Synthesis and evaluation of a broad range of new chiral phosphine-carbene ligands for asymmetric hydrogenation

Article abstract of DOI:10.1016/j.tetasy.2011.02.017

A straightforward and gram scale synthesis (six-step synthesis from enantioenriched β-hydroxy esters) of new structurally simple phosphine-carbene ligands bearing a single stereogenic centre has been achieved. Enantioselectivities of up to 60-63% could be achieved in the hydrogenation of methylstilbene and dehydroaminoacids when the reactions were performed under 20-50 bar hydrogen pressure.

Full text of DOI:10.1016/j.tetasy.2011.02.017

Tetrahedron: Asymmetry 22 (2011) 562–574
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis and evaluation of a broad range of new chiral
phosphine–carbene ligands for asymmetric hydrogenation
Johan Passays a, Tahar Ayad b, Virginie Ratovelomanana-Vidal b, Annie-Claude Gaumont c,
a,
Philippe Jubault a, , Eric Leclerc
⇑
⇑
a INSA de Rouen et Université de Rouen, UMR CNRS 6014 C.O.B.R.A & FR 3038, IRCOF, 1 rue Tesnière, 76821 Mont-Saint-Aignan cedex, France
b Laboratoire Charles Friedel, UMR CNRS 7223, Ecole Nationale Supérieure de Chimie de Paris, Chimie Paristech, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France
c Laboratoire de Chimie Moléculaire et Thioorganique, UMR CNRS 6507, INC3M, FR 3038, ENSICAEN & Université de Caen, 14050 Caen, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A straightforward and gram scale synthesis (six-step synthesis from enantioenriched b-hydroxy esters)
of new structurally simple phosphine–carbene ligands bearing a single stereogenic centre has been
achieved. Enantioselectivities of up to 60–63% could be achieved in the hydrogenation of methylstilbene
and dehydroaminoacids when the reactions were performed under 20–50 bar hydrogen pressure.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 2 February 2011
Accepted 15 February 2011
Available online 12 April 2011
1. Introduction
asymmetric hydrogenation and conjugate addition reactions (up
to 99% ee) has also been published by Helmchen et al.8a,b Finally,
N-Heterocyclic carbenes have recently generated growing inter-
est in organometallic chemistry.1 In particular, their use as ligands
has rapidly been explored since the first synthesis of an isolable
carbene species of this type by Arduengo et al. in 1991.2 A wide
range of very active catalysts have been synthesized, the most
prominent examples being the Grubbs olefin catalysts,3 as well
as several new catalysts for Pd-catalyzed coupling reactions.4 As
a logical extension of this development, chiral N-heterocyclic car-
bene ligands have also been successfully applied to asymmetric
catalysis.5 Initially, monodentate N-heterocyclic carbene ligands
were investigated because of their straightforward preparation
from simple chiral building blocks. Later on, chiral bidendate li-
gands, in which the N-heterocyclic carbene scaffold is linked to
other coordinating units, such as alkoxy,6 imino,7 phosphine,8
phosphinite8f or dihydrooxazole9 groups have been synthesized.
In some cases, successful applications of these ligands were re-
ported, especially in Rh- and Ir-catalyzed hydrogenation reactions,
in the Rh-catalyzed hydrosilylation of ketones and in conjugate
additions.
Pfaltz et al.8f have prepared chiral phosphine/N-heterocyclic car-
bene and phosphine oxide/N-heterocyclic carbene ligands which
have been used in iridium-catalyzed asymmetric hydrogenation
reactions.
Our group has recently reported the synthesis of chiral
a-
substituted b-amidophosphines,10 chiral
a
-substituted -amino-
c
phosphines and, for the latter, their application in asymmetric
hydrogenation.11 We have also reported the synthesis of a new chi-
ral bidentate phosphine–phosphinite ligand.12 In view of our previ-
ous results, we decided to investigate the synthesis and evaluate
the asymmetric catalysis of original chiral diphenylphosphine/N-
heterocyclic carbene ligands bearing in each case a stereogenic
center next to the phosphine moiety.
2. Results and discussions
Our main purpose was to develop a straightforward and scal-
able synthesis of structurally simple ligands featuring a stereogenic
center
a to the phosphine as the sole source of asymmetry. An effi-
In view of the great importance of phosphines as ligands in
homogeneous catalysis, it is surprising that only a few chiral struc-
tures of mixed donor ligands (incorporating a phosphine and N-
heterocyclic carbene moieties) have been reported. Bolm et al.8d,e
have described the synthesis and the application of iridium com-
plexes featuring new chiral phosphinyl-imidazoylidene ligands
based on a [2,2]-paracyclophane backbone. The use of rhodium
complexes derived from chiral diphenylphosphinocarbenes in
cient chiral induction thanks to these ligands would be valuable
since they can be easily prepared. We envisioned that the struc-
tures of type 1 might easily be obtained from chiral 1,3-diols by
two successive nucleophilic substitutions using, respectively, an
appropriate imidazole and the lithiated anion of diphenylphos-
phine (Scheme 1). Chiral b-hydroxyesters would be the obvious
precursors for the 1,3-diols and could be obtained in enantioen-
riched form thanks to asymmetric hydrogenation of the corre-
sponding b-ketoesters.
b-Hydroxyesters 2 featuring a methyl, ethyl, iso-propyl or phe-
nyl group were thus prepared using a Ru-SYNPHOS catalyzed
⇑
Corresponding authors.
E-mail address: philippe.jubault@insa-rouen.fr (P. Jubault).
0957-4166/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.02.017

J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
563
O
O
Ir-1 and Rh-1, thanks to athen in situ generation of the carbene func-
tion with potassium tert-butoxide (Scheme 3). A small library of
hydrogenation catalysts was thus prepared with variations on the
N-aryl substituent of the N-heterocyclic carbene moiety, the substi-
OH
*
OH
R
N
R
OEt
R
Ph2P
X
N
1
Ar
tuent on the stereogenic center
a to the diphenylphosphine group
and on the metal. These complexes were then tested in asymmetric
Scheme 1. Retrosynthetic analysis of the phosphine-imidazolium ligands.
hydrogenation reactions of typical substrates.
asymmetric hydrogenation of the corresponding b-ketoesters13
and submitted to a LAH reduction which provided the required
corresponding 1,3-diols 3 in good yields (Scheme 2).14 Selective
tosylation of the primary alcohol15 and substitution by N-mesity-
limidazole (Mes) or N-(2,6-di-iso-propylphenyl)imidazole (DiPP)
proceeded smoothly to afford the corresponding imidazolium salts
5. The counter-ion exchange from tosylate to BArFꢀ, initially
planned at a later stage of the synthesis, was performed prior to
the mesylation of the remaining alcohol function in order to avoid
the formation of a mixture of chloride and tosylate salts. The mesy-
lation reaction was efficient except in the case of the phenyl deriv-
ative 5d, for which chloride 6d was obtained instead of the desired
mesylate. This transformation proceeded with nearly complete
racemization and confirmed that SN1 reactions could take place
when using this substrate. Only the Me, Et and i-Pr derivatives
6a–c were thus further elaborated and submitted to the mesylate
substitution using alkali diphenylphosphide. The direct addition
of lithium16 or potassium17 diphenylphosphide was considered
first, but led to poorly reproducible yields of the desired compound
and to the production of phosphine oxide by-products. Conversely
the use of the lithiated anion of the diphenylphosphine–borane
complex was extremely efficient as the protected phosphine-imi-
dazolium compounds 7 were obtained in reproducible, moderate
to excellent yields (Scheme 2).
,BArF
R
Ph2P
R
N
76-93%
,BArF
N
N
Ar
PPh2
M
N
Ar
1
Ir-1 or Rh-1
Scheme 3. Synthesis of phosphine/N-heterocyclic carbene Ir(I) and Rh(I) catalysts.
Reagents and conditions: [M(COD)Cl]2 (0.5 equiv), t-BuOK (1.5 equiv), THF.
3. Ligand activity
Dimethyl itaconate 8 appeared to be a poor substrate for our
catalysts. If complete conversion was observed after 48 h under
38 bar of hydrogen pressure using iridium catalysts Ir-1b-DiPP
and Ir-1c-DiPP, the hydrogenation product was obtained in nearly
racemic form (Scheme 4). The use of a less deactivated olefin, such
as 10, did not improve the stereochemical outcome of the reaction
using the same type of catalysts (Scheme 4).
On the other hand, the use of methylstilbene gave encouraging
results (Table 1). If the different iridium catalysts were poorly
active at room temperature (entries 1 and 2), performing the
reaction at 50 °C under 40–50 bar of hydrogen pressure allowed
complete conversion in most cases with ee’s in the range of
31–63% (entries 3–9). Optimal results were obtained using the
ligand which features the most sterically demanding substituents
A standard deprotection of the phosphine moiety using DABCO18
afforded the phosphine-imidazolium compounds 1, which were
converted to the corresponding iridium and rhodium complexes
N
N
Ar
TsCl (1 equiv.)
R
*
OTs
R
*
OH
R
*
O
Et3N (1.1 equiv.)
R
LAH (1 equiv.)
2 equiv.
N
Et2O
81-98%
DMAP(1.5%mol)
CH2Cl2
HO
HO
HO
OEt
EtOH, rfx
54-94%
OH
5a-d
N
,TsO
3a-d
4a-d
66- 69%
Ar
2a (R = Me)
2b (R = Et)
2c (R = i-Pr)
2d (R = Ph)
1- NaBArF
2- MsCl (2 equiv.)
Et3N (2 equiv.)
CH2Cl2
51-89%
R
R
R
DABCO
PhCH3, 40°C
,BArF
Ph2PLi.BH3 (2 equiv.)
N
N
N
THF
63-90%
OMs
PPh2
PPh2
H3B
N
N
,BArF
,BArF
,BArF
N
6a-c
Ar
Ar
7a-c
Ar
1a-c
or
Ph
N
N
N
N
Cl
6d
PPh2
PPh2
PPh2
N
N
N
N
,BArF
,BArF
,BArF
Ar
Ar
Ar
Ar
1a-Mes (Ar = Mes)
1a-DiPP (Ar = DiPP)
1b-Mes (Ar = Mes)
1b-DiPP (Ar = DiPP)
1c-Mes (Ar = Mes)
1c-DiPP (Ar = DiPP)
iPr
CF3
DiPP =
Mes =
BArF =
H3B
iPr
CF3
4
Scheme 2. Synthesis of phosphine-imidazolium ligands from chiral b-hydroxyesters.

564
J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
Ir-1b-DiPP 3 mol%
or
Ir-1-DiPP 2 mol%
Ir-1c-DiPP 3 mol%
H
2 20 bars
MeO2C
H2 40 bars
MeO2C
CH2Cl2, rt, 24h
CH2Cl2, rt, 48h
MeO
CO2Me
CO2Me
MeO
11
8
9
10
61-100% conv.
< 10% ee
100% conv.
< 10% ee
Scheme 4. Ir-Catalyzed hydrogenation of methyl itaconate and 2-(4-methoxyphenyl)but-1-ene.
Table 1
Ir-Catalyzed hydrogenation of methylstilbene
Ph
Ph
Ir-1 2 mol%
H2 20-50 bars
Ph
Ph
CH2Cl2, 50°C, 24h
12
13
Entry
Cat.
T (°C)
P (bar)
Time (h)
Conv.a (%)
eeb (%) (config.)
1
2
3
4
5
6
7
8
9
Ir-1b-DiPP
Ir-1c-DiPP
Ir-1a-DiPP
Ir-1b-DiPP
Ir-1c-DiPP
Ir-1c-DiPP
Ir-1a-Mes
Ir-1b-Mes
Ir-1c-Mes
Ir-1c-Mes
Ir-1c-Mes
rt
rt
38
38
40
40
40
50
50
50
50
30
20
3
3
5
7
nd
nd
50
50
50
50
50
50
50
50
50
24
24
24
12
24
24
24
24
24
73
100
100
100
38
95
95
62
2
46 (S)
38 (R)
49 (R)
63 (R)
53 (S)
40 (R)
31 (R)
55 (R)
nd
10
11
a
Conversions were determined by 1H NMR.
Ee’s were determined by chiral HPLC on an OJ-H column.
b
(complex Ir-1c-DiPP, R = i-Pr and Ar = DiPP) at 50 bar of hydrogen
pressure (entry 6). Lowering the hydrogen pressure resulted in a sig-
nificant loss of enantioselectivity using the DiPP ligands (entry 5).
Results using the mesityl ligands were noteworthy since the enanti-
oselectivity decreased from R = Me to R = i-Pr (entries 7–9) and from
30 to 50 bar of hydrogen pressure (entries 9 and 10). However,
completion could only be reached at 50 bar since decreasing the
pressure to 20 bar resulted in a complete loss of catalytic activity.
Rhodium-catalyzed hydrogenation reactions of dehydroalanine
and dehydrophenylalanine derivatives were also tested (Table 2).
Catalysts derived from the DiPP ligands were totally inactive in
the hydrogenation of dehydrophenylalanine (entry 3) whereas a
61% ee for 47% conversion could be obtained using catalyst Rh-
1c-Mes (entry 2). Similar results were observed using dehydroala-
nine as the substrate since DiPP catalysts led to considerably lower
conversions than mesityl catalysts (entries 4–9 vs entries 10–15). A
60% ee could be reached with a conversion of 42% when using rho-
dium complex Rh-1c-DiPP under a 40 bar of hydrogen pressure
(entry 12). The results observed with the mesityl ligands were
much more encouraging in terms of conversion, but only led to
poor enantioselectivity. The best result was obtained using the
Rh-1c-Mes catalyst for which a 37% ee (90% conversion) could be
reached (entry 9). A substantial loss in enantioselectivity for all
the mesityl catalysts was again observed when the hydrogen pres-
sure was increased from 20 to 40 bar (entries 7–9 compared to en-
tries 4–6).
