Cyclopentadienyl transfer reaction: Thermal reaction between Re2(CO)10 and a series of cyclopentadienyl transition metal complexes

Article abstract of DOI:10.1016/S0022-328X(99)00618-X

A thermal ligand transfer reaction between a series of organometallic cyclopentadienyl complexes and Re₂(CO)₁₀ as a source of Re(CO)₃ is described. The expected CpRe(CO)₃ complex, a very robust molecule, is obtained in yields ranging from poor, when the cyclopentadienyl precursor is thermally too stable or subject to a facile decomposition giving rise too easily to the volatile cyclopentadiene molecule, to excellent, such as with Cp₂TiCl₂ or Cp₂Ni. We interpret the observed behavior by the fact that the hapticity of the ligand in the Ti and Ni substrates changes easily allowing for an extra temporary coordination of [Re₂(CO)₉], for example, generated in situ and leading to CpRe(CO)₃. Heating titanium compound 1 with Re₂(CO)₁₀ led to CpRe(CO)₃ and the substituted cyclopentadienyltricarbonylrhenium compound 2 with yields of 36 and 37%, respectively.

Full text of DOI:10.1016/S0022-328X(99)00618-X

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 167–174
Cyclopentadienyl transfer reaction: thermal reaction between
Re2(CO)10 and a series of cyclopentadienyl transition metal
complexes
Siden Top 1, Christophe Lescop, Jean-Se´bastien Lehn, Ge´rard Jaouen *
Laboratoire de Chimie Organome´tallique, Ecole Nationale Supe´rieure de Chimie de Paris, UMR CNRS 7576, 11, rue Pierre et Marie Curie,
75231 Paris Cedex 05, France
Received 29 May 1999; accepted 18 October 1999
Abstract
A thermal ligand transfer reaction between a series of organometallic cyclopentadienyl complexes and Re2(CO)10 as a source
of Re(CO)3 is described. The expected CpRe(CO)3 complex, a very robust molecule, is obtained in yields ranging from poor, when
the cyclopentadienyl precursor is thermally too stable or subject to a facile decomposition giving rise too easily to the volatile
cyclopentadiene molecule, to excellent, such as with Cp2TiCl2 or Cp2Ni. We interpret the observed behavior by the fact that the
hapticity of the ligand in the Ti and Ni substrates changes easily allowing for an extra temporary coordination of [Re2(CO)9], for
example, generated in situ and leading to CpRe(CO)3. Heating titanium compound 1 with Re2(CO)10 led to CpRe(CO)3 and the
substituted cyclopentadienyltricarbonylrhenium compound 2 with yields of 36 and 37%, respectively. © 2000 Elsevier Science S.A.
All rights reserved.
Keywords: Ligand transfer reaction; Cyclopentadienyl transfer; Thermal reaction; Rhenium carbonyl; Cyclopentadienyltricarbonylrhenium
duce the intermediate [Re2(CO)9] [5]. For the purposes
of this paper, we chose to focus our work on the
1. Introduction
formation of cyclopentadienyltricarbonylrhenium from
Transfer of an organic ligand from one transition
the thermal reaction of Re2(CO)10 with cyclopentadi-
metal unit to another is an interesting reaction when
enyl complexes. Besides the fundamental understanding
the complex cannot be prepared by conventional meth-
of this ligand transfer process, this reaction may have
ods. Several examples have been discussed in literature
some interest in the synthesis of bio inspired rhenium
[1]. The organic ligands can be, for example, p-allyl,
complexes. For example, we prepared several cyclopen-
tadienyltricarbonylrhenium complexes of 17a-ethyny-
p-cyclobutadiene or p-cyclopentadienyl coordinates.
Several types of complexes have been used for such an
loestradiol which might act as radiopharmaceuticals if
exchange. For example, Cp2Ni reacted with Fe(CO)5 to
the complex could be prepared with radioactive rhe-
give a mixture of [CpFe(CO)2]2, CpNi(CO)2Fe(CO)Cp,
nium isotopes [6]. Because of time constraints and very
and [CpNi(CO)]2 [2]. A reaction between Cp2Ni and
low amounts of radioactive rhenium available for the
Ni(CO)4 produced [CpNi(CO)]2 [3]. Re2(CO)10 is the
synthesis, our multistep synthetic pathway was not
precursor for most rheniumcarbonyl complexes. The
compatible with the access to radioactive hormones.
