Synthesis and characterization of chiral mono N-heterocyclic carbene-substituted rhodium complexes and their catalytic properties in hydrosilylation reactions

Article abstract of DOI:10.1016/j.jorganchem.2011.04.001

Different chiral mono-substituted N-heterocyclic carbene complexes of rhodium were prepared, starting from [Rh(COD)Cl]₂ (COD = cyclooctadiene) by addition of free N-heterocyclic carbenes (NHC), or an in-situ deprotonation of the corresponding iminium salt. All new complexes were characterized by spectroscopy methods. In addition, the structures of chloro(η⁴-1,5-cyclooctadiene)(1,3-di-[(1R,2R,3R,5S)-2,6, 6-trimethylbicyclo[3.1.1]hept-3-yl] imidazolin-2-ylidene)rhodium(I) (5a), chloro(η⁴-1,5-cyclooctadiene)(1,3-di-[(1R,2S,5R) -2-isopropyl-5-menthylcyclohex-1-yl]imidazol-2-ylidene)rhodium(I) (5b) and chloro(η⁴-1,5-cyclooctadiene)(1,3-di-[(2R,4S,5S) -2-methyl-4-phenyl-1,3-dioxacyclohex-5-yl]imidazolin-2-ylidene)rhodium(I) (5i) were analyzed by DFT-calculations. The enantioselective hydrosilylation of acetophenone, ethylpyruvate and n-propylpyruvate with diphenylsilane and hydrolysis was carried out with chiral C₂-symmetrical mono-substituted N-heterocyclic carbene rhodium complexes giving for the first time an enantioselective excess of up to 74% ee in the case of the n-propylpyruvate.

Full text of DOI:10.1016/j.jorganchem.2011.04.001

Journal of Organometallic Chemistry 696 (2011) 3945e3954
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of chiral mono N-heterocyclic carbene-substituted
rhodium complexes and their catalytic properties in hydrosilylation reactions
,
,
,
Martin Steinbeck a, Guido D. Freya b, Wolfgang W. Schoeller b c, Wolfgang A. Herrmann a
*
a Department Chemie, Lehrstuhl für Anorganische Chemie, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, Germany
b Department of Chemistry, University of California, CA 92521-0403, Riverside, USA
c Fakultät für Chemie, Theoretische Chemie, Universität Bielefeld, Universitätsstraße 25, D-33615 Bielefeld, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Different chiral mono-substituted N-heterocyclic carbene complexes of rhodium were prepared, starting
from [Rh(COD)Cl]2 (COD ¼ cyclooctadiene) by addition of free N-heterocyclic carbenes (NHC), or an
in-situ deprotonation of the corresponding iminium salt. All new complexes were characterized by
Received 11 January 2011
Received in revised form
9 March 2011
spectroscopy methods. In addition, the structures of chloro(
2,6,6-trimethylbicyclo[3.1.1]hept-3-yl] imidazolin-2-ylidene)rhodium(I) (5a), chloro(
diene)(1,3-di-[(1R,2S,5R)-2-isopropyl-5-menthylcyclohex-1-yl]imidazol-2-ylidene)rhodium(I) (5b) and
chloro(
4-1,5-cyclooctadiene)(1,3-di-[(2R,4S,5S)-2-methyl-4-phenyl-1,3-dioxacyclohex-5-yl]imidazolin-
h
4-1,5-cyclooctadiene)(1,3-di-[(1R,2R,3R,5S)-
4-1,5-cycloocta-
Accepted 5 April 2011
h
Keywords:
Catalysis
Enantioselectivity
Hydrosilylation
N-Heterocyclic carbenes
Rhodium
h
2-ylidene)rhodium(I) (5i) were analyzed by DFT-calculations. The enantioselective hydrosilylation of
acetophenone, ethylpyruvate and n-propylpyruvate with diphenylsilane and hydrolysis was carried out
with chiral C2-symmetrical mono-substituted N-heterocyclic carbene rhodium complexes giving for the
first time an enantioselective excess of up to 74% ee in the case of the n-propylpyruvate.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
epoxides [5]. Conspicuously, most applications still use chiral
phosphine-based catalysts [6].
Chirality is one of the central themes of nature, and it therefore
follows that this must not be ignored whenever a synthetic
compound is introduced to an organism. The tragic case of the anti-
nausea drug Thalidomide is an often-used example for the need of
enantio- and dia-stereoisomeric purity in synthetic products [1].
This brings us back to the research laboratory where enantiose-
lective catalysis is a promising candidate for the preparation of
enantiomerically pure compounds. The influence of homogeneous
catalysis on industrial processes in recent years has attracted much
attention [2]. Homogeneous catalysts have the advantage of being
highly defined in their molecular structure in addition to the
possibility of broad structural variety [3]. Therefore the field of
stereoselective synthesisis of great interest. A particularlysuccessful
example of enantioselective catalysis in an industrial application is
Alternatively, metal complexes of imidazolin-2-ylidenes
(N-heterocyclic carbenes, or NHCs) have attracted considerable
attention as a rarely utilized class of homogeneous catalysts for this
purpose [7,8]. For example, complexes of ruthenium and palladium
where phosphine ligands have been replaced by NHCs show
excellent catalytic properties for metathesis and C,C-coupling
reactions [9]. In contrast to the corresponding phosphine
complexes, ligand dissociation was not observed with these cata-
lysts [10], and no excess of the ligand is necessary [11]. These
properties make such NHC-based catalysts suitable for chiral
modifications [12,13]. The first chiral N-heterocyclic carbenes as
ligands in metal complexes were published at the beginning of the
1980s by Lappert et al. [14]. In this case, electron rich olefins, first
described by Wanzlick [15], were reacted with metal precursors in-
situ to provide metal complexes containing saturated carbenes of
the imidazolidine type as ligands. These first studies were mainly of
structural interest and were not focused on their usage in catalysis.
Therefore a large body of work on chiral NHC complexes has been
published [16] since our group reported the first example of a chiral
NHC complex employed in homogeneous catalysis [17]. One
drawback of these carbene ligands is the possible free rotation
around the metalecarbene bond, thus effecting imperfect transfer
the synthesis of L-DOPA, a drug used for treatment of Parkinson’s
disease, catalyzed by a chiral bis(phosphine) rhodium complex [4],
or the titanium-catalyzed formation of enantiomerically pure
* Corresponding author. Tel.: þ49 89 289 13080; fax: þ49 89 289 13473.
E-mail addresses: guido.frey@ch.tum.de (G.D. Frey), lit@arthur.anorg.chemie.tu-
muenchen.de (W.A. Herrmann).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.04.001

3946
M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
of the ligand’s chiral information to the substrate [18]. In the
literature this problem is often combated with the use of chelating
NHC ligands [13d,19,20].
We now report the synthesis of novel, non-chelating chiral-
substituted imidazol-2-ylidene complexes of rhodium and their
application in a comparative study of enantioselective hydro-
silylation, in which chiral imidazol-2-ylidene complexes of
rhodium, previously reported by our group [17,21,22] and others
[13d,18,20,23] are employed.
H
O
H
+ ClO4
-
R
N
O
HClO4
R NH2
1
R
1
+ H2N
N
R
2
O
H
H
2a: R = (-)-Isopinocanphenyl
(1a)
NH2
2. Results and discussions
2b: R = (1R,2S,5R)-2-isopropyl-5-menthylcyclohexane
2.1. Ligand synthesis
2c: R-NH2 = 1c
2d: R-NH2 = 1d
The first chiralNHCs wereconstructed with derivatives of natural
NH2
L
-amino acids under formation of a saturated backbone in the five-
membered NHC ring; electron rich ligands situated approximately
with middle ranged -donor ability for such NHCs is [24,25]. Natural
amines such as -alanine, -leucine,
2e: R-NH2 = 1e
(1b)
s
Scheme 1. Synthesis of chiral imidazolium salts from the chiral amines. A detailed
drawing and preparation procedure for compounds 1ce1e is shown in Scheme 2.
L
L
L
-proline, (ꢀ)-cis-myrtanyl-
amine and (ꢀ)-trans-1,2-diaminocyclohexane were employed. For
the resulting NHC ligands the chiral center is, without exception,
located far from the metal center.
b-position of the ring will stabilize the desired conformation and
will prevent the rotation of the substituent at the nitrogen to
increase the steric hindrance at the metal center. An alternative
possibility to generate such sterically protected amines is the use of
substituted 1,3-dioxanes, which later could serve as building blocks
for chiral imidazolium salts.
In this regard, the (1S,2S)-2-amino-1-phenyl-1,3-propanediol
(3) (see Scheme 2) serves as an inexpensive starting material that is
produced commercially as a side product during the production of
chloramphenicol [(1R,2R)-2-dichloracetamino-1-(4-nitrophenyl)-
1,3-propanediol] the first synthetically produced broad-spectrum
antimycoticum [30]. The side product, (1S,2S)-2-amino-1-phenyl-
1,3-propanediol (3), is therefore very cheap and available in large
quantities. The amine has two chiral centers, they can react with an
In order to achieve high optical induction a sterically demanding
ligandnexttothemetalcentercombinedwithhighrigidityisrequired
[26]. One possibility is the use of cyclohexane-based substituents
bearing chiral groups, which are attached to the nitrogens of the
imidazoline ring. Such cyclohexane-type moieties themselves have
a high steric demand, especially if appropriate substituents gener-
ating chiral centers are additionally introduced which prevent the
system from ring-flipping. In this manner, the correct orientation of
the substituents toward the metal center can be enforced.
The most severe problem for such cyclohexyl-substituted car-
bene ligands is the possibility to have more than 4 chiral centers, all
of which must be delivered enantiomerically pure; thus convenient
organic synthesis routes can be elusive. Therefore we looked to the
chiral pool of natural products for our ligand precursors. The family
of terpenes seemed quite successful for this purpose, and especially
the commercial compound [1R,2R,3R,5S]-3-amino-2,6,6-trime-
thylbicyclo[3.1.1]heptane (1a), which contains a methyl group in
aldehyde or ketone resulting in
a six-membered ring. This
compound has many advantages, as was realized by Weinges in the
asymmetric Strecker-synthesis [31]. Unfortunately the common
method for the preparation of cyclic acetals cannot be used for
2-amino-1-phenyl-1,3-propanediols, as the functional groups can
undergo side reactions. For example the benzylic hydroxyl group
can lose water by an elimination reaction, or the amino group can
the
b-position, but its conformation is highly stabilized by the
methylene bridge and can be used as a starting material. Another
possibility is the family of isoprenoids such as (ꢀ)-menthol. The
react with the carbonyl group to an imine or as a b-amino alcohol to
corresponding (ꢀ)-menthylamine (1b) is
a very expensive
an oxazolidine derivative. Weinges published two procedures
where the reaction was carried out at room temperature by
suppression of the possible water elimination with simultaneous
protection of the amino group by a Lewis acid [32].
commercial chemical, which can however be produced on a labo-
ratory scale relatively cheaply starting from (ꢀ)-menthone [27].