4. Conclusion
A straightforward and gram scale synthesis of new structurally
simple phosphine–carbene ligands bearing a single stereogenic
center has been achieved. A six-step synthesis from enantioen-
riched b-hydroxy esters provided protected phosphine-imidazoli-
um compounds, which can be readily complexed to iridium (I)
and rhodium (I) thanks to a simple deprotection/deprotonation
sequence. A small library of metal catalysts with variations on
the N-substituent of the carbene moiety and the substituent of
the stereogenic center was thus prepared and tested in various
asymmetric hydrogenation reactions. Despite moderate activities,
enantioselectivities of up to 60–63% could be achieved in the

J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
565
Table 2
electrospray source. Melting points were measured on a Kofler
apparatus and are uncorrected.
Rh-Catalyzed hydrogenation of dehydroaminoacids
CO2Me
CO2Me
NHAc
Rh-1 2 mol%
5.2. General procedure for the synthesis of 1,3-diols from b-
hydroxyesters
H2 20-40 bars
CH2Cl2, rt, 24h
R
NHAc
R
14 (R = Ph)
15 (R = H)
16 (R = Ph)
17 (R = H)
This method was adapted from the literature.14 To a suspension
of LiAlH4 (7.6 mmol, 1 equiv) in dry diethyl ether (6 mL) was added
a solution of b-hydroxyester (7.6 mmol, 1 equiv) in dry diethyl
ether (5 mL) at 0 °C. The mixture was stirred for 3 h at room tem-
perature and then quenched with distilled water (1 mL). After 10
mn, a 30% NaOH solution (1.5 mL) was added followed by 1 mL
of distilled water. The reaction mixture was passed through a Cel-
ite pad. The filtrate was dried over MgSO4, concentrated under vac-
uum and purified by column chromatography if necessary (silica
gel, cyclohexane/ethyl acetate 20/80) to afford the desired diol.
Entry Substrate Cat.
P (bar) Conv.a (%) eeb (%) (config.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
16
16
17
17
17
17
17
17
17
17
17
17
17
17
Rh-1a-Mes
Rh-1c-Mes
Rh-1a,b,c-DiPP 40
40
40
27
47
<5
95
100
100
50
57
90
14
8
50 (R)
61 (S)
nd
Rh-1a-Mes
Rh-1b-Mes
Rh-1c-Mes
Rh-1a-Mes
Rh-1b-Mes
Rh-1c-Mes
Rh-1a-DiPP
Rh-1b-DiPP
Rh-1c-DiPP
Rh-1a-DiPP
Rh-1b-DiPP
Rh-1c-DiPP
40
40
40
20
20
20
40
40
40
20
20
20
22 (R)
17 (S)
26 (S)
29 (R)
24 (S)
37 (S)
58 (R)
32 (S)
60 (S)
33 (R)
39 (S)
26 (S)
5.2.1. (R)-Butane-1,3-diol 3a
42
26
10
37
Yield: 81%. Colourless oil. Rf = 0.16 (80% AcOEt in cyclohexane).
½
a 2D0
ꢁ
¼ ꢀ30:7 (c 1.625, MeOH) (Lit.: ½a D20
ꢁ
¼ ꢀ31:0 (c 1.20, MeOH).19
1H NMR (300.3 MHz; CDCl3): d 4.66 (1H, br s, OH), 4.17 (1H, br s,
3
OH), 3.78–3.70 (m, 1H), 3.57–3.43 (2H, m), 1.45 (2H, dt, JH-H
=
Conversions were determined by 1H NMR.
Ee’s were determined by chiral HPLC on a ADH column 16 or a b-cyclodextrin
a
6.3 Hz), 0.99 (3H, d, JH-H = 6.2 Hz). 13C NMR (75.5 MHz; CDCl3): d
65.6, 59.4, 40.4, 23.1. IR (cmꢀ1): 3340, 2968, 1655, 1376, 1054,
664.
3
b
column 17.
5.2.2. (S)-Pentane-1,3-diol 3b
hydrogenation of methylstilbene and dehydroaminoacids when
the reactions were performed under a 20–50 bar hydrogen pres-
sure. If these ee’s do not compete with the highest standards for
such reactions, it is nonetheless remarkable that a single stereo-
Yield: 92%. Colourless oil. Rf = 0.3 (80% AcOEt in cyclohexane).
½
a 2D0
ꢁ
¼ þ14:1 (c 1.03, EtOH) (Lit.: ½a D20
ꢁ
¼ þ16:6 (c 1.04, EtOH).14b
1H NMR (300.3 MHz; CDCl3): d 3.93–3.75 (3H, m), 2.67 (1H, br s,
OH), 2.63 (1H, br s, OH), 1.82–1.59 (2H, m), 1.57–1.47 (2H, m),
3
0.94 (3H, t, JH-H = 7.5 Hz). 13C NMR (75.5 MHz; CDCl3): d 73.8,
genic center
a to the phosphine bearing a substituent not bulkier
62.0, 37.8, 30.7, 9.9. IR (cmꢀ1): 3351, 2936, 1462, 1058, 772.
than an i-Pr group might induce such enantioselectivities. Work
is currently in progress regarding the preparation and evaluation
of dialkylphosphine–carbenes, which would induce a tighter bind-
ing to the metal than their diphenylphosphine counterparts, and
phosphite-imidazolium ligands. Results in this area will be re-
ported in due course.
5.2.3. (R)-4-Methylpentane-1,3-diol 3c
Yield: 98%. Colourless oil. Rf = 0.4 (80% AcOEt in cyclohexane).
½
a 2D0
ꢁ
¼ þ30:4 (c 1.37, MeOH) (Lit.: ½a D20
ꢁ
¼ þ37:3 (c 1.07, MeOH).19
1H NMR (300.3 MHz; CDCl3): d 3.90–3.70 (2H, m), 3.61–3.55 (1H,
3
m), 3.01 (2H, br s, 2ꢂOH), 1.71–1.60 (3H, m), 0.91 (3H, d, JH-H
=
3
5. Experimental
5.1. General
5.5 Hz), 0.89 (3H, d, JH-H = 5.5 Hz). 13C NMR (75.5 MHz; CDCl3): d
77.0, 62.0, 34.9, 34.0, 18.4, 17.6. IR (cmꢀ1): 3349, 2960, 1653,
1471, 1053.
Experiments were carried out under an argon atmosphere. All
moisture-sensitive reagents were handled under argon atmo-
sphere. All commercial solvents were dried and distilled under a
nitrogen atmosphere before use: THF and Et2O were distilled from
sodium benzophenone ketyl, dichloromethane over CaH2, toluene
from sodium. TLC’s were performed on Merck 60F-250 silica gel
plates. Flash column chromatography purifications were carried
5.2.4. (R)-1-Phenylpropane-1,3-diol 3d
Yield: 90%. Colourless oil. Rf = 0.5 (80% AcOEt in cyclohexane).
½
a 2D0
ꢁ
¼ þ61:8 (c 1.00, CHCl3) (Lit.: ½a D20
ꢁ
¼ þ64 (c 1.0, CHCl3).20 1H
NMR (300.3 MHz; CDCl3): d 7.30–7.24 (5H, m), 4.91 (1H, dd, 3JH-H
=
3
8.5 Hz, JH-H = 4.0 Hz), 3.84–3.76 (2H, m), 3.13 (2H, br s, 2 ꢂ OH),
2.03–1.84 (2H, m). 13C NMR (75.5 MHz; CDCl3): d 144.4, 128.6,
127.7, 125.8, 74.3, 61.5, 40.5. IR (cmꢀ1): 3350, 2946, 1603, 1455,
1049.
out using silica gel (40–63 lm). Optical rotations were measured
on a PERKIN–ELMER 341 using a sodium lamp (k = 589 nm) at
room temperature and specific rotations are reported as follows:
5.3. General procedure for the monotosylation of the 1,3-diols
½
a 2D0
(c in cg/mL, solvent). NMR spectra were recorded on a
ꢁ
Bruker DPX 300 spectrometer operating at 300.13 MHz for proton,
75.47 MHz for carbon, 121.5 MHz for phosphorus and 282.40 MHz
for fluorine. This probe is equipped with pulsed-field (z) gradients.
Chemical shifts (d) are expressed in ppm relative to TMS for 1H and
13C nuclei, to H3PO4 for 31P nuclei and to CFCl3 for 19F nuclei. Data
are reported as follows: chemical shift, mulitiplicity (s = singlet,
d = doublet, t = triplet, q = quartet, br = broad, and m = multiplet).
J was used to indicate coupling constants in Hertz. IR spectra were
recorded on a Perkin–Elmer 1420. Absorption bands are reported
in cmꢀ1. Elemental analyses were carried out on a ThermoScientific
Flash 200 Elemental Analyzer. Mass spectra were performed on
a Thermo Finnigan MAX (ion trap) apparatus equipped with an
This method was adapted from the literature.15 To a flask con-
taining the 1,3-diol (25 mmol, 1 equiv) dissolved in dichlorometh-
ane (40 mL) at ꢀ15 °C under an argon atmosphere, were added
triethylamine (27.5 mmol, 1.1 equiv) and 4-(dimethylamino)pyri-
dine (0.375 mmol, 1.5 mol %). After 15 min, p-toluenesulfonyl chlo-
ride (25 mmol, 1 equiv) in dichloromethane (8 ml) was added
dropwise. The reaction mixture was kept below ꢀ15 °C for 12 h
and then allowed to warm to room temperature for 4 h. The reac-
tion mixture was cooled to 0 °C, 100 ml of dichloromethane were
added and the organic solution was washed with 1% HCl
(2 ꢂ 40 ml), saturated sodium bicarbonate (2 ꢂ 40 ml), brine
(2 ꢂ 40 ml), dried over magnesium sulfate and concentrated in

566
J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
vacuo to yield the crude product. Purification by column chroma-
tography (silica gel, cyclohexane/ethyl acetate 80/20) afforded
the desired monotosylated alcohol.
MeOD): d 143.4, 142.1, 141.5, 138.6, 135.7, 132.3, 130.5, 129.8,
126.8, 125.2, 124.6, 65.5, 48.5, 39.4, 23.9, 21.4, 21.2, 17.4. MS
(ESI+, m/z): 259.3 ([MꢀTsO]+). MS (ESI-, m/z): 171.2 ([TsO]ꢀ). IR
(cmꢀ1): 3436, 1610, 1355, 1278, 1125, 772. Elemental Anal. Calcd
for C23H30N2O4S: C, 64.16; H, 7.02; N, 6.51; S, 7.45. Found: C,
64.09; H, 6.96; N, 6.43; S, 7.50.
5.3.1. (R)-3-Hydroxybutyl 4-methylbenzenesulfonate 4a
Yield: 68%. Colourless oil. Rf = 0.65 (80% AcOEt in cyclohexane).
½
a 2D0
ꢁ
¼ ꢀ23:1 (c 2.41, EtOH) (Lit.: ½a D20
ꢁ
¼ ꢀ23:1 (c 2.32, EtOH).21 1
H
NMR (300.3 MHz; CDCl3): d 7.79 (2H, d, 3JH-H = 8.5 Hz), 7.34 (2H, d,
3JH-H = 7.9 Hz), 4.19–4.27 (1H, m), 4.07–4.14 (1H, m), 3.88–3.99
(1H, m), 2.44 (3H, s), 1.69 (1H, s, OH), 1.63–1.88 (2H, m), 1.18
5.4.2. (R)-3-(2,6-Diisopropylphenyl)-1-(3-hydroxybutyl)-1H-
imidazol-3-ium 4-methyl benzene sulfonate 5a-DiPP
Yield: 85%. White viscous oil. Rf = 0.4 (10% methanol in dichlo-
(3H, d, JH-H = 6.2 Hz). 13C NMR (75.5 MHz; CDCl3): d 145, 133,
romethane). ½a 2D0
ꢁ
¼ ꢀ5 (c 0.33, MeOH). 1H NMR (300 MHz; MeOD):
3
3
130, 128, 68, 64.2, 38, 23.7, 21.79 (CH3-Ts). MS (ESI+, m/z): 245.0
([M+H]+); 262.0 ([M+H2O]+); 488.8 ([2M+H]+). IR (cmꢀ1): 3376,
2971, 1598, 1355, 1176, 1097, 947, 817, 665, 555.
d 9.35 (1H, s), 7.93 (1H, s), 7.78 (1H, s), 7.66 (2H, d, JH-H = 8.3 Hz),
3
3
7.58 (1H, t, JH-H = 7.8 Hz), 7.40–7.35 (2H, m), 7.18 (2H, d, JH-H
=
3
7.9 Hz), 4.46 (2H, t, JH-H = 6.8 Hz), 3.77–3.70 (1H, m), 2.40–2.30
(2H, m), 2.32 (3H, s), 2.16–2.03 (1H, m), 2.00–1.88 (1H, m), 1.19
3
3
5.3.2. (S)-3-Hydroxypentyl 4-methylbenzenesulfonate 4b
Yield: 68%. Colourless oil. Rf = 0.8 (80% AcOEt in cyclohexane).
(3H, d, JH-H = 6.2 Hz), 1.19 (12H, d, JH-H = 6.8 Hz). 13C NMR
(75.5 MHz; CDCl3): d 146.8, 143.4, 141.6, 139.2, 132.9, 131.9,
129.8, 126.9, 126.6, 125.6, 124.7, 65.6, 48.7, 39.4, 29.8, 24.4, 23.8
(C9), 21.3 (CH3-Ts). MS (ESI+, m/z): 301.4 ([MꢀTsO]+). MS (ESI-, m/
z): 171.2 ([TsO]ꢀ). IR (cmꢀ1): 3430, 2967, 1461, 1189, 1124,
1035, 1012, 815, 758, 684. Elemental Anal. Calcd for C26H36N2O4S:
C, 66.07; H, 7.68; N, 5.93; S, 6.78. Found: C, 66.27; H, 7.64; N, 5.98;
S, 6.74.
