Chiral iridium(I) bis(NHC) complexes as catalysts for asymmetric transfer hydrogenation

Article abstract of DOI:10.1002/aoc.1650

The common use of NHC complexes in transition-metal mediated C-C coupling and metathesis reactions in recent decades has established W-heterocyclic carbenes as a new class of ligand for catalysis. The field of asymmetric catalysis with complexes bearing N

Full text of DOI:10.1002/aoc.1650

Full Paper
Received: 19 October 2009
Revised: 29 December 2009
Accepted: 18 February 2010
Published online in Wiley Interscience: 1 April 2010
(www.interscience.com) DOI 10.1002/aoc.1650
Chiral iridium(I) bis(NHC) complexes
as catalysts for asymmetric transfer
hydrogenation
Claus Diez and Ulrich Nagel∗
The common use of NHC complexes in transition-metal mediated C–C coupling and metathesis reactions in recent decades
has established N-heterocyclic carbenes as a new class of ligand for catalysis. The field of asymmetric catalysis with complexes
bearing NHC-containing chiral ligands is dominated by mixed carbene/oxazoline or carbene/phosphane chelating ligands. In
contrast, applications of complexes with chiral, chelating bis(NHC) ligands are rare. In the present work new chiral iridium(I)
bis(NHC) complexes and their application in the asymmetric transfer hydrogenation of ketones are described. A series of
chiral bis(azolium) salts have been prepared following a synthetic pathway, starting from L-valinol and the modular buildup
allows the structural variation of the ligand precursors. The iridium complexes were formed via a one-pot transmetallation
procedure. The prepared complexes were applied as catalysts in the asymmetric transfer hydrogenation of various prochiral
ketones, affording the corresponding chiral alcohols in high yields and moderate to good enantioselectivities of up to 68%. The
enantioselectivities of the catalysts were strongly affected by the various, terminal N-substituents of the chelating bis(NHC)
ligands. The results presented in this work indicate the potential of bis-carbenes as stereodirecting ligands for asymmetric
c
catalysis and are offering a base for further developments. Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Keywords: chiral iridium(I)-NHC complexes; asymmetric transfer hydrogenation; ketones
Introduction
Moreover the synthetic pathway allowed us to prepare a bis(NHC)
ligand and its iridium(I) complex combining two different azolin-2-
ylidenes. The influence of the ligand shape on the catalytic activity
and selectivity of the corresponding iridium(I) bis(NHC) complexes
was determined.
Since their discovery, stable N-heterocyclic carbenes (NHCs) have
been the subject of intense interest, primarily as strong σ-donor
ligands for transition metals. In comparison with phosphane com-
plexes, NHC complexes display significant advantages, particularly
their stability towards air, moisture and heat. Their common use in
transition-metal mediated C–C coupling and metathesis reactions
has established N-heterocyclic carbenes as a new class of ligand in
catalysis beside phosphane and oxazoline ligands.[1–5]
Results and Discussion
Ligand and Complex Synthesis
The field of asymmetric catalysis with complexes bearing chiral
NHC-containing ligands is dominated by chelating ligands with a
carbeneunitandasecondcoordinatinggroup, suchasphosphane
or oxazoline.[6–9] Apart from the well-known bis(benzimidazolin-
2-ylidene) palladium (II) and rhodium(III) complexes derived from
BINAM, applications of chiral bis(NHC) complexes in asymmetric
catalysis are notably rare.[10,11]
As recently demonstrated by Peris and Crabtree et al., rhodium
(III) and iridium (III) complexes of achiral chelating bis(carbene)
ligands are promising catalysts for the transfer hydrogenation
of ketones using 2-propanol as hydrogen source and various
amounts of KOH as cocatalyst.[12–14] Using benzophenone as the
substrate and bis(imidazolin-2-ylidene) iridium (III) complexes as
catalysts, Crabtree et al. observed turnover frequencies of up to
50 000 [h−1].[12]
As previously reported, the bis-imidazolium salts 3a–f are
accessible via a modular synthesis starting from L-valinol. The
modular buildup of the ligand precursors makes it possible to
introduce different substituents at the terminal nitrogen atoms in
two steps using the chiral imidazolebromide 1 as a bifunctional
synthon. The first reaction step was the alkylation of 1-R1-
imidazoles (R1 = Me, iso-Pr and Ph) with 1 as alkylating agent. The
resulting imidazolium salts 2a–c were then treated with an excess
ofvariouselectrophilesR2Br(R2 = n-Prandiso-Pr)inacetonitrileor
methyliodide in dichloromethane giving the bis-imidazolium salts
3a–f in good yields (Scheme 1).[15] In a similar manner the mixed
bis-azolium salt 5, combining an imidazole and a benzimidazole
unit, was obtained.
The iridium(I) complexes 6a–f and 7 were prepared from
the corresponding bis-imidazolium salts 3a–f, silver(I) oxide
We recently reported the synthesis and structural characteriza-
tion of Rh(I) and Ir(I) complexes bearing chiral bis(NHC) ligands
derived from L-valinol.[15] In this article we wish to report the appli-
cation of these iridium complexes as catalysts for the asymmetric
transfer hydrogenation of prochiral ketones. For this purpose,
chiral bis(NHC) ligands with various combinations of terminal
N-substituents and their iridium(I) complexes were prepared.
∗
¨
Correspondence to: Ulrich Nagel, Universitat Tu¨bingen, Institut fu¨r Anorganis-
che Chemie, 72076 Tu¨bingen, Germany.
E-mail: Ulrich.Nagel@uni-tuebingen.de
¨
Institut fu¨r Anorganische Chemie, Universitat Tu¨bingen, Auf der Morgensteue
18, 72076 Tu¨bingen, Germany
c
Appl. Organometal. Chem. 2010, 24, 509–516
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

C. Diez and U. Nagel
Scheme 1. Syntheses of ligand precursors.
Scheme 2. Complex syntheses by one-pot transmetallation.
and [Ir(cod)Cl]2 according to a one-pot transmetallation pro-
cedure developed by Mata et al.[12,16,17] All complexes were
purified by gradient column chromatography on SiO2 using
dichloromethane–acetone mixtures as eluent and KPF6 for an-
ion exchange. The iridium(I) compounds 6a–f were obtained
as orange-red solids in 52–63% yield. Complex 7, bearing an
imidazolin-2-ylidene–benzimidazolin-2-ylidene ligand, was ob-
tained in a lower yield of 38% (Scheme 2). The iridium complexes
were obtained as mixtures of exo and endo stereoisomers, refer-
ring to the position of the backbone iso-propyl group relative to
the coordination plane. Hence, the iso-propyl group of the exo
isomer lies outside the C–Ir–C plane, while in the endo form it
is oriented to the metal. The transmetallation reactions always
gave excess exo isomers, ranging from 55% for 6a to 94% for
6d. The isomers were not separable by column chromatography,
but crystals containing the exo isomers exclusively were obtained
by layering concentrated THF–DCM solutions of complexes 6b–f
and 7 with cyclohexane.[15] Compound 6c was also prepared as a
65 : 35 exo/endo mixture by increasing the reaction temperature
during the transmetallation in acetonitrile to 80 ◦C. Complex 6a
did not crystallize and was obtained as a 55 : 45 exo/endo mixture
after column chromatography.