Both amines can be converted via a known ring-closing
synthesis using perchloric acid to the corresponding imidazolium
salts 2a {1,3-di[1R,2R,3R,5S]-2,6,6-trimethylbicyclo[3.1.1]hept-3-yl]
imidazolium perchlorate} [28] and 2b {1,3-di[(1R,2R,5R)-2-iso-
propyl-5-methylcyclohex-1-yl]imidazolium perchlorate} [29] (see
for comparison Scheme 1). We found that the use of hypochloric
acid was unsuccessful for this reaction, and with increasing steric
R
+ Br-
O
O
OH
O
O
P2O5
OH
OH
+
+
R
H
NH2
NH3
- H2O, - HBr
demand of the b-substituent the yield decreased.
3
1c: R = Ph
The possibility for further modifications at the carbene ligand
was then investigated to modify and optimize the influence of the
carbene ligand in chiral hydrosilylation. The first point would be to
1d: R = 1-Naphthyl
R2
O
R1
increase the steric bulk of the substituent in
b-position to the
+ Br-
OH
O
nitrogen, for example by substitution with a phenyl group, which
should provide better protection of the metal center and should
restrict rotation around the nitrogen-a-carbon bond. Another point
is that the bulky substituent could be coordinated in cis-position to
the amino group, which should result in an axial position of the
substituent or amino group. Therefore the heterocycle will be
perpendicular to the cyclohexane plane, resulting in increased
protection of the metal center. Another bulky group at the other
AlCl3, CH3CN
- H2O
R1
R2
NH3
NH2
1e: R1, R2 = Ph
3
1f: R1 = t-Bu, R2 = Ph
1g: R1 = t-Bu, R2 = Me
Scheme 2. Synthesis of chiral 1,3-dioxanes (1ce1g).

M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
3947
Aldehydes that are liquids at room temperature and are not able
to undergo aldol-condensation can be used directly as the solvent
itself, if the (1S,2S)-2-amino-1-phenyl-1,3-propanediol (3), which
is protected as its hydrobromide salt, is sufficiently soluble in it.
With P2O5 as the condensation agent, the chiral amines 1c and 1d
could be synthesized according to Scheme 2.
Though the amino group is protected, there is a large amount of
imine produced during the reaction. In the case of 1c, the benzal-
dehyde is distilled off and a basic hydrolysis and workup of the P2O5
was carried out. The residue was treated with a steam strip, in
which most of the imine was hydrolyzed and the aldehyde could be
removed. The remaining imine (about 15%) can be separated
quantitatively via column chromatography, but its presence does
not negatively effect the ring closure in the next reaction step.
Because of the very high boiling point of the aldehyde in the case of
1d, it could not be distilled off and therefore an extraction workup
of the product with dilute acetic acid from the ether phase was
required. The following neutralization precipitates the imines as
solids which, after separation, can be hydrolyzed selectively with
acetic acid or formic acid in a THF/water mixture.
Ketones that can undergo an aldol condensation or are solids at
room temperature had to be treated in a different manner. In this
case, dry aluminum chloride was used as a condensation agent in
dry acetonitrile; after alkali hydrolysis of the aluminum chloride,
1eeg could be extracted with dilute acetic acid from the diethyl
ether phase (Scheme 2). In all cases the yields were relatively low
and rarely over 10%.
Fig. 1. Ball and Stick model of compound 5b in the solid state [29]. Hydrogen atoms are
omitted for clarity.
position
6 shows an ABX-spin system with large geminal
(JAB ¼ 11e12 Hz) and small vicinal (JAx, JBx ¼ 1e2 Hz) coupling
constants. The amino group in an equatorial position with two axial
protons would result in a nearly 180ꢁ dihedral angle and the
coupling constant should be approximately Jaa ¼ 9e13 Hz.
Since cyclic acetals serve as common protecting groups [34] in
basic media and are usually cleaved under acidic conditions, it was
only possible to form the corresponding imidazolium salts 2ce2e
analogously to 2a and 2b, by using HClO4 as the corresponding acid
required for ring closure reaction (Scheme 1). In 1997 Enders et al.
published a similar unsymmetrical triazolium compound with only
one 2,2-dimethyl-4-phenyl-1,3-dioxan-5-yl group [23]. The synthesis
of 2c and 2d [28,35] is complicated by solubility problems which can
beavoidedbyaddingwaterand/ormethylenechloridetothereaction.
If methylene chloride is added the product can be precipitated after-
ward byadditionofdiethylether tothereactionmixture. Thisreaction
method failed for the amines 1f and 1g.
The prepared 5-amino-4-phenyl-1,3-dioxanes 1ce1g are
viscous yellow oils which precipitate when left open to the atmo-
sphere, in the cases of the larger substituents phenyl and 1-naph-
thyl. During the acetal-formation, compounds 1c, 1d, 1f, 1g may
form two diastereomers. The absolute configuration at the second
carbon atom was determined by probing the nuclear Overhauser
effect and no further diastereomers were observed [32]. The acetal
formation is highly stereoselective because the most sterically
Starting from the free carbenes 4b [29] and 4c the corre-
sponding chiral mono(carbene) rhodium(I) complexes 5b [29] and
bulky substituent in
a-position is forced to be in equatorial position.
The syn-axial interactions in 1,3-dioxane are much stronger
compared to cyclohexane, due to the shorter CO-bonds (relative to
the CC-bonds in cyclohexane), which results in a stronger folding in
the acetal region and simultaneously less space between the axial
substituents. Subsequently it was ascertained that in the case of
polar substituents not only the steric van der Waals interactions are
present, but also interactions with the two oxygens, which show
a preference in the 5-position for an axial coordination [33]. For the
5-amino-4-phenyl-1,3-dioxanes (1ce1g) this effect is highly
favored, because intramolecular hydrogen bridges with the axially-
orientated amino group can also be formed. Additionally, the
conformation is fixed for these (4S,5S)-5-amino-4-phenyl-1,3-
dioxanes by the substituents in position 4 and 5. These results are
supported by the 1H NMR spectra, where the methylene group in
5c were prepared (Scheme 3). To a solution of the binuclear bis[
chloro(
4-1,5-cyclooctadiene)rhodium(I)] in THF was added a THF
solution of the free carbenes 4b and 4c. The two complexes
5b [chloro(
4-1,5-cyclooctadiene)(1,3-di[(1R,2S,5R)-2-isopropyl-5-
methylcyclohex-1-yl]imidazolin-2-ylidene)rhodium(I)] [29] and 5c
[chloro(
4-1,5-cyclooctadiene)-(1,3-di[(2R,4S,5S)-2,4-diphenyl-1,3-
dioxocyclohex-5-yl]imidazolin-2-ylidene)rhodium(I)] were obta-
ined after purification in good yields. Both complexes can be
recrystallized from a methylene chloride/diethyl ether solution.
The solid state structure of complex 5b [29] was examined
crystallographically and theoretically at PBE-D/TZVP level (see for
computational details the theoretical section). A plot of the solid
state structure of 5b is given in Fig. 1, the most important bonding
parameters are listed in Table 1.
m-
h
h
h
Table 1
Most important bonding parameters of the calculated versus experimental structure
of 5b. Selected bond lengths [Å] and bond angles [deg]. Cg1 and Cg2 define the
midpoints of the double bonds in the COD ligand, C2 is the carbene carbon.
NHC
Cl
[Rh(COD)Cl]2
THF, -78 °C
NHC
Rh
Bonding parameter
Experimental
value [29]
Theoretical
value
4b, 4c
5b, 5c
RheCl
RheCg1
RheCg2
RheC2
CleRheCg1
CleRheCg2
CleRheC2
Cg1eRheCg2
Cg1eRheC2
2.3832(5)
1.991
2.093
2.052(2)
174.3
90.13
89.89(4)
86.98
93.34
2.396
2.011
2.110
2.030
172.2
90.3
89.5
86.9
94.2
[Rh(COD)Cl]2
NHC
LiOtBu
NHC H X-
X- = ClO4
Rh
THF, -78 °C
Cl
5a, 5d, 5e
-
2a, 2d, 2e
Scheme 3. Synthesis of NHC complexes 5ae5e.

3948
M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
The computational data are in perfect agreement with the
influenced than the other by the sterically hindered coordination
with a geminal (JAB z 12 Hz) and a vicinal (JAx, JBx ¼ 0e3 Hz)
coupling constant. It is on this basis that the inversion of the six-
membered ring from a chair to a twist conformation can be
excluded for further informations see the Supporting Information.
The chiral monocarbene complexes 5a, 5d, and 5e were obtained
by in-situ deprotonation of the corresponding imidazolium salts
with lithium-tert-butanolate (Scheme 3). To a THF solution of the bis
results of the X-ray study. The experimental and quantum chemical
investigations reveal the same trend. The solid state structure of
complex 5b [29] shows a square planar coordination of the central
metal atom, which is not unusual for this type of complex [36]. As
in comparable known complexes, the distance of the rhodium to
the double bond of the COD-ring trans to the carbene ligand is
significantly longer (0.1 Å) as compared to the double bond trans to
the chloro-ligand, due to the trans-effect. The metalecarbene
distance (2.052(2) Å, experimental value in Table 1) is only slightly
longer than other carbene ligands with less steric hindrance, for
example as in the unsubstituted 1,3-dicyclohexylimidazolin-2-yli-
dene ligand (2.021 Å) [37], or other small substituted imidazolin-2-
ylidene ligands (1.998e2.037 Å) [11,38,39]. The same region of
bond distances around 2.049e2.067 Å are only known from
imidazolin-2-ylidene ligands substituted with bulky mesityl or
diisopropylphenyl groups in 1,3-position [40]. The six-membered
ring substituents are nearly perpendicular to the carbene frame-
work and are oriented 180ꢁ to one another. This structural assign-
ment is also in accord with the results from the quantum chemical
calculations and experimental NMR data from the original publi-
cation, where all carbon atoms are inequivalent both at low
temperature (233.15 K) and room temperature [29]. An orientation
[m-chloro(h
4-1,5-cyclooctadiene)rhodium(I)] complex was added
3 eq. lithium-tert-butanolate, and after 30 min 1.2 eq. of the imida-
zolium salt 2a [35], 2d, and 2e were added. The carbene complexes
5a, 5d, and 5e were obtained after 3 days of stirring and purification
in very high yields. Enders published three unsymmetrical rho-
dium(I) triazolinylidene complexes, where the triazolinylidene
ligand was substituted with one 2,2-dimethyl-4-phenyl-1,3-dioxan-
5-yl group [23]. The rhodium complexes were used in asymmetric
hydrosilylation reactions with high enantiomerical selectivities
(19e44% ee).
