Coordination chemistry of perhalogenated cyclopentadienes and alkynes. XXVIII [1] new high-yield synthesis of monobromoferrocene and simplified procedure for the synthesis of pentabromoferrocene. Molecular structures of1,2,3-tribromoferrocene and 1,2,3,4,5-pentabromoferrocene

Article abstract of DOI:10.1016/j.jorganchem.2010.12.028

Monobromoferrocene (1) was obtained in 95% yield from ferrocene via lithiation with tert-BuLi/KO-tert-Bu and bromination with dibromotetrachloroethane. Starting from 1 mixtures of 1,2-dibromoferrocene (2) and apparently unreacted 1 (ranging from 80:20 to 50:50, depending on the reaction conditions) can be obtained via a lithiation- zincation- bromination sequence. These mixtures can be transferred directly with a tenfold excess of Lithium-tetramethylpiperidinide, followed by bromination with 1,1,2,2-tetrabromoethane to pentabromoferrocene (3), in an overall yield of 36% starting from ferrocene. The molecular structures of 3 and of 1,2,3-tribromoferrocene (4) have been determined by X-Ray diffraction.

Full text of DOI:10.1016/j.jorganchem.2010.12.028

Journal of Organometallic Chemistry 696 (2011) 1536e1540
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Coordination chemistry of perhalogenated cyclopentadienes and alkynes. XXVIII
[1] new high-yield synthesis of monobromoferrocene and simplified procedure
for the synthesis of pentabromoferrocene. Molecular structures of
1,2,3-tribromoferrocene and 1,2,3,4,5-pentabromoferrocene
*
Karlheinz Sünkel , Stefanie Bernhartzeder
Department of Chemistry, Ludwig-Maximilians-University Munich, Butenandtstr. 9, 81377 Munich, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Monobromoferrocene (1) was obtained in 95% yield from ferrocene via lithiation with tert-BuLi/KO-tert-
Bu and bromination with dibromotetrachloroethane. Starting from 1 mixtures of 1,2-dibromoferrocene
(2) and apparently unreacted 1 (ranging from 80:20 to 50:50, depending on the reaction conditions) can
be obtained via a lithiation- zincation- bromination sequence. These mixtures can be transferred directly
with a tenfold excess of Lithium-tetramethylpiperidinide, followed by bromination with 1,1,2,2-tetra-
bromoethane to pentabromoferrocene (3), in an overall yield of 36% starting from ferrocene. The
molecular structures of 3 and of 1,2,3-tribromoferrocene (4) have been determined by X-Ray diffraction.
Ó 2010 Elsevier B.V. All rights reserved.
Received 14 September 2010
Received in revised form
6 December 2010
Accepted 20 December 2010
Keywords:
Ferrocene
Lithiation
Bromoferrocenes
Crystal structures
1. Introduction
for pentabromoferrocene starting from ferrocene. We reasoned
that another synthetic alternative might be the synthesis of the
The lithium-halogen-exchange reaction on halogenated metal-
locenes has proven to be a valuable synthetic tool for the intro-
“key intermediate” 1,2-dibromoferrocene starting from mono-
bromoferrocene via directed lithiation-bromination. A literature
survey shows for all of the known preparations of mono-
bromoferrocene rather low yields [8], under the aspect of a needed
starting material for a multi-step synthesis (Scheme 1).
We decided therefore to devise a new synthetic procedure
for monobromoferrocene and examine its transformation to
1,2-dibromoferrocene and further to pentabromoferrocene.
