Cobalt alkyl complexes of a new family of chiral 1,3-bis(2-pyridylimino) isoindolates and their application in asymmetric hydrosilylation

Article abstract of DOI:10.1021/ic3020749

The synthesis of a new family of chiral tridentate monoanionic NNN-pincer ligands based on the 1,3-bis(2-pyridylimino)isoindoline (BPI) framework is reported. Ligands with substituents of varying steric demand were prepared starting from achiral and low priced materials. A kinetic enzymatic resolution was used as a key step for the preparation of enantiomerically pure ligands. In this way, both enantiomers of a given ligand could be produced enantioselectively (>99.5% ee). The corresponding cobalt alkyl complexes were obtained using a pyridine alkyl cobalt precursor complex and were applied in asymmetric hydrosilylation of several prochiral alkylaryl ketones with high yields (up to 100%) and enantioselectivity (up to 91% ee) to give the chiral alcohols after hydrolysis.

Full text of DOI:10.1021/ic3020749

Article
pubs.acs.org/IC
Cobalt Alkyl Complexes of a New Family of Chiral 1,3-Bis(2-
pyridylimino)isoindolates and Their Application in Asymmetric
Hydrosilylation
Desiree C. Sauer, Hubert Wadepohl, and Lutz H. Gade*
́
́
Anorganisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: The synthesis of a new family of chiral
tridentate monoanionic NNN-pincer ligands based on the
1,3-bis(2-pyridylimino)isoindoline (BPI) framework is re-
ported. Ligands with substituents of varying steric demand
were prepared starting from achiral and low priced materials. A
kinetic enzymatic resolution was used as a key step for the
preparation of enantiomerically pure ligands. In this way, both
enantiomers of a given ligand could be produced enantiose-
lectively (>99.5% ee). The corresponding cobalt alkyl
complexes were obtained using a pyridine alkyl cobalt
precursor complex and were applied in asymmetric hydro-
silylation of several prochiral alkylaryl ketones with high yields (up to 100%) and enantioselectivity (up to 91% ee) to give the
chiral alcohols after hydrolysis.
in the catalytic hydrosilylation of various ketones. Although
displaying good catalytic activity at room temperature with
PhSiH3 as reducing agent they showed only low to modest
enantioselectivity.
INTRODUCTION
■
Asymmetric hydrosilylation is one possible method for the
preparation of chiral alcohols which are important building
blocks in the synthesis of pharmaceutical and agrochemical
products as well as advanced materials.1 Despite its disadvantages
compared to direct hydrogenations2 or transfer hydrogenations,3
such as the need for a silane as reducing agent and the
consecutive hydrolysis, hydrosilylation has emerged as a useful
tool in organic synthesis. This is due to the mild reaction
conditions, the development of environmentally friendly
catalysts and reducing agents as well as a manifold of substrates
which can be applied in this reaction.4
The asymmetric reduction of prochiral ketones with silanes
was first investigated using precious metal catalysts, such as
rhodium,5 iridium,6 and ruthenium7 complexes with different N-,
P-, or mixed N,P-ligand systems.8 During the last few years an
increasing demand for the substitution of those expensive and
rare metals has arisen, and the reaction has been tested using
more economical and environmentally benign first row transition
metals as catalysts.9 In this context, highly active and selective
titanium and copper complexes as well as organocatalysts have
been developed for the reduction of aldehydes and ketones.8,10
Moreover, an increasing interest in the use of iron has emerged
and different catalytic systems especially concerning Fe(OAc)2 in
combination with different ligands and typically tertiary silanes
such as (EtO)3SiH, (EtO)2MeSiH, or PMHS (polymethylhy-
drosiloxane) as reducing agents have been tested.11−14 Addi-
tionally, iron dialkyl complexes have been employed in
asymmetric hydrosilylation reactions by Chirik et al. in 2009.15
Complexes with pyridine bis(oxazoline) (pybox) and bis-
(oxazoline) (BOX) ligands have been prepared and evaluated
In comparison, Co catalyzed asymmetric hydrosilylations have
not been investigated in much detail so far. In 1991 Brunner and
Amberger reported the first stereoselective version with 56% ee
for the reduction of acetophenone as benchmark substrate using
0.5 mol % of a cobalt complex with a chiral monooxazolinylpyr-
idine ligand and Ph2SiH2 as reducing agent.16 Higher
enantioselectivity was achieved by Nishiyama et al. in 2010
when they investigated the reduction of various ketones with
cobalt acetate and a bis(oxazolinylphenyl)amine ligand. With 5
mol % of the catalyst and (EtO)2MeSiH as reagent they were able
to isolate the chiral alcohols with enantioselectivities of up to
96%.17 Finally, in 2011 Chan et al. reported the asymmetric
hydrosilylation using cobalt(II) acetate and dipyridylphosphine
ligands in air. PhSiH3 was employed as reducing agent and the
reaction took place at elevated temperatures using 10 mol %
catalyst. The chiral alcohols could be obtained in yields from 5 to
99% with up to 96% ee.18
During the past decade pincer ligands have been investigated
thoroughly, especially with regard to their catalytic abilities.19
1,3-Bis(2-pyridylimino)isoindolines (BPI) belong to the class of
tridentate monoanionic NNN-pincer ligands,20 and chiral BPI-
iron and -cobalt complexes with appropriately substituted ligand
backbones proved to be efficient catalysts for asymmetric
transformations.14 The stereodirecting ligands used in these
Received: September 25, 2012
Published: November 15, 2012
© 2012 American Chemical Society
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a
Scheme 1. Preparation of Chiral Pyridyl Amines R- and S-4a-e for the Synthesis of the New Family of Chiral BPI Ligands
a
For clarity only the (R) enantiomer is shown.
Scheme 2. The Protio-Ligands Were Prepared Using a Modular Synthesis via Condensation of the Chiral Amines with Various
a
Phthalonitriles
a
Only preparation of the (R,R) enantiomer is shown.
cases were available by a synthesis starting from chiral natural
products. Therefore only one enantiomer of the ligand was
readily accessible. A more general approach for the synthesis of
chiral BPI ligands in both enantiomeric forms involves their
preparation employing achiral starting materials which are
functionalized enantioselectively.
1), which can be easily prepared in its racemic form rac-1 on a
multigram scale using a well-established protocol21 and is also
commercially available. Conversion of the racemic alcohol into
its enantiomerically pure form was achieved by a kinetic
enzymatic resolution. Novozyme 435 was applied for this
synthesis which consists of Candida antarctica lipase B (CAL-B)
immobilized on polyacrylamide and shows a very high and
general specificity for the (R) enantiomer in the acylation of
chiral secondary alcohols.22 In this way, the (S) enantiomer S-1
could be recovered unreacted from the reaction mixture, while
RESULTS AND DISCUSSION
■
Ligand Synthesis via Kinetic Enzymatic Resolution. The
starting material of the ligand synthesis is the alcohol 1 (Scheme
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Figure 1. Molecular structures of the protio-ligands S,S-10 (left, only one of the two independent molecules is shown) and S,S-14 (right). Thermal
ellipsoids are drawn at the 50% probability level. Most hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°) for S,S-10:
N(1)−C(1)/C(4) = 1.397(3)/1.391(3), N(2)/N(4)−C(4)/C(1) = 1.291(3)/1.282(3), N(2)/N(4)−C(9)/C(20) = 1.398(3)/1.404(3), C(4)/
C(1)−N(2)/N(4)−C(9)/C(20) = 122.2(2)/123.5(2), N(2)/N(4)−C(4)/C(1)−N(1) = 139.5(2)/130.3(2), N(3)/N(5)−C(9)/C(20)−N(2)/
N(4) = 121.1(2)/ 121.4(2); the geometry of the second molecule is very similar. Selected bond lengths (Å) and angles (°) for S,S-14: N(1)−C(4) =
1.387(1), N(2)−C(4) = 1.288(1), N(2)−C(9) = 1.403(1), N(2)−C(4)−N(1) = 130.7(1), N(3)−C(9)−N(2) = 121.9(1), C(4)−N(2)−C(9) =
122.2(1).
