Rhodicenium salts: From basic chemistry to polyelectrolyte and dendritic macromolecules

Article abstract of DOI:10.1021/om500028e

A new, facile synthesis of rhodicenium chloride is described, leading to the synthesis of rhodicenium tetraarylborate, the first rhodicenium salt that is soluble in less polar solvents. This opens the route to further chemistry that was prevented by the insolubility of the formerly available rhodicenium salts. This strategy has been extended to the synthesis of water-soluble polyelectrolyte and dendritic macromolecular cobaltocenium and rhodicenium salts.

Full text of DOI:10.1021/om500028e

Article
pubs.acs.org/Organometallics
Rhodicenium Salts: From Basic Chemistry to Polyelectrolyte and
Dendritic Macromolecules
Amalia Rapakousiou, Lucia Herrer Jimenez, Yanlan Wang, Claire Mouche, and Didier Astruc*
ISM, UMR CNRS No. 5255, Univ. Bordeaux, 33405 Talence Cedex, France
S
* Supporting Information
ABSTRACT: A new, facile synthesis of rhodicenium chloride is described, leading to the synthesis of rhodicenium
tetraarylborate, the first rhodicenium salt that is soluble in less polar solvents. This opens the route to further chemistry that was
prevented by the insolubility of the formerly available rhodicenium salts. This strategy has been extended to the synthesis of
water-soluble polyelectrolyte and dendritic macromolecular cobaltocenium and rhodicenium salts.
Geiger’s group reported the electrochemical reduction of the
rhodicenium ion in nonaqueous solvents (CH3CN and DMF)
in two one-electron-reduction processes, and the dimer
[RhCp(η4-C5H5−)]2 was isolated by electrolysis of rhodice-
nium solutions in good yield.8 This material was quantitatively
oxidized back to [Cp2Rh][BF4] by [(C6H5)3C][BF4] in
dichloromethane. Rhodocene has been also observed in mass
spectral studies of rhodicenium.9 The instability of this odd-
electron rhodocene in comparison to its thermally stable
analogue cobaltocene is due to the fact that, in contrast to the
first-row 19-electron transition-metal sandwich complexes, for
which the orbital of the 19th valence electron is mostly metal
based,10 second- and third-row transition-metal sandwich
complexes with one electron in excess vs the 18-electron
configuration are ligand-based radicals. The first isolated
polysubstituted rhodocene was [Rh(C5HPh4)2], obtained
from the reduction of [Rh(C5HPh4)2]+ due to the very large
tetraphenylcyclopentadienyl ligands, which inhibited dimeriza-
tion.11
Various rhodicenium complexes with substituted cyclo-
pentadienyl ligands have been reported,12 including mono-
phosphorylated rhodicenium analogues13 and functionalized
rhodicenium salts containing two acyl and/or imidoyl
substituents.14 Polymethyl rhodicenium complexes have been
also reported,15 including decamethylrhodicenium16 and non-
amethylrhodicenium,17 imparting greater stability and solubil-
ity. Heteronuclear compounds such as rhodocenylferrocene,
1,1′-dirhodocenylferrocene, and 1-cobaltocenyl-1′-rhodocenyl-
ferrocene have also been prepared by the statistical nucleophilic
INTRODUCTION
■
After 60 years of metallocene chemistry, it is remarkable that
rhodicenium chemistry has been so little developed. Following
Wilkinson’s seminal synthesis in 1953 from a cyclopentadienyl
salt and tris(acetylacetonato)rhodium(III),1 the generation of
rhodicenium cations was reported in the gas phase by a metal
switching reaction2 and by the gas-phase photoinduced reaction
of RhC5H6 with cyclopentane3 before the use of modern
+
microwave techniques.4 Rhodicenium cations share with their
