Enantioselective hydrogenation of olefins with planar chiral iridium ferrocenyloxazolinylphosphine complexes

Article abstract of DOI:10.1016/j.tetasy.2007.02.018

Chiral iridium Fc-PHOX complexes were readily prepared from Fc-PHOX, [Ir(cod)Cl]₂ and NaBArF (or NaPF₆) in high yields. They were applied as catalysts in the enantioselective hydrogenation of olefins to afford the corresponding produ

Full text of DOI:10.1016/j.tetasy.2007.02.018

Tetrahedron: Asymmetry 18 (2007) 629–634
Enantioselective hydrogenation of olefins with planar chiral iridium
ferrocenyloxazolinylphosphine complexes
a,b,
b
b
b
*
Xinsheng Li,
Qing Li, Xiaohua Wu, Yongguang Gao,
a,b
b
Dongcheng Xu and Lichun Kong
a
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University,
Jinhua 321004, PR China
b
Department of Chemistry and Life Science, Zhejiang Normal University, Jinhua 321004, PR China
Received 18 December 2006; accepted 14 February 2007
2 6
Abstract—Chiral iridium Fc-PHOX complexes were readily prepared from Fc-PHOX, [Ir(cod)Cl] and NaBArF (or NaPF ) in high
yields. They were applied as catalysts in the enantioselective hydrogenation of olefins to afford the corresponding products with high
conversions and good enantioselectivities (up to 99% ee).
ꢀ
2007 Elsevier Ltd. All rights reserved.
1. Introduction
excellent results for the enantioselective hydrogenation of
both unfunctionalized and functionalized olefins. After
5
The enantioselective hydrogenation of olefins is one of the
more important methods in asymmetric synthesis.
this discovery, a number of chiral Ir-based systems with
1
6
7
8
N–P C–P and C–N ligands were applied to improve
the catalytic efficiency and expand the reaction scope.
Since little was known about the mechanism and enantio-
selectivity-determining factors of the highly substrate
dependent Ir-catalyzed hydrogenation, the develop-
ment of new Ir-based catalytic systems still remains a
challenge.
Although Ru- and Rh-based systems with bidenate phos-
phine ligands have been developed since 1970s, the results
of the hydrogenation of some olefins, especially unfunc-
2
tionalized olefins, were unsatisfactory with these systems.
[
Ir(cod)(py)Pcy ]PF was used for the first time in the
3 6
hydrogenation of substituted olefins to provide good
3
results by Crabtree et al. However, Ir-based bidenate
phosphine ligand catalysts have not been explored as exten-
sively as Ru- and Rh-based systems. Recently, Pfaltz et al.
developed phosphino-oxazoline (PHOX) (Scheme 1)
ligands to mimic a chiral Crabtree’s catalyst and obtained
Planar chiral ferrocenyloxazolinylphosphines (Fc-PHOX)
(Scheme 1) are versatile ligands and have a wide range of
applications in asymmetric synthesis, such as the hydro-
4
9
10
genations of quinolines and ketones, transfer hydro-
1
1
12
genation
and a-alkylation of ketones,
oxidative
1
3
kinetic resolution of racemic alcohols, allylic substitu-
tions, Heck reactions and 1,3-dipolar cycloadditions.
1
4
15
16
O
R
It is noteworthy that Fc-PHOX have not only a stereogenic
centre in the oxazoline ring, but also a planar chirality in
the ferrocene moiety. It is believed that the Fc-PHOX
and some cations can form a rigid six-membered chelate
ring, and the planar chirality forms a better chiral environ-
ment for chirality transfer during the asymmetric reaction,
which has been demonstrated by Zhou et al. In their
N
O
PPh2
PAr2 N
PHOX
Fe
R
Fc-PHOX
Scheme 1.
