A Tethered Ru–S Complex with an Axial Chiral Thiolate Ligand for Cooperative Si–H Bond Activation: Application to Enantioselective Imine Reduction

Article abstract of DOI:10.1002/chem.201700304

An axial chiral version of the 2,6-dimesitylphenyl group attached to sulfur is reported. Its multistep preparation starts from (S)-binol, and the thiol group is established by a racemization-free thermal Newman–Kwart rearrangement. The new chiral thiolate ligand decorated with one mesityl group is used in the synthesis of a tethered ruthenium chloride complex. Its spectroscopic characterization revealed solvent-dependent epimerization at the ruthenium center. The major diastereomer is crystallographically characterized. Chloride abstraction with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBAr^F₄) yields the corresponding coordinatively unsaturated ruthenium complex with the Ru?S bond exposed. Si?H bond activation at this Ru?S bond proceeds in syn fashion but with moderate facial selectivity (d.r.=70:30), generating diastereomeric chiral-at-ruthenium hydrosilane adducts. Their application to catalytic imine hydrosilylation led to promising enantioinduction (40 % ee), thereby providing proof of concept for asymmetric catalysis involving cooperative Si?H bond activation.

Full text of DOI:10.1002/chem.201700304

A Journal of
Accepted Article
Title: A Tethered Ru-S Complex with an Axial Chiral Thiolate Ligand for
Cooperative Si-H Bond Activation: Application to Enantioselective
Imine Reduction
Authors: Simon Wübbolt, Modhu Sudan Maji, Elisabeth Irran, and
Martin Oestreich
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To be cited as: Chem. Eur. J. 10.1002/chem.201700304
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Supported by

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A Tethered Ru–S Complex with an Axial Chiral Thiolate Ligand for
Cooperative Si‒H Bond Activation: Application to
Enantioselective Imine Reduction
Simon Wübbolt, Modhu Sudan Maji, Elisabeth Irran, and Martin Oestreich*[a]
Abstract: An axial chiral version of the 2,6-dimesitylphenyl group
attached to sulfur is reported. Its multistep preparation starts from
(S)-binol, and the thiol group is established by a racemization-free
thermal Newman–Kwart rearrangement. The new chiral thiolate
ligand decorated with one mesityl group is used in the synthesis of a
unprecedented whereas tethered ruthenium complexes for
Noyori-type enantioselective hydrogenation[10] were intensively
investigated by Wills and co-workers.[11] Asymmetric catalysis
with [(R)-3]+[BArF ]– is predictably difficult as the chiral backbone
4
in [(R)-3]+[BArF ]– renders the syn Si‒H bond activation[2]
4
tethered
ruthenium
chloride
complex.
Its
spectroscopic
diastereoselective ([(R)-3]+→[syn-(R,RuS)-4]+ and/or [syn-
(R,RuR)-4]+, Scheme 1, right), hence adding another
stereoselectivity-controlling factor to the asymmetric C=N
reduction with hydrosilanes. We describe here the synthesis of
characterization revealed solvent-dependent epimerization at the
ruthenium center. The major diastereomer is crystallographically
characterized.
Chloride
abstraction
with
tetrakis[3,5-
bis(trifluoromethyl)phenyl]borate (NaBArF ) yields the corresponding
the chiral Ru‒S complex [(R)-3]+[BArF ]–, its behaveior in the
4
4
coordinatively unsaturated ruthenium complex with the Ru–S bond
exposed. Si–H bond activation at this Ru–S bond proceeds in syn
fashion but with moderate facial selectivity (d.r. = 70:30), generating
diastereomeric chiral-at-ruthenium hydrosilane adducts. Their
application to catalytic imine hydrosilylation led to promising
enantioinduction (40% ee), thereby providing proof of concept for
asymmetric catalysis involving cooperative Si–H bond activation.
Si‒H bond activation, and application to the enantioselective
hydrosilylation of imines.
previous work:
this work:
Ru
S
PR3
Ru
S
–
PEt3
BArF
BArF
4
4
Introduction
–
[1]+[BArF
]
–
[(R)-3]+[BArF
]
4
4
a: R = Et, b: R = iPr, and
c: R = 4-FC6H4
Heterolytic splitting of Si‒H bonds at the Ru‒S bond of
Ohki‒Tatsumi complexes[1] [1]+[BArF ]– has become a useful
4
synthetic tool for the catalytic generation of silicon electrophiles.
The mechanism of the Si‒H bond activation step is fully
understood and proceeds in syn fashion on either of the
enantiotopic faces of the CS-symmetric, trigonal planar
ruthenium site ([1]+→[syn-2]+, Scheme 1, left).[2] Chiral-at-metal[3]
adduct [syn-2]+ is formed reversibly in racemic form. While the
stereogenicity at the metal is irrelevant in the various
[Ru]
ArS
[Ru]
ArS
PR3
PEt3
3]+
[1a c]+
[(R)-
[Ru]
ArS
[Ru]
ArS
[Ru]
ArS
+
PR3
PEt3
PEt3
H
H
H
Si
[syn-2]+
racemic
Si
Si
[syn-(R,RuS)-
4]+ [syn-(R,RuR)-4]+
dehydrogenative coupling reactions promoted by [1]+[BArF ]–,[4] it
4
diastereomeric
chiral-at-metal complexes
will be vital in asymmetric reduction processes[2,5] where the
hydride transfer from the asymmetrically substituted ruthenium
center is the enantioselectivity-determining step.[8] We therefore
chiral-at-metal complex
Scheme 1. Tethered Ru–S complexes with an achiral ([1a–c]+[BArF4]–, left) or
a chiral ([(R)-3]+[BArF4]–, right) thiolate ligand applied to Si–H bond activation.
ArF = 3,5-bis(trifluoromethyl)phenyl; Si = triorganosilyl.
set out to prepare an axial chiral congener of [1]+[BArF ]–, namely
4
tethered complex [(R)-3]+[BArF ]– (Scheme 1, right). Chiral [(R)-
4
3]+[BArF ]– was designed to promote enantioselective C=N
4
hydrosilylation reactions[9] involving cooperative Si‒H bond
Results and Discussion
activation. It is interesting to note that such catalysts are
Thiol (R)-5 was prepared from (S)-binol [(S)-6] in eleven steps
(Scheme 2). Orthogonally protected (S)-9 was accessed by
following a reported three-step sequence by Maruoka and co-
workers [(S)-6→(S)-9, see the Supporting Information].[12] The
mesityl group that will later become the arene ligand was
installed by Kumada coupling [(S)-9→(S)-10]. Fluoride-mediated
cleavage of the silyl ether [(S)-10→(S)-11] and direct triflation of
the free hydroxy group [(S)-11→(S)-12] set the stage for nickel-
catalyzed methylation in this position [(S)-12→(R)-13]. Acid-
[a]
S. Wübbolt, Dr. M. S. Maji, Dr. E. Irran, Prof. Dr. M. Oestreich
Institut für Chemie, Technische Universität Berlin
Straße des 17. Juni 115, 10623 Berlin (Germany)
E-mail: martin.oestreich@tu-berlin.de
Homepage: http://www.organometallics.tu-berlin.de
Supporting information for this article is given via a link at the end of
the document.