½
a 2D0
ꢁ
¼ ꢀ21:4 (c 2.03, EtOH). 1H NMR (300.3 MHz; CDCl3): d 7.80
3
3
(2H, d, JH-H = 8.3 Hz), 7.35 (2H, d, JH-H = 7.9 Hz), 6.1 (1H, s, OH),
4.30–4.22 (1H, m), 4.16–4.08 (1H, m), 3.70–3.62 (1H, m), 2.45
(3H, s), 1.92–1.81 (1H, m), 1.70–1.61 (1H, m), 1.50–1.40 (2H, m),
0.92 (3H, t, JH-H = 7.4 Hz). 13C NMR (75.5 MHz; CDCl3): d 145,
3
133, 130, 127.9, 69.3, 68, 35.6, 30.1, 21.6, 9.8. IR (cmꢀ1): 3412,
2965, 1556, 1176, 1097, 963, 816, 665, 555.
5.4.3. (S)-1-(3-Hydroxypentyl)-3-mesityl-1H-imidazol-3-ium 4-
methylbenzenesulfonate 5b-Mes
5.3.3. (R)-3-Hydroxy-4-methylpentyl 4-methyl-
benzenesulfonate 4c
Yield: 69%. White viscous oil. Rf = 0.5 (10% methanol in dichlo-
Yield: 69%. Colourless oil. Rf = 0.65 (50% AcOEt in cyclohexane).
romethane).
½
a 2D0
ꢁ
¼ þ8:2 (c 1.0, MeOH). 1H NMR (300 MHz;
½
a 2D0
ꢁ
¼ þ24:4 (c 2.295, EtOH). 1H NMR (300.3 MHz; CDCl3): d 7.78
MeOD): d 9.19 (1H, s), 7.92 (1H, m), 7.70 (2H, d, JH-H = 8.1 Hz),
3
3
3
3
(2H, d, JH-H = 8.1 Hz), 7.34 (2H, d, JH-H = 7.9 Hz), 4.29–4.21 (1H,
m), 4.17–4.10 (1H, m), 3.51–3.45 (1H, m), 2.44 (3H, s), 1.90–1.79
(1H, m), 1.70–1.55 (3H, m, H4, OH), 0.88 (3H, s), 0.86 (3H, s). 13C
NMR (75.5 MHz; CDCl3): d 145, 133, 130, 128, 72.6, 68.4, 33.8,
33.2, 21.8, 18.6, 17.3. IR (cmꢀ1): 3418, 2961, 2359, 1355, 1176,
1097, 1042, 816, 665.
7.69 (1H, m), 7.23 (2H, d, JH-H = 7.9 Hz), 7.12 (2H, s), 4.48 (2H, t,
3JH-H = 7.0 Hz), 3.50–3.42 (1H, m), 2.37 (6H, s), 2.21–1.85 (2H, m),
2.07 (6H, s), 1.50–1.57 (2H, m), 0.95 (3H, t, JH-H = 7.4 Hz). 13C
3
NMR (75.5 MHz; MeOD): d 143.4, 142.5, 141.7, 138.8, 135.8,
132.5, 130.7, 129.8, 126.9, 125.5, 124.6, 71.0, 48.5, 37.4, 31.5,
21.3, 21.1, 17.3, 10.2. MS (ESI+, m/z): 273.3 ([MꢀTsO]+). MS (ESI-,
m/z): 171.3([TsO]ꢀ). IR (cmꢀ1): 3418, 2925, 1455, 1207, 1124,
1035, 1011, 771, 684, 567. Elemental Anal. Calcd for C24H32N2O4S:
C, 64.84; H, 7.25; N, 6.30; S, 7.21. Found: C, 64.82; H, 7.16; N, 6.46;
S, 7.39.
5.3.4. (R)-3-Hydroxy-3-phenylpropyl 4-methyl-
benzenesulfonate 4d
Yield: 66%. Colourless oil. Rf = 0.80 (80% AcOEt in cyclohexane).
½
a 2D0
ꢁ
¼ þ20:7 (c 1.0, CHCl3). 1H NMR (300.3 MHz; CDCl3): d 7.80
3
3
(2H, d, JH-H = 8.3 Hz), 7.35 (2H, d, JH-H = 7.9 Hz), 7.32–7.26 (5H,
5.4.4. (S)-3-(2,6-Diisopropylphenyl)-1-(3-hydroxypentyl)-1H-
imidazol-3-ium 4-methyl benzene sulfonate 5b-DiPP
Yield: 94%. Green viscous oil. Rf = 0.3 (10% methanol in dichloro-
3
m), 4.80 (1H, t, JH-H = 6.7 Hz), 4.32–4.25 (1H, m), 4.09–4.02 (1H,
m), 2.46 (3H, s), 2.2 (1H, s, OH), 2.06–2.00 (2H, m). 13C NMR
(75.5 MHz; CDCl3): d 145, 143.6, 133, 130, 128.7, 128.0, 125.7,
70.3, 67.7, 38.1, 21.8. MS (ESI+, m/z): 324.2([M+H2O]+). IR (cmꢀ1):
3414, 1598, 1356, 1174, 1097, 968, 924, 816, 765, 702, 665, 555.
methane). ½a 2D0
ꢁ
¼ þ3:6 (c 0.072, EtOH). 1H NMR (300 MHz; MeOD):
3
d 9.35 (1H, m), 7.93 (1H, m), 7.79 (1H, m), 7.66 (2H, d, JH-H
=
3
4
8.1 Hz), 7.57 (1H, t, JH-H = 7.8 Hz), 7.40 (2H, d, JH-H = 7.7 Hz),
3
3
7.18 (2H, d, JH-H = 7.9 Hz), 4.47 (2H, t, JH-H = 6.9 Hz), 3.45–3.40
5.4. General procedure for the introduction of the imidazole
moiety
(1H, m), 2.40–2.20 (2H, m), 2.33 (3H, s), 2.17–2.06 (1H, m), 1.97–
3
1.85 (1H, m), 1.43–1.53 (2H, m), 1.16 (12H, d, JH-H = 6.8 Hz), 0.92
3
(3H, t, JH-H = 7.4 Hz). 13C NMR (75.5 MHz; MeOD): d 146.8, 143.5,
A solution of the tosylate (8 mmol, 1 equiv) and the required
imidazole (16 mmol, 2 equiv) in absolute ethanol (20 mL) was re-
fluxed overnight. After cooling to room temperature, the solvent
was removed under vacuum. The crude product was purified by
column chromatography (silica gel, CH2Cl2/methanol) to eliminate
the excess of imidazole and to afford the pure imidazolium tosylate
salt.
141.7, 139.2, 132.9, 131.9, 129.8, 126.9, 126.6, 125.7, 124.8, 70.9,
48.7, 37.5, 31.4, 29.8, 24.4, 21.3, 10.3. MS (ESI+, m/z): 315.3
([MꢀTsO]+). MS (ESI-, m/z): 171.3 ([TsO]ꢀ). IR (cmꢀ1): 3401,
2965, 1462, 1210, 1122, 1034, 1012, 814, 682, 568. Elemental Anal.
Calcd for C27H38N2O4S: C, 66.63; H, 7.87; N, 5.76; S, 6.59. Found: C,
66.67; H, 7.59; N, 5.58; S, 6.52.
5.4.5. (R)-1-(3-Hydroxy-4-methylpentyl)-3-mesityl-1H-
imidazol-3-ium 4-methylbenzene sulfonate 5c-Mes
Yield: 54%. White viscous oil. Rf = 0.5 (10% methanol in dichlo-
5.4.1. (R)-1-(3-Hydroxybutyl)-3-mesityl-1H-imidazol-3-ium 4-
methylbenzenesulfonate 5a-Mes
Yield: 63%. White viscous oil. Rf = 0.15 (10% methanol in dichlo-
romethane). ½a 2D0
ꢁ
¼ þ9:4 (c 1.01, MeOH). 1H NMR (300 MHz;
romethane).
½
a 2D0
ꢁ
¼ ꢀ6:0 (c 1.0, MeOH). 1H NMR (300 MHz;
CDCl3): d 9.69 (1H, s), 7.76 (1H, s), 7.62 (2H, d, JH-H = 7.9 Hz),
3
3
3
MeOD): d 7.63 (1H, s), 7.90 (1H, s), 7.65 (2H, d, JH-H = 8.1 Hz),
7.08 (1H, s), 7.04 (2H, d, JH-H = 7.9 Hz), 6.96 (2H, s), 4.81–4.73
3
7.59 (1H, s), 7.16 (2H, d, JH-H = 8.1 Hz), 7.05 (2H, s), 4.45 (2H, t,
(1H, m), 4.69–4.60 (1H, m), 3.34–3.40 (1H, m), 2.33 (3H, s), 2.30
(3H, s), 2.05–1.90 (2H, m), 2.01 (3H, s), 2.00 (3H, s), 1.65–1.55
3JH-H = 6.9 Hz), 3.71–3.77 (1H, m), 2.31 (6H, s), 2.01 (6H, s), 2.14–
3
3
3
1.87 (2H, m), 1.18 (3H, d, JH-H = 6.2 Hz). 13C NMR (75.5 MHz;
(1H, m), 0.86 (3H, d, JH-H = 7.0 Hz), 0.83 (3H, d, JH-H = 7.0 Hz).

J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
567
13C NMR (75.5 MHz; CDCl3): d 143.2, 141.2, 139.4, 138.7, 134.6,
134.4, 130.9, 129.9, 129.8, 128.6, 126.0, 123.2, 123.1, 73.3, 48.7,
34.6, 34.3, 21.42, 21.24, 18.76, 18.06, 17.51. MS (ESI+, m/z): 287.3
([MꢀTsO]+). MS (ESI-, m/z): 171.3 ([TsO]ꢀ). IR (cmꢀ1): 3418,
3136, 2960, 1548, 1462, 1207, 1124, 1035, 1012, 816, 754, 684,
568. Elemental Anal. Calcd for C25H34N2O4S: C, 65.47; H, 7.47; N,
6.11; S, 6.99. Found: C, 65.60; H, 7.09; N, 6.67; S, 7.11.
overnight. The organic layer was decanted and washed succes-
sively with distilled water (20 mL) and brine (20 mL), and dried
over magnesium sulfate. The solvent was then removed under vac-
uum to give the imidazolium/BArFꢀ salt.
5.6. General procedure for mesylation of the imidazolium salt
To a solution of the imidazolium salt (2.5 mmol, 1 equiv) in
dichloromethane (10 mL) at 0 °C, were added triethylamine
(5 mmol, 2 equiv) and methanesulfonyl chloride (5 mmol, 2 equiv).
The reaction mixture was stirred 24 h at room temperature. The
solvent was then removed under vacuum and the crude product
was suspended in water (10 mL) and stirred overnight. Dichloro-
methane (10 mL) was then added and the organic layer was
washed with water (2 ꢂ 10 ml), dried over magnesium sulfate
and concentrated in vacuo to yield the crude product, which was
purified by column chromatography (silica gel, CH2Cl2/methanol).
5.4.6. (R)-3-(2,6-Diisopropylphenyl)-1-(3-hydroxy-4-
methylpentyl)-1H-imidazol-3-ium 4-methylbenzenesulfonate
5c-DiPP
Yield: 89%. Green viscous oil. Rf = 0.3 (10% methanol in dichloro-
methane). ½a 2D0
ꢁ
¼ þ5:1 (c 2.0, EtOH). 1H NMR (300 MHz; MeOD): d
9.34 (1H, s), 7.93 (1H, m), 7.80 (1H, m), 7.66 (2H, d, 3JH-H = 8.1 Hz),
3
3
7.58 (1H, t, JH-H = 7.8 Hz), 7.39 (2H, d, JH-H = 7.7 Hz), 7.18 (2H, d,
3JH-H = 7.9 Hz), 4.47 (2H, t, JH-H = 6.8 Hz), 3.23–3.16 (1H, m),
3
2.37–2.25 (2H, m), 2.33 (3H, s), 2.17–2.06 (1H, m), 1.96–1.84
3
(1H, m), 1.69–1.58 (1H, m), 1.16 (12H, d, JH-H = 6.8 Hz), 0.90 (3H,
3
3
d, JH-H = 6.8 Hz), 0.88 (3H, d, JH-H = 6.8 Hz). 13C NMR (75.5 MHz;
MeOD): d 146.8, 143.4, 141.7, 139.2, 132.9, 131.9, 129.8, 126.9,
126.6, 125.7, 124.8, 74.2, 49.0, 35.2, 35.0, 29.8, 24.4, 21.3, 18.9,
18.1. MS (ESI+, m/z): 329.3 ([MꢀTsO]+). MS (ESI-, m/z): 171.2
([TsO]ꢀ). IR (cmꢀ1): 3414, 2964, 1460, 1193, 1123, 1034, 1011,
815, 771, 683. Elemental Anal. Calcd for C28H40N2O4S: C, 67.17;
H, 8.05; N, 5.59; S, 6.40. Found: C, 66.96; H, 7.94; N, 5.33; S, 6.61.