Complex 5d shows a similar 13C{1H} NMR spectrum compared
to 5c with a chemical shift of
d
¼ 182.7 ppm for the carbene carbon
and a rhodium(I) coupling constant of J ¼ 53 Hz. Remarkably all 32
aromatic carbon atoms were found as single signals, which shows
that all rotations are blocked e an unusually rigid structure for
a monodentate NHC ligand. In the 1H NMR spectrum the signals
appear as pairs, except in the aromatic and aliphatic region were an
overlap was found. For example the COD ligand, the acetal protons
of the alkyl group in b-position of the substituent to the rhodium
atom, which would give stronger and direct asymmetric shielding
at the metal center, was not obtained.
Incomplex5b it waspossible tolock all relevant rotationaxes and
to create a relatively rigid structure, which is an indispensable
requirement for asymmetric catalysis. The hindered free rotation
(
d
¼ 6.53 and 6.47 ppm), the protons of the
atoms (
¼ 6.05 and 5.94 ppm), and the in
groups (
¼ 5.66 and 5.56 ppm). The asymmetry of the split ABX-
signals of the -positioned methylene groups is not significantly
a
-positioned carbon
d
b-position methine
d
around the rhodiumecarbene carbon and nitrogen-a-carbon bond
b
was proven in the NMR spectrum. In fact, complex 5b has only
C1-symmetry; thus all carbon atoms of the imidazoline ring, the
methyl substituents and the olefinic ligand are magnetically ineq-
uivalent. The samewas also observed for the hydrogenatoms, except
for the regions where free rotation is possible in the molecule, such
as for the methyl groups. In the 13C{1H} NMR spectrum couples of
signals were found with chemical shifts between Dd ¼ 0.1e1.6 ppm.
For the 1H NMR spectrum pairs of signals were found for the back-
revealed in the chemical shifts (dA ¼ 4.75, and 4.63 and dB ¼ 4.48
and 4.35 ppm, respectively), with a large geminal (JAB z 12 Hz) and
a small vicinal coupling. It could not be further resolved due to
effects mentioned above.
Complex 5e, which has only four chiral centers, has the further
consequence that in the backbone of the dioxanyl ring an additional
phenyl substituent compared to complex 3c shows a similar basic
structure as the latter one in the 13C{1H} and 1H NMR spectra. The
bone of the imidazoline ring, at the
a
-carbon atoms, and the olefinic
carbene carbon atom has a chemical shift of
d
¼ 182.5 ppm and
protons of the COD ligand, in addition to overlapping multiplets in
the aliphatic region. The carbene carbon, which shows only one
signal in the 13C{1H} NMR spectrum, has a characteristically down-
a rhodium(I) coupling constant of J ¼ 52.9 Hz.
Complex 5a shows an extra ordinary solubility in all organic
solvents, except in n-pentane, analogous to chloro(h
4-1,5-cyclo-
field chemical shift of
d
¼ 180.2 ppm and a coupling constant to
octadiene)(1,3-dicyclohexylimidazolin-2-ylidene) rhodium(I). The
crystallization of this compound was therefore very difficult and
single crystals suitable for solid state X-ray analysis could not be
obtained. The substituents at the imidazoline ring of compound 5a
two relatively small and compact pinane groups, which have only
the rhodium atom of J ¼ 51.5 Hz, and appears in a region similar to
less sterically hindered rhodium complexes [24,41].
Similar results were found for complex 5c. In accordance with
the C1-symmetry of the complex nearly all carbon atoms are
magnetically inequivalent, and in the 13C{1H} NMR spectrum all
carbon atoms appear as pairs: the imidazoline backbone at
an anti-positioned methyl group in b-position, thus only a small
steric interaction with the COD ligand and a low rotation barrier is
d
¼ 122.5; 121.6 ppm, the acetal carbon atoms at
102.0 ppm, the
-carbon atoms at dPh ¼ 81.9; 80.1; dH ¼ 73.0;
72.4 ppm and the -carbon atoms at
¼ 58.2 and 55.9 ppm. An
exception is the trivalent carbene carbon atom at
d
¼ 102.2;
b
a
d
d
¼ 183.0 ppm
with a coupling constant of J ¼ 52.9 Hz to rhodium(I).
Because of the overlapping of the signals in the aromatic region,
it is difficult to predict if the phenyl rings can freely rotate. This
should not be possible because of the interactions with the COD
ligand. For the acetal phenyl rings and their positions it is not
known why free rotation should not be possible, consequently
a reduced dataset was obtained. In the 1H NMR spectrum the
chemical shifts for the COD and the protons of the dioxanyl ring
also appear as pairs. With exception of the downfield-shifted
protons at the
the imidazolium salt 2c. For the ABX-signal sets of the
groups an asymmetry was observed, i.e., one proton pair is more
a
-carbon atoms the signal sets are very similar to
b
-methyl
Fig. 2. Ball and Stick model of the most stable conformer of compound 5a at
a computational level of PBE-D/TZVP, hydrogens are omitted for clarity.

M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
3949
Table 3
O
H
HO
OH
H
1. H2SiPh2, THF
1 mol% Catalyst
Catalytic hydrosilylation of ethylpyruvate with diphenylsilane and hydrolysis.
Catalyst
Temperature
[ꢁC]
Reaction time
[h]
Conversion
[%]
Yield
[%]a
ee [%]
2. MeOH, p-TSA
5a
5b
5c
5c
5d
ꢀ20
ꢀ20
ꢀ20
25
48
48
48
2.5
48
9
62
92
95
62
4
27
55
35
33
4 (S)
(R)
(S)
29 (S)
72 (R)
60 (R)
67 (R)
Scheme 4. Catalytic hydrosilylation of acetophenone and hydrolysis resulting in
1-phenylethanol.
ꢀ20
a
Isolated yield after a distillation via a ball condenser.
expected [42]. Surprisingly we found in the 13C{1H} NMR spectrum
two complete signal sets, where all carbon atoms were magneti-
cally inequivalent, demonstrating that free rotation is not possible
in this complex anymore. The reason for this phenomenon could
by Lappert et al. if acetophenone is used, this enol ether reaction can
account for around 30% of the conversion, depending on the catalyst
used and temperature [44]. In principle this problem is under control
at low temperatures, where the disproportionation of the silane to
disilane plays a reduced role. The reactions presented in Tables 2e4
are not optimized and only the temperature was varied. The usual
conditions for this reaction were used to obtain datasets, which can
be compared with other previous published systems [17]. The
quantity of these experiments was chosen to be 3 and 4.5 mmol of
the carbonyl compound. The catalyst (5ae5e) (1 mol%) was added at
low temperatures as a THF solution, afterward an equimolar amount
of diphenylsilane was added. The reaction was quenched by addition
of a 2% p-toluenesulfonic acid/methanol solution, and the solvent
was removed under vacuum. The determination of the enantiomeric
access was carried out on a chiral GC-column.
In general it is proposed that the catalysts, with a general square
planar structure used before by Nile [45] and Lappert, stays intact
during the whole catalytic cycle and no de-coordination of the COD
ligand occurs. Corresponding to a postulated mechanism observed
in our group an oxidative addition of the silane at the square planar
rhodium(I) complex occurs to form an octahedral moiety, where
the COD ligand sterically blocks one side of the complex with high
efficiency [17]. A similar coordination mode was published earlier
by the group of Nishiyama for the enantionselective hydrosilylation
using a bis(oxazolinyl)pyridine rhodium(I) complex [46]. Therefore
the coordination of the substrate occurs mainly from the side
where the chiral information is located, which could explain why
an optical induction was observed.
not be definitively resolved here, whether the b-trans positioned
methyl group, the axial methyl groups at the quarternized carbon
atom, or the methylene bridge, which provides a rigid ring. The
divalent carbon atom has a chemical shift in the same region as the
complexes mentioned above (
d
¼ 182.2 ppm) and a rhodium
coupling constant of J ¼ 51.3 Hz. As expected, 1H NMR spectrum
shows no characteristic differences for the inequivalent protons.
The two
b
-trans positioned methyl groups can be selected as an
¼ 1.33 and 1.24 ppm.
example with chemical shifts of
d
Additionally, we performed DFT-calculations on complex 5a, to
obtain a better understanding of the conformation of the carbene
ligand in this complex. The most stable conformation obtained by
DFT calculations is depicted in Fig. 2, the methylene moieties of the
two substituents at the imidazoline ring are found to be pointing
away from the metal center. The other less stable conformations are
(3.2 and 4.4 kcal/mol higher in energy compared to the most stable
conformer depicted in Fig. 2) the conformer where the methylene
moieties are oriented at an angle of 180ꢁ with one another, and
where both methylene moieties are pointing to the metal center,
respectively.
All monocarbene complexes 5ae5e are air-stable in the solid
state as well as in solution. Given that high purity is necessary for
catalytic applications, in all cases purification was carried out using
a 100:1 mixture of methylene chloride/methanol as eluent on
a silica column.
To compare with other published results acetophenone was
used as the initial substrate, yielding optically active 1-phenyl-
ethanol. The obtained conversions and enantiomerical excesses are
summarized in Table 2.
2.2. Catalytic hydrosilylation
The chiral carbene complexes 5ae5e were tested for their efficacy
in the asymmetric hydrosilylation of ketones. In this reaction the
carbonyl compound is typically reacted with diphenylsilane in the
presence of a catalyst. In the literature copper complexes substituted
with phosphines or NHCs are also used as effective catalysts for this
reaction [43]. At the end of the reaction methanol is added in the
presence of catalytic amounts of p-toluenesulfonic acid to obtain the
chiral alcohol (see Scheme 4). Because of the high reactivity of
the silane, the reaction can be carried out under low temperatures
and in short time. In a side reaction the formation of an enol ether is
possible, which will be cleaved after hydrolysis back to the ketone
and reduce the yield of this reaction. According to a study carried out
In complex 5b, the
b-cis-positioned isopropyl groups in the
cyclohexyl ring are positioned 180ꢁ to each other, and the steric
interaction with the phenyl group of the substrate kinetically favors
the Si-side. A methyl group in the same position is not enough to
exert chiral induction, as in complex 5a shown, where only the
racemate was obtained. The fact that for complex 5b an increase
from ꢀ20 ꢁC to room temperature corresponds to a decrease of the
enantiomeric excess by half clearly shows the dominant role of the
steric interactions. The enantiomeric excess of 38% at ꢀ20 ꢁC and
20% at room temperature are the highest known values for rhodium
complexes with non-chelating C2-symmetrical ligands compared
Table 2
Catalytic hydrosilylation of acetophenone with diphenylsilane and hydrolysis
resulting in 1-phenylethanol.
Table 4
Catalytic hydrosilylation of n-propylpyruvate with diphenylsilane and hydrolysis.