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mediated cleavage of the MOM group [(R)-13→(R)-14] liberated
the other phenol that was reacted with dimethylthiocarbamoyl
chloride [(R)-14→(R)-15]. The thus-obtained O-thiocarbamate
(R)-15 was converted into the corresponding S-thiocarbamate
(R)-16 by thermal Newman‒Kwart rearrangement [(R)-15→(R)-
16]. Hydride reduction [(R)-16→(R)-5] afforded the desired thiol
(R)-5 in excellent 31% overall yield. The enantiomeric purity of
98% ee was determined by comparison with a racemic sample.
I
NiCl2(PPh3)2 (7.0 mol%)
NiCl2(dppe) (10 mol%)
OMOM
MesMgBr (1.6 equiv)
OMOM
OR
MeMgBr (3.0 equiv)
Et2O, , 3.5 h
78%
THF, , 3 h
87%
OTBDPS
(S)-9
(S)-10: R = TBDPS
(S)-11: R = H
TBAF (1.1 equiv)
THF, RT, 4 h
Tf2O (2.1 equiv), Et3N (5.0 equiv)
CH2Cl2, 78 °C
95%
RT, 15 min
(S)-12: R = Tf
NaH (2.0 equiv)
S
(2.5 equiv)
NMe2
OR
R
LiAlH4 (1.5 equiv)
SH
Cl
DMF, 85 °C, 24 h
95%
THF, RT, 7 h
96%
S
(R)-13: R = MOM
(R)-15: R =
(R)-5
98% ee
conc. HCl
MeOH, 70 °C, 15 h
O
S
NMe2
NMe2
99%
neat, 280 °C,
83%
(R)-14: R = H
50 min
O
(R)-16: R =
Scheme 2. Preparation of chiral thiolate ligand (R)-5.
We next applied the procedure, previously reported by Ohki
solvent. Measurements in C6D6 and CD2Cl2 led to
diastereomeric ratios of 80:20 and 60:40, respectively (reached
after 2 h in the indicated solvent). The major diastereomer in
C6D6 was (R,RuS)-17 as verified by 2D-NOESY experiments.
This diastereomer also gave suitable single crystals for X-ray
diffraction, allowing us to secure the molecular structure of
and Tatsumi for complexes [1]+[BArF ]–,[1] to thiol (R)-5 to obtain
4
the ruthenium chloride (R,RuRS)-17 precursor. Thiol (R)-5 was
deprotonated with n-BuLi and then combined with [Ru(p-
cymene)Cl2]2 in THF. After solvent change to toluene and
filtration, Et3P was added to furnish (R,RuRS)-17 [(R)-
5→(R,RuRS)-17]. As expected, the 1H NMR spectroscopic
analysis of this compound showed the formation of two
diastereomers whose ratio was found to be dependent on the
(R,RuS)-17 (Figure 1). Chloride abstraction with NaBArF then
4
afforded the coordinatively unsaturated 16-electron complex
[(R)-3]+[BArF ]– {(R,RuRS)-17→[(R)-3]+[BArF ]–}.
4
4
Scheme 3. Preparation of the chiral, coordinatively unsaturated Ru–S complex [(R)-3]+[BArF4]–.
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Scheme 4. 1H NMR spectroscopic analysis of the diastereoselective Si‒H
bond-activation step.[b,c] [a] Diastereomeric ratios were determined by
integration of the 1H NMR resonances of the protons bound to the tethered
aryl group. [b] Reactions were performed in sealed NMR tubes on a 10 μmol
scale. [c] Full assignment of all resonance signals was difficult due signal
overlapping and byproduct formation (selected spectra are given in the
Supporting Information).
We tested the new catalyst [(R)-3]+[BArF ]– in the asymmetric
4
hydrosilylation of N-aryl-substituted, acetophenone-derived
imines 19a‒19f (Table 1, entries 1‒6). All reactions were
performed at room temperature overnight, routinely employing
Me2PhSiH (18a) as the hydride source. Parent 19a was
converted into amine 20a in quantitative yield with 41% ee (entry
1). This moderate enantiomeric excess did not improve with
MePh2SiH (18b), essentially affording the amine with the same
level of enantioinduction (entry 2). As before in the reversible
Figure 1. Molecular structure of (R,RuS)-17. Thermal ellipsoids are shown at a
50% possibility level. Hydrogen atoms are omitted for clarity. Selected
interatomic distances (Å): Ru–S, 2.382(2), Ru–Cl, 2.410(2), Ru–P, 2.355(2).
For comparison, the distances of the chloride precursor of [1a]+ are as follows
(Å): Ru–S, 2.388(2), Ru–Cl, 2.489(2), Ru–P, 2.329(2).[1]
hydrosilane adduct formation with [(R)-3]+[BArF ]– (see Scheme
4
4), the influence of the substitution pattern at the silicon atom
had hardly any influence on the stereochemical outcome. An
increase of the steric bulk of the aryl group at the nitrogen atom
(phenyl versus xylyl) resulted in lower enantioinduction
(19b→20b, entry 3). Electronic modification of the aryl group
with either an OMe (as in 19c) or a CF3 group (as in 19d) shut
down the reaction (entries 4 and 5). Conversely, a bromine
substituent in the ortho position of the aryl group slowed down
the reaction without affecting the enantiomeric excess
(19e→20e, entry 6). Replacing the phenyl by the benzyl
protection group led to lower yield and poor enantiomeric excess
(19f→20f, entry 7).
The Si‒H bond activation by [(R)-3]+[BArF ]– was analyzed by
4
1H NMR spectroscopy to learn about the diastereoselectivity of
this syn addition.[2] For this, [(R)-3]+[BArF ]– was mixed with
4
excess of Me2PhSiH (18a) as well as MePh2SiH (18b) at room
temperature {[(R)-3]+→[syn-(R,RuS)-4]+ and [syn-(R,RuR)-4]+,
Scheme 4}. The resonance signals of the hydrosilane adducts
appeared to be too broad at 300 K but better resolution was
observed at 250 K. Adducts [syn-(R,RuS)-4]+ and [syn-(R,RuR)-4]+
formed with diastereomeric ratios of 70:30 for both 18a and 18b.
