The first planar-chiral stable carbene and its metal complexes

Article abstract of DOI:10.1021/om010679v

Starting from (S)-S-ferrocenyl-S-4-tolyl sulfoxide the planar-chiral imidazolium salt (R_p)-1-[2-(trimethylsilyl)ferrocenylmethyl]-3-methylimidazolium iodide was synthesized utilizing the directed ortho-metalation strategy. Deprotonation thereof

Full text of DOI:10.1021/om010679v

Organometallics 2002, 21, 707-710
707
Th e F ir st P la n a r -Ch ir a l Sta ble Ca r ben e a n d Its Meta l
Com p lexes
Carsten Bolm,* Martin Kesselgruber, and Gerhard Raabe
Institut fu¨r Organische Chemie der RWTH Aachen, Prof.-Pirlet-Strasse 1,
D-52056 Aachen, Germany
Received J uly 30, 2001
Starting from (S)-S-ferrocenyl-S-4-tolyl sulfoxide the planar-chiral imidazolium salt (Rp)-
1-[2-(trimethylsilyl)ferrocenylmethyl]-3-methylimidazolium iodide was synthesized utilizing
the directed ortho-metalation strategy. Deprotonation thereof yielded the first planar-chiral
carbene, (Rp)-3-methyl-1-[2-(trimethylsilyl)ferrocenylmethyl]imidazolin-2-ylidene, which is
stable in tetrahydrofuran at room temperature for several hours. Conversion with sulfur
resulted in the formation of the corresponding thiourea derivative. Reaction with the metal
precursors [Rh(COD)Cl]2 and Cr(CO)6 gave air-stable complexes. For the latter product an
X-ray structural analysis was conducted.
The isolation and characterization of free and stable
carbenes has been an appealing target for a long time.1
Compound 1 has already been studied by Wanzlick as
early as in 1960.2 Very soon after O¨ fele and Wanzlick
prepared the first transition metal complexes thereof.3
At that time, however, direct evidence for the existence
of free carbenes in solution was unavailable.4 Finally,
in 1991 Arduengo reported on N-heterocyclic carbenes
(NHCs) such as 2, which were so stable that their
structure could be determined by X-ray diffraction.5-7
Soon after, the enormous potential of carbenes in
mimicking phosphine ligands in catalysis was recog-
nized. A recent prominent example illustrating this
concept is the new olefin metathesis catalyst 3, which
shows enhanced performance compared to Grubbs’s
original system, having tricyclohexylphosphine and a
NHC as ligands on ruthenium.8,9
Chiral carbenes were first synthesized by Lappert,
who introduced compounds with substituents at nitro-
gen having a stereogenic center.10 Later, those carbenes
have been applied in asymmetric catalysis,11 and re-
spectable results in terms of activity and enantioselec-
tivity have been achieved in the hydrosilylation of
ketones.12,13 Surprisingly, up to now no planar-chiral
carbenes have been described despite the fact that this
element of chirality is a vital part of many highly
successful ligands, especially those based on the fer-
rocene scaffold.14 As part of our ongoing studies on the
impact of planar chirality on asymmetric catalysis,15,16
we have prepared the first planar-chiral free NHC and
investigated its reactivity as well as capability to form
metal complexes.17
The synthetic methodology to generate planar-chiral
ferrocenes is well established.18 Most protocols rely on
the directed ortho-metalation strategy19 in combination
with a chiral anchoring group. For reasons of flexibility,
we chose Kagan’s sulfoxide route, which allows the
synthesis of a wide range of 1,2-substituted ferrocenes.20
* Corresponding author. Fax: ++49(241)8092391. E-mail:
Carsten.Bolm@oc.rwth-aachen.de.
(1) (a) Houben-Weyl, Methoden der Organischen Chemie, E19b;
Regitz, M., Ed.; Thieme: Stuttgart, 1989. (b) Metal Carbenes in Organic
Synthesis; Zaragoza, D. F., Ed.; Wiley-VCH: Weinheim, Germany,
1995.
(2) (a) Wanzlick, H.-W.; Schikora, E. Angew. Chem. 1960, 72, 494.
(b) Wanzlick, H.-W.; Kleiner, H. J . Angew. Chem. 1961, 73, 493. (c)
Wanzlick, H.-W.; Esser, F.; Kleiner, H. J . Chem. Ber. 1963, 96, 1208.