ReꢀRe bond can be cleaved photochemically leading to
the formation of the radical [Re(CO)5] [4], or under
We also demonstrated that Re2(CO)10 can be prepared
in 1 h under mild conditions, 1 atm of CO gas at 70°C,
thermal reaction, Re2(CO)10 loses a CO ligand to pro-
from perrhenate [7]. Therefore, a ligand transfer reac-
tion between preformed cyclopentadienyl complexes
* Corresponding author. Tel.: +33-1-43269555; fax: +33-1-
and Re2(CO)10 would be a solution to organometallic
43260061.
radiopharmaceuticals providing that this reaction
proves to be a fast and efficient way to prepare cy-
E-mail address: siden@ext.jussieu.fr (G. Jaouen)
1 Also corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00618-X

168
S. Top et al. / Journal of Organometallic Chemistry 593–594 (2000) 167–174
Scheme 1.
clopentadienyltricarbonylrhenium complexes from
Re2(CO)10.
Cp2TiCl2, being a complex of Group 4 transition
metal, reacted slowly with Re2(CO)10, after 2 h of
heating, the solution was still red with a formation of a
red mastic on the flask walls. The IR of the solution
showed the presence of CpRe(CO)3 but also Cp2TiCl2
and Re2(CO)10. Chromatography of the solution per-
mitted the isolation of CpRe(CO)3 with a 45% yield. It
is interesting to note that the infrared spectrum of the
red mastic showed, besides absorption frequencies of
Cp2TiCl2, two other frequencies at 2046 and 1985 cm−1
which may have belonged to ClRe(CO)5. If the heat was
maintained for 4 h, all of the Re2(CO)10 was consumed
and CpRe(CO)3 was isolated in a very good yield, 84%.
CpTiCl3 did not give a yield as good as Cp2TiCl2. After
2 h of heating, much Re2(CO)10 was still present and
only a 40% yield of CpRe(CO)3 was obtained. Heating
for 4 h did not increase the yield. Cp2ZrCl2 was less
reactive than Cp2TiCl2, after 4 h of heating, Re2(CO)10
was still largely present in the solution, and only a 23%
yield of CpRe(CO)3 was obtained.
Before studying the reaction with sophisticated com-
plexes, it is necessary to investigate the thermal reaction
of Re2(CO)10 with a range of cyclopentadienyl com-
plexes to identify the best molecules that might serve as
sources of cyclopentadienyl ligands. Since it is not
possible to test all of the known cyclopentadienyl com-
plexes, we selected representative models from Groups
4, 5, 6, 7, 8, 9 and 10. The compounds chosen were
Cp2TiCl2, CpTiCl3, Cp2ZrCl2, Cp2V, Cp2VCl2, CpV-
(CO)4, Cp2Cr, CpMo(CO)3Me, CpW(CO)3Me, Cp2-
WCl2, CpMn(CO)3, Cp2Fe, CpFe(CO)2Me, CpFe-
(CO)2I, [CpFe(CO)2]2, (h4-C5H6)Fe(CO)3, Cp2Ni, Cp2-
Co, CpCo(CO)2, CpTl, C5H5SiMe3, and C5H5SnMe3.
We extended the exchange reaction to a titanium alkene
complex related to tamoxifen in order to evaluate its
potential with substituted cyclopentadienyls. We report
here our results on this thermal reaction.
Table 1
mesitylene
CpnMLm+Re2(CO)10ꢀꢀꢀꢀꢀꢀꢁCpRe(CO)3
2. Results and discussion
reflux
CpnMLm
Cp2TiCl2
Heating time (h)
Yield of CpRe(CO)3 (%)
2.1. Results
4
2
2
4
2
2
2
2
3
7
2
4
8
2
2
2
2
2
2
7
2
1
2
82
45
40
23
30
60
6
24
0
0
0
0
0
0
0
0
0
The thermal reactions were performed by heating
Re2(CO)10 with cyclopentadienyl complexes in
mesitylene at reflux for several hours (Scheme 1).
Mesitylene was chosen as a solvent because of its high
boiling point (b.p. 162–163°C). In order to consume all
of the Re2(CO)10 reagent, the amount of cyclopentadi-
enyl metal complex was calculated to contain two
equivalents of Cp for one Re. Any CpRe(CO)3 that was
formed was isolated by TLC. The results are presented
in Table 1.
