Selective oxidants for organometallic compounds containing a stabilising anion of highly reactive cations: (3,5(CF3)2C6H3)4B -)Cp2Fe+ and (3,5(CF3)2C6H3)4B -)Cp*2Fe+

Article abstract of DOI:10.1016/S0022-328X(00)00044-9

A major interest in ferrocenium compounds arises from their usefulness as selective oxidants to prepare mixed-valence metallocenic stable compounds. In this paper, Cp₂FeBAr′₄=((3,5(CF₃)₂C ₆H₃)₄B^-)Cp₂Fe ⁺) (a), and Cp*₂FeBAr′₄=((3,5(CF₃) ₂C₆H₃)₄B^-) Cp*₂Fe⁺) (b) are reported. These compounds have wide applications in the obtention of new organometallic salts with improved stability. The selective oxidation capacity of compounds a and b was investigated by the reaction of [Cp*Co^II(C₈H₆)Fe^II(C ₈H₇)] with stoichiometric quantities of Cp₂FeBAr′₄ or Cp*₂FeBAr′₄ where [Cp*Co^III(C₈H₆)Fe^II(C ₈H₇)]BAr′₄ was exclusively obtained. All salts that have BAr′₄^- as counterion showed an enhanced solubility in low-polarity solvents, especially in diethyl ether. This fact allowed us to perform non-conventional measurements like cyclic voltammetry in diethyl ether as solvent with NaBAr′₄ as supporting electrolyte. Single-crystal structural determination of a and b was also achieved.

Full text of DOI:10.1016/S0022-328X(00)00044-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 601 (2000) 126–132
Selective oxidants for organometallic compounds containing a
stabilising anion of highly reactive cations:
(3,5(CF3)2C6H3)4B−)Cp2Fe+ and (3,5(CF3)2C6H3)4B−)Cp*Fe+
2
Ivonne Cha´vez a, Angel Alvarez-Carena b, Elies Molins c,*,1, Anna Roig c,
Waldemar Maniukiewicz c,2, Alenjandra Arancibia a, Vero´nica Arancibia a,
Holger Brand a, Juan Manuel Manr´ıquez a,*,3
a Facultad de Qu´ımica, Pontificia Uni6ersidad Cato´lica de Chile, Casilla 306, Correo 22, Santiago de Chile, Chile.
b Departamento de Geolog´ıa, Uni6ersidad Auto´noma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
c Institut de Cie`ncia de Materials de Barcelona (CSIC), Campus Uni6ersitat Auto`noma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
Received 9 September 1999; received in revised form 4 November 1999; accepted 5 January 2000
Abstract
A major interest in ferrocenium compounds arises from their usefulness as selective oxidants to prepare mixed-valence
metallocenic stable compounds. In this paper, Cp2FeBAr4% =((3,5(CF3)2C6H3)4B−)Cp2Fe+) (a), and Cp*FeBAr4% =
2
((3,5(CF3)2C6H3)4B−) Cp2*Fe+) (b) are reported. These compounds have wide applications in the obtention of new organometallic
salts with improved stability. The selective oxidation capacity of compounds a and b was investigated by the reaction of
[Cp*CoII(C8H6)FeII(C8H7)] with stoichiometric quantities of Cp2FeBAr4% or Cp*FeBAr%4 where [Cp*CoIII(C8H6)FeII(C8H7)]BAr4%
2
was exclusively obtained. All salts that have BAr%4− as counterion showed an enhanced solubility in low-polarity solvents,
especially in diethyl ether. This fact allowed us to perform non-conventional measurements like cyclic voltammetry in diethyl ether
as solvent with NaBAr%4 as supporting electrolyte. Single-crystal structural determination of a and b was also achieved. © 2000
Elsevier Science S.A. All rights reserved.