first-row analogues cobaltocenium cations similar robustness
owing to their 18-electron nature. Their salts with mineral acids
are all very soluble in water; however, even with very large
counteranions they are difficult to precipitate from water. A
polarographic study by Wilkinson’s group of [RhCp2][Cl]
showed a cathodic wave at −1.53 V vs SCE representing a one-
electron reduction; however, the neutral RhCp2 could not be
isolated from aqueous solutions. The reaction of anhydrous
rhodium chloride with sodium cyclopentadiene produced the
diamagnetic compound RhC10H11, which was formulated as the
RhI cyclopentadiene complex [Rh(η4-C5H6)Cp] (Cp = η5-
C5H5), and the same compound was formed from reduction of
[RhCp2][Cl] in aqueous ethanol by NaBH4.5 The suggested
mechanism involved attack by a hydride either on the Cp ring
or intermediately on the metal atom. Oxidation of RhC10H11
with HCl gave 50% of the initial rhodicenium cation. A gas also
evolved consisting of hydrogen together with C5 olefinic
hydrocarbons. Rhodocene was reported upon reduction of
rhodicenium cation with molten sodium and could be trapped
only on a liquid-nitrogen-cooled ESR probe,6 but it
decomposed at room temperature with formation of the
dimer [RhCp(η4-C5H5−)]2, isolated in 8% yield, in which the
η8,μ2-dicyclopentadiene ligand bridges the two RhI centers.7
Received: January 13, 2014
Published: February 18, 2014
© 2014 American Chemical Society
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attack of 1,1′-dilithioferrocene on [CoCp2][PF6] and [RhCp2]-
[PF6], followed by subsequent hydride abstraction with
tritylium hexafluorophosphate, yielding the respective terme-
tallocene dications.18
Altogether, rhodicenium chemistry is rather limited, and
applications are scarce with only some mentions of biomedical
usage.19 Indeed, a major problem is the insolubility of the
tetrafluoroborate and hexafluorophosphate salts in common
solvents. Therefore, we have reinvestigated the basic
rhodicenium chemistry, including an alternative synthesis of
rhodicenium chloride from rhodium(III) chloride hydrate, in a
two-step reaction which parallels that known for the synthesis
of decamethylrhodicenium,16 and we have disclosed the access
to rhodicenium salts, including rhodicenium salts containing
polymeric and dendritic macromolecular anions. Finally, the
new family of ionic metallocenium dendrimers has been
extended to the analogous and comparable cobaltocenium
dendrimers.
RESULTS AND DISCUSSION
■
Synthesis of Rhodicenium Chloride. The new synthesis
of rhodicenium chloride started from the reaction of
(trimethylsilyl)cyclopentadiene20 with rhodium(III) chloride
hydrate in 2-propanol at room temperature, forming the
cyclopentadiene rhodium dichloride oligomer20 that is soluble
only in water, DMF, and DMSO. Then, the synthesis of
rhodicenium chloride1 was achieved from the reaction of this
oligomer with sodium cyclopentadiene in THF. The product
was extracted with hot water, and washing with diethyl ether
several times permitted the removal of unreacted organic
species. Extraction with nitromethane (in which the other
reaction product, NaCl, is insoluble) gave rhodicenium chloride
as a yellowish oil (Scheme 1).
Figure 1. Comparative 1H NMR spectra in D2O of [RhCp(Cl)2]n (3),
[RhCp2][Cl] (4), and [RhCp2][PF6] (5): (a) 3, δ 6.04 ppm (10H,
Cp); (b) 4, δ 5.98 ppm (10H, Cp); (c) 5, δ 5.89 ppm (10H, Cp).
the synthesis of rhodicenium salts with adequate counteranions
for a better solubility in less polar solvents was envisaged.