The cyclopentadienyl compounds can roughly be di-
vided into two groups. The first group that gives fair to
good yields of CpRe(CO)3 involves Cp2TiCl2, CpTiCl3,
Cp2ZrCl2, Cp2VCl2, Cp2V, Cp2Cr, Cp2Co, CpCo(CO)2,
Cp2Ni, CpTl. The second group is the group of com-
pounds which does not produce CpRe(CO)3. This
group contains: CpV(CO)4, CpMo(CO)3Me, Cp-
W(CO)3Me, CpMn(CO)3, CpFe(CO)2Me, CpFe(CO)2I,
[CpFe(CO)2]2 and (h4-C5H6)Fe(CO)3.
CpTiCl3
Cp2ZrCl2
Cp2V
Cp2VCl2
CpV(CO)4
Cp2Cr
CpMo(CO)3Me
CpW(CO)3Me
Cp2WCl2
CpMn(CO)3
Cp2Fe
CpFe(CO)2Me
CpFe(CO)2I
[CpFe(CO)2]2
(h5-C5H6)Fe(CO)3
Cp2Co
25
27
45
75
95
26
CpCo(CO)2
Cp2Ni
CpTl
C5H5SnMe3

S. Top et al. / Journal of Organometallic Chemistry 593–594 (2000) 167–174
169
Scheme 2.
Cp2Co and CpCo(CO)2 react with Re2(CO)10 to pro-
duce CpRe(CO)3 in moderate yields, 25 and 27%, re-
spectively. After 2 h of heating, Re2(CO)10 had
completely disappeared. In contrast with other metal-
locenes Cp2Fe, Cp2V, Cp2Cr, and Cp2Co, nickelocene
Cp2Ni gave a good yield of CpRe(CO)3, 75%.
Vanadium complexes also reacted with Re2(CO)10.
Heating Cp2V with Re2(CO)10 for 4 h gave only a 23%
yield of CpRe(CO)3. The Re2(CO)10 had almost disap-
peared. Cp2VCl2 gave a better yield of CpRe(CO)3, 60%
after 2 h of heating. By contrast, CpV(CO)4 produced
only a 6% yield of CpRe(CO)3. CpV(CO)4 disappeared
progressively from the solution, and after 2 h of heat-
ing, it had disappeared completely but Re2(CO)10 was
still present. This was due to a simple thermal decom-
position of CpV(CO)4.
Cp2Cr gave a moderate yield, 24%, of CpRe(CO)3.
No CpRe(CO)3 was detected in the reaction medium
with CpMo(CO)3Me, and CpW(CO)3Me but a red
product was formed in both cases. CpMo(CO)3Me
completely disappeared after 2 h of heating. In the case
of Cp2WCl2, this compound was not soluble in
mesitylene even at high temperature. After 4 h of
heating, the solution was almost colorless and there was
a black solid on the flask walls. No CpRe(CO)3 was
detected.
Reactions with other cyclopentadienyl metals: CpTl
reacted very quickly with Re2(CO)10. Within 1 h of
heating, a 95% yield of CpRe(CO)3 was obtained. CpTl,
a classic reagent, is usually used to react with
Re(CO)5X to produce CpRe(CO)3 but the yield was
lower,
60%
[9].
C5H5SiMe3
produced
(h5-
C5H4SiMe3)Re(CO)3, and not CpRe(CO)3 while
C5H5SnMe3 gave a mixture of CpRe(CO)3 and (h5-
C5H4 SnMe3)Re(CO)3.
Titanium complex 1 was synthesized. 1 contains both
cyclopentadienyl and substituted cyclopentadienyl lig-
ands. Heating 1 with Re2(CO)10 in mesitylene for 3 h
produced rhenium complex 2 and CpRe(CO)3 in 37 and
36% yields, respectively (Scheme 2).
CpMn(CO)3, as expected, did not react with
Re2(CO)10. After 4 h of heating, no CpRe(CO)3 was
detected, and CpMn(CO)3 was still present in the
solution.