Keywords: Oxidants; Ferrocenium; Inert anion
1. Introduction
materials [3] or in the preparation of mixed-valence
compounds with expected conducting properties (new
unidimensional materials) [4]. The cation almost invari-
ably behaves as an innocent one-electron oxidant, an
observation that was experimentally clarified in the
comparative studies of the oxidative activation of CꢀH
by (CPH3)+ and (Cp2Fe)+ [5]. Systematic variation of
Cp-ring substituents enables the redox potential to be
tailored to the particular need by providing a range of
half-wave potentials (vs. calomel electrode) of −0.63 V
for [(C5H4NMe2)2Fe] and of 0.64 V for [(C5H4CF3)2Fe]
[6]. These substitutions also influence other physico-
chemical properties as evidenced by the bulky pen-
tamethylcyclopentadienyl ligand (Cp*), which gives
higher solubility and greater kinetic and thermody-
namic stability on its oxidised iron complexes as com-
pared with [Cp2Fe] [6,7].
The ferrocenium ion [Cp2Fe]+ is a mild one-electron,
outer-sphere oxidant, which has found widespread ap-
plications in stoichiometric and catalytic oxidation [1].
The ferrocenium ion is particularly useful where selec-
tive oxidation is required, for example, in the synthesis
of mixed-valence complexes [2]. At the same time, is a
useful building block in the synthesis of new magnetic
1*Corresponding author. Tel.: +34-93-5801853; fax: +34-93-
5805729; e-mail: elies.molins@icmab.es
2Present address: Institute of General and Ecological Chemistry,
Technical University of Lodz, Lodz, Poland.
3*Corresponding author.
E-mail addresses: ichavez@puc.cl (I. Cha´vez), angel@
salduba.uab.es (A. Alvarez-Carena), waldemar@ck-sg.p.lodz.pl (W.
Maniukiewicz)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 0 ) 0 0 0 4 4 - 9

I. Cha´6ez et al. / Journal of Organometallic Chemistry 601 (2000) 126–132
127
Ferrocenium salts incorporating a large variety of
counterions, such as (BF4)−, (PF6)−, and (BPh4)− or
(SbF6)−, are well known [6,8–10]. Air stability, as well
as solubility, greatly depends on the nature of the anion
employed [6,11]. For example, (Cp2Fe)PF6 is barely
soluble in coordinating solvents whereas the counterion
BF−4 improves the solubility markedly. The general low
solubility of these ferrocenium salts in coordinating
solvent requires oxidation to be performed under het-
erogeneous conditions. Beside, there is large evidence in
the literature that in some complexes, where the desig-
nated counterions were expected to be inert, they react
with the organometallic complexes [12–15].
method (2) as the corresponding tetrafluoroborate salt
is not easily accessible.
The metathesis reaction in method (1) readily gives a
high yield (\90%) of the [Cp2Fe]+[BAr%]− salt. It
4
involves the treatment under reflux of one equivalent of
the sodium salt, NaBAr%, with one equivalent of the
4
ferrocenium tetrafluoroborate in dichloromethane, re-
moval of solvent in vacuum and extraction of the
product with diethyl ether. Further filtration of the
sodium tetrafluoroborate salt and precipitation of the
corresponding ferrocenium with pentane renders the
compound with high purity.
By method (2), both ferrocenium salts can be ob-
tained in good yield (\85%) by mixing 1 mol of a
dichloromethane solution of the corresponding fer-
rocene with a dichloromethane solution that contains 1
Usually, in an organometallic redox reaction where
the oxidant is ferrocenium, the products are ferrocene
and an organometallic salt that contains the inert coun-
terion (Reaction (1)):
mol of the acid, HBAr%, and 0.5 mol of p-benzo-
4
Cp2FeX+A“AX+Cp2Fe
(1)
quinone. Addition of pentane to the resulting dark
solution gives a precipitate of the ferrocenium salt.
We found that for the ferrocenium salts synthesis, the
where X=inert counterion and A=organometallic
compound.
acid HBAr%, can be prepared either from the sodium
4
In numerous cases the new salt AX presents poor
solubility in common organic solvents, preventing a
good characterisation of the saline derivative [16].
Our interest in ferrocenium compounds arises from
their usefulness as selective oxidants to prepare mixed-
valence metallocenic stable compounds (AX) [17],
which are useful building blocks for the synthesis of
novel materials with magnetic properties and in the
construction of one-dimensional polymetallic conduct-
ing arrays [4]. Difficulties in the past to cleanly produce
and to isolate some of these materials (attributed to the
poor solubility properties either of the salt AX and/or
kinetic instability) have stimulated our search for alter-
native reagents.
salt and HCl gas as reported originally [21], or by using
the stoichiometric amount of concentrated aqueous
HCl.
