Development of catalysts for the stereoselective hydrogenation of α,β-unsaturated ketones

Article abstract of DOI:10.1021/jo300246c

Iridium phosphinitoxazoline complexes were found to be new efficient catalysts for the asymmetric hydrogenation of arylated α,β- unsaturated ketones. Linear as well as cyclic substrates are hydrogenated with similar success, giving selectivities of up to 99.7% ee.

Full text of DOI:10.1021/jo300246c

Note
pubs.acs.org/joc
Development of Catalysts for the Stereoselective Hydrogenation of
α,β-Unsaturated Ketones
Frauke Maurer, Volker Huch, Angelika Ullrich, and Uli Kazmaier*
Institute for Organic Chemistry, Saarland University, Building C4.2, D-66123 Saarbruecken, Germany
S
* Supporting Information
ABSTRACT: Iridium phosphinitoxazoline complexes were
found to be new efficient catalysts for the asymmetric
hydrogenation of arylated α,β-unsaturated ketones. Linear as
well as cyclic substrates are hydrogenated with similar success,
giving selectivities of up to 99.7% ee.
symmetric hydrogenations belong to the most important
catalytic processes for the synthesis of optically active
hydroxyalkyl)oxazolines 1.39 These can be obtained by a
Passerini-type reaction of hydroxyisonitriles40 and aldehydes
such as pivaldehyde (Scheme 1). The products are obtained as
A
compounds. Their high efficiency, ecofriendliness, and cost−
benefit ratio made them one of the best investigated methods in
the last 40 years.1 The homogeneous hydrogenation of
functionalized alkenes containing an additional coordinating
group (except the alkene) started in 1965 with the rhodium
catalyst Rh(PPh3)3Cl, developed by Wilkinson2,3 and Coffey.4
First asymmetric versions were reported two years later
independently by Horner5 and Knowles.6 In 1977, Knowles
introduced the bidentate P-stereogenic phosphine ligand
DIPAMP, which allowed the stereoselective hydrogenation of
α-acylaminoacrylates with up to 96% ee.7 This process was used
as a key step in the synthesis of Dopa, the first industrially
applied asymmetric hydrogenation.8,9 In the meantime, a wide
range of other ligands have been developed for not only Rh-
but also Ru-catalyzed processes.10−14 Nevertheless, the
asymmetric hydrogenation of nonfunctionalized alkenes was a
challenge for a long time.15
In 1977, Crabtree described the first homogeneous achiral
iridium catalyst which allowed the reduction of a wide range of
unfunctionalized, also highly substituted, alkenes.16,17 On the
basis of this pioneering work, Pfaltz et al. developed a new class
of hydrogenation catalysts, based on bidentate P,N-ligands, the
so-called PHOX ligands.18,19 These ligands gave already
excellent selectivities in various Pd-catalyzed reactions, such
as allylic alkylations or Heck reactions.20−23 The Ir complexes
were highly active in the asymmetric hydrogenation of
unfunctionalized alkenes, providing excellent ee’s.24 During
the past decade, the family of the PHOX and related ligands
improved significantly, and today a wide range of unfunction-
alized alkenes can be hydrogenated with up to 99% ee.25−34
In 2008, Bolm35,36 and Hou37,38 more or less simultaneously
reported that the Ir-catalyzed enantioselective hydrogenation is
also a suitable protocol for the stereoselective synthesis of α-
substituted chiral ketones. In addition, the best results were
obtained with the PHOX ligand. Linear as well as cyclic ketones
gave selectivities of up to 99% ee.
Scheme 1. Syntheses of 2-(1-Hydroxyalkyl)oxazolines and
-thiazolines
a mixture of diastereomers, which can easily be separated by
flash chromatography. The (S,S)-isomers were found to be
excellent ligands for stereoselective additions of alkyl- and
arylzinc reagents toward aldehydes (up to 98% ee). A strong
nonlinear effect could be observed in these reactions.41
The analogous thiazoline derivatives 2 can be obtained in an
analogous manner in the presence of Na2S2O3.42,43 In this case,
the cyclization toward the heterocycle does not proceed
automatically but requires an activation of the hydroxyl
functionality. This allowed us to get access, e.g., to 2a, the S-
analogue ligand to 1a.41
Reaction with chlorophosphine and phosphite bidentate P,N-
ligands should be easily accessible and applicable to a wide
range of asymmetric reactions. The free choice of the
chlorophosphines and the modular approach toward the
heterocyclic alcohols should allow the generation of libraries
of interesting ligand candidates in a straightforward manner.