5.6.1. (R)-3-Mesityl-1-(3-(methylsulfonyloxy)butyl)-1H-
imidazol-3-ium tetrakis(3,5-bis (trifluoromethyl)phenyl)borate
6a-Mes
Yield: 71%. White solid. Rf = 0.7 (5% methanol in dichlorometh-
ane). ½a 2D0
ꢁ
¼ ꢀ5:0 (c 1.04, CHCl3). 1H NMR (300 MHz; CDCl3): d 8.54
(1H, s), 7.85 (8H, br s), 7.66 (br s, 4H), 7.42 (1H, s), 7.28 (1H, s), 7.09
(2H, s), 4.74–4.64 (1H, m), 4.62–4.52 (1H, m), 4.39–4.32 (1H, m),
3.05 (3H, s), 2.38 (3H, s), 2.27–2.18 (2H, m), 2.06 (3H, s), 1.99
3
5.4.7. (R)-1-(3-Hydroxy-3-phenylpropyl)-3-mesityl-1H-
imidazol-3-ium 4-methylbenzene sulfonate 5d-Mes
Yield: 64%. White viscous oil. Rf = 0.1 (2% methanol in ethyl ace-
(3H, s), 1.43 (3H, d, JH-H = 6.2 Hz). 19F NMR (282.4 MHz; CDCl3):
d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d 161.9 (q, JC-B = 49.8 Hz),
1
2
142.2, 136.6, 135.0, 134.1, 133.8, 130.3, 129.9, 129.2 (qq, JC-F
=
tate). ½a 2D0
ꢁ
¼ þ9:8 (c 1.0, MeOH). 1H NMR (300 MHz; MeOD): d 9.21
31.3 Hz, JC-B = 2.7 Hz), 125.3, 124.8 (q, JC-F = 272.9 Hz), 122.0,
117.7, 73.9, 46.6, 38.6, 36.0, 20.9, 20.7, 16.8. MS (ESI+, m/z):
337.2 ([MꢀBArF]+). MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1):
3159, 1611, 1356, 1278, 1137, 889, 716, 682, 670. Elemental Anal.
Calcd for C49H37BF24N2O3S: C, 49.02; H, 3.11; N, 2.33; S, 2.67.
Found: C, 49.05; H, 3.09; N, 2.66; S, 2.60. Mp = 92 °C.
1
1
3
3
(1H, s), 7.92 (1H, d, JH-H = 1.7 Hz), 7.70 (2H, d, JH-H = 8.1 Hz), 7.67
3
3
(1H, d, JH-H = 1.9 Hz), 7.39–7.25 (5H, m), 7.22 (2H, d, JH-H
=
3
3
7.9 Hz), 7.11 (2H, s), 4.70 (1H, dd, JH-H = 8.1 Hz, JH-H = 4.7 Hz),
4.51 (2H, t, JH-H = 6.7 Hz), 2.36 (6H, s), 2.36–2.28 (2H, m), 2.07
3
(6H, s). 13C NMR (75.5 MHz; MeOD): d 145.6, 143.4, 142.5, 141.8,
138.9, 135.9, 132.6, 130.7, 129.8, 129.6, 128.6, 127.0, 126.8,
125.4, 124.7, 72.1, 48.7, 39.9, 21.4, 21.2, 17.4. MS (ESI+, m/z):
321.5 ([MꢀTsO]+). MS (ESI-, m/z): 171.4 ([TsO]ꢀ). IR (cmꢀ1):
3390, 1455, 1205, 1123, 1034, 1012, 682, 567. Elemental Anal.
Calcd for C28H32N2O4S: C, 68.27; H, 6.55; N, 5.69; S, 6.51. Found:
C, 68.50; H, 6.66; N, 5.76; S, 6.59.
5.6.2. (R)-3-(2,6-Diisopropylphenyl)-1-(3-
(methylsulfonyloxy)butyl)-1H-imidazol-3-ium tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate (6a-DiPP)
Yield: 69%. Yellow solid. Rf = 0.8 (10% methanol in dichloro-
methane). ½a 2D0
ꢁ
¼ ꢀ0:3 (c 1.02, acetone). 1H NMR (300 MHz;
3
CDCl3): d 8.49 (1H, s), 7.69 (8H, br s), 7.59 (1H, t, JH-H = 7.9 Hz),
7.53 (br s, 4H), 7.35–7.23 (4H, m), 4.61–4.53 (1H, m), 4.51–4.42
(1H, m), 4.33–4.20 (1H, m), 3.03 (3H, s), 2.21–2.04 (4H, m, H7),
5.4.8. (R)-3-(2,6-Diisopropylphenyl)-1-(3-hydroxy-3-
phenylpropyl)-1H-imidazol-3-ium 4-methylbenzenesulfonate
5d-DiPP
3
3
1.36 (3H, d, JH-H = 7.3 Hz), 1.18 (3H, d, JH-H = 6.8 Hz), 1.17 (3H, d,
3
3
Yield: 58%. White viscous oil. Rf = 0.4 (10% ethyl acetate in cyclo-
3JH-H = 6.8 Hz), 1.13 (3H, d, JH-H = 6.8 Hz), 1.12 (3H, d, JH-H
=
hexane). ½a 2D0
ꢁ
¼ þ3:7 (c 0.99, MeOH). 1H NMR (300 MHz; MeOD): d
6.4 Hz). 19F NMR (282.4 MHz; CDCl3):
d
ꢀ62.3. 13C NMR
3
1
9.40 (1H, s), 7.94 (1H, s), 7.74 (1H, s), 7.68 (2H, d, JH-H = 8.1 Hz),
(75.5 MHz; CDCl3):
136.9, 134.9, 132.9, 128.8 (qq, JC-F = 31.3 Hz, JC-B = 2.7 Hz),
128.3, 126.2, 125.2, 123.8, 124.6 (q, JC-F = 272.9 Hz), 122.0, 117.7,
d
161.8 (q, JC-B = 49.8 Hz), 145.3, 145.1,
3
3
2
1
7.58 (1H, t, JH-H = 7.8 Hz), 7.38–7.19 (7H, m), 7.16 (2H, d, JH-H
=
3
3
1
7.9 Hz), 4.69 (1H, dd, JH-H = 7.9 Hz, JH-H = 4.5 Hz), 4.52 (2H, t,
3JH-H = 6.6 Hz), 2.37–2.26 (4H, m), 2.31 (3H, s), 1.16 (6H, d,
73.3, 46.7, 38.8, 35.9, 29.0, 28.9, 24.2, 24.2, 24.1, 24.0, 21.0. MS
(ESI+, m/z): 379.3 ([MꢀBArF]+). MS (ESI-, m/z): 863.4 ([BArF]ꢀ). IR
(cmꢀ1): 3428, 2973, 1611, 1355, 1278, 1125, 888, 839, 756,
713 682. Elemental Anal. Calcd for: C, 49.02; H, 3.11; N, 2.33; S,
2.67. Found: C, 49.19; H, 3.23; N, 2.34; S, 2.57. Mp = 95 °C.
3JH-H = 6.8 Hz), 1.15 (6H, d, JH-H = 6.8 Hz). 13C NMR (75.5 MHz;
3
MeOD): d 146.7, 145.5, 143.4, 141.5, 139.1, 132.8, 131.8, 129.7,
129.4, 128.4, 126.8, 126.6, 126.4, 125.5, 124.3, 71.9, 48.7, 39.9,
29.6, 24.3, 21.3. MS (ESI+, m/z): 363.4 ([MꢀTsO]+). MS (ESI-, m/z):
171.3 ([TsO]ꢀ). IR (cmꢀ1): 3392, 2968, 1459, 1279, 1222, 1178,
1125, 1012, 815, 683, 571. Elemental Anal. Calcd for C31H38N2O4S:
C, 69.63; H, 7.16; N, 5.24; S, 6.00. Found: C, 69.85; H, 7.36; N, 5.38;
S, 6.09.
5.6.3. (S)-3-Mesityl-1-(3-(methylsulfonyloxy)pentyl)-1H-
imidazol-3-ium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate
6b-Mes
Yield: 65%. White solid. Rf = 0.75 (10% methanol in dichloro-
5.5. General procedure for the counter-ion exchange from the
tosylate salt to the BArFꢀ salt
methane). ½a 2D0
ꢁ
¼ þ3:8 (c 1.005, CHCl3). 1H NMR (300 MHz; CDCl3):
d 8.48 (1H, s), 7.74 (8H, br s), 7.56 (br s, 4H), 7.34 (1H, s), 7.21 (1H,
s), 7.03 (2H, m), 4.51–4.61 (1H, m), 4.83–4.40 (1H, m), 4.32–4.25
(1H, m), 3.04 (3H, s), 2.34 (3H, s), 2.22–2.16 (2H, m), 1.99 (3H, s),
The imidazolium tosylate salt (2 mmol, 1 equiv) and NaBArF
(2 mmol, 1 equiv), were dissolved in dichloromethane and distilled
water (20 mL, solution 1:1) and the biphasic mixture was stirred
1.94 (3H, s), 1.78–1.62 (1H, m), 0.90 (3H, t, JH-H = 7.4 Hz). 19F
3
NMR (282.4 MHz; CDCl3): d ꢀ62.3 ppm. 13C NMR (75.5 MHz;

568
J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
CDCl3): d 161.8 (q, 1JC-B = 49.8 Hz), 142.7, 136.6, 134.9, 134.1, 133.8,
Elemental Anal. Calcd for C54H47BF24N2O3S: C, 51.04; H, 3.73; N,
2.20; S, 2.52. Found: C, 51.02; H, 3.66; N, 2.32; S, 2.58. Mp = 90 °C.
2
1
130.3, 129.8, 129.1 (qq, JC-F = 31.8 Hz, JC-B = 2.7 Hz), 125.2, 124.7
1
(q, JC-F = 272.5 Hz), 121.8, 117.7, 68.3, 46.5, 38.5, 33.8, 27.9, 21.0,
16.9, 9.7. MS (ESI+, m/z): 351.1 ([MꢀBArF]+). MS (ESI-, m/z):
863.3 ([BArF]ꢀ). IR (cmꢀ1): 3160, 2979, 1611, 1357, 1278, 1137,
889, 682, 670. Elemental Anal. Calcd for C50H39BF24N2O3S: C,
49.44; H, 3.24; N, 2.31; S, 2.64. Found: C, 49.40; H, 3.19; N, 2.04;
S, 2.59. Mp = 106 °C.
5.6.7. 1-(3-Chloro-3-phenylpropyl)-3-mesityl-1H-imidazol-3-
ium tetrakis(3,5-bis(trifluoro methyl)phenyl)borate 6d-Mes
Yield: 52%. Yellowish viscous oil. Rf = 0.6 (5% methanol in
dichloromethane). 1H NMR (300 MHz; CDCl3): d 8.18 (1H, s), 7.73
(8H, br s), 7.53 (br s, 4H), 7.38 (1H, s), 7.38–7.29 (5H, m), 7.23
3
3
(1H, s), 7.03 (2H, s), 4.76 (1H, dd, JH-H = 9.4 Hz, JH-H = 4.3 Hz),
4.51–4.45 (2H, m), 2.75–2.54 (2H, m), 2.33 (3H, s), 1.93 (6H, s).
19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3):
d 161.8 (q, 1JC-B = 50.0 Hz), 143.0, 138.5, 134.9, 134.9, 133.6, 130.4,
5.6.4. (S)-3-(2,6-Diisopropylphenyl)-1-(3-
(methylsulfonyloxy)pentyl)-1H-imidazol-3-ium tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate 6b-DiPP
2
1
129.7, 129.6, 129.4, 129.0 (qq, JC-F = 31.3 Hz, JC-B = 2.7 Hz), 126.5,
125.3, 124.7 (q, 1JC-F = 272.7 Hz), 122.9, 117.7, 59.4, 48.5, 39.2, 21.0,
16.9. MS (ESI+, m/z): 339.3 ([MꢀBArF]+). MS (ESI-, m/z): 863.3
([BArF]ꢀ). IR (cmꢀ1): 3152, 2931, 1612, 1356, 1280, 1120, 895,
839, 711, 671. Elemental Anal. Calcd for C53H36BClF24N2: C,
52.91; H, 3.02; N, 2.33. Found: C, 52.97; H, 3.01; N, 2.32.
Mp = 135 °C.