research, [Ir(cod)Cl] /(S,S)-Fc-PHOX was applied in the
2
hydrogenation of quinolines and excellent enantiomeric
9
*
Corresponding author. Tel.: +86 579 2283702; fax: +86 579 2282610;
e-mail: sky33@zjnu.cn
excess values were obtained. To the best of our knowl-
edge, there have been no results reported on the successful
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.02.018

630
X. Li et al. / Tetrahedron: Asymmetry 18 (2007) 629–634
use of [Ir(cod)Fc-PHOX]BArF complex (BArF: tetra-
kis[3,5-bis(trifluoromethyl)phenyl]borate) in the enantio-
selective hydrogenation of unfunctionalized and function-
was hydrogenated to test the effectiveness of these com-
plexes. The hydrogenation procedures were carried out in
the presence of 0.2–2 mol % of iridium complexes under
20–90 bar of hydrogen pressure at room temperature
1
7,18
alized olefins.
Herein, we report our recent study on
ꢀ
the synthesis and application of these chiral iridium com-
plexes in the enantioselective hydrogenation of olefins.
(Table 1). The hydrogenation using 1f with PF6 as an anion
led to only 5.8% conversion (Table 1, entry 16). Complex
ꢀ
1
g with Cl as the anion resulted in a complete loss of
catalytic activity (Table 1, entry 17). The results showed
strongly coordinating anions deactivating the catalyst.
Similar to the reported result of iridium catalysts, good
conversions were obtained in chlorinated solvents {Table
2
. Results and discussion
3
,6
All the iridium complexes were readily synthesized in good
yields (Scheme 2). To investigate the influence of the rela-
tive configuration of the chirality in the oxazoline ring
and the planar chirality of the ferrocene ring, two diaste-
reomeric complexes 1c and 1h were synthesized. A series
of complexes 1a–1h were also synthesized to study the
influence of the anion and the R group in the oxazoline
ring. (E)-1,2-Diphenyl-1-propene as a typical substrate
1, entries 1–6, CH
30.3%; Et O and THF, 0%; toluene, 4.9%}. Middle to com-
plete conversion was obtained in the presence of 0.5 mol %
1a–1e or 1h as catalysts in CH Cl (Table 1 entries 1, 7–15
Cl , 100%; (CH Cl) , 60.9%; CH Cl,
2 2 2 3
2
2
2
2
and 18). Higher catalyst loading (2 mol %) did not increase
the enantioselectivity (Table 1, entry 8). Lower catalyst
loading (0.2 mol %) resulted in extremely low conversion
O
R
O
R
Ir
Ph2P
Fe
N
N
1) [Ir(cod)Cl]2, CH2Cl2; 2) NaBArF
N
Ir
or 1) [Ir(cod)Cl]2, CH2Cl2; 2) NaPF6
or [Ir(cod)Cl]2, CH2Cl2
P
PPh2
BArF
Bu-t
Fe
a - 1g
Ph2
O
Fe
X
1
1h
1a: R = Me, X = BArF
1b: R = i-Pr, X = BArF
1c: R = t-Bu, X = BArF
1d: R = Ph, X = BArF
1
1
1
e: R = Bn, X = BArF
f: R = Me, X = PF6
g: R = t-Bu, X = Cl
Scheme 2. Synthesis of catalysts.
Table 1. Asymmetric hydrogenation of (E)-1,2-diphenyl-1-propene in the presence of 1a–1h
.2 - 2 mol % 1a - 1h
0
Ph
Ph
Ph
Ph
2
0-90 bar H , 5h
2
2
a
3a
) (bar)
a
b
Entry
Cat.
mol % Cat.
Sol.
CH
(CH
CH
Et
P (H
2
Conversion (%)
ee
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
1c
1d
1e
1f
0.5
0.5
0.5
0.5
0.5
0.5
0.2
2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
2
2
Cl
Cl)
Cl
2
50
50
50
50
50
50
50
50
90
20
50
50
90
50
50
50
60
50
100
60.9
30.3
0
0
4.9
51
100
100
37
66
38
98
74
100
5.8
0
87.4 (R)
2
2
85.1
c
3
Nd
2
O
THF
Toluene
c
Nd
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
2
2
2
2
2
2
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
2
2
2
2
2
2
2
2
2
2
2
2
86.1 (R)
89.2 (R)
82.5 (R)
84.7 (R)
71.6 (R)
77.6 (R)
79.7 (R)
62.4 (R)
74.3 (R)
1
1
1
1
1
1
1
1
1
c
Nd
1g
1h
2
0.5
45
60.4 (R)
a
Determined by GC.
b
Determined by HPLC using a chiral Chiracel OJ-H column. The absolute configurations were assigned by comparison of the HPLC retention times with
5
literature values.
c
Not determined.