This shows that facial selectivity is indeed enforced by the chiral
thiolate ligand but ratios are moderate. However, attempts to
assign the relative configuration of the major diastereomer were
unsuccessful. 29Si NMR resonances of the adducts were in the
expected range: δ 29.2 ppm (major) and δ 25.9 ppm (minor) for
[syn-(R,RuS)-4a]+/[syn-(R,RuR)-4a]+ and δ 18.7 ppm (major) and δ
10.8 ppm (minor) for [syn-(R,RuS)-4b]+/[syn-(R,RuR)-4b]+. For
hydrosilane adducts [syn-(R,RuS)-4a+]/[syn-(R,RuR)-4a]+, the 31P
NMR resonances were shifted downfield to δ 40.7 ppm (major)
and δ 41.5 ppm (minor) relative to [(R)-3]+ (δ 23.0 ppm); [syn-
(R,RuS)-4b]+/[syn-(R,RuR)-4b]+ showed a single resonance at δ
40.5 ppm. As in previously reported similar experiments, the
reaction also yielded the corresponding disiloxanes and
Et3POSi+ adducts as byproducts.[2]
–
Table 1. Asymmetric hydrosilylation of imines catalyzed by [(R)-3]+[BArF
]
4
[a]
.
Entry
Imine
R
PG
Hydrosilane
Yield
[%][c]
ee
[%][d]
1
2
3
4
5
6
19a
19a
19b
19c
19d
19e
H
Ph
18a
18b
18a
18a
18a
18a
99
95
99
41
40
30
—
—
48
H
Ph
H
3,5-Xylyl
4-Anisyl
4-CF3C6H4
Ph
[e]
H
—
[f]
H
—
2-Br
70
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plates by Merck. Flash column chromatography was performed on silica
gel LC60A (40–63 µm) by Grace using the indicated solvents. 1H, 13C,
11B, 31P, and 29Si NMR spectra were recorded in CDCl3, C6D6, or CD2Cl2
on Bruker AV700, Bruker AV500 or Bruker AV400 instruments. Chemical
shifts are reported in parts per million (ppm) and are referenced to the
residual solvent resonance as the internal standard (CHCl3: δ 7.26 ppm
for 1H NMR and CDCl3: δ 77.16 ppm for 13C NMR, C6D5H: δ 7.16 ppm for
1H NMR and C6D6: δ 128.06 ppm for 13C NMR, CDHCl2: δ = 5.32 ppm for
1H NMR and CD2Cl2: δ = 53.84 ppm for 13C NMR).[14] Data are reported
as follows: chemical shift, multiplicity (br s = broad singlet, s = singlet, d =
doublet, t = triplet, q = quartet, m = multiplet, mc = centrosymmetric
multiplet), coupling constants (Hz), and integration. 1H,29Si HMQC NMR
spectra were measured with an optimized coupling constant of 7.0 Hz for
7
19f
H
Bn
18a
56
17
[a] Reactions were performed on a 0.1 mmol scale. [b] Hydrolysis of the N-
silylated amine during flash chromatography on silica gel, affording the free
amines. [c] Determined after purification by flash chromatography on silica
gel. [d] Determined by HPLC analysis using chiral stationary phases. [e]
Inseparable mixture. [f] N-silylated enamine as major component.
3
Conclusions
the JH,Si coupling. The peak intensities in the 1H,29Si HMQC NMR
spectra cannot be correlated to the amount of compound. Infrared (IR)
spectra were recorded on an Agilent Technologies Cary 630 FTIR
spectrophotometer equipped with an ATR unit and are reported as
wavenumbers [cm–1] (w = weak, m = medium, s = strong). Melting points
(m.p.) were determined with a Stuart Scientific SMP20 melting point
apparatus and are not corrected. Enantiomeric excesses were
determined by analytical high performance liquid chromatography
(HPLC) analysis on an Agilent Technologies 1200 Infinity instrument with
a chiral stationary phase using a Daicel Chiralcel OD-H or OJ-H column
(n-heptane/i-PrOH mixtures as solvents). Optical rotations were
measured on a Schmidt & Haensch Polatronic H532 polarimeter with []λ
values reported in 10–1 (° cm2 g–1); concentration c is in g/100 mL and λ =
589 nm. Mass spectrometry (MS) was obtained from the Analytical
Facility of the Institut für Chemie, Technische Universität Berlin.
We disclosed here the preparation, characterization, and
application of an Ohki–Tatsumi complex[1] with axial chirality in
the tethered thiolate backbone. For this, we elaborated, starting
from (S)-binol, an eleven-step synthesis of the corresponding
mesityl-substituted thiol that essentially is an axial chiral version
of the previously used terphenyl-type thiol. A thermal Newman–
Kwart rearrangement was employed to install the thiol group,
and no racemization was seen in that high-temperature step
(280 °C) as verified by comparison with an independently
prepared racemic sample. The tethered ruthenium chloride
complex made from this ligand is chiral at the ruthenium center
and showed solvent-dependent epimerization at the ruthenium
center. The molecular structure of the major diastereomer was
confirmed by X-ray diffraction. This catalyst precursor was
transformed into the active catalyst by chloride abstraction with
General Procedure for Enantioselective Reduction of Imines
In a glove box, a flame-dried GLC vial equipped with a magnetic stir bar
NaBArF . The resulting coordinatively unsaturated ruthenium
–
was charged with [(R)-3]+[BArF
]
4
(1.00 mol%) and the indicated imine
4
complex with its Ru–S bond engages in reversible heterolytic
splitting of the Si–H bond of moderately hindered hydrosilanes.
The addition of the Si–H bond across the Ru–S bond proceeds
in syn fashion[2] but the facial selectivity is rather low (d.r. =
70:30). The thus-generated diastereomeric chiral-at-ruthenium
hydrosilane adducts were applied to catalytic imine
hydrosilylation but enantioinduction (40% ee) was at best
promising. One challenge could be that there is no bonding
interaction between the neutral ruthenium hydride and the
silyliminium ion in the enantioselectivity-determining hydride
transfer.[7] This work is nevertheless proof of concept for
asymmetric catalysis involving cooperative Si–H bond activation.
(1.00 equiv). C6H6 (0.10 mL) was added, and the vial was closed with a
rubber septum cap. Either Me2PhSiH (18a) or MePh2SiH (18b) (1.10
equiv) was added dropwise through the cap, and the resulting reaction
mixture was maintained at room temperature for the indicated time. The
vial was removed from the glove box and the reaction was quenched by
the addition of a solution of cyclohexane and tert-butyl methyl ether
(90:10) containing 4% Et3N (0.5 mL). The resulting solution was filtered
through a pad of Celite® coated by a small layer of silica gel with a
solution of cyclohexane and tert-butyl methyl ether (90:10) containing 4%
Et3N (3–4 mL). Solvents are removed under reduced pressure, and the
residue is purified by flash column chromatography on silica gel using the
indicated cyclohexane/ethyl acetate mixtures. The procedure affords the
amines as colorless to yellow oils.