Scheme 3. Synthesis of the Alkyl Precursor Complex According to Budzelaar et al.25
a
Scheme 4. General Method for the Synthesis of Cobalt Alkyl Complexes 15−22 by Ligand Displacement
a
Only the (R,R) enantiomer is shown.
the (R) enantiomer was isolated as acetate R-1-acet which can be
easily saponified to the corresponding alcohol R-1. The alcohols
were obtained as colorless crystalline solids in 48% yield and
>99.5% ee. Subsequently, they were transformed into various
primary ethers R- and S-2a-d after deprotonation with sodium
hydride and reaction with the corresponding alkyl halides. The
tert-butyl ether derivatives R- and S-2e could not be prepared in a
similar way but were obtained by reaction of tert-butyl bromide
with the alcohol using basic lead carbonate as catalyst.23 The final
step of the ligand synthesis involves conversion to a chiral
pyridine amine. A Buchwald-Hartwig amination only led to
racemization at the stereogenic center probably due to
deprotonation by the auxiliary base and reprotonation at the
acidic, quasi-benzylic position. An alternative route involved the
synthesis of the corresponding tetrazoles R- and S-3a-e (for a
crystallographic characterization see Supporting Information),
which were readily hydrogenated using Lindlar’s catalyst to the
enantiomerically pure amines R- and S-4a-e.
These amines were then reacted with different phthalonitriles
according to the well-established procedure20 to give the protio-
ligands 5−14 as yellow to red solids in good to moderate yields
(Scheme 2); these were characterized by NMR spectroscopy,
mass spectrometry as well as elemental analysis.
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Scheme 5. Synthesis of Achiral Cobalt Alkyl Model Complex 23
1
The structural details of the ligand molecules in the solid state
were established by X-ray diffraction of several derivatives.
Invariably, the molecules display approximate or crystallographic
C2 molecular symmetry in the solid state just as in solution, with
the rotational axis passing through the N(1)−H bond. Two
typical examples are presented in Figure 1.
In the H as well as 13C NMR spectra all of these metal
complexes display Curie behavior in solution over the studied
temperature range of 280−340 K, i.e., the expected linear
correlation between chemical shifts and inverse temperature (see
Supporting Information). No dynamic behavior in the 1H NMR
spectra was observed.24 Finally, measuring the paramagnetic
susceptibility of the complexes in solution by the Evans’
method26 gave values between μeff = 3.9−4.5 μB, which are
comparable to those of previously reported high-spin CoII BPI
complexes.27
As expected, the isoindoline backbones of the tridentate ligand
systems are almost planar while their pyridyl side groups are
rotated out of the plane to avoid steric congestion caused by the
substituents at the stereogenic center. The pyridine groups are
linked to the central isoindoline unit via imine bonds as is evident
from the alternating bond lengths between nitrogen and carbon
atoms (typically N(2)−C(4) = 1.30 Å, N(2)−C(9) = 1.40 Å).
The ligands show an effective preorganization with bifurcated
hydrogen bonding between the central isoindoline proton and
the pyridine nitrogen atoms. This preorganization is further
enhanced by the delocalized π-system which favors a coplanar
arrangement of the isoindoline and pyridyl rings. The sterically
crowded nature of the metal binding site is the reason why no
octahedral “homoleptic” metal complexes are formed with these
BPI ligands.24
Preparation of Chiral Cobalt Alkyl Complexes. The
chiral alkyl complexes of the general formula (BPI)Co-
(CH2SiMe3) could not be obtained by reacting a corresponding
chloro complex with an alkyllithium or Grignard reagent. Instead
they had to be prepared using a route developed by Budzelaar et
al. in 2010 by pyridine displacement from the metal dialkyl
precursor (py)2Co(CH2SiMe3)2.25
Synthesis and Structural Characterization of an Achiral
CoII Model Complex. It proved difficult to obtain single crystals
of the chiral CoII complexes 15−22 and thus to establish the
details of the molecular structures of the new alkyl complexes. To
this end, a model compound for the chiral complexes, a cobalt
complex bearing the achiral pentBPIH ligand, was prepared (see
Supporting Information). It was obtained via the same synthetic
route already used for the synthesis of the chiral derivatives and
showed the same catalytic activity in hydrosilylations (in this case
non-enantioselective). The compound was isolated as a dark
green solid, highly sensitive toward oxygen and moisture. The
different color in comparison to the chiral complexes may be
explained by a weak coordination of the oxygen atoms of the
ether moieties of the chiral ligands as was also observed in the
case of the copper complexes of these chiral ligands.28
At 295 K, 11 signals with chemical shifts in the range of −80 to
45 ppm with a line width of 40−600 Hz were detected in the 1H
NMR. The resonances for the methylene protons at the alkyl
ligand were not observed probably due to their close proximity to
the paramagnetic metal center. The methylene protons at the
cyclopentenyl rings are inequivalent as they point either toward
the alkyl ligand or the free coordination site thus leading to two
different signals. By measuring NMR spectra at variable
temperatures no coalescence of the signals and thus no dynamic
behavior was observable which is consistent with a Cs symmetric
and thus nonplanar complex on the time scale of the NMR
experiment in solution. In the 13C NMR spectrum 14 resonances
in the range of 0−850 ppm were assigned based on proton-
coupled as well as two-dimensional 1H−13C coupled spectra.
In this way a series of paramagnetic monoalkyl CoII complexes
were synthesized via protolytic ligand exchange. The most stable
cobalt complexes were observed in the case of the sterically less
crowded ligands S,S-5, S,S-6, S,S-12 and R,R-13. All alkyl
complexes were obtained as dark red extremely air and moisture
sensitive solids which are thermally labile and decompose at
room temperature over periods of several days.
For all complexes paramagnetic 1H as well as 13C NMR spectra
were recorded at variable temperatures. The complexes gave rise
to well resolved paramagnetic NMR spectra in THF-d8, due to
rapid electron relaxation of the high-spin d7 systems. At 295 K
1
1
Again, temperature-dependent measurements of all H and
line widths in the H NMR in the range of 30−160 Hz were
13C shifts showed a linear dependency from the inverse
temperature as expected for the paramagnetic complex. Para-
magnetic susceptibility in solution was measured using the Evans
method26 giving a value of μeff = 4.16 μB which is somewhat
higher than the spin only value (3.87 μB) and in accordance with
previously reported values for CoII (d7) high spin complexes.27
In order to establish the structural details for this type of BPI
cobalt complexes, which are the focus of this work, a single crystal
X-ray structure analysis of complex 23 was carried out. Its
observed in a signal range of −100 to 140 ppm. Signal patterns
were consistent with the presence of the expected C1 symmetric
species. The use of cryogenically cooled 13C NMR detection
probe and optimized repetition times allowed recording of
paramagnetic 13C NMR spectra within a few minutes. At 295 K
not all signals could be detected but those observed were
recorded within the range of 0−900 ppm. The carbon resonances
were partially assigned via the measurement of proton coupled
spectra.
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molecular structure is depicted in Figure 2 along with selected
bond lengths and angles.
the corresponding sec-phenethyl alcohol could be obtained in
high yield (90−100%) as well as enantioselectivity (up to 91%
ee).
Optimization of the reaction conditions showed that high
catalyst activities were observed using THF as solvent allowing
for catalyst loadings of 2.5 mol %. At reaction temperatures of 15
°C reaction times of less than 8 h were needed for complete
conversion. Other hydrosilanes such as the secondary
diphenylsilane proved to be less reactive in this transformation.
Analysis of the sec-phenethyl alcohol produced from the
reduction with the (S,S) enantiomer of the cobalt complex
established preference for formation of the (R) enantiomer of the
product (Table 2, entry 1). Likewise, performing the catalytic
hydrosilylation with the (R,R) cobalt compound yielded the (S)
enantiomer as major stereoisomer of the alcohol (Table 2, entry
3).
Variation of the substitution patterns in the stereodirecting
ligand showed no dependence of the activity and selectivity of the
reaction on the type of substitution of the ligand backbone.