As a showcase, we synthesized the diphenylphosphinites 3
and 4 (table 1). These compounds were found to be sensitive
to hydrolysis and oxidation, and therefore, the workup should
be carried out under inert conditions. This fact might also
Our group is also involved in the development of new ligands
and catalysts for asymmetric reactions. Recently, we reported
an easy and highly flexible protocol for the synthesis of 2-(1-
Received: February 28, 2012
Published: May 9, 2012
© 2012 American Chemical Society
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The Journal of Organic Chemistry
Note
Table 1. Syntheses of New Iridium Complexes As Potential Hydrogenation Catalysts
entry
oxazoline/thiazoline
R
X
phosphinite
yield (%)
57
Ir complex
yield (%)
1
2
3
4
5
6
(R,S)-1a
(S,S)-1a
(R,S)-1b
(S,S)-1b
(R,S)-2a
(S,S)-2a
i-Pr
i-Pr
t-Bu
t-Bu
i-Pr
i-Pr
O
O
O
O
S
(R,S)-3a
(S,S)-3a
(R,S)-3b
(S,S)-3b
(R,S)-4a
(S,S)-4a
(R,S)-5a
97
62
(R,S)-5b
93
49
42
(R,S)-6a
(S,S)-6aa
80
80
a
S
a
This compound proved to be unstable and decomposed in a few days.
explain the moderate isolated yields of the posphinites (42−
62%), although the conversion was clean and complete.
Interestingly, no reactions were observed with the (S,S)-
configured oxazoline derivatives 1, while the (R,S)-isomers gave
rise to the derived products 3. In the case of the thiazoline 2a,
both isomers reacted to give the phosphinites 4a in comparable
yields.
Unfortunately, the phosphinites could not be stored for a
longer time, and this forced us to convert them directly into the
corresponding Ir complexes 5 and 6 by heating a CH2Cl2
solution with [Ir(COD)Cl]2 for 1 h. Subsequently, the
−
counterion chloride was replaced by BArF [tetrakis[3,5-
Figure 2. Substrate classes investigated in catalytic hydrogenations
(ee’s given for catalyst (R,S)-5a).
bis(trifluoromethyl)phenyl]borate] to get air- and moisture-
stable complexes.44,45 We were pleased to see that these
colored complexes are stable compounds which could be
purified easily by flash chromatography. On crystallization, all
complexes gave orange-red crystals which were suitable for X-
ray structure analysis (Figure 1, ORTEP plots of all complexes
A−F, even after 24 h at a H2 pressure of 50 atm and a catalyst
loading of up to 3 mol %. The unsaturated amino acid
derivative G showed a very slow conversion (7%), and the ee
was low. By far the best result was obtained with the α,β-
unsaturated ketone H, which provided the (S)-configured α-
chiral ketone with 94% ee (with catalyst (R,S)-5a) in a perfect
yield.
Therefore, we tested our new catalysts in the hydrogenation
of substrates of type H (Table 2). Independent of the
substitution pattern and the catalyst used, all substrates showed
almost complete conversion. With linear ketones 7a−f the
valine-derived ligand (R,S)-5a gave high ee’s in the range of 95
2%, which could even be improved by switching to the
sterically more hindered tert-leucine ligand (R,S)-5b (entries
1−6). Except for the ortho-substituted arylated ketone 7f (entry
6) all substrates gave ee’s >99% with quantitative conversion.
The oxazoline ligands 5 proved to be superior to the thiazoline
analogue (R,S)-6a. Although a good conversion was observed,
the ee’s found with the same substrates were only in the range
of 65−81%. This effect was even more dramatic when we
investigated another class of the substrates, unsaturated
cyclohexanone derivatives (entries 7−9). Here, with the
thiazoline complex (R,S)-6a the ee’s dropped to 29−51%,
while oxazoline catalyst (R,S)-5b still gave excellent selectivities
of 98 1% ee.