(S)-tert-Butyl((3'-(2,4,6-trimethylphenyl)-2'-(methoxymethoxy)-[1,1'-
binaphthalen]-2-yl)oxy)diphenylsilane (10)
Experimental Section
Aryl iodide (S)-9 (7.65 g, 11.0 mmol, 1.00 equiv) and NiCl2(PPh3)2 (544
mg, 0.770 mmol, 0.07 equiv) were dissolved in Et2O (70 mL). Freshly
prepared 2,4,6-trimethylphenylmagnesium bromide (1.00M in Et2O, 17.6
mL, 17.6 mmol, 1.60 equiv) was added dropwise, and the resulting
solution was stirred for 10 min at room temperature followed by heating
at reflux for 3.5 h. As TLC analysis indicated complete consumption of
the starting material, the reaction mixture was allowed to cool to room
temperature and was quenched by addition of saturated aqueous NH4Cl
solution (30 mL). The phases were separated, and the aqueous phase
was extracted with Et2O (3 × 50 mL). The combined organic extracts
were dried over Na2SO4 and concentrated under reduced pressure.
Purification by flash column chromatography on silica gel using
cyclohexane/CH2Cl2 (10:1 to 5:1) afforded (S)-10 (5.9 g, 78%) as a
General Remarks.
All reactions were performed in flame-dried glassware using an MBraun
glove box or conventional Schlenk techniques under a static pressure of
argon or nitrogen. Liquids and solutions were transferred with syringes.
Solvents (THF, toluene, C6H6, Et2O, DMF, and CH2Cl2) were dried and
purified following standard procedures. Technical grade solvents for
extraction or chromatography (tert-butyl methyl ether, CH2Cl2,
cyclohexane, and ethyl acetate) were distilled prior to use. C6D6, CD2Cl2,
and CDCl3 (purchased from Eurisotop) were degassed by three freeze–
pump–thaw cycles and dried over 4 Å molecular sieves. Imines 19a–19f
were synthesized according to reported procedures.[13] Analytical thin
layer chromatography (TLC) was performed on silica gel 60 F254 glass
gummy solid. m.p.: 98 °C (tert-butyl methyl ether); Rf
= 0.62
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(cyclohexane/tert-butyl methyl ether 5:1); IR (ATR): nu(tilde) = 3526 (w),
3050 (w), 2928 (w), 2855 (w), 1590 (m), 1427 (m), 1242 (m), 997 (s), 810
(s) cm‒1; HRMS (APCI) calculated for C46H43O2Si [M–OMe]+: 665.3032;
found: 665.3008; 1H NMR (500 MHz, C6D6): δ 0.66 (s, 9H), 2.24 (s, 3H),
2.35 (s, 3H), 2.36 (s, 3H), 2.38 (s, 3H), 4.48 (d, J = 5.7 Hz, 1H), 4.78 (d, J
= 5.7 Hz, 1H), 6.95 (d, J = 16.8 Hz, 2H), 7.10–7.13 (m, 3H), 7.17–7.23 (m,
8H), 7.29 (d, J = 9.0 Hz, 1H), 7.52 (d, J = 8.1 Hz, 1H), 7.58 (d, J = 8.5 Hz,
1H), 7.64 (s, 1H), 7.66 (d, J = 8.5 Hz, 1H), 7.70 (d, J = 8.1 Hz, 1H), 7.81–
7.83 (m, 2H), 7.88–7.86 ppm (m, 2H); 13C{1H} NMR (126 MHz, C6D6): δ
19.2 (s), 21.0 (s), 21.2 (s), 21.5 (s), 26.3 (s, 3C), 55.5 (s), 98.7 (s), 120.5
(s), 122.2 (s), 124.1 (s), 125.3 (s), 126.1 (s), 126.3 (s), 126.7 (s), 126.8
(s), 127.3 (s), 128.2 (s, 2C), 128.2 (s, 3C), 128.3 (s), 128.4 (s), 128.6 (s),
129.3 (s), 129.7 (s), 130.3 (s), 130.3 (s), 130.6 (s), 131.8 (s), 133.0 (s),
133.4 (s), 134.3 (s), 135.0 (s), 135.6 (s), 136.0 (s, 2C), 136.0 (s, 2C),
136.4 (s), 136.8 (s), 136.8 (s), 137.4 (s), 151.3 (s), 151.7 (s) ppm.
bromide (3.0M in Et2O, 4.0 mL, 12 mmol, 3.0 equiv) was added dropwise,
and the resulting solution was stirred for 10 min at room temperature
followed by heating at reflux for 3 h. As TLC analysis indicated complete
consumption of the starting material, the reaction mixture was allowed to
cool to room temperature and was quenched by addition of saturated
aqueous NH4Cl solution (20 mL). The phases were separated, and the
aqueous phase was extracted with Et2O (3 × 40 mL). The combined
organic extracts were dried over Na2SO4 and concentrated under
reduced pressure. Purification by flash column chromatography on silica
gel using cyclohexane/tert-butyl methyl ether (50:1 to 25:1) afforded (R)-
13 (1.55 g, 87%) as a gummy solid. m.p.: 72 °C (tert-butyl methyl ether);
Rf = 0.45 (cyclohexane/tert-butyl methyl ether 50:1); IR (ATR): nu(tilde) =
3522 (w), 3047 (w), 2915 (w), 2243 (w), 2108 (w), 2083 (w), 1907 (w),
1610 (w), 1434 (m), 1376 (w), 1151 (m), 987 (s), 905 (m), 810 (m), 729
(s) cm‒1; HRMS (EI) calculated for C31H27O [M–OCH3]+: 415.2062; found:
415.2052; [α]DRT: ‒45.8 (c 0.70, CHCl3); 1H NMR (400 MHz, CDCl3): δ
2.16 (s, 3H), 2.22 (s, 6H), 2.25 (s, 3H), 2.34 (s, 3H), 4.16 (d, J = 5.6 Hz,
1H), 4.23 (d, J = 5.6 Hz, 1H), 6.97 (s, 2H), 7.12 (d, J = 8.4 Hz, 1H), 7.22–
7.28 (m, 4H), 7.38–7.44 (m, 2H) 7.74 (s, 1H), 7.86–7.89 ppm (m, 3H);
13C{1H} NMR (100 MHz, CDCl3): δ 20.7 (s), 20.9 (s), 21.1 (s), 21.2 (s),
55.7 (s), 97.9 (s), 124.9 (s), 125.2 (s), 125.9 (s), 126.2 (s), 126.3 (s, 2C),
127.8 (s), 128.0 (s), 128.0 (s), 128.2 (s), 128.3 (s), 128.8 (s), 129.0 (s),
130.7 (s), 131.2 (s), 132.2 (s), 132.6 (s), 133.2 (s), 133.7 (s), 134.9 (s),
135.6 (s), 135.6 (s), 136.8 (s), 137.0 (s), 137.0 (s), 151.1 (s) ppm.
