Organometallic synthesis in ambient temperature chloroaluminate(III) ionic liquids. Ligand exchange reactions of ferrocene

Article abstract of DOI:10.1039/a702978k

The ambient temperature ionic liquid system [bmim]Cl-AlCl₃ (where [bmim]⁺ = 1-butyl-3-methylimidazolium cation) has been used to prepare a number of arene(cyclopentadienyl)iron(II) complexes of the type [Fe(C₅H₅)(arene)]⁺ from ferrocene. The ionic liquid acts as both solvent and Lewis acid source ([Al₂Cl₇]^-). The products were only formed on addition of a proton source, [bmim][HCl₂], confirming mechanistic formulations involving a combination of Lewis and Bronsted acid activity. The X-ray crystal structure analysis of [Fe(η⁵-C₅C₅)(η⁶-C ₆H₅C₆H₄Br)][PF₆] is also reported. The structure clearly shows both π-π stacking interactions between neighbouring cations and hydrogen bonds between the cations and anions.

Full text of DOI:10.1039/a702978k

View Article Online / Journal Homepage / Table of Contents for this issue
Organometallic synthesis in ambient temperature chloroaluminate(III)
ionic liquids. Ligand exchange reactions of ferrocene
Paul J. Dyson,a Martin C. Grossel,b Narmatha Srinivasan,a Tracey Vine,b Thomas Welton,*,†,a
David J. Williams,a Andrew J. P. Whitea and Theodore Zigrasa
a
Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London, UK SW7 2AY
b Department of Chemistry, University of Southampton, Highfield, Southampton, UK SO9 5NH
The ambient temperature ionic liquid system [bmim]Cl–AlCl3 (where [bmim]ϩ = 1-butyl-3-methylimidazolium
cation) has been used to prepare a number of arene(cyclopentadienyl)iron() complexes of the type
[Fe(C5H5)(arene)]ϩ from ferrocene. The ionic liquid acts as both solvent and Lewis acid source ([Al2Cl7]Ϫ). The
products were only formed on addition of a proton source, [bmim][HCl2], confirming mechanistic formulations
involving a combination of Lewis and Brønsted acid activity. The X-ray crystal structure analysis of [Fe(η5-
C5H5)(η6-C6H5C6H4Br)][PF6] is also reported. The structure clearly shows both π–π stacking interactions between
neighbouring cations and hydrogen bonds between the cations and anions.
From the initial elucidation of the structure of ferrocene,
transition-metal cyclopentadienyl complexes have constituted a
key area of activity in the development of modern organo-
metallic chemistry.1 Benzene and other arene complexes, while
studied to a lesser extent, also occupy an important position in
the development of organometallic chemistry.2 Complexes con-
taining both cyclopentadienyl and arene ligands are rarer still.
Salts of the benzene(cyclopentadienyl)iron() cation [Fe(η5-
C5H5)(η6-C6H6)]ϩ, were first prepared from the reaction
between [FeCp(CO)2Cl] (Cp = η5-C5H5) and benzene in the
presence of aluminium() chloride at high temperatures.3 Sub-
sequently, it was found that the same product could be obtained
from the reaction of ferrocene with benzene in the presence of
aluminium powder and aluminium() chloride.4 Using this
method, it was also possible to replace one of the cyclopenta-
dienyl groups in ferrocene with a variety of arene ligands.5–8 It
has also been found that electron donating groups on the arene
encourage the ring substitution reaction, whereas electron-
withdrawing substituents inhibit the exchange process.6 With
polyaromatics, such as biphenyl and naphthalene both of the
rings may take part in the exchange with ferrocene.4,9
Although the ambient temperature ionic liquids have
now been known for some time, little synthetic chemistry
has been reported in them. Notable exceptions to this are the
use of acidic ionic liquids as a combination of catalyst and
solvent for a number of Friedel–Crafts reactions and the poly-
merization of ethene using titanocene dichloride derived
catalysts.10–12
In this paper, we report a direct synthetic approach using
the acidic [bmim]Cl–AlCl3 ionic liquid (where [bmim]ϩ = 1-
butyl-3-methylimidazolium cation) to the following mono-
cations: [FeIICp(R)]ϩ (where R = benzene, toluene, biphenyl, 4-
bromobiphenyl or naphthalene). These reactions are ideally
suited to this medium which acts as both solvent and Lewis acid
source.