The ferrocenium salts can be recrystallised by slow
diffusion of pentane into a concentrated dichloro-
methane solution of a or b. The [Cp2FeBAr%] is ob-
4
tained as blue crystals while [Cp*FeBAr%] as green
2
4
crystals, and both are remarkably soluble in diethyl
ether. The crystalline salts are thermally stable, remain-
ing analytically pure (C and H analysis) when stored in
air for at least one month.
The ferrocenium salt characterisation was accom-
plished by elemental analysis and by IR spectroscopy
(KBr pellet). The IR spectra show the characteristic
bands of the anion at 1355, 1277 and 1121 cm−1 for a
and 1356, 1276 and a broad band 1161–1120 cm−1 for
b (see Table 1 for crystal data and structure refinement
of a and b).
(3,5(CF3)2C6H3)4B−, an inert, non-coordinating an-
ion, has found widespread use in the stabilisation of
highly reactive cationic species [18–20]. Aside from
improving chemical stability, salts containing this bulky
anion show enhanced solubility in relatively non-polar
solvents [21], prompting us to prepare ferrocenium
derivatives incorporating this anion, and to investigate
their synthetic usefulness.
The usefulness of both ferrocenium salts as selective
oxidants was checked for the paramagnetic complex
[Cp*Co(C8H6)Fe(C8H7)] [4]. The oxidation of 1 mol of
[Cp*Co(C8H6)Fe(C8H7)] with 1 mol of Cp2FeBAr% or
4
Cp2*FeBAr% gave the diamagnetic-oxidised derivative
4
2. Results and discussion
[Cp*Co(C8H6)Fe(C8H7)]BAr% where only the cobalt
4
was oxidised. It was characterised by 1H- and 13C-
2.1. Synthesis of [Cp2FeBAr%] (a) and [Cp*FeBAr%] (b)
4
2
4
NMR spectroscopy (see Section 3).
The corresponding salt [Cp*Co(C8H6)Fe(C8H7)]BAr%
showed more solubility and stability than the analogous
[Cp*Co(C8H6)Fe(C8H7)]BF4 salt [4]. The enhanced sol-
4
The ferrocenium salt can be prepared by two alterna-
tive methods:
1. by a metathesis reaction between ferrocenium te-
ubility in different solvents is a general behaviour of
trafluoroborate, Cp2FeBF4, and the NaBAr% salt;
4
−
4
AX compounds when X=BAr% [18–20]. In particular,
2. by one-electron oxidation of ferrocene with p-ben-
most of the salts of this anion show a high solubility in
diethyl ether as shown in Table 2.
zoquinone in the presence of the HBAr% acid.
The decamethyl ferrocenium salt was prepared by
4

128
I. Cha´6ez et al. / Journal of Organometallic Chemistry 601 (2000) 126–132
Table 1
ing. A potential benefit from the use of low-polarity
solvents could be an increase in the chemical stability of
the product, since displacement of ligands from the
primary redox product should be less prone due to the
lower coordinating properties of the solvent.
Crystal data and structure refinement for (3,5(CF3)2C6H3)4B)Cp2Fe
and (3,5(CF3)2C6H3)4B)Cp*Fe
2
(3,5(CF3)2C6H3)4- (3,5(CF3)2C6H3)4-
B)Cp2Fe (a)
B)Cp*Fe (b)
2
The enhanced solubility of the ferrocenium salts con-
taining the anion [BAr%]− as counteranion, as well the
Empirical formula
Formula weight
Temperature (K)
C42H22BF24Fe
1049.26
293(2)
C52H42BF24Fe
1189.52
294(2)
4
high solubility of the sodium salt (NaBAr%) in diethyl
4
ether, suggested the possibility of using this less polar
medium to perform the cyclic voltammetry using the
sodium salt as supporting electrolyte and as a coun-
teranion to stabilise the oxidised species.