2.2. Discussion
The thermal reaction of Re2(CO)10 with cyclopenta-
dienyl complexes may follow several mechanisms. Two
different mechanisms have been advanced for the acti-
vation of Re2(CO)10. The reaction may start by the loss
of a CO ligand to form [Re2(CO)9] or by the cleavage of
the ReꢀRe bond to produce the [Re(CO)5] radical
(Scheme 3) [4,5]. The substitution reaction of Re2(CO)10
was carefully studied by Stolzenberg and Muetterties
[5a]. They heated 185Re2(CO)10 and 187Re2(CO)10 to-
gether, at 150°C in a sealed tube, either under argon or
under pressure of CO gas. They observed that, under
Iron complexes such as Cp2Fe, CpFe(CO)2Me,
CpFe(CO)2I, [CpFe(CO)2]2, (h4-C5H6)Fe(CO)3 were
tested. None of the iron compounds yielded any
CpRe(CO)3. Ferrocene was unchanged even after heat-
ing for 8 h. CpFe(CO)2I disappeared after 2 h of
heating, leading to the formation of a yellow solution
and a black solid. Chromatography of the yellow solu-
tion gave 73% yield of ferrocene. Neither ReꢀFe clus-
ters nor [CpFe(CO)2]2 were observed. We noticed that a
heating of CpFe(CO)2I alone for 2 h also produced
ferrocene indicating that Re2(CO)10 was not involved in
the reaction. [CpFe(CO)2]2 is a robust compound, no
CpRe(CO)3 was formed from this compound. Heating
(h4-C5H6)Fe(CO)3 gave only [CpFe(CO)2]2, in a yield of
47%. This is not surprising because (h4-C5H6)Fe(CO)3
is thermally sensitive and is transformed easily into
[CpFe(CO)2]2 via CpFe(CO)2H [8].
Scheme 3.

170
S. Top et al. / Journal of Organometallic Chemistry 593–594 (2000) 167–174
Scheme 4.
Following the reaction by IR, CpV(CO)4 was found to
disappear rapidly from the solution while Re2(CO)10
argon, the crossover took place while, under CO gas,
this crossover did not occur. They concluded that the
thermal ligand substitution of Re2(CO)10 proceeded by
reversible CO dissociation and not by a scission of the
ReꢀRe bond as suggested by Poe¨ et al. [10]. The same
mechanism has been found with Mn2(CO)10 [11]. On
the other hand, it has been demonstrated that the
cleavage of ReꢀRe bond is the main process in photol-
ysis [4]. Therefore it is reasonable to admit that, in our
case, Re2(CO)10 begins its activation by losing a CO
ligand before the scission of ReꢀRe bond. Considering
cyclopentadienyl complexes, at high temperatures, these
compounds may lose their ligands and completely de-
compose to produce [Cp] radical and ultimately CpH
[12]. Another possibility is the change in the hapticity
of the Cp ligand from h5 to h3 or h1 (Eq. 2).
remained in the mixture. Only
CpRe(CO)3 was isolated.
a 6% yield of
Another situation was when the cyclopentadienyl
complexes were thermally stable. These compounds
were Cp2TiCl2, CpTiCl3, Cp2ZrCl2, Cp2VCl2, Cp2Fe,
[CpFe(CO)2]2, and Cp2Ni. The yields of CpRe(CO)3
obtained were different from one compound to an-
other. Cp2TiCl2, CpTiCl3, Cp2ZrCl2, Cp2VCl2, and
Cp2Ni gave fair to good yields while Cp2ZrCl2, Cp2Fe,
and [CpFe(CO)2]2 did not produce CpRe(CO)3. To
explain the result with Cp2TiCl2, we postulate a change
in the hapticity of the cyclopentadienyl ligand from h5
to h3 or h1 as the key process. This is not uncommon
behavior for CpTi complexes. Tsutsui and Hudman
demonstrated that Cp2TiCl2 undergoes (h1-C5H5)2TiCl2
upon dissolution in DMSO even at −70°C [15].
Brubaker et al. also suggested this p–s rearrangement
of Cp2TiCl2 for the reaction between Cp2TiCl2 and
(h5-C4D5)2TiCl2 [16]. In addition, a p–s cyclopentadi-
enyl scrambling has been found on Cp4Ti [17]. It has
also been suggested that CpFe(CO)3Br reacts with
(R4C4)Co(CO)2Br to form (R4C4)CoCp via the interme-
diate 3 (Scheme 4) [1]. We propose that this situation
occurred during our reaction as drawn in Scheme 5.
Several situations must be considered. First, the cy-
clopentadienyl complex does not resist high tempera-
tures and decomposes to produce free cyclopentadiene.