formed by the direct combination of substituted imidazolium
chloride salts and aluminium() chloride.13 There are a number
of ways in which the precise composition of the ionic liquid can
be described, in this paper we use a [bmim]Cl–AlCl3 ionic liquid
with an apparent mol fraction of AlCl3 of 0.65 which we refer
to simply as the ‘acidic’ ionic liquid. In fact, the ionic liquids
contained no free AlCl3; the acidic ionic liquids contain sig-
nificant concentrations of the [Al2Cl7]Ϫ ion, which is the
active Lewis acid species.14 Hence, the room temperature
chloroaluminate() ionic liquids offer an ideal potential
environment for the investigation of Lewis acid catalysed
reactions.
We have found that arene-exchange reactions of ferrocene
using the methods described in the literature often result in
lower yields than those reported especially when the arene is
solid at the reaction temperature and a solvent is required to
homogenize the reaction. By using the acidic [bmim]Cl–AlCl3
ionic liquid as a combination of both catalyst and solvent, these
problems are largely avoided.
In a typical reaction, ferrocene is first dissolved in the acidic
ionic liquid and aluminium powder, [bmim][HCl2] and the
appropriate arene are added. The mixture is then heated to ca.
80 ЊC for several hours. The arenes employed in this study
together with the reaction time and yield of the arene(cyclo-
pentadienyl)iron() products are listed in Table 1 (fuller details
are given in the Experimental section).
The need to add a Brønsted acid to the reaction mixture in
these reactions has been known for some time.15 This has often
been achieved adventitiously by using wet starting materials
which produce HCl on contact with aluminium() chloride.
The mixture of HCl and aluminium() chloride is highly
Brønsted acidic and will protonate the ferrocene. In the absence
of a suitable reducing agent, aluminium powder in this case,
this is followed by oxidation of the metal and the formation of
the ferrocenium ion. However, under the conditions used here
the proton is transferred to one of the cyclopentadienyl rings
which then becomes a good leaving group, viz. cyclopentadiene.
Finally, the cyclopentadiene ring is displaced by the arene,
yielding the product.
Results and Discussion
The room temperature chloroaluminate() ionic liquids are
Great care is always taken to exclude moisture during the
preparation of the ionic liquids. Hence a proton source must be
specifically added. Although in early experiments both water
† E-Mail: t.welton@ic.ac.uk
J. Chem. Soc., Dalton Trans., 1997, Pages 3465–3469
3465

View Article Online
Table 1 Products and yields obtained from the arene exchange reactions of ferrocene in the acidic ionic liquid
Reaction
Arene
t/h
Product
Yield (%)
Benzene
Toluene
Biphenyl
4-Bromobiphenyl
Naphthalene
8
8
18
18
18
[Fe(C5H5)(C6H6)][PF6]
53
64
46
47
53
[Fe(C5H5)(C6H5Me)][PF6]
[Fe(C5H5)(C6H5Ph)][PF6]
[Fe(C5H5)(C6H5C6H4Br)][PF6]
[Fe(C5H5)(C10H8)][PF6]
Table 2 Selected bond lengths (Å) for the [Fe(C5H5)(C6H5C6H4Br)]ϩ
cation
Fe᎐C(2)
Fe᎐C(3)
Fe᎐C(4)
Fe᎐C(9)
Fe᎐C(7)
Fe᎐C(11)
2.033(6)
2.034(6)
2.054(6)
2.070(6)
2.083(6)
2.099(5)
Fe᎐C(2)
Fe᎐C(1)
Fe᎐C(10)
Fe᎐C(8)
Fe᎐C(6)
2.035(6)
2.045(7)
2.066(6)
2.077(6)
2.087(5)
Fig. 2 Back-to-back packing of pairs of [Fe(η5-C5H5)(η6-C6H5-
C6H4Br)]ϩ cations and their associated [PF6]Ϫ anions. The interaction
geometries are (a) Br ؒ ؒ ؒ F 3.20 Å, C᎐Br ؒ ؒ ؒ F 178Њ; (b) centroid ring–
centroid ring distance 4.14 Å with a mean interplanar separation of
3.78 Å and (c) C ؒ ؒ ؒ F 3.43, H ؒ ؒ ؒ F 2.74 Å and C᎐H ؒ ؒ ؒ F 132Њ
pairs of cations pack back-to-back, the bromophenyl ring of
one ring overlaying that of another, with a mean interplanar
separation of 3.78 Å and a ring centroid–ring centroid distance
of 4.14 Å, indicative of a weak π–π stacking interaction (Fig.