Yield: 51%. Brown viscous oil. Rf = 0.7 (10% methanol in dichlo-
romethane). ½a 2D0
ꢁ
¼ ꢀ0:6 (c 1.065, acetone). 1H NMR (300 MHz;
3
CDCl3): d 8.52 (1H, s), 7.72 (8H, br s), 7.58 (1H, t, JH-H = 7.9 Hz),
7.55 (br s, 4H), 7.36–7.26 (4H, m), 4.62–4.52 (1H, m), 4.46–4.38
(1H, m), 4.32–4.24 (1H, m), 3.05 (3H, s), 2.25–2.11 (4H, m), 1.78–
3
3
1.64 (2H, m), 1.18 (3H, d, JH-H = 7.0 Hz), 1.13 (3H, d, JH-H
=
6.8 Hz), 1.12 (6H, d, JH-H = 6.8 Hz), 0.91 (3H, t, JH-H = 7.3 Hz). 19F
3
3
NMR (282.4 MHz; CDCl3): d ꢀ62.3 ppm. 13C NMR (75.5 MHz;
1
5.6.8. 1-(3-Chloro-3-phenylpropyl)-3-(2,6-diisopropylphenyl)-
1H-imidazol-3-ium tetrakis(3,5-bis(trifluoromethyl)-
phenyl)borate 6d-DiPP
CDCl3): d 161.8 (q, JC-B = 49.8 Hz), 145.3, 145.0, 136.9, 134.9,
2
1
132.9, 129.0 (qq, JC-F = 31.3 Hz, JC-B = 2.7 Hz), 129.2, 126.2,
125.3, 125.2, 124.7 (q, JC-F = 272.7 Hz), 121.9, 117.7, 78.1, 46.6,
1
Yield: 89%. Yellow viscous oil. Rf = 0.7 (5% methanol in dichloro-
38.5, 33.9, 29.0, 28.9, 28.0, 24.1, 24.1, 24.0, 24.0, 9.2. MS (ESI+, m/
z): 393.2 ([MꢀBArF]+). MS (ESI-, m/z): 863.4 ([BArF]ꢀ). IR (cmꢀ1):
2930, 1434, 1355, 1277, 1124, 887, 839, 772, 713, 682. Elemental
Anal. Calcd for C53H45BF24N2O3S: C, 50.65; H, 3.61; N, 2.23; S,
2.55. Found: C, 50.47; H, 3.58; N, 2.19; S, 2.34.
methane). 1H NMR (300 MHz; CDCl3): d 8.30 (1H, s), 7.74 (8H, br s),
3
7.59 (1H, t, JH-H = 7.9 Hz), 7.55 (br s, 4H), 7.43 (1H, s), 7.39–7.30
3
3
(8H, m), 4.75 (1H, dd, JH-H = 4.1 Hz, JH-H = 9.8 Hz), 4.62–4.45
(2H, m), 2.77–2.56 (2H, m), 2.24–2.09 (2H, m), 1.18–1.12 (12H,
m). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz;
1
CDCl3): d 161.8 (q, JC-B = 50.0 Hz), 145.1, 145.0, 138.5, 135.5,
5.6.5. (R)-3-Mesityl-1-(4-methyl-3-(methylsulfonyloxy)pentyl)-
1H-imidazol-3-ium tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate 6c-Mes
2
1
134.9, 133.1, 129.7, 129.4, 129.0 (qq, JC-F = 31.3 Hz, JC-B
=
=
1
2.7 Hz), 129.0, 126.5, 126.3, 125.3, 125.2, 124.7 (q, JC-F
272.7 Hz), 122.7, 117.7, 59.6, 48.6, 39.0, 29.1, 29.0, 24.1, 24.0,
23.9, 23.9. MS (ESI+, m/z): 381.3 ([MꢀBArF]+). MS (ESI-, m/z):
863.4 ([BArF]ꢀ). IR (cmꢀ1): 2973, 1610, 1355, 1278, 1125, 887,
839, 758, 713, 670. Elemental Anal. Calcd for C56H42BClF24N2: C,
54.02; H, 3.40; N, 2.25. Found: C, 54.10; H, 3.32; N, 2.01.
Yield: 67%. White solid. Rf = 0.7 (10% methanol in dichlorometh-
ane). ½a 2D0
ꢁ
¼ þ5:1 (c 1.08, CHCl3). 1H NMR (300 MHz; CDCl3): d 8.51
(1H, s), 7.76 (8H, br s), 7.57 (br s, 4H), 7.39 (1H, s), 7.34 (1H, s), 7.05
(2H, s), 4.66–4.56 (1H, m), 4.38–4.30 (2H, m), 3.07 (3H, s), 2.35 (3H,
s), 2.26–2.16 (2H, m), 2.02–1.92 (1H, m), 2.01 (3H, s), 1.95 (3H, s),
0.94 (3H, d, JH-H = 6.8 Hz), 0.90 (3H, d, JH-H = 7.0 Hz). 19F NMR
3
3
5.7. General procedure for the introduction of a
diphenylphosphine-borane group
(282.4 MHz; CDCl3): d ꢀ62.3 ppm. 13C NMR (75.5 MHz; CDCl3): d
1
161.8 (q, JC-B = 49.8 Hz), 142.7, 136.7, 134.9, 134.1, 133.8, 130.3,
129.8, 128.9 (qq, 2JC-F = 31.8 Hz, 1JC-B = 2.7 Hz), 125.3, 124.7 (q, 1JC-F
=
At first, Ph2P(BH3)Li was prepared by the addition of n-BuLi
(1.5 M in hexanes, 2 equiv) to a solution of diphenylphosphine–
borane (2 equiv) in freshly degassed anhydrous THF (0.5 M solu-
tion) at ꢀ78 °C followed by stirring for 30 min at this temperature.
To a solution of the appropriate imidazolium salt (1 equiv) in
freshly degassed anhydrous THF at 0 °C was added the previously
prepared Ph2P(BH3)Li solution. The mixture was allowed to warm
up to rt overnight and was then quenched with H2O (1 mL), ex-
tracted with dichloromethane, dried over magnesium sulfate, and
concentrated in vacuo. The crude product was passed through a sil-
ica gel pad using pure dichloromethane as the eluant. After evapo-
ration of the solvent, the crude product was purified by column
chromatography (silica gel, AcOEt/cyclohexane 1:1 to AcOEt pure)
to afford the phosphine–borane.
272.5 Hz), 121.8, 117.7, 81.35, 46.7, 38.4, 32.4, 30.9, 21.0, 17.4,
17.3, 16.9. MS (ESI+, m/z): 365.1 ([MꢀBArF]+). MS (ESI-, m/z): 863.3
([BArF]ꢀ). IR (cmꢀ1): 3439, 2975, 1610, 1355, 1278, 125, 914, 839,
713, 670. Elemental Anal. Calcd for C51H41BF24N2O3S: C, 49.85; H,
3.36; N, 2.28; S, 2.61. Found: C, 50.55; H, 3.24; N, 2.03; S, 2.78.
Mp = 90 °C.
5.6.6. (R)-3-(2,6-Diisopropylphenyl)-1-(4-methyl-3-
(methylsulfonyloxy)pentyl)-1H-imidazol-3-ium tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate 6c-DiPP
Yield: 53%. Pink solid. Rf = 0.75 (10% methanol in dichlorometh-
ane). ½a 2D0
ꢁ
¼ þ2:6 (c 1.025, acetone). 1H NMR (300 MHz; CDCl3): d
3
8.54 (1H, s), 7.72 (8H, br s), 7.58 (1H, t, JH-H = 8.0 Hz), 7.54 (br s,
4H), 7.36–7.26 (4H, m, H4, H5), 4.65–4.56 (1H, m), 4.34–4.25 (2H,
m), 3.06 (3H, s), 2.29–2.05 (4H, m, H7), 2.02–1.91 (2H, m), 1.18
5.7.1. (S)-3-Mesityl-1-(3-(diphenylphosphine borane)butyl)-1H-
imidazol-3-ium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate
7a-Mes
3
3
3
(3H, d, JH-H = 6.8 Hz), 1.13 (3H, d, JH-H = 7.0 Hz), 1.12 (6H, d, JH-H
=
6.8 Hz), 0.92 (3H, d, JH-H = 6.7 Hz), 0.89 (3H, d, JH-H = 7.3 Hz). 19F
3
3
NMR (282.4 MHz; CDCl3): d ꢀ62.3 ppm. 13C NMR (75.5 MHz;
Yield: 84%. Colourless viscous oil. Rf = 0.7 (5% methanol in
1
a 2D0
ꢁ
¼ ꢀ1:1 (c 1.005, CHCl3). 1H NMR
CDCl3): d 161.8 (q, JC-B = 49.8 Hz), 145.3, 145.0, 136.9, 134.9,
dichloromethane).
½
2
1
132.9, 129.0 (qq, JC-F = 31.8 Hz, JC-B = 2.9 Hz), 129.2, 126.3,
125.3, 125.2, 124.7 (q, JC-F = 272.7 Hz), 121.8, 117.7, 81.0, 46.7,
(300 MHz; CDCl3): d 8.22 (1H, s), 7.80 (8H, br s), 7.80–7.72 (4H,
m), 7.59 (br s, 4H), 7.55–7.44 (6H, m), 7.32 (1H, s), 7.19 (1H, s),
7.03 (2H, s), 4.51–4.41 (1H, m), 4.30–4.22 (1H, m), 2.76–2.65
(1H, m), 2.45–2.30 (1H, m), 2.33 (3H, s), 2.24–2.13 (1H, m), 1.92
1
38.4, 32.4, 31.2, 29.1, 28.9, 24.1, 24.1, 24.0, 24.0, 17.5, 17.4. MS
(ESI+, m/z): 407.3 ([MꢀBArF]+). MS (ESI-, m/z): 863.4 ([BArF]ꢀ). IR
(cmꢀ1): 3149, 2973, 1611, 1469, 1356, 1278, 1128, 904, 713, 669.
3
(6H, s), 1.60–0.80 (3H, m), 1.23 (3H, dd, JH-P = 15.1 Hz,

J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
569
3
3JH-H = 7.0 Hz). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR
(1H, s), 7.76–7.68 (4H, m), 7.72 (8H, br s), 7.58 (1H, t, JH-H =
1
(75.5 MHz; CDCl3):
d
161.9 (q, JC-B = 49.5 Hz), 142.9, 135.0,
7.9 Hz), 7.53 (br s, 4H), 7.54–7.45 (6H, m), 7.35–7.25 (4H, m),
4.58–4.49 (1H, m), 4.35–4.25 (1H, m), 2.46–2.26 (3H, m), 2.14–
2.07 (3H, m, H7), 1.70–0.60 (3H, m), 1.62–1.73 (1H, m), 1.44–1.34
3
4
134.6, 133.7, 132.9 (d, JC-P = 8.8 Hz), 132.4 (d, JC-P = 2.2 Hz),
4
3
132.2 (d, JC-P = 2.2 Hz), 132.2 (d, JC-P = 8.8 Hz), 130.3, 129.7,
129.5 (d, JC-P = 9.9 Hz), 129.3 (d, JC-P = 9.9 Hz), 129.2 (qq, JC-F
2
2
2
3
=
=
(1H, m), 1.15–1.08 (12H, m), 0.89 (3H, t, JH-H = 7.3 Hz). 19F NMR
3
1
1
31.6 Hz, JC-B = 2.7 Hz), 127.2 (d, JC-P = 55.4 Hz), 125.7 (d, JC-P
(282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d 161.8
1
1
3
56.0 Hz), 125.0, 124.8 (q, JC-F = 272.9 Hz), 122.8, 117.7, 48.9 (d,
(q, JC-B = 49.8 Hz), 145.0, 135.2, 134.9, 133.1 (d, JC-P = 8.8 Hz),
3JC-P = 9.3 Hz), 32.0 (d, JC-P = 4.9 Hz), 26.7 (d, JC-P = 35.4 Hz), 20.9,
16.9, 14.3. 31P NMR (121.5 MHz; CDCl3): d 23.7: br s). MS (ESI+,
m/z): 441.2 ([MꢀBArF]+). MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR
(cmꢀ1): 3453, 2930, 2388, 1610, 1355, 1278, 1127, 887, 839, 713,
670. Elemental Anal. Calcd for C60H47B2F24N2P: C, 55.24; H, 3.63;
N, 2.15. Found: C, 55.58; H, 3.42; N, 1.98.
133.0, 132.4 (d, JC-P = 2.2 Hz), 132.2 (d, JC-P = 2.2 Hz), 132.0 (d,
2
1
4
4
3JC-P = 8.2 Hz), 129.6 (d, JC-P = 9.9 Hz), 129.3 (d, JC-P = 9.9 Hz),
2
2
2
3
1
129.0 (qq, JC-F = 31.3 Hz, JC-B = 2.7 Hz), 129.1, 127.7 (d, JC-P
=
=
=
1
1
55.5 Hz), 125.7 (d, JC-P = 55.4 Hz), 125.9, 125.2, 124.7 (q, JC-F
3
1
272.5 Hz), 122.5, 117.7, 48.9 (d, JC-P = 3.3 Hz), 33.4 (d, JC-P
2
33.5 Hz), 29.9 (d, JC-P = 4.9 Hz), 29.0, 24.1, 24.0, 22.4, 12.7
(d, JC-P = 9.9 Hz). 31P NMR (121.5 MHz; CDCl3): d 22.7 (br s). MS
3
5.7.2. (S)-3-(2,6-Diisopropylphenyl)-1-(3-(diphenylphosphine
borane)butyl)-1H-imidazol-3-ium tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate 7a-DiPP
(ESI+, m/z): 497.2 ([MꢀBArF]+). MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR
(cmꢀ1): 2973, 2391, 1612, 1464, 1440, 1356, 1279, 1126, 887,
839, 713, 670. Elemental Anal. Calcd for C64H55B2F24N2P: C, 56.49;
H, 4.07; N, 2.06. Found: C, 56.57; H, 4.13; N, 2.07.