Figure 1. Iridium complex (R,S)-5b.
will be found in the Supporting Information). And indeed, as
expected, both the (R,S)-oxazolines 5 and the (R,S)-thiazoline
6a coordinate toward the iridium as bidentate P,N-ligand.
Interestingly, the Ir complex of (S,S)-6a could not be
crystallized, and the complex decomposed in a few days.
The Ir complexes obtained were subsequently used as
catalysts for asymmetric hydrogenations of unsaturated
substrates. Because it was not clear which substance class is
best suited for our new catalysts, we decided to investigate a
wide range of substrates (Figure 2) such as α-hydroxy ketones
(A), phosphinates (B), substituted cinnamates (C) and
cinnamyl alcohols (D), enamides (E and F), α-amino acrylates
(G), and α,β-unsaturated ketones (H). We chose substrates
which could easily be analyzed by GC on chiral phase.
Interestingly, no reaction was observed with substrate classes
For the screening of our catalysts we used rather high H2
pressures and long reaction times to guarantee a complete
conversion of our substrates. To get an impression of the
reactivity of our catalysts and to figure out if chlorinated
solvents such as CH2Cl2 are required, we also changed the
reaction parameters. Using ketone 7h as a model substrate, we
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Note
Table 2. Asymmetric Hydrogenations of α,β-Unsaturated Ketones 7
(R,S)-5a
conv (%)
(R,S)-5b
conv (%)
(R,S)-6a
conv (%)
entry
7
Ar
R1
R2
product
ee (%)
ee (%)
ee (%)
1
2
3
4
5
6
7
8
9
7a
7b
7c
7d
7e
7f
Ph
Ph
Ph
Me
Me
Et
8a
8b
8c
8d
8e
8f
>99
>99
96
94
97
93
94
94
95
92
90
93
>99
>99
>99
>99
99
99.4
99.1
99.7
99.1
99.5
98
>99
>99
96
71
81
75
65
68
73
42
29
51
Me
Et
Me
Me
Me
Me
4-MeO-Ph
4-Me-Ph
2-Me-Ph
Ph
Me
>99
98
>99
98
Me
Me
92
>99
>99
>99
>99
88
7g
7h
7i
−(CH2)4−
−(CH2)4−
−(CH2)4−
8g
8h
8i
>99
>99
>99
99
>99
>99
>99
4-MeO-Ph
2-Me-Ph
97
98
analyzed the conversion by dependence of the pressure and the
solvent used (Table 3). Under the reaction conditions
also many other transition-metal-catalyzed reactions. Inves-
tigations of such complexes are currently in progress.
Table 3. Influence of the Reaction Parameters on the
Reaction Rate
EXPERIMENTAL SECTION
■
General Procedure for the Synthesis of the Phosphinitox-
azolines 3 and -thiazoline 4. The corresponding oxazoline39 or
thiazoline41 (n mmol) was dissolved in dry hexanes (10n mL), and
TMEDA (1.3n mmol) was added at room temperature. The solution
was cooled to −78 °C before n-butyllithium (1.3n mmol, 1.6 M in
hexanes) was added. The mixture was stirred for 15 min at −78 °C
and further 60 min at 0 °C. Then chlorodiphenylphosphine (1.3n
mmol) was added, and the solution was stirred at room temperature.
After the reaction was complete, the solid was filtered off and the
solvent was evaporated in vacuo. The residue was purified by flash
chromatography on SiO2 (hexanes/diethylether/triethylamine). The
ligands were found to be highly sensitive toward air and moisture and
where therefore directly converted into the corresponding Ir
complexes.