duction of
a large number of functional groups into the
cyclopentadienyl ring. [2] This could be shown impressively at
the perhalocymantrenes [(C5X5)Mn(CO)3] [3]. Although there are
meanwhile quite a number of perhalocyclopentadienyl complexes
available, it was only until recently that pentabromoferrocene
could be prepared [4]. The analogous pentachloroferrocene was
prepared already nearly 40 years ago, [5] however, in a rather low
overall yield, and several preliminary examinations of its reactivity
by one of us showed it to be too stable to be a useful starting
material for systematic functionalization. [6] The key step in the
recent synthesis of the bromo derivative was Butler’s discovery [7]
that 1,10-dibromoferrocene could be easily transferred to its 1,2
regioisomer. Unfortunately, the bromination reagent used by
Butler, dibromotetrafluoroethane, is due to EU regulations no
longer available in continental Europe. Attempts to repeat Butler’s
synthesis with other bromination reagents like tetrabromoethane
or dibromotetrachloroethane lead in our hands to a marked
decrease from the reported 85% yield in the isomerization step to
36e46% with the consequence of a rather low overall yield of 5.2%
2. Experimental
2.1. General remarks
Reactions were performed either under dry nitrogen or argon,
using standard Schlenk techniques. Absolute dry solvents were
purchased from Aldrich and used without further purification. As
the reaction products are generally air-stable, isolation and purifi-
cation steps were performed in air. Ferrocene and the reagents
(n-BuLi solution, 2.5
M
in hexane; tert-BuLi solution 1.7
M in hexane;
ZnCl2 solution, 1.9
M in Me-THF; KO(tert-Bu), C2Cl4Br2; C2H2Br4;
TMP) were commercially available (Aldrich) and used without
further purification. The alumina for chromatography was obtained
from VWR (Al2O3 90 “standardized”).
* Corresponding author. Tel.: þ49 89 2180 77773; fax: þ49 89 2180 77774.
E-mail address: suenk@cup.uni-muenchen.de (K. Sünkel).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.12.028

K. Sünkel, S. Bernhartzeder / Journal of Organometallic Chemistry 696 (2011) 1536e1540
1537
Scheme 1. Known preparations of 1 starting from ferrocene: (a): 1. nBuLi, 2. B(OBu)3, 26%; (a’): CuBr2, 80%, [8a]; (b): Hg(OAc)2/LiCl,73%; (b’): N-Bromosuccinimide, 57%, [8b]; (c)
tBuLi, 77%; (c’): Br2 , 66%, [8c]; (d): 1. nBuLi/TMEDA, 2. C2Br2F4, 60% [8e]; (d’): 1. nBuLi 2. H2O, 95% [8d].
2.2. Monobromoferrocene, [(C5H4Br)(C5H5)Fe], (1)
to room temperature over a period of 16 h and quenched with
water. The product was extracted two times with CH2Cl2 and the
organic layers were washed with water and dried over MgSO4. The
solvent was removed under vacuum and the residue was purified
by flash column chromatography using hexane as solvent. Yield:
3.67 g of a mixture of 1,2,3,4-tetrabromoferrocene (7%), 1,2,3-tri-
bromoferrocene (18%), 1,2-dibromoferrocene (24%) and bromo-
ferrocene (51%).
Ferrocene (2.00 g, 10.8 mmol) and potassium tert-butoxide
(150 mg, 1.34 mmol) were dissolved in 100 mL THF and the solution
was cooled to ꢀ78 ꢁC. Over a period of 15 min, 12.7 mL (21.6 mmol)
of tert-BuLi were added dropwise, while ensuring the temperature
remained below ꢀ70 ꢁC. The mixture was stirred at this tempera-
ture for 1.5 h.1,2-dibromotetrachloroethane (5.25 g,16.1 mmol) was
added and the mixture was stirred for 30 min at ꢀ78 ꢁC. The cooling
bath was removed and the solution was allowed to warm to room
temperature and quenched with water. The product was extracted
two times with CH2Cl2 and the organic layers were washed with
water and dried over MgSO4. The solvent was removed under
vacuum and the residue was purified by flash column chromatog-
raphy using neutral alumina as the stationary phase and hexane as
solvent. Yield: 2.74 g (10.3 mmol, 95%). 1H NMR (400 MHz, CDCl3):
4.41 (t, 2H), 4.22 (s, 5H), 4.09 (t, 2H). 13C NMR (100.5 MHz, CDCl3):
77.8 (CBr), 70.7 (C5H5), 70.2 (CH), 67.2 (CH).
2.4. 1,2,3,4,5-Pentabromoferrocene, [(C5Br5)(C5H5)Fe], (3)
2.4.1. Preparation from a mixture containing 1, 2, 4 and 5
The mixture from experiment 2.3.2. (3.60 g, corresponds to
10.8 mmol) was dissolved in 15 mL THF. At ꢀ30 ꢁC, this solution was
added to freshly prepared lithiated TMP (100 mmol) in 100 mL THF.