(S)-3'-(2,4,6-Trimethylphenyl)-2'-(methoxymethoxy)-[1,1'-
binaphthalen]-2-ol (11)
To a stirred solution of (S)-10 (5.8 g, 8.4 mmol, 1.0 equiv) and THF (50
mL), TBAF (2.9 g, 9.3 mmol, 1.1 equiv) was added. The resulting mixture
was stirred at room temperature for 4 h and quenched by the addition of
H2O (50 mL). The aqueous phase was extracted with tert-butyl methyl
ether (3 × 50 mL). The combined organic extracts were dried over
Na2SO4, and the solvent was removed under reduced pressure. The title
compound (S)-11 was isolated along with TBDPSOH and used without
further purification.
(R)-3-(2,4,6-Trimethylphenyl)-2'-methyl-[1,1'-binaphthalen]-2-ol (14)
(R)-13 (3.4 g, 7.6 mmol, 1.0 equiv) was dissolved in a mixture of CHCl3
(45 mL) and methanol (30 mL). Concentrated aqueous HCl solution (8
mL) was added, and the resulting reaction mixture heated at 70 °C for 15
h. After the mixture was allowed to cool to room temperature, the
solvents were removed under reduced pressure. The residue was
dissolved in CH2Cl2 (40 mL), H2O (40 mL) was added, the layers were
separated, and the aqueous solution was extracted with CH2Cl2 (3 × 40
mL). The combined organic extracts were dried over Na2SO4 and
concentrated under reduced pressure. Purification by filtration over silica
gel using cyclohexane/tert-butyl methyl ether (25:1) afforded (R)-14 (3.05
g, 99%) as a white solid. m.p.: 108 °C (cyclohexane); Rf = 0.58
(cyclohexane/tert-butyl methyl ether 5:1); IR (ATR): nu(tilde) = 3471 (m),
3048 (w), 2914 (m), 2854 (w), 1614 (w), 1498 (m), 1425 (m), 1376 (m),
1237 (m), 1193 (m), 1140 (m), 1026 (m), 940 (m), 849 (m), 811 (s), 744
(s), 681 (m) cm‒1; HRMS (EI) calculated for C30H26O [M]+: 402.1984;
found: 402.1977; [α]DRT: ‒61.6 (c 1.25, CHCl3); 1H NMR (500 MHz,
CDCl3): δ 2.13 (s, 3H), 2.16 (s, 3H), 2.21 (s, 3H), 2.36 (s, 3H), 4.75 (br s,
1H), 7.02–7.04 (m, 3H), 7.23–7.26 (m, 1H), 7.30 (d, J = 3.9 Hz, 2H), 7.36
(mc, 1H), 7.41–7.47 (m, 1H), 7.56 (d, J = 8.4 Hz, 1H), 7.71 (s, 1H), 7.87
(d, J = 8.1 Hz, 1H), 7.93 ppm (t, J = 7.5 Hz, 2H); 13C{1H} NMR (126 MHz,
CDCl3): δ 20.3 (s), 20.6 (s), 20.6 (s), 21.3 (s), 118.3 (s), 123.7 (s), 124.8
(s), 125.4 (s), 125.6 (s), 126.5 (s), 126.7 (s), 128.2 (s), 128.3 (s), 128.6 (s,
2C), 128.7 (s), 129.0 (s), 129.4 (s), 129.4 (s), 129.8 (s), 130.2 (s), 132.6
(s), 133.3 (s), 133.4 (s), 133.4 (s), 136.5 (s), 137.2 (s), 137.3 (s), 137.7
(s), 148.8 (s) ppm.
(S)-3'-(2,4,6-Trimethylphenyl)-2'-(methoxymethoxy)-[1,1'-
binaphthalen]-2-yl Trifluoromethanesulfonate (12)
To a solution of (S)-11 (65 wt%, 5.85 g, 8.43 mmol, 1.00 equiv) in CH2Cl2
(60 mL) cooled to –78 °C, Et3N (6.0 mL, 42 mmol, 5.0 equiv) and
subsequently trifluoromethanesulfonic anhydride (3.0 mL, 18 mmol, 2.1
equiv) were added. The cooling bath was removed after 10 min, and the
mixture was allowed to warm within 15 min. As TLC analysis indicated
complete consumption of the starting material, the reaction was
quenched with H2O (50 mL). After extraction of the aqueous phase, the
combined organic extracts were dried over Na2SO4 and concentrated
under reduced pressure. Purification of the residue by flash column
chromatography on silica gel using cyclohexane/CH2Cl2 (8:1 to 5:1) as
eluent afforded (S)-12 (4.7 g, 95% over two steps) as a gummy solid.
m.p.: 84 °C (tert-butyl methyl ether); Rf = 0.5 (cyclohexane/tert-butyl
methyl ether 10:1); IR (ATR): nu(tilde) = 3518 (w), 2920 (w), 1592 (w),
1495 (w), 1418 (m), 1205 (s), 1137 (m), 1076 (m), 989 (m), 939 (s), 831
(s), 748 (m), 675 (m) cm‒1; HRMS (EI) calculated for C31H24F3O4S [M–
OCH3]+: 549.1347; found: 549.1345; [α]DRT: +38.8 (c 0.70, CHCl3); 1H
NMR (500 MHz, CDCl3): δ 2.17 (s, 3H), 2.18 (s, 3H), 2.19 (s, 3H), 2.34 (s,
3H), 4.20 (s, 2H), 6.79 (d, J = 5.1 Hz, 2H), 7.15 (d, J = 8.5 Hz, 1H), 7.29
(mc, 1H), 7.40–7.46 (m, 3H), 7.54–7.57 (m, 1H), 7.61 (d, J = 9.1 Hz, 1H),
7.80 (s, 1H), 7.88 (d, J = 8.2 Hz, 1H), 7.97 (d, J = 8.2 Hz, 1H), 8.05 ppm
(d, J = 9.1 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3): δ 20.5 (s), 21.13 (s),
1
21.24 (s), 55.7 (s), 98.1 (s), 118.4 (q, JC,F = 320.1 Hz), 119.6 (s), 122.8
(R)-O-(3-(2,4,6-Trimethylphenyl)-2'-methyl-[1,1'-binaphthalen]-2-yl)
Dimethylcarbamothioate (15)
(s), 125.4 (s), 126.1 (s), 126.5 (s), 127.1 (s), 127.4 (s), 127.5 (s), 127.7
(s), 128.0 (s), 128.2 (s), 128.3 (s), 128.4 (s), 130.5 (s), 131.0 (s), 132.4
(s), 132.5 (s), 133.1 (s), 134.1 (s), 134.4 (s), 135.1 (s), 136.4 (s), 137.3
(s), 137.8 (s), 145.9 (s), 151.8 (s) ppm.