Complexes S,S-15 and S,S-16 gave similar results with regard to
conversion and enantiomeric excess (Table 2, entry 1 and 2), as
was the case for complex R,R-21 with diphenyl substitution in the
backbone (Table 2, entry 8). This implies that the stereo-
discriminating step of the catalysis does not involve an approach
of the substrate from the backside of the ligand.
The substitution pattern at the ether moiety of the ligand
proved to be more significant. The chiral induction decreased for
complexes R,R-17 and S,S-18 and dramatically for complexes
S,S-19 and S,S-22 which displayed the lowest enantioselectivity
(Table 2, entries 3, 4, 5, 6). Complexes S,S-15, S,S-16, S,S-20 and
R,R-21 gave similar results yielding high enantiomeric excess
between 85 and 90% ee. Longer alkyl chains (ethyl and
methoxymethyl) and bulkier chiral moieties (tert-butyl)
appeared to hinder the stereoselective reaction and favor catalyst
decomposition pathways.
Other aromatic ketones were examined to establish the
substrate scope under the optimized reaction conditions.
Different arylmethylketones and naphthylketones were success-
fully employed as substrates for the catalytic reaction.
Introduction of electron rich or electron poor groups in 3,4- or
5-position had no effect on the productivity and selectivity of the
catalytic hydrosilylation. Unfortunately, substitution at the
aromatic ring in 2-position to the keto group led to a significant
decrease in activity and selectivity of the reaction, while 2,6-
disubstituted acetophenones underwent no catalytic reduction at
all.
Figure 2. Molecular structure of the cobalt BPI complex 23. Thermal
ellipsoids are drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°): Co−N(1)
= 1.949(5), Co−C(27) = 2.022(6), Co−N(3)/N(5) = 2.076(4)/
2.078(4), Si−C(27) = 1.845(6), N(1)−C(1)/C(4) = 1.355(7)/
1.376(7), N(2)/N(4)−C(4)/C(1) = 1.284(7)/1.304(7), N(2)/
N(4)−C(9)/C(18) = 1.391(7)/1.404(7), N(1)−Co−C(27) =
128.1(2), N(1)−Co-N(3)/N(5) = 88.2(2)/87.6(2), C(27)−Co−
N(3)/N(5) = 103.4(2)/111.4(2), N(3)−Co−N(5) = 138.6(2),
N(1)−C(4)/C(1)−N(2)/N(4) = 128.8(5)/128.8(5), C(4)/C(1)−
N(2)/N(4)−C(9)/C(18) = 124.5(5)/123.3(5).
The approximately Cs symmetric complex adopts a distorted
tetrahedral coordination geometry around the cobalt center.
While three coordination sites are occupied by the rigid BPI
ligand the alkyl ligand is bound as the fourth ligand. The N(1)−
Co−N(3) and N(1)−Co−N(5) angles (88.2(2)° and 87.6(2)°)
are mostly influenced by the connectivity of the ligand backbone,
whereas the N(3)−Co−N(5) angle (138.6(2)°), which deviates
significantly from the ideal value expected for either tetrahedral
or square planar coordination, reflects a distorted coordination
geometry.
The Co−N bond lengths (Co−N(1) shorter than Co−N(3)/
N(5)) are characteristic of monoanionic BPI ligands, and the
Co−C(27) bond length is in accordance with previously
published data for alkyl cobalt(II) species.29
Asymmetric Hydrosilylation of Ketones. The chiral
cobalt alkyl complexes were first tested as catalysts for the
enantioselective hydrosilylation of acetophenone as reference
substrate, and diethoxymethylsilane as reducing agent according
to the simple reduction protocol previously reported for iron
catalysts14 (Scheme 6). As frequently observed in hydrosilylation
catalysis studies of ketones in our group an excess of the silane
was required for high turnovers while no other additive was
necessary. After basic hydrolysis and column chromatography
CONCLUSIONS
■
A new family of chiral C2 symmetric BPI ligands has been
prepared, and the corresponding tetracoordinated cobalt alkyl
complexes were synthesized establishing a reliable and
convenient synthetic route. These complexes proved to be
efficient and stereoselective catalysts for the asymmetric
hydrosilylation of a variety of arylalkyl ketones with a tertiary
silane. Whereas backbone substitution in the ligand had no
significant effect on the catalytic performance, substitution at the
chiral center in the “wingtips” of the pincers seemed to influence
catalyst stability and performance. Further investigations aimed
at elucidation of the reaction mechanism are currently under way.
Scheme 6. Catalytic Hydrosilylation of Aromatic Ketones
EXPERIMENTAL SECTION
General Methods. All manipulations of air- and moisture-sensitive
materials were carried out under an inert atmosphere of dry argon using
■
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Table 1. Optimization of the Reaction Conditions for the Asymmetric Hydrosilylation of Acetophenone Using Co BPI Complex
a,b
S,S-15
a
b
Determined via NMR. Determined via HPLC.
a
Table 2. Catalytic Ketone Hydrosilylation with (BPI)Co(CH2SiMe3) Compounds
a
Enantiomeric excess determined by HPLC.
lized from toluene. Full shells of intensity data were collected at low
temperature with a Bruker AXS Smart 1000 CCD diffractometer (Mo-
Kα radiation, sealed tube, graphite monochromator) or an Agilent
Technologies Supernova-E CCD diffractometer (Cu-Kα radiation,
microfocus tube, multilayer mirror optics). Data were corrected for air
and detector absorption, Lorentz and polarization effects;30,31
absorption by the crystal was treated numerically (Gaussian grid)31
(complex 23) or with a semiempirical multiscan method (all
others).31−33 The structures were solved by the charge flip procedure34
and refined by full-matrix least-squares methods based on F2 against all
unique reflections.35 Hydrogen atoms were generally placed at
calculated positions and refined with a riding model. When justified
by the quality of the data the positions of some hydrogen atoms (except
those of the methyl groups) were taken from difference Fourier
syntheses and refined.
During reduction of the data sets collected with Mo X-radiation from
the compounds without heavy elements, Friedel opposites were merged
and δf″ were set to zero. In addition, separate refinements of both
enantiomorphs were carried out with complex atomic f and Friedel pairs
unmerged. In all these cases, likelihood36 and Parsons’ quotient (based
on [I+-I−]/[I++I−]) methods37 indicated that the absolute structure had
been correctly assigned (better, but not always highly significant
indicators were calculated for the expected enantiomorph).
Scheme 7. Optimized Reaction Conditions for the
Asymmetric Hydrosilylation
standard Schlenk techniques. All substrates were obtained commercially
and used as received if not otherwise stated. Solvents were purified and
dried by standard methods before use. The racemic alcohol was
prepared according to a literature procedure.21 The pyridine Co alkyl
precursor was also prepared using the method described in the
literature.25 1H and 13C spectra were recorded on Bruker Avance II 400
and Bruker Avance III 600 NMR spectrometers and were referenced
using the residual protio solvent (1H) or solvent (13C) resonances. The
paramagnetic 13C NMR spectra were measured with a Bruker QNP
Cryo Probe. Mass spectrometry and elemental analysis were obtained by
the analytical service of the Heidelberg Chemistry Department. IR
spectra were recorded on an Excalibur 3100 FT-IR spectrometer by
Varian as potassium bromide pellets. UV−vis spectra were measured
using a Varian Cary 5000 instrument. HPLC was performed on an
Agilent 1200 series HPLC. The analyses were performed using Chiralcel
AS-H, AD-H, OD-H or OJ-H columns.