2). This arrangement results in the directing of one of the
co-ordinated phenyl ring hydrogen atoms towards one of the
fluorine atoms of the anion, the H ؒ ؒ ؒ F distance of 2.74 Å
suggesting a possible weak C᎐H ؒ ؒ ؒ F hydrogen bond sup-
plementing the electrostatic anion–cation interaction (see
above). The ordered arrangement of the [PF6]Ϫ anion, which is
relatively unusual in crystal structures, led us to analyse pos-
sible stabilizing interactions involving the fluorine atoms on the
opposite face to that approached by the bromine atom. This
search revealed additional C᎐H ؒ ؒ ؒ F approaches from sym-
metry related cations involving both C(3) and C(6) of the
co-ordinated cyclopentadienyl and aryl ring systems with
associated C ؒ ؒ ؒ F and H ؒ ؒ ؒ F distances (Å) with C᎐H ؒ ؒ ؒ F
angles (Њ) of 3.46, 2.69 and 141, and 3.30, 2.63 and 129
respectively.
There has been some discussion of the degree of rotation of
the unco-ordinated ring of iron-co-ordinated biphenyls in the
literature and Roberts et al.18 have developed a technique for
estimating this angle, based on 13C NMR spectroscopic data.
Our NMR spectroscopic data (see Experimental section) would
predict the angle to be 38.5Њ, somewhat larger than found in the
solid state structure (ca. 26Њ). This may, to some degree, be
explained by the geometry of the weak π–π stacking between
neighbouring bromophenyl rings which places a limit on the
degree of rotation possible between the co-ordinated and unco-
ordinated ring systems before unfavourable steric interactions
occur between the η6 ring of one molecule and the bromine
atom of the other.
Fig. 1 Molecular structure of the cation [Fe(η5-C5H5)(η6-C6H5C6-
H4Br)]ϩ
and concentrated aqueous HCl were used as the proton source,
we prefer the use of [HCl2]Ϫ salts which were first used by
Trulove and Osteryoung.16 These allow the ionic liquid to be
made Brønsted acidic without also adding oxide (from water)
which reduces the Lewis acidity of the system. They can also be
used with much greater ease than anhydrous HCl.
The solid state structure of 4-bromobiphenyl(cyclopentadienyl)-
iron(II) hexafluorophosphate
Single crystals of 4-bromobiphenyl(cyclopentadienyl)iron()
hexafluorophosphate suitable for X-ray analysis were grown
from an acetone–water solution at 5 ЊC. Selected bond lengths
for the 4-bromobiphenyl(cyclopentadienyl)iron() cation are
presented in Table 2. A view of the cation, with atom number-
ing, is shown in Fig. 1. The iron atom is co-ordinated to the
cyclopentadienyl ring at a ring centroid–iron distance of
1.666(6) Å and to the unsubstituted ring of the 4-bromo-
biphenyl moiety at a ring centroid–iron distance of 1.530(6) Å,
these values being typical of η5–Fe–η6 co-ordination.17 The two
co-ordinated rings are essentially parallel, with the ring
centroid–iron–ring centroid vectors collinear to within 2Њ. The
iron is only very slightly offset from the ring centroids. The C(5)
atom of the cyclopentadienyl ring is ‘eclipsed’ relative to C(11)
of the co-ordinated phenyl ring. The plane of the bromophenyl
ring is rotated by ca. 26Њ out of the co-ordinated phenyl ring
plane (see below). In addition to this rotation, the bromophenyl
ring is folded out of the plane of the co-ordinated phenyl
ring, the C(11) ؒ ؒ ؒ C(15) vector being 5Њ out of this plane in the
direction of the Fe atom.
