Enantioselective Ir-catalyzed hydrogenation of minimally functionalized olefins using pyranoside phosphinite-oxazoline ligands

Article abstract of DOI:10.1002/ejic.201201485

Pyranoside phosphinite-oxazoline ligands prepared from readily available (+)-D-glucosamine were applied to the Ir-catalyzed asymmetric hydrogenation of minimally functionalized olefins. Our results show that the enantioselectivity is dependent on the ozaxoline and the phosphinite moieties and the substrate structure. By carefully selecting the ligand components, enantioselectivities up to 99 % were obtained in the asymmetric reduction of several (E)- and (Z)-trisubstituted and 1,1-disubstituted olefins. The asymmetric hydrogenation was also performed using propylene carbonate as solvent, which allowed the iridium catalysts to be reused and maintained the high enantioselectivities. Copyright

Full text of DOI:10.1002/ejic.201201485

FULL PAPER
DOI:10.1002/ejic.201201485
Enantioselective Ir-Catalyzed Hydrogenation of Minimally
Functionalized Olefins Using Pyranoside Phosphinite-
Oxazoline Ligands
[a]
[a]
[a]
Javier Mazuela, Oscar Pàmies,* and Montserrat Diéguez*
Keywords: Hydrogenation / Iridium / Olefins / P,N-ligands / Pyranosides / Enantioselectivity
Pyranoside phosphinite-oxazoline ligands prepared from
readily available (+)- -glucosamine were applied to the Ir-
catalyzed asymmetric hydrogenation of minimally function-
alized olefins. Our results show that the enantioselectivity is
dependent on the ozaxoline and the phosphinite moieties
and the substrate structure. By carefully selecting the ligand
components, enantioselectivities up to 99% were obtained in
the asymmetric reduction of several (E)- and (Z)-trisubsti-
tuted and 1,1-disubstituted olefins. The asymmetric hydro-
genation was also performed using propylene carbonate as
solvent, which allowed the iridium catalysts to be reused and
maintained the high enantioselectivities.
D
Introduction
Metal-catalyzed asymmetric reactions have become one
of the most powerful tools for the production of enantio-
merically pure compounds. The permanently growing large
number of chemical processes suitable for asymmetric catal-
ysis, as well as the large variety of substrates to which they
can be applied represent a permanent need for the discovery
Figure 1. Uemura-based pyranoside P-oxazoline ligands.
[
1]
of new catalysts. The performance of catalytic enantiose-
lective reactions largely depends on appropriate chiral li-
gands being selected for the catalyst structure. Most of the
research in this area, then, has focused on finding new series
of efficient chiral ligands. Although many thousands of chi-
ral ligands have been prepared and tested, very few of them
Because of its high efficiency, atom economy and opera-
tional simplicity, asymmetric hydrogenation that uses mo-
lecular hydrogen to reduce prochiral olefins has become one
of the most reliable catalytic methods for preparing op-
[
1]
[1]
tically active compounds. Whereas the reduction of ole-
fins containing an adjacent polar group (i.e., dehydroamino
acids) by Rh- and Ru-catalyst precursors modified with
phosphorus ligands has a long history, the asymmetric
hydrogenation of minimally functionalized olefins is less de-
veloped, because these substrates have no adjacent polar
have been found to have general applicability. So, the se-
arch for highly efficient and easy-to-synthesize ligands from
simple feedstocks is still of great importance. One of the
simplest ways of obtaining chiral ligands is to transform
or derivatize natural chiral compounds. Carbohydrates have
many advantages: they are readily available, they are highly
functionalized and they have several stereogenic centers.
This enables series of chiral ligands to be synthesized and
[
1,4]
group to direct the reaction.
In recent decades, iridium
complexes with chiral P,N ligands have become established
as one of the most efficient catalyst types for the hydrogena-
tion of minimally functionalized olefins, and they comple-
[
2]
screened in the search for high activities and selectivities.
In this context, Uemura-based pyranoside P-oxazoline li-
gands (Figure 1) have emerged as privileged ligands that
provide excellent results in several metal-catalyzed asym-
[
4–6]
ment Rh– and Ru–diphosphane complexes.
successful Ir–P,N catalytic systems contained phosphane/
phosphinite-oxazoline-based ligands.