Synthesis of a Rhodicenium Tetraarylborate. Na-
[BArF ] (ArF = 3,5-bis(trifuoromethyl)phenyl) was used as a
4
starting material to react with rhodicenium chloride in order to
form the salt [RhCp2][BArF ] (6), in addition to easily
4
removable NaCl (Scheme 2). Extraction of the product in
Scheme 2. Synthesis of a Rhodicenium Tetraarylborate
Scheme 1. New Synthesis of Rhodicenium Chloride (4)
dichloromethane and evaporation of the solvent gave a red-
1
violet powder. H NMR in CDCl3 showed the two typical
signals of the aryl groups with the expected 4 and 8 protons and
the 10 protons of the two Cp rings, whose signal is now found
at 5.63 ppm. This new rhodicenium salt 6 is soluble in lower-
polarity solvents such as diethyl ether, dichloromethane, and
THF (Table 1). Further reactions of 6 can thus be conveniently
achieved in less polar solvents, including hydride addition to
rhodicenium salts. For instance, the reaction of 3 with NaBH4
occurs in aqueous ethanol in 30 min,5 whereas that of 6
proceeds in THF in 5 min followed by extraction with pentane,
giving [Rh(η4-C5H6)Cp] (see the Supporting Information). It
is likely that 6 will be an appropriate starting material for
various nucleophilic reactions with rhodicenium that are
impossible with 4 and 5 due to their insolubility in less polar
solvents such as THF and dichloromethane, in which 6 is
readily soluble.
Access to the rhodicenium hexafluorophosphate 5 was also
easily achieved by adding HPF6 into the aqueous solution of
1
rhodicenium chloride. H NMR is a practical tool allowing
comparison among the three rhodium complexes 3−5 (Figure
1).
The protons of the Cp ring of rhodicenium chloride are
deshielded by ∼0.1 ppm in comparison to rhodicenium
hexafluorophosphate. The complexes 3−5 are soluble only in
very polar solvents such as water, DMF, and DMSO, which is a
drawback for further reactions of a rhodicenium salt. Therefore,
A sample of the complex 6 in diethyl ether solution was
analyzed by FD mass spectrometry, showing the mass peak of
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Table 1. Solubilities of the Cyclopentadienylrhodium Dichloride Oligomer 3 and Rhodicenium Complexes 4−6, 8, 10, and 12 as
a
a Function of Their Counteranion, at 25 °C
compd
counteranion
(C2H5)2O
CH2Cl2
THF
CH3CN
H2O
DMSO
3
−
−
−
+
−
−
−
+
−
−
−
+
−
−
+
+
+
+
−
+
+
+
+
+
+
−
+
+
+
4
Cl−
−
5
PF6
BArF
−
6
+
4
−
8
Poly-SO3
−
−
−
−
−
−
−
−
−
−
−
−
10
12
Dend-COO−
Dend-COO−
a
Legend: +, very soluble; −, insoluble.
Figure 2. FD MS of [RhCp2][BArF ] (6) and photo of the FD MS sample of 6 in diethyl ether.
4
Figure 3. Cyclic voltammetry of [RhCp2][BArF ] (6) in THF at (a) 22 °C and (b) −50 °C. The wave at 0.0 V corresponds to the internal reference
4
[FeCp*2].22 Conditions: reference electrode, Ag; working and counter electrodes, Pt; scan rate, 0.05 V/s; supporting electrolyte, [n-Bu4N][BArF ].
4
the ionized rhodicenium cation at m/z 232.98 that confirmed
(ipa/ipc = 0.30). This confirms the results by Geiger et al.
including the great instability of the single-electron-transfer
product rhodocene, even at −50 °C in THF, and the absence of
significant structural rearrangement along the single-electron
transfer to the rhodicenium salt 6.8
Synthesis of Water-Soluble Rhodicenium Polystyrene
Sulfonate Polymer. Ionic macromolecules such as polymers
and dendrimers have been mentioned previously, even though
this field of chemistry has not been extensively explored. We
envisaged synthesizing ionic rhodicenium polymers and
dendrimers in order to study the properties of these new
kinds of ionic metallomacromolecules. The starting polymer
material sodium polystyrene sulfonate reacted with compound
the [RhCp2][BArF ] structure (Figure 2).