(S)-2-[(R)-1-[(Diphenylphosphino)oxy]-2,2-dimethylpropyl]-
4-isopropyl-4,5-dihydrooxazole [(R,S)-3a]: 57% yield; colorless
oil; 1H NMR (400 MHz, CDCl3) δ 0.76 (d, J = 6.8 Hz, 3 H), 0.87 (d, J
= 6.8 Hz, 3 H), 1.02 (s, 9 H), 1.55 (qqd, J = 6.8, 6.8, 6.5 Hz, 1 H), 3.69
(dd, J = 8.8, 8.1 Hz, 1 H), 3.79 (ddd, J = 9.6, 8.8, 6.5 Hz, 1 H), 4.14
(dd, J = 9.6, 8.1 Hz, 1 H), 4.29 (d, J = 9.0 Hz, 1 H), 7.29−7.35 (m, 6
H), 7.49−7.54 (m, 4 H); 13C NMR (100 MHz, CDCl3) δ 18.1, 19.1,
26.2, 32.2, 35.5 (d, J = 6.0 Hz), 69.6, 71.7, 83.6 (d, J = 19.3 Hz), 127.9
(d, J = 6.7 Hz), 128.2 (d, J = 7.2 Hz), 128.9, 129.3, 130.4 (d, J = 21.6
Hz), 130.8 (d, J = 22.7 Hz), 142.0 (d, J = 16.9 Hz), 142.5 (d, J = 18.3
Hz), 165.0; 31P NMR (162 MHz, CDCl3) δ 117.0. On the basis of the
instability of this compound, no acceptable elemental analysis and
HRMS data could be obtained.
entry
solvent
pressure (atm)
time (h)
conv (%)
1
2
3
4
5
6
7
8
CH2Cl2
toluene
EtOAc
EtOH
50
50
50
50
50
20
5
2
4
>99
>99
60
24
24
24
2
traces
−
dioxane
CH2Cl2
CH2Cl2
CH2Cl2
>99
>99
35
8
1
24
described, the hydrogenation was complete after 2 h (entry
1). Toluene might be a suitable substitute. Although the
hydrogenation is not as fast as in CH2Cl2 (80% conversion after
2 h), it was also complete after 4 h (entry 2). In EtOAc, the
reaction is much slower (entry 3), and EtOH and dioxane are
completely unsuitable (entries 4 and 5). CH2Cl2 seems to be
the solvent of choice. Even at a lower H2 pressure of 20 atm,
the reaction was complete after 2 h (entry 6). In principle, a
Parr apparatus can be used for hydrogenation, although the
reaction slows down significantly. At 5 atm H2 it takes 8 h for
completion (entry 7), and at 1 atm only 35% conversion was
observed after 24 h (entry 8). It should be mentioned that the
ee value was unchanged, even in toluene as solvent.
(S)-4-tert-Butyl-2-[(R)-1-[(diphenylphosphino)oxy]-2,2-dime-
thylpropyl]-4,5-dihydrooxazole [(R,S)-3b]: 62% yield; colorless
1
oil; H NMR (400 MHz, CDCl3) δ 0.81 (s, 9 H), 1.02 (s, 9 H), 3.79
(dd, J = 9.4, 9.2 Hz, 1 H), 3.85 (dd, J = 9.4, 7.9 Hz, 1 H), 4.12 (dd, J =
9.2, 7.9 Hz, 1 H), 4.31 (d, J = 9.0 Hz, 1 H), 7.27−7.36 (m, 6 H), 7.48−
7.55 (m, 4 H); 13C NMR (100 MHz, CDCl3) δ 26.0, 26.3, 33.3, 35.6,
68.4, 75.3, 83.7, 127.9 (d, J = 6.6 Hz), 128.2 (d, J = 7.3 Hz), 128.8,
129.4, 130.2 (d, J = 21.3 Hz), 131.0 (d, J = 22.9 Hz), 142.0, 142.4,
165.4; 31P NMR (162 MHz, CDCl3) δ 116.5. On the basis of the
instability of this compound, no acceptable elemental analysis and
HRMS data could be obtained.