Most of the
[
7]
metric transformations.[
3]
Although the
number of substrates that can be successfully reduced with
these systems was high, there is still a problem of substrate
range limitation, since high enantioselectivities were mainly
[
a] Departament de Química Física i Inorgànica, Universitat
Rovira i Virgili, Campus Sescelades,
C/ Marcel·lí Domingo, s/n. 43007 Tarragona, Spain
Fax: +34-977-55-95-63
[
8]
limited to trisubstituted substrates. Research into more
versatile phosphane/phosphinite-oxazoline ligand systems
from simple starting materials in this reaction is therefore
currently of great importance.
E-mail: montserrat.dieguez@urv.cat
Homepage: http://www.quimica.urv.cat/tecat/
modular_ligands.php
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Following our interest in carbohydrates as an inexpensive
and highly modular chiral source for preparing ligands and
encouraged by the success of the Uemura-based pyranoside
phosphorus-oxazoline ligands,[3] we describe here the appli-
cation of a small but structurally relevant set of phosphin-
ite-oxazoline ligands L1–L4 to the Ir-catalyzed hydrogena-
tion of minimally functionalized olefins (Figure 2). With
these ligands we investigate the effect of varying the elec-
tronic and steric properties of the oxazoline substituent
Scheme 2. Synthesis of catalyst precursors [Ir(cod)(L)]BAr
F
(L =
L1–L4).
(
(
L1–L3), and the substituents at the phosphinite group
L3–L4), in an attempt to maximize catalyst performance.
All complexes were isolated as air-stable orange solids in
pure form, and they were then used without further purifi-
cation. The complexes were characterized by elemental
1
13
31
analysis and H, C, and P NMR spectroscopy. The spec-
1
1
tral assignments were based on information from H– H
and 13C– H correlation measurements and were as expected
1
for these C iridium complexes. The elemental analysis of
1
C,H,N matched the stoichiometry [Ir(cod)(P-N)] (BAr ) .
n
F n
Figure 2. Pyranoside phosphinite-oxazoline ligands L1–L4.
For all complexes, the variable-temperature NMR
measurements (from +40 °C to –80 °C) indicate that only
3
1
one isomer was present in solution. In this context, the
P
NMR spectra showed one sharp signal. The 13C NMR
showed four signals for the olefinic carbon atoms of the
Results and Discussion
coordinated cyclooctadiene, as expected for C -symmetrical
complexes. Two of the four signals, those corresponding to
1
Synthesis of Ligands
The new pyranoside phosphinite-oxazoline ligand L4 can the olefinic carbon atoms located trans to the phosphorus
be straightforwardly synthesized using the procedure pre- atom, appeared low-field-shifted. The 13C NMR spectra
viously described for ligands L1–L3 (Scheme 1).[
3a,3b]
It was also showed the expected four signals of the methylene car-
therefore efficiently synthesized in one step by reacting the bon atoms of the cyclooctadiene. The signals from the pho-
corresponding sugar oxazoline-alcohol 1 with 1 equiv. of sphinite-oxazoline ligands in these complexes produced the
1
13
chlorodi(o-tolyl)phosphane in the presence of triethylamine. expected H and C NMR pattern for the glucopyranoside
Oxazoline-alcohol 1 is easily prepared from inexpensive d- nucleus.
glucosamine on a large scale.[
3a,3b]
Ligand L4 was stable
during purification on neutral alumina under argon and
isolated in moderate yield as a white solid. It was stable at
room temperature and very stable to hydrolysis. The ele- Asymmetric Hydrogenation of Minimally Functionalized
mental analysis was in agreement with the assigned struc- Olefins
1
13
31
ture. The H, C, and P NMR spectra were as expected
for this C ligand.
In an initial set of experiments we used the Ir-catalyzed
1
hydrogenation of substrates trans-α-methylstilbene (S1) and
2-(4-methoxyphenyl)but-1-ene (S2) to study the potential of
phosphinite-oxazoline ligands L1–L4. Substrate S1 was
chosen as a model for the hydrogenation of trisubstituted
olefins, because it has been reduced with a wide range of
ligands, and the efficiency of the various ligand systems can
Scheme 1. Synthesis of new pyranoside phosphinite-oxazoline li-
gand L4.