Experimental
Inspection of the crystal packing reveals the absence of any
single dominant anion–cation interaction. Of note, however, is
a coulombic interaction involving the approach of the bromine
atom to one of the faces of the [PF6]Ϫ anion, the shortest
Br ؒ ؒ ؒ F separation being 3.20 Å. Centrosymmetrically related
Proton and 13C NMR spectra were recorded on a JEOL
JNM-EX270 Fourier-transfer spectrometer, elemental analyses
and fast atom bombardment (FAB) mass spectra were recorded
by the microanalytical and mass spectrometry laboratories of
the Department of Chemistry at Imperial College, London.
3466
J. Chem. Soc., Dalton Trans., 1997, Pages 3465–3469

View Article Online
1
Solvents and starting materials
38.40; H, 3.29. Calc. for C11H11F6FeP: C, 38.50; H, 3.21%). H
NMR [(CD3)2CO, 270 MHz]: δ 6.49 (s, C6H6), 5.23 (s, C5H5);
FAB mass spectrum: m/z 199, [FeC11H9]ϩ and 543,
{[FeC11H9]2[PF6]}ϩ.
Acetonitrile, benzene, toluene, 1-chlorobutane, light petroleum
(b.p. 60–80 ЊC) and diethyl ether were distilled from the
appropriate drying agent, under dry nitrogen, immediately
prior to use; 1-methylimidazole was distilled from KOH, again
immediately prior to use. The preparation of the ionic liquids,
by addition of aluminium() chloride to 1-butyl-3-methyl-
imidazolium chloride, followed previously described methods
in a dry nitrogen atmosphere glove box.19,20 All other starting
materials were used as supplied.
Toluene(cyclopentadienyl)iron(II) hexafluorophosphate
In an inert atmosphere glove box, ferrocene (1.00 g, 0.0054
mol) was dissolved in an acidic [bmim]Cl–AlCl3 ionic liquid
(5.00 cm3). The solution that resulted was transferred to a
Schlenk flask, which was then sealed and removed from the
glove box. Under N2, aluminium powder (0.12 g), [bmim]-
[HCl2] (two drops) and freshly distilled toluene (1 cm3) were
added to the ferrocene solution. The reaction mixture was
then heated at approximately 80 ЊC for 8 h, maintaining a N2
atmosphere.
1-Butyl-3-methylimidazolium chloride21
Under N2, freshly dried 1-methylimidazole (40 cm3, 0.50 mol)
and 1-chlorobutane (90 cm3, 0.86 mol) were added to dry tolu-
ene (50 cm3) in a round-bottomed Schlenk flask. The mixture
was heated under reflux under N2 for 24 h, upon which two
layers had formed. The flask was allowed to cool to room tem-
perature and was then cooled to Ϫ10 ЊC overnight, during
which time a white solid was formed. The excess toluene was
decanted, while N2 was being passed over the product layer. The
white product was recrystallized from the minimum amount of
dry acetonitrile (30 cm3) by addition of dry diethyl ether (10
cm3). The resulting white precipitate was isolated by filtration
and then dried in vacuo for 24 h. Yield: 56 g (64%) (Found: C,
54.23; H, 8.96; N, 16.12. Calc. for C8H15ClN2: C, 54.31; H, 9.62;
The reaction mixture was allowed to cool to room tem-
perature and was finally placed in an ice-bath. Ice–water (200
cm3) was slowly added to the cold reaction mixture. The
aqueous solution was filtered and washed with light petroleum
(60–80 ЊC, 5 × 20 cm3). The washed aqueous layer was collected
and filtered directly into a concentrated aqueous solution of
ammonium hexafluorophosphate (2.00 g in 10 cm3). A pale
green precipitate formed immediately. The pale green salt
was isolated by filtration and recrystallized from acetone and
characterized as [Fe(η5-C5H5)(η6-C6H5Me)][PF6]. Yield: 0.60 g
(64%) (Found: C, 39.99; H, 3.59. Calc. for C12H13F6FeP: C,
1
N, 15.84%). H NMR (CDCl3, 270 MHz): δ 11.0 (s, H2), 7.3
1
40.46; H, 3.09%). H NMR [(CD3)2CO, 270 MHz]: δ 7.20 (s,
(d, H4), 7.2 (d, H5), 4.4 (t, NCH2), 4.1 (s, NCH3), 1.9 (m,
NCH2CH2), 1.4 (m, NCH2CH2CH2) and 1.0 (t, CH3); FAB
mass spectrum: m/z 139 [bmim]ϩ, 313 {[bmim]2Cl}ϩ and 487
{[bmim]3Cl2}ϩ.
