Synthesis of arylcalcium halides - General procedure, scope and limitations

Article abstract of DOI:10.1055/s-2007-965909

A general procedure for the synthesis of a wide variety of arylcalcium halides by activation of the alkaline earth metal as well as bromo- or iodoarenes is reported. Chloro- and fluoroarenes are not suitable substrates for an insertion of calcium into the carbon-halogen bond. Furthermore, ortho-fluoro substitution prevents the formation of the corresponding heavy calcium organometallics. The ipso-carbon atoms show a strong low-field shift in the ¹³C NMR spectra. The arylcalcium iodides crystallize monomeric as tetrakis(THF) complexes. Naphthylcalcium iodide shows a Ca-C bond length of 255.2(6) pm which lies in the characteristic region. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-965909

PAPER
725
Synthesis of Arylcalcium Halides – General Procedure, Scope and Limitations
S
M
ynthesis of
A
rylcalciu
a
m
H
alidesrtin Gärtner, Helmar Görls, Matthias Westerhausen*
Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, August-Bebel-Str. 2, 07743 Jena, Germany
Fax +49(3641)948110; E-mail: m.we@uni-jena.de
Received 16 November 2006; revised 21 November 2006
Due to the difficulties in performing the direct synthesis,
Abstract: A general procedure for the synthesis of a wide variety
the metathesis reaction of organic potassium compounds
of arylcalcium halides by activation of the alkaline earth metal as
well as bromo- or iodoarenes is reported. Chloro- and fluoroarenes
are not suitable substrates for an insertion of calcium into the car-
with calcium diiodide represents the standard procedure
5
for the synthesis of organocalcium compounds. An addi-
bon–halogen bond. Furthermore, ortho-fluoro substitution prevents tional stabilization can be achieved via an a-substitution
the formation of the corresponding heavy calcium organometallics. with phenyl and trialkylsilyl groups in order to stabilize
1
3
The ipso-carbon atoms show a strong low-field shift in the
C
10
the anionic charge. However, the calcium atom tends to
NMR spectra. The arylcalcium iodides crystallize monomeric as
tetrakis(THF) complexes. Naphthylcalcium iodide shows a Ca–C
bond length of 255.2(6) pm which lies in the characteristic region.
bind to the p-system of the benzyl anion rather than form-
ing a Ca–C s-bond.
General Remarks: The preparation of 2,4,6-trimethylphe-
Keywords: Grignard reaction, arylcalcium halides, direct synthe-
sis, calcium, metal activation
1
1
nylcalcium iodide (mesitylcalcium iodide), phenylcalci-
um iodide and p-tolylcalcium iodide12 showed the
suitability of insertion of calcium into a carbon–halogen
bond according to Equation 1. The decomposition via
ether cleavage reactions occurred already at temperatures
below –35 °C. Therefore, a variety of arylcalcium halides
were prepared and a general procedure was developed.
The organic chemistry of the alkali metals has a long tra-
1
dition and is well established. Especially the organolithi-
um chemistry has found a wide spectrum of applications.2
The interest in the organic chemistry of the alkaline earth
3
metals was mainly limited to magnesium. Due to the tox-
R2
R3
R2
4
R3
icity of beryllium and the difficulties during the forma-
tion of metal–carbon bonds of the heavy alkaline earth
metals, only the direct synthesis of alkyl- and arylmagne-
THF
°C
R1
R1
5
X
+ Ca
Ca(THF)4–X
0
sium halides by insertion of magnesium into a carbon–
halogen bond gained tremendous importance. Even
though several review articles on the organic chemistry of
R3
R2
R3
R2
Equation 1
calcium, strontium and barium appeared approximately
6
3
0 years ago, these compounds remained poorly charac-
Activation of Calcium: Due to the low reactivity of calci-
um metal, activation prior to use is necessary. Distillation
of calcium affords pure metal. However, the metal surface
of these calcium crystals is rather small and long reaction
periods and activation methods such as ultrasound have to
be applied which also promote side reactions. Therefore,
activation via dissolution in liquid ammonia proved to be
advantageous. In order to prevent amide formation, the
ammonia should be removed immediately from these so-
lutions. The remaining calcium powder is dried in vacuo
and then a suspension in THF is formed. Instead of a stir-
ring bar, glass balls in a shaken flask proved to be advan-
tageous for grinding the metal powder during the reaction
with aryl halides.
terized or were deduced solely from derivatization reac-
tions. In contrast to this lack of knowledge, the
metallocenes of the heavy alkaline earth metals represent
an exception and are easily accessible in good yields.7
The main challenge of the organic chemistry of the heavy
alkaline earth metals stems from the discrepancy of the
low reactivity of the calcium metal and the extreme high
reactivity of the organocalcium compounds with the ten-
dency to cleave ethers. Due to this fact, low temperatures
have to be maintained throughout the synthesis, which af-
fords an activation of the alkaline earth metal prior to use.