[4d]
be compared directly.
In order to assess the potential of
the ligand library L1–L4 for the more demanding 1,1-di-
substituted terminal olefins, which are usually hydrogenated
less enantioselectively than the corresponding trisubstituted
[
9,10]
[4e]
olefins,
we chose substrate S2 as a model. The lower
Synthesis of the Ir-Catalyst Precursors
enantioselectivity obtained with 1,1-disubstituted terminal
The catalyst precursors were prepared by refluxing a olefins than that obtained with trisubstituted olefins has
[
4e]
dichloromethane solution of the appropriate ligand in the been attributed to two main factors. The first is that en-
presence of 0.5 equiv. of [Ir(μ-Cl)cod] for 1 h and then ex- antioface olefin coordination is difficult to control because
2
changing the counterion with sodium tetrakis[3,5-bis(tri- of the comparable steric size of the alkyl and aryl substitu-
fluoromethyl)phenyl]borate (NaBAr ) (1 equiv.), in the ent at the olefinic C atom. The second reason is that the
F
presence of water (Scheme 2).
terminal double bond can isomerize to form the more stable
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internal trans-alkene, which usually leads to the predomi- high enantioselectivities can also be obtained for the more
nant formation of the opposite enantiomer of the hydroge- demanding (Z) isomers S5 and S6 (Table 2, Entries 5–8),
nated product.
which usually react with much lower enantioselectivities
[
4]
Our catalytic results showed that for both types of sub- than those of the corresponding (E) isomers. For this sub-
strates the reactions proceeded smoothly at room tempera- strate class, we found that the steric hindrance of the phos-
ture under standard conditions (50 bar of H for S1 and phinite moiety had a considerable effect. So, the Ir/L4 cata-
2
[11]
1
bar of H for S2). High activities and enantioselectivit- lytic system provided higher enantioselectivity than the Ir/
2
ies (up to 96% for S1 and 94% for S2) were obtained. The L3 system (Table 2, Entries 6 and 8). It should also be
results, which are summarized in Table 1, indicate that both pointed out that the enantioselectivities obtained in the
activities and enantioselectivities are mainly affected by the hydrogenation of trisubstituted olefins containing a neigh-
oxazoline substituent.
boring polar group were also high. These substrates are
interesting, because they allow for further functionalization
and they are therefore important synthons in the synthesis
of more complex chiral molecules. High enantioselectivities
Table 1. Ir-catalyzed asymmetric hydrogenation of S1 and S2 using
[
a]
ligands L1–L4.
(up to 99%) have been obtained in the hydrogenation of
α,β-unsaturated ester S7, allylic alcohol S8, and vinylsilane
S9 (Table 2, Entries 9–14).
The results indicated that the enantioselectivity of the
hydrogenation of several 1,1-disubstituted alkyl-phenyl sub-
strates (S10–S14) is affected by the nature of the alkyl chain
(ee 73–99%, Table 2, Entries 15–21). This behavior can be
explained by the competition between direct hydrogenation
vs. isomerization for the various substrates. This is sup-
ported by the fact that the hydrogenation of substrates S12–
[
a] Reactions carried out using 0.5 mmol of substrate and 2 mol-%
of Ir-catalyst precursor at 50 bar of H for S1 and 1 bar of H for
2
2
S2 with dichloromethane (2 mL) as solvent at room temperature. S13, which form the most stable isomerized tetrasubstituted
1
[
b] Conversion measured by H NMR spectroscopy after 2 h. [c]
olefins, provides the lowest enantioselectivities (Table 2, En-
tries 18 and 19), while the highest enantioselectivity of the
series is found with substrate S14, which contains a tBu
Enantiomeric excess determined by HPLC (S1) and GC (S2). [d]
Reaction carried out at 0.25 mol-% of Ir-catalyst precursor.
With ligands L1–L3 we studied the effect of the oxazol- group and for which isomerization cannot occur (Table 2,
ine substituent on the catalytic performance. We found that Entries 20 and 21). However, the large difference in steric
the best trade-off between activity and enantioselectivity size of Ph vs. tBu may well be the principal factor in this
was obtained using the Ir/L3 catalyst precursor (Table 1, case.