CCDC 901898−901907 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Synthesis of Chiral Alcohols S-1 and R-1-acet. The racemate of
the alcohol (6.00 g, 32.67 mmol) was dissolved in vinyl acetate (60 mL)
X-ray Crystal Structure Determinations. Crystal data and details
of the structure determinations are listed in Tables 4−7. Single crystals
of the protio-ligands were obtained by slow diffusion of pentane in
concentrated solutions in dichloromethane. Complex 23 was crystal-
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Table 3. Catalytic Ketone Hydrosilylation with
(BPI)Co(CH2SiMe3) S,S-20
Table 4. Details of the Crystal Structure Determinations of S-
3a, R,R-7, and S,S-8
a
S-3a
R,R-7
S,S-8
formula
Mr
C10H12N4O
204.24
C40H53N5O2
635.87
C40H37N5O2
619.75
monoclinic
P21
crystal system
space group
a /Å
orthorhombic
P212121
6.799(4)
8.888(4)
15.767(8)
90
triclinic
P1
8.265(4)
12.523(7)
18.640(9)
95.869(9)
99.529(8)
107.30(1)
1792.9(15)
2
15.171(7)
7.052(3)
16.168(7)
90
b /Å
c /Å
α /°
β /°
γ /°
V /Å3
90
113.144(7)
90
90
952.7(8)
4
1590.6(12)
2
Z
F000
432
688
656
dc /Mg·m−3
X-radiation, λ /Å
μ /mm−1
1.424
1.178
1.294
Mo-Kα, 0.71073
0.098
Mo-Kα, 0.71073 Mo-Kα, 0.71073
0.073
0.081
max, min
transmission
factors
0.8623, 0.7671
0.8623, 0.7953
0.8623, 0.8106
data collect. temp
/K
100(2)
100(2)
100(2)
θ range /°
2.6 to 32.2
2.2 to 32.3
2.4 to 32.3
index ranges h,k,l
−10 ... 10, −13 ... −12 ... 12, −18 ... −22 ... 20, −10 ...
13, −22 ... 22 18, −27 ... 27 10, −23 ... 24
reflections
measured
20140 45236 40254
unique [Rint]
1862 [0.0334]
1735
11787 [0.0409] 5802 [0.0329]
observed [I ≥
2σ(I)]
10190
5463
a
Determined by HPLC.
parameters refined 158
865
507
GOF on F2
1.099
0.0384, 0.1045
1.027
1.058
R indices [F >
4σ(F)] R(F),
wR(F2)
0.0462, 0.1129
0.0422, 0.1091
and novozyme 435 (6.00 g) was added. The resulting suspension was
vigourously stirred at r. t. for 4 h. Afterward, the enzyme was separated
via filtration and washed with dichloromethane. The solvent was then
removed under reduced pressure and the resulting mixture separated via
column chromatography (SiO2, pentane:ethyl acetate 1:1). The (S)
alcohol S-1 was obtained as a white crystalline solid (2.71 g, 45.2%) and
the (R) acetate R-1-acet was isolated as yellow oil (3.63 g, 49.3%). The
analytical data are in accordance to the literature data found for the
racemic compound.21
R indices (all data) 0.0418, 0.1072
R(F), wR(F2)
0.0569, 0.1208
0.0453, 0.1128
absolute structure
parameter
largest residual
0.536, −0.212
0.479, −0.261
0.579, −0.261
peaks/e·Å−3
General Method for the Etherification. To a suspension of
sodium hydride (1.8 equiv) in THF a solution of the enantiomerically
pure alcohol 1 (1.0 equiv) in THF was added at 0 °C. After stirring at 0
°C for 1 h the alkyl halide (2.0 equiv) was added and the resulting
suspension was stirred for an additional hour at 0 °C. The reaction
mixture was warmed to r. t. overnight. After careful addition of water to
the mixture the product was extracted with diethyl ether, dried over
magnesium sulfate and the solvent was removed. The crude product was
purified via column chromatography on silica gel. As an example the
analytical data for R- and S-2a is given here, whereas the analytical data
for all other derivatives is available in the Supporting Information.
Synthesis of tert-Butylether R- and S-2e. A mixture of the
enantiomerically pure alcohol 1 (1.00 g, 5.45 mmol) and basic lead
carbonate (2.11 g, 2.72 mmol) was cooled to 0 °C and tert-butylbromide
(1.23 mL, 10.90 mmol) was added slowly. The mixture was then
suspended in chloroform (10 mL) and stirred under reflux for 7 days.
After cooling to r. t. the suspension was diluted with water and ethyl
acetate and stirred for 30 min at r. t. Afterward the insoluble parts were
separated via filtration and the aqueous layer extracted with ethyl
acetate. The combined organic phases were dried over magnesium
sulfate, the solvent removed and purified via column chromatography on
silica gel (pentane:ethyl acetate 1:1) to give the product as a yellow oil
0.80 g, (3.35 mmol, 61.5%). 1H NMR (600 MHz, CDCl3) δ [ppm] =
6.97 (s, 1H, H3), 4.96 (m, 1H, H7), 2.92 (m, 1H, H5), 2.63 (m, 1H, H5),
2.41 (m, 1H, H6), 2.22 (s, 3H, H8), 2.02 (m, 1H, H6), 1.32 (s, 9H,
OC(CH3)3). 13C NMR (150 MHz, CDCl3): δ [ppm] = 163.9 (C7a),
150.4 (C2), 146.3 (C4), 134.8 (C4a), 123.3 (C3), 74.8 (C7), 74.4
(OC(CH3)3), 33.2 (C6), 28.8 (OC(CH3)3), 25.7 (C5), 18.4 (C8). MS
(FAB+) m/z (%) = 240.11 (51.1) [M + H]+, 166.04 (100.0) [M-Ot-
Bu]+. HR-MS (HR-FAB+): calcd. for C13H19NO37Cl 242.1126, found:
242.1124 [17.7]; calcd. for C13H19NO35Cl 240.1155, found: 240.1139
[51.1]. Anal. Calcd. for C13H19NOCl: C 65.13; H 7.57; N 5.84; found C
1
R- and S-2a. 1.43 g (7.26 mmol = 94.8%). H NMR (600 MHz,
CDCl3) δ [ppm] = 7.04 (s, 1H, H3), 4.69 (m, 1H, H7), 3.52 (s, 3H,
OCH3), 2.95 (m, 1H, H5), 2.71 (m, 1H, H5), 2.37 (m, 1H, H6), 2.26 (s,
3H, H8), 2.14 (m, 1H, H6). 13C NMR (150.9 MHz, CDCl3) δ [ppm] =
162.48 (C7a), 150.07 (C2), 146.96 (C4), 135.50 (C4a), 123.98 (C3),
83.17 (C7), 57.15 (OCH3), 29.87 (C6), 26.03 (C5), 18.55 (C8). MS
(EI+) m/z (%) = 196.1 (4.2) [M]+•, 166.0 (100.0) [M−OCH3]+. HR-
MS (HR-EI+): calcd. for C9H9NO35Cl 166.0423, found 166.0422
[100.0]. Anal. Calcd. for C10H12NOCl: C 60.76, H 6.12, N 7.09; found C
60.78, H 6.17, N 7.00. IR v 3067 (w), 2927 (m), 2852 (w), 2820 (w),
̃
1720 (s), 1589 (m), 1440 (m), 1285 (w), 1202 (m), 1112 (s), 893 (m),
870 (m). HPLC Chiralcel AD-H, hexane:i-propanol 90:10, 0.5 mL/min,
detection at 254 nm, t(S) = 9.5 min, t(R) = 11.0 min, >99.5% ee.