Catalyst
Temperature
[ꢁC]
Reaction time
[h]
Conversion
[%]
Yield
[%]a
ee [%]
Catalyst
Temperature
[ꢁC]
Reaction time
[h]
Conversion
[%]
Yield
[%]a
ee [%]
5a
5b
5b
5c
5d
5e
ꢀ20
ꢀ20
25
ꢀ20
ꢀ20
ꢀ20
48
48
4.5
48
48
48
9
29
18
46
53
34
7
11
11
44
49
22
e
5b
5c
5c
5d
5d
5e
25
ꢀ20
25
4.5
48
1.5
48
4
7
98
81
51
88
49
6
66
49
33
48
38
9 (S)
38 (R)
20 (R)
14 (R)
8 (S)
5 (R)
74 (R)
60 (R)
64 (R)
57 (R)
58 (R)
ꢀ20
25
ꢀ20
48
a
a
Isolated yield after a distillation via a ball condenser.
Isolated yield after a distillation via a ball condenser.

3950
M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
O
reaction. A monodentate ligand system is presented that does not
HO
H
1. H2SiPh2, THF
1 mol% Catalyst
H
OH
necessitate a ligand excess in chiral catalysis, due to the strong
metalecarbon (carbene) bond, and which can compete with
chelating ligands in terms of ee values obtained. These results show
the high potential for this C2-symmetrical ligand system in the
broader field of asymmetric catalysis, particularly if non-chelating
ligands are necessary for steric or electronic (strong donors)
reasons, e.g. for the use as a ligand in a Grubbs-catalyst system.
O
O
O
R
R
R
+
2. MeOH, p-TSA
O
O
(R)
O
(S)
R = Et, n-Pr
Scheme 5. Catalytic hydrosilylation of pyruvic acid and hydrolysis resulting in pyruvic
acid esters.
with the literature [11,17,22]. For non C2-symmetrical rhodium
complexes with a non-chelating NHC ligand the same or slightly
higher ees [20e44%] have been obtained in the past [20d,21b,c].
The highest enantioselectivities are obtained for rhodium
complexes with chiral chelating NHC ligands, in these cases up to
99% ee was obtained [13d,20a–d,46].
4. Experimental section
General Considerations. All reactions were carried out under an
atmosphere of dry argon using standard Schlenk techniques or in
a MBraun glove box containing less than 1 ppm of oxygen and
water. Compounds 2a [35], 2b [29], 4b [29], 5b [29], and bis[
m-
Complexes 5ce5e show up to four times higher yields compared
to 5b but with much lower enantiomeric excess. The b-trans posi-
ethoxy-(
h
4-1,5-COD)rhodium] [48] were prepared according to the
literature. Experimental details for the known compounds 1c [32],
1f [32], 1g [32], can be found in the Supporting Information. 1H and
13C{1H} NMR spectra were recorded on a JEOL-JMX-GX 270 or
400 MHz spectrometer at room temperature and referenced to the
residual 1H and 13C signals of the solvents. NMR multiplicities are
abbreviated as follows: s ¼ singlet, d ¼ doublet, t ¼ triplet,
m ¼ multiplet, br. ¼ broad signal. Coupling constants J are given in
Hz. Elemental analyses were carried out by the Microanalytical
Laboratory at the TU München. Enantiomeric excess was deter-
mined with a Chrompack CP9000 gas chromatograph using a Lip-
odex A and Lipodex D column from MachereyeNagel and a FID
detector. Starting at 40 ꢁC for 20 min, ramp in 20 min from 40 to >
80 ꢁC, and hold at 80 ꢁC.
tioned phenyl groups increase the sterical bulk of the complexes so
much that a specific orientation of the relatively rigid acetophe-
none, and therefore a kinetic differentiation between the Re- and
Si-sides, is rarely possible. These catalysts might be much more
efficient for smaller and less rigid substrates, where the carbonyl
function is not in conjugation with an aromatic system. Given this,
pyruvic acid ester was used for the next experiments, which could
be converted after hydrosilylation and hydrolysis of the silylether to
the optically active 2-hydroxypropanoic acid esters (Scheme 5).
This reaction is known since the seventies with chiral phosphine
ligands, like BMPP and DIOP, first mentioned by Ojima [47]. The
different enantiomeric excess values obtained with the catalysts
5ae5d are summarized in Table 3 for the ethyl ester and in Table 4
for the n-propyl ester of pyruvic acid. The b-cis positioned methyl
4.1. (2R,4S,5S)-5-Amino-2-(1-naphthyl)-4-phenyl-1,3-
dioxacyclohexane (1d)
group in complex 5a shows nearly no enantiomeric excess for the
catalytic hydrosilylation of ethylpyruvate. For the more sterically
protected system 5ce5e higher yields were obtained than for the
less demanding complexes 5a and 5b.
The trend for the enantiomeric excess is opposite to the results
obtained for the hydrosilylation of acetophenone: Complex 5b still
shows a reasonable enantiomeric excess (29%), but it is now much
lower than the values obtained with complexes 5ce5e, which
increased dramatically. Although the optical induction tends to
decrease with the introduction of larger substituents at the back-
bone of the dioxanyl ring, enantiomeric excesses of around 70%
were obtained at ꢀ20 ꢁC, and even at room temperature a decrease
of only 10% was noted.
Analogous to the preparation procedure of 1c, (1S,2S)-2-amino-
1-phenyl-1,3-propandiol hydrobromide (c) (11.1 g, 44.7 mmol) was
dissolved in 75 mL freshly distilled 1-naphthaldehyde and under
stirring phosphorus(V) oxide (15 g,105.7 mmol) was added in small
portions. Because the aldehyde can not be removed under mild
conditions directly a steam distillation was carried out at 180 ꢁC.
The mother liquor was extracted with diethyl ether, and the ether
phase was treated with glacial acidic acid. The organic phase was
washed ten times with 30 mL water and the water phases were
combined and a mixture of KOH and K2CO3 was added until an
alkaline pH-value was obtained. The water phase was extracted
with CHCl3. At this stage the side product (imine) precipitates as
a white solid, which can be recycled to the corresponding amine by
the addition of acidic or formic acid in a THF/water solution. The
organic phases are combined and dried over MgSO4, the solvent
was removed in vacuum afterward. The yield was 5.3 g of a high
viscous yellow oil, which precipitates slowly under air. 1H NMR
The small temperature dependence for the optical induction
could be caused by steric and/or different electrostatic interaction
in the current complex. Another point is the influence of the
substitution pattern of the ligand on the absolute configuration of
the product: the catalysts with a b-cis positioned allyl group (5a,
5b) provide the opposite enantiomer compared to the
positioned phenyl groups of complexes 5ce5e.
b-trans
(400 MHz, CDCl3):
d
¼ 8.19e7.28 (12H, m), 6.31 (1H, s, CH(OR)2),
The hydrosilylation of n-propylpyruvate yields in principle
similar results (Table 4), with an unsurprising small increase of the
enantiomeric excess. For example, an enantiomeric excess of 74%
was obtained at a reaction temperature of ꢀ22 ꢁC with complex 5c.
Similar results were found by Ojima with the catalytic systems of
5.29 (1H, d, JHH ¼ 1.1 Hz, HCPh), 4.45 and 4.41 (2H, ABX-system,
JAB ¼ 11.4 Hz, JAx ¼ 2.2 Hz, JBx ¼ 1.5 Hz, CH2), 3.03 (1H, m,
HCNH2), 1.54 (2H, br., NH2); 13C{1H} NMR (100 MHz, CDCl3):
d
¼ 139.0, 133.8, 133.4, 130.6 (CCAr), 129.6, 128.6, 128.6, 128.5, 127.6,
126.3,125.6,125.6,125.5, 125.1,124.1,123.9 (CHAr),100.5 (OCO), 81.7
(CH2), 73.3 (CPh), 50.0 (CNH2).
bis[m-chloro(h
4-1,5-cyclooctadiene)rhodium(I)] and BMPP (60% ee)
and DIOP (76% ee) [47]. The yields obtained with 5c are higher than
the results obtained with a monophosphine ligand, and in the same
region as for the bidentate ligand DIOP.
4.2. (4S,5S)-5-Amino-2,2,4-triphenyl-1,3-dioxacyclohexane (1e)
Water-free aluminum chloride (25.5 g, 191.3 mmol) was dis-
solved under ice cooling in 100 mL of acetonitrile. The cold bath
was removed and in small portions (1S,2S)-2-amino-1-phenyl-1,3-
propandiol (c) (15.3 g, 91.6 mmol) was added. A solution of
benzophenone (19.6 g, 107.7 mmol) in 50 mL of dry acetonitrile was
3. Conclusions
These results show some of the highest enantiomeric excess
values for non-chelating ligands for the catalytic hydrosilylation

M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
3951
slowly added. The mixture was sealed and stirred for 11 days, added
to a mixture of crushed ice (500 g) and 50 g of K2CO3. The mixture
was stirred until the ice melted and filtered to remove the
aluminum salts. The solid was washed with acetonitrile and the
combined filtrates were extracted six times with 50 mL diethyl
ether, and the organic phase was dried with MgSO4. The solvent
was removed in vacuum and the residue was redissolved with
100 mL diethyl ether. The organic phase was extracted six times
with 40 mL of a 10% acidic acid solution, and to the water phase
were added KOH and K2CO3 until an alkaline pH-value was
obtained. The water phase was extracted four times with 50 mL of
CHCl3. To the organic phase was added MgSO4, the solid was
filtered off and the solvent was removed to obtain a high viscous
yellow oil in 3% yield (950 mg, 2.87 mmol), which precipitates
128.8, 128.7, 128.3, 126.6, 125.9, 125.6, 125.6, 125.0, 124.6, 123.3, 123.1
(CAr), 122.0 ((NCH)2), 99.6 (OCO), 78.3 (CPh), 69.5 (CH2), 57.5 (CNH2).
4.5. 1,3-Di-[(4S,5S)-2,2,4-triphenyl-1,3-dioxacyclohex-5-yl]
imidazolium perchlorate (2e)
Analogous to the preparation procedure of 2c were used 950 mg
(2.9 mmol) (4S,5S)-5-amino-2,2,4-triphenyl-1,3-dioxacyclohexane
(1e), paraformaldehyde (41 mg, 1.4 mmol), 3.3 N perchloric acid
(0.39 mL, 1.29 mmol) and a 40% aqueous glyoxal solution (0.25 mL,
2.2 mmol) were stirred in 5 mL of toluene. To the aqueous phase
were added 25 mL diethyl ether and 25 mL of a concentrated K2CO3
solution. The white precipitate was washed twice with diethyl
ether (15 mL) and dried in vacuum. The yield was 252 mg
(0.32 mmol, 26%) of a light brown solid. 1H NMR (270 MHz, CDCl3):
slowly under air. 1H NMR (400 MHz, CDCl3):
d
¼ 7.80e7.21 (15H, m),
5.09 (1H, d, JHH ¼ 1.8 Hz, HCPh), 4.31 and 4.12 (2H, ABX-system,
JAB ¼ 11.4 Hz, JAx ¼ 2.2 Hz, JBx ¼ 1.8 Hz, CH2), 2.79 (1H, m,
HCNH2), 1.66 (2H, br., NH2).
d
¼ 8.70 (1H, s, NCHN), 7.66e7.05 (32H, m, CHAr and NCH), 5.38 (2H,
m, HCPh), 4.56 (2H, m, HCNR2), 4.51 and 4.22 (4H, ABX-system,
JAB ¼ 12.9 Hz, JAx ¼ 2.2 Hz, JBx ¼ n/a, CH2).