All complexes were characterized by NMR spectroscopy,
high-resolution mass spectrometry and elemental analysis. As
previously reported, the structures of 6b and 6c were determined
by single crystal X-ray crystallography (CCDC deposit numbers
696020 for 6b and 696021 for 6c). The 13C NMR spectra of the
iridium compounds 6a–f show typical signals between 171 and
177 ppm for metallated carbene carbons.[16,18] In comparison,
the signal of the metallated benzimidazolin-2-ylidene carbene
carbon of complex 7 appears at 184 ppm. The amounts of exo
and endo stereoisomers were determined by integration of their
characteristic backbone proton signals in the 1H NMR spectra.[15]
In addition to transfer hydrogenation, the prepared iridium(I)
complexes were tested in further catalytic reactions and
showed no activity in the hydrogenation of itaconic acid and
1-methylcyclohexene even at elevated hydrogen pressure. Only
low activity with low to moderate enantioselection was observed
in the hydrosilylation of prochiral ketones.
Asymmetric Transfer Hydrogenation
The iridium(I) complexes 6a–f and 7 were used as catalysts
for the asymmetric transfer hydrogenation of various ketones
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 509–516

Chiral iridium(I) bis(NHC) complexes
Scheme 3. ATH of ketones.
with 2-propanol as solvent/hydrogen donor and 1 mol% KOH as
cocatalyst (Scheme 3).[12,19] All reactions were heated for 15 h at
82 ◦C using ketone–catalyst–base ratios of 1000 : 1:10. It is well
known that the catalyst–base ratio is essential to activate the
catalysts for hydrogen transfer if no internal base is involved.[20,21]
While rhodium–NHC catalysts basically require higher amounts
of cocatalyst, iridium complexes are activated at lower base
concentrations.[13] In the present case a catalyst–base ratio of
1 : 10 has been proven to be optimal.
The results of the catalytic transfer hydrogenations of acetophe-
none, propiophenone and α-methylpropiophenone are listed in
Table 1. Generally all ketones were converted into the correspond-
ing alcohols in high yields. To investigate the effect of various
combinations of terminal N-substituents at the ligands on the
enantioselectivity, all complexes were tested in ATH with different
phenylalkylketones as substrates.
Starting with acetophenone, the obtained enantiomeric ex-
cesses of (S)-1-phenylethanol were low for all complexes. The
highest ee value of 14% (S)-1-phenylethanol was achieved with
complex 7 (entry 6, Table 1). Higher ee values of up to 42% (entry 9,
table 1)wereobtainedusingpropiophenoneassubstrate,whereas
theenantioselectivitiesofthecatalystswereaffectedbythesubsti-
tution patterns of the NHC-ligands. For α-methylpropiophenone
as the substrate, the ee values of the corresponding product
alcohol increased again for all catalysts.
Starting from the N-dimethyl substituted complex 6a, the
enantioselectivitywasenhancedusingligandswithstericallymore
demanding R2 N-substituents, like n-propyl and particularly iso-
propyl. However complex 6d bearing the bulky diphenylmetyl
group was generally less selective than complex 6c. Changing
the R1 group from methyl to iso-propyl (6e, R2 = n-Pr) or phenyl
(6f, R2 = n-Pr) resulted in lower ee values in asymmetric transfer
hydrogenations of the ketones 8a–c. The obtained ee values
indicate that the combination of a small R1 group with a branched
R2-alkyl group at the ligand, lead to enhanced catalyst selectivity.
While most of the catalysts preferably generated the (S)-alcohols,
the hydrogenation of α-methylpropiophenone with catalyst 6f
gave an excess of 21% (R)-1-phenyl-2-methylpropanol (entry 21,
Table 1).
Table 1. ATH of ketones catalyzed by 6a–f and 7a
Conversionb
eec (%)
Entry
Catalyst
R1/R2
(%)
(config.)d
Substrate: 8a
Me/Me
1
2
3
4
5
6
6ae
6b
6c
6d
6d
7
85
97
6 (R)
0
Me/n-Pr
Me/iso-Pr
Me/CHPh2
Ph/n-Pr
>99
>99
>99
98
11 (S)
7 (S)
7 (R)
14 (S)
Me/n-Pr
Substrate: 8b
Me/Me
7
6ae
6b
6c
6cf
6d
6e
6f
>99
>99
97
20 (S)
12 (S)
42 (S)
40 (S)
36 (S)
8 (S)
8
Me/n-Pr
9
Me/iso-Pr
Me/iso-Pr
Me/CHPh2
n-Pr/iso-Pr
Ph/n-Pr
10
11
12
13
14
98
94
90
99
6 (S)
7
Me/n-Pr
91
20 (S)
Substrate: 8c
Me/Me
15
16
17
18
19
20
21
22
6ae
6b
6c
6cf
6d
6e
6f
98
98
24 (S)
44 (S)
55 (S)
49 (S)
37 (S)
13 (S)
21 (R)
25 (S)
Me/n-Pr
Me/iso-Pr
Me/iso-Pr
Me/CHPh2
n-Pr/iso-Pr
Ph/n-Pr
>99
>99
95
78
>99
91
7
Me/n-Pr
a Reactionconditions:10 ml2-propanol,2.0 mmolketone,temperature
= 82 ◦C, time 15 h, ketone–catalyst–KOH = 1000 : 1 : 10, catalysts
were applied in pure exo form, unless otherwise stated. b Conversion
was determined by GC. c Measured by GC using chiral columns.
d Determined by comparison of the sign of optical rotation to literature
values. e Appliedas55: 45mixtureofexo/endoisomers.f 65 : 35mixture
of exo/endo isomers.
substituents. Additionally some catalytic runs were carried out at
lower temperatures (entries 1 and 5, Table 2) or with an alternative
cocatalyst (entry 2, Table 2).
Similar yields and slightly lower enantiomeric excesses of the
(S) product alcohols were obtained if a 65 : 35 exo/endo mixture of
catalyst 6c was used instead of enantiomerically pure 6c (entries
9/10 and 17/18, Table 1). If the exo/endo mixture was applied, for
example, to α-methylpropiophenone the ee value decreased from
55to49%.Theseresultsareindicatingeitheraslightlydifferent,but
aligned stereoselectivity of both isomers or an opposite selectivity,
associated with a lower activity of the endo isomer.
The highest enantiomeric excess of 58% of the (S)-alcohol was
obtained for the substrate n-butyrophenone (entry 3, table 2). The
reduction of 2ꢁ,4ꢁ,6ꢁ-trimethylacetophenone (8h) bearing a very
bulky phenylring with catalyst 6c gave a marginally lower ee value
of57%ofthe(R)-enantiomer(entry8, Table 2). Alkylphenylketones
with sterically demanding alkylgroups like tert-butyl in 8e or iso-
butyl in 8f were hydrogenated to the corresponding alcohols with
ee values of 54 and 28% (entries 4 and 6, Table 2). Alkylketones
The most selective catalyst 6c was then applied to other
ketones with long or branched alkyl chains and bulky phenyl
c
Appl. Organometal. Chem. 2010, 24, 509–516
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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C. Diez and U. Nagel
the bulky phenyl ring now dominates the enantiofacial selectiv-
ity, while for the other alkylphenylketones the long or branched
alkylchains are determining the formation of (S)-alcohols.