After aging for 5 h at ꢀ30 ꢁC, the mixture was cooled to ꢀ78 ꢁC and
1,1,2,2-tetrabromoethane (11.7 mL, 100 mmol) was added. The
solution was allowed to warm to room temperature over a period of
16 h and quenched with water. The product was extracted two
2.3. 1,2-Dibromoferrocene, [(C5H3Br2)(C5H5)Fe], (2)
times with CH2Cl2, the organic layers were washed with 1 M HCl
followed by water and dried over MgSO4. The solvent was removed
under vacuum and the residue was purified by flash column
chromatography using hexane as solvent. The solution was
concentrated and allowed to stand at 5 ꢁC for 16 h. Brown crystals of
the product were formed. Yield: 3.59 g (6.18 mmol, 57%). 1H NMR
(400 MHz, CDCl3): 4.30; (270 MHz, C6D6): 3.88. 13C NMR
(100.5 MHz, CDCl3): 80.9 (CBr), 80.8 (C5H5); (67.9 MHz, C6D6): 81.0
(CBr), 80.5 (C5H5). EA (calc./found): C: 20.69/20.72; H: 0.87/0.84;
Br: 68.82/68.79; Fe: 9.62/10.26%. HRMS: calc: 579.5618, found:
579.5634.
2.3.1. Isolation of pure 1,2-dibromoferrocene
A solution of 1 (0.63 g, 2.38 mmol) in 14 mL THF was added at
ꢀ30 ꢁC to freshly prepared LiTMP (2.62 mmol) in 4 mL THF. After
aging for 3 h at ꢀ30 ꢁC, ZnCl2 solution (1.40 mL, 2.66 mmol) was
added dropwise and the mixture stirred for additional 30 min at
ꢀ30 ꢁC. The solution was cooled to ꢀ78 ꢁC and bromine (0.18 mL,
3.50 mmol) was added dropwise, while ensuring the temperature
remained below ꢀ50 ꢁC. After 45 min, the cooling bath was
removed and the solution was allowed to warm to room temper-
ature and quenched with water. The product was extracted two
times with CH2Cl2 and the organic layers were washed with 1
M
HCl
2.4.2. Preparation from bromoferrocene
followed by water and dried over MgSO4. The solvent was removed
under vacuum and the residue was purified by flash column
chromatography using hexane as solvent. Yield: 0.43 g (1.25 mmol,
53%). 1H NMR (270 MHz, CDCl3): 4.43 (d, 2H), 4.25 (s, 5H), 4.11
(t, 1H). 13C NMR (100.5 MHz, CDCl3): 80.4 (CBr), 73.3 (C5H5), 69.0
(CH), 66.1 (CH).
A solution of 1 (1.26 g, 4.76 mmol) in 7 mL THF at ꢀ30 ꢁC was
added to freshly prepared LiTMP (47.5 mmol) in 48 mL THF. After
stirring for 5 h at ꢀ30 ꢁC, the mixture was cooled to ꢀ78 ꢁC and
1,1,2,2-tetrabromoethane (5.54 mL, 47.5 mmol) was added. The
solution was allowed to warm to room temperature over a period of
16 h and quenched with water. The product was extracted two
times with CH2Cl2, the organic layers were washed with 1
M HCl
2.3.2. Treatment of a 1:1 mixture of 1 and 2 with 0.5 equivalents of
LiTMP
followed by water and dried over MgSO4. The solvent was removed
under vacuum and the residue was purified by flash column
chromatography using hexane as solvent. The solution was
concentrated and allowed to stand at 5 ꢁC for 16 h. Brown crystals of
the product were formed. Yield: 0.31 g (0.53 mmol, 11%). The
solvent was removed under vacuum because no more crystals were
formed from the solution. Yield: 3.18 g of a mixture of 1,2,3,4,5-
pentabromoferrocene (7%, corresponds to 0.72 mmol, 15% yield
based on 1), 1,2-dibromoferrocene (28%, corresponds to 2.9 mmol,
61% yield based on 1) and Tribromoethylene (65%).