Prior to studying the electrochemical behaviour of
the ferrocenium salts a and b in diethyl ether, a cyclic
,
Wavelength (A)
0.71069
Triclinic
0.71069
Monoclinic
P21/c
Crystal system
Space group
(
P1
Unit cell dimensions
,
a (A)
13.043(3)
13.342(3)
14.563(5)
93.07(2)
90.19(2)
118.68(2)
2218.9(10)
2
13.119(4)
35.254(6)
11.784(3)
90
97.48(1)
90
5404(2)
4
1.462
,
b (A)
,
c (A)
voltammogram of a 0.2 M solution of NaBAr% in this
h (°)
i (°)
k (°)
Volume (A )
Z
4
medium was traced. This system provides an electro-
chemical window from 1.80 to −1.60 V vs. SCE, which
is adequate for the study of these complexes. With the
same electrolyte using dimethyl formamide as solvent, a
window from 1.00 to −1.70 V vs. SCE is obtained.
Then the cyclic voltammograms of a and b in diethyl
3
,
Dcalc (Mg m−3
Absorption coefficient
(mm−1
F(000)
Crystal size (mm)
q Range for data collec-
tion (°)
)
1.570
0.471
0.397
)
1042
0.58×0.29×0.11
1.40–24.98
2404
0.50×0.48×0.06
1.16–24.99
ether (0.2 M NaBAr%) (see Fig. 1(a and b)) and
4
dichloromethane (0.2
M tetrabutylammonium te-
trafluoroborate) were recorded. For both ferrocenium
salts, one redox pair was observed corresponding to the
oxidation (Fe2+/Fe3+) and its respective reduction.
Complex a in diethyl ether has an E1/2 value of 0.44 V
(6=50 mV s−1 vs. SCE), while complex b has an E1/2
of −0.12 V (6=50 mV s−1 vs. SCE). In dichloro-
methane (DCM), complex a has an E1/2 value of 0.46
V (6=50 mV s−1 vs. SCE), while complex b has an
E1/2 of −0.01 V (6=50 mV s−1 vs. SCE).
In both solvents the ratio ipc/ipa=1 was obtained,
indicating that the oxidation products are chemically
stable. With the purpose of corroborating the reversibil-
ity of the system, ferrocene was added to both solvents.
The potential redox pair of ferrocene in diethyl ether is
0.49/0.38 vs. SCE (E1/2=0.44 V) and in DCM 0.52/
0.40 vs. SCE (E1/2=0.46 V). A DE value of 100 mV for
both systems, is slightly superior to the expected for a
reversible process (60 mV) and it could be due either to
the resistance of the reference electrode cell or to the
limited conductivity of the solution.
Index ranges
−155h515, −
155k515, 05l5 05k541,
17
7786
Empirical
0.999 and 0.923
05h515,
−145l513
9917
Emprical
Independent reflections
Absorption correction
Max and min transmis-
sion
0.999 and 0.936
Refinement method
Full-matrix least-
Full-matrix least-
squares on F2
9324/55/772
1.029
R1=0.0855,
wR2=0.2329
R1=0.2651,
wR2=0.5339
squares on F2
Data/restraints/parameters 7786/49/720
Goodness-of-fit on F2
0.932
Final R indices [I\2|(I)] R1=0.0748,
wR2=0.2084
R indices (all data)
R1=0.1407,
wR2=0.2237
0.520 and −0.378 0.436 and −0.317
Largest difference peak
and hole (e A
−3
,
)
2.2. Cyclic 6oltammetry (CV) analysis
The stability of these complexes in both solvents is
very similar. However both compounds are more
In electrochemistry, the use of solvents with polarities
less than those of CH2Cl2 and THF is quite difficult
because the electrolyte salt must dissolve and apprecia-
bly dissociate in order to render the solution conduct-
difficult to oxidise in DCM. Cp2FeBAr% is oxidised at a
4
more positive potential in DCM than in diethyl ether
(DE1/2=20 mV). For Cp2*FeBAr%, DE1/2=110 mV.