In this case, the situation becomes similar to the classic
heating of Re2(CO)10 with dicyclopentadiene and sub-
stituted cyclopentadienes [13]. Usually an excess of the
cyclopentadiene ligand is used in this reaction. In our
situation, the amount of cyclopentadiene formed was
always low. As cyclopentadiene is a volatile compound,
b.p.=40°C, cyclopentadiene can be lost at high tem-
peratures. Therefore, the yield of CpRe(CO)3 should
have been very low. This probably occurred with Cp2V,
CpV(CO)4, Cp2Cr, Cp2Co, CpCo(CO)2, and Cp-
Mo(CO)3Me. Prolonged heating, even under an argon
atmosphere, progressively decomposed the complex to
produce cyclopentadiene which was captured by
[Re2(CO)9]. When the decomposition rate was faster
than the dissociation of Re2(CO)10, the free cyclopenta-
diene could not be captured by [Re2(CO)9]. That was
the case for CpMo(CO)3Me which decomposed at
124°C [14], no CpRe(CO)3 was isolated from the reac-
tion. CpV(CO)4 showed a rapid decomposition too.
Scheme 5.

S. Top et al. / Journal of Organometallic Chemistry 593–594 (2000) 167–174
171
these compounds were separately heated in mesitylene
at reflux for 4 h. Neither compound showed any de-
composition, and they were quantitatively recovered.
Therefore, it is clear that Re2(CO)10 reacts with
Cp2TiCl2 and CpTiCl3 and not with their decomposi-
tion species. Cp2Ni gave CpRe(CO)3 with a good yield.
Cp2Ni is a versatile compound, it reacted with Fe(CO)5
to give a mixture of [CpFe(CO)2]2, CpNi(CO)2Fe-
(CO)Cp, and [CpNi(CO)]2 [2], and the reaction with
Ni(CO)4 produced [CpNi(CO)]2 and Cp3Ni3(CO)2 [3].
Some substituted cyclopentadienes were conveniently
obtained from the reaction of Cp2Ni with RX in the
presence of PR% [19]. This reaction has been explained
3
in terms of a p–s rearrangement of cyclopentadienyl
ligand to produce the intermediate 6 (Scheme 6) [19a].
Furthermore, it was shown that Cp2Ni reacts with
[CpNi]+, generated from Cp2Ni, to give a triple-decker
sandwich [Cp3Ni2]+ cation 7 [20]. Other compounds
such as [Cp*Ru(m-Cp)RuCp*]+ and [Cp*Fe(m-
Cp)RuCp*]+ were also isolated from the attack of
[CpRu(L)3]+ on Cp2Ru and Cp2Fe [21]. We are not
aware of these types of compounds with rhenium. In
addition, many rhenium complexes containing a Re-
[h2-ene] bond have been synthesized [22]. For example:
CpRe(CO)2(h2-C5H6) (8) [22a], [ fac-Re(dien)(PPh3)-
(PF3)(h2-C5H6)][OTf] (9) [22b], [CpRe(NO)(PPh3)(h2-
(RHCꢂCH2))]BF4] (10) [22c], (m-H)(m-R1CꢂCR2R3)-
Re2(CO)8 (11) [22d] (Scheme 7). CpMn(CO)2(h2-C5H6)
and [CpMn(CO)2]2(h2,h2-C5H6) have also been isolated
[23]. Moreover, a photochemical reaction of Re2(CO)10
with cyclopentadiene has produced different complexes,
one of them has shown a Reꢀ(h2-C5H6) bond [24].
These examples demonstrate that a Reꢀ[h2-ene] bond is
often generated and can be relatively stable. We suggest
that the intermediate 4 is the most plausible for the
thermal reaction with Re2(CO)10. Cp2Fe, [CpFe(CO)2]2,
and Cp2WCl2 are robust 18 electron compounds, they
are inert in the reaction with Re2(CO)10. Even heated
for 8 h, ferrocene did not give CpRe(CO)3. Neverthe-
less, Cp2Fe has been found to react with RuCl3 at
250°C to afford Cp2Ru in a 42% yield [25], and both
Cp2Fe and [CpFe(CO)2]2 reacted with TiCl4 to produce
CpTiCl3 in only 5% yield [26]. The ease of the reaction
with C5H5SiMe3 and C5H5SnMe3 is another example of
the reactivity of s-cyclopentadienyl compounds [27].