4.6. 1,3-Di-[(2R,4S,5S)-2,4-diphenyl-1,3-dioxacyclohex-5-yl]
imidazolin-2-ylidene (4c)
4.3. 1,3-Di-[(2R,4S,5S)-2,4-diphenyl-1,3-dioxacyclohex-5-yl]
imidazolium perchlorate (2c)
In a mixture of 80 mL of liquid ammonia and 20 mL of THF 1.87 g
(2.9 mmol) 1,3-di-[(2R,4S,5S)-2,4-diphenyl-1,3-dioxacyclohex-5-yl]
imidazolium perchlorate (2c) and 285 mg (11.9 mmol) of NaH was
added. The solvent was removed in vacuo and the residue was
extracted with 20 mL n-hexane and 20 mL THF. The solvent was
removed in vacuo to obtain a pale yellow solid in 95% yield (1.50 g,
To
a solution of (1.96 g, 7.7 mmol) (2R,4S,5S)-5-Amino-
2,4-diphenyl-1,3-dioxacyclohexane 1c, paraformaldehyde (117 mg,
3.9 mmol), 3.3 N perchloric acid (1.2 mL, 4.0 mmol) and a 40%
aqueous glyoxal solution (1.2 mL, 10.5 mmol) was reacted in 10 mL
of toluene. After the addition of the glyoxal solution an additional
2 mL of water were added to obtain a stirrable solution. To the
aqueous phase were added 50 mL of diethyl ether and 25 mL of
a concentrated Na2CO3 solution. The white slime was washed twice
with diethyl ether (20 mL). The extract was dried over Na2SO4, and
afterward the solvent was removed and the residue was recrys-
tallized from CH2Cl2 with a methanol/diethyl ether solution. The
yield was 947 mg (1.47 mmol, 38%) of a white solid. 1H NMR
2.75 mmol).13C{1H} NMR (100 MHz, THF-d8):
d
¼ 212.3 (NCN),139.4,
138.8 (CCAr), 129.6, 129.0, 127.2, 127.0, 126.2, 124.9 (CHAr), 121.0
((NCH)2), 101.6 (OCO), 79.8 (CPh), 69.7 (CH2), 57.4 (CNR2).
4.7. Chloro (
trimethylbicyclo[3.1.1]hept-3-yl] imidazolin-2-ylidene) rhodium(I) (5a)
h
4-1,5-cyclooctadiene)(1,3-di-[(1R,2R,3R,5S)-2,6,6-
(400 MHz, CDCl3):
d
¼ 8.60 (1H, s, NCHN), 7.55e7.01 (22H, m, CHAr
A solution of 399 mg (0.81 mmol) bis[m-chloro(h
4-1,5-cyclo-
and NCH), 5.87 (2H, s, CH(OR)2), 5.47 (2H, d, JHH ¼ 2.2 Hz, HCPh),
4.80 (2H, m, HCNR2), 4.60 and 4.38 (4H, ABX-system, JAB ¼ 13.2 Hz,
JAx ¼ 2.6 Hz, JBx ¼ <1 Hz, CH2); 13C{1H} NMR (100 MHz, CDCl3):
octadiene)rhodium(I)]in20mLTHFwascooledtoꢀ78ꢁCand179mg
(2.24 mmol) lithium tert-butanolate was added and stirred for
30 min. Afterward 860 mg (1.95 mmol) 1,3-di-[(1R,2R,3R,5S)-2,6,6-
trimethylbicyclo[3.1.1]hept-3-yl]imidazolium perchlorate (2a) was
added. The mixture was stirred for 3 days at room temperature, the
solvent was removed in vacuo, and the precipitate was purified by
column chromatography (Rf z 0.8) and dried in vacuo. Yield: 773 mg
(1.32 mmol, 81%) of a light yellow powder.1H NMR (270 MHz, CDCl3):
d
¼ 136.7, 135.3 (CCAr), 136.6 (NCHN), 129.3, 128.8, 128.5, 128.4,
125.9, 124.4 (CHAr), 122.0 ((NCH)2), 101.7 (OCO), 78.3 (CPh), 69.4
(CH2), 57.3 (CNR2); anal. calcd. for C35H33N2O8Cl (645.1 g molꢀ1):
C 65.16; H 5.16; N 4.34; found: C 64.92; H 5.16; N 4.29.
4.4. 1,3-Di-[(2R,4S,5S)-2-(1-naphthyl)-4-phenyl-1,3-dioxacyclohex-
5-yl]imidazolium perchlorate (2d)
d
¼ 7.01 (1H, d, JHH ¼ 9.3 Hz, NCHCHN), 7.00 (1H, d, JHH ¼ 9.3 Hz,
NCHCHN), 5.86 (2H, m, HCNR2), 5.03 (2H, m, CH), 3.51 (1H, m, CH),
3.40 (1H, m, CH), 3.19, 2.68, 2.54e1.83, 1.58, 1.04 (22H, m, CH, CH2),
1.39 (3H, d, JHH ¼ 6.9 Hz, CH3), 1.30 (6H, s, C(CH3)2), 1.28 (6H, s,
C(CH3)2), 1.24 (3H, d, JHH ¼ 7.2 Hz, CH3); 13C{1H} NMR (68 MHz,
Analogous to the preparation procedure of 2c were used 1.36 g
(4.5 mmol) (2R,4S,5S)-5-amino-2-(1-naphthyl)-4-phenyl-1,3-dioxa-
cyclohexane (1d), paraformaldehyde (68 mg, 2.3 mmol), 3.3 N
perchloric acid (0.65 mL, 2.2 mmol) and a 40% aqueous glyoxal
solution (0.4 mL, 3.5 mmol) were stirred in 5 mL of toluene. After the
addition of the acid additional water and CH2Cl2 were added to
obtain a stirrable solution. For the workup of the gummy light brown
precipitate, which was formed after addition of 50 mL diethyl ether
and 25 mL of a concentrated K2CO3 solution, it was dissolved in
a mixture of CH3Cl, CH2Cl2, methanol and water. The solvent was
removed and a light colored precipitate was formed in the water
phase, which was washed with diethyl ether and dried afterward
under vacuum. The yield was 618 mg (0.83 mmol, 39%) of a light
CDCl3):
d
¼ 182.2 (d, J ¼ 51.3 Hz, NCN), 118.3, 118.1 ((NCH)2), 98.2 (d,
J ¼ 6.7 Hz, CH), 97.5 (d, J ¼ 7.3 Hz, CH), 67.8 (d, J ¼ 14.5 Hz, CH), 67.0 (d,
J ¼ 14.5 Hz, CH), 60.3, 60.0 (C-3), 48.5, 48.0 (C-2), 45.9, 43.8 (C-4), 41.8,
41.7 (C-6), 39.1, 39.0 (C-7), 38.3, 38.2 (C-1), 35.7, 34.9 (C-5), 33.0, 28.8,
28.7 (CH2), 28.2, 27.9, 23.5, 23.2, 21.1, 21.0 (CH3); anal. calcd. for
C31H48N2ClRh (587.08 g molꢀ1): C 63.42, H 8.24, N 4.77; found:
C 63.41, H 8.20, N 4.59.
4.8. Chloro (
1,3-dioxacyclohex-5-yl]imidazolin-2-ylidene) rhodium(I) (5c)
h
4-1,5-cyclooctadiene)(1,3-di-[(2R,4S,5S)-2,4-diphenyl-
brown solid. 1H NMR (400 MHz, CDCl3):
d
¼ 8.83 (1H, s, NCHN),
A solution of 457 mg (0.93 mmol) bis[m-chloro(h
4-1,5-cyclo-
7.93e7.02 (26H, m, CHAr and NCH), 6.44 (2H, s, CH(OR)2), 5.61 (2H, d,
JHH ¼ 1.1 Hz, HCPh), 4.91 (2H, m, HCNR2), 4.74 and 4.45 (4H, ABX-
system, JAB ¼ 12.8 Hz, JAx ¼ 1.8 Hz, JBx ¼ <1 Hz, CH2); 13C{1H} NMR
octadiene)rhodium(I)] in 20 mL THF was cooled to ꢀ78 ꢁC and
a solution of 1.02 g (1.87 mmol) 1,3-di-[(2R,4S,5S)-2,4-diphenyl-1,3-
dioxacyclohex-5-yl]imidazolin-2-ylidene (4c) in 10 mL of THF was
added. The solution was stirred for 45 min and at the beginning
(67 MHz, CDCl3):
d
¼ 136.6 (NCHN), 135.3, 133.6, 131.9, 130.3, 130.0,

3952
M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
a visible color change occurred. Afterward the solvent was removed
in vacuo. The precipitate was purified by column chromatography
(Rf z 0.15), and crystallized from a CH2Cl2/diethyl ether solution.
Yield: 555 mg (0.70 mmol, 38%) of light yellow rectangular crystals.
JAB ¼ 12.1 Hz, CH2), 4.49 and 4.12 (2H, ABX-system, JAB ¼ 12.2 Hz,
CH2), 2.52 (1H, m, CH), 2.34 (1H, m, CH), 2.17e1.55 (8H, m, CH2); 13
{1H} NMR (68 MHz, CDCl3):
¼ 182.5 (d, J ¼ 52.9 Hz, NCN), 143.8,
C
d
143.6, 139.1, 139.0, 137.8, 135.6 (CCAr), 129.2, 129.0, 129.0, 128.5,
128.3, 128.3, 128.3, 128.2, 128.1, 127.9, 127.8, 127.6, 126.8, 126.6,
126.1, 125.2, 124.9, 124.9 (CHAr), 122.5, 121.4 ((NCH)2), 102.1 (OCO),
98.4 (d, J ¼ 7.3 Hz, CH), 98.0 (d, J ¼ 6.7 Hz, CH), 75.0, 73.5 (CPh), 69.0
(d, J ¼ 14.0 Hz, CH), 67.5, 66.7 (CH2), 65.9 (d, J ¼ 14.5 Hz, CH), 58.0,
56.1 (CNH2), 34.4, 31.4, 30.0, 27.3 (CH2); anal. calcd. for
C55H52N2O4ClRh$0.66 CH2Cl2 (999.99 g molꢀ1): C 66.86, H 5.38,
N 2.80; found: C 66.94, H 5.80, N 2.63.