Entry 3). The enantiomeric excesses obtained with catalyst
Interestingly, the Ir/L3 catalyst system was also able to
precursors Ir/L2 and Ir/L3 were comparable and the high- hydrogenate pyridyl-containing substrate S15 with excellent
est, but the activity obtained with the Ir/L2 system was the activities and enantioselectivities (99% ee, Table 2, En-
lowest. Conversely, the Ir/L1 catalyst precursor containing try 22). We also obtained excellent levels of enantio-
the ligand with the small methyl substituent on the oxazol- selectivities in the reduction of diaryl substrate S16, with a
ine provided high relative conversion but the enantio- steric differentiation between the aryl groups, using the Ir/
selectivities were the lowest (Table 1, Entry 1).
L4 catalyst precursor (Table 2, Entry 24). The hydrogena-
Finally, we found that the Ir/L4 catalytic system, which tion of 1,1-disubstituted heteroaromatic alkenes and di-
differs from Ir/L3 in that it contains a bulkier aryl phos- arylalkenes provides an easy entry point for the preparation
[
12]
phinite moiety, provided similar results (Table 1, Entries 3 of drugs and research materials.
and 4). Our results also indicated that the efficiency at transfer-
In summary, the best results were achieved with ligands ring the chiral information of these catalyst precursors is
L3 and L4. Note that at a low catalyst loading (0.25 mol- highly dependent on the nature of the neighboring polar
%), the excellent enantioselectivities and activities were group in these 1,1-disubstituted substrates. Thus, while the
maintained (Table 1, Entries 5 and 6). These results are reduction of allylic alcohol S17 provides lower ee values
[
4]
among the best reported for these types of substrate.
than the best ones reported in the literature (Table 2, En-
We then studied the potential of [Ir(cod)(L3)]BAr and tries 25 and 26), the hydrogenation of vinylsilane S18 and
F
[
Ir(cod)(L4)]BArF catalyst precursors in the asymmetric trifluoromethyl substrates S19 and S20 provides fairly good
[
3d,8a,13]
hydrogenation of other minimally functionalized (E)- and ee values (Table 2, Entries 27–32).
(Z)-trisubstituted (S3–S9) and 1,1-disubstituted (S10–S20)
Finally, we decided to study the possibility of using pro-
olefins. The results are shown in Table 2. Comparing the pylene carbonate (PC) as an environmentally friendly sol-
results obtained using substrates S1 (Table 1, Entry 3) and vent. PC has recently emerged as an environmentally
S3–S4 (Table 2, Entries 1–4), we found that enantio- friendly alternative to standard organic solvents that allows
selectivity is relatively insensitive to the electronic nature of catalysts to be repeatedly recycled by a simple two-phase
[
14]
both the phenyl ring (S3 vs. S4) and the substituent trans extraction with an apolar solvent. For this purpose, sub-
to the aryl group (S1 vs. S3) of the substrate. Interestingly, strates S2, S12, and S14 were hydrogenated in PC with the
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Table 2. Asymmetric hydrogenation of several tri- and disubstituted substrates using Ir-pyranoside phosphinite-oxazoline catalyst precur-
sors.[
a]
[
a] Reactions carried out using 0.5 mmol of substrate and 2 mol-% of Ir-catalyst precursor at 50 bar of H
solvent at room temperature. Full conversions were obtained in all cases after 2 h. [b] Enantiomeric excess determined by HPLC or GC.
c] Reaction carried out at 1 bar of H
2
with dichloromethane as
[
2
.