The use of alkalicarbonates K2CO3 and Cs2CO3 as alternative
cocatalysts gave slightly lower ee values of 64 and 63% in
comparison to potassium hydroxide (entries 5 and 6, Table 3).[22]
Table 2. ATH of various ketones catalyzed by 6ca
Catalyst: 6c (R1 = Me/R2 = iso-Pr)
Entry Ketone Conversionb (%) eec (%) (configuration)d TON
1e
2f
3
8b
8b
8d
8e
8e
8f
<5
92
–
–
42 (S)
58 (S)
54 (S)
53 (S)
28 (S)
30 (S)
57 (R)
21 (S)
920
820
830
150
1000
920
930
460
82
4
5g
83
Conclusions
15
In conclusion we have synthesized a series of new chiral irid-
ium(I)–bis(NHC) complexes. The versatile synthetic pathway
makesitpossibletovarytheterminalN-substituentsatbothimida-
zole rings separately. In this way, the chiral environment of the irid-
ium center can be formed specifically. Furthermore we described
the synthesis of a mixed imidazolin-2-ylidene–benzimidazolin-
2-ylidene chelating ligand and its iridium complex.
The obtained iridium(I) complexes were then used as cata-
lysts for asymmetric transfer hydrogenations of prochiral ketones
and showed high activities under the described reaction condi-
tions. Lower yields and ee values were observed if the reaction
temperature was decreased. To determine how the enantios-
electivity is affected by the substrates and different combi-
nations of terminal N-substituents at the imidazolin-2-ylidene
units, various catalyst/ketone pairs have been tested in ATH.
The highest enantioselectivties, within this work, of 58 and 68%
ee were obtained by catalysts, bearing methyl-/iso-propyl and
methyl-/phenyl-N-substituents. These results were obtained us-
ingalkylphenylketoneswithlongalkylchainsormethylatedphenyl
rings as substrates. Currently efforts are in progress to improve
the activity of the complexes for other catalytic reactions as well
as the enantioselectivity.
6
>99
92
7
8g
8h
8i
8
93
10
46
a Reactionconditions:10 ml2-propanol,2.0 mmolketone,temperature
= 82 ◦C, time 15 h, ketone–catalyst–KOH = 1000 : 1 : 10, unless
otherwise stated, catalyst 6c was applied as pure exo isomer.
b Conversion was determined by GC. c Measured by GC using chiral
columns. d Determined by comparison of the sign of optical rotation
to literature values. e Reaction temperature 60 ◦C. f Base: t-BuOK.
g Reaction temperature: 70 ◦C.
Table 3. ATH of various ketones catalyzed by 6fa
Catalyst: 6f (R1 = Ph/R2 = n-Pr)
Entry Ketone Conversionb (%) eec (%) (configuration)d TON
1
8d
8e
8g
8h
8h
8h
8i
98
67
22 (S)
10 (S)
10 (R)
68 (R)
64 (R)
63 (R)
31 (S)
980
670
1000
820
790
750
970
2
3
>99
82
4
5e
6f
7
79
75
97
Experimental
a Reactionconditions:10 ml2-propanol,2.0 mmolketone,temperature
= 82 ◦C, time 15 h, ketone–catalyst–KOH = 1000 : 1:10, unless
otherwise stated, catalyst 6f was applied as pure exo isomer.
b Conversion was determined by GC. c Measured by GC using chiral
columns. d Determined by comparison of the sign of optical rotation
to literature values. e Base: K2CO3. f Base: Cs2CO3.
General Remarks
NMR spectra were recorded on a Bruker DRX-400 spectrometer,
with CDCl3, CD3OD and D2O as solvents. Elemental analyses were
carried out in a Vario EL analyzer. Electron impact (EI+) and
Fast Atom Bombardment (FAB+) mass spectra were recorded
on a Finnigan MAT, TSQ 70 instrument, using 3-nitrobenzyl
alcohol as matrix. Electrospray mass spectra were recorded on
a Bruker Daltonics APEX II FT-ICR instrument using CH3OH as
solvent and nitrogen as drying and nebulizing gas. Melting
points are uncorrected and were determined on a Mel-Temp
Z15 apparatus. Chiral GC was performed on a Chrompack 438A
with chiral columns from Macherey-Nagel (FS-Lipodex E, 50 m,
0.25 mm diameter) and Chrompack (FS-Cyclodex beta-I/P, 60 m,
0.25 mm diameter). Optical rotations of chiral alcohols were
determined on a Knauer, Polar-M polarimeter. Imidazolebromide
1 was prepared from L-valinol (97% ee, Sigma-Aldrich) according
to our previously reported procedure.[15] All other reagents are
commercially available and were used as received.
like pinacolone were generally reduced in lower yields (entry 10,
Table 2). In summary the selectivity of catalyst 6c strongly depends
onthesubstrateandketoneswithlong, unbranchedalkylchainsor
bulky phenylrings yielded the highest ee values. Low conversions
of 5 and 15% were obtained, if the reaction temperatures were
decreased from 82 to 60 and 70 ◦C, while the ee values were
affected only marginally (entries 1 and 5, Table 2). Similar ee and
conversion were observed when the base was changed from KOH
to tert-BuOK (entry 2, Table 2).
The results of the transfer hydrogenations of various ke-
tones using catalyst 6f (R1 = Ph; R2 = n-Pr) are listed
in Table 3. Alkylphenylketones like butyrophenone or 2,2-
dimethylpropiophenone were transferred into the corresponding
alcohols with only low ee values. Interestingly, the highest ee
value within this work of 68% was obtained when catalyst 6f
was applied to ketone 8h, bearing a bulky, trimethylsubstituted
phenylring (entry 4, Table 3). The configurations of the product
alcohols changed from (S) to (R) if ketones with short alkyl chains
and methylated phenyl rings like 8g,h were used. Presumably
Preparation of 2a
A mixture of 1 (495 mg, 2.28 mmol) and 1-methylimidazole
(936 mg, 11.4 mmol) was stirred at 50 ◦C for 72 h. After cooling to
ambient temperature, diethyl ether (20 ml) was added, while
stirring to dissolve excess 1-methylimidazole. The ether was
removed via syringe and the colorless, oily precipitate was washed
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 509–516

Chiral iridium(I) bis(NHC) complexes
two more times with diethyl ether and dried in vacuo. The oil was
then dissolved in CHCl3 (10 ml) and extracted in water (2 × 8 ml).