Yield: 86%. Colourless oil. Rf = 0.8 (5% methanol in dichloro-
methane). ½a 2D0
ꢁ
¼ ꢀ0:3 (c 1.0, CHCl3). 1H NMR (300 MHz; CDCl3):
d 8.51 (1H, s), 7.87 (8H, br s), 7.83–7.77 (4H, m), 7.65 (br s, 4H),
7.61–7.46 (7H, m), 7.45–7.33 (4H, m), 4.63–4.53 (1H, m), 4.41–
4.31 (1H, m), 2.82–2.71 (1H, m), 2.50–2.35 (1H, m), 2.30–2.10
5.7.5. (S)-3-Mesityl-1-(4-methyl-3-(diphenylphosphineborane)-
pentyl)-1H-imidazol-3-ium tetrakis(3,5-bis(trifluoromethyl)-
phenyl)borate 7c-Mes
3
3
(3H, m), 1.65–0.70 (3H, m), 1.31 (3H, dd, JH-P = 15.1 Hz, JH-H
=
Yield: 71%. Colourless oil. Rf = 0.7 (5% methanol in dichlorometh-
7.1 Hz), 1.20–1.11 (12H, m). 19F NMR (282.4 MHz; CDCl3): d
ane). ½a 2D0
ꢁ
¼ ꢀ8:7 (c 1.005, CHCl3). 1H NMR (300 MHz; CDCl3): d 8.13
ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d 161.9 (q, JC-B = 50.0 Hz),
(1H, s), 7.94–7.80 (4H, m), 7.80 (8H, br s), 7.60–7.47 (6H, m), 7.59 (br
s, 4H), 7.31 (1H, m), 7.20 (1H, m), 7.03 (2H, s), 4.14–4.03 (2H, m),
2.30–2.60 (3H, m), 2.34 (3H, s), 2.13–2.06 (1H, m), 1.93 (3H, s),
1
3
4
145.0, 135.3, 135.0, 132.9 (d, JC-P = 8.8 Hz), 132.9, 132.4 (d, JC-P
=
4
3
2.2 Hz), 132.2 (d, JC-P = 2.2 Hz), 132.1 (d, JC-P = 8.8 Hz), 129.4 (d,
2JC-P = 10.4 Hz), 129.3 (d, JC-P = 10.4 Hz), 129.3, 129.2 (qq, JC-F
=
=
1.92 (3H, s), 1.80–0.70 (3H, m), 0.99 (3H, t, JH-H = 6.8 Hz), 0.86
2
2
3
3
1
1
3
31.6 Hz, JC-B = 2.7 Hz), 127.2 (d, JC-P = 55.5 Hz), 125.7 (d, JC-P
(3H, t, JH-H = 6.8 Hz). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C
1
1
55.5 Hz), 125.9, 125.2, 124.7 (q, JC-F = 272.7 Hz), 122.8, 117.7,
NMR (75.5 MHz; CDCl3): d 161.8 (q, JC-B = 50.0 Hz), 142.8, 135.0,
3
2
1
3
49.0 (d, JC-P = 9.3 Hz), 32.0 (d, JC-P = 4.9 Hz), 29.0, 26.7 (d, JC-P
=
134.5, 133.6, 132.9 (d, JC-P = 8.8 Hz), 132.3–132.1, 132.1 (d,
2
2
36.2 Hz), 23.9, 14.1. 31P NMR (121.5 MHz; CDCl3): d 23.9: br s).
MS (ESI+, m/z): 483.1 ([MꢀBArF]+). MS (ESI-, m/z): 863.3 ([BArF]ꢀ).
IR (cmꢀ1): 3438, 1611, 1356, 1278, 1125, 887, 839, 713, 682, 670.
Elemental Analysis: calculated for C63H53B2F24N2P: C, 56.19; H,
3.97; N, 2.08. Found: C, 56.15; H, 3.93; N, 1.99.
3JC-P = 8.2 Hz), 130.3, 129.7, 129.6 (d, JC-P = 9.3 Hz), 129.3 (d, JC-P
=
=
2
3
1
10.4 Hz), 129.1 (qq, JC-F = 31.3 Hz, JC-B = 2.7 Hz), 126.6 (d, JC-P
1
55.5 Hz), 124.9, 124.7 (q, JC-F = 272.7 Hz), 122.7, 117.7, 50.0
3
3
2
(d, JC-P = 3.3 Hz), 37.1 (d, JC-P = 31.8 Hz), 28.3, 27.2 (d, JC-P
=
4.9 Hz), 23.3 (d, JC-P = 9.9 Hz), 20.9, 17.5, 16.9. 31P NMR
(121.5 MHz; CDCl3): d 21.1 (br s). MS (ESI+, m/z): 469.1 ([MꢀBArF]+).
MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 3437, 1610, 1355, 1278,
1125, 886, 838, 713, 682, 670. Elemental Anal. Calcd for
3
5.7.3. (R)-3-Mesityl-1-(3-(diphenylphosphineborane)pentyl)-
1H-imidazol-3-ium tetrakis(3,5-
bis(trifluoromethyl)phenyl)borate 7b-Mes
C62H51B2F24N2P: C, 55.88; H, 3.86; N, 2.10. Found: C, 55.90; H,
Yield: 90%. Colourless viscous oil. Rf = 0.7 (5% methanol in
3.75; N, 2.08.
dichloromethane).
½
a 2D0
ꢁ
¼ ꢀ4:4 (c 0.99, CHCl3). 1H NMR
(300 MHz; CDCl3): d 8.18 (1H, s), 7.75–7.68 (4H, m), 7.69 (8H, br
s), 7.57–7.44 (6H, m), 7.51 (br s, 4H), 7.27 (1H, m), 7.14 (1H, m),
7.01 (2H, s), 4.49–4.39 (1H, m), 4.27–4.17 (1H, m), 2.46–2.27
5.7.6. (S)-3-(2,6-Diisopropylphenyl)-1-(4-methyl-3-
(diphenylphosphineborane)pentyl)-1H-imidazol-3-ium
tetrakis(3,5-bis(trifluoromethyl)phenyl)borate 7c-DiPP
Yield: 63%. Colourless oil. Rf = 0.75 (5% methanol in dichloro-
(2H, m), 2.33 (3H, s), 2.21–2.05 (1H, m), 1.89 (6H, s), 1.70–0.50
(3H, m), 1.70–1.60 (1H, m), 1.48–1.33 (1H, m), 0.89 (3H, t, JH-H
=
methane). ½a 2D0
ꢁ
¼ ꢀ7:7 (c 1.0, CHCl3). 1H NMR (300 MHz; CDCl3):
3
7.3 Hz). 19F NMR (282.4 MHz; CDCl3):
d
ꢀ62.3. 13C NMR
d 8.14 (1H, s), 7.84–7.68 (4H, m), 7.69 (8H, br s), 7.59 (1H, t,
3JH-H = 7.8 Hz), 7.51 (br s, 4H), 7.55–7.43 (6H, m), 7.36–7.31 (2H,
m), 7.23–7.19 (2H, m), 4.14–4.04 (1H, m), 2.53–2.45 (1H, m),
2.37–2.16 (2H, m), 2.13–1.95 (3H, m, H9), 1.60–0.50 (3H, m), 1.14
1
(75.5 MHz; CDCl3):
d
161.8 (q, JC-B = 49.8 Hz), 142.9, 134.9,
3
4
134.6, 133.7, 133.1 (d, JC-P = 9.3 Hz), 132.4 (d, JC-P = 2.2 Hz),
4
3
132.2 (d, JC-P = 2.2 Hz), 132.0 (d, JC-P = 8.8 Hz), 130.4, 129.7,
2
2
2
3
3
3
129.6 (d, JC-P = 9.9 Hz), 129.4 (d, JC-P = 9.9 Hz), 129.0 (qq, JC-F
=
=
(6H, d, JH-H = 6.6 Hz), 1.09 (6H, d, JH-H = 6.8 Hz), 0.93 (3H, d, JH-
3
1
1
31.3 Hz, JC-B = 2.7 Hz), 127.9 (d, JC-P = 54.9 Hz), 125.9 (d, JC-P
H = 7.0 Hz), 0.75 (3H, d, 3JH-H = 6.7 Hz). 19F NMR (282.4 MHz; CDCl3):
1
1
55.5 Hz), 125.0, 124.8 (q, JC-F = 272.5 Hz), 122.7, 117.7, 48.9 (d,
d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d 161.8 (q, JC-B = 49.8 Hz),
3JC-P = 3.3 Hz), 33.4 (d, JC-P = 33.5 Hz), 29.9 (d, JC-P = 4.4 Hz), 22.5,
145.0, 134.9, 134.9, 133.1 (d, JC-P = 8.8 Hz), 133.0, 132.4 (d, JC-P =
3
2
3
4
21.1, 17.0, 12.7 (d, JC-P = 9.9 Hz). 31P NMR (121.5 MHz; CDCl3): d
2.2 Hz), 132.3 (d, JC-P = 2.2 Hz), 132.0 (d, JC-P = 8.2 Hz), 129.6 (d,
3
4
3
22.6 (br s). MS (ESI+, m/z): 455.2 ([MꢀBArF]+). MS (ESI-, m/z):
863.4 ([BArF]ꢀ). IR (cmꢀ1): 3429, 1611, 1355, 1278, 1124, 887,
839, 713, 670. Elemental Anal. Calcd for C61H49B2F24N2P: C,
55.56; H, 3.75; N, 2.12. Found: C, 55.42; H, 3.58; N, 1.89.
2JC-P = 9.3 Hz), 129.3 (d, JC-P = 10.4 Hz), 129.1, 129.0 (qq, JC-F
=
2
2
3
1
31.3 Hz, JC-B = 3.1 Hz), 126.3 (d, JC-P = 54.9 Hz), 125.8, 125.3,
124.7 (q, 1JC-F = 272.7 Hz), 122.6, 117.6, 50.0 (d, 3JC-P = 3.3 Hz), 36.8
1
2
(d, JC-P = 31.3 Hz), 29.0, 28.9, 28.3, 27.5 (d, JC-P = 5.5 Hz), 24.3,
24.2, 24.1, 24.0, 23.4 (d, JC-P = 9.3 Hz), 17.5. 31P NMR (121.5 MHz;
3
5.7.4. (R)-3-(2,6-Diisopropylphenyl)-1-(3-
CDCl3): d 21.3 (br s). MS (ESI+, m/z): 511.1 ([MꢀBArF]+), 497.4. MS
(ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2974, 2394, 1611, 1356,
1279, 1127, 887, 839, 713, 682, 670. Elemental Anal. Calcd for
(diphenylphosphineborane)pentyl)-1H-imidazol-3-ium
tetrakis(3,5-bis(trifluoromethyl)phenyl)borate 7b-DiPP
Yield: 87%. Colourless oil. Rf = 0.7 (5% methanol in dichlorometh-
C65H57B2F24N2P: C, 56.79; H, 4.18; N, 2.04. Found: C, 56.77; H,
ane). ½a 2D0
ꢁ
¼ ꢀ5:2 (c 1.0, CHCl3). 1H NMR (300 MHz; CDCl3): d 8.31
4.15; N, 1.98.

570
J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
5.8. General procedure for diphenylphosphine borane
deprotection
m), 3.58–3.48 (1H, m), 2.36–1.97 (5H, m), 1.90–1.80 (1H, m), 1.11–
3
3
1.06 (12H, m), 0.99 (6H, d, JH-H = 6.6 Hz), 0.95 (6H, d, JH-H
=
6.6 Hz). 31P NMR (121.5 MHz; CDCl3): d ꢀ10.3 (s).
An oven-dried Schlenk tube containing a magnetic stirring bar
and filled with argon was charged with phosphine–borane/imi-
dazolium salt (1 equiv) and 1,4-diazabicyclo[2.2.2]octane
(4 equiv). Freshly degassed anhydrous toluene (in order to obtain
a 0.05 M solution) was then added and the solution stirred for
8 h at 40 °C. The solvent was then removed under vacuum and
the crude product was purified by column chromatography (silica
gel, CH2Cl2). Dichloromethane was then removed under vacuum to
give the phosphine–imidazolium salt.
5.9. General procedure for the synthesis of iridium complexes
An oven-dried Schlenk tube containing a magnetic stirrer bar
and filled with argon was charged with the phosphine/imidazoli-
um salt (1 equiv) and [Ir(COD)Cl]2 (0.5 equiv). Freshly degassed
anhydrous THF (in order to obtain a 0.02 M phosphine-imidazo-
lium solution) was added to the mixture. The suspension was
stirred for 5 min at room temperature, during which time the
color of the solution changed from orange-red to yellow. Freshly
sublimed t-BuOK (1.5 equiv) was then added. During the addi-
tion, the color changed from yellow to dark red and the reaction
mixture was then stirred overnight. The solvent was then re-
moved under vacuum and the crude product was filtered using
a short silica column and CH2Cl2 as eluent. Dichloromethane
was then removed under vacuum to give the iridium complex
as red solid.
5.8.1. (S)-1-(3-(Diphenylphosphino)butyl)-3-mesityl-1H-
imidazol-3-ium-tetrakis(3,5-bis(trifluoromethyl)phenyl)borate
1a-Mes
Yield = 100%. Colourless viscous oil. 1H NMR (300 MHz; CDCl3): d
7.86 (1H, s), 7.70 (8H, br s), 7.52 (br s, 4H), 7.12–7.48 (12H, m), 7.01
(2H, s), 4.48–4.39 (1H, m), 4.34–4.16 (1H, m), 2.33 (3H, s), 2.20–1.90
(2H, m), 1.89 (6H, s), 1.10 (3H, dd, 3JH-P = 12.8 Hz, 3JH-H = 7.0 Hz). 31
NMR (121.5 MHz; CDCl3): d ꢀ5.6 (s).
P
5.9.1. Complex Ir-1a-Mes
Yield: 76%. Red solid. ½a D20
ꢁ
¼ ꢀ15:0 (c 0.1, CHCl3). 1H NMR
5.8.2. (S)-3-(2,6-Diisopropylphenyl)-1-(3-(diphenylphosphino)-
butyl)-1H-imidazol-3-ium-tetrakis(3,5-
(300 MHz; CDCl3): d 8.00 (2H, m), 7.72 (8H, br s), 7.60–7.43 (8H,
m), 7.52 (4H, br s), 7.11–6.94 (6H, m), 5.28 (1H, m), 5.15 (1H, dt,
bis(trifluoromethyl)phenyl)borate 1a-DiPP
2
3JH-H = 4.3 Hz, JH-H = 14.1 Hz), 3.97–3.87 (2H, m), 3.57–3.43 (1H,
Yield = 100%. Colourless viscous oil. 1H NMR (300 MHz; CDCl3):
3
m), 3.14–3.05 (1H, m), 2.40–1.10 (11H, m), 2.30 (3H, s), 2.16 (3H,
d 7.97 (1H, s), 7.69 (8H, br s), 7.58 (1H, t, JH-H = 8.0 Hz), 7.51 (br s,
3
3
s), 1.94 (3H, s), 1.00 (3H, dd, JH-P = 11.8 Hz, JH-H = 6.4 Hz). 19F
4H), 7.45–7.33 (14H, m), 4.51–4.38 (1H, m), 4.27–4.18 (1H, m),
2.36–2.29 (1H, m), 2.15–1.55 (4H, m), 1.26–1.04 (15H, m). 31P
NMR (121.5 MHz; CDCl3): d ꢀ5.5 (s).
NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d
2
1
174.7 (d, JC-P = 8.8 Hz), 161.8 (q, JC-B = 50.0 Hz), 140.3, 135.4 (d,
4
JC-P = 11.5 Hz), 135.2, 134.9, 134.4, 132.6 (d, JC-P = 2.7 Hz), 131.6
(d, JC-P = 8.2 Hz), 131.0 (d, JC-P = 1.6 Hz), 129.6, 129.2–128.8,
129.0 (qq, JC-F = 31.8 Hz, JC-B = 2.9 Hz), 126.9, 124.8 (d, JC-P
49.4 Hz), 124.7 (q, JC-F = 272.7 Hz), 120, 117.6, 87.2, 86.8
(d, JP-C = 6.6 Hz), 77.2(d, JC-P = 17.0 Hz), 75.6, 47.7 (d, JC-P
5.0 Hz), 37.3, 34.9 (d, JC-P = 4.4 Hz), 33.9, 27.0 (d, JC-P = 27.4 Hz),
4
5.8.3. (R)-1-(3-(Diphenylphosphino)pentyl)-3-mesityl-1H-
imidazol-3-ium-tetrakis(3,5-bis (trifluoromethyl)phenyl)borate
1b-Mes
2
3
1
=
1
2
2
3
=
Yield = 100%. Colourless viscous oil. 1H NMR (300 MHz; CDCl3):
d 7.86 (1H, s), 7.72 (8H, br s), 7.54 (br s, 4H), 7.54–7.13 (12H, m),
7.01 (2H, s), 4.41–4.32 (1H, m), 4.17–4.07 (1H, m), 2.33 (3H, s),
2.20–2.09 (3H, m), 1.88 (6H, s), 1.65–1.56 (1H, m), 1.45–1.20 (1H,
2
1
3
3
26.9 (d, JC-P = 2.2 Hz), 26.5, 21.5, 21.0, 18.0, 17.0 (d, JC-P
=
6.6 Hz). 31P NMR (121.5 MHz; CDCl3): d 10.4 (br s). MS (ESI+, m/
z): 725.3 (55%), 726.2 (20%), 727.2 ([MꢀBArF]+, 100%), 728.2
(31%). MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2926, 1611,
1355, 1279, 1126, 887, 839, 712, 670. Elemental Anal. Calcd for
3
m), 1.10 (3H, t, JH-H = 7.3 Hz). 31P NMR (121.5 MHz; CDCl3): d
ꢀ9.2 (s).
C
68H55BF24IrN2P: C, 51.36; H, 3.49; N, 1.76. Found: C, 51.23; H,
5.8.4. (R)-3-(2,6-Diisopropylphenyl)-1-(3-(diphenylphosphino)-
pentyl)-1H-imidazol-3-ium tetrakis(3,5-
3.83; N, 1.71. Mp = decomposition from 75 °C.
bis(trifluoromethyl)phenyl)borate 1b-DiPP
5.9.2. Complex Ir-1a-DiPP
Yield = 100%. Colourless viscous oil. 1H NMR (300 MHz; CDCl3):
Yield: 85%. Red solid. ½a D20
ꢁ
¼ ꢀ11:0 (c 0.1, CHCl3). 1H NMR
3
d 7.94 (1H, s), 7.69 (8H, br s), 7.58 (1H, t, JH-H = 7.8 Hz), 7.51 (br s,
(300 MHz; CDCl3): d 7.99 (2H, m), 7.73 (8H, br s), 7.52 (4H, br s),
7.62–7.43 (8H, m), 7.26 (1H, t, JH-H = 6.9 Hz), 7.15 (1H, d, JH-
H = 1.7 Hz), 7.15–7.08 (2H, m), 7.08 (1H, d, JH-H = 2.1 Hz), 5.30–
5.25 (1H, m), 5.21 (1H, dt, JH-H = 5.1 Hz, JH-H = 14.1 Hz), 4.04–
4H), 7.48–7.17 (14H, m), 4.40–4.32 (1H, m), 4.19–4.09 (1H, m),
2.15–2.03 (5H, m), 1.70–1.59 (1H, m), 1.05–1.11 (12H, m), 0.94
3
3
3
3
(3H, t, JH-H = 7.3 Hz). 31P NMR (121.5 MHz; CDCl3): d ꢀ9.1 (s).
3
2
3.94 (2H, m, H6), 3.68–3.60 (1H, m), 3.23–3.08 (2H, m), 2.42–1.81
(7H, m), 1.71–0.80 (5H, m), 1.20 (3H, d, JH-H = 6.8 Hz), 1.11 (3H,
3
5.8.5. (S)-1-(3-(Diphenylphosphino)-4-methylpentyl)-3-mesityl-
1H-imidazol-3-ium tetrakis(3,5-bis(trifluoromethyl)-
phenyl)borate 1c-Mes
3
3
3
d, JH-H = 6.8 Hz), 1.05 (3H, d, JH-H = 6.8 Hz), 1.00 (3H, dd, JH-P
=
12.2 Hz, JH-H = 6.6 Hz), 0.92 (3H, d, JH-H = 6.8 Hz). 19F NMR
3
3
Yield = 100%. Colourless viscous oil. 1H NMR (300 MHz; CDCl3):
d 7.70 (8H, br s), 7.59–7.17 (11H, m, H2), 7.51 (br s, 4H), 7.05 (1H,
(282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d
2
1
174.4 (d, JP-C = 8.8 Hz), 161.8 (q, JB-C = 49.8 Hz), 146.0, 144.9,
4
s), 7.00 (2H, s), 6.95 (1H, s), 3.85–3.75 (1H, m), 3.53–3.43 (1H, m),
135.5 (d, JC-P = 9.3 Hz), 135.4, 134.9 (br s), 132.5 (d, JC-P = 2.2 Hz),
131.3 (d, JC-P = 8.2 Hz), 130.9 (d, JC-P = 1.6 Hz), 130.7, 129.9,
3
4
2.32 (3H, s), 2.20–1.90 (4H, m), 1.83 (6H, s), 0.98 (3H, d, JH-H
=
8.1 Hz), 0.95 (3H, d, JH-H = 7.0 Hz,). 31P NMR (121.5 MHz; CDCl3):
3
2
3
129.5–128.7, 129.0 (qq, JC-F = 31.3 Hz, JC-B = 2.9 Hz), 124.9, 124.8
1
1
d ꢀ10.3 (s).
(d, JC-P = 49.4 Hz), 124.7 (q, JC-F = 272.5 Hz), 123.7, 120.0, 117.6
2
2
(m), 87.6, 85.8 (d, JP-C = 6.0 Hz), 76.8 (d, JP-C = 17.6 Hz), 76.7,
47.8 (d, JP-C = 6.0 Hz), 37.2, 34.6 (d, JP-C = 4.4 Hz), 33.5, 30.9,
3
2
5.8.6. (S)-3-(2,6-Diisopropylphenyl)-1-(3-(diphenylphosphino)-
4-methylpentyl)-1H-imidazol-3-ium tetrakis(3,5-
1
3
28.3, 28.1 (d, JP-C = 30.2 Hz), 27.0 (d, JP-C = 2.7 Hz), 26.5, 26.0,
3
bis(trifluoromethyl)phenyl)borate 1c-DiPP
24.8, 23.4, 21.3, 17.0 (d, JP-C = 7.1 Hz). 31P NMR (121.5 MHz;
Yield = 100%. Colourless viscous oil. 1H NMR (300 MHz; CDCl3):
d 7.70 (8H, br s), 7.60–6.97 (16H, m), 7.52 (br s, 4H), 3.84–3.74 (1H,
CDCl3): d 10.6 (s). MS (ESI+, m/z): 770.3 (45%), 769.3 ([MꢀBArF]+,
100%), 768.3 (29%), 767.3 (59%). MS (ESI-, m/z): 863.3 ([BArF]ꢀ).

J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
571
IR (cmꢀ1): 2926, 1613, 1464, 1356, 1278, 1125, 887, 839, 713, 670.
Elemental Anal. Calcd for C71H61BF24IrN2P: C, 52.25; H, 3.77; N,
1.72. Found: C, 52.46; H, 4.10; N, 1.55. Mp = decomposition from
70 °C.
(3H, s), 1.93–1.74 (5H, m), 1.68–1.20 (3H, m), 1.13–1.03 (2H, m),
3
3
0.89 (3H, d, JH-H = 7.0 Hz), 0.30 (3H, d, JH-H = 6.8 Hz). 19F NMR
(282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d
2
1
174.6 (d, JC-P = 8.8 Hz), 161.8 (q, JC-B = 50.0 Hz), 140.1, 135.0,
3
134.9 (br s), 134.8 (d, JC-P = 8.2 Hz), 134.5, 132.5 (d, JC-P
=
3
5.9.3. Complex Ir-1b-Mes
2.2 Hz,), 132.1 (d, JC-P = 8.8 Hz), 131.1 (d, JC-P = 1.7 Hz), 129.6,
Yield: 86%. Red solid. ½a D20
ꢁ
¼ þ22:0 (c 0.1, CHCl3). 1H NMR
129.2 (d, JC-P = 43.9 Hz), 129.3–128.9, 129.0 (qq, JC-F = 31.3 Hz,
1
2
1
1
(300 MHz; CDCl3): d 8.00 (2H, m), 7.72 (8H, br s), 7.60–7.50 (3H,
m), 7.52 (4H, br s), 7.45–7.43 (3H, m), 7.09–7.06 (2H, m), 7.06–
7.00 (2H, m), 6.96 (1H, s), 6.95 (1H, s), 5.31–5.27 (1H, m), 5.19
3JC-B = 2.7 Hz), 127.0, 126.2 (d, JC-P = 46.7 Hz), 124.7 (q, JC-F
=
2
272.7 Hz), 120.2, 117.6, 86.6, 85.5 (d, JC-P = 6.6 Hz), 77.4, 76.7 (d,
2JC-P = 17.0 Hz), 48.0 (d, JC-P = 6.0 Hz), 38.6 (d, JC-P = 25.2 Hz),
3
1
3
2
3
2
2
3
(1H, dt, JH-H = 4.9 Hz, JH-H = 14.2 Hz), 3.98 (1H, dd, JH-H = 6.2 Hz,
2JH-H = 14.5 Hz), 3.89–3.84 (1H, m), 3.52–3.44 (1H, m), 3.13–3.04
(1H, m), 2.56–2.33 (2H, m), 2.30 (3H, s), 2.18 (3H, s), 1.94 (3H, s),
1.92–1.75 (7H, m), 1.63–1.25 (2H, m), 1.23–1.02 (3H, m), 0.86
37.0, 34.7 (d, JC-P = 4.4 Hz), 27.3 (d, JC-P = 6.6 Hz), 27.1 (d, JC-P =
3
2.7 Hz), 26.5, 25.7, 25.0 (d, JC-P = 8.9 Hz), 21.3, 21.0, 18.1, 17.9.
31P NMR (121.5 MHz; CDCl3): d 12.4 (s). MS (ESI+, m/z): 756.3
(30%), 755.3 ([MꢀBArF]+, 100%), 754.3 (31%), 753.2 (77%), 751.1
(23%). MS (ESI-, m/z): 863.4 ([BArF]ꢀ). IR (cmꢀ1): 2963, 1611,
1356, 1278, 1127, 887, 839, 714, 670. Elemental Anal. Calcd for
(3H, m). 19F NMR (282.4 MHz; CDCl3):
d
ꢀ62.3. 13C NMR
2
1
(75.5 MHz; CDCl3): d 174.7 (d, JC-P = 8.8 Hz), 161.8 (q, JC-B
=
49.8 Hz), 140.0, 135.4 (d, JC-P = 10.4 Hz), 135.2, 134.9 (br s), 134.4,
C70H59BF24IrN2P: C, 51.96; H, 3.67; N, 1.73. Found: C, 51.95; H,
3.66; N, 1.74. Mp = decomposition from 80 °C.
4
4
132.5 (d, JC-P = 2.7 Hz), 131.3 (d, JC-P = 8.2 Hz), 130.9 (d, JC-P
1.6 Hz), 129.8, 129.7, 129.3–129.0, 129.0 (qq, JC-F = 31.8 Hz,
=
2
1
1
3JC-B = 2.7 Hz), 127.0, 125.3 (d, JC-P = 49.4 Hz), 124.7 (q, JC-F
=
5.9.6. Complex Ir-1c-DiPP
2
Yield: 82%. Red solid. ½a D20
ꢁ
¼ þ37:0 (c 0.1, CHCl3). 1H NMR
272.7 Hz), 120.3, 117.6, 87.4, 86.7 (d, JC-P = 6.0 Hz), 76.9
(d, JC-P = 17.0 Hz), 75.6, 47.6 (d, JC-P = 6.0 Hz), 37.3, 35.3
(d, JC-P = 27.5 Hz), 34.9 (d, JC-P = 4.4 Hz), 30.7, 27.0 (d, JC-P
2
3
(300 MHz; CDCl3): d 7.97 (2H, m), 7.73 (8H, br s), 7.53 (4H, br s),
1
2
3
=
3
7.62–7.49 (4H, m), 7.45 (1H, t, JH-H = 7.8 Hz), 7.36–7.13 (7H, m),
2
3
2
3.3 Hz), 26.5, 24.0 (d, JC-P = 6.6 Hz), 21.5, 21.0, 18.0, 12.8
5.32 (1H, dt, JH-H = 4.9 Hz, JH-H = 14.2 Hz), 5.22–5.16 (1H, m),
4.20–4.06 (2H, m), 3.62–3.49 (1H, m), 3.15–3.03 (2H, m), 2.35–
2.05 (4H, m), 1.97–1.77 (7H, m), 1.70–1.46 (2H, m), 1.18 (3H, d,
(d, JC-P = 8.2 Hz). 31P NMR (121.5 MHz; CDCl3): d 11.78 (s). MS
3
(ESI+, m/z): 742.2 (42%), 741.3 ([MꢀBArF]+, 100%), 740.3 (26%),
739.4 (53%). MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2927,
1612, 1488, 1355, 1281, 1128, 887, 838, 715, 670, 524. Elemental
Anal. Calcd for C69H57BF24IrN2P: C, 51.66; H, 3.58; N, 1.75. Found:
C, 51.59; H, 3.79; N, 1.71. Mp = 166–168 °C.