X. Li et al. / Tetrahedron: Asymmetry 18 (2007) 629–634
631
(
Table 1, entry 7). The steric bulk of the R group in the
Table 2. The results of asymmetric hydrogenation in the presence of 1a
(
0.5 mol %)
oxazoline ring controlled both the activation and the
enantioselectivity of the catalysts. The Ir-complexes 1a
and 1e with little steric bulk in the oxazoline ring gave com-
plete conversion (Table 1, entries 1 and 15). The highest ee
value was achieved with 1a as the catalyst (87.4% ee). A de-
crease in activity was found upon the introduction of bulky
R substituents. Conversions of 66%, 38% and 74% were
obtained with catalysts 1b, 1c and 1d, respectively (Table 1,
entries 11, 12 and 14). Higher hydrogen pressure could
enhance the conversion of substrates (Table 1, entries 12
and 13). The same configuration of product was found with
0
.5 mol % 1a,
5
0 bar H2
Ph
2b
Ph
Ph
Ph
CH Cl , r.t., 5 h
2
2
3
b
Ph
p-MeOC H4
6
p-MeOC H4
6
MeO
2
c
2d
2e
1
c and 1h as catalysts, which indicated that the central
chirality in the oxazoline ring of the catalyst determined
the configuration of the product (Table 1, entries 12, 13
and 18). The lower ee induced by 1h suggested the
mismatched nature of the (R) planar chirality with the
Ph
OH
Ph
OAc
CO Et
2
Ph
2
h
2
f
2g
a
b
(
6
S) central chirality of the oxazoline ring (77.6% ee vs
0.4% ee). Complexes 1a–1e with (S,S) configuration are
Entry
Substrate
Conversion (%)
ee
1
2
3
4
5
6
7
8
2b
2c
2c
2d
2e
2f
100
100
100
100
95
100
100
100
67.0 (S)
14.3 (S)
22.1 (S)
the matched case in terms of planar and central chiralities.
c
Other unfunctionalized olefins 2b–2e could also be hydro-
genated using complex 1a as a catalyst to afford the prod-
ucts in high yields and moderate to high ee values.
Asymmetric hydrogenation of a (Z)-1,2-diphenyl-1-pro-
pene led to a product with a different configuration, and
a lower enantiomeric excess was obtained (Table 2, entry
88.5 (R)
89.0 (S)
d
98.8
d
2g
2h
99.0
81.8 (R)
a
1
Determined by H NMR.
Determined by HPLC using a chiral Chiracel OJ-H, OD-H and OB-H
column. The absolute configurations were assigned by comparison of the
HPLC retention times with literature values.
0 bar pressure was used.
b
1
). Substrates 2c, 2d and 2e were subjected to hydrogena-
tion to provide 22.1%, 88.5% and 89% ee, respectively
Table 2, entries 3, 4 and 5). Reduction of the hydrogen
5
,6a
(
c
2
pressure caused an increase in the enantioselectivity of
the terminal olefin 2c (Table 2, entries 2 and 3, 14.3% vs
d
The absolute configurations were not determined.
2
2.1% ee). The functionalized 2-methyl-3-phenylpropenol
2
f and 3-acetoxy-2-methylphenylpropene 2g were hydro-
genated to afford the product with the highest ee (Table 2,
entries 6 and 7). b-Methyl cinnamic ester 2h could be
hydrogenated in 100% conversion and 81.8% ee (Table 2,
entry 8).
The conversion was determined on an Agilent 6820 or a
1
Bruker AV-400 MHz spectrometer. The H NMR (at
1
3
31
4
00 MHz), C NMR (at 100 MHz) and P NMR (at
1
60 MHz) spectra were recorded in CDCl with tetrameth-
3
1
13
ylsilane as an internal reference for H NMR and
NMR or 85% H PO as external reference for P NMR.