After removal of the water under reduced pressure, the resulting
solid was washed with diethyl ether (2×15 ml) and dried invacuo,
giving 2a as a hygroscopic, white solid. Yield: 556 mg (82%). MS
(FAB):m/z 219(100%). MS(HRESI+):calcdforC12H19N4, 219.16042;
found, 219.16042. 1H NMR (CD3OD, 400 MHz): δ 8.93 (s, 1H, NCHN),
7.77 (s, 1H, NCHN), 7.54 (t, 3JHH = 1.6 Hz, 1H, CHimid), 7.47 (brs, 1H,
(89%). MS (FAB): m/z 313 [M − Br]+ (40%). 1H NMR (CD3OD,
400 MHz): δ 9.17, 9.03 (s, 2H, NCHN), 7.83, 7.61 (s, 2H, CHimid),
7.48 (m, 2H, CHimid), 4.98–4.87 (m, 3H, CHCH2N), 3.89, 3.85 (s, 6H,
3
NCH3), 2.39–2.31 [m, 1H, CHCH(CH3)2], 1.12 [d, JHH = 6.7 Hz,
3
1
3H, CH(CH3)2], 0.83 [d, JHH = 6.7 Hz, 3H, CH(CH3)2]. 13C{ H}
NMR (CD3OD, 100 MHz): δ 138.73 (NCHN), 138.18 (NCHN), 126.33,
125.71, 123.77, 122.51 (CHimid), 67.86 (CH2CHN), 51.89 (NCH2CH),
37.71, 37.52 (NCH3), 32.44 [CHCH(CH3)2], 19.77, 19.04 [CH(CH3)2].
3
CHimid), 7.42 (t, JHH = 1.7 Hz, 1H, CHimid), 7.08 (brs, 1H, CHimid),
4.98–4.81 (m, 2H, NCH2CH), 4.60 (qd, 3JHH = 3.4 Hz, 1H, CH2CHN),
3.90 (s, 3H, NCH3), 2.35 [m, 1H, CHCH(CH3)2], 1.20 [d, 3JHH = 6.7 Hz,
Compound 3b
1
3H, CHCH(CH3)2], 0.86 [d, 3JHH = 6.7 Hz, 3H, CHCH(CH3)2]. 13C{ H}
Hygroscopic white solid; Yield: 200 mg (86%) MS (FAB), m/z
341 (40%). 1H NMR (CD3OD, 400 MHz): δ 9.32 (s, 1H, NCHN),
NMR (CD3OD, 100 MHz): δ 139.06, 138.40 (NCN), 129.89, 124.99,
123.88, 119.21 (CHimid), 65.41 (CH2CHN), 52.93 (NCH2CH), 36.83
(NCH3), 32.79 [CHCH(CH3)2], 20.03, 19.43 [CH(CH3)2].
3
9.08 (s, 1H, NCHN), 7.91 (d, JHH = 1.8 Hz, 1H, CHimid), 7.75 (d,
3
3JHH = 1.7 Hz 1H, CHimid), 7.52 (d, JHH = 1.7 Hz, 1H, CHimid),
3
7.50 (d, JHH = 1.8 Hz, 1H, CHimid), 5.00–4.85 (m, 3H, CH2CHN,
3
NCH2CH), 4.18 (t, JHH = 7.1 Hz, 2H, NCH2CH2), 3.88 (s, 3H,
Preparation of 2b
3
NCH3), 2.38 [m, 1H, CHCH(CH3)2], 1.87 (sext, JHH = 3.6 Hz, 2H,
The same procedure as for2a was carried out by stirring imidazole-
bromide 1 (230 mg, 1.1 mmol) and 1-iso-propylimidazole (473 mg,
4.5 mmol) at 60 ◦C for 48 h. Compound 2b was obtained as a hy-
groscopic white solid. Yield: 267 mg (74%). MS (FAB): 247 (100%).
MS (HRESI+): calcd for C14H23N4, 247.19172; found, 247.19171. 1H
NMR (CD3OD, 400 MHz): δ 9.06 [s, 1H, NCHN CH(CH3)2], 7.75 (bs,
2H, NCHN), 7.57 (s, 1H, CHimid), 7.51 (bs, 1H, CHimid), 7.07 (s, 1H,
CHimid), 4.95–4.80 (m, 2H, CHCH2N), 4.64–4.55 (m, 1H, CH2CHN),
4.38 [m, 1H, NCH(CH3)2], 2.44–2.33 [m, 1H, CHCH(CH3)2], 1.51
3
NCH2CH2), 1.17 [d, JHH = 6.7 Hz, 3H, CHCH(CH3)2], 1.06 [m,
1
6H, CH2CH3, CHCH(CH3)2]. 13C{ H} NMR (CD3OD, 100 MHz): δ
138.91, 137.82 (NCN), 125.76, 125.29, 123.91, 122.70 (CHimid), 68.27
(CH2CHN), 52.96 (NCH2CH), 51.96 (NCH2CH2), 37.19 (NCH3), 32.53
[CHCH(CH3)2], 24.45 (NCH2CH2), 19.75, 19.11 [CH(CH3)2], 11.00
(CH2CH3).
Compound 3c
3
3
[d, JHH = 6.7 Hz, 6H, NCH(CH3)2], 1.21 [d, JHH = 6.7 Hz, 3H,
Hygroscopic, white solid; Yield: 190 mg (79%) MS (FAB), m/z 341
(30%). 1H NMR (CD3OD, 400 MHz): δ 9.41 (s, 1H, NCHN), 9.09 (s, 1H,
CHCH(CH3)2], 0.87 [d, JHH = 6.7 Hz, 3H, CHCH(CH3)2]. 13C{ H}
NMR(CD3OD, 100 MHz):δ 136.38[NCHNCH(CH3)2], 129.10(NCHN),
123.98, 122.14, 121.97, 119.40 (CHimid), 65.88 (CH2CHN), 54.78
[NCH(CH3)2], 52.96 (NCH2CH), 32.67 [CHCH(CH3)2], 23.14, 22.91
[NCH(CH3)2], 19.85, 19.50 [CH(CH3)2].
3
1
3
NCHN), 7.90 (d, JHH = 1.8 Hz, 1H, CHimid), 7.82 (brs, 1H, CHimid),
3
7.49 (d, JHH = 1.8 Hz, 1H, CHimid), 7.44 (brs, 1H, CHimid), 4.95
3
(t, JHH = 4.8 Hz, 2H, NCH2CH), 4.87 (m, 1H, CH2CHN), 4.65 [m,
1H, NCH(CH3)2], 3.85 (s, 1H, NCH3), 2.36 [m, 1H, CHCH(CH3)2],
3
3
1.48 [d, JHH = 6.7 Hz, 6H, NCH(CH3)2], 1.13 [d, JHH = 6.6 Hz,
3
Preparation of 2c
3H, CHCH(CH3)2], 0.82 [d, JHH = 6.7 Hz, 3H, CHCH(CH3)2].
13C{ H} NMR (CD3OD, 100 MHz): δ 138.85, 136.40 (NCN), 125.54,
1
The same procedure as for 2a was used by stirring imidazole-
bromide 1 (173 mg, 0.8 mmol) and 1-phenylimidazole (473 mg,
4.5 mmol) at 65 ◦C for 72 h. The title compound 2c was ob-
tained as hygroscopic white solid. Yield: 198 mg (69%). MS (FAB):
281 (100%).MS (HRESI+): calcd for C17H21N4, 281.17607; found,
123.75,123.38,122.78(CHimid),68.21(CH2CHN),55.23[NCH(CH3)2],
51.88 (NCH2CH), 37.19 (NCH3), 32.31 [CHCH(CH3)2], 23.22, 23.13
[NCH(CH3)2], 19.69, 19.15 [CH(CH3)2].