C6H5), 5.95 (s, C5H5), 3.35 (s, CH3); FAB mass spectrum: m/z
213, [FeC12H13]ϩ and 571, {[FeC12H13]2[PF6]}ϩ.
Biphenyl(cyclopentadienyl)iron(II) hexafluorophosphate
1-Butyl-3-methylimidazolium hydrogen dichloride
In an inert atmosphere glove box, ferrocene (5.58 g, 0.03 mol)
was dissolved in an acidic [bmim]Cl–AlCl3 ionic liquid (25.00
cm3). Biphenyl (4.62 g, 0.03 mol) was also dissolved in an acidic
[bmim]Cl–AlCl3 ionic liquid (10.00 g) in another beaker. The
two solutions were combined and then transferred to a Schlenk
flask, which was sealed and removed from the glove box. Under
N2, aluminium powder (1.35 g) and two drops of [bmim][HCl2]
were added to the ferrocene solution. The reaction mixture was
then heated at approximately 85 ЊC for 18 h, maintaining a N2
atmosphere.
The compound [bmim]Cl was placed in a three-necked flask,
containing a magnetic stirrer bar, immersed in a solid CO2–
acetone slush bath. Hydrogen chloride gas was passed (via a
Dreschel bottle containing concentrated sulfuric acid, in order
to remove any water) into the flask containing the solid, while it
was immersed in the solid CO2–acetone slush bath. The mixture
was stirred while the hydrogen chloride was being condensed
onto the solid. Once approximately 3 cm3 of liquid was present
in the flask and all of the solid had dissolved, the reaction was
stopped. The flask was removed from the slush bath, and
allowed to reach room temperature with a stream of N2 passing
The reaction mixture was allowed to cool to room tem-
perature and was then placed in an ice-bath. Ice–water (200
cm3) was slowly added to the cold reaction mixture. The
aqueous solution was filtered and washed with light petroleum
(60–80 ЊC, 5 × 20 cm3). The washed aqueous layer was collected
and filtered directly into a concentrated aqueous solution of
ammonium hexafluorophosphate (2.00 g in 10 cm3). An orange
precipitate formed immediately. After standing for 1 h, the
orange salt was isolated by filtration and recrystallized from a
warm acetone–water mixture. The resulting orange-yellow solid
was isolated by filtration and dried in vacuo for 24 h and then
over phosphorus() oxide for another 24 h. The solid was
characterized as [Fe(η5-C5H5)(η6-C6H5Ph)][PF6] Yield: 5.78 g
(46%) (Found: C, 48.87; H, 3.58. Calc. for C17H15F6FeP: C,
1
over the product. H NMR (CDCl3, 270 MHz): δ 12.11 (s,
Ϫ
HCl2 ), 9.55 (s, H2), 7.68 (d, H4), 7.65 (d, H5), 4.34 (t, NCH2),
4.09 (s, NCH3), 1.92 (m, NCH2CH2), 1.39 (m, NCH2CH2CH2)
and 0.98 (t, NCH2CH2CH2CH3).
Benzene(cyclopentadienyl)iron(II) hexafluorophosphate
In an inert atmosphere glove box, ferrocene (1.00 g, 0.0054
mol) was dissolved in an acidic [bmim]Cl–AlCl3 ionic liquid
(5.00 cm3). The resulting solution was transferred to a
Schlenk flask, which was then sealed and removed from
the glove box. Under N2, aluminium powder (0.12 g), [bmim]-
[HCl2] (2 drops) and freshly distilled benzene (1 cm3) were
added to the ferrocene solution. The reaction mixture was then
heated at approximately 80 ЊC for 8 h, maintaining a N2
atmosphere.