C
3
1
3
4
3. Conclusions
IR spectra were determined on a Nicolet-670 FT spectro-
photometer. Elemental analyses were performed on a Car-
lo Erba 1110 analyser. All reactions were carried out in dry
glassware under nitrogen.
In conclusion, the work presented here serves to expand the
scope of Ir-based catalysts. [Ir(cod)Fc-PHOX]BArF com-
plexes are effective catalysts for the asymmetric hydrogena-
tion of both unfunctionalized and functionalized olefins.
High yields and moderate to good enantioselectivities were
obtained when using the complexes as catalysts. Central
chirality dominates the configuration of the product in
the hydrogenation of (E)-1,2-diphenyl-1-propene. The
facile synthesis of ligands and catalysts provides a useful
method for the preparation of this type of chiral
compounds.
4.1. General procedure for the preparation of iridium
complexes 1a–1h
Oxazolines (0.1 mmol), [Ir(cod)Cl] (33.6 mg, 0.05 mmol)
2
and CH Cl (5 mL), were added to a flask under N . The
2
2
2
solution was stirred at room temperature for about 2 h
until TLC indicated that the ligand had been consumed.
NaPF or Na[BArF] (0.15 mmol) was added followed by
6
H O (5 mL), and the resulting two-phase mixture was stir-
2
4. Experimental
red vigorously for 30 min. The organic layer was separated,
and the aqueous layer extracted with CH Cl (2 · 5 mL).
2
2
Melting points were determined on a Yanagimoto micro
apparatus and are uncorrected. Optical rotations were
The combined organic phase was washed with H O
2
(5 mL) and dried over anhydrous Na SO . After removing
2
4
measured with WZZ-2B digital polarimeter. The ee values
the solvent under reduced pressure, the residue was purified
by column chromatography with CH Cl as the eluent to
TM
were determined by HPLC using Chiralcel
OD-H, OB-
2
2
H and OJ-H column with 2-propanol–hexane as the eluent.
afford yellow or red complexes.

632
X. Li et al. / Tetrahedron: Asymmetry 18 (2007) 629–634
4
4
oxazolyl)-2-diphenylphosphinoferrocene] iridium(I) tetra-
.2. (g -1,5-Cyclooctadiene) [(S,S)-(4,5-dihydro-4-methyl-2-
1.64 (m, 1H, COD), 1.93–2.07 (m, 2H, COD), 2.20–2.37
(m, 3H, COD), 2.43–2.53 (m, 1H, COD), 3.43–3.47 (m,
1H, COD), 3.80 (s, 5H, CpH), 3.89 (dd, 1H, J = 3.2,
kis[3,5-bis(trifluoromethyl)phenyl]borate (S,S)-1a