4
Product 6 was also characterized by cyclic voltammetry using
decamethylferrocene as the internal reference.22 The cyclic
voltammograms were recorded in THF, a very good solubility
being accessible with this solvent, at two different temperatures:
22 and −50 °C (Figure 3). At 22 °C an irreversible wave is
observed at Epc = −1.340 V, due to a one-electron reduction of
compound 6 (RhIII/II). However, under the same conditions,
lowering the temperature to −50 °C allowed the observation of
a partial chemical reversibility of the same wave at E1/2
=
−1.345 V. This wave is electrochemically reversible (ΔE = 65
mV) but only partially chemically reversible, as the intensity of
the anodic peak is much smaller than that of the cathodic peak
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4 to give the rhodicenium polystyrene sulfonate polymer 8 and
NaCl (Scheme 3).
Scheme 3. Synthesis of a Polystyrene Sulfonate Rhodicenium
Polymer
The sodium polystyrene sulfonate polymer has an average
molecular weight of m/z 70.000; thus, the number of
rhodicenium units in polymer 8 is 330
30. The solubility
of this new polymer 8 in water is good, being similar to that of
1
its precursor compounds 4 and 7. The H NMR spectrum in
water shows the correct ratio between the rhodicenium and
polymer protons. The downfield shift of 0.175 ppm for the 10H
of Cp of the rhodicenium cation also shows the formation of
ionic bonds between the sulfonate anion and the rhodicenium
cation (Table 2). Infrared spectroscopy is also a remarkable
Figure 4. Comparative IR spectra of polymers 7 and 8.
terminated dendrimer 9 from a polyiodomethylsilyl precur-
sor.32 This dendrimer reacted as a sodium salt with complex 4
according to a metathesis ion exchange among the two reacting
ion pairs to form a polybenzoate rhodicenium-terminated
dendrimer (Scheme 4). Dendrimer 10 (Chart 1) presents a
1
Table 2. H NMR and IR Data for the Metallocenium
Complexes 3, 8, and 10−12
complex/
counteranion
Cp
(ppm)
Δδ
IR in KBr (cm−1
)
1
(ppm)
good solubility in methanol and water. Its H NMR spectrum
a
3 /Cl−
5.977
5.969
5.802
5.957
5.907
5.823
3104
3104
discloses the corresponding ratio for the dendritic/peripheral
protons (Cp), showing a downfield shift of 0.012 for the 10H
of Cp of the rhodicenium cation. The 13C NMR spectrum also
confirms the structure of the dendrimeric salt 10. The nature of
the carboxylate anion has changed between dendrimers 9 and
10, and this is clearly shown by the IR spectrum, in which the
absorption due to the carboxylate anion (area 1600−1690
cm−1) in dendrimers 9 and 10 undergoes significant changes
(Table 2). Additionally, the DOSY NMR spectrum of 10
provided the diffusion coefficient D = [4.8( 0.2)] × 10−11 m2/
s (Supporting Information).
b
3 /Cl−
a
d
−
8 /Poly-SO3
0.175
1698; 1216; 1129; 1042; 1010
b
e
10 /Dend-COO−
0.012
3107; 1603
3100
c
11 /Cl−
c
f
12 /Dend-COO−
0.084
3099; 1690
a
b
c
NMR in D2O at 25 °C. NMR in methanol-d4 (1). NMR in
d
e
methanol-d4 (5). Δδppm = δ(Cp of 3) − δ(Cp of 8). Δδppm = δ(Cp
of 3) − δ(Cp of 10). Δδppm = δ(Cp of 11) − δ(Cp of 12).
f
tool to study the differences in the sulfonate anions between
polymers 7 and 8 (Figure 4). The bands at 1191, 1129, and
1042 cm−1 of polymer 7 are assignable to sulfonate anions. The
change of the band from 1191 to 1216 cm−1 in polymer 8 is
due to the change of the ionic bond that is now formed
between the sulfonate anion and the rhodicenium cation.
Another difference is the aromatic CC bending band that
appears at 1633 cm−1 in polymer 7 and in polymer 8 changes to
1698 cm−1 (Table 2). Finally, DOSY NMR provided the
diffusion coefficient of the polymer: D = [1.38( 0.1)] × 10−10
m2/s. The spectrum is in agreement with rhodicenium being
bound to the polymer 7, providing polymer 8 (Supporting
Information).