1
48.57; H, 3.57%). H NMR [(CD3)2CO, 270 MHz]: δ 7.76 (m,
aromatic), 4.81 (s, C5H5); FAB mass spectrum: m/z 275,
[FeC17H15]ϩ and 695, {[FeC17H15]2[PF6]}ϩ.
The reaction mixture was allowed to cool to room tem-
perature and was finally placed in an ice-bath. Ice–water (200
cm3) was slowly added to the cold reaction mixture. The aque-
ous solution was filtered and washed with light petroleum (60–
80 ЊC, 5 × 20 cm3). The washed aqueous layer was collected and
filtered directly into a concentrated aqueous solution of
ammonium hexafluorophosphate (2.00 g in 10 cm3). A green
precipitate formed immediately. The green salt was isolated by
filtration and recrystallized from acetone and characterized as
[Fe(η5-C5H5)(η6-C6H6)][PF6]. Yield: 0.99 g (53%) (Found: C,
4-Bromobiphenyl(cyclopentadienyl)iron(II) hexafluorophosphate
In an inert atmosphere glove box, ferrocene (5.58 g, 0.03 mol)
was dissolved in an acidic [bmim]Cl–AlCl3 ionic liquid (25.00
cm3). 4-Bromobiphenyl (6.99 g, 0.03 mol) was also dissolved
in an acidic [bmim]Cl–AlCl3 ionic liquid (10.00 g). The two
solutions were combined and then transferred to a Schlenk
flask, which was then sealed and removed from the glove box.
Under N2, aluminium powder (1.35 g) and [bmim][HCl2] (two
drops) were added to the solution. The reaction mixture was
J. Chem. Soc., Dalton Trans., 1997, Pages 3465–3469
3467

View Article Online
cm3) was slowly added to the cold reaction mixture. The
Table 3 Crystal data, data collection and refinement parametersa
aqueous solution was filtered and washed with light petroleum
(60–80 ЊC, 5 × 20 cm3). The washed aqueous layer was collected
and filtered directly into a concentrated aqueous solution of
ammonium hexafluorophosphate (2.00 g in 10 cm3). A red
precipitate formed immediately. After standing for 1 h, the red
salt was isolated by filtration and recrystallized from a warm
acetone–water mixture. The resulting red solid was filtered
and first dried in vacuo for 24 h and then over phosphorus()
oxide for another 24 h. The red solid was characterized as
[Fe(η5-C5H5)(η6-C10H8)][PF6] Yield: 6.25 g (53%) (Found: C,
45.15; H, 3.43. Calc. for C15H13F6FeP: C, 45.69; H, 3.30%).
1H NMR [(CD3)2CO, 270 MHz]: δ 7.86 (m, aromatic), 4.80
(s, C6H5); FAB mass spectrum: m/z 249, [FeC15H13]ϩ and 643,
{[FeC15H13]2[PF6]}ϩ.
Formula
M
C17H14BrFeؒPF6
499.0
Colour, habit
Crystal size/mm
Lattice type
Space group
Orange-yellow, blocks
0.70 × 0.57 × 0.20
Triclinic
¯
P1 (no. 2)
T/K
293
a/Å
b/Å
c/Å
α/Њ
7.498(1)
8.863(1)
13.957(2)
83.67(1)
77.46(1)
79.08(1)
886.7(2)
2
β/Њ
γ/Њ
U/Å3
Z
Dc/g cmϪ3
1.87
Crystal data for 4-bromobiphenyl(cyclopentadienyl)iron(II)
hexafluorophosphate
F(000)
492
Radiation used
Mo-Kα
3.25
µ/mmϪ1
Table 3 provides a summary of the crystal data, data collection
and refinement parameters for [Fe(η5-C5H5)(η6-C6H5C6H4Br)]-
[PF6]. The structure was solved by direct methods and all of the
non-hydrogen atoms were refined anisotropically using full-
matrix least squares based on F 2. The positions of the hydrogen
atoms were idealized, assigned isotropic thermal parameters,
U(H) = 1.2Ueq(C), and allowed to ride on their parent carbon
atoms. Computations were carried out using the SHELXTL PC
program system.22
θ Range/Њ
2.4–25.0
3092
2251
Semiempirical
0.48, 0.27
235
0.053
0.133
0.077, 0.826
0.89, Ϫ0.48
No. unique reflections measured
observed, |Fo| > 4σ(|Fo|)
Absorption correction
Maximum, minimum transmission
No. variables
R1b
wR2c
Weighting factors a, bd
Largest difference peak, hole/e ÅϪ3
CCDC reference number 186/647.