4
Table 2
Solubility in diethyl ether
Compound
Solubility at 0°C (g l−1
)
Solubility at 0°C (M)
Solubility at 25°C (g l−1
)
Solubility at 25°C (M)
NaBAr4%
Cp2FeBAr4%
Cp2*FeBAr4%
237.04
73.06
20.07
0.268
0.070
0.017
364.12
84.02
25.5
0.411
0.080
0.021

I. Cha´6ez et al. / Journal of Organometallic Chemistry 601 (2000) 126–132
129
2.3. X-ray structural characterisation
The crystal structures of the two complexes could be
described as packing of alternated layers of cations and
anions (see Figs. 2 and 3). The CF3 groups of the anion
present orientational disorder in both compounds as
being usual in many structures containing this group.
Concerning the cation, different conformations are
present in each crystal structure.
In a, an average staggered conformation has been
found, being the Fe atom on an inversion centre. The
thermal ellipsoids are elongated with U33/U11 ratios
close to five. Two kinds of disorder can be considered
according to U33 directions, a dynamic disorder involv-
ing a rotation or a libration of the rings about an axis
perpendicular to the rings and containing the Fe atom,
and a static disorder emerging of different sandwich
conformations (see Fig. 4).
In b, one of the two rings of the cation is disordered.
A model with two conformations with identical occu-
pancy (SOF=0.5) has been refined. One of them is
staggered and the other is partly eclipsed (their relative
orientation angles are 33.3 and 18.3°). Although more
conformations exist there, only the mean is observed.
This kind of disorder is frequent in other metallocenes
[22–24].
Fig. 1. Cyclic voltammetry of Cp2FeBAr4% (a) and Cp*2 FeBAr4% (b) in
diethyl ether. Scan rate 0.2 V s−1. Supporting electrolyte NaBAr4% 0.2
M. Working electrode platinum disc.
Fig. 2. Perspective view of the unit cell of Cp2FeBAr4% along the
x-axis.
Fig. 3. Perspective view of the unit cell of Cp*FeBAr%4 along the
x-axis.
2

130
I. Cha´6ez et al. / Journal of Organometallic Chemistry 601 (2000) 126–132
Cyclic voltammetric (CV) measurements were carried
out with a Potentiostat Bank (model Wenking ST-72)
coupled to a Voltage Scan Generator (model USG-72)
and a Graphtec Recorder (model WX-1100). The work-
ing electrode used in the CV was a platinum inlay
electrode (Beckman). The auxiliary electrode was a
platinum-coil electrode, which was isolated from the
bulk solution by a glass tube with a porosity glass frit
at the end; it contained a 0.2 M solution of supporting
electrolyte. The reference was an Ag/AgCl (aqueous
tetramethylammonium chloride) cracked glass bead
electrode, which was adjusted to 0.00 versus the satu-
rated calomel electrode (SCE). The reference electrode
was located inside a Luggin capilar in the cell compart-
ment. All the experiments were performed under an
argon atmosphere, at room temperature (r.t., 20°C) in
dichloromethane solution. Solutions were 3 mM in
complex and 200 mM in tetraethylammonium te-
trafluoroborate (TBA TFB) as the supporting
electrolyte.
Fig. 4. Perspective view of two Cp2FeBAr4% cations of the asymmetric
unit.
All FeꢀC distances are similar to those described in
the literature [23]. The distances between the Fe atoms
,
and the ring mean planes are 1.700 (a) and 1.609 A (b)
(see Fig. 5).
3. Experimental
3.1. General
3.2. Preparation of Cp2FeBAr% (1) by metathesis
4
All reactions were carried out using Schlenk tech-
niques under a nitrogen atmosphere and the products
were subsequently handled in a dry, oxygen-free glove-
box. NaBAr% and HBAr%(Et2O)2 were prepared follow-
ing published procedures [21]. 3,5-bis(trifluoromethyl)-
bromobenzene, NaBF4, p-benzoquinone (used as sub-
limed), DCM, HCl (analysed) and pentane were from
Merck. Diethyl ether was from Riedel of Ha¨en.
Cp2FeBF4 (0.520 g, 1.91 mmol) dissolved in CH2Cl2
(60 ml) was added to NaBAr% (1.690 g, 1.91 mmol) and
4
the mixture was heated under reflux for 30 min. The
solvent was removed in vacuum and the product was
extracted with diethyl ether. The diethyl ether was
concentrated in vacuum to ca. 10 ml. Pentane (70 ml)
was added and the blue precipitate which formed was
filtered, washed with pentane and then dried in vac-
uum. The solid was recrystallised by slow diffusion of
pentane into a concentrated dichloromethane solution.