Synthesis of Water-Soluble G1-Carboxylate Rhodice-
nium and Cobaltocenium Dendrimers. The supramolecu-
lar aspects of dendrimers23 have been largely considered for
various uses such as molecular boxes,24 exoreceptors,25
sensors,25 electron-transfer nanodevices,26 molecular micelles,27
nanoreactors,28 and catalysts.29 Ionic interactions of dendrimers
have been studied previously for different applications such as
drug vectors,30 molecular batteries, and modified electrodes.
Polyanionic dendrimers usually display acceptable biocompat-
ibility.30,31 Therefore, we have synthesized the polybenzoate-
The expected similar properties of rhodicenium cations and
cobaltocenium cations suggest that analogous structures and
properties can be obtained for related cobaltocenium salts.
Thus, the dendrimer 12 containing cobaltocenium cations in
the periphery was also synthesized (Chart 1). Cobaltocenium
chloride 11 reacted with the polybenzoate sodium dendrimer 9,
giving the polybenzoate cobaltocenium dendrimer 12 (Scheme
1
4). The H NMR spectrum shows a downfield shift of 0.084
ppm for the 10H of the Cp of the cobaltocenium cation, and
the IR spectrum showed a change in the band of the
carboxylate anion (Table 2). Finally, the DOSY NMR spectrum
of 12 provided the diffusion coefficient D = [5.5( 0.2)] ×
10−11 m2/s (Supporting Information).
CONCLUDING REMARKS
■
The insolubility of classic rhodicenium salts contrasted with the
good solubility of rhodium analogues, possibly because the
larger inter-ring distance led to more exposed positive charge in
rhodicenium than in cobaltocenium, which prevented extension
of the organorhodium chemistry. An alternative synthesis of
rhodicenium chloride and the preparation of new rhodicenium
salts that are soluble in less-polar solvents open the possibilities
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a
Scheme 4. Synthesis of the Rhodicenium and Cobaltocenium Dendrimers
a
G1 stands for a first-generation dendrimer; see the structures in Chart 1.
Chart 1
of further carrying on organorhodium chemistry. In parallel,
ionic water-soluble cobaltocenium and rhodicenium polyelec-
trolytes and dendrimers with unusual properties have now been
made available.
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(BCCH, CF3CCHCCF3), 122.1 (BCCHCCF3), 117.5 (CF3), 87.1
(Cp). FD MS (m/z): calcd for C10H10Rh+ 232.984, found 232.984.
Anal. Calcd for C42H22BF24Rh: C, 46.01; H, 2.02. Found: C, 45.93; H,
2.08.
EXPERIMENTAL SECTION
■
General Data. Reagent-grade diethyl ether and tetrahydrofuran
(THF) were predried over Na foil and distilled from sodium
benzophenone anion under argon immediately prior to use.
Dichloromethane (DCM) was distilled over CaH2 under argon prior
to use. All other solvents and chemicals were used as received. The 1H
NMR spectra were recorded at 25 °C with a 300 MHz spectrometer.
The 13C NMR spectra were obtained in the pulsed FT mode at 75.0
MHz with a 300 MHz spectrometer. All chemical shifts are reported in
parts per million (δ, ppm) with reference to Me4Si (TMS). The
infrared (IR) spectra were recorded on a FT-IR spectrophotometer.
All electrochemical measurements were recorded under a nitrogen
atmosphere. Conditions: dried solvent; temperature, 22 °C;
Complex 8. To a stirred solution of polymer 7 (20 mg, 0.00028
mmol) in 2 mL of H2O was added a solution of 2 mL of compound 4
1
(25.6 mg, 0.096 mmol) in MeOH. The mixture was stirred for /2 h.