A mixture of 48% 1,2-dibromoferrocene and 52% bromoferro-
cene (3.65 g, 12.0 mmol, obtained by a procedure similar to 2.3.1.,
starting from 4.44 g 1, 3.12 mL TMP and 7.38 mL BuLi solution in
a total of 80 mL THF, with no chromatography step) was dissolved
in 50 mL THF. At ꢀ30 ꢁC, this solution was added to freshly prepared
LiTMP (6.00 mmol) in 10 mL THF. After aging for 4 h at ꢀ30 ꢁC, the
mixture was cooled to ꢀ78 ꢁC and 1,1,2,2-tetrabromoethane
(0.71 mL, 6.09 mmol) was added. The solution was allowed to warm

1538
K. Sünkel, S. Bernhartzeder / Journal of Organometallic Chemistry 696 (2011) 1536e1540
Table 1
2.5. 1,2,3-Tribromoferrocene [(C5Br3H2)(C5H5)Fe], (4)
Experimental parameters of the crystal structure determinations.
A solution of 1,10-dibromoferrocene (8.60 g, 25.0 mmol) in THF
(150 mL) was treated at ꢀ70 ꢁC with n-BuLi solution (10.0 mL,
25.0 mmol), and after 30 min stirring with TMP (4.22 mL,
25.0 mmol). Stirring was continued for 3 h at ꢀ30 to ꢀ40 ꢁC. After
cooling to ꢀ70 ꢁC 1,1,2,2-tetrabromoethane (2.92 mL, 25.0 mmol)
was added. The temperature was raised to ambient over the course
of 18 h, when 50 mL water was added. The aqueous phase was
separated and extracted with 50 mL Et2O. The combined organic
phases were dried over MgSO4. Evaporation of the filtered extract
and chromatography on alumina gave an orange solid, which
contained ferrocene and 2. Ferrocene could be removed from this
mixture by sublimation, yielding pure 2 (3.09 g, 8.99 mmol, 36%).
A solution of TMP (1.51 mL, 8.96 mmol) in THF (15 mL) was
treated at ꢀ30 ꢁC with n-BuLi solution (3.58 mL, 8.96 mmol). After
stirring for 15 min at 0 ꢁC this solution was added to 2, dissolved in
60 mL THF, at ꢀ30 ꢁC. Stirring was continued at this temperature for
3 h. After cooling to ꢀ70 ꢁC, this solution was treated with 1,1,2,2-
tetrabromoethane (1.05 mL, 8.96 mmol). Again, the reaction
mixture was brought to room temperature within 18 h, water
(50 mL) was added, the aqueous phase extracted with ether
(50 mL), the combined organic phases dried over MgSO4 and the
filtered solution evaporated in vacuo. The residue was taken up in
petrol ether and filtered through a 3 cm plug of alumina. Partial
evaporation of the solvent and cooling to 4 ꢁC left 4 as light brown
needles (2.63 g, 6.23 mmol, 69%). Another recrystallization gave
crystals suitable for X-ray determination. 1H NMR (400 MHz,
CDCl3): 4.27 (5H), 4.49 (2H). 13C NMR (100.5 MHz, CDCl3): 83.2
(CBr), 78.8 (CBr), 75.9 (C5H5), 67.8 (CH).
Identification code
3
4
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
C10H5Br5Fe
580.54
Triclinic
C10H7Br3Fe
422.74
Monoclinic
P2(1)/n
P -1
a ¼ 829.0(5) pm
b ¼ 1222.0(5) pm
c ¼ 1403.9(5) pm
a ¼ 693.0(5) pm
b ¼ 1048.6(5) pm
c ¼ 1540.7(5) pm
a
b
g
¼ 106.329(5)ꢁ
¼ 96.166(5)ꢁ
¼ 97.007(5)ꢁ
a
b
g
¼ 90.000(5)ꢁ
¼ 90.677(5)ꢁ
¼ 90.000(5)ꢁ
Volume
Z
1.3396(11) nm3
2 ꢂ 2 indep. Mol.
2.879 Mg/m3
1.1195(10) nm3
4
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data
collection
2.508 Mg/m3
12.009 mm-1
792
16.008 mm-1
1064
0.24 ꢂ 0.2 ꢂ 0.15 mm3
0.15 ꢂ 0.14 ꢂ 0.13 mm3
4.24e26.34ꢁ
3.21e27.54ꢁ
Index ranges
ꢀ10 ꢃ h ꢃ 10,
ꢀ12 ꢃ k ꢃ 15,
ꢀ17 ꢃ l ꢃ 17
10007
ꢀ9ꢃh ꢃ 8,
ꢀ13 ꢃ k ꢃ 13,
ꢀ20 ꢃ l ꢃ 20
30867
Reflections collected
Independent
reflections
5418 [R(int) ¼ 0.0276]
2562 [R(int) ¼ 0.0804]
Completeness to
theta ¼ 26.34ꢁ
Max. and min.
transmission
Data/restraints
/parameters
99.0%
99.5%
1 and 0.47567
5418/0/289
0.2494 and 0.1180
2562/0/148
Goodness-of-fit on F2
Final R indices
[I > 2sigma(I)]
R indices (all data)
868
1078
R1 ¼ 0.0330,
wR2 ¼ 0.0716
R1 ¼ 0.0587,
wR2 ¼ 0.0744
0.727 and
R1 ¼ 0.0267,
wR2 ¼ 0.0626
R1 ¼ 0.0311,
wR2 ¼ 0.0645
0.690 and
2.6. 1,2,3,4-Tetrabromoferrocene, [(C5Br4H)(C5H5)Fe], (5)
Largest diff. peak
and hole
CCDC numbers
ꢀ1.407 e.Åꢀ3
79126
ꢀ0.682 e.Åꢀ3
79127
A solution of TMP (2.67 mL, 15.8 mmol) in THF (25 mL) was
treated at ꢀ30 ꢁC with n-BuLi solution (6.32 mL, 15.8 mmol) and
stirred for 15 min at 0 ꢁC. This solution was then added to a solution
of 4 (2.68 g, 6.34 mmol) in 40 mL THF at ꢀ30 ꢁC. Stirring was
continued for 3 h at this temperature. After cooling to ꢀ70 ꢁC,
1,1,2,2-tetrabromoethane (1.84 mL, 15.8 mmol) was added, and
then the reaction mixture was allowed to reach room temperature
within 18 h, followed by standard work-up. Careful recrystallization
from petrol ether/Et2O at 4 ꢁC gave first 3 (0.65 g, 1.12 mmol, 18%) as
dark brown crystals, suitable for X-ray determination, and then
5 (1.41 g, 2.81 mmol, 44%) as light brown powder. 1H NMR
(400 MHz, CDCl3): 4.30 (5H), 4.93 (1H); (270 MHz, C6D6): 3.91 (5H),
4.31 (1H); 13C NMR (67.9 MHz, C6D6): 82.1 (CBr), 78.1 (C5H5), 77.9
(CBr), 69.5 (CH). EA: (calc/found): C: 23.94/23.96; H: 1.21/1.15; Br:
63.72/63.45; Fe: 11.13/11.00%. HRMS: calc.501.6513/found:
501.6505.
(
l
¼
0.71073, graded multilayer X-ray optics). A multi-scan
absorption correction was applied using the SADABS [9b] program.
The structure was solved with the SIR-97 software as implemented
in the WinGX software package. Refinement (full matrix least
square on F2) was done with SHELXL 97, also as implemented in
WinGX. Further details can be seen in Table 1.
3. Results and discussion
After a decades long search for a clean high-yield preparation of
monolithioferrocene Kagan’s procedure in the modification by
Mueller- Westerhoff [10] using a combination of tert-butyllithium
and potassium tert-butylate has been established as the method of
choice. Using the same lithiation procedure, followed by bromi-
nation with 1,2-dibromotetrachloro-ethane, we obtained the
desired monobromoferrocene (1) in 95% yield. NMR analysis
showed no traces of unreacted ferrocene or higher brominated
ferrocenes. (Scheme 2)
For the preparation of 1,2-dibromoferrocene (2) we used
a recent synthetic protocol for 1,2-dibromoarenes via a lithium-zinc
transmetallation, published by Menzel et al [11]. 1 was selectively
orthometalated with LiTMP followed by lithium- zinc- exchange
2.7. Experimental details of the crystal structure determinations of
3 and 4 [9]
An X-ray quality crystal of 3 was mounted on a glass fiber and
cooled to 173(3) K during measurement. The data were collected on
an Oxford Xcalibur3 CCD diffractometer using graphite-mono-
chromated Mo K
a
radiation (
l
¼ 0.71073). A multi-scan absorption
correction was applied using the ABSPACK [9a] program. The
structure was solved with the SIR-97 software [9c] as implemented
in the WinGX software package [9e]. Refinement (full matrix least
square on F2) was done with SHELXL 97 [9d], also as implemented
in WinGX. Further details can be seen in Table 1.
An X-ray quality crystal of 4 was mounted on a glass fiber and
cooled to 173(3) K during measurement. The data were collected
on a Nonius KappaCCD diffractometer using Mo K
a
radiation
Scheme 2. Preparation of 1.

K. Sünkel, S. Bernhartzeder / Journal of Organometallic Chemistry 696 (2011) 1536e1540
1539
Scheme 3. Preparation of 2.
via ZnCl2 and then the intermediate aryl zinc species was carefully
brominated with elemental bromine. After work-up product
mixtures of 2 and apparently unreacted 1 in relative proportions
ranging from 1:1 to 4:1, depending on the reaction conditions,
could be obtained. Isolated yields were usually around 40e45%,
with a maximum of 53%. If the primary lithiation product was
treated directly with 1,2-dibromotetrachloroethane, isolated yields
were substantially lower. (Scheme 3)
In another experiment, we treated a 1:1 mixture of 1 and 2 with
half an equivalent of LiTMP followed by bromination with 1,1,2,2-
tetrabromoethane. Unexpectedly, the relative amount of 1 in the
mixture didn’t change, while appreciable amounts of 1,2,3-tri-
bromoferrocene 4 and tetrabromoferrocene 5 were formed. This
result suggested that the reactivity in the lithiation/bromination
reaction increased with increasing bromine content. Therefore, we
tried out what would happen if we treated this mixture of 1, 2, 4
and 5 with a large excess of LiTMP followed by bromination with
1,1,2,2-tetrabromoethane. To our delight we found out that after
work-up a 57% yield of pentabromoferrocene 3 could be isolated,
corresponding to an overall yield of 36% starting from ferrocene.
Finally, we tried what would happen, if we treated bromo-
ferrocene 1 directly with a large excess of LiTMP followed by
bromination with C2H2Br4. After work-up and recrystallization an
11% yield of brown crystals of 3 could be isolated. NMR examination
of the evaporated mother liquor showed the presence of more
3 (corresponding to a further 15% yield) besides dibromoferrocene
2 and tribromoethylene as the organic product from C2H2Br4. In our
hands, it was not possible to isolate the contained 3 from this
mixture without substantial losses. (Scheme 4)
Pentabromoferrocene has a high tendency to crystallize, and
thus we decided to perform an X-ray crystal structure determina-
tion. Fig. 1 shows an ORTEP view of one of the two independent
molecules in the unit cell. There are only minute differences
between the two molecules, except for the degree of deviation from
ideal eclipsed conformation: The torsion angle between corre-
sponding ring-centroid ring-carbon vectors is ca. 2.5ꢁ in molecule
A and ca. 8ꢁ in molecule B. The other structural parameters are
quite similar to other pentabromocyclopentadienyl complexes [12].
As our X-ray structure determination proved that we actually
had prepared the compound, we were quite astonished to find out
Fig. 1. Molecular Structure of 3, Molecule A. Thermal Ellipsoids are drawn at the 50%
probability level.
spectrometry) in 44% yield. Comparison of the published NMR data
with our data for 3 and 5 (
(CH)) suggests that the published product actually is a mixture of
these latter compounds.
d
¼ 82.1 (CBr), 78.1 (C5H5), 77.9 (CBr), 69.5
Also our one-pot synthesis produces minor amounts of 5, which
can be separated by careful recrystallization. However, depending
on the desired further use of 3, the mixture might be used as it is.
As, by chance, purification of tribromoferrocene 4 lead to crystals
of X-ray quality, we also undertook its crystal structure determi-
nation. Fig. 2 shows an ORTEP view of its molecular structure. This
shows also that the three bromine atoms are in the expected 1,2,3-
orientation. Quite interestingly, there seems to be a kind of ring
slippage in the C5Br3H2 ring, as the distances from the iron atom to
the bromine bearing carbon atoms are significantly shorter than to
the other two (201.2(3) pm vs 205.3(3) pm). The iron ring-centroid
distance to the substituted ring is approximately 3 pm shorter than
the one to the unsubstituted ring. In comparison to the structure of 3
that our 13C NMR data (
disagreed with the literature data (
d
¼ 80.9 (CBr) and 80.8 (CH) ppm in CDCl3)
d
¼ 78.8 and 80.8 ppm in CDCl3,
[4]). We had therefore a closer look at the published procedure.
When we repeated the bromination step of 1,2,3-tri-
bromoferrocene 4 by using 1,1,2,2-tetrabromoethane and carefully
recrystallized the crude product, we could actually obtain two
different products- the described pentabromoferrocene, in only
18% yield, and tetrabromoferrocene 5 (first identified by mass
Fig. 2. Molecular Structure of 4. Thermal Ellipsoids are drawn at the 50% probability
Scheme 4. Preparation of 3.
level.

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K. Sünkel, S. Bernhartzeder / Journal of Organometallic Chemistry 696 (2011) 1536e1540
[4] I.R. Butler, Inorg. Chem. Commun. 11 (2008) 484.
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[6] K. Sünkel, U. Birk, A. Blum, W. Kempinger, J. Organomet. Chem. 465 (1994) 167.
[7] I.R. Butler, Inorg. Chem. Commun. 11 (2008) 15.
[8] (a) A.N. Nesmejanov, W.A. Ssasonova, V.N. Drosd, Chem. Ber 93 (1960) 2717;
(b) R.W. Fish, M. Rosenblum, J. Organomet. Chem. 30 (1965) 1253;
(c) B. Bildstein, M. Malaun, H. Kopacka, K. Wurst, M. Mitterböck, K.-H. Ongania,
G. Opromolla, P. Zanello, Organometallics 18 (1999) 4325;
(d) A.G. Tennyson, D.M. Khramov, C.D. Varnado Jr., Ph.T. Creswell, J.W. Kamplain,
V.M. Lynch, Ch.W. Bielawski, Organometallics 28 (2009) 5142;
(e) T.-Y. Dong, L.-L. Lai, J. Organomet. Chem. 509 (1996) 131.
[9] (a) ABSPACK, Oxford Diffraction (2005);
the CeBr bonds in 5 are slightly longer (on average 187.9 pm vs
186.9 pm), as well as the CeC bonds in the brominated ring
(142.5 pm vs 141.9 pm) and the distance from Fe to the centroid of
this ring (162.7 pmvs.160.9 pm). The two cyclopentadienyl rings are
slightly staggered (torsion angle ca. 15ꢁ). The C5Br3H2 ring deviates
only by 1.7 pm from planarity; the three bromine atoms are shifted
away from the Fe side of the ring by 6 (Br3) to 12 pm (Br2).
4. Conclusion
(b) G.M. Sheldrick, SADABS, Version 2. Multi-Scan Absorption Correction.
University of Göttingen, Germany, 2001;
(c) SIR-97 A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giacovazzo,
A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Crystallogr. 32
(1999) 115;
A new high-yield preparation of monobromoferrocene has been
achieved. It could be shown that for the synthesis of pentabro-
moferrocene the mixture of mono- and 1,2-dibromoferrocene can
be directly used without the need of isolation and purification of
the less substituted intermediate bromoferrocenes. Where the
C2Br2F4 is still available even higher yields might be achievable.
(d) SHELXL-97 G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112;
(e) WinGX L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[10] (a) D. Guillaneux, H.B. Kagan, J. Organomet. Chem. 60 (1995) 2502;
(b) R. Sanders, U.T. Mueller- Westerhoff, J. Organomet. Chem. 512 (1996)
219.
References
[11] K. Menzel, E.L. Fisher, L. DiMichele, D.E. Frantz, T.D. Nelson, M.H. Kress,
J. Organomet. Chem. 71 (2006) 2188.
[12] (a) (C5Br5)2Ru C.H. Winter, Y.-H. Han, R.L. Ostrander, A.L. Rheingold, Angew.
Chem. 105 (1993) 1247;
[1] Part XXVII: K. Sünkel, U. Birk, S. Soheili, Polyhedron, submitted for publication.
[2] For a review see K. Sünkel, Chem. Ber./Recl. 130 (1997) 1721 [microreview].
[3] e.g. for the synthesis of a pentaphosphanyl-derivative K. Sünkel, C. Stramm,
S. Soheili, J. Chem. Soc. Dalton Trans. (1999) 4299.
(b) (C5Br5)Re(CO)3 L.V. Dinh, F. Hampel, J.A. Gladysz, J. Organomet. Chem. 690
(2005) 493.