(3) Review: Herrmann, W. A.; Ko¨cher, C. Angew. Chem. 1997, 109,
2256; Angew. Chem., Int. Ed. Engl. 1997, 36, 2163.
(10) (a) Coleman, A. W.; Hitchcock, P. B.; Lappert, M. F.; Maskell,
R. K.; Mu¨ller, J . H. J . Organomet. Chem. 1983, 250, C9. (b) Coleman,
A. W.; Hitchcock, P. B.; Lappert, M. F.; Maskell, R. K.; Mu¨ller, J . H.
J . Organomet. Chem. 1985, 296, 173.
(11) For
a leading reference in this area see: Comprehensive
Asymmetric Catalysis; J acobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
Springer: Berlin, 1999.
(4) (a) O¨ fele, K. J . Organomet. Chem. 1968, 12, P42. (b) Wanzlick,
H.-W.; Scho¨nherr, H. J . Angew. Chem. 1968, 80, 154; Angew. Chem.,
Int. Ed. Engl. 1968, 7, 141.
(5) Arduengo, A. J ., III; Harlow, R. L.; Kline, M. J . Am. Chem. Soc.
1991, 113, 361.
(12) (a) Herrmann, W. A.; Goossen, L. J .; Ko¨cher, C.; Artus, G. R.
J . Angew. Chem. 1996, 108, 2980; Angew. Chem., Int. Ed. Engl. 1996,
35, 2805. For early attempts in the asymmetric Heck reaction see: (b)
Enders, D.; Gielen, H.; Raabe, G.; Runsink, J .; Teles, J . H. Chem. Ber.
1996, 129, 1483.
(6) (a) Arduengo, A. J ., III; Rasila Dias, H. V.; Harlow, R. L.; Kline,
M. J . Am. Chem. Soc. 1992, 114, 5530. (b) Arduengo, A. J ., III. Acc.
Chem. Res. 1999, 32, 913.
(7) For a comprehensive review about stable carbenes see: Bour-
issou, D.; Guerret, O.; Gabba¨ı, F. P.; Bertrand, G. Chem. Rev. 2000,
100, 39.
(8) (a) Weskamp, T.; Schattenmann, W., C.; Spiegler, M.; Herrmann,
W. A. Angew. Chem. 1999, 111, 2573; Angew. Chem., Int. Ed. 1999,
38, 2416. (b) Scholl, M.; Trnka, T. M.; Morgan, J . P.; Grubbs, R. H.
Tetrahedron Lett. 1999, 40, 2247. (c) Huang, J .; Schanz, H.-J .; Stevens,
E. D.; Nolan, S. P. Organometallics 1999, 18, 5375.
(9) (a) Louie, J .; Grubbs, R. H. Angew. Chem. 2001, 113, 253; Angew.
Chem., Int. Ed. 2001, 40, 247, and references therein. (b) Minireview:
J afarpour, L.; Nolan, S. P. J . Organomet. Chem. 2001, 617-618, 17.
(c) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18.
(13) (a) Enders, D.; Gielen, H.; Breuer, K. Tetrahedron: Asymmetry
1997, 8, 3571. (b) Enders, D.; Gielen, H. J . Organomet. Chem. 2001,
617-618, 70.
(14) Ferrocenes; Hayashi, T., Togni, A., Eds.; VCH: Weinheim,
Germany, 1995.
(15) Mun˜iz, K.; Bolm, C. Chem. Eur. J . 2000, 6, 2309.
(16) For recent examples, see: (a) Bolm, C.; Kesselgruber, M.;
Hermanns, N.; Hildebrand, J . P.; Raabe, G. Angew. Chem. 2001, 113,
1536; Angew. Chem., Int. Ed. 2001, 40, 1488. (b) Bolm, C.; Ku¨hn, T.
Synlett 2000, 899.
(17) Review on carbenes with ferrocenyl substituents: Bildstein, B.
J . Organomet. Chem. 2001, 617-618, 28.
(18) For a review on the generation of planar-chiral ferrocenes see:
Richards, C. J .; Locke, A. J . Tetrahedron: Asymmetry 1998, 9, 2377.
(19) Snieckus, V. Chem. Rev. 1990, 90, 879.
10.1021/om010679v CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/18/2002

708 Organometallics, Vol. 21, No. 4, 2002
Bolm et al.
Sch em e 2
F igu r e 1.
