Preparation and characterization of substituted pentaarylcyclopentadienyliron dicarbonyl bromide complexes containing methyl or fluorine substituents on the arene rings

Article abstract of DOI:10.1016/S0022-328X(02)01578-4

The bromopentaarylcyclopentadienes C₅(C₆H₅)₄(Ar′)(Br) (Ar′ = 3,5-C₆H₃Me₂, 1a3; Ar′ = 2,4,6-C₆H₂Me₃, 1a5; Ar′ = 3,4-C₆H₃F

Full text of DOI:10.1016/S0022-328X(02)01578-4

Journal of Organometallic Chemistry 656 (2002) 146ꢁ155
/
www.elsevier.com/locate/jorganchem
Preparation and characterization of substituted
pentaarylcyclopentadienyliron dicarbonyl bromide complexes
containing methyl or fluorine substituents on the arene rings
Jean-Yves The´pot, Claude Lapinte*
UMR CNRS 6509 Organome´talliques et Catalyse, Institut de chimie de Rennes, Universite´ de Rennes 1, 35042 Rennes Cedex, France
Received 11 March 2002; accepted 13 May 2002
Abstract
The bromopentaarylcyclopentadienes C5(C6H5)4(Ar?)(Br) (Ar?ꢀ
C6H3F2, 1a7; Ar?ꢀ2,6-C6H3F2, 1a8), and C5(3,5-C6H3Me2)4(Ar?)(Br) (Ar?ꢀ
1b4; 2,4,6-C5H2Me3, 1b5; Ar?ꢀ3-C6H4F, 1b6; Ar?ꢀ3,5-C6H3F2, 1b7; Ar?ꢀ2,6-C6H3F2, 1b8) containing either methyl groups or
/
3,5-C6H3Me2, 1a3; Ar?ꢀ
/
2,4,6-C6H2Me3, 1a5; Ar?ꢀ
/
3,5-
/
/3-C5H4Me, 1b2; 3,5-C5H3Me2, 1b3; 3,6-C5H3Me2,
/
/
/
fluorine atoms on the Ar? rings were reacted with Fe(CO)5. At 20 8C, the reaction quantitatively produces the corresponding
radicals [C5(C6H5)4(Ar?)]+ and [C5(3,5-C6H3Me2)4(Ar?)]+ which were isolated and characterized by ESR. A bromide-containing iron
derivative, identified by far FTIR was also formed in this reaction. Above 50 8C, a second reaction took place yielding the
corresponding bromo iron complexes {C5(C6H5)4(Ar?)}Fe(CO)2Br (Ar?ꢀ
/
3,5-C6H3Me2, 3a3, Ar?ꢀ/3,5-C6H3F2, 1a7) and {C5(3,5-
C6H3Me2)4(Ar?)}Fe(CO)2Br (Ar?ꢀ3-C5H4Me, 3b2; 3,5-C5H3Me2, 3b3; 3,6-C5H3Me2, 3b4; Ar?ꢀ
/
/
3-C6H4F, 3b6; Ar?ꢀ/3,5-C6H3F2,
3b7). In the case of the bromopentaarylcyclopentadienes 1a5, 1a8, 1b5, and 1b8, the presence of two methyl groups or two fluorine
atoms on the ortho and ortho? position of Ar? prevents the complexation of the iron atom onto the substituted cyclopentadienyl
radicals. A discussion of the mechanism of the reaction, supported by ESR, cyclic voltammetry, and far-FTIR spectroscopy, is also
reported. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Pentaarylcyclopentadienyliron dicarbonyl bromide complexes; ESR; Cyclic voltammetry; Far-FTIR spectroscopy
1. Introduction
[10,12,13]. For these reasons, we have synthesized a
series of iron complexes containing pentaarylcyclopen-
tadienyl ligands with methyl or fluorine groups in the
ortho or meta positions of the C6 rings. The ultimate
goal of this project is the preparation of metal com-
plexes with (i) better solubility, fine tuning of the (ii)
steric and (iii) electronic environment of the metal
center, (iv) labeling of the peripheral arene for NMR
spectroscopy, and (v) stabilization of radicals. In a
previous paper we reported a convenient route to
bromopentaarylcyclopentadienes containing methyl or
fluorine substituents [14]. In this second paper, we now
describe the synthesis of pentaarylcyclopentadienyliron
dicarbonyl bromide complexes containing methyl or
fluorine substituents on the arene rings. We have
prepared two families of bromo iron derivatives contain-
The development of bulky and electron withdrawing
pentasubstitutedꢁ
in organometallic chemistry not only to stabilize anionic
and radical complexes [1ꢁ10] but also in the design of
new donor-acceptor organometallic molecular devices,
which display preferential one-way electron transfer
acting as a rectifier [11]. Moreover, the molecular
dynamics of the propeller-type systems (C5Ar5)MLx is
particularly rich, but the analysis of the rotational
barriers requires incorporation of suitable labels on
the molecule to monitor peripheral ring rotation
/
cyclopentadienyl ligands is of interest
/
* Corresponding author
E-mail addresses: jean-yves.thepot@univ-rennes1.fr (J.-Y. The´pot),
claude.lapinte@univ-rennes1.fr (C. Lapinte).
ing four equivalents arene rings {C5Ar4Ar?Br (Arꢀ
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 5 7 8 - 4

J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ
/155
147
considerable bulk of the five aryl rings prevents the
coupling of two radicals. However, these radicals are
very sensitive to small molecules like dioxygen and water
as previously noted [18ꢁ
/
20]. The EIMS of radical 2b5
(Ar?ꢀ2,4,6-C6H2Me3) does not display the molecular
/
ion peak (m/z 599.3756). It appears that the radical
reacts with water during the introduction process in the
spectrometer and the molecular ion peaks of the
resulting products [MÃ
/
H] (m/z 600.3764) and [MÃ
/
OH] (m/z 616.3713) were both observed [20]. Exposure
to dioxygen of 2b5 gives a dioxygen adduct, the formula
of which, C46H47O2, was found by elemental analysis.
Similar findings have previously been reported for the
radical pentaisopropylcyclopentadienyl [21].
1
Scheme 1.
The H-NMR spectra of 2a5 and 2b5 (Ar?ꢀ
/
2,4,6-
2.17 (CH3,
150 Hz)
C6H2Me3) show two broad signals at dꢀ
/
C6H5, series a; Arꢀ
/
3,5-C6H3Me2, series b)}1. The fifth
arene bears either 0, 1, 2, or 3 methyl substituents or 0,
1, or 2 fluorine atoms (Scheme 1). To complement this
work, we have also investigated the mechanism of the
reaction of C5Ar4Ar?Br with iron pentacarbonyl and
show the formation of the radical [C5Ar4Ar?]+ as an
intermediate.