a
Graphite-monochromated radiation, ω scans, Siemens P4 diffract-
ometer, refinement based on F 2. b R1 = Σ||Fo| Ϫ |Fc||/Σ|Fo|. c wR2 =
¹
[Σ[w(Fo2 Ϫ Fc )2]/Σ[w(Fo )2]]². d wϪ1 = σ2(Fo ) ϩ (aP)2 ϩ bP; P = (Fo2 ϩ
2
2
2
2
Acknowledgements
2Fc )/3.
We would like to thank the Royal Society for a University
Research Fellowship (P. J. D.) and the EPSRC for a studentship
(N. S.).
then heated at approximately 85 ЊC for 18 h, maintaining a
N2 atmosphere.
The reaction mixture was allowed to cool to room tem-
perature and was finally placed in an ice-bath. Ice–water (200
cm3) was slowly added to the cold reaction mixture. The aque-
ous solution was filtered and washed with light petroleum (60–
80 ЊC, 5 × 20 cm3). The washed aqueous layer was collected and
filtered directly into a concentrated aqueous solution of
ammonium hexafluorophosphate (2.00 g in 10 cm3). A yellow-
green precipitate formed immediately. After standing for 1 h,
the yellow-green salt was isolated by filtration and recrystal-
lized from a warm acetone–water mixture. The resulting
yellow-green solid was filtered and first dried in vacuo for 24 h
then over phosphorus() oxide for another 24 h. The yellow-
green solid was characterized as [Fe(η5-C5H5)(η6-C6H5C6-
H4Br)][PF6] Yield: 5.91 g (47%) (Found: C, 40.64; H, 2.80.
Calc. for C17H14BrF6FeP: C, 40.88; H, 2.81%). 1H NMR
[(CD3)2CO, 270 MHz]: δ 8.095 (m, aromatic), 6.95 (s, C5H5);
13C NMR [(CD3)2CO, 90.55 MHz]: δ 87.27 (C8), 88.51 (C6,10),
89.30 (C7,9), 103.52 (C11), 130.67 (C13,17), 124.98 (C14,16),
133.34 (C12) and 135.43 (C15); FAB mass spectrum: m/z 353,
[FeC17H14Br]ϩ.
References
1 A. Togni and T. Hayashi (Editors), Ferrocenes: Homogenous Cata-
lysis, Organic Synthesis, Materials Science, VCH, Weinheim, 1995.
2 W. E. Silverthorn, Adv. Organomet. Chem., 1975, 13, 47; H. Le
Bozec, D. Touchard and P. H. Dixneuf, Adv. Organomet. Chem.,
1989, 29, 163; H. Wadephol, Angew. Chem., Int. Ed. Engl., 1992, 31,
247.
3 M. L. H. Green, L. Pratt and G. Wilkinson, J. Chem. Soc., 1960,
989.
4 A. N. Nesmeyanov, N. A. Vol’kenau and I. N. Bolesova, Tetrahedron
Lett., 1963, 1725.
5 A. N. Nesmeyanov, N. A. Vol’kenau and I. N. Bolesova, Dokl.
Akad. Nauk SSSR, 1966, 160, 1327.
6 A. N. Nesmeyanov, N. A. Vol’kenau and I. N. Bolesova, Dokl.
Akad. Nauk SSSR, 1966, 166, 607.
7 A. N. Nesmeyanov, N. A. Vol’kenau, E. I. Sirotkina and V. V.
Deryabin, Dokl. Akad. Nauk SSSR, Ser. Khim., 1969, 1524.
8 E. I. Serotkina, A. N. Nesmeyanov and N. A. Vol’kenau, Izv. Akad.
Nauk SSSR, Ser. Khim., 1969, 1524.
