligand-Transfer Reagent with Ferrocene Derivatives
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