1H NMR (400 MHz, CDCl3):
d
¼ 7.74e7.18 (22H, m, CHAr and NCH),
5.97 (1H, s, CH(OR)2), 5.95 (1H, m, HCNR2), 5.86 (1H, s, CH(OR)2),
5.78 (1H, m, HCNR2), 5.55 (1H, d, JHH ¼ 2.6 Hz, HCPh), 5.39 (1H, d,
JHH ¼ 2.6 Hz, HCPh), 5.07 (1H, m, CH), 4.75 (1H, m, CH), 4.65 and
4.29 (2H, ABX-system, JAB ¼ 12.1 Hz, JAx ¼ 2.6 Hz, JBx ¼ 2.2 Hz, CH2),
4.43 and 4.28 (2H, ABX-system, JAB ¼ 12.4 Hz, JAx ¼ 2.6 Hz, JBx ¼ n/a,
CH2), 2.52 (1H, m, CH), 2.43 (1H, m, CH), 2.20e1.59 (8H, m, CH2); 13
C
{1H} NMR (100 MHz, CDCl3):
d
¼ 183.0 (d, J ¼ 52.9 Hz, NCN), 137.7,
137.6, 137.6, 135.3 (CCAr), 129.3, 129.0, 128.5, 128.5, 128.5, 128.3,
127.9, 126.8, 126.1, 126.0, 126.0, 126.0 (CHAr), 122.5, 121.6 ((NCH)2),
102.2, 102.0 (OCO), 98.6 (d, J ¼ 7.3 Hz, CH), 98.1 (d, J ¼ 6.7 Hz, CH),
81.9, 80.1 (CPh), 73.0, 72.4 (CH2), 69.3 (d, J ¼ 14.5 Hz, CH), 66.0 (d,
J ¼ 14.5 Hz, CH), 58.2, 55.9 (CNR2), 34.6, 31.5, 30.2, 27.4 (CH2); anal.
calcd. for C43H44N2O4ClRhꢂ0.33 CH2Cl2 (819.49 g molꢀ1): C 63.51, H
5.49, N 3.42; found: C 63.40, H 5.51, N 3.43.
5. Theoretical section
All calculations were performed with the Turbomole-6.0 [49]
set of program systems. Throughout density functional theory
was employed. The geometries of the molecules were optimized
with the PBE (Perdew, Burke, Ernzerhof) functional [50]. As a basis
set the triple-z-quality basis set of Ahlrichs et al. was used exclu-
sively [51]. Further corrections for the dispersion energies were
added, in order to account properly for the different van der Waals
interactions among the phenyl groups and with the chlorine at the
transition metal center. The dispersion corrections were performed
according to the approach of Grimme et al. [52] Overall this
computational level is denoted as PBE-D/TZVP. The vibrational
calculations were carried out with numerical derivatives. All energy
minima are derived without symmetry constraints and are char-
acterized according to their vibrational frequencies. The chosen
grid-size is m ¼ 4 and the scf accuracy is scfconv ¼ 7.
4.9. Chloro (
4-phenyl-1,3-dioxacyclohex-5-yl]imidazolin-2-ylidene) rhodium(I) (5d)
h
4-1,5-cyclooctadiene)(1,3-di-[(2R,4S,5S)-2-(1-naphthyl)-
A solution of 160 mg (0.32 mmol) bis[m-chloro(h
4-1,5-cyclo-
octadiene)rhodium(I)] in 12 mL of THF was cooled to ꢀ78 ꢁC and
83 mg (1.04 mmol) lithium-tert-butanolate was added and stirred
for 30 min. Afterward 550 mg (0.74 mmol) 1,3-di-[(2R,4S,5S)-2-(1-
naphthyl)-4-phenyl-1,3-dioxacyclohex-5-yl]imidazolium perchlo-
rate (2d) was added and a color change from orange to yellow
occurred. The mixture was stirred for 3 days at room temperature,
the solvent was removed in vacuo and the precipitate was purified
by column chromatography (Rf z 0.2) and dried in vacuo. Yield:
294 mg (0.33 mmol, 51%) of a light yellow powder. 1H NMR
Acknowledgment
G.D.F thanks Dr. Rian D. Dewhurst for his continued interest in
this work. This work was generously supported by the Stiftung
Stipendien-Fonds des Verbandes der Chemischen Industrie e.V.
(Kékulé fellowship for M.S.). G.D.F gratefully acknowledges the
financial support of the Alexander von Humboldt Foundation
(Feodor-Lynen postdoctoral fellowship).
(400 MHz, CDCl3):
d
¼ 8.12e7.22 (26H, m, CHAr and NCH), 6.53 (1H, s,
CH(OR)2), 6.47 (1H, s, CH(OR)2), 6.05 (1H, m, HCNR2), 5.94 (1H, m,
HCNR2), 5.66 (1H, m, HCPh), 5.56 (1H, m, HCPh), 5.22 (1H, m, CH),
4.93 (1H, m, CH), 4.75 and 4.48 (2H, ABX-system, JAB ¼ 12.4 Hz, CH2),
4.63 and 4.35 (2H, ABX-system, JAB ¼ 12.1 Hz, CH2), 2.63 (1H, m, CH),
2.54 (1H, m, CH), 2.37e1.75 (8H, m, CH2); 13C{1H} NMR (100 MHz,
CDCl3):
d
¼ 182.7 (d, J ¼ 53.0 Hz, NCN),137.5,137.4,135.2,133.5,133.4,
Appendix. Supplementary material
132.7,132.6,130.2,130.2,129.7,129.7,129.5,128.7,128.6,128.4,128.3,
128.1,127.9,127.7,126.5,126.3,126.2,125.8,125.8,125.6,125.5,125.0,
124.9,123.3,123.2,123.0,122.9 (CAr),122.3,121.5 ((NCH)2), 99.6, 99.2
(OCO), 98.4 (d, J ¼ 6.1 Hz, CH), 97.9 (d, J ¼ 6.1 Hz, CH), 81.7, 79.7 (CPh),
72.8, 72.2 (CH2), 69.2 (d, J ¼ 13.8 Hz, CH), 65.9 (d, J ¼ 14.6 Hz, CH), 58.1,
55.6 (CNH2), 34.5, 31.3, 30.1, 25.4 (CH2); anal. calcd. for
C51H48N2O4ClRh$0.15 CH2Cl2 (904.05 g molꢀ1): C 67.96, H 5.38, N
3.10; found: C 67.93, H 5.70, N 2.92.
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.04.001.
References
[1] H. Brunner, Rechts oder links in der Natur und Anderswo. Wiley-VCH,
Weinheim, Germany, 1999.
[2] B. Cornils, W.A. Herrmann, Applied Homogenous Catalysis with Organome-
tallic Compounds, second ed. VCH, Weinheim, 2002.
[3] W.A. Herrmann, B. Cornils, Angew. Chem. 109 (1997) 1074e1095;
Angew. Chem. Int. Ed. Engl. 36 (1997) 1048e1067.
4.10. Chloro (
1,3-dioxacyclohex-5-yl] imidazolin-2-ylidene) rhodium(I) (5e)
h
4-1,5-cyclooctadiene)(1,3-di-[(4S,5S)-2,2,4-triphenyl-
[4] Nobel Lecture: W.S. Knowles Angew. Chem. 114 (2002) 2096e2107;
Angew. Chem. Int. Ed. 41 (2002) 1998e2007.
[5] Nobel Lecture: K.B. Sharpless Angew. Chem. 114 (2002) 2126e2135;
Angew. Chem. Int. Ed. 41 (2002) 2024e2032.
[6] Nobel Lecture: R. Noyori Angew. Chem. 114 (2002) 2108e2123;
Angew. Chem. Int. Ed. 41 (2002) 2008e2022.
[7] (a) S.P. Nolan (Ed.), N-heterocyclic Carbenes in Synthesis, Wiley-VCH, Wein-
heim, Germany, 2006;
A solution of 68 mg (0.14 mmol) bis[m-chloro(h
4-1,5-cyclo-
octadiene)rhodium(I)] in 7 mL of THF was cooled to ꢀ78 ꢁC and
34 mg (0.43 mmol) lithium tert-butanolate was added and stirred
for 30 min. Afterward 243 mg (0.31 mmol) of 1,3-di-[(4S,5S)-2,2,4-
triphenyl-1,3-dioxacyclohex-5-yl]imidazolium perchlorate (2e)
was added and a color change from orange to yellow occurred. The
mixture was stirred for 3 days at room temperature, the solvent
was removed in vacuo, and the precipitate was purified by column
chromatography (Rf z 0.5) and dried in vacuo. Yield: 138 mg
(0.15 mmol, 48%) of a light yellow powder. 1H NMR (270 MHz,
(b) F. Glorius (Ed.), Topics in Organometallic Chemistry 21 (N-heterocyclic
Carbenes in Transition Metal Catalysis), Springer, Berlin/Heidelberg, Germany,
2007;
(c) P.L. Arnold, S. Pearson, Coord. Chem. Rev. 251 (2007) 596e609;
(d) D. Pugh, A.A. Danopoulos, Coord. Chem. Rev. 251 (2007) 610e641;
(e) V.P.W. Böhm, T. Weskamp, C.W.K. Gstöttmayr, W.A. Herrmann, Angew.
Chem. 112 (2000) 1672e1674;
Angew. Chem. Int. Ed. 39 (2000) 1602e1604;
(f) T. Weskamp, W.C. Schattenmann, M. Spiegler, W.A. Herrmann, Angew.
Chem. 110 (1998) 2631e2633;
CDCl3):
d
¼ 7.79e7.21 (32H, m, CHAr and NCH), 5.85 (1H, m, HCNR2),
5.68 (1H, m, HCNR2), 5.54 (1H, m, HCPh), 5.43 (1H, m, HCPh), 4.99
(1H, m, CH), 4.71 (1H, m, CH), 4.65 and 4.17 (2H, ABX-system,

M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
3953
Angew. Chem. Int. Ed. 37 (1998) 2490e2493;
(g) W.A. Herrmann, C.W. Kohlpaintner, Angew. Chem. 105 (1993) 1588e1609;
Angew. Chem. Int. Ed. Engl. 32 (1993) 1524e1544.
(f) C. Marshall, M.F. Ward, W.T.A. Harrison, Tetrahedron Lett. 45 (2004)
5703e5706;
(g) Y. Suzuki, K. Yamauchi, K. Muramatsu, M. Sato, Chem. Commun. (2004)
2770e2771;
(h) C.L. Winn, F. Guillen, J. Pytkowicz, S. Roland, P. Mangeney, A. Alexakis,
J. Organomet. Chem. 690 (2005) 5672e5695;
(i) S. Okamoto, S. Tominaga, N. Saino, K. Kase, K. Shimoda, J. Organomet.