The solvent was removed under vacuum, and the product was
extracted twice in nitromethane and filtered. Evaporation of the
1
solvent provided product 8 as a yellowish gel in quantitative yield. H
NMR of 8 (D2O, 300 MHz): δ 7.56, 6.62 (4H, CH of Ar of styrenyl),
5.80 (10H of Cp), 1.70 (CH and CH2 of polymer chain). 13C NMR of
8 (D2O, 75 MHz): δ 141.6 (Cq of Ar), 128.3 (Cq-CH2 of Ar), 126.4
and 126.0 (CH of Ar), 86.66 (Cp of rhodicenium), 40.1 (CH and CH2
of polymeric chain). DOSY NMR: D = [1.38( 0.1)] × 10−10 m2/s.
Complex 10. To a stirred solution of dendrimer 9 (20 mg, 0.002
mmol) in 2 mL of MeOH was added 2 mL of a solution of compound
4 (15.2 mg, 0.056 mmol) in MeOH. The mixture was stirred for 0.5 h.
The solvent was removed under vacuum; the product was extracted
twice in nitromethane and filtered. Evaporation of the solvent gave
product 10 as a yellow-orange gel in quantitative yield. 1H NMR
(CD3OD, 300 MHz): δ 7.84 and 6.78 (144H, CH arom), 5.96 (270H,
Cp), 3.42 (54H, SiCH2-trz), 1.56 (72H, CH2CH2CH2Si), 1.10 (72H,
CH2CH2CH2Si), 0.49 (72H, CH2CH2CH2Si), −0.07 (216H, Si-
(CH3)2). 13C NMR (MeOD, 75 MHz): δ 169.3 (CO), 163.6 (arom
OCq), 131.0 (Cq of arom core), 128.0 and 114.3 (arom CH), 86.9
(Cp), 60.1 (CH2OAr), 44.0 (CqCH2CH2CH2Si), 42.8
(CqCH2 CH2 CH2 Si), 17.9 (CqCH2 CH2 CH2 Si), 14.4
(CqCH2CH2CH2Si), −5.3 (Si(CH3)2). DOSY NMR: D =
[4.8( 0.2)] × 10−11 m2/s.
supporting electrolyte, [nBu4N][BArF ] 0.1 M; working and counter
4
electrodes, Pt; reference electrode, Ag; internal reference, FeCp*2
(Cp* = η5-C5Me5); scan rate, 0.200 V/s. Diffusion measurements were
performed at 25 °C with a 400 MHz spectrometer. They were
performed using a 1H NMR pulsed-gradient experiment: the simulated
spin−echo sequence leads to the measurement of the diffusion
coefficient D, where D is the slope of the straight line obtained when
ln I is displayed against the square of the gradient-pulse power
according to the equation ln I = −γ2G2Dδ2(Δ − δ/3), where I is the
relative intensity of a chosen resonance, γ is the proton gyromagnetic
ratio, Δ is the intergradient delay (150 ms), δ is the gradient pulse
duration (5 ms), and G is the gradient intensity. The diffusion constant
of water (2.3 × 10−9 m2/s) was used to calibrate the instrument. The
mass spectra were measured by the CESAMO (University of Bordeaux
1, France) on a AccuTOF-GcV instrument which is a GC-TOF. The
instrument was equipped with an FD (field desorption) sample
introduction system. The elemental analyses were performed by the
CESAMO (University of Bordeaux 1, France). The results were
obtained with a Thermo Flash 2000 EA instrument. The sample was
introduced in a tin container for NCHS analysis.
Complex 12. To a stirred solution of the dendrimer 9 (20 mg,
0.002 mmol) in 2 mL of MeOH was added a solution of 11 (12.6 mg,
1
0.056 mmol) in 2 mL of MeOH. The mixture was stirred for /2 h.
The solvent was removed under vacuum, and the product was
extracted twice with nitromethane and filtered. Evaporation of the
solvent gave 12 as a yellow gel in quantitative yield. 1H NMR
(CD3OD, 300 MHz): δ 7.88 and 6.86 (144H, CH arom), 5.82 (270H,
Cp), 3.46 (54H, SiCH2-trz), 1.56 (72H, CH2CH2CH2Si), 1.12 (72H,
CH2CH2CH2Si), 0.49 (72H, CH2CH2CH2Si), −0.05 (216H, Si-
(CH3)2). 13C NMR (MeOD, 75 MHz): δ 165.3 (CO), 163.6 (arom
OCq), 131.5 (Cq of arom core), 122.3 and 115.5 (arom CH), 84.8
(Cp), 60.4 (CH2OAr), 42.9 (CqCH2CH2CH2Si), 41.7
(CqCH2 CH2 CH2 Si), 17.5 (CqCH2 CH2 CH2 Si), 14.3
(CqCH2CH2CH2Si), −5.5 (Si(CH3)2). DOSY NMR: D =
[5.5( 0.2)] × 10−11 m2/s.