Sch em e 1
liquid ammonia.22 Since ferrocene 8 is soluble in THF,
reduced reaction times are possible.
The resulting planar-chiral free carbene 9 is reason-
ably stable in THF at room temperature. A proton NMR
spectrum of 9 was obtained after conducting the depro-
tonation of 8 in THF-d8. In comparison with the corre-
sponding signals of the imidazolium salt the character-
istic high-field shift for the two remaining imidazole
protons gives evidence for the presence of a free electron
pair at the carbene carbon.
To investigate the reactivity of 9, it was subjected to
various carbene-typical reactions (Scheme 2). Treatment
with sulfur yielded the expected thiourea derivative 10.
Reactions with [Rh(COD)Cl]2 or Cr(CO)6 led to the
formation of air-stable complexes 11 and 12, respec-
tively. In the former case the formation of diastereomers
was observed by NMR spectroscopy, which was at-
tributed to a hindered rotation around the Rh-carbene
carbon bond. Furthermore, the chloride at rhodium was
exchanged by iodide, which was present in the reaction
mixture.
Suitable single crystals for X-ray structure analysis
were obtained for chromium carbonyl complex 12. Its
molecular structure in the solid state is depicted in
Figure 2.
The structure of 12 in the solid state has been
determined by means of single-crystal analysis and is
shown in Figure 2. The absolute configuration of 12 has
been elucidated using Flack’s method.24 At 2.155(5) Å
the CrdC bond is quite long but still lies in the upper
part of the range usually found for chromium carbene
complexes. Spatial demands of the bulky ferrocenyl
ligand might at least in part account for this bond
length.
Starting with (S)-S-ferrocenyl-S-4-tolyl sulfoxide (4),
ortho-functionalization with lithium diisopropylamide
(LDA) and Me3SiCl afforded 5. Treatment of 5 with
t-BuLi replaced the sulfoxide moiety by lithium. The
resulting anion was then converted into hydroxymethyl
derivative 6 by addition of N,N-dimethyl formamide
followed by reduction of the intermediate aldehyde with
sodium borohydride (Scheme 1). Reaction of alcohol 6
with N,N′-carbonyl diimidazole (CDI)21 afforded imida-
zole 7 in excellent yield. As a precursor for stable NHC
9 imidazolium salt 8 was prepared by quaternization
of 7 with methyl iodide. Finally, following Arduengo’s
protocol, the deprotonation of 8 to give NHC 9 was
performed in THF at ambient temperature with 5 mol
% of KO-t-Bu and stoichiometric NaH. All reactions gave
good to excellent yields and could be conducted on a
multigram scale.
The conversion of 8 into 9 could readily be monitored
by observing the evolution of hydrogen. The reaction
was usually complete within 60 min. Full conversion
was indicated by the change of the initial suspension of
NaH in the reaction mixture into a clear solution with
precipitated NaI. This result is in contrast with the
syntheses of many other free carbenes, where the
insolubility of the imidazolium salt precursors requires
either longer deprotonation times6 or the addition of
In conclusion, we have synthesized the first planar-
chiral free carbene and demonstrated its capability to
form metal complexes. Currently, we are varying the
substitution pattern of the ferrocene backbone by utiliz-
ing other ortho-directing groups and exploring the
potential of planar-chiral carbenes as ligands in asym-
metric catalysis.25
(20) (a) Rebie`re, R.; Riant, O.; Ricard, L.; Kagan, H. B. Angew. Chem.
1993, 105, 644; Angew. Chem., Int. Ed. Engl. 1993, 32, 568. (b) Riant,
O.; Argouarch, G.; Guillaneux, D.; Samuel, O.; Kagan, H. B. J . Org.
Chem. 1998, 63, 3511.
(22) Herrmann, W. A.; Ko¨cher, C.; Goossen, L. J .; Artus, G. R. J .
Chem. Eur. J . 1996, 2, 1627.
(23) J ohnson. A FORTRAN Thermal-Ellipsoid Plot Program for
Crystal Structure Illustrations, Report ORNL-3794, 1970.
(24) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
(21) For this reaction, see: Njar, V. C. O. Synthesis 2000, 2019.