W1/2 100 Hz) and dꢀ6.81 (Ph, W1/2
ꢀ
/
/
ꢀ
/
indicating the effect of the paramagnetic system on the
proton resonances. The unique difference between these
two spectra is the relative intensity of the signal of the
methyl groups with respect to that of the phenyl which,
are in a 9/22 and 33/14 ratio for 2a5 and 2b5,
respectively. The UVꢁvis spectrum of 2b5 shows strong
/
and broad absorption bands without vibrational fine
structure at 356 and 598 nm. Similar observations have
previously been reported for other arylcyclopentadienyl
2. Results and discussion
2.1. Reaction of the substituted
bromopentaarylcyclopentadienes 1 with Fe(CO)5 at
20 8C
radicals [18ꢁ20]. The out-of-plane aryl rings are subject
/
to bond rotation affecting conjugation and the presence
of a multitude of conformers in the solution could be
responsible of the broadness of the absorption bands.
The ESR spectra of the radicals 2 obtained from
either isolated samples or in situ generated species by
reaction of 1 with Fe(CO)5 were run at 20 8C in toluene.
According to the pioneering study on pentaphenylcy-
clopentadienyliron compounds reported by Pauson in
1965 [1] the reaction of the C5Ph5Br with iron penta-
carbonyl still constitutes the best route to (h5-
C5Ph5)Fe(CO)2Br, the entry complex in this series
As shown in Fig. 1 for 2b3 (Ar?ꢀ3,5-C6H3Me2), the
/
spectra display a hyperfine structure due to the coupling
[10,15ꢁ
substituted bromopentaarylcyclopentadienes 1a1, 1a3,
1a5, 1a7, 1a8, and 1b2ꢁ1b8 with iron pentacarbonyl in
/
17]. Following the same way, we reacted the
/
toluene. At 20 8C, we observed that the solution
progressively turned purple and after 2 h the corre-
sponding pentaarylcyclopentadienyl radicals 2 were
isolated in 90% yield. The radicals were identified by
ESR spectroscopy and comparison of the experimental
spectra with the simulated ones. Additional character-
izations were carried out for the radicals 2a5 and 2b5
(Ar?ꢀ2,4,6-C6H2Me3). The radicals 2a7, 2a8, 2b6, 2b7,
/
and 2b8 which contain one or two fluorine atoms
decompose around 110 8C. As pure compounds, all
the other pentaarylcyclopentadienyl radicals 2 are
thermally very stable, since they can be recovered after
refluxing for several hours in mesitylene [18ꢁ
/
21]. The
1
In the compounds numbers, the letter referring to series a or b
together with the last digit, indicate the substitution of Ar? as shown on
Scheme 1.
Fig. 1. EPR spectra of 2b3 (a) in toluene at 293 K, (b) a computer
simulation using parameters given in Table 1.

148
J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ155
/
Table 1
ESR parameters for radicals 2 measured in toluene at 293 K. The hyperfine coupling constants were determined by simulation of the spectra
[C5Ar4Ar?]+
2a1
2a3
2a5
2a7
2a8
2b2
2b3
2b4
2b5
2b6
2b7
2b8
G
AHortho
2.0014 2.0014
690 680
(10H) (10H)
340 370
2.0014
2.0014 2.0014 2.0014
240
2.0014 2.0015 2.0013 2.0014 2.0014 2.0013
a
c
590
590
220
340
230
(10H) (10H) (8H)
460 370 712
170
356
(10)
590
(10H) (10H)
470
(27 H)
(10H)
480
(30 H)
(8H)
680
a
AHmeta or ACH3meta
a
(10 H) (8 H)
710
(8 H)
(24 H) (24 H) (24 H) (24 H)
a
AX
810
(2 CH3)meta (2 CH3)ortho
d
720
930
720
178
(1 H) (5 Hpara
1170
(2 F)
)
(1 H)
1380
(1 F)
200
(2 Hmeta
1424
(2 F)
200
)
a
AF
1140
(2 F)
600
1400
(2 F)
200
b
LW
310
350
600
600
200
200
400
a
In 10ꢂ3 Gauss.
b
Line width in 10ꢂ3 Gauss.
The spectrum does not present an hyperfine structrure.
The hyperfine coupling with the methyl groups of the mesitylene ring cannot be detected.
c
d
with most of the hydrogen atoms of the aryl rings. The
isotropic g values are not sensitive to the substitution of
the phenyl groups (Table 1). Simulations of the spectra
allow the determination of the jaHj and jaFj values. The
assignments of the protons of the methyl groups and
aryl rings in para, ortho, and meta positions were
performed on the basis of their multiplicity (see Table
1). We were able to observe all the couplings in the
unique case of the {C5[(C6H3)(m,m?CH3)2]5}+ (2b3).
Indeed, in most of the radicals studied the couplings
with the protons located in the para position were not
resolved even for the highly symmetric radical 2a1. As
expected, the jaFj values are significantly larger than the
1a8, 1b5, 1b8), which contain either two methyl groups
or two fluorine atoms on the ortho and ortho? positions
of the Ar? ring, the solution remained purple even after
refluxing overnight, suggesting the persistence of the
radical [C5Ar4Ar?]+. ESR monitoring of the reaction
mixture confirmed this assumption. Replacement of
toluene by mesitylene did not allow the radicals 2a5
and 2b5 to react. They remained stable even after
refluxing for 48 h at 165 8C.
The iron complexes (C5Ar4Ar?)Fe(CO)2Br 3a3, 3a7,
3b2ꢁ3b4, 3b6, and 3b7 were isolated as orange powders
/
in yields ranging from 60 to 80%. Note that the presence
of one or two fluorine atoms on the meta and meta?
position induces a significant decrease in the yield,
whereas the presence of a single methyl group on one
of the ortho position has no effect on the reactivity.
These compounds are thermally stable as powders and
in solution. However, the fluorine-containing complexes
3a7, 3b6, and 3b7 slowly decompose in solution,
suggesting that the electron withdrawing effect of the
fluorine facilitates the decoordination of the C5Ar4Ar?
ligand. The bromo iron derivatives were characterized
by multi NMR and FTIR spectroscopies, cyclic voltam-
metry and elemental analysis or FABMS.
jaHj values [22,23]. Note that the spectrum of 2b4 (Ar?ꢀ
/
3,6-C6H3Me2) did not display a hyperfine pattern. This
unusual behavior in this series could be due to the lack
of symmetry of this species.