9
.6 Hz, CH O), 4.22 (t, 1H, J = 9.6, CHN), 4.62 (dd, 1H,
2
2
D
0
Yield 86.4%, mp 193–196 ꢁC. ½aꢁ ¼ ꢀ336:7 (c 0.28,
J = 3.2, 9.6 Hz, CH O), 4.73–4.74 (m, 1H, CpH), 4.82–
2
1
CH Cl ) H NMR (400 MHz, CDCl ) 1.26–1.31 (m, 1H,
4.84 (m, 1H, COD), 4.85–4.86 (m, 1H, CpH), 4.87–4.89
(m, 1H, COD), 5.13–5.15 (m, 1H, CpH), 7.08–7.10 (m,
2H, PhH), 7.36–7.40 (m, 3H, PhH), 7.53 (s, 4H, BArF–
H), 7.66–7.68 (m, 3H, PhH), 7.71 (sbr, 8H, BArF–H),
2
2
3
COD), 1.41 (d, 3H, J = 6.5 Hz, CH ), 1.67–1.75 (m, 2H,
3
COD), 2.09–2.20 (m, 2H, COD), 2.27–2.37 (m, 3H,
COD), 2.42–2.48 (m, 1H, COD), 3.35–3.42 (m, 1H,
COD), 3.67 (s, 5H, CpH), 4.16–4.22 (m, 1H, CHN), 4.29
1
3
8.10–8.15 (m, 2H, PhH). C NMR (100 MHz, CDCl3)
(
d, 2H, J = 5.2, CH O), 4.66–4.67 (m, 1H, CpH), 4.78–
25.2 ((CH ) ), 26.2 (COD), 27.4 (COD), 33.0 (COD),
2
3 3
4
(
2
.79 (m, 1H, COD), 4.83–4.85 (m, 1H, CpH), 4.91–4.98
m, 1H, COD), 5.15–5.17 (m, 1H, CpH), 7.08–7.14 (m,
H, PhH), 7.34–7.44 (m, 3H, PhH), 7.51 (s, 4H, BArF–
H), 7.65–7.68 (m, 3H, PhH), 7.77 (br s, 8H, BArF–H),
34.3 (t-BuC), 36.9 (COD), 60.9 (COD), 63.0 (COD), 70.3
(CpH), 71.8 (CH O), 72.7 (CpH), 73.4 (CHN), 73.5
2
(CpH), 74.7 (CpH), 74.8 (CpH), 78.2 (CpH), 90.0 (COD),
96.5 (COD), 117.4 (BArF), 123.2 (CF ), 125.9, 128.4,
3
1
3
8
.13–8.17 (m, 2H, PhH). C NMR (100 MHz, CDCl3)
128.6, 128.8 (BArF), 131.3, 132.8 (BArF), 132.9, 133.0,
2
3.3 (CH ), 26.9 (COD), 28.5 (COD), 31.8 (COD), 35.4
134.8 (BArF), 136.2, 136.4, 160.9 (ArB), 171.6 (C@N).
3
3
1
(
COD), 59.6 (COD), 60.4 (COD), 61.3 (CH O), 64.8 (d,
P NMR (160 MHz, CDCl ) 13.1 (PPh ). IR (KBr):
2
3 2
CHN), 72.5, 72.6, 74.2, 74.3, 74.6, 77.9 (CpH), 91.7
COD), 95.3 (COD), 117.7 (m, BArF), 123.2 (CF3),
1856. Anal. Calcd for C H BF FeIrNOP: C, 49.95; H,
69 54 24
3.28; N, 0.84. Found: C, 49.58; H, 3.08; N, 0.83.
(
1
1
1
25.9, 128.5 (BArF), 128.6, 129.0, 129.1, 129.2, 132.4,
32.8, 134.8 (BArF), 135.8, 136.3, 136.8, 161.0 (ArB),
4
4.5. (g -1,5-Cyclooctadiene) [(S,S)-(4,5-dihydro-4-phenyl-2-
oxazolyl)-2-diphenylphosphinoferrocene] iridium(I) tetra-
kis[3,5-bis(trifluoromethyl)phenyl]borate (S,S)-1d
3
1
71.5 (C@N). P NMR (160 MHz, CDCl ) 9.8 (PPh ).
3
2
IR (KBr): 1587. Anal. Calcd for C H BF FeIrNOP: C,
6
6
48
24
4
9.03; H, 2.99; N, 0.87. Found: C, 48.65; H, 2.87; N, 0.88.