After 24 h the blue crystals (91%) were washed with
pentane and dried in vacuum. IR (KBr pellet): 1355 (s),
4
4
Cp2FeBF4 and Cp*Fe were prepared in the laboratory.
2
IR spectra were recorder on a Perkin–Elmer 1710 FT
spectrophotometer using KBr pellets. Elemental analy-
ses were obtained with a Fison 1108 microanalyser.
1H-NMR spectra were determined using a Brucker
ACT insstrument, 200 MHz.
1277 (s), 1121 (s, br) cm−1
C42H22BF24Fe: C, 48; H, 2.09. Found: C, 47.7; H, 2.1%.
. Anal. Calc. for
Fig. 5. Perspective view of the Cp*2 FeBAr4% cation indicating the two orientations of the disordered Cp* ring.

I. Cha´6ez et al. / Journal of Organometallic Chemistry 601 (2000) 126–132
131
3.3. Synthesis of Cp*FeBAr% (b) by oxidation of
[C5(CH3)5]2Fe with p-benzoquinone
2.67 (m, 2H), 3.8 (t, 1H), 4.2 (t, 1H), 4.3 (d, 1H), 4.5 (d,
1H), 4.6 (t, 1H), 5.0 (d, 1H), 5.1 (d, 1H), 5.2 (t, 2H),
2
4
6.17–6.30 (dd, 2H), 7.57 (s, 4H, BAr%) and 7.73 (s, 8H,
4
[C5(CH3)5]2Fe (0.368 g, 1.13 mmol) dissolved in
CH2Cl2 (15 ml) was added slowly to CH2Cl2 (15 ml)
containing 1,4 p-benzoquinone fresh sublimated (0.06
g, 0.57 mmol) and HBAr4(OEt2) (1.146 g, 1.13 mmol).
The mixture was stirred at room temperature (r.t.) for 1
h. The solvent was removed in vacuum and concen-
trated to ca. 10 ml. Pentane (40 ml) was added and the
green precipitate that formed was filtered, washed with
pentane and then dried in vacuum. The solid was
recrystallised by slow diffusion of pentane into a con-
centrated dichloromethane solution. After 24 h the
green crystal (86%) was filtered, washed with pentane
and dried in vacuum. IR (KBr pellet) 1356 (s), 1276 (s),
1161–1120 (br) cm−1. Anal. Calc. for C52H42BF24Fe:
C, 52.46; H, 3.53. Found: C, 52.42; H, 3.52%.
BAr%).
4
IR (Nujol) cm−1: 1612.3 (w), 1284.5 (s, BAr%), 1154–
4
1133.9 (vs, BAr%), 887 (m), 839.1 (w), 807.8 (w), 725.4
(m), 714.4 (m), 682.1 (m), 669.2 (m).
4
3.7. Crystal structure determinations for Cp2FeBAr%
(a) and Cp*FeBAr% (b)
4
2
4
Crystals of a and b suitable for single-crystal X-ray
diffraction experiments were obtained by slow diffusion
of pentane into a concentrated CH2Cl2 solution of the
respective ferrocenium salt. Crystal data and details of
the structure solutions are summarised in Table 1.
For both compounds data were collected at r.t. on an
Enraf–Nonius CAD4 diffractometer. The following ex-
perimental set-up was used: graphite-monochromated
Mo–Ka radiation, scan-mode=ꢀ–2q, scan-width=
3.4. Synthesis of Cp2FeBAr% by oxidation of
4
[C5(CH3)5]2Fe with p-benzoquinone
0.80+0.35 tg q and scan-speed of 1.3–5.5° min−1
.
Structures were solved by direct methods (SHELXS-86
program) [25] and full-matrix least-squares refinement
on F2 for all reflections (SHELXL-93 program) [26] was
used.
This complex was prepared in 82% yield in a manner
identical to that used for b.