9 C. C. Lee, R. G. Sutherland and B. J. Thomson, J. Chem. Soc.,
Chem. Commun., 1972, 907.
10 J. Boon, J. Levisky, J. Pflug and J. Wilkes, J. Org. Chem., 1986, 51,
480.
11 J. K. D. Surette, L. Green and R. Singer, Chem. Commun., 1996,
2753.
12 R. T. Carlin and J. S. Wilkes, J. Mol. Catal., 1990, 63, 125.
13 J. S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg.
Chem., 1982, 21, 1263.
14 C. L. Hussey, Adv. Molten Salt Chem., 1983, 5, 185.
15 A. N. Nesmeyanov, N. A. Vol’kenau and V. A. Petrakova, Izv. Akad.
Nauk SSSR, Ser. Khim., 1974, 9, 2159.
16 P. C. Trulove and R. A. Osteryoung, Inorg. Chem., 1976, 41, 280.
17 S. H. Simonsen, V. M. Lynch, R. G. Sutherland and A. Piorko,
J. Organomet. Chem., 1985, 290, 387; V. M. Lynch, S. N. Thomas,
S. H. Simonsen, A. Piorko and R. G. Sutherland, Acta Crystallogr.,
Sect. C, 1986, 42, 1144; K. A. Abboud, V. M. Lynch, S. H.
Simonsen, A. Piorko and R. G. Sutherland, Acta Crystallogr., Sect.
C, 1990, 46, 1018; K. A. Abboud, S. H. Simonsen, A. Piorko and
ç6-Naphthalene(cyclopentadienyl)iron(II) hexafluorophosphate
In an inert atmosphere glove box, ferrocene (5.58 g, 0.03 mol)
was dissolved in an acidic [bmim]Cl–AlCl3 ionic liquid (25.00
cm3). Naphthalene (3.84 g, 0.03 mol) was dissolved in an acidic
[bmim]Cl–AlCl3 ionic liquid (10.00 g) in another beaker. The
two solutions were combined and then transferred to a Schlenk
flask, which was then sealed and removed from the glove box.
Under N2, aluminium powder (1.35 g) and [bmim][HCl2] (two
drops) were added to the ferrocene solution. The reaction
mixture was then heated at approximately 85 ЊC for 18 h,
maintaining a N2 atmosphere.
The reaction mixture was allowed to cool to room tem-
perature and was finally placed in an ice-bath. Ice–water (200
3468
J. Chem. Soc., Dalton Trans., 1997, Pages 3465–3469

View Article Online
19 J. S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg.
Chem., 1982, 21, 1263.
20 A. K. Abdul-Sada, A. M. Greenway, K. R. Seddon and T. Welton,
Org. Mass Spectrom., 1993, 28, 759.
21 B. K. M. Chan, N-H. Chang and M. R. Grimmel, Aust. J. Chem.,
1977, 30, 2005.
22 SHELXTL PC version 5.03, Siemens Analytical X-Ray
Instruments, Inc., Madison, WI, 1994.
R. G. Sutherland, Acta Crystallogr., Sect. C, 1991, 47, 860;
K. A. Abboud, S. H. Simonsen, A. Piorko and R. G. Sutherland,
Acta Crystallogr., Sect. C, 1991, 47, 1198; A. Piorko, S. Christie and
M. J. Zaworotko, Acta Crystallogr., Sect. C, 1994, 50, 1544;
A. Piorko, S. Christie and M. J. Zaworotko, Acta Crystallogr., Sect.
C, 1994, 50, 1868; Zuowei Xie, T. Jelinek, R. Bau and C. A. Reed,
J. Am. Chem. Soc., 1994, 116, 1907; A. Piorko, S. Christie and
M. J. Zaworotko, Acta Crystallogr., Sect. C, 1995, 51, 26.
18 R. M. G. Roberts, J. Silver, A. S. Wells and S. P. Wilkinson,
J. Organomet. Chem., 1987, 327, 247.
Received 1st May 1997; Paper 7/02978K
J. Chem. Soc., Dalton Trans., 1997, Pages 3465–3469
3469