64.75; H 7.55; N 5.67. IR v 3065 (w), 2965 (m), 2927 (w), 2903 (w),
̃
1653 (m), 1559 (m), 1262 (s), 1100 (s), 1050 (s), 1040 (s), 1019 (s),
12954
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Inorganic Chemistry
Article
Table 5. Details of the Crystal Structure Determinations of
R,R-9, S,S-10·CH2Cl2, and S,S-11
Table 6. Details of the Crystal Structure Determinations of
R,R-12, S,S-12, and S,S-14
R,R-9
S,S-10.CH2Cl2
S,S-11
R,R-12
S,S-12
S,S-14
formula
Mr
C30H33N5O2
495.61
monoclinic
I2
C33H39Cl2N5O2
608.59
C30H33N5O4
527.61
formula
Mr
C40H37N5O2
619.75
C40H37N5O2
619.75
C34H41N5O2
551.72
crystal system
space group
a /Å
triclinic
monoclinic
C2
crystal system
space group
a /Å
monoclinic
P21
monoclinic
P21
orthorhombic
P212121
9.7536(1)
17.8086(2)
17.8545(2)
90
P1
13.362(6)
12.353(6)
15.330(8)
90
8.0452(2)
13.3300(3)
15.0284(3)
89.484(2)
74.921(2)
88.934(2)
1555.91(6)
2
21.095(12)
12.889(6)
19.284(10)
90
18.4159(2)
14.0269(1)
25.7679(2)
90
18.4175(1)
14.0280(1)
25.7702(2)
90
b /Å
b /Å
c /Å
c /Å
α /°
β /°
γ /°
V /Å3
α /°
β /°
γ /°
V /Å3
93.210(12)
90
95.88(1)
90
102.0747(9)
90
102.0858(6)
90
90
90
2526(2)
4
5216(5)
8
6509.1(1)
8
6510.41(7)
8
3101.28(5)
4
Z
Z
F000
1056
644
2240
F000
2624
2624
1184
dc /Mg·m−3
X-radiation, λ /Å
μ /mm−1
1.303
1.299
1.344
dc /Mg·m−3
X-radiation, λ /Å
μ /mm−1
1.265
1.265
1.182
Mo-Kα, 0.71073 Cu-Kα, 1.54184
Mo-Kα, 0.71073
0.091
Cu-Kα, 1.54184 Cu-Kα, 1.54184 Cu-Kα, 1.54184
0.084
2.178
0.626
0.626
0.588
max, min
transmission
factors
0.8623, 0.8037
1.00000, 0.88175
0.8623, 0.8113
max, min
transmission
factors
1.00000,
0.79595
1.00000,
0.76431
1.00000, 0.75282
data collect. temp 100(2)
/K
120(1)
100(2)
data collect. temp
/K
120(1)
120(1)
115(1)
θ range /°
2.1 to 32.2
4.5 to 71.9
1.9 to 32.2
θ range /°
3.5 to 71.9
3.5 to 71.9
3.5 to 71.8
index ranges h,k,l
−19 ... 19, −18 ... −9 ... 9, −16 ... 16, −31 ... 31, −19 ...
index ranges
(indep. set) h,k,l
−22 ... 22, −17 ... −22 ... 22, −17 ... −11 ... 12, −21 ...
18, −22 ... 22 −17 ... 18 19, −28 ... 28
17, −31 ... 31 17, −31 ... 31 21, −21 ... 22
reflections
measured
31824 46907 65021
reflections
measured
214499 183894 67023
unique [Rint]
4422 [0.042]
3953
10781 [0.0427]
10752
9136 [0.0451]
7390
unique [Rint]
25387 [0.0360] 25284 [0.0404] 6048 [0.0349]
observed [I ≥
2σ(I)]
observed [I ≥
2σ(I)]
24973
24575
5878
parameters refined 341
776
838
parameters refined 1754
1754
437
GOF on F2
1.033
0.0444, 0.1117
1.013
1.026
GOF on F2
1.018
1.007
1.054
R indices [F >
4σ(F)] R(F),
wR(F2)
0.0475, 0.1198
0.0660, 0.1715
R indices [F >
4σ(F)] R(F),
wR(F2)
0.0304, 0.0772
0.0346, 0.0766
0.0253, 0.0647
R indices (all data) 0.0518, 0.1183
R(F), wR(F2)
0.0476, 0.1198
0.04(1)
0.0838, 0.1899
R indices (all data) 0.0309, 0.0778
R(F), wR(F2)
0.0357, 0.0778
0.04(7)
0.0262, 0.0652
0.01(12)
absolute structure
parameter
absolute structure
parameter
0.01(7)
largest residual
0.669, −0.290
0.543, −0.501
0.810, −0.305
largest residual
0.181, −0.201
0.167, −0.173
0.118, −0.163
peaks/e·Å−3
peaks/e·Å−3
873 (m), 802 (s). HPLC Chiralcel AD-H, hexane:i-propanol 90:10, 0.5
mL/min, detection at 254 nm, t(S) = 7.3 min, t(R) = 7.8 min, >99.5% ee.
General Method for the Synthesis of Tetrazoles. The
chloropyridine 2 (1.0 equiv) was added to tetrabutylammonium-
fluoride-trihydrate (1.0 equiv) under ice cooling and trimethylsilyl azide
(4.0 equiv) was carefully added dropwise. After the exothermic reaction
was finished the mixture was stirred at 85 °C for 96 h. Then it was cooled
to r.t. and water was carefully added. The reaction mixture was extracted
with ethyl acetate and the combined organic layers were washed with
brine, dried over magnesium sulfate, and the solvent was removed under
reduced pressure. The raw product was purified via column
chromatography on silica gel. As an example the analytical data for R-
and S-3a is given here, whereas the analytical data for all other
derivatives is available in the Supporting Information.
146.0847 [100.0]. Anal. Calcd. for C10H12N4O: C 58.81, H 5.92, N
27.43; found C 58.79, H 5.84, N 27.13. IR v 3059 (w), 2995 (m), 2955
̃
(w), 2829 (w), 1644 (m), 1551 (m), 1492 (m), 1455 (m), 1438 (m),
1392 (m), 1374 (m), 1262 (m), 1188 (m), 1107 (s), 1090 (s), 1060 (s),
1040 (m), 1012 (m), 955 (m), 891 (w), 867 (m), 803 (m).
General Method for the Hydrogenation. The tetrazole 3 (1.0
equiv) was dissolved in ethanol and Lindlar catalyst (0.27 w/w) was
added. The reaction mixture was stirred at r.t. at 20 bar H2 pressure for
72 h. Afterward the catalyst was filtered off and the solvent was removed
under reduced pressure. The raw product could be used for the ligand
synthesis without further purification. As an example the analytical data
for R- and S-4a is given here, whereas the analytical data for all other
derivatives are available in the Supporting Information.
R- and S-4a: Quantitative. 1H NMR (600 MHz, CDCl3) δ [ppm] =
6.25 (s, 1H, H3), 4.65 (m, 1H, H7), 4.32 (br s, 2H, NH2), 3.50 (s, 3H,
OCH3), 2.84 (m, 1H, H5), 2.61 (m, 1H, H5), 2.35 (m, 1H, H6), 2.15 (s,
3H, H8), 2.04 (m, 1H, H6). 13C NMR (150 MHz, CDCl3) δ [ppm] =
159.72 (C7a), 158.45 (C2), 145.68 (C4), 126.48 (C4a), 108.77 (C3),
84.01 (C7), 56.79 (OCH3), 29.43 (C6), 25.64 (C5), 18.71 (C8). MS
(FAB+) m/z (%) = 178.11 (17.0) [M]+•, 147.07 (100.0) [M−OCH3]+.
HR-MS (HR-FAB+): calcd. for C10H14N2O 178.1106, found 178.1094
[17.0]; calcd. for C9H11N2 147.0922; found 147.0908 [100.0]. HPLC
Chiralcel AD-H, hexane/i-propanol 90:10, 0.5 mL/min, detection at
254 nm, t(S) = 22.5 min, t(R) = 23.8 min, >99.5% ee.
1
R- and S-3a. 2.72 g (13.34 mmol = 60.6%). H NMR (600 MHz,
CDCl3) δ [ppm] = 7.67 (s, 1H, H3), 5.40 (m, 1H, H7), 3.60 (s, 3H,
OCH3), 3.12 (m, 1H, H5), 2.88 (m, 1H, H5), 2.56 (m, 1H, H6), 2.42 (s,
3H, H8), 2.36 (m, 1H, H6). 13C NMR (150 MHz, CDCl3) δ [ppm] =
149.66 (C2), 141.63 (C7a), 136.01 (C4), 133.80 (C4a), 113.48 (C3),
81.10 (C7), 58.43 (OCH3), 30.21 (C6), 27.81 (C5), 19.41 (C8). MS
(EI+) m/z (%) = 204.10 (28.5) [M]+., 174.09 (47.2) [M−OCH3]+,
146.09 (100.0) [M−OCH3N2]+. HR-MS (HR-EI+): calcd. for
C10H12N4O 204.1011, found 204.1020 [28.5]; calcd. for C9H10N4
174.0906, found 174.0884 [47.2]; calcd. for 146.0844, found
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Inorganic Chemistry
Article
Afterward, the solution was filtered and the solvent removed under
reduced pressure. The crude product was purified by washing with either
toluene or diethyl ether. As an example the analytical data for S,S-15 is
given here, whereas the analytical data for all other derivatives is available
in the Supporting Information.