1
281.17630. H NMR (D2O, 400 MHz): δ 8.91 (s, 1H, NCHNCPhenyl),
Preparation of 3d
7.72 (s, 1H, NCHN), 7.52 (s, 1H, CHimid), 7.48 (m, 4H, C6H5,
CHimid), 7.36 (m, 3H, C6H5, CHimid), 7.12 (br s, 1H, CHimid),
4.96–4.80 (m, 2H, CHCH2N), 4.44 (m, 1H, NCH2CH), 2.23 [m, 1H,
An acetonitrile solution of 2a (83 mg, 0.28 mmol) and bro-
modiphenylmethane (178 mg, 0.72 mmol) was heated at reflux
temperature for 18 h. After all volatiles were removed un-
der reduced pressure, the remaining solid was dissolved in
dichloromethane and extracted in water (2 × 5 ml). The water
was removed under reduced pressure. The resulting white solid
was then washed with ether and dried in vacuo to give 3d as
hygroscopic, white solid. Yield: 109 mg (71%). MS (FAB): m/z 465
[M − Br]+ (20%). 1H NMR (CDCl3, 400 MHz): δ 8.63, 8.24 (s, 2H,
NCHN), 7.37–7.31 (m, 8H, C6H5), 7.25–7.19 (m, 2H, CHimid), 7.14
(m, 2H, C6H5), 7.08 (m, 2H, CHimid), 5.82–5.64 [m, 3H, CHCH2N,
NCH(C6H5)2], 4.91 (m, 1H, CH2CHN), 3.85 (s, 3H, NCH3), 2.41 [m,
3
CHCH(CH3)2], 1.09 [d, JHH = 6.6 Hz, 3H, CHCH(CH3)2], 0.74 [d,
1
3JHH = 6.6 Hz, 3H, CHCH(CH3)2]. 13C{ H} NMR (D2O, 100 MHz):
δ 136.91 (NCHNCPhenyl), 136.05 (NCPhenyl), 131.60 (C6H5), 129.89
(NCHN), 128.96, 124.75 (CHimid), 123.36 (C6H5), 122.95 (CHimid),
122.37 (C6H5), 119.23 (CHimid), 65.44 (CH2CHN), 53.46 (NCH2CH),
32.81 [CHCH(CH3)2], 19.95, 19.56 [CH(CH3)2].
Preparation of 3a
To a solution of 2a (132 mg, 0.44 mmol) in dichloromethane (3 ml),
methyliodide (0.5 ml) was added in one portion. The clear solution
was then stirred for 18 h at ambient temperature. After all volatiles
were removed under reduced pressure, the remaining white
solid was redissolved in dichloromethane and added dropwise
to diethylether while stirring. The resulting white precipitate was
washed several times with ether and dried invacuo to give the title
compound 3a as very hygroscopic, white powder. Yield: 172 mg
3
1H, CHCH(CH3)2], 1.10 [d, JHH = 6.5 Hz, 3H, CH(CH3)2], 0.86 [d,
1
3JHH = 6.4 Hz, 3H, CH(CH3)2]. 13C{ H} NMR (CDCl3, 100 MHz):
δ 137.72, 137.08 (NCN), 136.20, 136.06 (CPhenyl,quart.), 129.46
(C6H5), 129.38 (C6H5), 128.30 (C6H5), 128.20 (C6H5), 127.78 (C6H5),
123.79, 123.56, 123.14, 121.53 (CHimid), 67.02 [NCH(C6H5)2], 65.84
(CH2CHN), 50.11 (NCH2CH), 37.03 (NCH3), 31.49 [CHCH(CH3)2],
19.45, 18.66 [CH(CH3)2].
c
Appl. Organometal. Chem. 2010, 24, 509–516
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/aoc

C. Diez and U. Nagel
Preparation of 3e
3H, CHCH(CH3)2], 0.85 [d, 3JHH = 6.5 Hz 3H, CHCH(CH3)2], 0.47 (t,
1
3JHH = 7.3 Hz,3H,CH2CH3).13C{ H}NMR(D2O,100 MHz):δ 141.78,
Following the procedure described for 3d, reaction between 2b
(165 mg, 0.50 mmol) and 1-bromopropane (0.4 ml) gave the title
compound 3e as hygroscopic white solid. Yield: 187 mg (84%).
MS (FAB): m/z 369 [M − Br]+ (20%). 1H NMR (CDCl3, 400 MHz): δ
10.02 (s, 1H, NCHN), 9.91 (s, 1H, NCHN), 8.37, 8.12, 7.40, 7.33 (s,
4H, CHimid), 5.61–5.53 (m, 2H, NCH2CH), 4.79 (m, 1H, CH2CHN),
4.57 [m, 1H, NCH(CH3)2], 4.28–4.23 (m, 2H, NCH2CH2), 2.35 [m, 1H,
141.20 (NCHN), 135.47, 131.72 (CHquart.Benzimid.), 127.69, 126.80
(CHBenzimid.), 124.22, 120.71 (CHimid), 113.67, 111.93 (CHBenzimid.),
66.94 (CH2CHN), 51.40 (NCH2CH2), 48.70 (NCH2CH), 33.04 (NCH3),
30.41 [CHCH(CH3)2], 22.70 (NCH2CH2), 18.66, 18.15 [CH(CH3)2],
9.58 (CH2CH3).
3
Complex Synthesis: General Procedure
CHCH(CH3)2], 1.83 (m, 2H, NCH2CH2), 1.48 [d, JHH = 6.5 Hz, 6H,
3
NCH(CH3)2] 1.12 [d, JHH = 6.4 Hz, 3H, CHCH(CH3)2], 0.84–0.78
Silver(I) oxide (0.70 mmol) was added to a dichloromethane
(15 ml) solution of bis imidazolium salts (0.35 mmol) and stirred
in the dark at room temperature for 2.5 h under argon. Then
[Ir(COD)Cl]2 (0.17 mmol) was added to the gray suspension in one
portion, under formation of a white precipitate. To complete the
reaction, the mixture was stirred in the dark at room temperature
for 14 h. To remove insoluble silver salts, the suspension was
filtered through celite and the resulting orange-red solution was
concentrated under reduced pressure. The crude solid was then
purified by gradient column chromatography (SiO2, first CH2Cl2;
CH2Cl2 –acetone 2 : 1; then CH2Cl2 –acetone 1 : 1 with 2 equiv.
KPF6). Analytically pure material was obtained by a second flash
column chromatography, with CH2Cl2 –acetone 4 : 1 as elutant.
The title compounds were obtained as orange-red solids.
[m, 6H, CHCH(CH3)2, CH2CH3]. 13C{ H} NMR (CDCl3, 100 MHz): δ
1
136.46, 135.78 (NCN), 123.96, 123.33, 122.47, 120.31 (CHimid), 65.42
(CH2CHN), 53.74 [NCH(CH3)2], 51.74 (CHCH2N), 50.19 (NCH2CH2),
31.69 [CHCH(CH3)2], 23.38 (NCH2CH2), 22.93, 22.66 [NCH(CH3)2],
19.78, 19.18 [CHCH(CH3)2], 10.49 (CH2CH3).
Preparation of 3f
Following the procedure described for 3d, reaction between 2c
(120 mg, 0.34 mmol) and 1-bromopropane (0.3 ml) gave the title
compound 3f as hygroscopic white solid. Yield: 147 mg (91%).