The First Planar-Chiral Stable Carbene
Organometallics, Vol. 21, No. 4, 2002 709
layers are dried (MgSO4), the solvent is evaporated, and the
crude product is purified by column chromatography (pentane/
diethyl ether, 3:2) to yield 1.00 g (79%) of the title compound
as an orange solid: mp 56-58 °C; [R]D -7° [c 1.2, CH2Cl2]; 1H
NMR (CDCl3) δ 0.27 (s, 9H), 1.70 (b, 1H), 4.08-4.15 (m, 6H),
4.25-4.38 (m, 4H); 13C NMR (CDCl3) δ 0.3, 60.8, 68.3, 70.0,
71.5, 71.7, 74.6, 92.3; MS (EI, 70 eV) m/z (%) 288 (100, M+),
255 (5), 223 (7), 195 (9), 138 (31); IR (KBr) ν˜ 3261, 3096, 2956,
2892, 1406, 1304, 1246. Anal. Calcd for C14H20FeOSi: C, 58.34;
H, 6.99. Found: C, 58.36; H, 6.93.
(Rp)-1-[2-(Tr im eth ylsilyl)fer r ocen ylm eth yl]im id a zole
(7). A solution of 723 mg (2.51 mmol) of 6 and 1.22 g (7.52
mmol) of 1,1′-carbonyl diimidazole is refluxed for 1 h in 35
mL of acetonitrile. After cooling to ambient temperature the
reaction mixture is separated between 100 mL of water and
100 mL of diethyl ether. The aqueous layer is extracted with
diethyl ether (2 × 50 mL), the combined organic layers are
washed with water (2 × 50 mL) and brine (50 mL) and dried
(MgSO4), the solvent is evaporated, and the crude product is
purified by column chromatography (dichloromethane/metha-
nol, 95:5) to yield 819 mg (97%) of the title compound as a red
oil: [R]D -16° [c 1.3, CH2Cl2]; 1H NMR (CDCl3) δ 0.17 (s,
9H), 3.92-3.98 (m, 6H), 4.21-4.30 (m, 2H), 4.75 (d, J ) 14.3
Hz, 1H), 4.83 (d, J ) 14.3 Hz, 1H), 6.76 (b, 1H), 6.95 (b, 1H),
7.33 (b, 1H); 13C NMR (CDCl3) δ 0.1, 46.6, 68.6, 70.4, 71.1,
72.4, 74.9, 86.1, 118.4, 128.7, 136.2; MS (EI, 70 eV) m/z (%)
338 (100, M+), 271 (38), 188 (9); IR (neat) ν˜ 3097, 2954, 2895,
1687, 1504, 1403; HRMS calcd for C17H22FeN2Si 338.0902;
found 338.0902.
F igu r e 2. Structure of 12 in the solid state (ORTEP23
plot). The ellipsoids represent a 50% probability level.
Selected bond lengths (Å) und angles (deg): Cr-C12 )
2.155(5), average Fe-C ) 2.024(7), average Cr-CO )
1.879(5), average CO ) 1.137(7), average C-C in Cp )
1.39(1), C13-C14 ) 1.349(6), C12-N1 ) 1.359(4), C12-
N2 ) 1.345(6), N1-C14 ) 1.390(6), N2-C13 ) 1.358(5);
N1-C12-N2 ) 103.7(4), N1-C12-Cr ) 127.7(3), N2-
C12-Cr ) 128.6(3), C12-Cr-C18 ) 177.5(2).
Exp er im en ta l Section
(Rp )-1-[2-(Tr im et h ylsilyl)fer r ocen ylm et h yl]-3-m et h -
ylim id a zoliu m Iod id e (8). A solution of 720 mg (2.13 mmol)
of 7 and 0.147 mL (2.35 mmol) of iodomethane in 2 mL of
2-propanol is heated to 40 °C for 24 h. The solvent is
evaporated and the crude product purified by column chro-
matography (dichloromethane/methanol, 95:5) to yield 881 mg
(86%) of the title compound as a red oil: [R]D -35° [c 1.0, CH2-
Cl2]; 1H NMR (CDCl3) δ 0.20 (s, 9H), 4.10 (s, 3H), 4.20 (b, 1H),
4.23 (s, 5H), 4.48 (b, 1H), 4.72 (b, 1H), 7.19 (b, 1H), 7.73 (b,
1H), 9.60 (b, 1H); 13C NMR (CDCl3) δ 0.1, 36.7, 49.8, 68.8, 71.5,
71.6, 73.2, 75.4, 81.6, 120.5, 123.3, 134.9; IR (neat) ν˜ 3097,
2954, 2895, 1687, 1504, 1403.