(Trimethylsilyl)cyclopentadiene.20 To a solution of sodium
cyclopentadienide (1.76 g, 0.02 mol) in 10 mL of THF was added
dropwise a solution of trimethylsilyl chloride (2.17 g, 0.02 mol) in 10
mL of THF at 0 °C. The reaction mixture was stirred at 0 °C for 3 h
and an additional 2 h at room temperature. Then, the reaction mixture
was cautiously treated with cold water and extracted with ether. The
organic phase was dried over Na2SO4. Further purification was
achieved by column chromatography (pentane), and the product was
obtained as a colorless liquid (1.8 g, yield 65%).
[CpRhCl2]n (3).20 To solution of (trimethylsilyl)cyclopentadiene in
7 mL of 2-propanol (0.250 g, 1.81 mmol) was added a solution of
hydrated rhodium trichloride (0.161 g, 0.77 mmol) in 7 mL of 2-
propanol. The mixture was stirred at room temperature overnight.
Pentane was added to the mixture (60 mL), and the precipitate was
filtered. The solid was washed several times with dichloromethane.
The oligomeric product [CpRhCl2]n was obtained as an orange
powder (178.3 mg, yield 97%).
Rhodicenium Chloride (4). The oligomer [CpRhCl2]n (152 mg,
0.64 mmol) was cooled to −78 °C, and then solid CpLi (92 mg, 1.28
mmol) was added slowly. The reaction mixture was stirred for 3 h at
−78 °C and then slowly warmed to room temperature and stirred
overnight. The solvent was removed under reduced pressure. The
solid was extracted with hot water, and the aqueous phase was washed
several times with diethyl ether to remove organic impurities.
Extraction overnight with nitromethane and filtration gave 106 mg
of a yellowish orange powder. Yield: 62%. (Addition of aqueous HPF6
to product 4 in water and extraction in nitromethane gave 140 mg of
rhodicenium hexafluorophosphate (5).)
ASSOCIATED CONTENT
■
S
* Supporting Information
Text giving additional experimental details and figures giving
spectroscopic data for all of the new complexes and NMR, IR,
and DOSY NMR spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for D.A.: d.astruc@ism.u-bordeaux1.fr.
Notes
The authors declare no competing financial interest.
Complex 6. To a solution of rhodicenium chloride (4) in 3 mL of
water (100 mg, 0.37 mmol) was added NaBArF4 (330 mg, 0.37 mmol)
as a solid. The solution was stirred for 1 h. NaCl was added to the
water solution until saturation. Product 6 was extracted in dichloro-
methane. Evaporation of the solvent gave 6 as a reddish violet powder
(397 mg, 0.36 mmol). Yield: 98%. 1H NMR of 6 (CDCl3, 300 MHz):
δ 7.68 (8H, CF3CH), 7.52 (4H, CF3CHCF3), 5.63 (10H, Cp). 13C
NMR of 6 (CD2Cl2, 75 MHz): δ 134.9 (CCF3), 129.0, 128.9, 127.6
ACKNOWLEDGMENTS
■
Helpful assistance and discussion with Drs. Jaime Ruiz, Noel
̈
Pinaud (DOSY NMR), and Jean-Michel Lanier (NMR) from
the CESAMO, Univ. Bordeaux, and financial support from the
Univ. Bordeaux, the Centre National de la Recherche
Scientifique (CNRS), the Chinese Research Council (CRC),
and the Agence Nationale de la Recherche (ANR) are gratefully
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