catalyst precursor [Ir(cod)(L3a)]BAr , and the products been observed by Börner and co-workers, and it is in agree-
F
were removed by extraction with hexane (Table 3). We were ment with the reduction in the isomerization when PC was
pleased to see that this catalyst can be used up to four times used as a solvent.[16]
with no significant loss in enantioselectivity, although the
reaction time increased.[ It should be pointed out that the
15]
reduction of S12 proceeds with higher enantioselectivity in Conclusions
PC than in dichloromethane. This behavior has already
Phosphinite-oxazoline ligands, which contain a pyrano-
side as a simple but effective backbone, were tested in the
asymmetric hydrogenation of a wide range of (E)- and (Z)-
trisubstituted and 1,1-disubstituted terminal olefins, includ-
ing examples with neighboring polar groups. A small but
structurally relevant library of Ir-phosphinite-oxazoline
precatalysts has been developed by changing the electronic
and steric properties of the oxazoline substituent, and the
substituents at the phosphinite group. Although the
enantioselectivity is dependent on the oxazoline and phos-
phinite moieties and the substrate structure, we found that
the introduction of a bulky ortho-tolyl phosphinite moiety
was crucial to achieving the highest enantioselectivities with
some of the most elusive substrate types [i.e., (Z)-trisubsti-
tuted and diaryl terminal substrates]. By carefully selecting
the ligand components, enantioselectivities up to 99% were
therefore obtained in the asymmetric reduction of several
Table 3. Recycling experiments with catalyst precursor [Ir(cod)-
(
L3a)]BAr
F
and S2, S12, and S14 as substrates in PC.[
a]
Conversion [%] (time [h])[b]
ee [%][c]
Cycle
Substrate
1
2
3
4
S2
S2
S2
S2
100 (4)
98 (6)
94 (10)
86 (14)
93 (S)
93 (S)
93 (S)
92 (S)
5
6
7
8
S12
S12
S12
S12
97 (4)
94 (6)
91 (10)
92 (14)
81 (S)
80 (S)
80 (S)
80 (S)
9
S14
S14
S14
S14
100 (4)
97 (6)
96 (10)
92 (14)
99 (S)
98 (S)
98 (S)
97 (S)
10
11
12
[
a] Reactions carried out using 0.5 mmol of substrate and 2 mol-%
(E)- and (Z)-trisubstituted olefins. This good performance
of Ir-catalyst precursor at 50 bar of H . [b] Conversion measured
by H NMR spectroscopy. [c] Enantiomeric excess determined by
GC.
2
1
extended even to the more challenging class of terminally
disubstituted olefins. For this substrate class, our results
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indicated that enantioselectivity is dependent on the nature Typical Procedure for the Preparation of [Ir(cod)(L)]BAr
F
: The cor-
Cl (2 mL),
(25 mg, 0.037 mmol) was added. The mixture
was refluxed at 50 °C for 1 h. After 5 min at room temperature,
NaBAr (77.1 mg, 0.082 mmol) and water (2 mL) were added and
responding ligand (0.074 mmol) was dissolved in CH
and [Ir(μ-Cl)cod]
2
2
of the alkyl substrate substituent, which has been attributed
to the presence of an isomerization process under hydrogen-
ation conditions. Enantioselectivities were therefore best in
the asymmetric reduction of aryl and pyridyl/tert-butyl sub-
strates as well as in the reduction of diaryl substrates (ee up
to 99%), for which isomerization cannot occur. The asym-
metric hydrogenations were also performed using propylene
2
F
the reaction mixture was stirred vigorously at room temperature
for 30 min. The phases were separated, and the aqueous phase was
extracted twice with CH
filtered through a Celite plug, dried with MgSO
2
Cl
2
. The combined organic phases were
, and the solvent
4
carbonate as solvent, which allowed the Ir catalyst to be was evaporated to give the product as an orange solid.
reused and maintained the excellent enantioselectivities.