MS (FAB): m/z 403 [M − Br]+ (70%). H NMR (CD3OD, 400 MHz):
1
δ 9.73, 9.35 (s, 2H, NCHN), 8.01, 7.92, 7.72, 7.53 (s, 4H, CHimid),
7.67 (m, 2H, C6H5), 7.59–7.48 (m, 3H, C6H5), 5.08–4.92 (m, 3H,
NCHCH2, NCHCH2), 4.13 (t, 3JHH = 7.1 Hz, 2H, NCH2CH2), 2.38 [m,
3
1H, CHCH(CH3)2], 1.79 (m, 2H, NCH2CH2), 1.16 [d, JHH = 6.6 Hz,
Compound 6a
3
3H, CHCH(CH3)2], 0.84 [d, JHH = 6.6 Hz, 3H, CHCH(CH3)2], 0.76
Complex 6a was obtained as 55 : 45 mixture of exo and endo
stereoisomers.Yield:120 mg(52%).M.p.:155–156 ◦C;MS(HRESI+):
calcd for C21H32IrN4, 533.22574; found, 533.22520. 1H NMR
3
1
(t, JHH = 7.4 Hz, 3H, CH2CH3). 13C{ H} NMR (CD3OD, 100 MHz):
δ 137.78, 137.33 (NCHN), 131.56 (C6H5), 125.13, 124.70, 123.52
(CHimid), 123.70, 123.42 (C6H5), 122.69 (CHimid), 67.94 (CH2CHN),
52.80 (NCH2CH), 52.32 (NCH2CH2), 32.52 [CHCH(CH3)2], 24.30
(CH2CH3), 19.64, 18.97 [CH(CH3)2], 10.85 (CH2CH3).
3
(CDCl3, 400 MHz): δ 6.98 (d, JHH = 2.0 Hz, 1H, CHimid), 6.88 (d,
3JHH = 1.9 Hz, 1H, CHimid), 6.81 (d, 3JHH = 2.0 Hz, 1H, CHimid), 6.77
3
3
(d, JHH = 1.9 Hz, 1H, CHimid), 6.43 (td, JHH = 4.6 Hz, 11.5 Hz,
1H, CH2CHN), 4.45–3.91 (m, 6H, CHCH2N, CHCOD), 3.84 (s, 1H,
NCH3), 3.57 (s, 1H, NCH3), 2.39–1.80 (m, CHCH(CH3)2, CH2,COD),
1.16 [d, 3JHH = 6.5 Hz, 3H, CH(CH3)2], 0.97 [d, 3JHH = 6.4 Hz, 3H,
Preparation of 4
Following the procedure described for 2a, reaction between
1 (120 mg, 0.34 mmol) and 1-methylbenzimidazole (462 mg,
3.5 mmol), the title compound 4 was obtained as a hygroscopic
white solid. Yield: 195 mg (52%). MS (FAB): m/z 269 (100%).
MS (HRESI+): calcd for C16H21N4, 269.36524; found, 269.36483.
1H NMR (CD3OD, 400 MHz): δ 8.48 (s, 1H, NCHNCH3), 7.96 (s,
1H, NCHN), 7.83 (s, 1H, CHimid), 7.69–7.52 (m, 2H, CHBenzimid.),
7.36–7.31 (m, 2H, CHBenzimid.) 7.05 (s, 1H, CHimid), 5.13–4.98 (m,
2H, CHCH2N), 4.62 (td, 3JHH = 4.2 Hz, 20.0 Hz, 1H, CH2CHN), 4.01
1
CH(CH3)2]. 13C{ H} NMR (CDCl3, 100 MHz): δ 176.74, 173.87 (IrC),
124.43, 123.19, 122.04, 117.44 (CHimid), 78.04, 75.43, 74.24, 73.57
(CHCOD), 63.95 (CH2CHN), 52.47 (NCH2CH), 39.21, 36.82 (NCH3),
32.52, 32.04, 30.28, 29.32 (CH2 COD), 29.98 [CHCH(CH3)2], 20.84,
19.82 [CH(CH3)2]. Anal. calcd for C21H32F6IrN4P (678.47), C, 37.18;
H, 4.75; N, 8.26; found, C, 37.70; H, 4.59; N, 8.37.
Compound 6b
3
(s, 3H, NCH3), 2.31 [m, 1H, CHCH(CH3)2], 1.21 [d, JHH = 6.7 Hz,
3H, CHCH(CH3)2], 0.79 [d, 3JHH = 6.7 Hz 3H, CHCH(CH3)2]. 13C{ H}
1
Diastereomerically pure (100% exo), crystalline material was
obtained by layering a THF–CH2Cl2 (3 : 1) solution of 6b with
cyclohexane. Yield: 152 mg (63%). M.p.: 159 ◦C, 209 ◦C dec.; MS
NMR (CD3OD, 100 MHz): δ 140.70 (NCHNCH3), 136.21, 133.54
(CHquart. Benzimid.), 128.95 (NCHN), 127.03 (CHimid), 123.04, 123.44
(CHBenzimid.), 117.93 (CHimid), 112.81, 111.52 (CHBenzimid.), 63.32
(CH2CHN), 49.34 (NCH2CH), 32.82 (NCH3), 30.49 [CHCH(CH3)2],
18.71, 18.16 [CH(CH3)2].
1
(HRESI+): calcd for C23H36IrN4, 561.25638; found, 561.25631. H
3
NMR (CDCl3, 400 MHz): δ 7.02 (d, JHH = 2.0 Hz, 1H, CHimid),
3
3
6.90 (d, JHH = 1.9 Hz, 1H, CHimid), 6.81 (d, JHH = 2.0 Hz, 1H,
CHimid), 6.78 (d, 3JHH = 2.0 Hz, 1H, CHimid), 6.49 (td, JHH = 4.3 Hz,
12.5 Hz, 1H, CH2CHN), 4.38 (td, JHH = 2.8 Hz, 7.2 Hz 1H, CHCH2N),
4.31–4.25 (m, 2H, CHCOD), 4.08 (m, 1H, CHCH2N), 3.99–3.87 (m,
2H, CHCOD),3.83 (s, 3H, NCH3), 3.79 (td, JHH = 3.4 Hz, 7.2 Hz,
2H, NCH2CH2), 2.42–1.78 [m, 9H, CH2,COD, CHCH(CH3)2], 1.67 (sext,
3JHH = 7.3 Hz, 2H, NCH2CH2), 1.16[d, 3JHH = 6.5 Hz, 1H, CH(CH3)2],
Preparation of 5
Following the procedure described for 3d, reaction between 4
(95 mg, 0.27 mmol) and 1-bromopropane (0.5 ml) gave the title
compound 5 as a hygroscopic white solid. Yield: 107 mg (85%).