In addition, shielding of the Ca–C bonds by coordinating
co-ligands such as ethers or bulky groups at the periphery
is advantageous. This concept allowed the isolation and
8
General Procedure: In order to evaluate the scope of the
direct synthesis of arylcalcium halides, the metal-bound
halogen atom and the substitution pattern of the aryl group
were varied (see Table 1). The highest yields were ob-
tained for aryl iodides whereas the aryl chlorides and
fluorides show nearly no reactivity towards activated cal-
cium. The fluorine substitution of the aryl group also
spoils the isolation of the arylcalcium iodides 10 and 11.
Whereas 1-bromo-3,4,5-triflourobenzene was not at-
structure determinations of (diox) Ca[CH(SiMe ) ]
2
3 2 2
(
prepared via co-condensation of calcium vapor and or-
ganic substrate) and solvent-free Ca[C(SiMe ) ] (from
3
3 2
9
the metathesis reaction of KC(SiMe ) with CaI ).
3
3
2
SYNTHESIS 2007, No. 5, pp 0725–0730
x
x
.
x
x
.2
0
0
7
Advanced online publication: 25.01.2007
DOI: 10.1055/s-2007-965909; Art ID: Z23706SS
Georg Thieme Verlag Stuttgart · New York
©

7
26
M. Gärtner et al.
PAPER
Table 1 Arylcalcium Halides Prepared According to Equation 1a
Compound R1
R2
H
R3
H
X
I
Yield (%)
93b
Remarks
Schlenk equilibrium in Et O, solubility in THF at r.t.:
1
a
H
2
–
1
–1
0
.25 mol·L (133 g·L )
1
1
2
3
4
5
6
7
8
9
9
0
b
c
H
H
H
H
H
H
H
H
H
H
H
H
H
F
Br
Cl
I
71c
<5
60
95
81
75
89
91
56
52
–
–
H
H
No reaction
Me
H
See ref.12
I
H
I
No formation of ICa-C H -CaI
6
4
Cl
H
I
No Wurtz-type coupling
F
H
I
No formation of CaF2
OMe
H
I
Schlenk equilibrium in THFd
Schlenk equilibrium in THFd
Schlenk equilibrium in THF
Schlenk equilibrium in THF
No reaction
NMe2
H
I
H
OMe
Me
Me
H
I
a
Me
I
b
Me
Br
Br
I
1
1
1
1
1
F
–
No reaction
1a
1b
2
F
F
F
–
Fast decomposition, Ca(F/I) formation
2
F
F
F
Br
I
–
Fast decomposition, Ca(F/Br) formation
2
1-naphthyl
Ph
68
–
Solubility in THF at r.t.: 0.1 mol·L–1 (58 g·L–1)
Fast decomposition, ether cleavage
3
H
H
I
a
b
c
d
1
2
3
The numbering of the substituents R (para position), R (ortho position) and R (meta position) is also shown in this equation.
12
Crystalline PhCa(THF) I can be isolated in a yield of 63%; in 70% yield after 3 h at 0 °C with 0.7 equiv of iodobenzene.
Yield is 50% after 3 h at r.t. with 0.7 equiv of bromobenzene.
Schlenk equilibrium shows a temperature dependency.