To a stirred solution of (R)-14 (1.55, 3.86 mmol, 1.00 equiv) and DMF (16
mL) cooled to 0 °C, sodium hydride (60% dispersion in mineral oil, 306
mg, 7.75 mmol, 2.00 equiv) was added. After stirring at room
temperature for 1.5 h, a solution of dimethylthiocarbomyl chloride (1.23 g,
9.65 mmol, 2.50 equiv) and DMF (3 mL) was added dropwise. The
resulting reaction mixture was heated at 85 °C for 24 h. After cooling to
room temperature, the reaction was quenched with an aqueous KOH
solution (2 wt%, 40 mL), and the resulting aqueous phase extracted with
(R)-3-(2,4,6-Trimethylphenyl)-2-(methoxymethoxy)-2'-methyl-1,1'-
binaphthalene (13)
(S)-12 (2.32 g, 4.00 mmol, 1.00 equiv) and NiCl2(dppe) (0.21 g, 0.40
mmol, 0.10 equiv) were dissolved in THF (32 mL). Methylmagnesium
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10.1002/chem.201700304
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ethyl acetate (3 × 40 mL). The combined organic extracts were dried over
Na2SO4 and concentrated under reduced pressure. Purification by flash
column chromatography on silica gel using cyclohexane/tert-butyl methyl
ether (50:1 to 20:1) afforded (R)-15 (1.79 g, 95%) as a white solid. m.p.:
112 °C (cyclohexane); Rf = 0.23 (cyclohexane/tert-butyl methyl ether
50:1); IR (ATR): nu(tilde) = 3044 (w), 2920 (m), 2847 (w), 1522 (m), 1446
(m), 1389 (m), 1284 (m), 1190 (m), 1136 (s), 849 (m), 810 (m), 743 (m)
cm‒1; HRMS (EI) calculated for C33H32NOS [M+H]+: 490.2199; found:
490.2193. 1H NMR (400 MHz, CDCl3): δ 2.04–2.76 (m, 18H), 6.87–6.97
(m, 2H), 7.08–7.62 (m, 7H), 7.78–7.95 ppm (m, 4H); 13C{1H} NMR (100
MHz, CDCl3): Two sets of signals are seen for this compound (see the
Supporting Information for copies of NMR spectra).
Ruthenium Chloride Complex (R,RuRS)-17
n-BuLi (1.58M in hexanes, 0.280 mL, 0.400 mmol, 1.00 equiv) was slowly
added to a solution of (R)-5 (167 mg, 0.400 mmol, 1.00 equiv) in THF (4
mL) at 0 °C. After 30 min, the orange solution was added dropwise to a
suspension of di-μ-chloridobis[chlorido(η6-p-cymene)ruthenium(II)] (122
mg, 0.200 mmol, 0.500 equiv) in THF (4 mL) at 0 °C. The resulting blue
suspension was stirred for 3 h at room temperature. All solvents were
removed under reduced pressure, and the residue was dissolved in
toluene (15 mL). Salts formed during the reaction were removed by
filtration under inert atmosphere, toluene (6 mL) and triethylphosphine
(10 wt% solution in n-hexane, 708 mg, 0.600 mmol, 1.50 equiv) were
added to the filtrate to form a red solution which was maintained at
100 °C for 3 d. The solvent was removed under reduced pressure and
the crude material was purified by recrystallization from toluene–n-
pentane to furnish ruthenium complex (R,RuRS)-17 (174 mg, 65%) as a
red powder. HRMS (ESI) calcd for C36H40PSRu [M‒Cl]+: 637.1632,
Found: 637.1636; NMR spectroscopic data major diastereomer: 1H NMR
(500 MHz, CD2Cl2): δ 0.83 (dt, J = 14.6 Hz, J = 7.6 Hz, 9H), 1.56‒1.69 (m,
3H), 1.72‒1.88 (m, 3H), 1.96 (s, 3H), 2.12 (d, J = 3.0 Hz, 3H), 2.17 (s,
3H), 2.21 (s, 3H), 5.27 (s, 1H), 5.56 (s, 1H), 6.84 (d, J = 8.2 Hz, 1H), 7.05
(d, J = 8.2 Hz, 1H), 7.09‒7.17 (m, 3H), 7.34 (mc, 1H), 7.55 (d, J = 8.6 Hz,
1H), 7.63 (s, 1H), 7.88 ppm (mc, 3H); Selected carbon signals
determined by 2D NMR spectra 13C{1H} NMR (125 MHz, CD2Cl2): δ 7.9
(s), 17.3 (s), 17.8 (s), 18.0 (s), 18.3 (s), 20.2 (s), 86.2 (s), 102.2 (s) ppm;
31P{1H} NMR (202 MHz, CD2Cl2): δ 22.9 ppm; Minor diastereomer: 1H
NMR (500 MHz, CD2Cl2): δ 1.00 (dt, J = 14.6 Hz, J = 7.6 Hz, 9H),
1.72‒1.88 (m, 3H), 1.88‒1.97 (m, 3H) 1.90 (s, 3H), 2.01 (s, 3H), 2.16 (d,
J = 3.1 Hz, 3H), 2.19 (s, 3H), 5.27 (s, 1H), 5.53 (s, 1H), 6.83 (d, J = 8.6
Hz, 1H), 7.09‒7.17 (d, underneath multiplet, 1H), 7.22‒7.27 (m, 3H), 7.40
(mc, 1H), 7.52 (d, J = 8.4 Hz, 1H), 7.84 (s, 1H), 7.72‒7.83 ppm (mc, 3H);
Selected carbon signals determined by 2D NMR spectra 13C{1H} NMR
(125 MHz, CD2Cl2): δ 8.0 (s), 17.9 (s), 18.1 (s), 18.2 (s), 20.0 (s), 84.8 (s),
102.4 (s) ppm; 31P{1H} NMR (202 MHz, CD2Cl2): δ 21.7 ppm; The
crystallographic data is available online in the CCDC database under
number CCDC 1515411.