Some mixed metalꢀmetal complexes have been re-
ported in literature. For examples, [CpCr(CO)3]-
[Re(CO)5] [28], [CpMo(CO)3][Re(CO)5] and [Cp-
Scheme 6.
Scheme 7.
[Re2(CO)9] adds to the first double bond released from
the cyclopentadienyl ligand (intermediate 4). Perhaps,
then, the next step is the cleavage of the ReꢀRe bond
followed by complexation of the second double bond.
The breaking of the CpꢀM bond eventually produces
CpRe(CO)3. A cyclopentadienyl transfer with Cp2TiCl2
is a known process. Heating Cp2TiCl2 with TiCl4 at
reflux of xylene gave CpTiCl3 in a very good yield [18].
The yields of CpRe(CO)3 from CpTiCl3 and Cp2ZrCl2
were moderate while Cp2VCl2 gave a fairly good yield,
60%. We are not aware of any evidence for a hapticity
change of the Cp ligand in CpTiCl3 and Cp2ZrCl2, but
the behavior of Cp2VCl2 was found to be similar to that
of Cp2TiCl2 [16b]. Thus irradiating Cp2VCl2 with
(MeCp)2VCl2 produced (MeCp)CpVCl2. We suggest
that the same process, as shown in Scheme 5, occurred
with Cp2VCl2 although at a slower rate. In order to
verify the thermal stability of Cp2TiCl2 and CpTiCl3,
W(CO)3][Re(CO)5]
[29],
C[p-MeC6H4][Co(CO)3]2-
[Re(CO)4] [30], (CO)4ReOs2(H)(CO]8 [31], (CO)5ReCo-
(CO)4 [32]. One may expect that mixed metalꢀmetal
complexes can be formed from the thermal reaction of
Re2(CO)10. We could not isolate any mixed
metalꢀmetal complexes, but the disappearance of
Re2(CO)10 without formation of CpRe(CO)3 in certain
cases could be the consequence of the intermediate
formation of such complexes.

172
S. Top et al. / Journal of Organometallic Chemistry 593–594 (2000) 167–174
Our results shows that Cp2TiCl2 is a good candidate
heated for 2 h. A red solid was observed on the walls
of the flask. Diethyl ether was added, the solution
was chromatographed. 45 mg of CpRe(CO)3 were
isolated with a 45% yield. The red solid on the flask
walls was identified as a mixture of unreacted
for ligand transfer reaction. CpCp%TiCl2 or Cp%TiCl2
2
could also be used. An example is shown in Scheme 2,
heating 1 with Re2(CO)10 for 3 h gave both 2 and
CpRe(CO)3. Clearly, titanium compounds can act as
versatile sources of the cyclopentadienyl ligand via a
metal exchange reaction. The moderate yields in iso-
lated compounds may be the consequence of the low
solubility of 1 in mesitylene. Indeed, 2 may also be
prepared from a classic reaction, namely the reaction of
BrRe(CO)5 on lithium intermediate, but the thermal
reaction is a straightforward one from Re2(CO)10 with-
out involving lithium salt.
1
Cp2TiCl2 and Re(CO)5Cl by IR and H-NMR (IR,
;
CH2Cl2, wCO: 2046 and 1985 cm−1 1H-NMR,
CDCl3, 6.60 (s, 10H).
“ Reactions with CpTiCl3, Cp2ZrCl2, Cp2Cr, Cp2VCl2,
Cp2V, CpV(CO)4, Cp2Ni. After the heating time, the
IR spectrum of the solution showed that all the
Re2(CO)10 was not consumed. CpRe(CO)3 was iso-
lated by TLC. The yields of CpRe(CO)3 are indi-
cated in Table 1.
“ Reactions with CpMo(CO)3Me, CpW(CO)3Me,
Cp2WCl2, CpMn(CO)3, Cp2Fe, CpFe(CO)2Me,
Cp2(CO)4Fe2. No significant yield of CpRe(CO)3 was
obtained with these compounds.
3. Experimental
The synthesis of all the compounds was performed
under an argon atmosphere, using the Schlenk line
technique and Schlenk flasks. Anhydrous THF and
anhydrous diethyl ether were obtained by distillation
from sodium–benzophenone. Mesitylene (Aldrich) was
used without any further purification. TLC chromatog-
raphy was performed on silica gel 60 GF254. Infrared
spectra were obtained on a IR-FT BOMEM Michel-
“ Reactions with CpFe(CO)2I and (h4-C5H6)Fe(CO)3.