4
12
tacked by calcium, bromopentafluorobenzene reacted chemical shifts of the other carbon atoms strongly depend
with calcium. However, the immediate formation of calci- on the substitution pattern of the aryl groups. The iodine
13
um dihalide Ca(F/Br) was observed. The isolation of atom leads to an enormous high-field shift of the C res-
2
pentafluorophenylcalcium units affords bulky shielding onance due to a heavy atom effect. Therefore, the chemi-
groups as was shown by Niemeyer and co-workers.13
cal shifts of the para-carbon atoms of 3 (R = I), 4
(
1
1
1
R = Cl) and 5 (R = F) relate to the d values of 94.4,
134.8 and 163.3 of the corresponding halogenoben-
The THF solutions of the arylcalcium halides 6 to 9
1
3
showed two resonance sets in the C NMR spectra, which
can be addressed to a Schlenk equilibrium. On cooling,
zenes.14
these solutions led to the precipitation of (THF) CaI . In Molecular Structure of (THF) Ca(Naph)I (12): The mo-
4
2
4
contrast to this observation, no Schlenk equilibrium was lecular structure of the THF complex of naphthylcalcium
operative for phenylcalcium iodide in THF. Therefore, the iodide (12) is shown in Figure 1. The disorder of the THF
isolation of crystalline arylcalcium iodide succeeded after ligand with O2 is not drawn. The Ca atom is in an octahe-
cooling the reaction mixtures. However, a solvent change dral environment with a C1–Ca–I angle of 177.7(2)°. The
to diethyl ether led to a dismutation reaction and diphenyl- Ca–C1 bond lengths of 255.2(6) and the Ca–I distance of
calcium decomposed immediately under these reaction 318.7(1) lie in characteristic regions. The endocyclic C2–
conditions via ether cleavage reactions.
NMR Spectroscopy: The 13C{1H} NMR parameters are
C1–C10 angle of 113.5(6)° is rather narrow. This fact can
be addressed to the repulsion forces between the anionic
lone pair and the C1–C2 as well as C1–C10 bonds. Due to
steric reasons, the coordination of the naphthyl group to
the calcium atom leads to different Ca–C1–C2/C10 angles
of 116.7(5)° and 129.8(5)°, respectively. The hindrance
between the C9-H moiety and the neighboring THF mol-
ecules leads to the enhancement of the appropriate Ca–
summarized in Table 2. The ipso-carbon atoms are low-
field shifted as one would expect for ionic compounds.
For phenyllithium and phenylmagnesium bromide d val-
1
4
ues of 186.6 and 164.3, respectively, were observed and
are comparable to those of the arylcalcium halides. The
Synthesis 2007, No. 5, 725–730 © Thieme Stuttgart · New York

PAPER
Table 2
Synthesis of Arylcalcium Halides
727
1
3
1
C{ H} NMR Parameters of the THF Complexes of Arylcalcium Halides
1
2
3
Compound
d (i-C)
190.3
190.0
185.3
188.9
187.8
186.6
178.0
173.6
152.0
182.5
d (o-C)
141.1
142.1
141.3
143.5
142.5
141.4
141.5
140.8
167.6
147.1
d (m-C)
125.3
128.9
126.2
133.9
125.0
111.6
111.6
111.8
103.9
124.2
d (p-C)
122.5
123.3
130.4
89.7
d (R , R , R )
1
1
2
3
4
5
6
7
8
9
2
a
–
b
–
21.8 (p-Me)12
–
129.0
161.3
157.3
147.4
127.5
131.0
–
–
54.4 (OMe)a
40.7 [NMe ]a
2
56.8 (OMe)
a
21.6 (p-Me), 27.7 (o-Me)11
1
122.2, 122.9, 123.1, 124.6, 128.8, 134.1, 136.9, 138.0, 146.2, 195.4b
a
The resonances of 4-MeOC H CaI and 4-Me NC H CaI, respectively, are summarized in this Table; the data for [4-MeOC H ] Ca and [4-
6
4
2
6
4
6
4 2
Me NC H ] Ca are given in the experimental section.
2
6
4 2
b
The data are listed without any assignments.
C1–C10 angle whereas on the opposite side the THF from the decomposition products; only the mesityl deriv-
ligands can move more freely which causes disordering.
atives have to be handled at lower temperatures.
Stability: Arylcalcium halides are highly reactive and tend
R3
R2
R3
R2
to cleave ethers. Due to the formation of cage compounds
1
5
such as [{(THF) CaPhI} ·(THF)CaO], a manifold
2
3
THF
R1
R1
Ca(THF)4–X
H
amount of heavy Grignard reagent is bound to the finally
resulting oxide. As a representative example, the decom-
position of 4-chlorophenylcalcium iodide (4) in THF was
investigated. The first reaction step is the a-deprotonation
of a THF molecule, followed by the formation of arene,
ethenolate and ethene according to Equation 2. All aryl-
calcium halides can be prepared at 0 °C and separated
–
H2C=CH2
– H C=CH–O–CaX
2
R3
R2
R3
R2
Equation 2
As a representative example, the decomposition reaction
of 4 in THF was followed by means of H NMR spectros-
1
copy in a sealed NMR tube. Selected spectra are displayed
in Figure 2 and show the formation of the decomposition
products, which consist mainly of chlorobenzene. The
first spectrum was recorded overnight directly after the
synthesis, whereas the other spectra were observed after
1
0, 30, and 50 days. For comparison reasons, the lowest
spectrum shows the resonances of pure chlorobenzene. It
is obvious that the major product of the decomposition is
C H Cl which stems from the ether cleavage reaction.