(R)-S-(3-(2,4,6-Trimethylphenyl)-2'-methyl-[1,1'-binaphthalen]-2-yl)
Dimethylcarbamothioate (16)
(R)-15 (845 mg, 1.72 mmol, 1.00 equiv) was heated with constant
rotation (50 rpm) at 280 °C in a Kugelrohr apparatus. Purification of the
crude reaction mixture by flash column chromatography on silica gel
using cyclohexane/tert-butyl methyl ether (50:1 to 20:1 respectively)
afforded (R)-16 (700 mg, 83%) as
a white solid. m.p.: 94 °C
(cyclohexane); Rf = 0.21 (cyclohexane/tert-butyl methyl ether 10:1); IR
(ATR): nu(tilde) = 2917 (m), 2848 (w), 1664 (vs), 1445 (m), 1356 (m),
1257 (m), 1084 (m), 849 (w), 809 (m), 744 (m), 684 (m) cm‒1; HRMS (EI)
calculated for C33H32NOS [M+H]+: 490.2205; found: 490.2192. [α]D
:
RT
‒164.7 (c 0.95, CHCl3); 1H NMR (400 MHz, CDCl3): δ 2.15‒2.16 (m, 6H),
2.21 (s, 3H), 2.24‒2.40 (m, 9H), 6.97 (s, 2H), 7.16 (d, J = 8.5 Hz, 1H),
7.21‒7.31 (m, 3H), 7.36‒7.43 (m, 1H), 7.46‒7.56 (m, 2H), 7.83 (s, 1H),
7.85‒7.95 ppm (m, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 20.7 (s), 21.0
(s), 21.1 (s), 21.3 (s), 36.9 (br s, 2C), 126.0 (s), 126.0 (s), 126.5 (s),
126.7 (s), 126.9 (s), 127.0 (s), 127.7 (s), 127.7 (s), 128.0 (s), 128.0 (s),
128,1 (s), 128.8 (s), 129.4 (s), 129.9 (s), 132.0 (s), 132.4 (s), 133.1 (s),
134.1 (s), 135.1 (s), 135.5 (s), 136.7 (s), 137.0 (s), 137.1 (s), 138.1 (s),
143.0 (s), 144.4 (s), 165.1 (s) ppm.
(R)-3-(2,4,6-Trimethylphenyl)-2'-methyl-[1,1'-binaphthalene]-2-thiol
(5)
–
Ruthenium Complex [(R)-3]+[BArF
]
4
To a stirred solution of (R)-16 (1.20 g, 2.45 mmol, 1.00 equiv) and THF
(20 mL) cooled to 0 °C, LiAlH4 (136 mg, 3.68 mmol, 1.50 equiv) was
added, and the resulting reaction mixture was maintained at room
temperature for 7 h. As TLC analysis indicated complete consumption of
the starting material, the reaction was cooled to 0 °C, diluted with Et2O
(10 mL), and carefully quenched with aqueous HCl (2 N, 5 mL). After
extraction of the crude reaction mixture with Et2O (3 × 40 mL), the
combined organic extracts were dried over Na2SO4, and concentrated
under reduced pressure. Purification by flash column chromatography on
silica gel using cyclohexane/tert-butyl methyl ether (20:1) afforded (R)-5
(0.98 g, 96%) with 98% ee as a white solid. m.p.: 109 °C (cyclohexane);
Rf = 0.65 (cyclohexane/tert-butyl methyl ether 10:1); IR (ATR): nu(tilde) =
3049 (w), 2944 (w), 2913 (m), 2853 (w), 2555 (w), 1610 (w), 1438 (m),
1389 (m), 1097 (m), 849 (m), 809 (s), 743 (s) cm‒1; HRMS (EI) calculated
for C30H26S [M]+: 418.1755; found: 418.0803; [α]DRT: ‒69.8 (c 0.95,
CHCl3); 1H NMR (500 MHz, CDCl3): δ 2.11 (s, 3H), 2.15 (s, 3H), 2.16 (s,
3H), 2.38 (s, 3H), 3.10 (s, 1H), 6.99 (d, J = 8.5 Hz, 1H), 7.04 (s, 2H), 7.18
(d, J = 8.4 Hz, 1H), 7.21‒7.34 (m, 2H), 7.38‒7.48 (m, 2H), 7.56 (d, J =
8.4 Hz, 1H), 7.70 (s, 1H), 7.86 (d, J = 8.1 Hz, 1H), 7.93 ppm (mc, 2H);
13C{1H} NMR (126 MHz, CDCl3): δ 20.0 (s), 20.4 (s), 20.5 (s), 21.4 (s),
125.2 (s), 125.3 (s, 2C) 125.4 (s), 126.7 (s), 126.7 (s), 128.1 (s), 128.2
(s), 128.3 (s), 128.5 (s), 128.6 (s), 128.6 (s), 129.1 (s), 131.8 (s), 132.4 (s,
2C), 132.6 (s), 132.9 (s), 133.2 (s), 134.6 (s), 135.3 (s), 136.8 (s), 136.8
(s), 137.2 (s), 137.4 (s), 137.8 (s) ppm; HPLC (Daicel Chiralcel OD-H,
20 °C, n-heptane/i-PrOH 99/1, flow rate 0.7 mL/min, λ = 254 nm): tR = 6.9
min (minor 5), tR = 7.6 min (major 5).
Chloride complex (R,RuRS)-17 (67 mg, 0.10 mmol, 1.0 equiv) and
NaBArF (89 mg, 0.10 mmol, 1.0 equiv) were suspended in CH2Cl2 (8
4
mL). After stirring the dark blue reaction mixture for 2 h, the precipitate
was filtered off under inert atmosphere, and the solvent was removed
–
under vacuum, yielding the ruthenium thiolate complex [(R)-3]+[BArF
]
4
(115 mg, 77%) as a blue powder. HRMS (ESI) calcd for C36H40PSRu+
[M‒BAr4F]+: 637.1626, Found: 637.1631; 1H NMR (500 MHz, CD2Cl2): δ
0.92 (dt, J = 17.3 Hz, J = 7.6 Hz, 9H), 1.73‒1.86 (m, 6H), 1.93 (s, 3H),
2.01 (s, 3H), 2.09 (s, 3H), 2.39 (s, 3H), 4.97 (s, 2H), 7.07 (d, J = 9.0 Hz,
1H), 7.20‒7.29 (m, 2H), 7.29‒7.45 (m, 2H), 7.52 (d, J = 8.5 Hz, 1H), 7.56
(s, 4H), 7.71 (mc, 10H), 7.90‒7.97 (m, 2H), 8.10 (d, J = 8.2 Hz, 1H), 8.28
ppm (s, 1H); Selected signals for 13C{1H} NMR (125 MHz, CD2Cl2): δ 8.4
(s), 18.0 (d, J = 27.8 Hz), 19.4 (s), 20.3 (s), 20.4 (s), 73.3 (s), 117.9 (m),
121.7 (s), 123.9 (s), 125.5 (s), 125.6 (s), 126.1 (s), 126.9 (s), 128.6 (s),
129.1 (s), 129.2 (m), 129.3 (m), 135.2 (s), 162.2 (q, J = 49.3 Hz) ppm;
31P{1H} NMR (202 MHz, CD2Cl2): δ 23.0 ppm; 11B{1H} NMR (161 MHz,
CD2Cl2): δ ‒6.6 ppm.