[
Ir(cod)(L1)]BAr
F
: Yield 110 mg (91%). 31P NMR (CDCl
3
): δ =
, cod),
), 2.21 (br., 2 H, CH
In summary, the reactivity and selectivity of these pyr-
anoside Ir-phosphinite-oxazoline catalysts are high but
somewhat lower compared to privileged phosphite-oxazol-
1
1
2
06.8 (s) ppm. H NMR (CDCl
3 2
): δ = 1.7–2.0 (br., 4 H, CH
.08 (m, 2 H, CH , cod), 2.14 (s, 3 H, CH
cod), 3.32 (br., 1 H, CH=, cod), 3.73 (m, 2 H, 4-H and 6Ј-H), 3.95
m, 1 H, 5-H and CH = cod), 4.17 (m, 1 H, 3-H), 4.31 (dd, J6-6Ј
2
3
2
[
3d]
ine analogues. Nevertheless, these Ir/phosphinite-oxazol-
2
(
3
ine systems represent one of the very few phosphinite-con- = 10.0, J = 4.8 Hz, 1 H, 6-H), 4.46 (m, 1 H, 2-H), 4.58 (m, 1
6
-5
taining P,N catalysts[ able to hydrogenate a broad range H, CH=, cod), 5.02 (br., 1 H, CH=, cod), 5.39 (s, 1 H, 7-H), 5.99
8a]
3
of terminal disubstituted olefins with high enantioselectivi- (d, J1-2 = 6.4 Hz, 1 H, 1-H), 7.0–8.4 (m, 27 H, CH=, aromatic H)
1
3
ppm. C NMR (CDCl
9.6 (br., CH , cod), 30.7 (br., CH
br., CH=, cod), 66.9 (C-5), 67.3 (C-2), 67.9 (C-6), 70.2 (br., CH=,
cod), 74.9 (d, JC-P = 7.4 Hz, C-4), 79.2 (C-3), 96.4 (d, JC-P
3
): δ = 16.8 (CH
3
), 25.7 (br., CH
2
, cod),
ties. Therefore, by appropriate selection of the ligand pa-
rameters phosphinite-based P,N ligands can also be success-
fully applied in the hydrogenation of this challenging sub-
strate class.
2
2
2
, cod), 34.6 (br., CH
2
cod), 65.3
(
=
19.7 Hz, CH=, cod), 100.9 (d, JC-P = 12.9 Hz, CH=, cod), 101.7 (s,
F
C-7), 104.5 (s, C-1), 117.7 (br., CH=BAr ), 120–134 (aromatic C),
1
35.0 (br., CH=BAr
F
), 135.5–150 (aromatic C), 161.9 (q, 1JC-B
=
Experimental Section
50 Hz, C-B BAr ), 173.6 (C=N) ppm.
F
C
67
H
50BF24IrNO
5
P
(
1639.09): calcd. C 49.10, H 3.07, N 0.85; found C 49.03, H 3.01,
General Considerations: All reactions were carried out using stan-
dard Schlenk techniques under argon. Solvents were purified and
dried by standard procedures. Ligands L1–L3 were prepared as
N . 0.82.
[Ir(cod)(L2)]BAr
106.7 (s) ppm. H NMR (CDCl
F
: Yield 119 mg (96%). 31P NMR (CDCl
3
): δ =
[
3a,3b]
1
described previously by Uemura and co-workers.
[Ir(cod)-
3
): δ = 1.49 (s, 9 H, CH
3
, tBu), 1.6–
L3)]BArF was prepared as previously reported.[17] 1H, 13C{ H},
1
(
2.3 (m, 8 H, CH
2
cod), 3.61 (m, 1 H, 4-H), 3.76 (m, 2 H, 6Ј-H and
31
1
and P{ H} NMR spectra were recorded with a 400 MHz spec-
5-H), 4.02 (m, 1 H, 3-H), 4.19 (m, 1 H, CH=, cod), 4.27 (m, 1 H,
6-H), 4.39 (m, 1 H, H2), 4.53 (br., 1 H, CH=, cod), 4.79 (br., 1 H,
CH=, cod), 5.37 (s, 1 H, 7-H), 5.45 (br., 1 H, CH=, cod), 6.03 (d,
1
13
4
trometer. Chemical shifts are relative to that of SiMe ( H and C)
31
1
13
as internal standard or H
3
PO
4
( P) as external standard. H, C,
31
1
1
3
and P assignments were made on the basis of H- H gCOSY and
J
1-2 = 6 Hz, 1 H, CH, H1), 7.1–8.2 (m, 27 H, CH=, aromatic H)
1
13
13
H- C gHSQC experiments. All catalytic experiments were per-
ppm. C NMR (CDCl
cod), 29.1 (CH , tBu), 32.1 (br., CH
CH , cod), 65.9 (C-5), 67.7 (C-6), 68.9 (C-2), 69.9 (CH=, cod), 70.4
CH=, cod), 74.5 (C-4), 80.4 (C-3), 90.8 (CH=, cod), 101.3 (C-
3
): δ = 23.8 (br., CH
2 2
, cod), 26.5 (br., CH ,
formed three times.