Both compounds had disappeared during heating,
but Re2(CO)10 was still in the solution in large
amounts. The reaction with CpFe(CO)2I gave fer-
rocene (73% yield) instead of CpRe(CO)3, while (h4-
C5H6)Fe(CO)3 was transformed into Cp2(CO)4Fe2
(47% yield).
son-100 spectrometer. H- and 13C-NMR spectra were
“ Reactions with Cp2Co and CpCo(CO)2. Both com-
pounds gave a dark red solution with the formation
of a red mastic after heating. The infrared spectrum
showed absorption for CpRe(CO)3 but no trace of
Re2(CO)10. Dichloromethane was added. After filtra-
tion and evaporation, diethyl ether was added to
extract CpRe(CO)3 which was purified by chro-
matography. A red solid, insoluble in diethyl ether,
was isolated. IR spectrum of the red solid showed
some wCO absorptions (for the reaction with Cp2Co:
wCO 2074w, 2005m, 1972s, 1960s cm−1 (CH2Cl2); for
the reaction with CpCo(CO)2: wCO 1967, 1889
cm−1(KBr).
1
recorded on 200 MHz and 250 MHz Bruker spectrome-
ters. Mass spectrometry was performed with a Nermag
R 10-10C spectrometer. Melting points were measured
with a Kofler device. Elemental analyses were per-
formed by the regional microanalysis department of
Universite´ Pierre et Marie Curie.
3.1. General procedure for the synthesis of CpRe(CO)3
The reaction was carried out under argon in a 5 ml
flask equipped with a reflux condenser. Re2(CO)10 and
the cyclopentadienyl compound were put in the flask
containing a magnetic stirrer. In a typical procedure, 98
mg of Re2(CO)10 (0.15 mmol) were used, the quantity
of cyclopentadienyl compound was calculated in order
to have two Cp ligands per Re. The flask was purged
with argon, and 0.5 ml of mesitylene was added. The
flask was then heated with an oil bath preheated to
190°C. The reaction was monitored by TLC and IR.
Unless otherwise mentioned, the reaction was stopped
after 2 h of heating. Products formed were separated by
classic chromatography on silica gel plates with pentane
“ Reaction with CpTl. 331 mg of CpTl (1.2 mmol) and
198 mg of Re2(CO)10 (0.3 mmol) were heated in 1 ml
of mesitylene. After 1 h of heating, the Re2(CO)10
had completely disappeared. 195 mg of CpRe(CO)3
were isolated by TLC, with a 93% yield.
“ Reaction with CpSiMe3. 324 mg of CpSiMe3 (3
mmol) and 326 mg of Re2(CO)10 (0.5 mmol) were
heated in 0.4 ml of mesitylene. After 3 h of heating,
Re2(CO)10 had completely disappeared. 184 mg of
[h5-C5H4SiMe3]Re(CO)3 were isolated by TLC, with
1
as an eluent. CpRe(CO)3 was identified by NMR and
93% yield. H-NMR (ppm, CDCl3): 5.41 (m, 4H),
IR. H-NMR (ppm, CDCl3): 5.38 (s, 5H). IR (cm−1
,
0.24 (s, 9H). IR(cm−1, CH2Cl2) wCO: 2020s, 1922s
1
CH2Cl2) wCO: 1925s, 2023s.
cm−1
.
“ Reaction with Cp2TiCl2. 75 mg of Cp2TiCl2 (0.3
mmol) were used. After 4 h of heating, a green–
black solid was formed and the solution was still red.
83 mg of CpRe(CO)3 were isolated by TLC with an
82% yield. In a second experiment, Cp2TiCl2 was
“ Reaction with CpSnMe3. 284 mg of CpSnMe3 (1.2
mmol) and 198 mg of Re2(CO)10 (0.3 mmol) were
heated in 1 ml of mesitylene. After 2 h of heating,
the solution became orange. Three compounds were
isolated by chromatography. The first compound

S. Top et al. / Journal of Organometallic Chemistry 593–594 (2000) 167–174
173
was Re2(CO)10, 25 mg. The second compound was a
References
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1
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Acknowledgements
We thank Amersham and the Centre National de la
Recherche Scientifique for their financial support and
Professor R. Adams for helpful discussion.
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