Gen er a l Com m en ts. All manipulations except workup and
purification were conducted under an inert atmosphere of Ar
using standard Schlenk techniques. Tetrahydrofuran was
distilled from sodium/benzophenone ketyl radical and aceto-
nitrile from calcium hydride prior to use. n-Butyllithium and
tert-butyllithium were purchased from Merck Schuchardt as
a 1.6 N solution in n-hexane, and (S)-(-)-4-toluenesulfinic acid
menthyl ester (Andersen’s reagent) and 1 N KO-t-Bu in THF
from Aldrich. [Rh(COD)Cl]2 was obtained from Strem Chemi-
cals. Compounds 4 and 5 were prepared according to literature
procedures.20 1H and 13C NMR spectra were recorded on a
Varian Gemini 300 spectrometer at 300 and 75 MHz, respec-
tively. Chemical shifts are given in ppm with internal refer-
encing to the solvent peaks. IR spectra were measured on a
Perkin-Elmer 1760 S spectrometer, MS spectra on a Varian
MAT 212, and HRMS spectra on a Finnigan MAT 95 mass
spectrometer, both with EI ionization. Elemental analyses
were carried out at the Institut fu¨r Organische Chemie der
RWTH Aachen on a Heraeus CHNO-Rapid apparatus. All
experiments were conducted at least twice to ensure reproduc-
ibility. The descriptors for planar chirality are based on the
rules introduced by Schlo¨gl.26
(Rp)-[2-(Tr im eth ylsilyl)fer r ocen yl]m eth a n ol (6). At -78
°C a solution of 1.71 g (4.32 mmol) of (S,Sp)-S-4-tolyl-S-[(2-
trimethylsilyl)ferrocene] (5) in 30 mL of THF is treated
dropwise with 2.96 mL (1.85 mmol) of tert-butyllithium. The
dark red solution is stirred at this temperature for 10 min,
then 0.99 mL (12.84 mmol) of N,N-dimethylformamide is
injected. After stirring at -78 °C for 1 h water (5 mL) and
methanol (10 mL) are added. At ambient temperature 567 mg
(14.98 mmol) of NaBH4 is added portionwise, resulting in
evolution of hydrogen and a color change to orange. After
stirring for 1 h, the reaction mixture is separated between 60
mL of water and 60 mL of diethyl ether. The aqueous layer is
extracted with diethyl ether (2 × 50 mL), the combined organic
(Rp )-3-Met h yl-1-[2-(t r im et h ylsilyl)fer r ocen ylm et h yl]-
im id a zolin -2-ylid en e (9). At ambient temperature 22 mg
(0.913 mmol) of sodium hydride and 46 µL of a 1 N solution of
KO-t-Bu in THF (0.046 mmol, 5 mol %) are added to a solution
of 400 mg (0.83 mmol) of 8 (azeotropically dried with benzene
prior to the reaction) in 20 mL of THF. Stirring is continued
for 60 min, during which time the precipitation of a white solid
(NaI) and evolution of hydrogen can be observed.
The carbene solution thus obtained is employed without any
further purification in the subsequent reactions: 1H NMR
(THF-d8) δ 0.20 (s, 9H), 3.72 (s, 3H), 4.05 (b, 1H), 4.18 (s, 5H),
4.25 (b, 1H), 4.46 (b, 1H), 5.12 (b, 2H), 6.72 (b, 1H), 6.93 (b,
1H).
(Rp )-3-Met h yl-1-[2-(t r im et h ylsilyl)fer r ocen ylm et h yl]-
im id a zolin e-2-th ion e (10). Carbene 9 (0.42 mmol) in THF
is added to a suspension of 13 mg (0.41 mmol) of sulfur in 5
mL of THF. After stirring at ambient temperature for 30 min
the reaction is stopped by the addition of 15 mL of water, and
resulting mixture is extracted with diethyl ether (3 × 25 mL).
The combined organic layers are dried (MgSO4), the solvent
is evaporated, and the product is purified by column chroma-
tography (pentane/diethyl ether, 1:1) to yield 104 mg (65%) of
the title compound as a yellow solid: mp 150-152 °C; [R]D
1
-11° [c 1.2, CH2Cl2]; H NMR (CDCl3) δ 0.22 (s, 9H), 3.61 (s,
(25) In preliminary studies we already demonstrated the capability
of complex 11 to serve as catalyst. Using 1-3 mol % of 11 in the
hydrosilylation of acetophenone and propiophenone with Ph2SiH2 as
reducing agent, ca. 50% conversion was achieved after 24 h at -10
°C. Hydrolysis of the resulting silyl ethers with catalytic amounts of
p-TosOH afforded the corresponding alcohols, alas as racemates.