(S)-2-[(R)-1-[(Diphenylphosphino)oxy]-2,2-dimethylpropyl]-
4-isopropyl-4,5-dihyrothiazole [(R,S)-4a]: 49% yield; colorless oil;
1H NMR (400 MHz, CDCl3) δ 0.86 (d, J = 6.8 Hz, 3 H), 0.97 (d, J =
6.8 Hz, 3 H), 1.01 (s, 9 H), 2.00 (qqd, J = 6.8, 6.8, 5.8 Hz, 1 H), 2.79
(dd, J = 10.6, 9.3 Hz, 1 H), 3.11 (dd, J = 10.6, 8.8 Hz, 1 H), 4.11 (ddd,
J = 9.3, 8.8, 5.8 Hz, 1 H), 4.40 (d, J = 10.3 Hz, 1 H), 7.29−7.37 (m, 6
H), 7.52−7.57 (m, 4 H); 13C NMR (100 MHz, CDCl3) δ 18.4, 19.8,
CONCLUSION
■
In conclusion, we could show that phosphinitoxazolines 3 are
new efficient ligands for Ir-catalyzed asymmetric hydro-
genations of arylated α,β-unsaturated ketones. By far, the best
results are obtained with the tert-leucine-derived ligand (R,S)-
5b, which gives excellent ee’s with linear as well as cyclic
substrates. By varying the central metal and the substitution
pattern, especially at the phosphorus atom, a wide range of
comparable complexes and catalysts are accessible, which
should be useful for not only asymmetric hydrogenations but
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Note
26.5, 32.2, 35.8, 35.8 (d, J = 5.9 Hz), 87.2, 87.4 (d, J = 17.6 Hz), 127.9
(d, J = 6.7 Hz), 128.2 (d, J = 7.3 Hz), 128.9, 129.5, 130.6 (d, J = 21.7
Hz), 131.2 (d, J = 23.0 Hz), 141.8 (d, J = 19.2 Hz), 142.2 (d, J = 17.0
Hz), 170.2; 31P NMR (162 MHz, CDCl3) δ 115.9. On the basis of the
instability of this compound, no acceptable elemental analysis and
HRMS data could be obtained.
CDCl3) δ 105.9; 19F NMR (376.5 MHz, CDCl3) δ − 62.8 ppm;
HRMS (CI) m/z calcd for C31H42IrNOPS (M − BArF)+ 700.2348,
found 700.2333. Anal. Calcd for C63H54BF24IrNOPS: C, 48.41; H,
3.48; N, 0.90. Found: C, 48.47; H, 3.20; N, 0.85.
Iridium-Catalyzed Hydrogenations. To a solution of the
corresponding ketone in dry dichloromethane in a test tube was
added 1 mol % catalyst. The tube was transferred into the autoclave. It
was purged three times with nitrogen and three times with hydrogen
before it was pressurized to 50 bar. The mixture was stirred at this
pressure. After 24 h, the pressure was released, and it was purged five
times with nitrogen. The tube was taken out, and the solvent was
removed in vacuo. The crude product was cleaned by flash
chromatography on SiO2 (hexanes/ethylacetate), and ee values were
determined via GC analysis [CP-Chirasil-Dex capillary column (25 m
× 0.25 mm)]. GC separation conditions T0 [3 min] = 90 °C, 1 °C/
min to T = 200 °C [20 min], injector 250 °C, detector 275 °C.
(S)-3-Methyl-4-phenylbutan-2-one [(S)-8a]:46 98% yield;
99.4% ee; [α]2D0 +34.1 (c = 1, CHCl3); GC tR [(R)-8a] 27.52 min,
tR [(S)-8a] 27.98 min.
Preparation of the Iridium Complexes. To a solution of n
mmol of the P,N-ligand in dry dichloromethane (10n mL)
[Ir(COD)Cl]2 (0.5n mmol) were added at room temperature. The
mixture was refluxed for 1 h and cooled to room temperature. Sodium
tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (1.1n mmol) and H2O
(10n mL) were added, and the mixture was stirred for 30 min. The
aqueous layer was extracted with dichloromethane, and the combined
organic layers were washed with H2O and brine and dried over
Na2SO4. The solvent was evaporated in vacuo, and the crude product
was purified by flash chromatography on SiO2 (dichloromethane).