Table 7. Details of the Crystal Structure Determinations of 23
23
formula
C30H35CoN5Si
552.65
Mr
S,S-15. 135.5 mg (0.22 mmol = 88.4%). 1H NMR (600 MHz,
toluene-d8, paramagnetic) δ [ppm] = 139.37, 55.96, 47.31, 44.95, 42.27,
18.13, 14.78, 14.12, 12.22, 10.81, 9.07, 7.59, 5.27, −0.99, −5.02, −12.27,
−14.43, −24.33, −41.86, −94.37. Not all resonances could be detected.
13C NMR (150 MHz, toluene-d8, paramagnetic) δ [ppm] = 814.0, 805.1,
crystal system
triclinic
space group
P1
̅
a /Å
10.5259(8)
11.787(2)
12.058(2)
87.71(1)
b /Å
c /Å
597.0, 564.9, 514.4, 505.2, 497.3, 458.4, 418.6, 394.1, 341.6, 329.3, 231.5,
227.4, 211.4, 208.8, 197.6, 192.7, 183.7, 165.2, 146.4, 84.7, 68.1, 56.4,
51.9, 45.0, 31.6, 26.4, 0.5. Not all resonances could be detected. Anal.
Calcd. for C32H39N5O2CoSi: C 62.73, H 6.42, N 11.43; found C 62.70,
H 6.39, N 11.45.
α /°
β /°
68.56(1)
γ /°
76.29(1)
V /Å3
1350.9(3)
2
Z
General Catalytic Procedure for the Asymmetric Hydro-
silylation. A catalyst stock solution (0.50 mL, 16.70 mmol−1) was filled
in a Schlenk tube in the glovebox and cooled to 15 °C using a cryostat.
To start the catalytic reaction the silane (2.0 equiv, 0.67 mmol) and the
ketone (1.0 equiv, 0.33 mmol) were added and the reaction was stirred
for 8 h. Afterward 2 mL of a solution of potassium carbonate in methanol
(1.0 mol−1) were added and the mixture was stirred for 2 h at r.t. until the
hydrolysis was completed. Then the mixture was extracted with diethyl
ether, dried over magnesium sulfate, and evaporated. The raw product
was purified via column chromatography on silica gel (pentane/diethyl
ether).
Characterization of Hydrosilylation Products by HPLC. 1-
Phenylethanol. Chiralcel OD-H, hexane/i-propanol 98:2, 0.8 mL/min,
20 °C. Enantiomer retention times: 15.51 min (R), 19.33 min (S).
1-(4-Phenylphenyl)ethanol. Chiralcel AD-H, hexane/i-propanol
95:5, 0.8 mL/min, 20 °C. Enantiomer retention times: 15.99 min (R),
17.73 min (S).
F000
582
dc /Mg·m−3
1.359
X-radiation, λ /Å
μ /mm−1
Cu-Kα, 1.54184
5.619
max, min transmission factors
data collect. temp /K
θ range /°
index ranges (indep. set) h,k,l
reflections measured
unique [Rint]
0.924, 0.376
110(1)
3.9 to 72.6
−12 ... 12, −14 ... 14, −12 ... 14
20629
5195 [0.0915]
3972
observed [I ≥ 2σ(I)]
parameters refined
GOF on F2
R indices [F > 4σ(F)] R(F), wR(F2)
R indices (all data) R(F), wR(F2)
largest residual peaks/e·Å−3
339
1.048
0.0895, 0.2138
0.1126, 0.2301
2.190, −0.599
1-(4-Fluorphenyl)ethanol. Chiralcel OD-H, hexane/i-propanol
98:2, 0.8 mL/min, 20 °C. Enantiomer retention times: 13.40 min (S),
14.30 min (R).
1-(4-Methoxyphenyl)ethanol. Chiralcel OD-H, hexane/i-propanol
98:2, 1 mL/min, 10 °C. Enantiomer retention times: 25.02 min, 30.00
min.
1-(3,4,5-Trimethoxyphenyl)ethanol. Chiralcel AS-H, hexane/i-
propanol 95:5, 1 mL/min, 20 °C. Enantiomer retention times: 48.50
min, 65.90 min.
1-Naphthalen-2-ethanol. Chiralcel OJ-H, hexane/i-propanol 95:5,
0.8 mL/min, 20 °C. Enantiomer retention times: 37.08 min, 50.58 min.
6-Methoxynaphthalen-2-ethanol. Chiralcel OD-H, hexane/i-prop-
anol 95:5, 0.8 mL/min, 20 °C. Enantiomer retention times: 20.59 min,
29.42 min.
General Method for Synthesis of the Protio-Ligands. The
amine 4 (2.3 equiv) and the appropriate phthalodinitrile (1.0 equiv)
were suspended together with calcium chloride (0.2 equiv) in n-hexanol
and stirred at 160 °C for 16 h. After cooling to r.t. the solvent was
removed in vacuo and the residue was dissolved in dichloromethane. The
mixture was filtered through Celite and the raw product was purified
using column chromatography on silica gel (dichloromethane/
diethylether) after removal of the solvent. As an example the analytical
data for R,R- and S,S-5 is given here, whereas the analytical data for all
other derivatives are available in the Supporting Information.
R,R- and S,S-5. 1.04 g (2.22 mmol = 58.8%). 1H NMR (600 MHz,
CDCl3) δ [ppm] = 12.49 (s, 1H, NH), 8.06 (m, 2H, H11), 7.64 (m, 2H,
H10), 7.14 (s, 2H, H3), 4.77 (m, 2H, H7), 3.26 (s, 6H, OCH3), 3.02 (m,
2H, H5), 2.80 (m, 2H, H5), 2.41 (m, 2H, H6), 2.32 (s, 6H, H6), 2.21 (m,
2H, H8). 13C NMR (150 MHz, CDCl3) δ [ppm] = 160.41 (C7a), 159.87
(C2), 152.53 (C9), 145.84 (C4), 135.55 (C9a), 133.30 (C4a), 131.41
(C10), 122.32 (C11), 122.01 (C3), 83.50 (C7), 56.28 (OCH3), 30.06
(C6), 26.33 (C5), 18.60 (C8). MS (EI+) m/z (%) = 467.24 (24.6) [M]+•,
436.21 (22.1) [M−OCH3]+, 422.20 (100.0) [M−OC2H5)]+. HR-MS
(HR-EI+): calcd. for C28H29N5O2 467.2321, found 467.2360 [24.6];
calcd. for C27H26N5O 436.2137, found 436.2099 [8.1]; calcd. for
C26H24N5O 422.1981, found 422.1964 [100.0]. Anal. Calcd. for
C28H29N5O2: C 71.93, H 6.25, N 14.98; found C 71.63, H 6.33, N
1-Naphthalen-1-ethanol. Chiralcel OJ-H, hexane/i-propanol 95:5,
0.8 mL/min, 20 °C. Enantiomer retention times: 22.57 min, 40.38 min.
1-(2-Methylphenyl)ethanol. Chiralcel AD-H, hexane/i-propanol
98:2, 0.8 mL/min, 20 °C. Enantiomer retention times: 17.63 min,
20.30 min.
ASSOCIATED CONTENT
■
S
* Supporting Information
15.12. IR v 3400 (br), 2960 (w), 2928 (w), 2855 (m), 2817 (m), 1735
̃
Analytical data for 2−22 and experimental procedures for the
synthesis of complex 23. This material is available free of charge
via the Internet at http://pubs.acs.org.