(26) Schlo¨gl, K. Top. Stereochem. 1967, 1, 39.
3H), 4.13-4.23 (m, 6H), 4.39 (b, 2H), 4.82 (d, J ) 14.5 Hz,
1H), 4.96 (d, J ) 14.5 Hz, 1H), 6.30 (b, 1H), 6.57 (b, 1H); 13C
NMR (CDCl3) δ 0.3, 34.8, 47.9, 69.0, 71.0, 72.2, 73.5, 75.2, 84.7,
115.5, 117.0, 161.3; MS (EI, 70 eV) m/z (%) 384 (80, M+), 319
(71), 271 (100), 169 (41); IR (KBr) ν˜ 2952, 2891, 1565, 1403.

710 Organometallics, Vol. 21, No. 4, 2002
Bolm et al.
Anal. Calcd for C18H24FeN2SSi: C, 56.24; H, 6.29; N, 7.29.
Found: C, 56.12; H, 6.17; N, 7.16.
temperature in the range -9 < h < 9, -12 < k < 12, -13 <
l < 12 on a Bruker Smart APEX CCD diffractometer employ-
ing Mo KR radiation (λ ) 0.71073 Å). Diffraction data have
been corrected for absorption effects (µ ) 1.048 mm-1) employ-
ing the empirical SADABS method27 (max. and min. effective
transmission are 1.000 and 0.656, respectively). The structure
has been solved employing direct methods as implemented in
the Xtal3.7 package28 of crystallographic routines using
GENSIN29 to generate structure invariant relationships and
GENTAN30 for the general tangent phasing procedure. All non-
hydrogen atoms have been subjected to an anisotropic full-
matrix least-squares refinement on F including 289 param-
eters and 5006 observed reflections (F > 4σ(F)) terminating
at R (Rw) ) 0.041 (0.044, w ) (σ2(F) + 0.0004F2) -1, a goodness
of fit of S ) 1.038, and a final residual electron density of
-0.41/+0.30 e Å-3. Some hydrogen atoms could be located. The
remaining ones have been calculated in idealized positions.
Their isotropic displacement parameters have been fixed at
1.5U of the relevant heavy atom. All hydrogen parameters
have been fixed in the refinement process. A separate calcula-
tion resulted in an absolute structure parameter of Xabs ) 0.13-
(3) for the structure shown in Figure 2. The crystal structure
has been deposited at the Cambridge Crystallographic Data
Centre and allocated the deposition number CCDC 167668.
(Rp)-(η4-Cycloocta d ien e)iod o-3-m eth yl-{1-[2-(tr im eth -
ylsilyl)fer r ocen ylm eth yl]im id a zolin -2-ylid en e}r h od iu m -
(I) (11). Carbene 9 (0.21 mmol) in THF is added to a solution
of 51 mg (0.10 mmol) of [Rh(COD)Cl]2 in 5 mL of THF. After
stirring at ambient temperature for 24 h the reaction is
stopped by the addition of 15 mL of water, and the resulting
mixture is extracted with diethyl ether (3 × 25 mL). The
combined organic layers are dried (MgSO4), the solvent is
evaporated, and the product is purified by column chroma-
tography (pentane/diethyl ether 1:1) to yield 135 mg (93%) of
the title compound as a yellow foam (2:1 diastereomeric ratio).
Recrystallization (hexane/methyl tert-butyl ether, 2:1) yields
90 mg (62%) of the major diastereomer as yellow crystals.