[(η4-1,5-Cyclooctadiene)-[(S)-2-[(R)-1-((diphenylphosphino)-
oxy)-2,2-dimethylpropyl]-4-isopropyl-4,5-dihydrooxazole]-
iridium(I)] tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
[(R,S)-5a]: 97% yield; red-orange crystals (crystallized from EtOH,
(S)-2-Methyl-1-phenylpentan-3-one [(S)-8b]:46 99% yield;
99.1% ee; [α]2D0 +57.6 (c = 1, CHCl3); GC tR [(R)-8b] 32.23 min,
tR [(S)-8b] 33.02 min;
1
mp 163−164 °C); [α]D20 +1.8 (c = 1, CH2Cl2); H NMR (400 MHz,
CDCl3) δ 0.25 (d, J = 6.7 Hz, 3H), 0.80 (d, J = 7.0 Hz, 3H), 1.07 (s,
9H), 1.61 (m, 1H), 1.74−1.93 (m, 2H), 2.07 (m, 2H), 2.53−2.34 (m,
4H), 2.85 (m, 1H), 3.51 (m, 1H), 3.95 (dd, J = 4.3, 3.7 Hz, 1H), 4.39
(dd, J = 9.8, 3.7 Hz, 1H), 4.54 (dd, J = 9.8, 4.3 Hz, 1H), 4.74 (d, J =
9.6 Hz, 1H), 4.94 (m, 1H), 5.31 (m, 1H), 7.31 (m, 2H), 7.45 (m, 2H),
7.49−7.61 (m, 8H), 7.72−7.78 (m, 10H); 13C NMR (100 MHz,
CDCl3) δ 13.2, 18.3, 25.9, 26.4, 29.1, 31.6, 32.4, 35.4, 35.5, 63.4, 66.3,
68.9, 71.0, 82.4, 98.1, 100.3, 117.5, 124.6 (J = 272.3 Hz), 128.9 (J = 2.7
Hz), 129.0 (J = 10.9 Hz), 129.4 (J = 11.4 Hz), 130.3, 130.9, 131.3 (J =
12.1 Hz), 132.3 (J = 13.7 Hz), 132.8 (J = 2.0 Hz), 133.0 (J = 2.4 Hz),
134.8, 161.7 (J = 49.7 Hz), 172.5; 31P NMR (162 MHz, CDCl3) δ
109.3; 19F NMR (376.5 MHz, CDCl3) δ − 62.8 ppm; HRMS (CI) m/
z calcd for C31H42IrNO2P (M − BArF)+ 684.2577, found 684.2581.
Anal. Calcd for C63H54BF24IrNO2P: C, 48.91; H, 3.52; N, 0.91. Found:
C, 49.07; H, 3.22; N, 0.85.
(S)-3-Benzylpentan-2-one [(S)-8c]:46 96% yield; 99.7% ee; [α]2D0
+41.8 (c = 1, CHCl3); GC tR [(R)-8c] = 32.65 min, tR [(S)-8c] =
32.89 min.
(S)-4-(4-Methoxyphenyl)-3-methylbutan-2-one [(S)-8d]:46
93% yield; 99.1% ee; [α]D20 +38.9 (c = 1, CHCl3); GC tR [(R)-8d]
51.36 min, tR [(S)-8d] 51.89 min.
(S)-3-Methyl-4-(p-tolyl)butan-2-one [(S)-8e]:46 92% yield;
99.5% ee; [α]2D0 +31.8 (c = 1, CHCl3); GC tR [(R)-8e] 34.54 min,
tR [(S)-8e] 35.91 min.
(S)-3-Methyl-4-(o-tolyl)butan-2-one [(S)-8f]:46 99% yield; 98%
ee; [α]2D0 +43.2 (c = 1, CHCl3); GC tR [(R)-8f] 32.85 min, tR [(S)-8f]
33.53 min.
(S)-2-Benzylcyclohexanone [(S)-8g]:46 99% yield; 99% ee; [α]2D0
−42.1 (c = 1, CHCl3); GC tR [(R)-8g] 59.86 min, tR [(S)-8g] 60.10
min.
[(η4-1,5-Cyclooctadiene)-[(S)-4-tert-butyl-2-[(R)-1-
((diphenylphosphino)oxy)-2,2-dimethylpropyl]-4,5-
dihydrooxazole]iridium(I)] tetrakis[3,5-bis(trifluoromethyl)-
phenyl]borate [(R,S)-5b]: 93% yield; orange crystals (crystallized
from Et2O/hexanes, mp 178−179 °C); [α]2D0 +20.0 (c = 1, CH2Cl2);
1H NMR (400 MHz, CDCl3) δ 0.72 (s, 9H), 1.08 (s, 9H), 1.56 (m,
(S)-2-(4-Methoxybenzyl)cyclohexanone [(S)-8h]:46 92% yield;
97% ee; [α]2D0 −40.2 (c = 1, CHCl3); GC tR [(R)-8h] 85.18 min, tR
[(S)-8h] 85.46 min.
(S)-2-(2-Methylbenzyl)cyclohexanone [(S)-8i]:47 96% yield;
98% ee; [α]2D0 −38.8 (c = 1, CHCl3); GC tR [(R)-8i] 66.43 min, tR
[(S)-8i] 66.70 min.
1H), 1.76 (m, 1H), 2.03 (m, 2H), 2.33 (m, 2H), 2.46 (m, 2H), 2.86
(m, 1H), 3.73−3.78 (m, 2H), 4.39 (dd, J = 9.8, 3.5 Hz, 1H), 4.68 (dd,
J = 9.8, 3.5 Hz, 1H), 4.85 (m, 1H), 4.90 (d, J = 10.5 Hz, 1H), 5.30 (m,
1H), 7.29 (m, 2H), 7.45 (m, 2H), 7.50−7.54 (m, 5H), 7.55−7.64 (m,
3H), 7.67−7.71 (m, 10H); 13C NMR (100 MHz, CDCl3) δ 25.1, 25.1,
25.3, 26.1, 28.6, 32.5, 33.6, 35.7, 62.9, 66.2, 72.4, 73.3, 82.4 (J = 3.4
Hz), 96.8, 100.0, 117.5, 124.6 (J = 272.6 Hz), 128.9 (J = 2.6 Hz),
129.0 (J = 10.9 Hz), 129.3 (J = 11.2 Hz), 130.5, 130.7, 131.0 (J = 11.7
Hz), 131.8 (J = 13.7 Hz), 132.8, 132.8, 134.8, 160.9, 172.8; 31P NMR
(162 MHz, CDCl3) δ 107.2; 19F NMR (376.5 MHz, CDCl3) δ − 62.8
ppm; HRMS (CI) m/z calcd for C32H44IrNO2P (M − BArF)+
698.2733, found 698.2732. Anal. Calcd for C64H56BF24IrNO2P: C,
49.24; H, 3.62; N, 0.90. Found: C, 49.65; H, 3.57; N, 0.84.
ASSOCIATED CONTENT
* Supporting Information
■
S
Analytical and spectroscopic data of all catalysts and hydro-
genation products as well as ORTEP plots and CIFs for the
Xray structures of complexes 5 and 6. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: u.kazmaier@mx.uni-saarland.de.
■
[(η4-1,5-Cyclooctadiene)-[(S)-2-[(R)-1-((diphenylphosphino)-
oxy)-2,2-dimethylpropyl]-4-isopropyl-4,5-dihyrothiazole]-
iridium(I)] tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
[(R,S)-6a]: 80% yield; red needles (crystallized from Et2O/hexanes,
Notes
The authors declare no competing financial interest.
mp 165−166 °C);[α]D20 −6.7 (c = 1, CH2Cl2); H NMR (400 MHz,
1
ACKNOWLEDGMENTS
This work was supported by the Deutsche Forschungsgemein-
schaft.
CDCl3) δ −0.05 (d, J = 6.7 Hz, 3H), 0.84 (d, J = 7.0 Hz, 3H), 1.24 (s,
9H), 1.50 (m, 1H), 1.78 (m, 1H), 1.95−2.16 (m, 3H), 2.41 (m, 2H),
2.58 (m, 2H), 2.95 (m, 1H), 3.18 (dd, J = 12.0, 3.1 Hz, 1H), 3.29 (dd,
J = 12.0, 2.6 Hz, 1H), 3.45 (m, 1H), 4.21 (dd, J = 3.1, 2.6 Hz, 1H),
5.03 (m, 1H), 5.08 (d, J = 10.4 Hz, 1H), 5.28 (m, 1H), 7.14 (m, 2H),
7.41 (m, 2H), 7.47 (m, 1H), 7.53 (m, 4H), 7.56−7.65 (m, 3H), 7.71
(m, 8H), 7.78 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 13.2, 19.4,
26.3, 27.1, 28.6, 30.2, 30.5, 35.1, 36.2, 42.1, 61.4, 68.3, 78.5, 88.9, 99.1,
103.3, 117.5, 124.6 (J = 272.5 Hz), 128.7 (J = 10.9 Hz), 129.0, 129.5 (J
= 11.6 Hz), 131.0 (J = 11.7 Hz), 132.2 (J = 13.9 Hz), 133.6, 133.7,
132.6, 133.0, 134.8, 161.6 (J = 50.4 Hz), 181.2; 31P NMR (162 MHz,
■
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