MS (FAB): m/z 395 [M − Br]+ (10%); 259, 261 (80%). 1H NMR
(D2O, 400 MHz): δ 9.21, 8.71 (s, 2H, NCHN), 7.81–7.58 (m, 5H,
CHimid, CHBenzimid.), 7.50 (s, 1H, CHimid), 5.29–5.02 (m, 3H, CHCH2N,
NCHCH2), 4.37 (t, 3JHH = 7.0 Hz, NCH2CH2), 4.02 (s, 3H, NCH3), 2.50
[m, 1H, CHCH(CH3)2], 1.48(m, 2H, NCH2CH2), 1.26[d, 3JHH = 6.3 Hz,
3
3
0.97 [d, JHH = 6.4 Hz, 3H, CH(CH3)2], 0.69 (t, JHH = 7.4 Hz, 1H,
3H, CH2CH3). 13C{ H} NMR (CDCl3, 100 MHz): δ 176.06, 173.35 (IrC),
1
124.59, 121.87, 121.65, 117.53 (CHimid), 77.86, 74.30, 74.23, 72.56
(CHCOD), 64.34 (CH2CHN), 52.54 (NCH2CH2),51.42 (NCH2CH), 39.31
(NCH3), 32.67 [CHCH(CH3)2], 32.64, 30.18, 29.89, 29.32 (CH2 COD),
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 509–516

Chiral iridium(I) bis(NHC) complexes
24.46 (NCH2CH2), 20.82, 19.88 [CH(CH3)2], 10.58 (CH2CH3). Anal.
calcd for C23H36F6IrN4P (705.74), C, 39.14; H, 5.14; N, 7.94; found,
C, 39.17; H, 5.19; N, 8.02.
CHCOD), 3.89–3.81 (m, 3H, NCH2CH2, CHCOD), 3.68-3.61 (m,
1H, NCH2CH2), 2.44–2.30 (m, 2H, CH2 COD), 2.24–1.58 [m, 9H,
3
CHCH(CH3)2, NCH2CH2, CH2 COD], 1.40 [d, JHH = 6.8 Hz, 3H,
3
NCH(CH3)2], 1.20 [d, JHH = 6.7 Hz, 3H, NCH(CH3)2], 1.16 [d,
3JHH = 6.5 Hz, 1H, CH(CH3)2], 0.96 [d, 3JHH = 6.4 Hz, 3H, CH(CH3)2],
Compound 6c
3
1
0.86 (t, JHH = 7.4 Hz, 1H, 3H, CH2CH3). 13C{ H} NMR (CDCl3,
100 MHz): δ 175.75, 172.15 (IrC), 125.39, 121.20, 117.92, 116.52
(CHimid), 78.10, 73.97, 73.85, 72.40 (CHCOD), 64.05 (CH2CHN), 54.21
[NC(CH3)2], 52.32 (NCH2CH2), 51.41 (NCH2CH), 32.91, 32.76, 29.96,
29.76 (CH2 COD), 29.32 [CHCH(CH3)2], 24.76 [NCH(CH3)2], 24.40
(NCH2CH2), 23.72 [NCH(CH3)2], 20.83, 19.88 [CH(CH3)2], 10.91
(CH2CH3). Anal. calcd for C25H40F6IrN4P (733.79), C, 40.87; H, 5.45;
N, 7.63; found, C, 40.59; H, 5.49; N, 7.27.
Diastereomerically pure (100% exo), crystalline material was
obtained by layering a THF–CH2Cl2 (1 : 1) solution of 6c with
cyclohexane. Yield: 143 mg (62%).
A 65 : 35 exo/endo mixture of complex 6c was obtained by
heating the transmetallation reaction in acetonitrile to 80 ◦C for
5 h.Thenthegeneralpurificationprocedurewasused.M.p.:151 ◦C,
205 ◦C dec.; MS (HRESI+): calcd for C23H36IrN4, 559.25404; found,
559.25396. 1H NMR (CDCl3, 400 MHz): δ 7.03 (d, 3JHH = 2.1 Hz, 1H,
CHimid), 6.89 (d, 3JHH = 2.0 Hz, 1H, CHimid), 6.81 (m, 2H, CHimid), 6.41
(td, 3JHH = 4.6 Hz, 10.9 Hz, 1H, CH2CHN), 4.54 [vsep, 3JHH = 6.8 Hz,
1H, NCH(CH3)2], 4.26 (m, 3H, CHCOD, NCH2), 4.09–3.92 (m, 3H,
Compound 6f
Yield: 105 mg (64%). M.p.: 146–147 ◦C, 185 ◦C dec. MS (HRESI+):
calcd for C28H38IrN4, 621.26969;found, 621.27053. 1H NMR (CDCl3,
400 MHz): δ 7.71 (m, 2H, C6H5), 7.43 (m, 3H, C6H5), 7.14 (d,
CHCOD, NCH2), 3.84 (s, 3H, NCH3), 2.39–2.20 [m, 3H, CH2 COD
,
CHCH(CH3)2], 2.09 (m, 3H, CH2 COD), 1.87 (m, 3H, CH2 COD), 1.35
3
3
3
[d, JHH = 6.8 Hz, 3H, NCH(CH3)2], 1.17 [d, JHH = 6.5 Hz, 3H,
3JHH = 2.1 Hz, 1H, CHimid), 7.12 (d, JHH = 2.1 Hz, 1H, CHimid),
3
3
3
NCH(CH3)2], 1.10 [d, JHH = 6.8 Hz, 3H, CHCH(CH3)2], 0.98 [d,
7.07 (d, JHH = 2.0 Hz, 1H, CHimid), 6.92 (d, JHH = 2.1 Hz, 1H,
3JHH = 6.4 Hz, 3H, CHCH(CH3)2]. 13C{ H} NMR (CDCl3, 100 MHz): δ
CHimid), 6.65 (td, JHH = 4.0 Hz, 11.4 Hz 1H, CH2CHN), 4.48–4.29
1
3
175.47, 173.61 (IrC), 124.72, 121.67, 118.17, 117.49 (CHimid), 77.82,
74.63, 74.34, 73.34 (CHCOD), 64.29 (CH2CHN), 52.59 [NCH(CH3)2],
52.08 (NCH2CH), 39.12 (NCH3), 32.12 [CHCH(CH3)2], 32.09, 30.67,
30.39, 29.34 (CH2 COD), 23.58, 23.32 [NCH(CH3)2], 20.87, 19.82
[CH(CH3)2]. Anal. calcd for C23H36F6IrN4P (705.74), C, 39.14; H,
5.14; N, 7.94; found, C, 38.82; H, 5.03; N, 8.06.
(m, 2H, CHCH2N), 4.24 (m, 1H, CHCOD), 4.11–3.93 (m, 3H, NCH2CH2,
CHCOD), 2.80 (m, 1H, CHCOD), 2.41 [m, 1H, CHCH(CH3)2], 2.06–1.91
(m, 4H, CH2 COD), 1.78–1.67(m, 4H, CH2 COD), 1.45(m, 2HNCH2CH2),
1.20 [d, 3JHH = 6.5 Hz, 1H, CH(CH3)2], 0.98 [d, 3JHH = 6.4 Hz, 3H,
CH(CH3)2], 0.89 (t, JHH = 7.4 Hz, 3H, CH2CH3). 13C{ H} NMR
(CDCl3, 100 MHz): δ 175.11, 172.74 (IrC), 140.24 (NCPhenyl), 129.01
(2C, C6H5), 128.90 (1C, C6H5), 124.17 (2C, C6H5), 125.29, 121.83,
121.02, 118.11 (CHimid), 78.31, 75.06, 74.46, 72.59 (CHCOD), 64.37
(CH2CHN), 53.06 (NCH2CH2), 51.33 (NCH2CH), 39.31 (NCH2CH2),
32.02 [CHCH(CH3)2], 32.02, 30.66, 29.71, 29.18 (CH2 COD), 24.46
(NCH2CH2), 20.78, 20.00 [CH(CH3)2], 10.83 (CH2CH3). Anal. calcd
for C28H38F6IrN4P (767.81), C, 43.80; H, 4.99; N, 7.30; found, C, 44.08;
H, 4.60; N, 7.44.