Analytical data for the major diastereomer: mp 179 °C (dec);
[R]D -3° [c 0.6, CH2Cl2]; 1H NMR (CDCl3) δ 0.31 (s, 9H), 1.70-
2.13 (m, 4H), 2.19-2.50 (m, 4H), 3.40-3.60 (m, 2H), 3.96 (s,
3H), 4.11-4.36 (m, 7H), 4.61 (b, 1H), 5.08 (d, J ) 14.2 Hz,
1H), 5.18-5.38 (m, 2H), 5.92 (d, J ) 14.2 Hz, 1H), 6.58
(b, 1H), 6.78 (b, 1H); 13C NMR (CDCl3) δ 0.6, 29.2, 30.1, 31.9,
32.8, 50.2, 69.1, 69.2, 70.7 (d, J C-Rh ) 13.7 Hz), 71.2, 71.4 (d,
J C-Rh ) 13.7 Hz), 73.8, 74.5, 86.4, 96.2 (d, J C-Rh ) 14.7 Hz),
96.3 (d, J C-Rh ) 14.7 Hz), 119.9, 121.7, 181.4 (d, J C-Rh ) 48
Hz); MS (EI, 70 eV) m/z (%) 690 (46, M+), 582 (48), 382 (100);
IR (KBr) ν˜ 3094, 2952, 2872, 2824, 1453, 1401; HRMS calcd
for C26H36FeIN2RhSi 690.0090; found 690.0089.
Ack n ow led gm en t. We are grateful to the Fonds der
Chemischen Industrie and the Deutsche Forschungs-
gemeinschaft (DFG) within the Collaborative Research
Center (SFB) 380 “Asymmetric Synthesis by Chemical
and Biological Methods” for financial support. M.K.
acknowledges DFG for a predoctoral fellowship (Gra-
duiertenkolleg 440 “Methods in Asymmetric Synthesis”).
We thank Dr. Chunhua Hu for data collection and Dr.
Hartmut Maisch for HR-SIMS measurements.
(Rp)-P en ta ca r bon yl-{3-m eth yl-1-[2-(tr im eth ylsilyl)fer -
r ocen ylm eth yl]im id a zolin -2-ylid en e}ch r om iu m (0) (12).
Carbene 9 (0.23 mmol) in THF is added to a solution of 46 mg
(0.21 mmol) of Cr(CO)6 in 5 mL of THF. After stirring at
ambient temperature for 24 h the solvent is evaporated and
the product purified by column chromatography (pentane/
diethyl ether, 1:1) to yield 78 mg (68%) of the title compound
as a yellow syrup crystallizing slowly: mp 135 °C (dec); [R]D
-141° [c 1.6, CH2Cl2]; 1H NMR (CDCl3) δ 0.27 (s, 9H), 3.87 (s,
3H), 4.15-4.27 (m, 7H), 4.35-4.45 (m, 2H), 4.96 (d, J ) 14.2
Hz, 1H), 5.46 (d, J ) 14.2 Hz, 1H), 6.62 (b, 1H), 6.82 (b, 1H);
13C NMR (CDCl3) δ 0.5, 39.2, 51.7, 69.1, 69.2, 71.6, 72.6, 73.2,
75.1, 85.3, 120.7, 122.7, 189.8, 218.1, 221.5; MS (EI, 70 eV)
m/z (%) 544 (11, M+), 404 (100), 266 (21), 198 (28); IR (KBr) ν˜
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
spectra for all new compounds and crystallographic data
concerning the X-ray structure of 12. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM010679V
(cm-1) 2957, 2053, 1966, 1907, 1440; HRMS calcd for C23H24
CrFeN2O5Si 544.0209; found 544.0207.
-
(27) Sheldrick, G. M. SADABS. Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(28) Hall, S. R.; du Boulay, D. J .; Olthof-Hazekamp, R. Xtal3.7
System; University of Western Australia, 2000.
(29) Subramanian, V.; Hall, S. R. GENSIN; Hall, S. R., du Boulay,
D. J ., Olthof-Hazekamp, R., Eds.; Xtal3.7 System; University of
Western Australia, 2000.
X-r a y Cr ysta l Str u ctu r e An a lysis of 12. Single crystals
of 12 have been obtained from methyl tert-butyl ether at 298
K. The complex crystallizes in triclinic space group P1 (No. 1)
with a ) 7.2543(6) Å, b ) 9.1986(7) Å, c ) 10.3309(8) Å, R )
103.215(2)°, â ) 104.883(2)°, and γ ) 90.391(2)°, resulting in
a cell volume of V ) 647.03(9) Å3. At Z ) 1 and Mr ) 544.39
the calculated density amounts to dcal ) 1.397 g cm-3. A total
number of 9007 reflections have been collected at room
(30) Hall, S. R. GENTAN; Hall, S. R., du Boulay, D. J ., Olthof-
Hazekamp, R., Eds.; Xtal3.7 System; University of Western Australia,
2000.