Chem. 690 (2005) 6001e6007;
(j) Q. Xu, W.-L. Duan, Z.-Y. Lei, Z.-B. Zhu, M. Shi, Tetrahedron 61 (2005)
11225e11229;
(k) Y. Suzuki, K. Muramatsu, K. Yamauchi, Y. Morie, M. Sato, Tetrahedron 62
(2006) 302e310;
(l) R. Corberan, J. Ramirez, M. Poyatos, E. Peris, E. Fernandez, Tetrahedron
Asymmetry 17 (2006) 1759e1762;
(m) C. Williamson, J.M.D. Storey, W.T.A. Harrison, J. Chem. Crystallogr. 36
(2006) 277e282;
[8] (a) F.E. Hahn, Angew. Chem. 118 (2006) 1374e1378;
Angew. Chem. Int. Ed. 45 (2006) 1348e1352;
(b) R.E. Douthwaite, Coord. Chem. Rev. 251 (2007) 702e717;
(c) J.A. Mata, M. Poyatos, E. Peris, Coord. Chem. Rev. 251 (2007) 841e859;
(d) R.H. Crabtree, J. Organomet. Chem. 690 (2005) 5451e5457;
(e) C.M. Crudden, D.P. Allen, Coord. Chem. Rev. 248 (2004) 2247e2273;
(f) W.A. Herrmann, Angew. Chem. 114 (2002) 1342e1363;
Angew. Chem. Int. Ed. 41 (2002) 1290e1309;
(g) D. Bourissou, O. Guerret, F.P. Gabbaï, G. Bertrand, Chem. Rev. 100 (2000)
39e91;
(h) W.A. Herrmann, C. Köcher, Angew. Chem. 109 (1997) 2256e2282;
Angew. Chem. Int. Ed. Engl. 36 (1997) 2162e2187;
(i) S. Diez-González, N. Marion, S.P. Nolan, Chem. Rev. 109 (2009) 3612e3676;
(j) M. Poyatos, J.A. Mata, E. Peris, Chem. Rev. 109 (2009) 3677e3707.
[9] Metathesis: (a) T. Weskamp, F.J. Kohl, W. Hieringer, D. Gleich, W.A. Herrmann,
Angew. Chem. 111 (1999) 2573e2576;
(n) J. Ding, V. Desikan, X. Han, T.L. Xiao, R. Ding, W.S. Jenks, D.W. Armstrong,
Org. Lett. 7 (2005) 335e337;
(o) D. Enders, H. Gielen, G. Raabe, J. Runsink, J.H. Teles, Chem. Ber. 129 (1996)
1483e1488;
Angew. Chem. Int. Ed. 38 (1999) 2416e2419;
(b) L. Ackermann, A. Fürstner, T. Weskamp, F.J. Kohl, W.A. Herrmann, Tetra-
hedron Lett. 40 (1999) 4787e4790;
(c) T.J. Seiders, D.W. Ward, R.H. Grubbs, Org. Lett. 3 (2001) 3225e3228;
(d) T.W. Funk, J.M. Berlin, R.H. Grubbs, J. Am. Chem. Soc. 128 (2006)
1840e1846;
(p) D. Enders, H. Gielen, J. Organomet. Chem. 617e618 (2001) 70e80;
(q) L.H. Gade, S. Bellemin-Laponnaz, Top. Organomet. Chem. 21 (2007)
117e157;
(r) E. Bappert, G. Helmchen, Synlett (2004) 1789e1793;
(s) D. Kremzow, G. Seidel, C.W. Lehmann, A. Fürstner, Chem. Eur. J. 11 (2005)
1833e1853;
(t) F.E. Hahn, M. Pass, D. Le Van, T. Lügger, Angew. Chem. 115 (2003)
5402e5405;
Angew. Chem. Int. Ed. 42 (2003) 5243e5246;
(u) D. Baskakov, W.A. Herrmann, E. Herdtweck, S.D. Hoffmann, Organome-
tallics 26 (2007) 626e632;
(v) M.-X. Tan, Y. Zhang, J.Y. Ying, Adv. Synth. Catal. 351 (2009)
1390e1394.
(e) J.M. Berlin, S.D. Goldberg, R.H. Grubbs, Angew. Chem. 118 (2006)
7753e7757;
Angew. Chem. Int. Ed. 45 (2006) 7591e7595 For recent reviews see;
(f) V. Dragutan, I. Dragutan, Platinum Met. Rev. 49 (2005) 183e188;
(g) E. Despagnet-Ayoub, T. Ritter, Top. Organomet. Chem. 21 (2006) 193e218;
(h) E. Colacino, J. Martinez, F. Lamaty, Coord. Chem. Rev. 251 (2007) 726e764;
(i) C. Samoj1owicz, M. Bieniek, K. Grela, Chem. Rev. 109 (2009) 3708e3742;
(j) W.A.L. van Otterlo, C.B. de Koning, Chem. Rev. 109 (2009) 3743e3782;
(k) B. Alcaide, P. Almendros, A. Luna, Chem. Rev. 109 (2009) 3817e3858 C, C-
coupling;
[17] W.A. Herrmann, L.J. Gooßen, C. Köcher, G.R.J. Artus, Angew. Chem. 108 (1996)
2980e2982;
(l) W.A. Herrmann, M. Elison, J. Fischer, C. Köcher, G.R.J. Artus, Angew. Chem.
107 (1995) 2602e2605;
Angew. Chem. Int. Ed. Engl. 34 (1995) 2371e2374;
(m) G.D. Frey, J. Schütz, E. Herdtweck, W.A. Herrmann, Organometallics 24
(2005) 4416e4426;
(n) G.D. Frey, J. Schütz, E. Herdtweck, W.A. Herrmann, Abstr. Pap. Am. Chem.
Angew. Chem. Int. Ed. Engl. 35 (1996) 2805e2807.
[18] J.W. Faller, P.P. Fontaine, Organometallics 25 (2006) 5887e5893.
[19] (a) M.T. Powell, D.-R. Hou, M.C. Perry, X. Cui, K. Burgess, J. Am. Chem. Soc. 123
(2001) 8878e8879;
(b) M.C. Perry, X. Cui, M.T. Powell, D.-R. Hou, J.H. Reibenspies, K. Burgess,
J. Am. Chem. Soc. 125 (2003) 113e123;
Soc. Natl. Meet. 229 (2005) INOR 226;
(c) M. Poyatos, E. Mas-Marzá, J.A. Mata, M. Sanaú, E. Peris, Eur. J. Inorg. Chem.
(2003) 1215e1221;
(d) M. Poyatos, A. Maisse-François, S. Bellemin-Laponnaz, L.H. Gade, Organ-
ometallics 25 (2006) 2634e2641;
(o) Y. Sato, T. Yoshino, M. Mori, J. Organomet. Chem. 690 (2005) 5753e5758;
(p) A.E.W. Ledger, M.F. Mahon, M.K. Whittlesey, J.M.J. Williams, Dalton Trans.
(2009) 6941e6947;
(q) J. Berding, T.F. van Dijkman, M. Lutz, A.L. Spek, E. Bouwman, Dalton Trans.
(2009) 6948e6955;
(r) Ö Dogan, N. Gürbüz, Ĭ Özdemir, B. Çetinkaya, O. S¸ ahin, O. Büyükgüngör,
(e) T. Chen, X.-G. Liu, M. Shi, Tetrahedron 63 (2007) 4874e4880;
(f) Y. Kuang, X. Sun, H. Chen, P. Liu, R. Jiang, Catal. Commun. 10 (2009)
1493e1496;
ꢀ
Dalton Trans. (2009) 7087e7093 For recent reviews see;
(s) W.A. Herrmann, K. Öfele, D. von Preysing, E. Herdtweck, J. Organomet.
Chem. 684 (2003) 235e248;
(g) G. Dyson, J.-C. Frison, A.C. Whitwood, R.E. Douthwaite, Dalton Trans.
(2009) 7141e7151;
(h) A.R. Chianese, A. Mo, D. Datta, Organometallics 28 (2009) 465e472;
(i) U. Nagel, C. Diez, Eur. J. Inorg. Chem. (2009) 1248e1255;
(j) C. Diez, U. Nagel, Appl. Organometal. Chem. 24 (2010) 509e516.
[20] (a) C. Michon, R.J. Angelici, Chemtracts: Inorg. Chem. 17 (2004) 534e541 and
references therein;
(t) S. Diez-González, S.P. Nolan, Top. Organomet. Chem. 21 (2007) 47e82;
(u) T.N. Tekavec, J. Louie, Top. Organomet. Chem. 21 (2007) 159e192.
[10] (a) J. Huang, H.-J. Schanz, E.D. Stevens, S.P. Nolan, Organometallics 18 (1999)
2370e2375;
(b) M.-T. Lee, C.-H. Hu, Organometallics 23 (2004) 976e983.
[11] W.A. Herrmann, M. Elison, J. Fischer, C. Köcher, G.R.J. Artus, Chem. Eur. J. 2
(1996) 772e780.
(b) Y. Yuan, G. Raabe, C. Bolm, J. Organomet. Chem. 690 (2005) 5747e5752;
(c) V. César, S. Bellemin-Laponnaz, H. Wadepohl, L.H. Gade, Chem. Eur. J. 11
(2005) 2862e2873;
[12] W.A. Herrmann, L.J. Goossen, G.R.J. Artus, C. Köcher, Organometallics 16
(1997) 2472e2477.
[13] (a) T. Kano, K. Sasaki, K. Maruoka, Org. Lett. 7 (2005) 1347e1349;
(b) D. Martin, S. Kehrli, M. D’Augustin, H. Clavier, M. Mauduit, A. Alexakis,
J. Am. Chem. Soc. 128 (2006) 8416e8417;
(d) A. Ros, M. Alcarazo, J. Iglesias-Sigüenza, E. Diez, E. Alvarez, R. Fernandez,
J.M. Lassaletta, Organometallics 27 (2008) 4555e4564;
(e) N. Schneider, M. Kruck, S. Bellemin-Laponnaz, H. Wadepohl, L.H. Gade, Eur.
J. Inorg. Chem. (2009) 493e500;
(f) R. Malacea, R. Poli, E. Manoury, Coord. Chem. Rev. 254 (2010) 729e752.
[21] (a) W.A. Herrmann, L.J. Gooßen, M. Spiegler, Organometallics 17 (1998)
2162e2168;
(c) V. Cesar, S. Bellemin-Laponnaz, L.H. Gade, Chem. Soc. Rev. 33 (2004)
619e636;
(d) L.H. Gade, S. Bellemin-Laponnaz, Coord. Chem. Rev. 251 (2007) 718e725.