2.2. Preparation of the substituted
pentaarylcyclopentadienyliron dicarbonyl bromide
complexes (3)
The
iron bromo complexes 3 were prepared by reaction of
polymethylatedꢁpentaphenylcyclopentadienyl
/
1
The H-NMR spectra clearly show that the presence
Fe(CO)5 with the corresponding bromide derivatives
of methyl groups on the meta and meta? positions of the
Ar and Ar? substituents does not limit the free rotation
of the peripheral rings. Indeed, in both series a and b,
the two methyl groups on the meta and meta? positions
are equivalent suggesting that the rotation of the aryl
C5Ar4Ar?Br, 1a3, 1a5, 1a7, 1a8, and 1b2ꢁ1b8 in toluene
/
following Pauson’s procedure (Scheme 3) [1]. Immedi-
ately after the addition of the iron pentacarbonyl at
20 8C, the yellow toluene solution turned dark purple as
described above. We observed that this color remained
for several days as long as the solution was kept below
50 8C. After warming for 2 h at 80 8C, the color of the
1
rings is not restricted on the H-NMR time scale (300
MHz). As in the pentamethylcyclopentadienyl series, the
30 equivalent methyl protons in compound 3b3 (Ar?ꢀ
/
solution turned from purple to redꢁbrown indicating
/
3,5-C6H3Me2) constitute a valuable 1H-NMR probe.
Moreover, the chemical shift of the CH3 protons is very
sensitive to structural modifications on the pentaarylcy-
clopentadienyl ligand. For instance, in the case of the
that the second step of the reaction had gone to
completion in the case of the C5Ar4Ar?Br derivatives
1a3, 1a7, 1b2ꢁ/1b4, 1b6, and 1b7. In contrast, the
bromopentaarylcyclopentadienes C5Ar4Ar?Br (1a5,

J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ
/155
149
complex 3b2 (Ar?ꢀ
/
3-C6H4Me), the absence of a methyl
[25] and (C5Me5)Fe(CO)2Br [26]. The absorption bands
of the complex 3a3, which contains ten methyl groups, is
weakly shifted to lower wavenumbers (ca. 5 cmꢂ1
relative to the respective complex 3a1. An opposite
effect on the frequency of the CO stretch is observed
when fluorine atoms are introduced on one of the arene
rings.
substituent on one of the meta positions of the aryl rings
allows the observation of three distinct resonances at d
2.05, 2.06 and 2.11 ppm in the 12:12:3 ratio for the 9
meta methyl groups. Similarly, in the case of the
)
complex 3b4 (Ar?ꢀ3,6-C6H3Me2), which has a central
/
C5 ring bearing four 3,5-C6H3Me2 rings and one 2,5-
C6H3Me2 ring, the 1H-NMR spectrum displays four
resonances at d 1.53, 1.95, 2.10, and 2.31 in the 3:12:12:3
ratio. The signals at d 1.95 and 2.10 correspond to the
methyl groups in meta positions of the aryl rings
occupying the a and b position with respect to Ar?.
For the methyl groups of the Ar? ring significant upfield
and downfield shifts are observed. This suggests that the
o-substitution induces a significant change of the
magnetic environment of the methyl groups. We assume
that the o-methyl is mainly directed toward the opposite
side of the C5 ring with respect to the metal, whereas the
m-methyl is directed toward the metal side. However, on
the basis of the NMR data it cannot be attributed either
to the hindrance towards free rotation of the C6 ring or
the orientation of the ortho methyl on the same or
opposite sides of the C5 ring with respect to the
Fe(CO)2Br moiety. More detailed investigations are
necessary to shed light on this point. Nevertheless, it is
noteworthy that it appears that 3b4 was formed as a
unique isomer in contrast with the results reported for
the related complex, [(o-tolyl)(C6H5)4C5)Fe(CO)2Br,
which was isolated as a mixture of two isomers with
the o-methyl substituents oriented on the same and
opposite sides of the C5 ring in the 4:7 ratio, respectively
[24].
Excluding the case of the meta-difluoro compound
(3b7), the cyclic voltammograms (CV) of the iron
complexes 3, performed in the range ꢃ
/
1.700 to ꢂ
/
1.300 V versus the standard calomel electrode (SCE),
display a reversible one-electron wave and a second
irreversible process. The irreversible process observed
between ꢂ
3b4 (Ar?ꢀ3,6-C6H3Me2) also involves one electron and
corresponds to the Fe(II)ꢁFe(I) reduction of the iron
/
0.896 for 3a1 and ꢂ
/
1.191 V versus SCE for
/
/
bromo derivatives. This reduction process shows a weak
reversible character in the case of the complexes 3a1 and
3b2. The transient character of these iron(I) species is
not surprising since it is well known that metal halide
radical anions are not thermally stable [27].
The reversible process, located between 1.242 and
1.465 V versus SCE, corresponds to the metal-centered
Fe(II)ꢁFe(III) oxidation. It seems that the Fe(III)
/
derivatives are stable at the Pt electrode. It is apparent
that the electron-releasing methyl substituents make the
oxidation of the iron(II) center easier. Moreover, the
location of the methyl groups provides a fine-tuning of
the redox potential. For instance, comparison of the E0
values of 3b3 and 3b4 shows that the displacement of
one methyl from the meta carbon to the ortho carbon of
the same arene ring decreases the oxidation potential of
0.006 V. Surprisingly, the oxidation potential of 3b2 is
0.029 V smaller than that of 3b3 despite the presence of
9 and 10 meta methyl substituents, respectively, on the
pentaarylcyclopentadienyl ligand. Such an effect could
be due to a different averaged orientation of the out-of-
plane aryl rings, affecting the conjugation between the
C6 and C5 rings and therefore the electron density on the
metal center. It can also be noted that the presence of
fluorine atoms makes the oxidation of the iron(II) center
more difficult and in the particular case of 3b7, the
oxidation wave is out of the observed potential range.
For purpose of comparison, we also ran the CV of the
related bromo iron derivatives (C5H5)Fe(CO)2Br [25]
and (C5Me5)Fe(CO)2Br [26] under the same conditions.