(m), 1701 (m), 1684 (m), 1653 (s), 1636 (m), 1559 (s), 1540 (m), 1521
(m), 1506 (m), 1473 (w), 1457 (m), 1435 (w), 1085 (w). UV−vis
(CH2Cl2, 50.58 μmol−1) λ = 398 nm (shoulder), ε = 9478 M−1 cm−1, λ =
379 nm, ε = 11388 M−1 cm−1, λ = 356 nm, ε = 10933 M−1 cm−1, λ = 339
nm, ε = 10933 M−1 cm−1, λ = 307 nm (shoulder), ε = 11720 M−1cm−1, λ
= 283 nm, ε = 13839 M−1 cm−1. [α]D = 684.9°.
AUTHOR INFORMATION
■
Corresponding Author
General Method for the Preparation of the Cobalt(II) Alkyl
Complexes. The protio-ligand (0.25 mmol) was dissolved in THF (5
mL) and slowly added dropwise to a solution of the alkyl precursor (0.27
mmol) in 4 mL of THF at −40 °C. After 20 min the solution was allowed
to warm to r. t. over a period of 3 h and stirred an additional hour at r.t.
*E-mail: lutz.gade@uni-hd.de.
Notes
The authors declare no competing financial interest.
12956
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Inorganic Chemistry
Article
Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 5640−5644. (c) Verdaguer,
X.; Lange, U. E. W.; Reding, M. T.; Buchwald, S. L. J. Am. Chem. Soc.
1996, 118, 6784−6785. (d) Verdaguer, X.; Lange, U. E. W.; Buchwald,
S. L. Angew. Chem., Int. Ed. 1998, 37, 1103−1107. Cu: see for example:
(a) Brunner, H.; Miehling, W. J. Organomet. Chem. 1984, 275, C17−
C21. (b) Lipshutz, B. H.; Noson, K.; Chrisman, W. J. Am. Chem. Soc.
2001, 123, 12917−12918. (c) Lipshutz, B. H.; Noson, K.; Chrisman, W.;
Lower, A. J. Am. Chem. Soc. 2003, 125, 8779−8789. (d) Lipshutz, B. H.;
Lower, A.; Kucejko, R.; Noson, K. Org. Lett. 2006, 8, 2969−2972.
(e) Yun, J.; Dong-won, L. Tetrahedron Lett. 2004, 45, 5415−5417.
(f) Sirol, S.; Courmarcel, J.; Mostefai, N.; Riant, O. Org. Lett. 2001, 3,
4111−4113. (g) Issenhuth, J. T.; Dagorne, S.; Bellemin-Laponnaz, S.
Adv. Synth. Catal. 2006, 348, 1991−1994. (h) Ito, H.; Yamanaka, H.;
Ishizuka, T.; Tateiwa, J.; Hosomi, A. Synlett 2000, 479−482.
ACKNOWLEDGMENTS
■
D.C.S. thanks the Studienstiftung des deutschen Volkes for a
doctoral fellowship. This work has been funded by the Deutsche
Forschungsgemeinschaft (SFB 623, TP B6).
REFERENCES
■
(1) (a) Breuer, M.; Ditrich, K.; Habicher, T.; Hauer, B.; Keßeler, M.;
Sturmer, R.; Zelinski, T. Angew. Chem., Int. Ed. 2004, 43, 788−824.
(b) Blaser, H. U. Chem. Commun. 2003, 293−296. (c) Kleemann, U.;
Engel, U.; Kutscher, B.; Reichert, D. Pharmaceutical Substances; Georg
Thieme Verlag: Stuttgart, 2001; (d) Nicolaou, K. C.; Sorensen, E. J.
Classics in Total Synthesis; Verlag Chemie: Weinheim, 1996.
̈
(2) (a) Noyori, R.; Okuma, T. Angew. Chem., Int. Ed. 2001, 40, 40−73.
(11) (a) Nishiyama, H.; Furuta, A. Chem. Commun. 2007, 760−762.
(b) Furuta, A.; Nishiyama, H. Tetrahedron Lett. 2008, 49, 110−113.
(12) (a) Shaikh, N. S.; Junge, K.; Beller, M. Org. Lett. 2007, 9, 5429−
5432. (b) Shaikh, N. S.; Enthaler, S.; Junge, K.; Beller, M. Angew. Chem.,
Int. Ed. 2008, 47, 2497−2501.
(b) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008−2022.
(3) (a) Samec, J. S. M.; Backvall, J. E.; Andersson, P. G.; Brandt, P.
̈
Chem. Soc. Rev. 2006, 35, 237−248. (b) Baratta, W.; Ballico, M.; Baldino,
S.; Chelucci, G.; Herdtweck, E.; Siega, K.; Magnolia, S.; Rigo, P.
Chem.Eur. J. 2008, 14, 9148−9160.
(13) Fluckiger, M.; Togni, A. Eur. J. Org. Chem. 2011, 4353−4360.
̈
(4) (a) Roy, A. K. Adv. Organomet. Chem. 2008, 55, 1−59.
(b) Nishiyama, H. Hydrosilylation of Carbonyl and Imino Groups, in:
Jacobsen, E. N.; Pfaltz, A. Comprehensive Asymmetric Catalysis; Springer:
New York, 2004; pp 267−287.
(14) Langlotz, B. K.; Wadepohl, H.; Gade, L. H. Angew. Chem., Int. Ed.
2008, 47, 4670−4674.
(15) (a) Tondreau, A. M.; Darmon, J. M.; Wile, B. M.; Floyd, S. K.;
Lobkovsky, E.; Chirik, P. J. Organometallics 2009, 28, 3928−3940.
(b) Monfette, S.; Turner, Z. R.; Semproni, S. P.; Chirik, P. J. J. Am. Chem.
Soc. 2012, 134, 4561−4564.
(5) (a) Dumont, W.; Poulin, J. C.; Dang, T. P.; Kagan, H. B. J. Am.
Chem. Soc. 1973, 95, 8295−8299. (b) Ojima, I.; Kogure, M.; Kumagai,
M. J. Org. Chem. 1977, 42, 1671−1679. (c) Sawamura, M.; Kuwano, R.;
Ito, Y. Angew. Chem., Int. Ed. 1994, 33, 111−113. (d) Enders, D.; Gielen,
H.; Breuer, K. Tetrahedron: Asymmetry 1997, 8, 3571−3574.
(e) Kromm, K.; Osburn, P. L.; Gladysz, L. Organometallics 2002, 21,
4275−4280. (f) Evans, D. A.; Forrest, E. M.; Tedrow, J. S.; Campos, K.
R. J. Am. Chem. Soc. 2003, 125, 3534−3543. (g) Duan, W. L.; Shi, M.;
Rong, G. B. Chem. Commun. 2003, 2916−2917. (h) Arena, C. G.;
Pattacini, R. J. Mol. Catal. A Chem. 2004, 222, 47−52. (i) Cesar, V.;
Bellemin-Laponnaz, S.; Wadepohl, H.; Gade, L. H. Chem.Eur. J. 2005,
11, 2862−2873. (j) Imamoto, T.; Itoh, T.; Yamanoi, Y.; Narui, R.;
Yoshida, K. Tetrahedron: Asymmetry 2006, 17, 560−565. (k) Xu, Q.; Gu,
X.; Liu, S. D. Q.; Shi, M. J. Org. Chem. 2007, 72, 2240−2242.
(l) Schneider, N.; Finger, M.; Haferkemper, C.; Bellemin-Laponnaz, S.;
Hofmann, P.; Gade, L. H. Angew. Chem., Int. Ed. 2009, 48, 1609−1613.
(m) Schneider, N.; Finger, M.; Haferkemper, C.; Bellemin-Laponnaz,
S.; Hofmann, P.; Gade, L. H. Chem.Eur. J. 2009, 15, 11515−11529.
(n) Schneider, N.; Kruck, M.; Bellemin-Laponnaz, S.; Wadepohl, H.;
Gade, L. H. Eur. J. Inorg. Chem. 2009, 493−500.
(16) Brunner, H.; Amberger, K. J. Organomet. Chem. 1991, 417, C63−
C65.
(17) (a) Inagaki, T.; Phong, L. T.; Furuta, A.; Ito, J.-i.; Nishiyama, H.