[14] (a) M.F. Lappert, in: A. Müller, E. Diemann (Eds.), Transition Metal Chemistry,
Verlag Chemie, Heidelberg, 1981, pp. 287e298;
(b) S.C. Zinner, M. Zhang-Presse, W.A. Herrmann, F.E. Kuehn, Z. Naturforsch. B.
64 (2009) 1607e1611;
(c) S.K.U. Riederer, P. Gigler, M.P. Högerl, E. Herdtweck, B. Bechlars,
W.A. Herrmann, F.E. Kühn, Organometallics 29 (2010) 5681e5692.
[22] W.A. Herrmann, D. Baskakov, E. Herdtweck, S.D. Hoffmann, T. Bunlaksananusorn,
F. Rampf, L. Rodefeld, Organometallics 25 (2006) 2449e2456.
[23] (a) D. Enders, H. Gielen, G. Raabe, J. Runsink, J.H. Teles, Chem. Ber./Recueil 130
(1997) 1253e1260;
(b) A.W. Coleman, P.B. Hitchcock, M.F. Lappert, R.K. Maskell, J.H. Müller,
J. Organomet. Chem. 250 (1983) C9eC14;
(c) A.W. Coleman, P.B. Hitchcock, M.F. Lappert, R.K. Maskell, J.H. Müller,
J. Organomet. Chem. 296 (1985) 173e196.
[15] (a) H.-W. Wanzlick, H.-J. Kleiner, Angew. Chem. 75 (1963) 1204;
(b) H.-W. Wanzlick, H.-J. Schönherr, Liebigs Ann. Chem. 731 (1970) 176e179;
(c) H.-W. Wanzlick, H.-J. Schönherr, Angew. Chem. 80 (1968) 154e155;
Angew. Chem. Int. Ed. Engl. 7 (1968) 141e142.
[16] (a) J.G. Hamilton, U. Frenzel, F.J. Kohl, T. Weskamp, J.J. Rooney,
W.A. Herrmann, O. Nuyken, J. Organomet. Chem. 606 (2000) 8e12;
(b) F. Guillen, C.L. Winn, A. Alexakis, Tetrahedron: Asymmetry 12 (2001)
2083e2086;
(b) D. Enders, H. Gielen, K. Breuer, Tetrahedron Asymmetry
8 (1997)
3571e3574;
(c) D. Enders, H. Gielen, J. Runsink, K. Breuer, S. Brode, K. Boehn, Eur. J. Inorg.
Chem. (1998) 913e919.
[24] (a) W.A. Herrmann, J. Schütz, G.D. Frey, E. Herdtweck, Organometallics 25
(2006) 2437e2448;
(b) G.D. Frey, J. Schütz, E. Herdtweck, W.A. Herrmann, Abstr. Pap. Am. Chem.
Soc. Natl. Meet. 231 (2006) INOR 279.
[25] (a) R.A. Kelly III, H. Clavier, S. Giudice, N.M. Scott, E.D. Stevens, J. Bordner,
I. Samardjiev, C.D. Hoff, L. Cavallo, S.P. Nolan, Organometallics 27 (2008)
202e210;
(c) A. Alexakis, C.L. Winn, F. Guillen, J. Pytkowicz, S. Roland, P. Mangeney, Adv.
Synth. Catal. 345 (2003) 345e348;
(d) M.C. Perry, K. Burgess, Tetrahedron: Asymmetry 14 (2003) 951e961;
(e) S. Tominaga, Y. Oi, T. Kato, D.K. An, S. Okamoto, Tetrahedron Lett. 45 (2004)
5585e5588;
(b) D.G. Gusev, Organometallics 28 (2009) 6458e6461.

3954
M. Steinbeck et al. / Journal of Organometallic Chemistry 696 (2011) 3945e3954
[26] Similar to an idea by: A. Fürstner, M. Alcarazo, H. Krause, C.W. Lehmann J. Am.
Chem. Soc. 129 (2007) 12676e12677.
[27] O. Wallach, Liebigs Ann. Chem. 276 (1893) 296e327.
[28] Y. Sato, N. Imakuni, M. Mori, Adv. Synth. Catal. 345 (2003) 488e491.
[29] (a) W.A. Herrmann, G.D. Frey, E. Herdtweck, M. Steinbeck, Adv. Synth. Catal.
349 (2007) 1677e1691;
Commun. (2007) 269e271;
(f) R.S. Simons, P. Custer, C.A. Tessier, W.J. Youngs, Organometallics 22 (2003)
1979e1982;
(g) S. Burling, M.F. Mahon, S.P. Reade, M.K. Whittlesey, Organometallics 25
(2006) 3761e3767;
(h) A. Bittermann, P. Härter, E. Herdtweck, S.D. Hoffmann, W.A. Herrmann,
J. Organomet. Chem. 693 (2008) 2079e2090.
(b) G.D. Frey, M. Steinbeck, E. Herdtweck, W.A. Herrmann, Abstr. Pap. Am.
Chem. Soc. Natl. Meet. 232 (2006) INOR 707.
[40] (a) P.A. Evans, E.W. Baum, A.N. Fazal, M. Pink, Chem. Commun. (2005) 63e65;
(b) S.I. Lee, S.Y. Park, J.H. Park, I.G. Jung, S.Y. Choi, Y.K. Chung, B.Y. Lee, J. Org.
Chem. 71 (2006) 91e96;
[30] (a) U. Schacht, in: G. Ehrhart, H. Ruschig (Eds.), Arzneimittel e Entwicklung,
Wirkung, Darstellung, vol. 2, Verlag Chemie, Weinheim, 1968, pp. 1717e1729;
(b) C.F. Boehringer, Söhne GmbH, Chem. Abstr. 50 (1956) 16857.
[31] K. Weinges, G. Graab, D. Nagel, B. Stemmle, Chem. Ber. 104 (1971)
3594e3606.
[32] K. Weinges, K.-P. Klotz, H. Droste, Chem. Ber. 113 (1980) 710e721.
[33] M.K. Kaloustian, N. Dennis, S. Mager, S.A. Evans, F. Alcudia, E.L. Eliel, J. Am.
Chem. Soc. 98 (1976) 956e965.
(c) M. Ahmed, C. Buch, L. Routaboul, R. Jackstell, H. Klein, A. Spannenberg,
M. Beller, Chem. Eur. J. 13 (2007) 1594e1601.
[41] (a) G.D. Frey, C.F. Rentzsch, D. von Preysing, T. Scherg, M. Muehlhofer,
E. Herdtweck, W.A. Herrmann, J. Organomet. Chem. 691 (2006) 5725e5738;
(b) G.D. Frey, S.C. Zinner, D. von Preysing, E. Herdtweck, W.A. Herrmann,
Abstr. Pap. Am. Chem. Soc. Natl. Meet. 233 (2007) INOR 956.
[42] (a) M.J. Doyle, M.F. Lappert, J. Chem. Soc. Chem. Commun. (1974) 679e680;
(b) A.R. Chianese, X.-W. Li, M.C. Janzen, J.W. Faller, R.H. Crabtree, Organo-
metallics 22 (2003) 1663e1667.
[34] T.W. Greene, Protective Groups in Organic Synthesis. John Wiley & Sons, New
York, 1981.
[35] (a) Y. Sato, Y. Hinata, R. Seki, Y. Oonishi, N. Saito, Org. Lett.
9 (2007)
5597e5599;
[43] (a) H. Kaur, F.K. Zinn, E.D. Stevens, S.P. Nolan, Organometallics 23 (2004)
1157e1160;
(b) J. Huang, L. Jafarpour, A.C. Hillier, E.D. Stevens, S.P. Nolan, Organometallics
20 (2001) 2878e2882.
(b) B.H. Lipshutz, B.A. Frieman, Angew. Chem. Int. Ed. 44 (2005) 6345e6348;
(c) S. Diez-Gonzalez, S.P. Nolan, Synlett (2007) 2158e2167;
(d) S. Diez-Gonzalez, S.P. Nolan, Acc. Chem. Res. 41 (2008) 349e358;
(e) S. Diez-Gonzalez, E.D. Stevens, N.M. Scott, J.L. Petersen, S.P. Nolan, Chem.
Eur. J. 14 (2008) 158e168;
[36] A solid state structure of complex 5b (CCDC 641593, CSD KIJDOX) was pre-
sented in a previous publication. See for comparison Ref. [29].
[37] W.A. Herrmann, C. Köcher, L.J. Gooßen, G.R.J. Artus, Chem. Eur. J. 2 (1996)
1627e1636.
[38] (a) D.M. Khramov, V.M. Lynch, C.W. Bielawski, Organometallics 26 (2007)
6042e6049;
(b) D.M. Khramov, E.L. Rosen, J.A.V. Er, P.D. Vu, V.M. Lynch, C.W. Bielawski,
Tetrahedron 64 (2008) 6853e6862.
[39] (a) W. Gil, T. Lis, A.M. Trzeciak, J.J. Ziolkowski, Inorg. Chim. Acta 359 (2006)
2835e2841;
(f) C. Deutsch, N. Krause, B.H. Lipshutz, Chem. Rev. 108 (2008) 2916e2927.
[44] M.F. Lappert, R.K. Maskell, J. Organomet. Chem. 264 (1984) 217e228.
[45] J.E. Hill, T.A. Nile, J. Organomet. Chem. 137 (1977) 293e300.
[46] H. Nishiyama, M. Kondo, T. Nakamura, K. Itoh, Organometallics 10 (1991)
500e508.
[47] I. Ojima, T. Kogure, M. Kumagai, J. Org. Chem. 42 (1977) 1671e1679.
[48] J. Chatt, L.M. Venanzi, J. Chem. Soc. (1957) 4735e4741.
[49] R. Ahlrichs, M. Bär, M. Häser, H. Horn, C. Kölmel, Chem. Phys. Lett. 162 (1989)
165e169.
(b) K.H. Park, S.Y. Kim, S.U. Son, Y.K. Chung, Eur. J. Org. Chem. (2003)
4341e4345;
(c) M.V. Jimenez, J.J. Perez-Torrente, M.I. Bartolome, V. Gierz, F.J. Lahoz,
L.A. Oro, Organometallics 27 (2008) 224e234;
(d) X.-Y. Yu, B.O. Patrick, B.R. James, Organometallics 25 (2006) 2359e2363;
(e) H. Sato, T. Fujikara, Y. Obora, M. Tokunaga, J. Kiyosu, Y. Tsuji, Chem.
[50] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865e3868.
[51] A. Schäfer, C. Huber, R. Ahlrichs, J. Chem. Phys. 100 (1994) 5829e5835.
[52] S. Grimme, J. Comput. Chem. 27 (2006) 1787e1799.