It appears that the electronic effect of (C5H5) and
The 13C-NMR spectrum of the complex 3b3 (Ar?ꢀ
/
3,5-C6H3Me2) shows a unique resonance for the C5 ring
at d 101.2, whereas three distinct resonances are
observed for the corresponding carbon atoms of the
complex 3b2 (Ar?ꢀ
similar pattern is observed for all other complexes as Ar
and Ar? are different. In compound 3b4 (Ar?ꢀ3,6-
/3-C6H4Me; d 100.7, 101.0, 101.5). A
/
C6H3Me2), the steric perturbation due to the presence of
the o-methyl substituent has electronic consequences on
the entire pentaarylcyclopentadienyl ligand, as shown by
the 13C resonances of the carbon atoms of the central
ring (d 97.5, 97.9, and 107.0). These chemical shifts
appear out of the range usually observed for the carbon
atoms of the C5 ring in these series (99ꢁ101 ppm). These
/
signals are consistent with a particular arrangement for
the peripheral arenes around the central C5 cycle
resulting from the presence of the o-methyl.
IR characterization of the complexes were run in
CH2Cl2 (Table 2). In all cases, the two strong absorption
(C5Ph5) are very close (DE0ꢀ
/
0.017 V) and the intro-
duction of two methyl groups on a single arene does not
greatly modify the electron richness of the iron center.
For instance, the oxidation potentials of the complexes
bands corresponding to the CÅ
/
O symmetric and anti-
3a1 and 3a3 are very close (DE0ꢀ
/
0.010 V). In the series
symmetric stretching modes were observed. The absorp-
tion bands of the bromo iron complexes of the
pentaarylcyclopentadienyl family are located between
the bands observed for the complexes (C5H5)Fe(CO)2Br
of the complexes 3b the oxidation potentials are ca. 100
mV lower than those of the derivatives of series 3a and
they appear intermediate between the values obtained
for the related complexes with C5H5 and C5Me5 ligands.

150
J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ155
/
Table 2
Electrochemical and IR data for complexes 3
e
f
c
Compound (C5H5)Fe-(CO)2Br
(C5Me5)Fe-(CO)2Br
3a1
3a3
3a7 3b2
3b3
3b4
3b6
3b7
a,b
g
h
E0
1.347
0.160
1
1.111
0.190
1.364
0.131
1
1.354
0.100
1
1.242
0.120
1
1.271
0.068
1
1.265
0.105
1
1.333
0.113
1
DEp
Ia/ic
1
h
a,c
g
E0
ꢂ1.083
ꢁ/
0
2003
2049
ꢂ0.896
0.190
0.5
ꢂ1.016
ꢁ/
0
1995
2037
ꢂ1.072
0.120
0.3
ꢂ1.170
ꢁ/
0
1991
2034
ꢂ1.191
ꢁ/
ꢂ1.133
ꢁ/
0
1994
2036
ꢂ0.927
0.250
0
i
DEp
Ic/ia
nCO
d
1975
2025
1996
2038
2001 1994
2041 2036
1992
2034
1996
2037
a
All E values in V vs. SCE. Conditions: CH2Cl2, 0.1 M [n-Bu4Nꢃ][PF6] supporting electrolyte, 20 8C, Pt electrode, sweep rate 0.100 V sꢂ1. The
ferroceneꢁ
/
ferrocerium [Fcꢁ
/
Fcꢃ] was used as internal reference for potential measurements. E0 values corrected for FcꢁFcꢃ at 0.460 vs. SCE in
/
CH2Cl2.
b
Fe(II)ꢁ
/
Fe(III) couple.
Fe(II) couple.
c
d
e
f
Fe(I)ꢁ
/
Values in cmꢂ1 obtained in CH2Cl2 solution.
From ref. [25].
From ref. [26].
g
h
i
Not determined.
Not observed in the range ꢃ1.700 to ꢂ1.300 V.
This wave was attributed to a ECE process.
As the interest for pentaarylcyclopentadienyl organo-
metallics might be lowered by poor solubility, we carried
out the determination of the solubility for selected
substituted pentaarylcyclopentadienyliron dicarbonyl
bromide complexes (3) in pentane and diethyl ether.
As expected, the solubility of these complexes increases
with the number of methyl groups borne by the arene
rings (Table 3). This effect is not considerable, but
significant. In particular, the solubility of the complex
3b3, which bears ten methyl substituents, was found to
be four and ten times higher than that of the pentaphe-
nylcyclopentadienyliron derivative 3a1 in diethyl ether
and pentane, respectively. In contrast, the presence of
two fluorine atoms on 3b7 partly counter balance the
positive effect of the methyl groups.
taken as a representative example of this series of
compounds by CV (Fig. 2). The initial scan in the range
ꢃ
/
0.4 to ꢂ
reduction wave at ꢂ
reverse oxidation presents an oxidation wave at ꢂ
/
2.0 V versus SCE, only shows an irreversible
1.55 V (wave A), whereas the
0.35
/
/
V which appeared to be reversible in the second
reduction scan (wave B). These data are consistent
with the one-electron reduction of 1b5 and subsequent
ꢂ
cleavage of 1b5+ into [C5Ar4Ar?]+ (2b5) and Brꢂ. The
formation of the radical 2b5 was established by compar-
ison of the CV of 1b5 and 2b5 (Fig. 2, waves B).
Formally, the reaction between the bromopentaarylcy-
clopentadiene 1 and iron pentacarbonyl (Scheme 2)
could involve an electron transfer (ET) process. How-
ever, the mechanism of this reaction cannot be as simple.
2.3. Mechanistic consideration
The formation of the radicals 2 upon treatment of the
bromopentaarylcyclopentadienes 1 with Fe(CO)5 are
expected to proceed by an electron transfer process.
To probe such a mechanism, we investigated the redox
properties of the bromopentaarylcyclopentadiene 1b5,
Table 3
Solubility (mg of complex per ml of solvent) for selected complexes 3
Compound
Pentane
Diethyl ether
3a1
3a3
1
4
8
12
3b2
3b3
10
10
5
35
35
3b7
(C5Me5)Fe(CO)2Br
15
130
Fig. 2. Cyclic voltammograms of the 1b5 (plain line) and 2b5 (dashed
line) in 0.1 M n-Bu4Nꢃ PF6ꢂ ꢁ
CH2Cl2 (Pt electrode, V vs. SCE, scan
15
/
rate 0.100 V sꢂ1, 20 8C).

J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ
/155
151
Scheme 4.
Scheme 2.