Chem.Eur. J. 2010, 16, 3090−3096. (b) Hosokawa, S.; Ito, J.-i.;
Nishiyama, H. Organometallics 2010, 29, 5773−5775. (c) Inagaki, T.;
Ito, A.; Ito, J.-i.; Nishiyama, H. Angew. Chem., Int. Ed. 2010, 49, 9384−
9387.
(18) Yu, F.; Zhang, X.-C.; Wu, F.-F.; Zhou, J.-N.; Fang, W.; Wu, J.;
Chan, A. S. C. Org. Biomol. Chem. 2011, 9, 5652−5654.
(19) (a) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40,
3750−3781. (b) van der Boom, M.; Milstein, D. Chem. Rev. 2003, 103,
1759−1792.
(20) (a) Elvidge, J. A.; Linstead, R. P. J. Chem. Soc. 1952, 5000−5007.
(b) Siegl, W. O. J. Organomet. Chem. 1976, 107, C27−C30. (c) Gagne,
́
R. R.; Marritt, W. A.; Marks, D. N.; Siegl, W. O. Inorg. Chem. 1981, 20,
3260−3267. (d) Meder, M. B.; Gade, L. H. Eur. J. Inorg. Chem. 2004,
2716−2722.
(6) (a) Tanke, R. S.; Crabtree, R. H. J. Am. Chem. Soc. 1990, 112,
7984−7989. (b) Doherty, S.; Knight, J. G.; Scanlan, T. H.; Elsegood, M.
R. J.; Clegg, W. J. Organomet. Chem. 2002, 650, 231−248. (c) Esteruelas,
(21) (a) Lyle, M. P. A.; Draper, N. D.; Wilson, P. D. Org. Biomol. Chem.
2006, 4, 877−885. (b) Lyle, M. P. A.; Wilson, P. D. Org. Lett. 2004, 6,
855−857. (c) Lyle, M. P. A.; Narine, A. A.; Wilson, P. D. J. Org. Chem.
2004, 69, 5060−5064.
́
M.; Olivan, M.; Oro, L. A.; Tolosa, J. I. J. Organomet. Chem. 1995, 487,
143−149. (d) Martín, M.; Sola, E.; Torres, O.; Pablo, P.; Oro, L. A.
Organometallics 2003, 22, 5406−5417. (e) Klei, S. R.; Tilley, T. D.;
Bergman, R. G. Organometallics 2002, 21, 4648−4661. (f) Field, L. D.;
Messerle, B. A.; Wren, S. L. Organometallics 2003, 22, 4393−4395.
(7) (a) Zhu, G.; Terry, M.; Zhang, X. J. Organomet. Chem. 1997, 547,
97−101. (b) Nishibayashi, I.; Takei, I.; Uemura, S.; Hidai, M.
Organometallics 1998, 17, 3420−3422. (c) Moreau, C.; Frost, C. G.;
Murrer, B. Tetrahedron Lett. 1999, 40, 5617−5620.
(22) (a) Woodmansee, D. H.; Muller, M.-A.; Neuburger, M.; Pfaltz, A.
̈
Chem. Sci. 2010, 1, 72−78. (b) Felluga, F.; Baratta, W.; Fanfoni, L.;
Pitacco, G.; Rigo, P.; Benedetti, F. J. Org. Chem. 2009, 74, 3547−3550.
(c) Maywald, M.; Pfaltz, A. Synthesis 2009, 21, 3654−3660.
(23) Rai, N. P.; Arunachalam, P. N. Synth. Commun. 2007, 37, 2891−
2896.
(24) Kruck, M.; Sauer, D. C.; Enders, M.; Wadepohl, H.; Gade, L. H.
Dalton Trans. 2011, 40, 10406−10415.
(8) (a) Brunner, H.; Becker, R.; Rielp, G. Organometallics 1984, 3,
(25) Zhu, D.; Janssen, F. F. B. J.; Budzelaar, P. H. M. Organometallics
2010, 29, 1897−1908.
1354−1359. (b) Brunner, H.; Kurzinger, A. J. Organomet. Chem. 1988,
̈
346, 413−424. (c) Gade, L. H.; Cesar, V.; Bellemin-Laponnaz, S. Angew.
Chem., Int. Ed. 2004, 43, 1014−1017. (d) Riant, O.; Mostefaï, N.;
Courmarcel, J. Synthesis 2004, 2943−2958. (e) Newman, L. M.;
Williams, J. M. J.; McCague, R.; Potter, G. A. Tetrahedron: Asymmetry
1996, 7, 1597−1598. (f) Langer, T.; Janssen, J.; Helmchen, G.
Tetrahedron: Asymmetry 1996, 7, 1599−1602. (g) Tao, B.; Fu, G. C.
Angew. Chem., Int. Ed. 2002, 41, 2892−2894. (h) Nishiyama, H.; Park, S.
B.; Itoh, K. Tetrahedron: Asymmetry 1992, 3, 1599−1602.
(26) Evans, D. F. J. Chem. Soc. 1959, 2003−2005.
(27) Meder, M. B.; Siggelkow, B. A.; Gade, L. H. Z. Allg. Anorg. Chem.
2004, 630, 1962−1968.
(28) Sauer, D. C.; Wadepohl, H.; Gade, L. H., unpublished results.
(29) (a) Owston, P. G.; Rowe, J. M. J. Chem. Soc. 1963, 3411−3419.
(b) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain, B.; Hursthouse, M.
B. Polyhedron 1990, 9, 931−937. (c) Leung, W.-P.; Lee, H. K.; Zhou, Z.-
Y.; Mak, T. W. C. J. Organomet. Chem. 1993, 443, C39−C40.
(d) Hursthouse, M. B.; Izod, K. J.; Motevalli, M.; Thornton, P.
Polyhedron 1996, 15, 135−145. (e) Jewson, J. D.; Liable-Sands, L. M.;
Yap, G. P. A.; Rheingold, A. L.; Theopold, K. H. Organometallics 1999,
(9) (a) Morris, R. H. Chem. Soc. Rev. 2009, 38, 2282−2291. (b) Arena,
C. G. Mini-Rev. Org. Chem. 2009, 6, 159−167.
́
(10) Ti: see for example: (a) Carter, M. B.; Schiott, B.; Gutierrez, A.;
Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 11667−11670. (b) Yun, J.;
12957
dx.doi.org/10.1021/ic3020749 | Inorg. Chem. 2012, 51, 12948−12958

Inorganic Chemistry
Article
18, 300−305. (f) Shirasawa, N.; Hguyet, T. T.; Hikichi, S.; Moro-oka, Y.;
Akita, M. Organometallics 2001, 20, 3582−3598.
(30) (a) SAINT; Bruker AXS; Karlsruhe, 1997−2008; (b) CrysAlisPro;
Agilent Technologies UK Ltd., Oxford, 2011.
(31) CrysAlisPro; Agilent Technologies UK Ltd.: Oxford, 2011.
(32) Blessing, R. H. Acta Crystallogr. 1995, A51, 33−38.
(33) Sheldrick, G. M. SADABS; Bruker AXS: Karlsruhe, 2004−2008.
(34) (a) Palatinus, L. SUPERFLIP; EPF Lausanne: Switzerland, 2007;
(b) Palatinus, L.; Chapuis, G. J. Appl. Crystallogr. 2007, 40, 786−790.
(35) (a) Sheldrick, G. M. SHELXL-97; University of Gottingen:
̈
Gottingen, Germany, 1997; (b) Sheldrick, G. M. Acta Crystallogr. 2008,
A64, 112−122.
̈
(36) (a) Hooft, R. W. W.; Straver, L. H.; Spek, A. L. J. Appl. Crystallogr.
2008, 41, 96−103. (b) Hooft, R. W. W.; Straver, L. H.; Spek, A. L. J.
Appl. Crystallogr. 2010, 43, 665−668.
(37) Parsons, S.; Flack, H. D. Abstracts of the 22nd European
Crystallography Meeting, Budapest, 2004, Abstract No. MS22.
12958
dx.doi.org/10.1021/ic3020749 | Inorg. Chem. 2012, 51, 12948−12958