3.5. Alternati6e synthesis of HBAr%
Cyclopentadienyl, pentamethylcyclopentadienyl and
phenyl groups were refined as rigid groups. The CF3
groups were highly disordered. We modelled the disor-
der using some rigid groups (two or three) for each CF3
and refining a torsion angle for every rigid group. The
analysis of thermal parameters revealed structural dis-
order for pentamethylcyclopentadienyl and cyclopenta-
dienyl groups. In this latter case, the disorder was not
modelled, but in the case of b one pentamethylcy-
clopentadienyl group was split. Non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were
placed in calculated positions with isotropic tempera-
ture factors fixed at 1.5 times (methyl hydrogens) or 1.2
times (the rest) Ueq of the corresponding carbon atoms.
The weighting scheme w=1/[|2(Fo2)+(aP)2+bP]
where P=[max(F2o, 0)+2Fc2]/3.
4
To a solution of NaBAr% (3.37 g, 3.8 mmol) in
4
diethyl ether (200 ml), cooled to −78°C, was added
concentrated aqueous HCl (0.4 ml, 32%, 4 mmol) via
syringe. The mixture was allowed to warm to 0°C and
stirred for 30 min at this temperature. The formed
NaCl was removed by filtration and the solution was
allowed to stand for 12 h over 4 A molecular sieves.
The clear solution was then decanted via cannula to a
separate flask and the solvent evaporated under re-
,
duced pressure to give HBAr% (Et2O)2 in 90% yield. The
4
IR spectrum showed a trace of water, but this does not
interfere with the ferrocenium synthesis.
3.6. Synthesis of [Cp*Co(C8H6)Fe(C8H7)]BAr%
4
For a, a=0.1444, b=0. Final R(F) and Rw(F2)
values were 0.0748 and 0.2084 for reflections with F2o\
2|(F2o).
A solution of [Cp*Co(C8H6)Fe(C8H7)] (150 mg,
0.330 mmol) in diethyl ether (15 ml) was added to
Cp2FeBAr4 (346 mg, 0.330 mmol) and the mixture was
stirred at r.t. for 30 min resulting in the formation of a
blue solution. Petroleum ether (45 ml) was added and
the precipitate that formed was filtered, washed with
petroleum ether, and then dried in vacuum. The solid
was recrystallised by slow diffusion of petroleum ether
For b, a=0.145, b=11.6987. Final R(F) and Rw(F2)
values were 0.0854 and 0.2336 for reflections with F2o\
2|(F2o).
4. Conclusions
into
a
concentrated diethyl ether solution of
[Cp*Co(C8H6)Fe(C8H7)]BAr%. Blue crystals (85%) were
The well-known selective capacity of oxidation of
ferrocenium, together with the stability given by the
BAr%− anion to the salts containing such anions, will
enable a wide range of applications in organometallic
synthesis. The more useful applications could be either
4
observed within 24 h. The crystals were filtered, washed
with petroleum and dried in vacuum. Anal. Calc. for
C58H36BF24FeCo: C, 52.84; H, 3.06. Found: C, 52.65;
1
H, 3.02%. H-NMR (CD2Cl2) l: 1.60 (s, 15H, Cp*),

132
I. Cha´6ez et al. / Journal of Organometallic Chemistry 601 (2000) 126–132
Bunel, J.S. Miller, J. Am. Chem. Soc. 117 (1995) 6182. (c) S.
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in the preparation of oxidised compounds or in the
preparation of mixed-valence complexes. These salts
can be prepared by chemical methods using the oxida-
tion with the ferrocenium or could be obtained ‘in-situ’
by electrochemical methods.
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5. Supplementary material
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Full details of the atomic parameters and bond
lengths and angles have been deposited with the Cam-
bridge Crystallographic Data Centre (CCDC nos.
138350 and 138351 for Cp2FeBAr% and Cp*2 FeBAr%,
4
4
respectively). Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
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Acknowledgements
We thank the CEE, CI1-CT91-0913 project, Ca´tedra
Presidencial en Ciencias 1996 (J.M.M.) and Fondecyt
1960133 for financial support. We are very grateful to
Dr Beatriz Oelckers and Gabriela Mun˜oz for providing
information on the synthesis and redox potential of
these ferrocenium compounds.
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