Indeed, comparison of the potentials for the redox
[Fe(CO)5]+ꢃ
] (E0ꢀ
couples Fe(CO)5ꢁ
/
/
(E0ꢀ
/
1 V) and C5Ar4A-
r?BrÃ
/
[C5Ar4Ar?Br+ꢂ
/
/
ꢂ
/
1 V) indicates that the
reduction of the bromopentaarylcyclopentadiene 1 by
Fe(CO)5 is strongly endergonic, and as an endergonic
ET never proceeds, one can eliminate such an hypoth-
esis.[27] As an alternative mechanism, the formation of a
transient adduct between the bromo derivatives 1 and
iron carbonyl as depicted on Scheme 4, constitutes a
plausible assumption. In this mechanism, the directions
of the ET and Brꢂ transfer are clearly opposite, so that
the overall result is a Br+ atom transfer and the reaction
can be exergonic [28]. This is an inner sphere electron
transfer process [27].
Fig. 3. Far IR spectra (polyethylene pellet, cmꢂ1
)
of the iron
intermediate generated by reaction of 1b5 with Fe(CO)5 (dashed line)
and 3a1 (plain line).
proven that metal carbonyl halides containing one to
four CO groups per molecule are stable at moderate
temperature [33].
A far-IR investigation was performed to establish the
formation of a FeÃ
/
Br bond-containing product. The
The IR characterization of the iron intermediate from
the reaction of complexation of the pentaarylcyclopen-
tadienyl ligand was complemented by a crossed radical
experiment. In a purple solution containing the bulky
radical 2b5 and the bromine-containing iron intermedi-
ate, generated by adding Fe(CO)5 to 1b5 in toluene, was
introduced the radical 2b3, independently prepared (see
Section 3). After warming the mixture to 80 8C for 30
min, the bromoiron complex 3b3 was isolated in a good
yield. This experiment clearly confirms that the pentaar-
ylcyclopentadienyl radical and a bromine-containing
iron carbonyl derivative are key intermediates in the
formation of the title complexes.
bromopentaarylcyclopentadiene 1b5 was reacted with
Fe(CO)5 in toluene at 20 8C. After 2 h, the solvent was
removed and the Nujol-mull IR spectrum of the
resulting crude product was recorded in the range
100ꢁ
400 cmꢂ1 (Fig. 3). The spectrum displays two
/
bands at 295 and 136 cmꢂ1. On the basis of the
literature data these bands of vibration may be assigned
to the FeÃ
/
Br stretching and bending modes, respectively
[29ꢁ32]. Similar frequencies have been reported for
/
bromoiron complexes and the far-IR spectrum of the
complex 3a1 also shows very close absorption band
(Fig. 3, n 302 and 135 cmꢂ1). Moreover, it has been
Scheme 3.

152
J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ155
/
2.4. Conclusions
V vs. SCE in CH2Cl2) [34]. X-band ESR spectra were
recorded on a Bruker EMX-8/2.7 spectrometer and
simulated spectra were obtained with the Bruker SIM-
FONIA program. MS analyses were recorded at the
‘Centre Regional de Mesures Physiques de l’Ouest’
(Rennes; C.R.M.P.O.); EIMS were obtained using a
Varian MAT 311 spectrometer and FABMS with a high
resolution MSMS ZabSpec TOF Micromass spectro-
meter (8 kV) using m-nitrobenzylic alcohol as a matrix.
Elemental analyses were performed at the Service
Central d’Analyses, USR CNRS 59, at Lyon-Vernaison
(France).
Adaptation of Pauson’s procedure for the preparation
of pentaarylcyclopentadienyliron dicarbonyl bromide
complexes containing methyl or fluorine substituents
on the arene rings allows facile access to these com-
pounds in good yields. We found that the presence of
two methyl groups or even two fluorine atoms on the
two ortho positions of one of the five arene rings
precludes the complexation of the C5 ring on the metal
center. We have clearly shown that the reaction does not
proceed through an oxidative addition, but through a
two-step process, which involves the formation of a
pentaarylcyclopentadienyl radical and a bromoiron
carbonyl intermediate. The presence of methyl or
fluorine substituents on the meta positions does not
apparently affect the free rotation of the C6 rings around
the central C5 ring, but allows a fine tuning of the
electron density at the metal center. Moreover, a
positive effect of the methyl groups on the solubility of
these complexes was noted.
3.2. Reactions of the bromocyclopentadienes (h5-
C5Ar4Ar?)Br (1) with Fe(CO)5 at 20 8C
In a Schlenk tube, iron pentacarbonyl (0.09 ml, 0.66
mmol) was added dropwise to a solution of 1 (0.5 mmol)
in toluene (20 ml). After stirring 2 h, the solution
became violet, and the solvent was removed under
reduced pressure. Purification achieved by chromato-
graphy on a silica gel column with pentane-diethyl ether
(9:1) provided a violet powder of the corresponding
3. Experimental
radical 2 in 85ꢁ90% yield. Radicals were characterized
/
by ESR spectroscopy in toluene at 293 K. Additional
characterizations were carried out for 2a5 and 2b5.
3.1. General data
All reactions were carried out either under an argon
atmosphere using standard Schlenk techniques or in a
Jacomex 532 dry box filled with nitrogen. Reagent grade
tetrahydrofuran (THF), pentane, diethylether, toluene
and mesitylene were predried and distilled over sodium
benzophenoneketyl prior to use. Dichloromethane and
acetonitrile were refluxed over P2O5 then distilled over
Na2CO3. Bromopentaarylcyclopentadienes containing
methyl or fluorine substituents were prepared as pre-
viously reported. [14] Deuterated solvents (Merck) were
used as received, except CDCl3 previously treated with
P2O5, then Na2CO3 and stored on basic alumina under
argon. High-field NMR spectra experiments were per-
formed on a multinuclear Bruker 300 MHz instrument
(AC300P). Chemical shifts are given in parts per million
relative to tetramethylsilane (TMS) for 1H and 13C-
NMR spectra, external H3PO4 for 31P-NMR spectra.
19F-NMR spectra were recorded at 288 MHz, and
chemical shifts are reported in ppm relative to external
CFCl3. Transmittance-FTIR spectra were recorded
3.2.1. [h5-C5(C6H5)4(2,4,6-C6H2Me3)]+ (2a5)
1H-NMR (300 MHz, CDCl3) 2.17 (s, 9 H, Me,
W1/2
ꢀ
/
100 Hz); 6.81 (s, 22 H, Ph, W1/2
ꢀ150 Hz).