Acknowledgements
This
research
was
supported
by
the
Deutsche
Forschungsgemeinschaft (Oe 249/10-1) and in part by the
Cluster of Excellence Unifying Concepts in Catalysis (EXC
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10.1002/chem.201700304
Chemistry - A European Journal
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prolonged reaction times, these are hydrogenated in the presence of
[1]+[BArF4]– by the released dihydrogen gas.[7,8]
314/2). M.O. is indebted to the Einstein Foundation (Berlin) for
an endowed professorship. We thank Dr. Hendrik F. T. Klare
and Susanne Bähr for insightful discussions (both TU Berlin).
[6]
[7]
C. D. F. Königs, H. F. T. Klare, M. Oestreich, Angew. Chem. Int. Ed.
2013, 52, 10076–10079.
For a synthetic and mechanistic study of hydrogenation catalyzed by
[1a]+[BArF4]–, see: A. Lefranc, Z.-W. Qu, S. Grimme, M. Oestreich,
Chem. Eur. J. 2016, 22, 10009‒10016.
Keywords: asymmetric catalysis • homogeneous catalysis •
hydrosilylation • Lewis acids • Si–H bond activation
[8]
[9]
For an in-depth investigation of this dehydrogenation‒hydrogenation
sequence, see: S. Bähr, M. Oestreich, Organometallics 2017, 36, DOI:
10.1021/acs.organomet.7b00030.
[1]
[2]
[3]
Y. Ohki, Y. Takikawa, H. Sadohara, C. Kesenheimer, B. Engendahl, E.
Kapatina, K. Tatsumi, Chem. Asian J. 2008, 3, 1625–1635.
For a summary of imine hydrosilylation, see: O. Riant, in Modern Re-
duction Methods; (Eds.: P. G. Andersson, I. Munslow), Wiley-VCH:
Weinheim, Germany, 2008; pp 321−337.
T. Stahl, P. Hrobárik, C. D. F. Königs, Y. Ohki, K. Tatsumi, S. Kemper,
M. Kaupp, H. F. T. Klare, M. Oestreich, Chem. Sci. 2015, 6, 4324–4334.
For selected reviews of chiral-at-metal complexes related to catalysis,
see: a) E. B. Bauer, Chem. Soc. Rev. 2012, 41, 3153–3167; b) C.
Ganter, Chem. Soc. Rev. 2003, 32, 130–138; c) H. Brunner, Angew.
Chem. Int. Ed. 1999, 38, 1194–1208.
[10] a) T. Ikariya, K. Murata, R. Noyori, Org. Biomol. Chem. 2006, 4, 393–
406; b) R. Noyori, S. Hashiguchi, Acc. Chem. Res. 1997, 30, 97–102.
[11] a) A. M. Hayes, D. J. Morris, G. J. Clarkson, M. Wills, J. Am. Chem.
Soc. 2005, 127, 7318–7319; b) F. K. K. Cheung, A. M. Hayes, J.
Hannedouche, A. S. Y. Yim, M. Wills, J. Org. Chem. 2005, 70, 3188–
3197; c) D. J. Morris, A. M. Hayes, M. Wills, J. Org. Chem. 2006, 71,
7035–7044; d) R. Soni, K. E. Jolley, G. J. Clarkson, M. Wills, Org. Lett.
2013, 15, 5110–5113; e) R. Hodgkinson, V. Jurčík, A. Zanotti-Gerosa,
H. G. Nedden, A. Blackaby, G. J. Clarkson, M. Wills, Organometallics
2014, 33, 5517–5524.
[4]
a) H. F. T. Klare, M. Oestreich, J.-i. Ito, H. Nishiyama, Y. Ohki, K.
Tatsumi, J. Am. Chem. Soc. 2011, 133, 3312–3315; b) C. D. F. Königs,
H. F. T. Klare, Y. Ohki, K. Tatsumi, M. Oestreich, Org. Lett. 2012, 14,
2842–2845; c) C. D. F. Königs, M. F. Müller, N. Aiguabella, H. F. T.
Klare, M. Oestreich, Chem. Commun. 2012, 49, 1506–1508; d) J.
Hermeke, H. F. T. Klare, M. Oestreich, Chem. Eur. J. 2014, 20, 9250–
9254; e) S. Wübbolt, M. Oestreich, Angew. Chem. Int. Ed. 2015, 54,
15876–15879.
The 1,4-selective reduction of pyridines[6] has been the only true
hydrosilylation promoted by catalysts [1]+[BArF4]–. Enolizable imines[4d]
and, likewise, ketones[4b] do undergo dehydrogenative couplings,
yielding N-silyl enamines and silyl enol ethers, respectively. At
[12] E. Tayama, A. Saito, T. Ooi, K. Maruoka, Tetrahedron 2002, 58, 8307–
8312.
[5]
[13] F.-M. Gautier, S. Jones, S. J. Martin, Org. Biomol. Chem. 2009, 7,
229‒231.
[14] A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A. Nudelman, B. M. Stoltz,
J. E. Bercaw, K. I. Goldberg, G. R. Fulmer, Organometallics 2010, 29,
2176–2179.
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FULL PAPER
Suggestion for the Entry for the Table of Contents
FULL PAPER
Chiral spine. The preparation of an
axial chiral version of the bulky 2,6-
dimesitylphenyl group attached to
sulfur is reported. This new thiol ligand
is used for the formation of a tethered
ruthenium complex (see scheme)
suitable for stereocontrolled Si‒H
bond activation. Its application as a
chiral catalyst in imine hydrosilylation
leads to moderate but promising
enantioinduction.
S. Wübbolt, M. S. Maji, E. Irran, M.
Oestreich*
Page No. – Page No.
A Tethered Ru–S Complex with an
Axial Chiral Thiolate Ligand for
Cooperative Si‒H Bond Activation:
Application to Enantioselective Imine
Reduction
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