3
2
, cod), 32.4 (C, tBu), 33.4 (br.,
2
Synthesis of L4: Chlorodi(o-tolyl)phosphane (136.5 mg, 0.55 mmol)
was slowly added at –40 °C to a solution of 1 (176.6 mg, 0.5 mmol)
and DMAP (5.7 mg, 0.05 mmol) in THF (3.3 mL) and triethyl-
amine (1.7 mL). The reaction mixture was stirred at room tempera-
ture for 15 min. Diethyl ether was then added, and the salts were
removed by filtration. The residue was purified by flash chromatog-
(
7
), 103.4 (C-1), 104.2 (d, JC-P = 15.6 Hz, CH=, cod), 117.7 (br.,
), 120–134 (aromatic C), 135.0 (br., CH=BAr ), 135.5–
), 175.3 (s,
P (1935.58): calcd. C 53.37, H 4.48,
N 0.72; found C 53.42, H 4.53, N 0.69.
CH=BAr
47 (aromatic C), 161.9 (q, JC-B = 50 Hz, C-B, BAr
C=N) ppm. C86 86BF24IrNO
F
F
1
1
F
H
7
3
raphy (eluent: toluene/NEt , 100:2) to produce the corresponding
31
[Ir(cod)(L4)]BAr
: Yield: 122 mg (96%). 31P NMR (CDCl
ligand as a colorless oil. Yield: 152 mg (54%). P NMR (CDCl
3
):
-Ph),
-Ph), 3.28 (m, 1 H, 6Ј-H), 3.45 (m, 2 H, 4-H and 1.89 (s, 3 H, CH
F
3
): δ =
, cod),
, cod), 2.48 (m, 1 H,
3
-Ph), 3.6–3.8 (m, 4 H, 3-H, 4-H, 5-
1
1
δ = 106.6 (s) ppm. H NMR (CDCl
3
): δ = 2.25 (s, 3 H, CH
3
116.2 (s) ppm. H NMR (CDCl
-Ph), 1.8–2.2 (br., 4 H, CH
CH=, cod), 2.99 (s, 3 H, CH
H, 6Ј-H), 3.86 (m, 1 H, CH=, cod), 4.28 (dd, J6-6Ј = 10.0, J6-5
H, 7-H), 5.58 (d, J1-2 = 8.0 Hz, 1 H, 1-H), 6.8–7.2 (m, 12 H, 4.0 Hz, 1 H, 6-H), 4.58 (m, 1 H, 2-H), 5.02 (m, 1 H, CH=), 5.47
3 2
): δ = 1.6–1.8 (m, 4 H, CH
2
.69 (s, 3 H, CH
3
2
3
2
3
5
J
-H), 3.97 (dd, J6-6Ј = 10.8, J6-5 = 3.6 Hz, 1 H, 6-H), 4.13 (dd,
3
3
2
3
2-1 = 8.0, J2-3 = 3.6 Hz, 1 H, 2-H), 4.43 (m, 1 H, 3-H), 5.02 (s,
=
3
1
3
CH=), 7.25 (m, 2 H, CH=), 7.64 (m, 1 H, CH=), 7.88 (m, 1 H,
CH=), 8.08 (m, 2 H, CH=) ppm. 13C NMR (CDCl
): δ = 20.8 (d, aromatic H), 7.0–7.8 (m, 26 H, CH= aromatic H), 8.32 (m, 2 H,
C-P = 21.4 Hz, CH -Ph), 21.5 (d, JC-P = 20.6 Hz, CH
C-5), 68.8 (C-6), 70.1 (d, JC-P = 4.6 Hz, C-2), 80.2 (C-4), 83.8 (d,
C-P = 22.1 Hz, C-3), 101.7 (C-7), 103.4 (C-1), 126.9 (CH=), 128.8 (br., CH
CH=), 128.9 (CH=), 129.0 (CH=), 129.1 (CH=), 129.6 (CH=), CH , cod), 65.9 (CH), 66.4 (CH), 67.7 (CH), 69.3 (CH=, cod), 75.1
(m, 1 H, 7-H), 6.28 (d, J1-2 = 6.0 Hz, 1 H, 1-H), 6.5 (m, 1 H, CH=
3
CH= aromatic H), 8.73 (m, 1 H, CH= aromatic H) ppm. 1 C NMR
(CDCl ): δ = 21.6 (CH -Ph), 23.0 (d, JC-P = 6.0 Hz, CH ), 25.6
, cod), 29.0 (br., CH , cod), 29.9 (br., CH , cod), 32.3 (br.,
3
J
3
3
-Ph), 63.6
(
J
(
3
3
3
2
2
2
2
1
30.2 (CH=), 130.5 (CH=), 130.6 (CH=), 130.8 (CH=), 130.9
(CH=, cod), 80.7 (CH), 93.0 (d, JC-P = 13.8 Hz, CH=cod), 101.8
(d, JC-P = 12.6 Hz, CH=cod), 102.2 (C-7), 104.4 (C-1) 117.7 (br.,
(
CH=), 131.2 (CH=), 131.3 (CH=), 131.4 (CH=), 131.5 (CH=),
32.1 (CH=), 138.2 (CH=), 140.3 (C), 140.4 (C), 140.6 (C), 141.3
C), 141.6 (C), 142.2 (C), 142.5 (C), 163.6 (C=N) ppm. 145 (aromatic C), 161.9 (q,
P (565.60): calcd. C 72.20, H 5.70, N 2.48; found C (C=N) ppm. C74 56BF24IrNO
2.17, H 5.72, N 2.43. N 0.81; found C 51.35, H 3.24, N 0.77.
1
(
C
7
CH=, BAr