/
3.2.2. [h5-C5(3,5-C6H3Me2)4(2,4,6-C6H2Me3)]+
(2b5)
1H-NMR (300 MHz, C6D6) 2.17 (s, 33 H, Me, W1/2
ꢀ
/
100 Hz); 6.81 (s, 14 H, Ph, W1/2
Found 600.3764, 616.3713. Calc. for [MÃ
600.3756, and [Mꢃ vis; toluene;
OH]ꢃ 616.3705. UVꢁ
106), 598 (0.72ꢄ
ꢀ
/
150 Hz).EIMS:
/
H]ꢃ
/
/
l, nm (o, l molꢂ1 cmꢂ1): 356 (3.5ꢄ
/
/
106). Anal. Found: C, 87.38; H, 7.57. Calc. for the
dioxygen adduct C46H47O2, C, 87.44; H, 7.50; O, 5.06%.
3.3. Syntheses of the (h5-C5Ar4Ar?)Fe(CO)2Br
Complexes (3)
In a schlenk tube 2.0 mmol of the corresponding
bromocyclopentadiene was dissolved in toluene (20 ml)
and iron pentacarbonyl (2.5 mmol, 330 ml) was added
via syringe. The yellow solution was warmed to 80 8C
for 2 h quickly became violet and then slowly turned to
using a Bruker IFS28 spectrometer (400ꢁ
and a Bruker EQUINOX 55 spectrometer (100ꢁ
cmꢂ1). UVꢁ
vis spectra were recorded on an UVIKON
942 spectrometer. Cyclic voltammograms were recorded
using an EG&G-PAR model 263 potentiostatꢁgalvano-
stat. The working electrode was a Pt wire (dꢀ1.0 mm)
/
4000 cmꢂ1
500
)
/
/
redꢁbrown. After cooling to 20 8C, the solvent was
/
removed under vacuum and the solid residue was
dissolved in CH2Cl2 and filtered through a 15 cm Celite
pad. Concentration of the solution (15 ml) and addition
of pentane afforded the iron complexes 2 as an orange
powder. Further recrystallization from CH2Cl2ꢁ
ether yielded pure product.
/
/
and the saturated calomel electrode (SCE) was used as a
reference electrode. The Cp2Fe0/ꢃ couple was used as an
internal calibrant for the potential measurements (0.460
/diethyl

J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ
/155
153
1
3.3.1. 3a3 (1.065 g, 1.6 mmol, 80%)
IR (cmꢂ1, CH2Cl2) 1610 (Ph), 1995 (CO), 2037 (CO).
C5(C6H3Me2)5), 129.7 (dm, JCÃH
ꢀ
/
155 Hz, p-
C6H3Me2), 129.9 (s, ipso-C6H3Me2), 130.4 (dq,
3
1H-NMR (300 MHz, CDCl3) 2.06 (s, 6H, Me), 6.67ꢁ
/
1JCÃH
2JCÃH
ꢀ
/
159 Hz, JCÃH
6 Hz, m-C6H3Me2), 214.4 (s, CO). FABHRMS
ꢀ
/
5 Hz, o-C6H3Me2), 136.6 (q,
7.23 (m, 23H, Ph). 13C-NMR (75 MHz, CDCl3) 21.3 (q,
1JCÃH
126 Hz, Me), 100.3 (s, C ÃPh), 101.7 (s, C Ã
C6H3Me2), 101.9 (s, CÃ Ph), 127.81 (d, JCÃH
ꢀ
/
79 56
ꢀ
/
/
/
Calc. for [C45H45 Br Fe+ꢃ] ([MÃ
/
2CO+ꢃ]): 720.2054.
1
/
ꢀ
/
161
161 Hz, o-Ph), 128.48
162 Hz, p-Ph), 128.52 (d, 1JCÃH
162 Hz, p-
Found: 720.2061.
1
Hz, o-Ph), 127.83 (d, JCÃH
(d, 1JCÃH
ꢀ
/
ꢀ
/
ꢀ
/
3.3.5. 3b4 (1.20 g, 1.5 mmol, 75%)
Ph), 129.3, 130.0, 130.1 (3 s, ipso-Ph, C6H3Me2), 130.2
(m, o-C6H3Me2, p-C6H3Me2), 130.3 (m, o-C6H3Me2, p-
IR (cmꢂ1, CH2Cl2) 1601 (Ph), 1992 (CO), 2034 (CO).
1H-NMR (300 MHz, CDCl3) 1.53 (s, 3H, Me), 1.95 (s,
12H, Me), 2.10 (s, 12H, Me), 2.31 (s, 3H, Me), 6.49 (m,
4H, o-3,5-C6H3Me2); 6.72 (m, 2H, p-3,5-C6H3Me2),
6.78 (m, 4H, o-3,5-C6H3Me2), 6.85 (m, 2H, p-3,5-
C6H3Me2), 6.93, 7.01, 7.76 (3 m, 3x1H, o,m,p-2,5-
1
C6H3Me2), 132.4 (d, JCÃH
ꢀ161 Hz, m-Ph), 132.5 (d,
/
2
1JCÃH
ꢀ
/
161 Hz, m-Ph), 137.1 (q, JCÃH
ꢀ5 Hz, m-
/
C6H3Me2), 213.8 (s, CO). Anal. Calc. for
C39H29BrFeO2: C, 70.40; H, 4.39. Found: C, 70.44; H
4.49%.