2
D
0
Yield, 73.1%, mp 190–192 ꢁC, ½aꢁ ¼ ꢀ578:0 (c 0.20,
4
1
4
.3. (g -1,5-Cyclooctadiene) [(S,S)-(4,5-dihydro-4-isopropyl-
CH Cl ). H NMR (400 MHz, CDCl ) 1.27–1.34 (m,
2
2
3
2-oxazolyl)-2-diphenylphosphinoferrocene] iridium(I) tetra-
kis[3,5-bis(trifluoromethyl)phenyl]borate (S,S)-1b
1H, COD), 1.50–1.56 (m, 1H, COD), 1.74–1.81 (m,
2H, COD), 2.07–2.10 (m, 1H, COD), 2.14–2.18 (m, 2H,
COD), 2.20–2.25 (m, 1H, COD), 2.31–2.39 (m, 1H,
COD), 3.22–3.24 (m, 1H, COD), 3.73 (s, 5H, CpH), 4.50
20
Yield, 81.3%, mp 135–137 ꢁC, ½aꢁ ¼ ꢀ471:2 (c 0.29,
D
1
CH Cl ). H NMR (400 MHz, CDCl ) 0.91 (d, 3H,
(dd, 1H, J = 3.2, 9.2 Hz, CH O), 4.70 (t, 1H, J = 8.8,
2
2
3
2
J = 6.8 Hz, CH ), 1.02 (d, 3H, J = 7.2 Hz, CH ), 1.25–
CHN), 4.73–4.76 (m, 1H, CpH), 4.78 (dd, 1H, J = 3.2,
3
3
1
(
4
.30 (m, 1H, COD), 1.52–1.55 (m, 1H, CH), 1.64–1.70
m, 1H, COD), 2.01–2.08 (m, 2H, COD), 2.27–2.39 (m,
H, COD), 2.43–2.48 (m, 1H, COD), 3.32–3.36 (m, 1H,
9.2 Hz, CH O), 4.87–4.88 (m, 1H, CHCOD), 4.89–4.90
2
(m, 1H, CHCOD), 4.90–4.91 (m, 1H, CpH), 5.20–5.21
(m, 1H, CpH), 7.10–7.12 (m, 2H, PhH), 7.28–7.29 (m,
3H, PhH), 7.30–7.34 (m, 5H, PhH), 7.52 (s, 4H, BArF–
H), 7.69–7.75 (m, 3H, PhH), 7.71 (br s, 8H, BArF–H),
COD), 4.33 (s, 5H, CpH), 4.00 (dd, 1H, J = 4.0, 8.0 Hz,
CH O), 4.26 (t, 1H, J = 9.2, CHN), 4.51 (dd, 1H,
J = 4.0, 8.0 Hz CH O), 4.70–4.72 (m, 1H, CpH), 4.78–
2
1
3
8.14–8.18 (m, 2H, PhH). C NMR (100 MHz, CDCl3)
27.4 (COD), 29.2 (COD), 31.2 (COD), 34.4 (COD), 60.6
2
4
(
2
.81 (m, 1H, COD), 4.82–4.83 (m, 1H, CpH), 4.86–4.89
m, 1H, COD), 5.12–5.13 (m, 1H, CpH), 7.14–7.19 (m,
H, PhH), 7.38–7.40 (m, 3H, PhH), 7.53 (s, 4H, BArF–
H), 7.65–7.68 (m, 3H, PhH), 7.72 (sbr, 8H, BArF–H),
(COD), 64.3 (COD), 66.7 (CH O), 71.6 (CHN), 72.8
2
(CpH), 72.9 (CpH), 74.6 (CpH), 74.7 (CpH), 74.8 (CpH),
78.4 (CpH), 93.0 (COD), 96.6 (COD), 117.4 (BArF),
1
3
8
1
.13–8.15 (m, 2H, PhH). C NMR (100 MHz, CDCl3)
4.9 (CH ), 18.6 ((CH ) ), 22.6 (COD), 26.1 (COD), 27.8
123.2 (CF ), 125.2, 125.9, 128.5 (BArF), 129.0, 129.1,
3
131.3, 132.4 (BArF), 132.8, 134.8, 136.3, 140.1, 160.9
3
3 3
3
1
(
(
(
(CH ) C), 32.8 (COD), 36.2 (COD), 61.4 (COD), 63.4
COD), 68.8 (CHN), 71.6 (CH O), 72.6 (CpH), 73.5
CpH), 73.6 (CpH), 74.5 (CpH), 74.6 (CpH), 77.9 (CpH),
(ArB), 173.9 (C@N). P NMR (160 MHz, CDCl ) 9.47
3
3
3
(PPh ). IR (KBr): 1856. Anal. Calcd for C H BF FeIr-
2
2
71 50
24
NOP: C, 50.79; H, 3.00; N, 0.83. Found: C, 50.31; H,
2.89; N, 0.84.
9
1
1
1
0.6 (COD), 96.1 (COD), 117.5 (BArF), 123.2 (CF3),
25.9, 128.4 (BArF), 129.0, 129.1, 131.3, 132.8 (BArF),
32.9, 134.8 (BArF), 136.2, 136.3, 136.8, 160.9 (ArB),
4
4.6. (g -1,5-Cyclooctadiene) [(S,S)-(4,5-dihydro-4-benzyl-2-
oxazolyl)-2-diphenylphosphinoferrocene] iridium(I) tetra-
kis[3,5-bis(trifluoromethyl)phenyl]borate (S,S)-1e
3
1
71.6 (C@N). P NMR (160 MHz, CDCl ) 11.6 (PPh ).
3
2
IR (KBr): 1586. Anal. Calcd for C H BF FeIrNOP: C,
6
8
52
24
4
9.65; H, 3.19; N, 0.85. Found: C, 49.14; H, 3.11; N, 0.86.
2
D
0
Yield, 69.6%, Mp 80–82 ꢁC, ½aꢁ ¼ ꢀ397:4 (c 0.20,
4
1
4
butyl-2-oxazolyl)-2-diphenylphosphinoferrocene] iridium(I)
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (S,S)-1c
.4. (g -1,5-Cyclooctadiene) [(S,S)-(4,5-dihydro-4-tert-
CH Cl ). H NMR (400 MHz, CDCl ) 1.25–1.32 (m, 1H,
COD), 1.52–1.65 (m, 2H, COD), 2.10–2.22 (m,
2H, COD), 2.30–2.39 (m, 3H, COD), 2.41–2.54 (m, 1H,
2
2
3
COD), 2.51–2.57 (m, 2H, PhCH ), 3.42–3.46 (m, 1H,
COD), 3.78 (s, 5H, CpH), 4.22 (t, 1H, J = 8.4 Hz, CHN),
2
2
D
0
Yield, 85.0%, mp 172–175 ꢁC, ½aꢁ ¼ ꢀ641:1 (c 0.18,
1
CH Cl ). H NMR (400 MHz, CDCl ) 1.18 (s, 9H, t-Bu),
4.46–4.57 (m, 2H, CH O), 4.69–4.71 (m, 1H, CpH), 4.86–
2
2
3
2
1
.26–1.33 (m, 1H, COD), 1.50–1.54 (m, 1H, COD), 1.56–
4.99 (m, 1H, CpH), 5.12–5.14 (m, 1H, COD), 5.18–5.19

X. Li et al. / Tetrahedron: Asymmetry 18 (2007) 629–634
633
(
m, 1H, CpH), 7.10–7.13 (m, 2H, PhH), 7.21–7.24 (m, 3H,
(100 MHz, CDCl ) 24.9 ((CH ) ), 25.4 (COD), 28.2
3 3 3
PhH), 7.35–7.43 (m, 5H, PhH), 7.51 (s, 4H, BArF–H),
(COD), 29.7 (COD), 32.6 (COD), 34.3 (COD), 37.0
7
8
.70–7.76 (m, 3H, PhH), 7.71 (br s, 8H, BArF–H), 8.20–
(t-BuC), 58.3 (COD), 60.2 (COD), 68.4 (CpH), 70.4
1
3
.22 (m, 2H, PhH). C NMR (100 MHz, CDCl ) 29.4
(CH O), 72.5 (CHN), 73.2 (CpH), 75.2 (CpH), 75.3
3
2
(
(
(
(
(
COD), 29.6 (COD), 31.9 (COD), 34.1 (COD), 42.9
(CpH), 75.5 (CpH), 76.3 (CpH), 91.3 (COD), 93.8
PhCH ), 61.6 (COD), 64.4 (COD), 65.2 (CpH), 71.8
(COD), 117.4 (BArF), 122.2, 123.2 (CF ), 125.9, 128.4,
2
3
CH O), 72.6 (CHN), 72.7 (CpH), 74.5 (CpH), 75.3
128.7 (BArF), 128.9, 129.0, 129.2, 132.0, 132.2, 133.4,
2
3
1
CpH), 76.6 (CpH), 78.3 (CpH), 92.3 (COD), 96.5
134.8 (BArF), 136.2, 160.9 (ArB), 172.9 (C@N).
P
COD), 117.4 (BArF), 123.2 (CF ), 125.9, 128.5 (BArF),
NMR (160 MHz, CDCl ) 10.9 (PPh ). IR (KBr): 1586.
3
3
2
1
28.6, 128.7, 128.9, 129.1, 129.4, 132.3, 134.1, 134.8
Anal. Calcd for C H BF FeIrNOP: C, 49.95; H, 3.28;
69 54 24
N, 0.84. Found: C, 49.53; H, 3.01; N, 0.80.
3
1
(
BArF), 135.8, 136.0, 161.0 (ArB), 171.9 (C@N).
P
NMR (160 MHz, CDCl ) 9.8 (PPh ). IR (KBr): 1857. Anal
3
2
Calcd for C H BF FeIrNOP: C, 51.08; H, 3.10; N, 0.83.
Found: C, 50.62; H, 2.94; N, 0.82.
7
2
52
24
4.10. General procedure for hydrogenation in the presence
of iridium complexes 1a–1h (0.5 mol %)
4
4
oxazolyl)-2-diphenylphosphinoferrocene] iridium(I) hexa-
fluorophosphate (S,S)-1f
.7. (g -1,5-Cyclooctadiene) [(S,S)-(4,5-dihydro-4-methyl-2-
Enantioselective hydrogenation of olefins: olefins 2a–2h
(0.5 mmol) and chiral Fc-PHOX (0.0025 mmol) in 2 mL
dry degassed CH Cl were added to the autoclave under
2
2
inert atmosphere. The autoclave was sealed immediately
and pressurized to 50 bar H . The mixture was then stirred
for 5 h. The CH Cl was removed and the crude product
2
D
0
Yield 56.4%, mp 153–156 ꢁC. ½aꢁ ¼ ꢀ160:1 (c 0.11,
2
1
CH Cl ) H NMR (400 MHz, CDCl ) 1.25–1.30 (m, 1H,
2
2
3
2
2
COD), 1.40 (d, 3H, J = 6.5 Hz, CH ), 1.65–1.71 (m, 2H,
3
was passed through a short silica-gel column with hexane
or 10% ethyl acetate in hexane as eluent. After evaporation
of the solvent, 3a–3h were obtained and analyzed for
COD), 2.07–2.22 (m, 2H, COD), 2.24–2.33 (m, 3H,
COD), 2.41–2.45 (m, 1H, COD), 3.34–3.42 (m, 1H,
COD), 3.68 (s, 5H, CpH), 4.14–4.21 (m, 1H, CHN), 4.30
1
conversion (GC or H NMR) and % ee (HPLC).
(
d, 2H, J = 5.2, CH O), 4.65–4.67 (m, 1H, CpH), 4.75–
2
4
.78 (m, 1H, COD), 4.82–4.86 (m, 1H, CpH), 4.92–4.97
(
5
m, 1H, COD), 5.13–5.16 (m, 1H, CpH), 7.11–7.45 (m,
H, PhH), 7.65–8.13 (m, 5H, PhH). C NMR (100 MHz,
Acknowledgements
1
3
CDCl ) 23.2 (CH ), 27.1 (COD), 28.4 (COD), 31.8
3
3
This paper was supported by the Natural Science Founda-
tion of Zhejiang Province (Y405013). Dr. Xiaoxia Wang is
thanked for the useful discussions.
(
(
(
COD), 35.5 (COD), 59.4 (COD), 60.5 (COD), 61.2
CH O), 65.2 (d, CHN), 72.5, 72.7, 74.2, 74.4, 74.5, 77.8
2
CpH), 91.8 (COD), 95.5 (COD), 126.0, 128.5, 128.9,
1
29.0, 129.2, 132.5, 132.9, 135.8, 136.2, 136.7, 172.5
3
1
(
C@N). P NMR (160 MHz, CDCl ) 32 (PPh ), ꢀ147.4
3
2
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6
C H F FeIrNOP : C, 45.44; H, 4.04; N, 1.56. Found:
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4
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