3
1
Compound 6d
Diastereomerically pure (100% exo), crystalline material was
obtained by layering a THF–CH2Cl2 (10 : 1) solution of 6d with
cyclohexane. Yield: 143 mg (56%).M.p.: 169–171 ◦C (Zers.). MS
(HRESI+): calcd for C33H40IrN4, 683.28534; found, 683.28606.
1H NMR (CDCl3, 400 MHz): δ 7.31–7.16 (m, 6H, C6H5), 7.11 (d,
3JHH = 2.1 Hz, 1H, CHimid), 6.98 (m, 3H, CHimid, C6H5), 6.79 [s,
Compound 7
3
1H, NCH(C6H5)2], 6.63 (d, JHH = 1.9 Hz, 1H, CHimid), 6.58 (d,
3JHH = 2.1 Hz, 1H, CHimid), 6.50 (td, JHH = 4.9 Hz, 11.3 Hz, 1H,
Yield: 49 mg (38%). M.p.: 157–159 ◦C, 187 ◦C dec. MS (HRESI+):
calcd for C27H38IrN4, 609.26969;found, 609.26960. 1H NMR (CDCl3,
400 MHz): δ 7.46 (m, 1H, CHBenzimid.), 7.25–7.19 (m, 3H, CHBenzimid.),
3
CH2CHN),6.41(m,2H,C6H5)4.48,4.29(m,2H,CHCH2N),4.24(m,1H,
CHCOD), 4.37–4.20 (m, 4H, NCH2CH2, CHCOD), 3.99 (m, 2H, CHCOD),
2.98 (s, 3H, NCH3), 2.80 (m, 1H, CHCOD), 2.41 [m, 1H, CHCH(CH3)2],
2.06–1.91 (m, 4H, CH2 COD), 1.78–1.67 (m, 4H, CH2 COD), 1.19
3
7.09 (d, JHH = 2.0 Hz, 1H, CHimid), 6.79 (m, 1H, CH2CHN), 6.75
3
(d, JHH = 2.0 Hz, 1H, CHimid), 4.59 (m, 1H, CHCOD), 4.36 (m,
3
3
[d, JHH = 6.5 Hz, 1H, CH(CH3)2], 1.01 [d, JHH = 6.4 Hz, 3H,
2H, NCH2CH2), 4.26 (m, 2H, CHCOD), 4.09 (s, 3H, NCH3), 3.92
(m, 1H, CHCOD), 3.78 (td, JHH = 3.0 Hz, 7.3 Hz, 2H, NCH2CH),
2.57 [m, 1H, CHCH(CH3)2], 2.42–2.03 (m, 5H, CH2 COD), 1.94–1.85
CH(CH3)2]. 13C{ H} NMR (CDCl3, 100 MHz): δ 177.41, 171.64 (IrC),
1
138.18, 137.54 (CPhenyl, quart.), 128.17 (C6H5), 127.95 (C6H5), 127.66
(C6H5), 127.21 (C6H5), 125.59 (C6H5), 123.87, 120.61, 119.88, 117.11
(CHimid), 77.86, 73.83, 73.22, 73.01 (CHCOD), 65.73 [NCH(C6H5)2],
63.57 (CH2CHN), 51.60 (NCH2CH), 37.09 (NCH3), 31.48, 31.31, 29.41,
29.07 (CH2 COD), 28.19 [CHCH(CH3)2], 19.93, 18.84 [CH(CH3)2]. Anal.
calcd for C33H40F6IrN4P (829.88), C, 47.76; H, 4.86; N, 6.75; found,
C, 48.14; H, 4.73; N, 6.90.
3
(m, 3H, CH2 COD), 1.65 (sext, JHH = 7.3 Hz, 2H, NCH2CH2), 1.27
3
3
[d, JHH = 6.5 Hz, 3H, NCH(CH3)2], 1.02 [d, JHH = 6.4 Hz, 3H,
CHCH(CH3)2], 0.68 (t, JHH = 7.4 Hz, 3H, NCH2CH2CH3). 13C{ H}
NMR (CDCl3, 100 MHz): δ 184.33 (IrCBenzimid.), 174.54 (IrC), 135.84,
134.37 (Cquart.,Benzimid.), 123.96, 123.92 (CHBenzimid.), 121.94, 117.75
(CHimid), 110.70, 109.87 (CHBenzimid.), 78.44, 77.21, 76.38, 73.52
(CHCOD), 64.48 (CH2CHN), 51.49 (NCH2CH), 49.40 (NCH2CH2),
36.84 (NCH3), 32.66, 32.50 (CH2 COD), 30.13 [CHCH(CH3)2], 29.94,
29.15 (CH2 COD), 24.51 (NCH2CH2), 20.91, 20.25 [CH(CH3)2], 10.68
(NCH2CH2CH3). Anal. calcd for C27H38F6IrN4P (755.80), C, 42.91; H,
5.07; N, 7.41; found, C, 41.98; H, 4.90; N, 7.34.
3
1
Compound 6e
Yield: 122 mg (62%). M.p.: 151–152 ◦C, 200 ◦C dec. MS (HRESI+):
calcd for C25H40IrN4, 587.28534; found, 587.28581. 1H NMR
3
(CDCl3, 400 MHz): δ 7.06 (d, JHH = 2.1 Hz, 1H, CHimid), 6.96 (d,
3
3JHH = 2.0 Hz, 1H, CHimid), 6.82 (d, JHH = 2.2 Hz, 1H, CHimid),
General Prodedure for Transfer Hydrogenations
3
3
6.80 (d, JHH = 2.1 Hz, 1H, CHimid), 6.49 (td, JHH = 4.3 Hz,
3
11.5 Hz, 1H, CH2CHN), 5.12 [sep, JHH = 6.8 Hz, 1H, NCH(CH3)2],
A solution of the catalyst (0.002 mmol), KOH (0.02 mmol) and
the ketone (2.0 mmol) in 2-propanol (10 ml) was heated under
4.35–4.27 (m, 2H, NCH2CH, CHCOD), 4.15–4.08 (m, 2H, NCH2CH,
c
Appl. Organometal. Chem. 2010, 24, 509–516
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/aoc

C. Diez and U. Nagel
argon in a Schlenktube at 82 ◦C for 15 h. After cooling to
ambient temperature, water was added to the reaction mixture
and extracted with ether (2 × 10 ml). The organic phase was
dried over Mg2SO4 and filtered through celite. After removing
all volatiles under reduced pressure, the product alcohols
were obtained as oils. Turnovers and enantiomeric excesses
were determined by GC with chiral columns (see General
Remarks). Absolute configurations of the product alcohols
were determined by comparing the retention times of the
products with enantiomerically pure samples (1-phenylethanol,
1-phenylpropanol) or by comparing the sense of optical rotations
of the product samples with literature values.
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c
www.interscience.wiley.com/journal/aoc
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 509–516