C6H3Me2). 13C-NMR (75 MHz, CDCl3) 19.9 (q,
1JCÃH
ꢀ
/
125 Hz, o-2,5-C6H3Me2), 21.2 (q, JCÃH
ꢀ125
/
1
3.3.2. 3a7 (0.810 g, 1.2 mmol, 60%)
IR (cmꢂ1, CH2Cl2) 2001 (CO), 2041 (CO). 19F-NMR
Hz, other Me), 97.5 (s, C Ã
3,5-C6H3Me2), 107.0 (s, C Ã
dm, ipso,p-3,5-C6H3Me2), 129.8 (dm, JCÃH
/
2,5-C6H3Me2), 97.9 (s, C Ã
/
/
3,5-C6H3Me2), 129.4 (sꢃ
/
3
1
(282 MHz, CDCl3) 109.70 (t, JFÃH
ꢀ
/
8 Hz). 13C-NMR
ꢀ
/
160 Hz,
160 Hz, o-3,5-
160 Hz, o-3,5-
C6H3Me2), 130.4 (s, ipso-3,5-C6H3Me2), 130.9 (s, ipso-
1
(75 MHz, CDCl3) 99.6 (s, C Ã
/
C6H3F2), 100.2 (s, C Ã
/
p-3,5-C6H3Me2), 129.9 (dm, JCÃH
C6H3Me2), 130.2 (dm, 1JCÃH
ꢀ
/
1
C6H5), 102.0 (s, C ÃC6H5), 104.2 (dt, JCÃH
/
ꢀ
/
160 Hz,
160 Hz,
160 Hz, o-
ꢀ
/
2JCÃF
2JCÃF
ꢀ
/
23 Hz, p-C6H3F2), 115.6 (dd, JCÃH
ꢀ
/
1
1
ꢀ
/
26 Hz, o-C6H3F2), 127.9 (d, 1JCÃH
ꢀ
/
2,5-C6H3Me2), 134.5 (dm, JCÃH
C6H3Me2), 134.8 (m, 2,5-C6H3Me2), 135.8 (m, 2,5-
ꢀ160 Hz, 2,5-
/
1
C6H5), 128.7 (d, JCÃH
ꢀ160 Hz, p-C6H5), 132.2 (d,
/
1JCÃH
162.1 (dm, JCÃF
ꢀ
/
160 Hz, m-C6H5), 133.9 (m, ipso-C6H3F2),
1
C6H3Me2), 136.2 (q, JCÃH
ꢀ6 Hz, m-3,5-C6H3Me2),
/
2
1
2
ꢀ/248 Hz, m-C6H3F2), 213.2 (s, CO);
136.9 (q, JCÃH
ꢀ
/
160 Hz, JCÃH
ꢀ
/
6 Hz, m-3,5-
C6H3Me2), 214.4 (s, CO). FABHRMS Calc. for
FABHRMS Calc. for [C35H2379BrF256Fe]ꢃ ([MÃ
/
2CO]+ꢃ): 616.0303. Found: 616.0300.
[C45H45 Br Fe+ꢃ] ([MÃ
720.2055.
/
2CO+ꢃ]): 720.2054. Found:
79 56
3.3.3. 3b2 (1.260 g, 1.6 mmol, 80%)
IR (cmꢂ1, CH2Cl2) 1601 (Ph), 1994 (CO), 2036 (CO).
1H-NMR (300 MHz, CDCl3) 2.05 (s, 12H, CH3), 2.06 (s,
12H, CH3), 2.11 (s, 3H, CH3), 6.68 (s, 8H, o-C6H3Me2),
3.3.6. 3b6 (1.105 g, 1.45 mmol, 72%)
IR (cmꢂ1, CH2Cl2) 1603 (Ph), 1994 (CO), 2036 (CO).
1H-NMR (300 MHz, CDCl3) 2.05 (s, 12H, Me), 6.66 (s,
6.81 (s, 4H, p-C6H3Me2), 6.93, 7.00 (2 d, 2H, C6H4Me).
8H, o-C6H3Me2), 6.81 (s, 4H, p-C6H3Me2), 6.9ꢁ7.0 (m,
/
1
13C-NMR (75 MHz, CDCl3) 21.1 (q, JCÃH
ꢀ
/
126 Hz,
C6H4F). 19F-NMR (282 MHz, CDCl3) 113.9 (m,
C6H4F). 13C-NMR , 75 MHz, CDCl3) 21.1 (q,
C6H3Me2), 21.3 (q, 1JCÃH
C ÃC6H3Me2), 101.0 (s, C Ã
C6H4Me), 127.3 (d, JCÃH
ꢀ
/
126 Hz, C6H4Me), 100.7 (s,
C6H3Me2), 101.5 (s, C Ã
160 Hz, m-C6H4Me),
154 Hz, p-C6H4Me), 129.5 (dm, o-
/
/
/
1JCÃH
C6H3Me2), 102.3 (s, C Ã
ꢀ
/
127 Hz, Me), 99.7 (s, C Ã
/
C6H4F), 100.0 (s, C Ã
/
1
ꢀ
/
/
C6H3Me2), 115.07 (ddm,
1
2
128.8 (dm, JCÃH
ꢀ
/
1JCÃH
ꢀ
/
160 Hz, JCÃF
ꢀ/21,3 Hz, p-C6H4F), 119.3
1
1
2
C6H4Me), 129.7 (dm, JCÃH
ꢀ
/
150 Hz, p-C6H3Me2),
150 Hz, p-C6H3Me2), 129.8 (s,
ipso-C6H3Me2), 129.9 (s, ipso-C6H3Me2), 130.3 (d,
(ddm, JCÃH
ꢀ
/
161 Hz, JCÃF
ꢀ22.9 Hz, o-C6H4F),
/
1
1
4
129.8 (dm, JCÃH
ꢀ
/
128.5 (ddm, JCÃH
ꢀ
/
160 Hz, JCÃF
ꢀ
/
2.44 Hz, o-
160Hz, JCÃF 8.55 Hz,
m-C6H4F), 129.36 (s, ipso-C6H3Me2), 129.56 (s, ipso-
1
4
C6H4F), 129.0 (ddm, JCÃH
ꢀ
/
ꢀ
/
3JCÃH
Hz, o-C6H3Me2), 130.4 (dm, JCÃH
ꢀ
/
7Hz, ipso-C6H4Me), 130.3 (dm, JCÃH
ꢀ
/
159
159 Hz, o-
152 Hz, o-C6H4Me),
1
1
1
ꢀ
/
C6H3Me2), 129.87 (d, JCÃH
ꢀ/160Hz, p-C6H3Me2),
1
1
C6H3Me2), 133.2 (dm, JCÃH
ꢀ
/
130.09 (d, JCÃH
1JCÃH
160Hz, o-C6H3Me2), 130.27 (d, JCÃH
160Hz, o-C6H3Me2), 133.22 (d, JCÃH
ꢀ
/
160Hz, p-C6H3Me2), 130.17 (d,
1
136.6 (m, m-C6H3Me2), 136.7 (m, m-C6H3Me2), 136.8
(m, m-C6H4Me), 214.2 (CO). FABHRMS Calc. for
ꢀ
/
ꢀ
/
2
ꢀ
/
7.33 Hz; ipso-
79 56
2
[C44H43 Br Fe+ꢃ] ([MÃ
706.1903.
/
2CO+ꢃ]): 706.1898. Found:
C6H4F), 136.76 (q, JCÃH
ꢀ
/6Hz, m-C6H4Me2), 136.90
2
1
(q, JCÃH
Hz, m-C6H4F), 213.9 (s, CO). FABHRMS Calc. for
[C43H4079BrF56Fe].ꢃ ([MÃ2CO]+ꢃ): 710.1649. Found:
710.1646.