F
), 120–134 (aromatic C), 135.0 (br., CH=, BAr
F
), 136–
), 170.5
5
P (1729.22): calcd. C 51.40, H 3.26,
1
JC-B = 49.6 Hz, C-B, BAr
F
34
H32NO
5
H
Eur. J. Inorg. Chem. 2013, 2139–2145
2143
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
Typical Procedure for the Hydrogenation of Olefins: The alkene
Forming Reactions (Ed.: P. G. Andersson), Wiley-VCH,
Weinheim, 2011, pp. 153–156.
(
(
0.5 mmol) and Ir complex (2 mol-%) were dissolved in CH
2 mL) in a high-pressure autoclave, which was purged four times
2 2
Cl
[
5] Chelating oxazoline-carbene ligands, mainly developed by Bur-
gess and co-workers, have also been successfully used – also to
a lesser extent chiral diphosphanes; see, for instance: a) M. C.
Perry, X. Cui, M. T. Powell, D. R. Hou, J. H. Reibenspies, K.
Burgess, J. Am. Chem. Soc. 2003, 125, 113; b) X. Cui, K. Bur-
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6] Very recently, the ligand range has been extended to include
the use of other non-nitrogen-containing heterodonor ligands
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Pugin, A. Pfaltz, Angew. Chem. 2011, 123, 9772; Angew. Chem.
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Adv. Synth. Catal. DOI: DOI10.1002/adsc.201200711.
with hydrogen. Subsequently, it was pressurized at the desired pres-
sure. After the required reaction time, the autoclave was depressur-
ized and the solvent evaporated. The residue was dissolved in Et
2
O
(1.5 mL) and filtered through a short Celite plug. The enantiomeric
excess was determined by chiral GC or chiral HPLC, and conver-
1
sions were determined by H NMR spectroscopy. The enantiomeric
excesses of hydrogenated products were determined using the con-
ditions previously described.[
17,18]
[
[
Typical Procedure for Catalyst Recycling: After each catalytic run,
the autoclave was depressurized. The colorless propylene carbonate
solution was then extracted with dry/deoxygenated hexane under
argon in order to remove the substrate and the hydrogenated prod-
uct. Upon extractions, the corresponding amount of substrate was
then added to start a new run.
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Acknowledgments
We would like to thank the Spanish Government for providing
grant CTQ2010-15835, the Catalan Government for grant
2009SGR116, and the ICREA Foundation for providing M. D. and
O. P. with financial support through the ICREA Academia Awards.
[
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2
2
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[7a]
[8a]
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[
2
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Eur. J. Inorg. Chem. 2013, 2139–2145
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FULL PAPER
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2
[
Received: December 10, 2012
[
Published Online: February 21, 2013
Eur. J. Inorg. Chem. 2013, 2139–2145
2145
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim