Synthesis of iridium complexes with new planar chiral chelating phosphinyl-imidazolylidene ligands and their application in asymmetric hydrogenation

Article abstract of DOI:10.1016/j.tetasy.2004.03.047

The synthesis of planar chiral phosphinoimidazolium salts such as (R _p)-3-(4-diphenyl-phosphino[2.2]paracyclophan-12-ylmethyl)-1-(2, 6-diisopropylphenyl)imidazolium bromide (R_p)-11c starting from enantiopure 4,12-dibromo[2.2]paracyclophane (R_p)-6 is reported. After deprotonation of these salts and a subsequent reaction with [Ir(COD)Cl] ₂, chelating iridium imidazolylidene complexes (R_p)-5a-c are obtained. These complexes catalyze the asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee.

Full text of DOI:10.1016/j.tetasy.2004.03.047

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 1693–1706
Synthesis of iridium complexes with new planar chiral chelating
phosphinyl-imidazolylidene ligands and their
application in asymmetric hydrogenation
Thilo Focken, Gerhard Raabe and Carsten Bolm*
Institut f€ur Organische Chemie der RWTH Aachen, Professor-Pirlet-Str. 1, D-52056 Aachen, Germany
Received 1 March 2004; accepted 31 March 2004
Abstract—The synthesis of planar chiral phosphinoimidazolium salts such as (Rp)-3-(4-diphenyl-phosphino[2.2]paracyclophan-12-
ylmethyl)-1-(2,6-diisopropylphenyl)imidazolium bromide (Rp)-11c starting from enantiopure 4,12-dibromo[2.2]paracyclophane
(Rp)-6 is reported. After deprotonation of these salts and a subsequent reaction with [Ir(COD)Cl]2, chelating iridium imidazolylidene
complexes (Rp)-5a–c are obtained. These complexes catalyze the asymmetric hydrogenation of functionalized and simple alkenes
with up to 89% ee.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
and shortly afterwards by Enders and co-workers.3d;10
Both applied chiral rhodium NHC complexes in enan-
tioselective hydrosilylations. Recently, this process was
improved by Shi and co-workers.11 Grubbs and Hov-
eyda demonstrated the application of chiral ruthenium
NHC complexes in asymmetric olefin metathesis.12;13
Other examples include the use of silver NHC complexes
in the conjugate addition of diethyl zinc to unsaturated
ketones,14 the synthesis of oxindoles by a palladium
catalyzed, intramolecular a-arylation of amides15 and
the palladium-catalyzed allylic substitution.16 Recently,
[2.2]paracyclophane-based saturated imidazolium salts
have been applied in the rhodium-catalyzed asymmetric
conjugate addition of aryl boron reagents to enones.17
N-Heterocyclic carbenes (NHC) and their use as ligands
on metal complexes were reported as early as 1968 by
1a
1b
€
€
Ofele and Wanzlick and Schonherr. The interest in
this new ligand class increased significantly after Ardu-
engo et al. described the first isolated free NHCs in
1991.2 Since then, much progress has been made with
respect to the synthesis and application of NHCs.3;4
They now represent an attractive alternative to phos-
phine ligands in homogenous catalysis5 since complexes
bearing them often exhibit superior properties. A highly
popular application for NHCs is olefin metathesis,
where ruthenium–carbene complexes constitute the
most active class of catalysts.6
Most reactions mentioned so far involve the use of
NHCs in C–C bond forming processes. However, tran-
sition metal NHC complexes have also been applied in
alkene-to-alkane reductions and the transfer hydroge-
nation of ketones. For this purpose Nolan and
co-workers prepared achiral iridium NHC complexes18
similar to Crabtree’s catalyst.19 The synthesis and
application of metal catalysts bearing chelating biscar-
bene ligands has been described by Crabtree and
co-workers.20 Asymmetric hydrogenations using unsatu-
rated chiral iridium NHC complexes were reported by
Burgess and co-workers.21 They successfully applied
iridium complex 1 bearing a chiral chelating imidazolyl-
idene ligand as a catalyst in the hydrogenations of
Chiral NHCs have been applied in asymmetric cataly-
sis.7 The first example of a catalytic process involving an
N-heterocyclic carbene was the use of a chiral thiazo-
lium salt in the Stetter reaction by Sheenan and
co-workers.8 Later, triazolium salts were introduced by
Enders and co-workers as organocatalysts in enantio-
selective benzoin condensations and Stetter reactions.9
The use of metal complexes bearing chiral NHCs as
ligands were first reported by Herrmann and co-workers
* Corresponding author. Tel.: +49-241-8094675; fax: +49-241-80923-
91; e-mail: carsten.bolm@oc.rwth-aachen.de
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.03.047

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T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
O
BF4
I
BARF
Si(CH3)3
Fe
R
Rh
N
N
N
N
N
Ir
Fe
S
Rh
N
i-Pr
N
i-Pr
3
1: R = Adamantyl
2
X
BARF
O
Ph2
P
Ir
N
Ir
Ar
N
N
N
N
R
(Rp)-5a: Ar = Ph, X = BARF
(Rp)-5b: Ar = 2,4,6-Me3Ph, X = BARF
(Rp)-5c: Ar = 2,6-i-Pr2Ph, X = BARF
(Rp)-5d: Ar = 2,4,6-Me3Ph, X = PF6
4: R = Mesityl
unfunctionalized alkenes giving products with up to 99%
ee in 98% yield. Chung and co-workers reported on the
application of NHC metal complexes of type 2 having a
planar chiral ferrocene backbone in the hydrogenation
of dimethyl itaconate. The ee, however, was rather low
(18%).22a Furthermore, ferrocene-based iridium and
rhodium NHC complexes have been used in transfer
hydrogenations of acetophenone derivatives giving
enantioselectivities of up to 53% ee.22b
salts having a phosphino substituent instead of the oxa-
zoline moiety. Again, iridium complexes were prepared,
and the applicability of 5 as catalysts in asymmetric
hydrogenations of functionalized and simple olefines was
tested.
2. Results and discussion
Recently, we reported on the synthesis of the first planar
chiral carbene and its chromium and rhodium com-
plexes 3.23 In this case, the planar chirality originated
from the substitution pattern of the ferrocene back-
bone.24 Then, planar chiral [2.2]paracyclophane-based
imidazolium salts were described, in which the imidazolyl-
idenyl and an oxazolinyl substituent were in pseudo-
ortho positions of the [2.2]paracyclophane.25;26 The cor-
responding iridium carbene complexes 4 were applied
in asymmetric hydrogenations of alkenes giving enantio-
selectivities of up to 46% ee. We have now extended those
studies and prepared [2.2]paracyclophanyl imidazolium
The syntheses of the planar chiral imidazolium salts
started from enantiopure pseudo-ortho-dibromo-
[2.2]paracyclophane 6.27;28 After treatment of (Rp)-6
with 1 equiv of n-BuLi, the resulting carbanion was
trapped with chlorodiphenylphosphine affording
monophosphino paracyclophane (Rp)-7 in 92% yield
(Scheme 1). Alcohol (Rp)-8 was then obtained by met-
allation of (Rp)-7 with n-BuLi followed by reaction with
CO2 and subsequent reduction of the intermediate lith-
ium carboxylate with LiAlH4 (84% yield). Treatment of
(Rp)-8 with PBr3 afforded methyl bromide (Rp)-9 in 63%
PPh2
PPh2
(b)
Br
(a)
Br
OH
Br
(Rp)-6
(Rp)-7
(Rp)-8
(c)
O
PPh2
Br
PPh2
PPh2
(d)
+
N
N
Br
Br
R
(Rp)-11a-c
a: R = H
(Rp)-9
(Rp)-10
b: R = 2,4,6-Me3
c: R = 2,6-i-Pr2
Scheme 1. Reagents and conditions: (a) i. n-BuLi, THF, )78 ꢁC; ii. PPh2Cl, 92% yield; (b) i. n-BuLi, THF, )78 ꢁC; ii. CO2; iii. LiAlH4, 84% yield;
(c) PBr3, THF, 63% (Rp)-9 and 25% yield (Rp)-10; (d) imidazoles, toluene or DMF, 80–90 ꢁC, 16–59% yield.

T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
1695
yield. However, even under careful exclusion of air small
X
quantities (25% yield) of the corresponding phosphine
oxide (Rp)-10 were obtained. All attempts to avoid the
formation of this side product by using other reagents
failed. Presumably, (Rp)-10 stems from an intramolec-
ular activation of the benzylic hydroxyl group in (Rp)-8
by the neighbouring phosphino moiety followed by an
attack of the former by bromine. Thus the process
would be similar to the bromination of alcohols with
reagent combinations like PPh3/Br2.
Ph2
P
Ir
i.
N
(Rp)-11a-c
R
N
ii.
(Rp)-5a: R = H, X = BARF
(Rp)-5b: R = Mesityl, X = BARF
(Rp)-5c: R = 2,6-i-Pr2Ph, X = BARF
(Rp)-5d: R = Mesityl, X = PF6
Scheme 3. Reagents and conditions: (i) LiOtBu or KOtBu,
[Ir(COD)Cl]2, THF, 25 ꢁC; (ii) NaBARF or KPF6, CH2Cl2, H2O,
54–91% yield.
Upon heating mixtures of methyl bromide (Rp)-9 and
1-phenylimidazole, 1-mesitylimidazole29 or 1-(2,6-di-
isopropylphenyl)imidazole30 in toluene or DMF, the
respective imidazolium salts (Rp)-11a–c were obtained in
yields ranging from 16% to 59%. The experimental
conditions had a significant impact on the outcome of
the reaction. For example, treatment of (Rp)-9 with
1-mesitylimidazole in DMF gave (Rp)-11b in 59% yield.
The same reaction with (Rp)-9 and 1-phenylimidazole in
toluene afforded (Rp)-11a in only 16% yield. Presum-
ably, the formation of phosphonium salts resulting from
an intra- or intermolecular alkylation of the phosphino
group limited the product yield.
treated with LiOtBu or KOtBu in THF, and subsequent
reaction of the in situ formed carbenes with
[Ir(COD)Cl]2 followed by anion exchange with Na-
BARF32 in CH2Cl2/H2O afforded complexes (Rp)-5a–c
in yields of 54–91%. When the ion exchange was per-
formed with KPF6, (Rp)-5d was obtained from (Rp)-11b
in 58% yield (Scheme 3).
Phosphino NHC iridium complexes 5a–d are bright red,
air-stable solids. The proposed chelation of the ligand is
supported by NMR spectroscopy, where in the 1H
NMR spectra the two ortho protons relative to the
functional groups at the [2.2]paracyclophane rings
exhibit significant chemical shifts to lower and higher
fields with d values of 9.4–9.7 and 5.8–6.4 ppm, respec-
tively. However, compared with the structurally related
[2.2]paracyclophanyl-NHC-iridium complexes 4 bearing
an oxazolinyl substituent, the high-field absorption is
less pronounced.25 In the 13C NMR spectra, the carbene
carbon absorbed at d ¼ 176:7–180:3 ppm as a doublet
with a coupling constant of JPC ¼ 7:6–8:9 Hz due to an
interaction with the phosphino substituent opposite to
the central iridium atom. The 31P NMR absorptions of
the phosphino moieties in the imidazolium salts were
shifted downfield from ðdÞ ¼ ꢀ4:2 to )5.7 ppm to
d ¼ 16:5–17:0 ppm when coordinated to iridium.
In the attempt to improve the yields, an alternative
synthesis of imidazolium salt 11c was developed. In this
sequence, [2.2]paracyclophane (Sp)-8 [obtained from
(Sp)-6 according to Scheme 1] served as the starting
material. Its phosphino group was first protected with
sulfur, and subsequently, the hydroxymethyl of the
resulting intermediate converted into a bromomethyl
group to give (Sp)-12 (Scheme 2). The yield of the bro-
mination step (including the proceeding sulfur addition)
increased to 85%. After reaction of methyl bromide (Sp)-
12 with 1-(2,6-diisopropylphenyl)imidazole, deprotec-
tion of the phosphine was achieved using freshly pre-
pared Raney nickel to give imidazolium salt (Sp)-11c in
32% yield.31
All products were air stable, but nevertheless, for ex-
tended periods of time were stored under an inert
atmosphere. The phosphino imidazolium salts were
difficult to dry even under high vacuum at elevated
temperatures and had the tendency to absorb moisture
upon exposure to ambient atmosphere. This behaviour,
however, did not influence the transformation of the
imidazolium salts to their corresponding metal com-
plexes.
Proof of the atom connectivity was finally obtained by
X-ray crystal structure analysis of complex (Rp)-5d (Fig.
1). Unfortunately, all attempts to grow high-quality
crystals from a solvent mixture of MeOH, EtOAc and
CH2Cl2 failed. Although the collected diffraction data
turned out to be sufficient enough to solve the structure,
they did not allow a completely anisotropic refinement
of the model on F or on F 2. Thus the structure shown in
Figure 1 is the result of a refinement where only the Ir,
the F and the P atoms have been treated anisotropically
while the parameters of all the other nonhydrogen
Next, we focused on the preparation of iridium com-
plexes 5. For their syntheses, imidazolium salts 11 were
OH
(a)
Br
N
N
(b)
PPh2
PPh2
S
PPh2
(Sp)-11c
Br
(Sp)-8
(Sp)-12
Scheme 2. Reagents and conditions: (a) i. S8, CH2Cl2; ii. PBr3, CH2Cl2, 85% yield; (b) i. 1-(2,6-diisopropylphenyl)imidazole, DMF, 80 ꢁC; ii. Ra-Ni,
CH3CN, 32% yield.

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T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
afforded (S)-configured products. Changing the solvent
from dichloromethane to chloroform or toluene had
only a marginal influence on the enantioselectivity. In
toluene, however, the reaction rate seemed to decrease
(Table 1, entry 5 vs 1). An important aspect appeared to
be the purity of the solvent. Thus, we presume that traces
of methanol or ethanol, which are often used for the
stabilization of CH2Cl2 and CHCl3, remained in the
solvent even after purification and distillation and that
they led to a decrease in catalytic activity in such solvents
(Table 1, entries 1, 2 and 4). Evidence for this assumption
stems from the observation that under otherwise
identical reaction conditions a catalysis performed in
amylene stabilized dichloromethane led to 89% substrate
conversion (Table 1, entry 3).
Figure 1. Representation (SCHAKAL plot) of the atom connectivity
in the cationic fragment of (Rp)-5d (as determined by X-ray crystal
structure analysis).
The catalytic activity of complex (Rp)-5a was tempera-
ture dependent. Thus, when the temperature was
increased from 25 to at 50 ꢁC, the substrate conversion
also increased from 42% to 99% (Table 1, entries 2 and
6). However, at the same time the enantioselectivity
decreased from 81% to 73% ee. When the temperature
was decreased to 0 and )20 ꢁC the catalytic activity
diminished with the ee of 14 being 78% and 67%,
respectively (Table 1, entries 7 and 8).
atoms have been optimized isotropically. While the ob-
tained structure is sufficient to prove the connectivity of
the atoms in the molecule, no discussion of the struc-
tural parameters is possible.
Next, iridium complexes 5a–d were tested as chiral cat-
alysts in the asymmetric hydrogenation of functional-
ized and simple alkenes.33–35 (E)-1,2-Diphenyl-1-propene
13 was chosen as the first substrate (Table 1). All com-
plexes exhibited low to good catalytic activity, with (Rp)-
5a being the best leading to a 89% conversion of alkene
13. The enantioselectivity in the formation of 14 reached
82% ee (Table 1, entry 3). Complexes (Rp)-5b and (Rp)-
5c bearing sterically more demanding substituents on
the carbene fragment afforded products with lower ee
values (up to 29%; Table 1, entries 9 and 10, respec-
tively). Interestingly, iridium complex (Rp)-5a gave 14
with an (R)-configuration, whereas (Rp)-5b and (Rp)-5c
The hydrogenation of the isomeric alkenes (E)-2-(4-
methoxyphenyl)-2-butene 15, (Z)-2-(4-methoxyphenyl)-
2-butene 16 and 2-(4-methoxyphenyl)-1-butene 17 re-
vealed an interesting dependence of the enantioselec-
tivity in the formation of 2-(4-methoxyphenyl)butane 18
on the substrate structure. Regardless of the catalyst,
hydrogenation of (E)-isomer 15 gave 18 with only 35–
37% ee (Table 2, entries 1–3); the ee increased to 79%
when (Z)-isomer 16 was the substrate and (Rp)-5a the
catalyst (Table 2, entry 4). Complexes (Rp)-5b and (Rp)-
5c catalyzed the formation of 18 with only 48% and 37%
ee, respectively. Interestingly, the absolute configuration
of the product was independent of the alkene stereo-
Table 1. Hydrogenation of (E)-1,2-diphenyl-1-propene 13 to give alkane 14 catalyzed by complexes (Rp)-5a–ca
H2 (50 bar),
(Rp)-5a-c (1 mol%)
Me
*
Me
CH2Cl2, 25 °C
13
14
Entry
Catalyst
Solvent
Temp. (ꢁC)
Conversion (%)b
(reaction time, h)
Ee (%)c (abs. config.)
1
2
3
4
5
6
7
8
9
10
(Rp)-5a
(Rp)-5a
(Rp)-5a
(Rp)-5a
(Rp)-5a
(Rp)-5a
(Rp)-5a
(Rp)-5a
(Rp)-5b
(Rp)-5c
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
25
25
25
25
25
50
0
34 (2)
80 (R)
81 (R)
82 (R)
80 (R)
78 (R)
73 (R)
78 (R)
67 (R)
29 (S)
22 (S)
42 (24)
89 (24)
64 (24)
16 (2)
d
Toluene
CH2Cl2
99 (24)
21 (24)
3 (24)
d
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
d
)20
25
25
13 (24)
41 (24)
a Reaction conditions: substrate (0.2–0.3 mmol), (Rp)-5a–c (1 mol %), solvent (1 mL), H2 (50 bar); see experimental section for details.
b Determined by 1H NMR.
c Determined by HPLC using a chiral column; the absolute configurations were revealed by comparison of the HPLC retention times with literature
values.
d CH2Cl2 stabilized with amylene.

T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
1697
Table 2. Hydrogenations of (E)-2-(4-methoxyphenyl)-2-butene 15, (Z)-2-(4-methoxyphenyl)-2-butene 16 and 2-(4-methoxyphenyl)-1-butene 17 to
give 2-(4-methoxyphenyl)butane 18 catalyzed by complexes (Rp)-5a–ca
Entry
Substrate
Catalyst
H2 pressure (bar)
Conversion (%)b
Ee (%)c
1
15
15
15
16
16
16
17
17
17
17
17
17
17
(Rp)-5a
(Rp)-5b
(Rp)-5c
(Rp)-5a
(Rp)-5b
(Rp)-5c
(Rp)-5a
(Rp)-5a
(Rp)-5b
(Rp)-5b
(Rp)-5b
(Rp)-5c
(Rp)-5c
50
50
50
50
50
50
50
1
100
100
100
100
99
37 (R)
36 (R)
35 (R)
79 (R)
48 (R)
37 (R)
37 (S)
79 (S)
32 (R)
11 (R)
37 (S)
38 (S)
39 (S)
2
3
4
5
6
99
7
100
100
100
100
100
100
100
8
9
50
10
1
10
11
12
13
50
10
a Reaction conditions: substrate (0.3 mmol), (Rp)-5a–c (1 mol %), solvent (1 mL), 25 ꢁC, 24–48 h; see experimental section for details.
b Determined by 1H NMR.
c Determined by HPLC using a chiral column; the absolute configurations were revealed by comparison of the HPLC retention times with literature
values.
chemistry with hydrogenations of both isomers leading
to (R)-18.
(Rp)-5a. Whereas a hydrogen pressure of 50 bar led to
(R)-22 with 8% ee, the enantioselectivity was 53% ee in a
catalysis at 1 bar of H2 (Table 3, entries 1 and 2).
*
CO2H
CO2Me
CO2Me
MeO
MeO
MeO
MeO
MeO2C
NHAc
21
15
16
17
18
19
20
Hydrogenations of trisubstituted alkenes 15 and 16 were
performed at a hydrogen pressure of 50 bar, since low-
ering the pressure to 1 bar led to low substrate conver-
sions. In contrast, the hydrogenation of 17 went to
completion even at 1 bar H2 pressure. Using complex
(Rp)-5a as catalyst, 18 was obtained with 79% under
these conditions (Table 2, entry 8). Since the H2 pressure
was expected to have an effect on the enantioselectivity
of the hydrogenations, the conversion of 17 with (Rp)-5a
as catalyst was also performed at 50 bar H2 with the
result being the ee dropping to 37%. Most interesting
was the pressure dependence of catalyses with (Rp)-5b.
Here, the enantioselectivity in the formation of (R)-18
decreased from 32% to 11% ee, when the H2 pressure
was lowered from 50 to 10 bar, respectively (Table 2,
entries 9 and 10). At 1 bar of H2 pressure the absolute
configuration of the product changed, with the (S)-
enantiomer of 18 being formed preferentially with an ee
of 37%. Catalyses with complex (Rp)-5c (Table 2, entries
12 and 13) showed almost no pressure dependence.
CO2R
*
CO2Me
*
CO2Me
MeO2C
NHAc
*
24: R = H; 25: R = Me
22
23
The highest ee achieved was in the hydrogenation of the
terminal alkene dimethyl itaconate 20. Using complex
(Sp)-5c as catalyst, (Rp)-23 was obtained with an ee of
89% (Table 3, entry 12). When (Rp)-5b, having a steri-
cally less bulky substituent at the carbene fragment of
the ligand, was applied, the ee of 23 decreased to 68%
(Table 3, entry 9). Remarkably, 23 had only 3% ee with
(Rp)-5a as catalyst. In all cases (Rp)-configured catalysts
yielded the (S)-enantiomer of 23 predominantly. Low-
ering the reaction temperature from 25 to 0 ꢁC had no
significant effect on the enantioselectivity (e.g., Table 3,
entries 9 and 10).
As in the reactions of the butene and cinnamate deriv-
atives, the conversion as well as the enantioselectivity in
the hydrogenation of dimethyl itaconate 20 was depen-
dent on the hydrogen pressure. Thus, in catalyses with
(Rp)-5a and (Rp)-5b at 1 bar, the conversion of 20 was
low, whereas full conversion was achieved at 50 bar of
hydrogen pressure. Complex (Rp)-5c was more active,
and with this catalyst 1 bar of H2 was sufficient to lead
to full conversion of 20. With respect to the enantio-
selectivity, the situation was more complex. Thus, while
in the hydrogenation of the butene and cinnamate
derivatives, products with higher ee values were
obtained at lower pressure, the opposite was observed in
The iridium complexes were also applied in hydroge-
nations of the functionalized alkenes methyl (E)-1-
methylcinnamate 19, dimethyl itaconate 20 and a-acet-
amidocinnamic acid 21. Reactions of 19 led to enantio-
selectivities between 8% and 60% ee (Table 3, entries
1–6). While (Rp)-5c was the most selective catalyst
(Table 3, entry 6), complexes (Rp)-5a and (Rp)-5b
appeared to be more active than (Rp)-5c. In all cases, the
(R)-configured product was formed in excess. As in the
hydrogenation of the isomeric butenes, the enantio-
selectivity was pressure dependent. This effect was par-
ticularly pronounced in hydrogenations with catalyst

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T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
Table 3. Hydrogenation of functionalized alkenes with iridium complexes 5a–ca
Entry
Catalyst
Substrate
p(H2) (bar)
Conversion (%)b
Product
Ee (%)c
1
(Rp)-5a
(Rp)-5a
(Rp)-5b
(Rp)-5b
(Rp)-5c
(Rp)-5c
(Rp)-5a
(Rp)-5a
(Rp)-5b
(Rp)-5b
(Rp)-5b
(Sp)-5c
(Rp)-5cf
(Rp)-5c
(Rp)-5b
(Rp)-5c
19
19
19
19
19
19
20
20
20
20
20
20
20
20
21
21
50
1
100
100
93d
87
22
22
22
22
22
22
23
23
23
23
23
23
23
23
24g
24g
8 (R)
53 (R)
46 (R)
53 (R)
35 (R)
60 (R)
3 (S)
2
3
50
1
4
5
50
1
12d
6
60
7
50
1
100
10
100d
100e
28
8
n.d.
9
50
50
1
68 (S)
70 (S)
46 (S)
89 (R)
88 (S)
35 (S)
6 (S)
10
11
12
13
14
15
16
50
50
1
100
100e
100
100
100
50
50
71 (S)
a Reaction conditions: substrate (0.3 mmol for 19, 0.2 mmol for 20 or 0.4 mmol for 21), 5a–c (1 mol %), solvent (1–2 mL; for entries 1–15 CH2Cl2, for
entries 15, 16: CH2Cl2–MeOH, 1:1), 25 ꢁC, 24 h; see experimental section for details.
b Determined by 1H NMR.
c Determined by HPLC using a chiral column; the absolute configurations were established by comparison of the HPLC retention times with
literature values.
d Reaction time: 2 h.
e Reaction temperature: 0 ꢁC.
f Catalyst loading: 0.4 mol %.
g Ee analyzed as compound 25.
the case of dimethyl itaconate. Here, the ee of 23
dropped from 70% to 46% [in a catalysis with (Rp)-5b],
when the hydrogen pressure was decreased from 50 to
1 bar (Table 3, entries 10 and 11). With (Rp)-5c as cat-
alyst, a decrease from 89% to 35% ee was found.
Interestingly, a reversed pressure dependence was found
in catalyses with the structurally similar [2.2]paracyclo-
phanyl-NHC-iridium complexes 4 bearing an oxazolinyl
substituent.25
bearing a phenyl substituent at the imidazole ring,
proved to be the most enantioselective catalyst in the
hydrogenation of unfunctionalized alkenes such as (E)-
1,2-diphenyl-1-propene 13 and the methoxyphenyl
butene isomers 15–17, giving products 14 and 18,
respectively, with up to 82% ee. In the hydrogenation of
the functionalized substrates methyl (E)-1-methylcinna-
mate 19, dimethyl itaconate 20 and a-acetamidocinna-
mic acid 21, complex (Rp)- or (Sp)-5c was the best,
yielding 22–24 with 60%, 89% and 71% ee, respectively.
In this case, the imidazole ring of the carbene ligand
was substituted with a highly sterically demanding
2,6-diisopropylphenyl group.
Finally, catalysts (Rp)-5b and (Rp)-5c were tested in the
hydrogenation of a-acetamidocinnamic acid 21. Re-
cently, Knochel applied iridium complexes with P, N-
ligands in the hydrogenation of a-methyl acetamido-
cinnamate for the first time, thus achieving enantio-
selectivities of up to 97% ee in the formation of phenyl
alanine derivatives.35 We found that the application of
(Rp)-5b in the reduction of 21 at a hydrogen pressure of
50 bar proceeded well and led to full conversion (Table
3, entry 15). The ee of the corresponding amino acid 24,
however, was only 6% (as determined at the ester stage
after treatment of 24 with diazo methane to give 25).
The use of complex (Rp)-5c resulted in an improvement
in the enantioselectivity, with 25 now obtained with 71%
ee. In both cases, the (S)-enantiomer of the amino acid
was formed in preference.
In general, the imidazole substituent appears to play a
major role for the activity and selectivity of the iridium
complexes. The mesityl and the 2,6-diisopropylphenyl
group in complexes (Rp)-5b and (Rp)-5c, respectively,
probably adopt an almost orthogonal arrangement with
respect to the imidazole ring (as shown in Fig. 1),
whereas the phenyl group in complex (Rp)-5a leads to a
rather coplanar alignment with the heterocycle. Conse-
quently, the steric properties of the imidazole sub-
stituent play an important role for the catalytic
properties of the NHC complexes. This becomes par-
ticularly apparent in the hydrogenations of (E)-1,2-
diphenylpropene and dimethyl itaconate. Whereas in the
latter case the enantioselectivity is dramatically in-
creased when the phenyl substituent at the imidazole
ring of the ligand is changed to a mesityl or 2,6-diiso-
propylphenyl group (Table 3, entries 7, 9 and 13), the
absolute configuration of the product changed from R
to S in the hydrogenation of the stilbene derivative
(Table 1, entries 3, 9 and 10). Although many differences
in the structure/activity relationship exist, we note that
similar trends have also been observed in the related
3. Conclusion
In summary, we have synthesized new iridium imidazolyl-
idene complexes with a planar chiral [2.2]paracyclo-
phane backbone. These complexes have been applied as
catalysts in the asymmetric hydrogenations of simple
and functionalized alkenes. Iridium complex (Rp)-5a,

T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
1699
iridium NHC complexes 4 based on the [2.2]paracyclo-
phane skeleton bearing an oxazoline moiety.25
MgSO4 and concentrated. The remaining residue was
purified by column chromatography on silica gel (pen-
tane–diethyl ether, 8:1 to 1:2) with degassed solvents to
give 10.06 g of the title compound (92% yield) as a
25
white solid. Mp 119–121 ꢁC; ½aꢁ ¼ þ33 (c 1.0, CHCl3);
1H NMR (400 MHz, CDCl3) d D2.60–2.71 (m, 2H, CH2),
2.74–2.81 (m, 1H, CH2), 2.86–2.95 (m, 2H, CH2), 3.22–
3.34 (m, 3H, CH2), 6.24 (dd, 1H, J ¼ 7:9, 1.6 Hz, PCp-
CH), 6.40–6.51 (m, 4H, PCp-CH), 7.11 (br s, 1H, PCp-
CH), 7.16–7.29 (m, 8H, PPh2-CH), 7.40–7.45 (m, 2H,
PPh2-CH); 13C NMR (100 MHz, CDCl3) d 32.9, 33.4
(CH2), 35.7 (d, JPC ¼ 11:4 Hz, CH2), 36.2 (CH2), 126.8
(qC), 128.4 (d, 2C, JPC ¼ 6:9 Hz, PPh2-CH), 128.54
(PPh2-CH), 128.6 (2C, PPh2-CH), 129.7 (PPh2-CH),
131.7, 132.3 (PCp-CH), 133.2 (d, 2C, JPC ¼ 19:1 Hz,
PPh2-CH), 133.7 (PCp-CH), 134.4 (d, JPC ¼ 5:4 Hz,
PCp-CH), 134.5 (d, JPC ¼ 4:6 Hz, PCp-CH), 135.0
(PCp-CH), 136.0 (d, JPC ¼ 8:4 Hz, qC), 136.6 (d, 2C,
JPC ¼ 22:1 Hz, PPh2-CH), 137.3 (d, JPC ¼ 11:5 Hz, qC),
138.5 (d, JPC ¼ 10:7 Hz, qC), 139.0, 139.4, 141.9 (qC),
143.4 (d, JPC ¼ 19:8 Hz, qC); 31P NMR (162 MHz,
4. Experimental
4.1. General information
Pseudo-ortho-dibromo[2.2]paracyclophane 6,27;28 1-
mesitylimidazole,29 1-(2,6-diisopropylphenyl)imidazol30
and NaBARF32 were prepared according to published
procedures. The following reagents and solvents are
commercially available and were used as received:
n-BuLi (1.6 M in n-hexane, Merck-Schuchardt), t-BuLi
(1.48 M in pentane, Merck-Schuchardt), anhydrous
DMF (Aldrich), chlorodiphenylphosphine (Aldrich),
KOtBu (1 M, Aldrich), LiOtBu (Fluka), 1-phenylimi-
dazole (Aldrich). [Ir(COD)Cl]2 was obtained as a gift
from Umicore (formerly OMG). THF was distilled
under nitrogen from sodium benzophenone ketyl and
CH2Cl2 from calcium hydride prior to use. All reactions
were performed under an inert atmosphere of argon
using standard Schlenk techniques. The NMR spectra
~
CDCl3) d )0.47 (s); IR (KBr): v ¼ 2954, 2925, 2851,
1583, 1476, 1460, 1449, 1433, 1390, 1034, 907, 890, 862,
817, 741, 696, 668, 644, 501, 481 cmꢀ1; MS (EI, 70 eV)
m=z (%) 473 (16), 472 (Mþ, 73), 471 (14), 470 (Mþ, 65),
289 (15), 288 (100), 209 (15), 178 (17). Anal. Calcd for
C28H24BrP: C, 71.35; H, 5.13. Found: C, 71.64; H, 5.09.
were recorded on either
a Varian Mercury 300
(1H NMR at 300 MHz, 13C NMR at 75 MHz, 31P NMR
at 121 MHz) or Varian Inova 400 (1H NMR at
400 MHz, 13C NMR at 100 MHz, 19F NMR at
376 MHz, 31P NMR at 162 MHz) spectrometer. Chem-
ical shifts are given in ppm with internal referencing to
TMS (1H NMR), external CFCl3 (19F NMR), external
H3PO4 (31P NMR) or the solvent peaks (1H NMR, 13C
NMR). Assignments are based on 2D NMR experi-
ments. IR spectra were measured on a Perkin–Elmer
1760 FT spectrometer. Mass spectra were obtained by
using a Varian MAT 212 (EI, ESI, APCI) and a Fin-
nigan MAT 95 (SIMS-FAB) spectrometer. Only frag-
ments containing the isotopes of the highest abundance
are listed. Elemental analyses were carried out at the
4.3. (+)-(Rp)-4-Diphenylphosphino-12-hydroxymethyl-
[2.2]paracyclophane (Rp)-8
At )78 ꢁC a solution of phosphine (Rp)-7 (9.9 g,
21.0 mmol) in THF (180 mL) was treated slowly with a
solution of n-BuLi in pentane (19.0 mL, 34.0 mmol).
After stirring for 1 h at this temperature, carbon dioxide
was bubbled through the reaction mixture for 30 min (at
)78 ꢁC). The reaction mixture was slowly warmed to
room temperature, after which it was carefully degassed
by means of a supersonic bath. Lithium aluminium
hydride (1.2 g, 31.9 mmol) was added at 0 ꢁC and the
mixture stirred at room temperature overnight. It was
then treated with aqueous HCl (5 M) until a pH of ꢂ4–5
was reached. After phase separation, the aqueous layer
was extracted with dichloromethane (3 · 50 mL). The
combined organic phase was dried over MgSO4, con-
centrated, and the remaining residue purified by column
chromatography on silica gel (degassed pentane–diethyl
ether, 3:2) to give 7.46 g of (Rp)-8 (84% yield) as a col-
ourless oil, which crystallized upon treatment with
€
Institut fur Organische Chemie der RWTH Aachen on a
Heraeus CHNO-Rapid apparatus. Melting points were
measured with a Buchi B-540 melting point determina-
tion apparatus. Optical rotations were measured on a
Perkin–Elmer 241 polarimeter.
€
4.2. (+)-(Rp)-4-Bromo-12-diphenylphosphino[2.2]para-
cyclophane (Rp)-7
25
1
(Rp)-Pseudo-ortho-dibromo[2.2]paracyclophane (Rp)-6
(8.5 g, 23.2 mmol) was placed in a Schlenk flask under an
argon atmosphere and dissolved in anhydrous THF
(100 mL). After cooling to )78 ꢁC in a dry ice/acetone
bath, a solution of n-BuLi in hexane (17.4 mL,
27.8 mmol) was added slowly. The reaction mixture was
stirred at )78 ꢁC for 1 h, after which chlorodiphenyl-
phosphine (6.7 mL, 37.4 mmol) was added via syringe.
The solution was then allowed to warm to room tem-
perature overnight. After the addition of saturated
NH4Cl solution (50 mL), and phase separation and
extraction of the aqueous layer with dichloromethane
(3 · 50 mL), the combined organic phase was dried over
pentane. Mp 126–128 ꢁC; ½aꢁ ¼ þ8 (c 1.0, CHCl3); H
NMR (400 MHz, CDCl3) dD2.62 (ddd, 1H, J ¼ 13:1,
10.0, 6.7 Hz, CH2), 2.71–2.81 (m, 2H, CH2), 2.99–3.10
(m, 2H, CH2), 3.28 (ddd, 1H, J ¼ 13:3, 10.0, 1.5 Hz,
CH2), 3.36–3.50 (m, 2H, CH2), 3.97 (d, 1H, J ¼ 12:6 Hz,
CH2OH), 4.27 (d, 1H, J ¼ 12:6 Hz, CH2OH), 5.87 (dd,
1H, J ¼ 8:2, 1.6 Hz, PCp-CH), 6.49–6.52 (m, 3H, PCp-
CH), 6.55 (dd, 1H, J ¼ 7:8, 1.5 Hz, PCp-CH), 6.97 (br s,
1H, CH2), 7.19–7.23 (m, 5H, PPh2-CH), 7.37–7.41 (m,
3H, PPh2-CH), 7.42–7.47 (m, 2H, PPh2-CH); 13C NMR
(100 MHz, CDCl3) d 33.3 (CH2), 33.9 (d, JPC ¼ 1:5 Hz,
CH2), 34.2 (CH2), 35.4 (d, JPC ¼ 13:0 Hz, CH2), 64.4
(CH2OH), 128.5 (d, 2C, JPC ¼ 6:9 Hz, PPh2-CH), 128.6

1700
T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
(PPh2-CH), 128.9 (d, 2C, JPC ¼ 8:4 Hz, PPh2-CH), 129.9
(PPh2-CH), 130.4 (d, JPC ¼ 4:6 Hz, PCp-CH), 132.4,
132.6 (PCp-CH), 133.1 (d, 2C, JPC ¼ 19:1 Hz, PPh2-
CH), 133.9 (PCp-CH), 134.7 (d, JPC ¼ 5:4 Hz, PCp-
CH), 135.0 (PCp-CH), 136.1 (d, 2C, JPC ¼ 22:9 Hz,
PPh2-CH), 136.4 (d, JPC ¼ 9:9 Hz, qC), 136.9 (d,
JPC ¼ 10:7 Hz, qC), 137.8 (qC), 138.4 (d, JPC ¼ 9:2 Hz,
qC), 139.5, 139.6, 140.6 (qC), 144.0 (d, JPC ¼ 20:6 Hz,
qC); 31P NMR (162 MHz, CDCl3) d )2.66 (s); IR (KBr)
NMR (400 MHz, CDCl3) d 2.71–2.99 (m, 4H, CH2),
3.11–3.17 (m 1H, CH2), 3.36–3.45 (m, 3H, CH2), 4.09 (d,
1H, J ¼ 10:1 Hz, CH2Br), 4.12 (d, 1H, J ¼ 9:9 Hz,
CH2Br), 6.30 (dd, 1H, J ¼ 14:6, 1.7 Hz, PCp-CH), 6.51
(d, 1H, J ¼ 7:7 Hz, PCp-CH), 6.56–6.64 (m, 3H, PCp-
CH), 7.05 (d, 1H, J ¼ 1:6 Hz, PCp-CH), 7.34–7.38 (m,
2H, P(O)Ph2-CH), 7.43–7.49 (m, 3H, P(O)Ph2-CH),
7.51–7.59 (m, 3H, P(O)Ph2-CH), 7.67–7.72 (m, 2H,
P(O)Ph2-CH); 13C NMR (100 MHz, CDCl3) d 33.1
(CH2), 33.4 (CH2Br), 33.9, 35.0 (CH2), 35.6 (d,
JPC ¼ 4:6 Hz, CH2), 128.56 (d, 2C, JPC ¼ 11:5 Hz,
P(O)Ph2-CH), 128.6 (d, 2C, JPC ¼ 11:5 Hz, P(O)Ph2-
CH), 130.3 (d, JPC ¼ 105:3 Hz, qC), 131.4 (d, 2C,
JPC ¼ 9:9 Hz, P(O)Ph2-CH), 131.7 (d, JPC ¼ 3:0 Hz,
P(O)Ph2-CH), 131.9 (d, JPC ¼ 2:3 Hz, P(O)Ph2-CH),
132.2 (d, 2C, JPC ¼ 9:1 Hz, P(O)Ph2-CH), 132.6 (d,
JPC ¼ 103:0 Hz, qC), 133.3 (PCp-CH), 133.5 (d,
JPC ¼ 12:2 Hz, PCp-CH), 134.6 (PCp-CH), 135.5
(d, JPC ¼ 103:8 Hz, qC), 136.36 (PCp-CH), 136.4 (d,
v 3416, 2926, 1435, 1026, 863, 754, 745, 483 cmꢀ1; MS
~
(EI, 70 eV) m=z (%) 423 (24), 422 (Mþ, 91), 289 (28), 288
(100), 287 (26), 210 (15), 209 (26), 183 (11), 179 (14), 178
(30), 165 (15). Anal. Calcd for C29H27OP: C, 82.44; H,
6.44. Found: C, 82.24; H, 6.43.
4.4. ())-(Rp)-12-Bromomethyl-4-diphenylphosphino[2.2]-
paracyclophane (Rp)-9
A solution of (Rp)-4-diphenylphosphino-12-hydroxy-
methyl[2.2]paracyclophane (Rp)-8 (0.845 g, 2.0 mmol) in
dichloromethane (10 mL) was treated with PBr3 (80 lL,
0.84 mmol) at )20 ꢁC. A white, cloudy precipitate
immediately formed. The reaction mixture was stirred at
room temperature overnight, diluted with CH2Cl2
(20 mL) and then washed with an ice-cold, saturated
NaHCO3 solution (10 mL). The organic phase was dried
over MgSO4, concentrated and the residue purified
using a short silica gel column and degassed pentane–
diethyl ether (6:1 to 1:1) as the eluent. Thus, 0.61 g (63%
yield) of (Rp)-9 was obtained as a white solid. As second
fraction, 0.25 g (25% yield) of the corresponding phos-
phine oxide (Rp)-10, was isolated. (Rp)-9: Mp 315 ꢁC
JPC ¼ 13:0 Hz,
PCp-CH),
136.8
(qC),
137.4
(d, JPC ¼ 2:3 Hz, PCp-CH), 137.8 (qC), 139.2 (d,
JPC ¼ 12:9 Hz, qC), 140.9 (qC), 146.1 (d, JPC ¼ 7:7 Hz,
qC); 31P NMR (162 MHz, CDCl3) d 26.82 (s); IR (KBr)
~
v 2927, 1436, 1178, 1134, 1118, 1104, 1069, 755, 748,
709, 697, 590, 560, 537, 515 cmꢀ1; MS (EI, 70 eV) m=z
(%) 503 (10), 502 (Mþ, 37), 501 (12), 500 (Mþ, 38), 422
(10), 421 (37), 420 (16), 305 (24), 304 (100), 303 (46), 225
(13), 178 (13), 115 (11). Anal. Calcd for C29H26BrOP: C,
69.47; H, 5.23. Found: C, 69.32; H, 5.23.
4.5. (+)-(Sp)-12-Bromomethyl-4-diphenylthiophosphino-
[2.2]paracyclophane (Sp)-12
25
D
1
(dec); ½aꢁ ¼ ꢀ4 (c 1.0, CHCl3); H NMR (400 MHz,
CDCl3) d 2.55 (ddd, 1H, J ¼ 13:3, 10.1, 6.9 Hz, CH2),
2.67–2.77 (m, 2H, CH2), 2.96–3.06 (m, 2H, CH2), 3.22–
3.28 (m, 1H, CH2), 3.31 (ddd, 1H, J ¼ 12:9, 10.0,
5.9 Hz, CH2), 3.45 (ddd, 1H, J ¼ 13:2, 10.2, 1.6 Hz,
CH2), 3.66 (d, 1H, J ¼ 10:2 Hz, CH2Br), 3.94 (d, 1H,
J ¼ 10:1 Hz, CH2Br), 5.78 (d, 1H, J ¼ 7:7 Hz, PCp-
CH), 6.42–6.46 (m, 3H, PCp-CH), 6.49 (dd, 1H, J ¼ 8:0,
1.6 Hz, PCp-CH), 6.83 (br s, 1H, PCp-CH), 7.08–7.18
(m, 5H, PPh2-CH), 7.32–7.43 (m, 5H, PPh2-CH); 13C
NMR (100 MHz, CDCl3) d 32.8 (CH2Br), 33.5, 33.8,
34.1 (CH2), 35.3 (d, JPC ¼ 13:7 Hz, CH2), 128.4 (d, 2C,
JPC ¼ 6:9 Hz, PPh2-CH), 128.5 (PPh2-CH), 129.0 (d, 2C,
JPC ¼ 8:4 Hz, PPh2-CH), 130.1 (PPh2-CH), 132.8 (d,
JPC ¼ 6:1 Hz, PCp-CH), 132.87 (d, 2C, JPC ¼ 19:0 Hz,
PPh2-CH), 132.9, 133.6, 133.9 (PCp-CH), 135.0 (d,
J ¼ 5:4 Hz, PCp-CH), 135.5 (PCp-CH), 136.2 (d, 2C,
JPC ¼ 22:8 Hz, PPh2-CH), 136.4 (d, JPC ¼ 10:7 Hz, qC),
136.7 (qC), 136.8 (d, JPC ¼ 11:5 Hz, qC), 138.1 (qC),
138.5 (d, JPC ¼ 9:9 Hz, qC), 139.4, 140.8 (qC), 144.3 (d,
JPC ¼ 21:4 Hz, qC); 31P NMR (162 MHz, CDCl3) d
To a solution of alcohol (Sp)-8 (0.97 g, 2.3 mmol) in
dichloromethane (20 mL) was added 0.1 g of sulfur
(3.12 mmol). While stirring at room temperature for 2 h,
the original yellow solution became colourless. PBr3
(0.22 mL, 2.31 mmol) was added under cooling and the
reaction mixture stirred overnight. After dilution with
CH2Cl2 (20 mL), the organic phase was washed with an
ice-cold, saturated NaHCO3 solution (15 mL), dried
over MgSO4 and concentrated. The product was
purified using a short silica gel column (pentane–
diethyl ether, 4:1) to give 1.02 g of (Sp)-12 (85% yield) as
25
D
a white solid. Mp 231–232 ꢁC; ½aꢁ ¼ þ57 (c 1.1,
1
CHCl3); H NMR (300 MHz, CDCl3) d 2.66–2.91 (m,
4H, CH2), 3.09–3.17 (m, 1H, CH2), 3.33–3.45 (m, 3H,
CH2), 4.10 (d, 1H, J ¼ 9:9 Hz, CH2Br), 4.34 (d, 1H,
J ¼ 9:9 Hz, CH2Br), 6.18 (dd, 1H, J ¼ 15:6, 1.7 Hz,
PCp-CH), 6.47–6.60 (m, 4H, PCp-CH), 7.33–7.47 (m,
6H, P(S)Ph2-CH), 7.57 (br s, 1H, PCp-CH), 7.72–7.83
(m, 4H, P(S)Ph2-CH); 13C NMR (75 MHz, CDCl3)
d 32.4 (CH2), 33.0 (CH2Br), 33.2, 34.1 (CH2), 34.4 (d,
JPC ¼ 4:8 Hz, CH2), 128.28(d, JPC ¼ 88:0 Hz, qC), 128.3
(d, 4C, JPC ¼ 12:5 Hz, P(S)Ph2-CH), 131.3 (d,
JPC ¼ 3:6 Hz, P(S)Ph2-CH), 131.4 (d, JPC ¼ 2:9 Hz,
P(S)Ph2-CH), 131.7 (d, 2C, JPC ¼ 10:2 Hz, P(S)Ph2-
CH), 132.4 (d, 2C, JPC ¼ 10:1 Hz, P(S)Ph2-CH), 132.56
(d, JPC ¼ 83:8 Hz, qC), 132.6 (d, JPC ¼ 10:8 Hz, PCp-
CH), 133.3, 133.9 (PCp-CH), 134.0 (PCp-CH), 134.7 (d,
JPC ¼ 85:0 Hz, qC), 136.4 (d, JPC ¼ 11:3 Hz, PCp-CH),
136.8 (qC), 137.0 (d, JPC ¼ 3:6 Hz, PCp-CH), 137.8
~
)3.47 (s); IR (KBr) v 2926, 2855, 1477, 1433, 1206, 744,
722, 698, 588, 507, 479 cmꢀ1; MS (EI, 70 eV) m=z (%) 487
(29), 486 (Mþ, 86), 485 (46), 484 (Mþ, 100), 483 (19), 406
(20), 405 (62), 395 (10), 393 (12), 369 (12), 367 (13), 298
(11), 297 (45), 289 (21), 288 (90), 287 (32), 210 (18), 209
(32), 183 (13), 179 (18), 178 (36), 165 (19), 115 (12).
Anal. Calcd for C29H26BrP: C, 71.76; H, 5.40. Found: C,
72.06; H, 5.56. Analytical data for phosphine oxide (Rp)-
25
D
10: Mp 240 ꢁC (dec); ½aꢁ ¼ ꢀ51 (c 0.9, CHCl3); 1H

T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
1701
(qC), 138.8 (d, JPC ¼ 13:1 Hz, qC), 140.5 (qC), 145.4 (d,
JPC ¼ 8:4 Hz, qC); 31P NMR (121 MHz, CDCl3) d 38.43
640, 616, 585, 541, 518, 501 cmꢀ1; MS (EI, 70 eV) m=z
(%) 519 (13), 518 (Mþ, 42), 517 (15), 516 (Mþ, 39), 472
(17), 438 (19), 437 (45), 3211 (24), 320 (100), 319 (31),
209 (12), 183 (12). Anal. Calcd for C29H26BrPS: C,
67.31; H, 5.06. Found: C, 67.34; H, 5.18.
to room temperature and concentration of the volume,
purification of the residue by column chromatography
on silica gel (degassed ethyl acetate–ethanol, 1:0 to 4:2)
~
(s); IR (KBr) v 2926, 2856, 1477, 1435, 1097, 750, 699,
yielded 0.51 g (59%) of (Rp)-11b as a white solid. Mp
25
D
274–275 ꢁC; ½aꢁ ¼ ꢀ90 (c 0.85, CHCl3); 1H NMR
(300 MHz, CDCl3) d 1.99 (s, 3H, CH3), 2.05 (s, 3H,
CH3), 2.28 (s, 3H, CH3), 2.74–2.85 (m, 2H, CH2), 3.01–
3.14 (m, 3H, CH2), 3.35–3.46 (m, 2H, CH2), 3.59 (ddd,
1H, J ¼ 13:4, 10.1, 1.7 Hz, CH2), 4.39 (d, 1H,
J ¼ 14:3 Hz, CH2N), 5.55 (d, 1H, J ¼ 14:2 Hz, CH2N),
6.14 (dd, 1H, J ¼ 7:7 Hz, J ¼ 1:3 Hz, PCp-CH), 6.55–
6.56 (m, 2H, PCp-CH), 6.61 (d, 1H, J ¼ 7:9 Hz, PCp-
CH), 6.69 (dd, 1H, J ¼ 7:8, 1.6 Hz, PCp-CH), 6.95 (br s,
2H, Mesityl-CH), 7.00 (br s, 1H, PCp-CH), 7.13–7.23
(m, 6H, PPh2-CH, NCH@CH), 7.28 (t, 1H, J ¼ 1:5 Hz,
NCH@CH), 7.42–7.58 (m, 5H, PPh2-CH), 9.58 (t, 1H,
J ¼ 1:5 Hz, NCHN); 13C NMR (75 MHz, CDCl3) d 18.3
(2C, CH3), 21.3 (CH3), 33.6, 33.8, 34.6 (CH2), 35.5 (d,
JPC ¼ 13:8 Hz, CH2), 52.5 (CH2N), 123.1, 123.4
(NCH@CH), 128.5 (d, 2C, JPC ¼ 7:2 Hz, PPh2-CH),
128.53 (PPh2-CH), 129.7 (d, 2C, JPC ¼ 8:3 Hz, PPh2-
CH), 130.1 (2C, Mesityl-CH), 130.5 (PPh2-CH, qC),
130.7, 131.3 (qC), 132.8 (d, 2C, JPC ¼ 19:2 Hz, PPh2-
CH), 133.5 (d, JPC ¼ 4:2 Hz, PCp-CH), 133.7, 134.0
(PCp-CH), 134.5 (2C, qC), 134.9 (d, J ¼ 6:0 Hz, PCp-
CH), 135.1 (PCp-CH), 136.2 (d, 2C, JPC ¼ 22:7 Hz,
PPh2-CH), 136.3 (PCp-CH), 136.9 (NCHN), 137.0 (d,
J ¼ 16:0 Hz, qC), 138.6 (d, J ¼ 8:9 Hz, qC), 139.4,
4.6. ())-(Rp)-3-(4-Diphenylphosphino[2.2]paracyclophan-
12-ylmethyl)-1-phenylimidazolium bromide (Rp)-11
A solution of methyl bromide (Rp)-9 (1.94 g, 4.00 mmol)
and 1-phenylimidazole (0.76 mL, 6.0 mmol) in degassed
toluene (30 mL) was stirred at 80 ꢁC for 72 h. After
cooling to room temperature and reduction of the vol-
ume, the residue was purified by column chromatogra-
phy on silica gel with degassed solvents (ethyl acetate–
ethanol, 9:1 to 7:3). For the first fraction, 0.51 g (26%) of
starting material (Rp)-9 was recovered. For the second
fraction, 0.41 g (0.65 mmol, 16% yield) of the title com-
pound was isolated as a white solid. Mp 175 ꢁC (dec);
25
½aꢁ ¼ ꢀ134 (c 1.0, CHCl3); 1H NMR (400 MHz,
D
CDCl3) d 2.77–2.86 (m, 2H, CH2), 3.01 (ddd, 1H,
J ¼ 13:9, 9.9, 7.1 Hz, CH2), 3.09–3.18 (m, 2H, CH2),
3.41 (ddd, 1H, J ¼ 12:9, 9.9, 6.3 Hz, CH2), 3.53–3.60 (m,
1H, CH2), 3.69–3.75 (m, 1H, CH2), 4.37 (d, 1H,
J ¼ 14:0 Hz, CH2N), 5.53 (d, 1H, J ¼ 14:0 Hz, CH2N),
6.07 (dd, 1H, J ¼ 7:3, J ¼ 1:5 Hz, PCp-CH), 6.52–6.58
(m, 2H, PCp-CH), 6.60 (d, 1H, J ¼ 7:7 Hz, PCp-CH),
6.68 (dd, 1H, J ¼ 8:0, 1.7 Hz, PCp-CH), 7.04 (br s, 1H,
PCp-CH), 7.06 (t, 1H, J ¼ 1:7 Hz, NCH@CH), 7.16–
7.24 (m, 5H, PPh2-CH), 7.41–7.51 (m, 6H, PPh2-CH,
NPh-CH), 7.56–7.59 (m, 2H, PPh2-CH), 7.69 (t, 1H,
J ¼ 1:8 Hz, NCH@CH), 7.79–7.81 (m, 2H, NPh-CH),
11.00 (t, 1H, J ¼ 1:4 Hz, NCHN); 13C NMR (100 MHz,
CDCl3) d 33.8, 34.1, 34.6 (CH2), 35.6 (d, JPC ¼ 13:0 Hz,
CH2), 52.0 (CH2N), 120.7 (NCH@CH), 122.0 (2C, NPh-
CH), 122.2 (NCH@CH), 128.5 (d, 2C, JPC ¼ 6:9 Hz,
PPh2-CH), 128.52 (PPh2-CH), 129.5 (d, 2C,
JPC ¼ 8:4 Hz, PPh2-CH), 130.3 (PPh2-CH), 130.5 (NPh-
CH), 130.7 (3C, NPh-CH, qC), 131.4 (qC), 132.8 (d, 2C,
JPC ¼ 18:3 Hz, PPh2-CH), 133.6 (d, J ¼ 3:8 Hz, PCp-
CH), 133.7, 133.8 (PCp-CH), 134.6 (qC), 134.9 (PCp-
CH), 135.0 (d, JPC ¼ 5:3 Hz, PCp-CH), 135.8 (NCHN),
136.2 (d, 2C, JPC ¼ 21:4 Hz, PPh2-CH), 136.21 (d,
J ¼ 11:4 Hz, qC), 136.3 (PCp-CH), 139.5, 140.0, 141.5
(qC), 144.1 (d, JPC ¼ 21:3 Hz, qC); 31P NMR (162 MHz,
139.9, 141.5, 141.7 (qC), 144.3 (d, JPC ¼ 21:6 Hz, qC);
31
~
P NMR (121 MHz, CDCl3) d )4.83 (s); IR (KBr) v
3057, 3007, 2918, 2856, 2809, 1545, 1477, 1432, 1204,
1157, 1069, 869, 756, 705, 507, 493 cmꢀ1; MS (ESI, pos.)
m=z (%) 592 (24), 591 (Mþ, 65), 406 (34), 405 (100).
Anal. Calcd for C41H40BrN2P: C, 73.32; H, 6.00; N,
4.17. Found: C, 73.02; H, 6.27; N, 3.99.
4.8. ())-(Rp)/(+)-(Sp)-3-(4-Diphenylphosphino[2.2]para-
cyclophan-12-ylmethyl)-1-(2,6-diisopropylphenyl)imi-
dazolium bromide (Rp)-11c and (Sp)-11c
Method A: The compound was prepared by the method
described for the synthesis of (Rp)-11b using (Rp)-9
(0.73 g, 1.5 mmol), 1-(2,6-diisopropylphenyl)imidazole
(0.67 g, 2.93 mmol) and DMF (8 mL). After purification
by column chromatography on silica gel (degassed ethyl
acetate–ethanol, 1:0 to 6:1), 0.34 g (32% yield) of (Rp)-
11c was isolated as a white solid.
~
CDCl3) d )4.18 (s); IR (KBr) v 3045, 2926, 1596, 1549,
Method B: A solution of the thiophosphine (Sp-12)
(0.90 g, 1.74 mmol) and 1.30 g (6.44 mol) of 1-(2,6-di-
isopropylphenyl)imidazole in degassed DMF (2 mL)
was heated to 100 ꢁC for 48 h. After cooling to room
temperature, diethyl ether was added. The precipitate
was washed several times with diethyl ether, dried in
vacuo and redissolved in degassed acetonitrile (20 mL).
Freshly prepared Ra-Ni (from 16 g NiAl alloy) was
added and the reaction mixture stirred overnight.
Reaction control by 31P NMR indicated full conversion
of the thiophosphine. After filtration and concentration
of the volume, the residue was purified by column
chromatography on silica gel (degassed ethyl acetate–
ethanol, 9:1). Thus, 0.4 g (32% yield) of (Sp-11c) was
1434, 1197, 1071, 756, 699, 506 cmꢀ1; MS (ESI, pos.)
m=z (%) 550 (14), 549 (Mþ, 41), 421 (23), 406 (30), 405
(100), 209 (10); MS (ESI, neg.) m=z (%) 81 (100), 79 (96).
Anal. Calcd for C38H34BrN2PÆ1.5H2O: C, 69.51; H, 5.68;
N, 4.27. Found: C, 69.47; H, 5.71; N, 4.13.
4.7. ())-(Rp)-3-(4-Diphenylphosphino[2.2]paracyclophan-
12-ylmethyl)-1-(2,4,6-trimethylphenyl)imidazolium bro-
mide (Rp)-11b
A solution of methyl bromide (Rp)-9 (0.62 g, 1.28 mmol)
and 1-mesitylimidazole (1.2 g, 6.44 mmol) in degassed
DMF (5 mL) was stirred at 90 ꢁC for 48 h. After cooling

1702
T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
isolated as a white solid. Mp 150 ꢁC (dec); for (Rp)-11c:
umn and CH2Cl2–pentane (3:2) as the eluent. Complex
(Rp)-5a was isolated as a bright red solid in 54% yield
25
½aꢁ ¼ ꢀ62 (c 1.4, CHCl3); (Sp)-11c: +64 (c 1.2, CHCl3);
D
25
1H NMR (400 MHz, CDCl3) d 1.07 (d, 3H, J ¼ 6:9 Hz,
CH(CH3)2), 1.12 (d, 6H, J ¼ 6:9 Hz, CH(CH3)2), 1.19
(d, 3H, J ¼ 6:6 Hz, CH(CH3)2), 2.11 (quin, 1H,
J ¼ 6:8 Hz, CH (CH3)2), 2.28 (quin, 1H, J ¼ 6:7 Hz, CH
(CH3)2), 2.73–2.85 (m, 2H, CH2), 3.07–3.16 (m, 3H,
CH2), 3.36–3.46 (m, 1H, CH2), 3.53–3.62 (m, 2H, CH2),
4.41 (d, 1H, J ¼ 14:2 Hz, CH2N), 5.79 (d, 1H,
J ¼ 14:3 Hz, CH2N), 6.14 (d, 1H, J ¼ 7:1 Hz, PCp-CH),
6.52–6.57 (m, 2H, PCp-CH), 6.61 (d, 1H, J ¼ 7:7 Hz,
PCp-CH), 6.67 (br d, 1H, J ¼ 7:6 Hz, PCp-CH), 7.02 (br
s, 1H, PCp-CH), 7.17–7.27 (m, 8H, PPh2-CH,
(0.233 g). Mp 190–191 ꢁC; ½aꢁ ¼ ꢀ0:8 (c 2.2, CHCl3);
D
1H NMR (300 MHz, CDCl3) d 1.15–1.28 (m, 1H, COD-
CH2), 1.41–1.85 (m, 6H, CH2, COD-CH2), 1.98–2.18
(m, 2H, CH2, COD-CH2), 2.23–2.37 (m, 2H, CH2,
COD-CH2), 2.42–2.50 (m, 1H, CH2), 2.93–3.02 (m, 1H,
CH2), 3.11–3.28 (m, 5H, CH2, COD-CH), 3.91–4.00 (m,
1H, COD-CH), 4.24–4.32 (m, 1H, COD-CH), 5.30 (d,
1H, J ¼ 16:8 Hz, CH2N), 5.71 (d, 1H, J ¼ 16:6 Hz,
CH2N), 5.83 (s, 1H, PCp-CH), 6.46–6.52 (m, 4H, PCp-
CH), 6.60–6.75 (br m, 2H, PPh2-CH), 7.04 (d, 1H,
J ¼ 2:2 Hz, NCH@CH), 7.07–7.13 (m, 2H, NPh-CH,
PPh2-CH), 7.22–7.34 (m, 8H, NPh-CH, PPh2-CH),
7.38–7.41 (m, 1H, NPh-CH, PPh2-CH), 7.43 (br s, 4H,
BARF-CH), 7.60 (d, 1H, J ¼ 2:0 Hz, NCH@CH), 7.65
(t, 8H, J ¼ 2:4 Hz, BARF-CH), 7.66–7.69 (m, 2H, NPh-
CH, PPh2-CH), 9.37 (dd, 1H, JPH ¼ 20:0 Hz,
J ¼ 1:3 Hz, PCp-CH); 13C NMR (75 MHz, CDCl3) d
29.9 (d, JPC ¼ 8:4 Hz, CH2), 30.3, 30.6, 31.5, 32.2, 32.7,
33.1, 34.6 (CH2, COD-CH2), 54.0 (CH2N), 79.4 (COD-
CH), 79.9 (d, JPC ¼ 13:1 Hz, COD-CH), 81.9 (d,
JPC ¼ 9:6 Hz, COD-CH), 82.6 (COD-CH), 117.6 (m, 4C,
BARF-CH), 122.9 (2C, NCH@CH, Aryl-CH), 123.3,
124.8 (Aryl-CH), 124.7 (q, JFC ¼ 272:5 Hz, BARF-CF3),
127.3, 127.9 (qC), 128.2, 128.3 (Aryl-CH), 129.1 (q,
JFC ¼ 30:8 Hz, BARF-CCF3), 129.2, 129.4 (Aryl-CH),
129.8 (3C, NCH@CH, Aryl-CH), 130.3, 130.9 (qC),
131.3, 131.6, 132.8, 133.1, 133.2, 134.4 (Aryl-CH), 135.0
(br s, 8C, BARF-CH), 135.6 (d, JPC ¼ 11:4 Hz, Aryl-
CH), 136.4 (qC), 138.1 (Aryl-CH), 138.3 (d,
JPC ¼ 21:8 Hz, Aryl-CH), 138.5, 138.7 (Aryl-CH), 139.0
(qC), 139.1 (d, JPC ¼ 15:0 Hz, qC), 139.14 (Aryl-CH),
140.7, 144.6 (qC), 161.9 (q, JCB ¼ 49:9 Hz, BC), 176.7 (d,
JPC ¼ 8:9 Hz, NCN); 19F NMR (282 MHz, CDCl3) d
)62.34 (s); 31P NMR (121 MHz, CDCl3) d 17.02 (s); IR
i
NCH@CH, Pr2Ph-CH), 7.42–7.59 (m, 7H, PPh2-CH,
i
NCH@CH, Pr2Ph-CH), 9.97 (br s, 1H, NCHN); 13C
NMR (100 MHz, CDCl3) d 24.1, 24.4, 24.5, 24.6
(CH(CH3)2), 28.77, 28.8 (CH(CH3)2), 33.5, 33.6, 34.4
(CH2), 35.4 (d, JPC ¼ 13:0 Hz, CH2), 52.2 (CH2N),
122.9, 124.2 (NCH@CH), 124.58, 124.6 (iPr2Ph-CH),
128.2 (d, 2C, JPC ¼ 6:9 Hz, PPh2-CH), 128.3 (PPh2-CH),
129.3 (d, 2C, JPC ¼ 8:4 Hz, PPh2-CH), 130.2 (2C, PPh2-
CH, qC), 131.6 (qC), 131.8 (iPr2Ph-CH), 132.6 (d, 2C,
JPC ¼ 18:3 Hz, PPh2-CH), 133.1 (d, JPC ¼ 3:1 Hz, PCp-
CH), 133.6 (2C, PCp-CH), 134.69 (d, JPC ¼ 4:6 Hz, PCp-
CH), 134.7 (PCp-CH), 135.9 (d, 2C, JPC ¼ 22:7 Hz,
PPh2-CH), 136.0 (PCp-CH), 136.0 (qC), 136.9 (d,
JPC ¼ 11:4 Hz,
qC),
137.6
(NCHN),
138.3
(d, JPC ¼ 8:4 Hz, qC), 139.1, 139.8, 141.3 (qC), 143.8 (d,
JPC ¼ 21:4 Hz, qC), 145.3 (2C, qC); 31P NMR
~
(162 MHz, CDCl3) d )5.36 (s); IR (KBr) v 3010, 2962,
2927, 2867, 1667, 1542, 1462, 1434, 1180, 1095, 1068,
806, 747, 701, 506 cmꢀ1; MS (ESI, pos.) m=z (%) 634
(29), 633 (Mþ, 78), 406 (33), 405 (100), 288 (18), 287
(15), 210 (11), 209 (47), 197 (13), 183 (11), 167 (10), 119
(11), 117 (45); MS (ESI, neg.) m=z (%) 81 (87), 79 (100).
No correct elemental analysis could be obtained from
this compound. Presumably, the presence of residual
water, which could even not be removed after drying of
the product under high vacuum at 60–80 ꢁC, led to an
unsatisfying result. Indirectly, the correct element com-
position was confirmed by the analysis of the corre-
sponding Ir complex (Sp)-11c.
(KBr) v 1355, 1279, 1128 cmꢀ1; MS (ESI, pos.) m=z (%)
~
850 (37), 849 (100, Mþ), 848 (41), 847 (22), 740 (10), 739
(26), 738 (26), 737 (41), 736 (19), 735 (24); MS (ESI,
neg.) m=z (%) 864 (38), 863 (100, Mꢀ), 862 (19), 650 (23),
649 (14), 629 (11), 580 (24), 579 (11), 435 (24), 367 (13).
Anal. Calcd for C78H57BF24IrN2P: C, 54.71; H, 3.36; N,
1.64. Found: C, 54.38; H, 3.63; N, 1.56.
4.9. (+)-(Rp)-(g4-1,5-Cyclooctadiene)(1-phenyl-3-(4-
(diphenylphosphinyl)[2.2]paracyclophan-12-ylmethyl)imid-
azolin-2-ylidene)iridium(I) tetrakis(3,5-bis(trifluoro-
methyl)phenyl)borate (Rp)-5a
4.10. (+)-(Rp)-(g4-1,5-Cyclooctadiene)(1-(2,4,6-trimethyl-
phenyl)-3-(4-(diphenylphosphinyl)[2.2]paracyclophan-12-
ylmethyl)imidazolin-2-ylidene)iridium(I) tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate (Rp)-5b
To a suspension of imidazolium salt (Rp)-11a (0.157 g,
0.25 mmol) and [Ir(COD)Cl]2 (0.084 g, 0.125 mmol) in
THF (10 mL) was added at room temperature a 1 M
solution of KOtBu in THF (0.37 mL, 0.37 mmol) via
syringe and the resulting mixture stirred at room tem-
perature overnight. After removal of the volatiles
in vacuo, NaBARF (0.332 g, 0.37 mmol), degassed water
(10 mL) and dichloromethane (15 mL) were added and
the mixture stirred vigorously for several hours. After
phase separation, the aqueous layer was washed with
CH2Cl2 (3 · 10 mL). The combined organic layers were
dried over MgSO4, evaporated and the residue purified
by column chromatography using a short silica gel col-
This compound was prepared by the same procedure
described for the synthesis of (Rp)-5a using imidazolium
salt (Rp)-11b (0.202 g, 0.3 mmol), [Ir(COD)Cl]2 (0.101 g,
0.15 mmol), KOtBu (0.4 mL, 0.4 mmol) and NaBARF
(0.40 g, 0.45 mmol). After purification using a short sil-
ica gel column (CH2Cl2–pentane, 3:2), complex (Rp)-5b
was obtained as a bright red solid (0.418 g, 79% yield).
25
D
Mp 89–90 ꢁC; ½aꢁ ¼ þ68 (c 1.8, CHCl3); 1H NMR
(400 MHz, CDCl3) d 1.05–1.14 (m, 1H, COD-CH2),
1.28–1.42 (m, 2H, COD-CH2), 1.68–1.77 (m, 3H, CH2,
COD-CH2), 1.75 (s, 3H, Mesityl-CH3), 1.83–1.91 (m,
2H, COD-CH2), 2.04 (s, 3H, Mesityl-CH3), 2.16–2.22
(m, 1H, COD-CH2), 2.25 (s, 3H, Mesityl-CH3), 2.35–

T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
1703
2.48 (m, 3H, CH2, COD-CH2), 2.90–3.01 (m, 2H, CH2,
COD-CH), 3.12–3.21 (m, 3H, CH2), 3.23–3.30 (m, 1H,
COD-CH), 4.04–4.08 (m, 1H, COD-CH), 4.78–4.83 (m,
1H, COD-CH), 5.32 (d, 1H, J ¼ 17:0 Hz, CH2N), 5.87
(d, 1H, J ¼ 17:0 Hz, CH2N), 6.24 (s, 1H, PCp-CH),
6.40–6.55 (m, 5H, PCp-CH, PPh2-CH), 6.89 (s, 2H,
Mesityl-CH), 7.05–7.36 (m, 8H, PPh2-CH), 7.19 (d, 1H,
J ¼ 2:2 Hz, NCH@CH), 7.29 (d, 1H, J ¼ 1:9 Hz,
NCH@CH), 7.44 (s, 4H, BARF-CH), 7.44–7.48 (m, 1H,
PPh2-CH), 7.64 (t, 8H, J ¼ 2:2 Hz, BARF-CH), 9.70 (d,
1H, JPH ¼ 19:8 Hz, PCp-CH); 13C NMR (100 MHz,
1H, PPh2-CH), 7.14–7.42 (m, 11H, PPh2-CH,
i
NCH@CH, Pr2Ph-CH), 7.44 (s, 4H, BARF-CH), 7.46–
7.53 (m, 1H, PPh2-CH), 7.65 (br s, 8H, BARF-CH), 9.70
(d, 1H, J ¼ 19:8 Hz, PCp-CH); 13C NMR (100 MHz,
CDCl3) d 23.4, 23.6 (iPr2Ph-CH(CH3)2), 26.2 (iPr2Ph-
CH(CH3)2), 27.3 (iPr2Ph-CH(CH3)2), 27.5, 27.7 (COD-
CH2), 29.0 (iPr2Ph-CH(CH3)2), 29.4 (d, JPC ¼ 4:6 Hz,
iPr2Ph-CH(CH3)2), 31.2, 31.9 (CH2, COD-CH2), 32.9
(d, JPC ¼ 3:8 Hz, CH2), 33.1, 34.8, 35.3 (CH2, COD-
CH2), 55.1 (CH2N), 76.5 (d, JPC ¼ 15:3 Hz, COD-CH),
77.7 (COD-CH), 80.4 (d, JPC ¼ 7:6 Hz, COD-CH), 84.7
(COD-CH), 117.5 (m, 4C, BARF-CH), 122.6
CDCl3)
d
18.6, 20.9, (Mesityl-CH3), 22.8 (d,
JPC ¼ 3:9 Hz, Mesityl-CH3), 27.7, 28.2, 31.2 (CH2,
COD-CH2), 33.0 (2C, CH2, COD-CH2), 33.1 (d,
J ¼ 3:9 Hz, CH2), 34.3, 35.1 (CH2, COD-CH2), 54.7
(CH2N), 77.0, 77.6 (COD-CH), 81.7 (d, J ¼ 8:7 Hz,
COD-CH), 84.5 (COD-CH), 117.4 (m, 4C, BARF-CH),
122.8 (NCH@CH), 124.5 (q, JFC ¼ 272:0 Hz, BARF-
CF3), 127.4–130.6 (m, Aryl-CH, NCH@CH, BARF-
CCF3, Cq), 131.0 (2C, Aryl-CH), 131.4, 132.5, 134.3
(Aryl-CH), 134.8 (br s, 8C, BARF-CH), 135.1, 135.5,
135.9, 136.1 (qC), 138.0 (Aryl-CH), 138.1 (d,
JPC ¼ 6:9 Hz, Aryl-CH), 138.5 (Aryl-CH), 138.76 (d, 2C,
JPC ¼ 16:9 Hz, Aryl-CH), 138.78 (Aryl-CH), 140.0,
140.6, 144.7 (qC), 161.7 (q, JCB ¼ 49:8 Hz, BARF-BC),
179.8 (d, JPC ¼ 8:1 Hz, NCN); 19F NMR (376 MHz,
CDCl3): d )62.38 (s); 31P NMR (162 MHz, CDCl3) d
(NCH@CH),
124.56
(Aryl-CH),
124.6
(q,
JFC ¼ 272:1 Hz, BARF-CF3), 124.7 (Aryl-CH), 125.9 (d,
JPC ¼ 11:4 Hz, Aryl-CH), 127.3 (qC), 128.7 (d,
JPC ¼ 11:8 Hz, Aryl-CH), 128.9 (q, JFC ¼ 31:0 Hz,
BARF-CCF3), 129.0 (d, JPC ¼ 8:4 Hz, Aryl-CH), 129.5
(Aryl-CH), 129.6 (qC), 129.9 (Aryl-CH), 130.0 (d,
JPC ¼ 3:9 Hz, qC), 130.2 (NCH@CH), 130.3 (d,
JPC ¼ 6:9 Hz, Aryl-CH), 131.0, 131.2, 131.4, 132.4 (Aryl-
CH), 132.7 (d, JPC ¼ 12:2 Hz, Aryl-CH), 134.0 (d,
JPC ¼ 5:3 Hz, Aryl-CH), 134.2 (Aryl-CH), 134.6 (qC),
134.9 (br s, 8C, BARF-CH), 135.2 (qC), 135.8 (d,
JPC ¼ 19:1 Hz,
Aryl-CH),
136.0
(qC),
138.0
(d, JPC ¼ 23:6 Hz, Aryl-CH), 138.2 (2C, Aryl-CH), 138.9
(d, JPC ¼ 16:8 Hz, qC), 140.7, 144.9, 145.6, 146.9 (qC),
161.7 (q, JCB ¼ 49:6 Hz, BARF-BC), 180.3 (d,
JPC ¼ 7:6 Hz, NCN); 19F NMR (376 MHz, CDCl3) d
)62.33 (s); 31P NMR (121 MHz, CDCl3) d 16.47 (s); IR
16.61 (s); IR (KBr) v ¼ 1355, 1279, 1127 cmꢀ1; MS (ESI,
~
pos.) m=z (%) 893 (12), 892 (57), 891 (100, Mþ), 890 (41),
889 (72), 829 (11), 823 (13), 822 (27), 820 (17), 782 (18),
781 (36), 779 (20), 120 (35); MS (ESI, neg.) m=z (%): 864
(29), 863 (100, Mꢀ), 862 (14). Anal. Calcd for
C81H63BF24IrN2P: C, 55.45; H, 3.62; N, 1.60. Found: C,
55.56; H, 3.95; N, 1.52.
(KBr) v 1355, 1279, 1127 cmꢀ1; MS (ESI, pos.) m=z (%)
~
933 (9, Mþ), 824 (21), 823 (83), 822 (64), 821 (70), 820
(90), 819 (100), 818 (33), 817 (15), 816 (19), 777 (11); MS
(ESI, neg.) m=z (%) 864 (18), 863 (100, Mꢀ), 862 (11),
650 (16), 580 (16), 435 (13). Anal. Calcd for
C84H69BF24IrN2P: C, 56.16; H, 3.87; N, 1.56. Found: C
56.43; H, 4.10; N, 1.37.
4.11. (+)-(Rp)/())-(Sp)-(g4-1,5-Cyclooctadiene)(1-(2,6-di-
isopropylphenyl)-3-(4-(diphenylphosphinyl)[2.2]paracyclo-
phan-12-ylmethyl)imidazolin-2-ylidene)iridium(I) tetra-
kis-(3,5-bis(trifluoromethyl)phenyl)borate (Rp)-5c and
(Sp)-5c
4.12. (+)-(Rp)-(g4-1,5-Cyclooctadiene)(1-(2,4,6-trimethyl-
phenyl)-3-(4-(diphenylphosphinyl)[2.2]paracyclophan-12-
ylmethyl)imidazolin-2-ylidene)iridium(I) hexafluorophos-
phate (Rp)-5d
This compound was prepared by the method described
for the synthesis of (Rp)-10a using imidazolium salt (Rp)-
or (Sp)-11c (0.163 g, 0.23 mmol), [Ir(COD)Cl]2 (0.077 g,
0.11 mmol), LiOtBu (0.027 g, 0.35 mmol) and NaBARF
(0.266 g, 0.3 mmol). After column chromatography on
silica gel (CH2Cl2–pentane, 3:3), the title compound was
obtained as a bright red solid (0.374 g, 91% yield). Mp
This compound was prepared by the same procedure
described for the synthesis of (Rp)-5a using imidazolium
salt (Rp)-11b (0.269 g, 0.4 mmol), [Ir(COD)Cl]2 (0.134 g,
0.2 mmol), KOtBu (0.6 mL, 0.6 mmol) and KPF6
(0.147 g, 0.8 mmol). After purification using a short sil-
ica gel column (CH2Cl2–pentane, 7:3 to 1:0), complex
(Rp)-5d was obtained as a bright red solid (0.242 g, 58%).
Crystallization from a mixture of dichloromethane,
ethyl acetate and methanol gave crystals, which in turn
79–80 ꢁC; for (Rp)-5c: ½aꢁ ¼ þ68 (c 1.1, CHCl3); for
D
(Sp)-5c: )71 (c 1.1, CHCl3); 1H NMR (300 MHz,
CDCl3) d 0.53 (d, 3H, J ¼ 6:7 Hz, CH(CH3)2), 0.98 (d,
3H, J ¼ 7:0 Hz, CH(CH3)2), 1.02–1.44 (m, 4H, COD-
CH2, CH(CH3)3), 1.08 (d, 3H, J ¼ 6:7 Hz, CH(CH3)2),
1.09 (d, 3H, J ¼ 7:0 Hz, CH(CH3)2), 1.62–1.94 (m, 5H,
CH2, COD-CH2), 2.02–2.09 (m, 1H, COD-CH2), 2.34–
2.49 (m, 3H, CH2, COD-CH2), 2.91–3.04 (m, 3H,
CH(CH3)2, CH2, COD-CH), 3.09–3.22 (m, 3H, CH2),
3.39–3.49 (m, 1H, COD-CH), 3.98–4.05 (m, 1H, COD-
CH), 4.75–4.83 (m, 1H, COD-CH), 5.35 (d, 1H,
J ¼ 17:4 Hz, CH2N), 5.96 (d, 1H, J ¼ 17:1 Hz, CH2N),
5.96–6.02 (m, 1H, PPh2-CH), 6.35 (s, 1H, PCp-CH),
6.47–6.57 (m, 5H, PCp-CH, PPh2-CH), 7.05–7.12 (m,
were used for the X-ray structural analysis. Mp 185–
25
D
190 ꢁC (dec); ½aꢁ ¼ þ95 (c 1.1, CHCl3); 1H NMR
(300 MHz, CDCl3) d 1.08–1.20 (m, 1H, COD-CH2),
1.34–1.46 (m, 2H, COD-CH2), 1.68–1.81 (m, 3H, CH2,
COD-CH2), 1.85–2.04 (m, 2H, COD-CH2), 1.93 (s, 3H,
Mesityl-CH3), 2.13 (s, 3H, Mesityl-CH3), 2.26–2.34 (m,
1H, COD-CH2), 2.34 (s, 3H, Mesityl-CH3), 2.38–2.60
(m, 3H, CH2, COD-CH2), 2.87–2.96 (m, 1H, COD-CH),
2.98–3.08 (m, 1H, CH2), 3.27–3.32 (m, 2H, CH2, COD-
CH), 3.35–3.47 (m, 2H, CH2), 4.02–4.08 (m, 1H, COD-
CH), 5.15–5.22 (m, 1H, COD-CH), 5.62 (d, 1H,

1704
T. Focken et al. / Tetrahedron: Asymmetry 15 (2004) 1693–1706
J ¼ 17:5 Hz, CH2N), 5.87 (d, 1H, J ¼ 17:3 Hz, CH2N),
6.32 (s, 1H, PCp-CH), 6.53–6.65 (m, 5H, PCp-CH,
PPh2-CH), 6.96 (s, 2H, Mesityl-CH), 7.10–7.26 (br m,
3H, PPh2-CH), 7.30 (d, 1H, J ¼ 1:9 Hz, NCH@CH),
7.33–7.45 (m, 5H, PPh2-CH), 7.41 (d, 1H, J ¼ 1:9 Hz,
NCH@CH), 7.53–7.58 (m, 1H, PPh2-CH), 9.85 (d, 1H,
JPH ¼ 20:1 Hz, PCp-CH); 13C NMR (75 MHz, CDCl3) d
18.7, 20.9 (Mesityl-CH3), 22.9 (d, JPC ¼ 3:6 Hz, Mesityl-
CH3), 27.8, 28.3, 31.2 (CH2 COD-CH2), 32.9 (d,
JPC ¼ 3:0 Hz, CH2), 33.0 (2C, CH2, COD-CH2), 34.2,
35.0 (CH2, COD-CH2) 54.6 (CH2N), 76.6, 77.7 (COD-
CH), 83.2 (d, JPC ¼ 8:4 Hz, COD-CH), 83.3 (COD-CH),
123.6 (NCH@CH), 128.1, 128.7 (Cq), 129.0, 129.3 (Aryl-
CH), 129.4 (Cq), 129.9 (3C, Aryl-CH, NCH@CH),
130.0 (Cq), 131.0 (2C, Aryl-CH), 131.9, 132.4 (Aryl-
CH), 132.6–133.6 (m, 4C, Aryl-CH), 134.3 (Aryl-CH),
135.2, 135.8, 136.5 (Cq), 136.6 (2C, Cq), 138.0 (Aryl-
CH), 138.1 (d, JPC ¼ 6:0 Hz, Aryl-CH), 138.9, 139.3
(Aryl-CH), 139.4 (d, 2C, JPC ¼ 13:9 Hz, Aryl-CH),
139.5, 140.2, 144.6 (qC), 178.5 (d, JPC ¼ 8:3 Hz, NCN);
4.14. Procedure for the alkene hydrogenation and analysis
of the products
The substrate, iridium complex 5a–c and dichloro-
methane (1 mL) were added to a small tube containing a
magnetic stirring bar, which was then placed in 100 mL
autoclave. The autoclave was sealed and pressurized to
10–50 bar of hydrogen. One sequence of experiments
was carried out at 50 ꢁC using a heating mantle. Reac-
tions at lower temperatures were performed using a
cryostate and a cooling bath. Hydrogenations at ambi-
ent pressure were carried out in a Schlenk tube using a
balloon and 2 mL of solvent. The tube containing the
catalyst and the substrate was evacuated and refilled
with hydrogen gas several times before adding the sol-
vent. After stirring for the indicated time (see tables) at
the appropriate temperature, the reaction vessel was
vented. If necessary, it was cooled to room temperature
before venting. Reaction times were not optimized. The
reaction mixture was diluted with pentane and passed
through a short silica gel plug using hexane–ethyl ace-
tate (3:1) as the eluent. After evaporation of the sol-
19F NMR (282 MHz, CDCl3)
d
)73.08 (d,
JPF ¼ 712:5 Hz); 31P NMR (121 MHz, CDCl3) d )144.25
1
(sep, JPF ¼ 713:0 Hz, PF6), 16.82 (s, P(Aryl)3); IR (KBr)
vents, the conversions and ees were determined by H
v 842, 703, 557 cmꢀ1; MS (SIMS-FAB, pos.) m=z (%) 894
NMR and HPLC using a chiral column, respectively. In
the case of a-acetamidocinnamic acid 21, product 24
was converted to methyl ester 25 by use of an ethereal
CH2N2 solution after hydrogenation and ethyl ether was
used as the eluent when passing through silica gel.
HPLC analysis: 1,2-diphenylpropane 14: Daicel Chi-
ralcel OJ column, 254 nm, 20 ꢁC, 0.5 mL minꢀ1, n-hep-
tane–2-propanol, 99:1, retention times (in min) ¼ 15.5
(R), 25.7 (S), 29.5 (starting material).33a 2-(4-Methoxy-
phenyl)butane 18: Daicel Chiralcel OD-H column,
254 nm, 20 ꢁC, 0.5 mL minꢀ1, n-heptane, retention times
(in min) ¼ 15.5 (S), 17.4 (R).34b 2-Methyl-3-phenyl-pro-
pionic acid methyl ester 22: Daicel Chiralcel OD-H
column, 254 nm, 20 ꢁC, 0.5 mL minꢀ1, n-heptane–2-pro-
panol, 99.5:0.5, retention times (in min) ¼ 21.5 (R), 25.4
(S).37 2-Methylsuccinic acid dimethyl ester 23: Daicel
~
(10), 893 (20), 891 (11, Mþ), 817 (15), 816 (21), 815 (22),
814 (20), 813 (13), 785 (16), 784 (42), 783 (78), 782 (56),
781 (100), 780 (35), 779 (46), 778 (13), 777 (12), 598 (11),
596 (11), 594 (12), 592 (13), 512 (10), 496 (16), 494
(12), 490 (10), 438 (15), 406 (14), 303 (11), 301 (17),
187 (34), 185 (25), 184 (18), 183 (23); MS (SIMS-
FAB, neg.) m=z (%) 145 (100, Mꢀ). Anal. Calcd for
C49H51F6IrN2P2ÆCH3OH: C, 56.22; H, 5.19; N, 2.62.
Found: C, 56.12; H, 5.19; N, 2.58.
4.13. X-ray structure determination of (Rp)-5d
The compound {[C49H51N2PIr][PF6] Mr 1036.12} crys-
tallizes in tetragonal space group P43212 (No. 96) with
cell dimensions a ¼ 12:190ð8Þ and c ¼ 62:65ð6Þ A. A cell
Chiralcel OD-H column, 215 nm, 20 ꢁC, 0.5 mL minꢀ1
,
ꢀ
3
ꢀ
volume of V ¼ 9310ð14Þ A and Z ¼ 8 result in a cal-
culated density of dcalcd ¼ 1:478 g cmꢀ3, 265,942 reflec-
tions have been collected at T ¼ 298 K on a Bruker
Smart Apex CCD diffractometer employing MoKa
n-heptane–2-propanol, 96:4, retention times (in min) ¼
13.7 (R), 18.9 (starting material), 21.6 (S).38 N-Acetyl
phenylalanine methyl ester 25: Daicel Chiralcel OD-H
column, 254 nm, 20 ꢁC, 0.6 mL minꢀ1, n-heptane–2-pro-
panol, 90:10, retention times (min) ¼ 17.1 (R), 23.8 (S).38
ꢀ
radiation (k ¼ 0:71073 A). Data collection covered the
range ꢀ14 6 h 6 14, ꢀ14 6 k 6 14 and ꢀ74 6 l 6 74 up
to Hmax ¼ 25:14ꢁ, l ¼ 2:996 mmꢀ1, absorption correc-
tion with SADABS (max: 1.0000, min: 0.7988). The
structure has been solved by direct methods as imple-
mented in the Xtal3.7 suite of crystallographic routines36
where GENSIN has been used to generate the structure
invariant relationships and GENTAN for the general
tangent phasing procedure. Due to the low crystal
quality the structure could not be refined completely
anisotropical (see text), 7931 observed reflections
(I > 2rðIÞ) have been included in the final refinement on
Acknowledgements
We are grateful to financial support by the Fonds der
Chemischen Industrie, the BMBF and Degussa AG. We
also thank Umicore (formerly OMG) and Degussa for
the generous gift of chemicals.
F
involving 286 parameters and converging at
RðRwÞ ¼ 0:113ð0:103; w ¼ 1=½r2ðF Þ þ 0:0004 ꢃ F 2ꢁÞ, S ¼
ꢀ3
ꢀ
4:994 and a residual electron density of )5.7/3.4 e A
.
References and notes
The hydrogen positions have been calculated in ideal-
ized positions. Their Us have been fixed at 1.5 times U
of the relevant heavy atom, and no hydrogen parameters
have been refined.
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