6
5
These reactions offer two perspectives in comparison to
the aryllithium and arylmagnesium chemistry. Due to the
low reactivity of the calcium metal, 1,4-diiodobenzene re-
acts only once with activated calcium to yield 3 even in
the presence of excess of calcium powder, whereas it is
16
able to react twice with magnesium shavings or lithium
17
reagents. On the other hand, the reactivity of the arylcal-
cium halides seems to be enhanced compared to the mag-
nesium derivatives. This fact can be utilized for a wide
field of applications such as metalation, metathesis and
addition reactions, which are under investigation in our
research group.
Figure 1 Molecular structure of (THF) Ca(Naph)I (12). The ellip-
4
soids represent a probability of 40%. The H atoms are neglected for
clarity. Symmetry-related atoms (x, –y + 0.5, z) are marked with an
apostrophe. The disordering of the THF ligands is not shown.
Synthesis 2007, No. 5, 725–730 © Thieme Stuttgart · New York

7
28
M. Gärtner et al.
PAPER
1H and 13C NMR spectra were recorded at r.t. on a Bruker AC 200
MHz spectrometer. All spectra were referenced to deuterated sol-
vent (THF-d ) as an internal standard.
8
All reactions were carried out by using standard Schlenk techniques
under argon. Prior to use, THF was dried (KOH) and distilled (Na/
benzophenone). Calcium (granules, 99%), distilled calcium (den-
dritic pieces, 99.5%), iodobenzene, bromobenzene, chlorobenzene,
1
,4-diiodobenzene, 4-iodoanisole, 4-chloro-1-iodobenzene, bro-
mopentafluorobenzene, iodopentafluorobenzene, 2-bromomesity-
lene, 4-iodotoluene, 5-bromo-1,2,3-trifluorobenzene, 1-iodonaph-
thalene, 2-iodomesitylene were used as purchased without further
purification. 4-Fluoro-1-iodobenzene and 4-iodo-N,N-dimethyl-
aniline were prepared from the corresponding Grignard com-
pounds, obtained from magnesium and 4-fluoro-1-bromobenzene
and 4-bromo-N,N-dimethylaniline, respectively, and then cleaved
with iodine. 1-Iodo-2,6-dimethoxybenzene was prepared from 1,3-
1
8
dimethoxybenzene, n-butyllithium and iodine. Acid-base titra-
tions to determine the metal content were conducted with HCl
–
1
(
0.1 mol·L ) using phenolphthalein as an indicator.
Activation of Calcium Metal
A Schlenk flask was equipped with calcium granules and glass balls
(5 mm diameter, ca. 2 g per 1 mmol Ca) and cooled to –60 °C. Then
a stream of gaseous ammonia was bubbled through the flask to form
liquid ammonia, which dissolves the calcium metal. After all calci-
um had dissolved, the ammonia was removed at r.t. in vacuo. Dur-
ing this process, the dark blue solution gave a gold-colored solid,
which lost further ammonia to yield activated calcium as a grey, py-
rophoric powder. This activated calcium was dried in vacuo for at
least 5 h prior to use for the direct synthesis.
Arylcalcium Halides; General Procedure
A Schlenk flask with activated calcium and glass balls was filled
with THF and cooled to 0 °C. Then, half of a stoichiometric equiv-
alent of the aryl halide was slowly added. Thereafter, the flask was
shaken at 0 °C for 1 h and for additional 6 h at r.t. The obtained,
brownish suspension was filtered through a Schlenk frit, covered
with diatomaceous earth and the residue was washed with THF
(
2 × 5 mL). The conversion was determined by acidic consumption
of a hydrolyzed aliquot of the filtrate. By cooling this solution to
90 °C, the precipitation of the appropriate arylcalcium halide re-
–
sulted within one day, which was isolated at this temperature and
dried in vacuo. The THF content was determined by titration of a
definite mass of each compound.
1
The particular size of the procedures as well as the H NMR data are
summarized in Table 3, yields are given in Table 2. NMR data of
the diarylcalcium derivatives which can be seen in the Schlenk
equilibrium are given below.
4
4
9
1
-Methoxyphenylcalcium Iodide (6)
-MeOC H CaI/(4-MeOC H ) Ca in a ratio of 77:23 (25 °C) and
1:9 (–50 °C); CaR2:
6
4
6
4 2
H NMR: d = 3.72 (s, 3 H, CH O), 6.68 (BB¢, J = 7.2 Hz, 2 H, H-3
3
+
H-5), 8,08 (AA¢, J = 7.2 Hz, 2 H, H-2 + H-6).
1
3
1
C{ H} NMR: d = 55.2 (1 C, CH O), 112.5 (2 C, C-3 + C-5), 143.9
3
(
2 C, C-2 + C-6), 159.6 (1 C, C-4), 173.9 (1 C, C-1).
4
4
6
1
-Dimethylaminophenylcalcium Iodide (7)
-Me NC H CaI/(4-Me NC H ) Ca in a ratio of 74:26 (25 °C) and
9:31 (–50 °C); CaR2:
2
6
4
2
6
4 2
3
H NMR: d = 2.78 [s, 6 H, (CH ) N], 6.64 (BB¢, J = 8.0 Hz, 2 H,
3
2
H-3 + H-5), 8.06 (AA¢, J = 7.6 Hz, 2 H, H-2 + H-6).
Figure 2 1H NMR spectroscopic follow-up of the decomposition
reaction of 4-chlorophenylcalcium iodide (4) in THF (d scale, r.t.);
from the top to the bottom: 12 h, 10 d, 30 d, 50 d after direct synthesis;
bottom spectrum shows C H Cl for comparison).
1
3
1
C{ H} NMR: d = 39.6 [1 C, (CH ) N], 112.2 (2 C, C-3 + C-5),
3
2
142.8 (2 C, C-2 + C-6), 149.5 (1 C, C-4), 169.5 (1 C, C-1).
6
5
Synthesis 2007, No. 5, 725–730 © Thieme Stuttgart · New York

PAPER
Synthesis of Arylcalcium Halides
729
1
Table 3 Experimental Details for the Direct Synthesis of Arylcalcium Halides Aryl-Ca(THF) X and THF Content n and H NMR Data
n
1
Compound
Amount of Ca
Amount of Aryl-X
5.73 g/28.1 mmol
1.08 g/6.86 mmol
2.60 g/11.9 mmol
4.69 g/14.2 mmol
5.95 g/25.0 mmol
4.51 g/20.3 mmol
3.15 g/13.5 mmol
3.36 g/13.6 mmol
4.94 g/18.7 mmol
5.64 g/22.2 mmol
n
H NMR (THF-d ), d, J (Hz)
8
1
1
2
3
4
5
6
7
8
2
a
2.25 g/56.1 mmol
0.55 g/13.7 mmol
0.66 g/16.5 mmol
1.14 g/28.4 mmol
2.00 g/49.9 mmol
1.63 g/40.7 mmol
1.08 g/26.9 mmol
1.09 g/27.2 mmol
1.50 g/37.4 mmol
1.78 g/44.4 mmol
4
6.62 (p-H), 6.75 (m-H), 7.60 (o-H)
6.7 (p-H), 6.81 (m-H), 7.80 (o-H)
2.06 (p-Me), 6.60 (m-H), 7.50 (o-H)
b
4
4
3
6
7.12 (m-H), 7.44 (o-H) ( J = 7.4)
3
4
6.78 (m-H), 7.61 (o-H) ( J = 7.6)
6.52 (m-H), 7.57 (o-H) ( J = 7.8)a
3
5
4
3.69 (OMe), 6.45 (m-H), 7.53 (o-H)
5
2.69 [NMe ], 6.41 (m-H), 7.53 (o-H)
2
2.5
4
3.69 (OMe), 6.39 (m-H), 6.91 (p-H)
1
–b
a 3
b 1
3
JH,F = 11.6 Hz, 4JH,F = 8.8 Hz.
3
3
4
3
4
H NMR: d = 7.04 (dd, J = 6.0 Hz, J = 8.0 Hz, 1 H, H-3), 7.12 (dt, J = 1.6 Hz, J = 6.8 Hz, 1 H, H-6 or H-7), 7.16 (dt, J = 1.6 Hz,
3
4
3
3
J = 6.8 Hz, 1 H, H-7 or H-6), 7.28 (d, J = 8.0 Hz, 1 H, H-4), 7.54 (dd, J = 1.6 Hz, J = 7.6 Hz, 1 H, H-5), 7.87 (d, J = 5.2 Hz, 1 H, H-8), 7.94
3
(
d, J = 8.0 Hz, 1 H, H-2).
Crystal Structure Determination of 12
(2) (a) Sapse, A.-M.; Schleyer, P. v. R. Lithium Chemistry: A
Theoretical and Experimental Overview; Wiley: New York,
1995. (b) Wakefield, B. Organolithium Methods; Academic
Press: London, 1988. (c) Schade, C.; Schleyer, P. v. R. Adv.
Organomet. Chem. 1987, 27, 169. (d) Setzer, W. N.;
Schleyer, P. v. R. Adv. Organomet. Chem. 1985, 24, 353.
(3) (a) Garst, J. F.; Soriaga, M. P. Coord. Chem. Rev. 2004, 248,
623. (b) Richey, H. G. Grignard Reagents: New
Developments; Wiley: Chichester, 2000. (c) Wakefield, B.
Organomagnesium Methods in Organic Synthesis;
Academic Press: London, 1995.
Cooling of a solution of 12 in THF to 0 °C led to the formation of
single crystals suitable for an X-ray structure determination. The in-
tensity data for the compounds were collected on a Nonius Kappa
CCD diffractometer using graphite-monochromated Mo-K radia-
tion. Data were corrected for Lorentz, polarization effects and for
a
1
9–21
absorption effects.
The structure was solved by direct methods
22
(
SHELXS) and refined by full-matrix least squares techniques
2
23
against Fo (SHELXL-97). The hydrogen atoms were included at
calculated positions with fixed thermal parameters. Without the dis-
ordered THF molecule all non-hydrogen atoms were refined aniso-
tropically.23 XP (Siemens Analytical X-ray Instruments, Inc.) was
used for structure representations.
(4) Klumberger, O.; Schmidbaur, H. Chem. unserer Zeit 1993,
27, 310.
(
5) (a) Hanusa, T. P. Coord. Chem. Rev. 2000, 210, 329.
(b) Westerhausen, M. Angew. Chem. Int. Ed. 2001, 40, 2975;
Angew. Chem. 2001, 113, 3063. (c) Alexander, J. S.;
Ruhlandt-Senge, K. Eur. J. Inorg. Chem. 2002, 2761.
(d) Westerhausen, M. Angew. Chem. Intl. Ed. 2007, Angew.
Chem. 2007, in press.
2
4
Crystal Data of 12
C H CaIO , M = 582.55
0
–
1
g
mol , colorless prism, size
.09 × 0.09 × 0.04 mm , orthorhombic, space group Pnma,
a = 23.5829(9), b = 13.4343(5), c = 8.7749(2) Å, V = 2780.06(16)
Å , T = –90 °C, Z = 4, r
cm , multiscan, transmin: 0.7456, transmax: 0.9600, F(000) = 1200,
6108 reflections in h(–30/30), k(–17/12), l(–11/9), measured in the
range 2.30° £ Q £ 27.47°, completeness Qmax = 99.5%, 3312 inde-
pendent reflections, Rint = 0.0635, 2284 reflections with F >4s(F ),
58 parameters, 0 restraints, R1obs = 0.0602, wR2obs = 0.1564,
2
6
39
4
3
3
–3
= 1.392 gcm , m (Mo-K ) = 13.63
calcd
a
–
1
(6) (a) Bähr, G.; Kalinowski, H.-O. In Houben-Weyl Methoden
der organischen Chemie, Vol. XIII/2a; Thieme Verlag:
Stuttgart, 1973, 529–551. (b) Gowenlock, B. G.; Lindsell,
W. E. J. Organomet. Chem. Libr. 3, Organomet. Chem. Rev.
1977, 1. (c) Lindsell, W. E. In Comprehensive
1
o
o
1
R1all = 0.0928, wR2all = 0.1777, GOOF = 1.042, largest difference
peak and hole: 1.288/–1.869 e Å .
Organometallic Chemistry - The Synthesis, Reactions and
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We thank the German Research Foundation (Deutsche Forschungs-
gemeinschaft, DFG) for generous financial support of this research
initiative. M. Gärtner gratefully acknowledges the PhD scholarship
of the Fonds der Chemischen Industrie.
(
(
g) Jutzi, P.; Burford, N. Chem. Rev. 1999, 99, 969.
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(24) CCDC-627216 contains the supplementary crystallographic
data for compound 12. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge CB2 1EZ, UK; fax: +44(1223)336
033; or deposit@ccdc.cam.ac.uk).
(
(
Synthesis 2007, No. 5, 725–730 © Thieme Stuttgart · New York