ꢀ
/
6Hz, m-C6H4Me2), 161.8 (dm, JCÃF
ꢀ245
/
3.3.4. 3b3 (1.17 g, 1.5 mmol, 75%)
/
IR (cmꢂ1, CH2Cl2) 1602 (Ph), 1991 (CO), 2034 (CO).
1H-NMR (300 MHz, CDCl3) 2.07 (s, 30 H, C6H3Me2),
6.70 (s, 10 H, o-C6H3Me2), 6.81 (s, 5 H, p-C6H3Me2).
3.3.7. 3b7 (1.18 g, 1.5 mmol, 75%)
IR (cmꢂ1, CH2Cl2) 1602 (Ph), 1996 (CO), 2037 (CO).
1H-NMR (300MHz, CDCl3) 2.06 (s, 12H, Me), 2.09 (s,
1
13C-NMR (75 MHz, CDCl3) 21.2 (qt, JCÃH
ꢀ
ꢀ
/
126 Hz,
4 Hz,
3
3JCÃH
ꢀ
/
4.5 Hz, C6H3Me2), 101.2 (t, JCÃH
/

154
J.-Y. The´pot, C. Lapinte / Journal of Organometallic Chemistry 656 (2002) 146ꢁ155
/
12H, Me), 6.56 (s, 4H, o-C6H3Me2), 6.62 (dt, 1H,
4
Acknowledgements
3JFÃH
4H, o-C6H3Me2), 6.71 (s, 2H, p-C6H3Me2), 6.76 (s, 2H,
ꢀ
/
8.8 Hz, JHÃH
ꢀ
/
2.3 Hz, p-C6H3F2), 6.63 (s,
The valuable contribution of pregraduate students
from the IUT of Lannion (France) is gratefully
acknowledged. The authors thank Dr. P. Gue´not, Dr.
P. Jehan and Dr. C. Mouro for mass spectra, and Dr. A.
Bondon, Dr. J.R. Hamon and Dr. F. Paul for helpful
discussions.
3
4
p-C6H3Me2), 7.11 (dd, 2H, JFÃH
ꢀ
/
8.8 Hz, JHÃH
ꢀ2.3
/
Hz, o-C6H3F2). 19F-NMR (282 MHz, CDCl3) ꢂ
/
110.55
8.8 Hz). 13C-NMR (75 MHz, CDCl3) 21.1
3
(t, JFÃH
ꢀ
/
(1JCÃH
ꢀ
ꢀ
/
126 Hz, Me), 21.2 (1JCÃH
ꢀ
/
126 Hz, Me), 99.1
C6H3F2), 99.6 (s, C ÃC6H3Me2),
18 Hz, p-
165 Hz, o-
C6H3F2), 129.0 (s, ipso-C6H3Me2), 129.3 (s, ipso-
4
(t, JCÃF
/
2.5 Hz, C Ã
/
/
2
102.4 (s, C Ã
/
C6H3Me2), 103.6 (tm, JCÃF
ꢀ
/
2
1
C6H3F2), 115.6 (dd, JCÃF
ꢀ
/
27 Hz, JCÃH
ꢀ
/
1
References
C6H3Me2), 129.9 (d, JCÃH
ꢀ
/
165 Hz, p-C6H3Me2),
1
130.0 (d, JCÃH
1JCÃH
165 Hz, o-C6H3Me2), 130.3 (d, JCÃH
Hz, p-C6H3Me2), 134.6 (t, JCÃF
ꢀ
/
165 Hz, o-C6H3Me2); 130.1 (d,
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1
ꢀ
/
ꢀ
/
165
11 Hz, ipso-
6 Hz, m-C6H3Me2), 136.8
6 Hz, m-C6H3Me2), 161.9 (ddm, 1JCÃF
248
13 Hz, m-C6H3F2), 213.7 (s, CO).
2
ꢀ
/
2
C6H3F2), 136.6 (q, JCÃH
ꢀ
/
[3] A. Schott, H. Schott, G. Wilke, J. Brandt, H. Hoberg, E.G.
Hoffmann, Liebigs Ann. Chem. (1973) 508.
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ꢀ
/
ꢀ
/
3
[4] T.R. Jack, C.J. May, J. Powell, J. Am. Chem. Soc. 99 (1977) 4707.
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ꢀ
/
FABHRMS Calc. for [C43H3979BrF256Fe].ꢃ ([MÃ
/
2CO]ꢃ): 728.1555. Found: 728.1559.
[6] J.W. Chambers, A.J. Baskar, S.G. Bott, J.L. Atwood, M.D.
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[7] G.A. Lane, W.E. Geiger, N.G. Connelly, J. Am. Chem. Soc. 109
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3.4. Solubility measurements
[8] N.G. Connelly, I. Manners, J. Chem. Soc. Dalton Trans. (1989)
283.
In a test tube, an aliquot of the complexes was treated
with 2 ml of the desired solvent. The mixture was shaken
for 5 min, then allowed to stand for an additional 5 min
1.0 ml of the supernatent solution was transferred via
syringe into a test tube, then the solvent was removed in
vacuo. The amount of soluble complex per ml of solvent
was determined by weighing.
[9] K.N. Brown, L.D. Field, P.A. Lay, C.M. Lindall, A.F. Masters, J.
Chem. Soc. Chem. Commun. (1990) 408.
[10] L. Li, A. Decken, B.G. Sayer, M.J. McGlinchey, P. Bre´gaint, J.Y.
The´pot, L. Toupet, J.R. Hamon, C. Lapinte, Organometallics 13
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C6H3Me2)4(2,4,6-C6H2Me3)]Br (1b5) and [h5-C5(3,5-
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(20 ml) with one equivalent of iron pentacarbonyl (0.5
mmol, 65 ml) to generate the radical 2b5. In an other
Schlenk tube, the bromopentaarylcyclopentadiene 1b3
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stirred for 2 h at 20 8C. From the second solution, the
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pentaneꢁdiethyl ether (9:1) provided a violet powder
/
of the corresponding radical 2b3. Dissolved in toluene
(20 ml), 2b3 was added to the first solution. The mixture
was heated to 80 8C for 30 min, then the solvent was
removed to dryness. The solid residue was washed with
pentane, giving the radical 2b5, identified by its ESR
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remaining solid allowed the isolation of the complex
3b3 (70%), which was characterized by comparison with
an authentic sample.
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