3JH-H = 6.8 Hz), 1.09 (3H, d, JH-H = 6.6 Hz), 1.02 (3H, d, JH-H
=
3
3
3
3
6.8 Hz), 0.93 (3H, d, JH-H = 6.8 Hz), 0.82 (3H, d, JH-H = 6.8 Hz),
3
0.27 (3H, d, JH-H = 6.8 Hz). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3.
13C NMR (75.5 MHz; CDCl3): d 174.5 (d, JC-P = 8.2 Hz), 161.83 (q,
2
1JC-B = 49.8 Hz), 146.1, 144.7, 135.3, 134.9 (br s), 132.6, 131.4 (d,
2
5.9.4. Complex Ir-1b-DiPP
JC-P = 8.2 Hz), 130.9, 130.7, 129.9, 129.6–129.0, 129.0 (qq, JC-F
=
Yield: 82%. Red solid. ½a D20
ꢁ
¼ þ12:2 (c 0.1, CHCl3). 1H NMR
3
1
31.3 Hz, JC-B = 3.1 Hz), 126.1 (d, JC-P = 46.7 Hz), 125.0, 124.7 (q,
1JC-F = 272.80 Hz), 123.7, 119.7, 117.6, 87.5, 84.7 (d, JP-C = 6.6 Hz),
2
(300 MHz; CDCl3): d 7.98 (2H, m), 7.71 (8H, br s), 7.52 (4H, br s),
3
7.61–7.43 (8H, m), 7.26 (1H, t, JH-H = 8.4 Hz), 7.14 (1H, d,
2
3
77.4, 75.9 (d, JC-P = 17.6 Hz), 48.0 (d, JC-P = 5.5 Hz), 38.4
3JH-H = 1.9 Hz), 7.10 (1H, d, JH-H = 2.1 Hz), 7.08–7.02 (2H, m),
3
1
2
(d, JP-C = 25.2 Hz), 37.1, 34.7 (d, JC-P = 4.4 Hz), 30.8, 28.3, 27.1,
3
2
5.30–5.27 (1H, m), 5.19 (1H, dt, JH-H = 4.7 Hz, JH-H = 13.7 Hz),
4.00–3.86 (2H, m), 3.61–3.52 (1H, m), 3.29–3.20 (1H, m), 3.17–
3.07 (1H, m), 2.55–2.27 (3H, m), 2.05–1.55 (8H, m), 1.42–1.25
3
27.0, 26.5, 26.1, 25.7, 25.3 (d, JC-P = 8.8 Hz), 24.6, 23.4, 21.0, 18.1.
31P NMR (121.5 MHz; CDCl3): d 13.3 (s). MS (ESI+, m/z): 798.2
(45%), 797.1 ([MꢀBArF]+, 100%), 796.2 (33%), 795.2 (62%),. MS
(ESI-, m/z): 863.2 ([BArF]ꢀ). IR (cmꢀ1): 2968, 1611, 1355, 1278,
1126, 887, 715, 669. Elemental Anal. Calcd for C73H65- BF24IrN2P:
C, 52.81; H, 3.95; N, 1.69. Found: C, 52.75; H, 3.94; N, 1.70.
Mp = 165 °C.
3
3
(2H, m), 1.19 (3H, d, JH-H = 6.6 Hz), 1.10 (3H, d, JH-H = 6.8 Hz),
3
3
1.04 (3H, d, JH-H = 6.8 Hz), 0.99 (3H, d, JH-H = 6.8 Hz), 0.87 (3H,
m). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz;
2
1
CDCl3): d 174.4 (d, JC-P = 8.8 Hz), 161.8 (q, JC-B = 50.0 Hz), 146.0,
4
144.7, 135.5, 135.4 (d, JC-P = 10.4 Hz), 134.9 (br s), 132.6 (d, JC-P
2.2 Hz), 131.2 (d, JC-P = 8.8 Hz), 130.9 (d, JC-P = 1.6 Hz), 130.7,
=
4
2
3
5.10. General procedure for the synthesis of rhodium complexes
130.1, 129.6–129.0, 129.0 (qq, JC-F = 31.3 Hz, JC-B = 2.9 Hz), 125.3
1
1
(d, JC-P = 47.2 Hz), 125.0, 124.7 (q, JC-F = 272.7 Hz), 123.7, 119.9,
An oven-dried Schlenk tube containing a magnetic stirrer bar
and filled with argon was charged with the phosphine/imidazoli-
um salt (1 equiv) and [Rh(COD)Cl]2 (0.5 equiv). Freshly degassed
anhydrous THF (in order to obtain a 0.02 M phosphine-imidazoli-
um solution) was added to the mixture. The suspension was stirred
for 5 min at room temperature. Freshly sublimed t-BuOK (1.5
equiv) was then added. During the addition, the color changed
from yellow to dark orange and the reaction mixture was then stir-
red overnight. The solvent was then removed under vacuum and
the crude product was filtered using a short silica column and
CH2Cl2 as eluent. Dichloromethane was then removed under vac-
uum to give the rhodium complex as a yellow solid.
2
2
117.6, 87.5, 86.0 (d, JC-P = 6.0 Hz), 76.9 (d, JC-P = 17.6 Hz), 76.2,
3
1
47.6 (d, JC-P = 6.4 Hz), 37.2, 35.8 (d, JC-P = 26.9 Hz), 34.7 (d,
2JC-P = 4.4 Hz), 31.0, 30.7, 28.3, 27.0 (d, JC-P = 3.3 Hz), 26.5, 26.1,
3
2
3
24.6, 24.1 (d, JC-P = 6.6 Hz), 23.4, 21.4, 13.1 (d, JC-P = 8.8 Hz). 31P
NMR (121.5 MHz; CDCl3): d 12.0 (s). MS (ESI+, m/z): 784.2 (42%),
783.3 ([MꢀBArF]+, 100%), 781.5 (48%). MS (ESI-, m/z): 863.3
([BArF]ꢀ). IR (cmꢀ1): 2930, 2027, 1611, 1466, 1355, 1279, 1127,
887, 839, 713, 670. Elemental Anal. Calcd for C72H63BF24IrN2P: C,
52.53; H, 3.86; N, 1.70. Found: C, 52.79; H, 4.07; N, 1.72.
Mp = decomposition from 75 °C.
5.9.5. Complex Ir-1c-Mes
Yield: 82%. Red solid. ½a D20
ꢁ
¼ þ26:0 (c 0.1, CHCl3). 1H NMR
3
5.10.1. Complex Rh-1a-Mes
(300 MHz; CDCl3): d 7.94 (2H, t, JH-H = 8.4 Hz), 7.72 (8H, br s),
Yield: 84%. Yellow solid. ½a D20
ꢁ
¼ ꢀ2:0 (c 0.1, CHCl3). 1H NMR
7.60–7.45 (6H, m), 7.52 (4H, br s), 7.21–7.15 (2H, m), 7.08 (1H, d,
3
3JH-H = 1.9 Hz), 7.04 (1H, d, JH-H = 1.7 Hz), 6.95 (1H, s), 6.91 (1H,
(300 MHz; CDCl3): d 8.04 (2H, m), 7.71 (8H, br s), 7.60–7.37 (8H,
3
3
2
m), 7.51 (4H, br s), 7.09 (2H, d, JH-H = 7.8 Hz), 7.05 (1H, d, JH-H
=
s), 5.34 (1H, dt, JH-H = 4.7 Hz, JH-H = 13.9 Hz), 5.14 (1H, m), 4.15
3
3
2
1.9 Hz), 7.02 (1H, d, JH-H = 1.9 Hz), 6.99 (1H, s), 6.98 (1H, s), 5.51
(1H, dd, JH-H = 6.4 Hz, JH-H = 14.3 Hz), 3.96 (1H, m), 3.40 (2H, m),
3
2
(1H, m), 5.31 (1H, dt, JH-H = 4.5 Hz, JH-H = 13.9 Hz), 4.09–3.99
3.14 (2H, m), 2.37–2.00 (2H, m), 2.30 (3H, s), 1.99 (3H, s), 1.93

572
J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
(2H, m, H6), 3.92 (1H, m), 3.61 (1H, m), 2.70–0.80 (11H, m), 2.32
1JP-Rh = 151.5 Hz). MS (ESI+, m/z): 666.2 (44%), 665.1 ([MꢀBArF]+,
100%). MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2959, 1611,
1356, 1279, 1128, 886, 839, 714, 669. Elemental Anal. Calcd for
C70H59BF24N2PRh: C, 54.99; H, 3.89; N, 1.83. Found: C, 55.10; H,
4.11; N, 1.74. Mp = 154–158 °C.
3
(3H, s), 2.25 (3H, s), 1.89 (3H, s), 0.98 (3H, dd, JH-P = 11.3 Hz,
3JH-H = 6.8 Hz). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR
1
2
(75.5 MHz; CDCl3): d 177.4 (dd, JC-Rh = 51.6 Hz, JP-C = 13.2 Hz),
1
161.8 (q, JC-B = 49.8 Hz), 140.0, 135.5 (d, JC-P = 12.1 Hz), 134.9 (br
s), 134.5, 132.4 (d, JC-P = 2.2 Hz), 131.4 (d, JC-P = 8.2 Hz), 130.6
(d, JC-P = 1.6 Hz), 129.8, 129.7 (d, JC-P = 35.7 Hz), 129.9–128.3,
4
4
1
5.10.4. Complex Rh-1a-DiPP
2
3
1
Yield: 81%. Yellow solid. ½a D20
ꢁ
¼ ꢀ12:2 (c 0.115, CHCl3). 1H NMR
129.0 (qq, JC-F = 31.8 Hz, JC-B = 2.7 Hz), 127.4, 124.7 (q, JC-F
=
=
1
2
272.7 Hz), 120.4, 117.6, 99.2 (d, JC-Rh = 7.7 Hz), 97.1 (dd, JC-P
(300 MHz; CDCl3): d 8.04 (2H, m), 7.72 (8H, br s), 7.60–7.06 (13H,
1
2
1
m), 7.52 (4H, br s), 5.52 (1H, m), 5.36 (1H, dt, JH-H = 4.7 Hz, 2JH-H
=
3
6.0 Hz, JC-Rh = 9.9 Hz), 90.2 (dd, JC-P = 7.7 Hz, JC-Rh = 15.4 Hz),
1
3
89.5 (d, JC-Rh = 7.1 Hz), 48.3 (d, JC-P = 7.7 Hz), 35.6, 33.9, 33.4 (d,
14.1 Hz), 4.20 (1H, m), 4.09–4.02 (2H, m), 3.63–3.55 (1H, m), 3.46–
3.37 (1H, m), 2.71–2.56 (1H, m), 2.38–1.43 (9H, m), 1.27–0.90 (2H,
m), 1.16 (3H, d, 3JH-H = 6.8 Hz), 1.07 (3H, d, 3JH-H = 6.8 Hz), 1.04 (3H,
2JC-P = 4.4 Hz), 27.0 (d, JC-P = 22.0 Hz), 26.8, 26.6, 21.0, 18.0, 16.4
1
(d, JC-P = 7.7 Hz). 31P NMR (121.5 MHz; CDCl3): d 17.0 (d, JP-Rh
=
3
1
154.4 Hz). MS (ESI+, m/z): 638.1 (37%), 637.1([M-BArF]+, 100%).
MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2927, 1611, 1439,
1355, 1278, 1127, 887, 839, 713, 670. Elemental Anal. Calcd for
C, 54.42; H, 3.69; N, 1.87. Found: C, 54.49; H, 3.77; N, 1.74.
Mp = 138–140 °C.
3
3
3
d, JH-H = 6.8 Hz), 0.97 (3H, d, JH-H = 6.8 Hz), 0.96 (3H, dd, JH-P
=
11.1 Hz, JH-H = 6.6 Hz). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C
3
1
2
NMR (75.5 MHz; CDCl3): d 177.5 (dd, JC-Rh = 51.6 Hz, JP-C
=
=
1
12.6 Hz), 161.8 (q, JC-B = 49.8 Hz), 146.2, 144.8, 135.7 (d, JC-P
9.9 Hz), 135.6, 134.9 (br s), 132.4 (d, JC-P = 2.2 Hz), 131.4
(d, JC-P = 8.2 Hz), 130.7, 130.5 (d, JC-P = 1.6 Hz), 129.9 (d, JC-P
35.1 Hz), 129.6–129.0, 129.0 (qq, JC-F = 31.8 Hz, JC-B = 2.7 Hz),
4
4
1
=
2
3
5.10.2. Complex Rh-1b-Mes
1
1
Yield: 84%. Yellow solid. ½a D20
ꢁ
¼ þ11:0 (c 0.1, CHCl3). 1H NMR
126.1 (d, JC-P = 38.4 Hz), 125.1, 124.7 (q, JC-F = 272.5 Hz), 123.9,
1
2
120.0, 117.6, 99.7 (d, JC-Rh = 7.7 Hz), 96.0 (dd, JC-P = 4.9 Hz,
(300 MHz; CDCl3): d 8.05 (2H, m), 7.72 (8H, br s), 7.62–7.35 (6H,
1JC-Rh = 9.3 Hz), 90.3 (d, JC-Rh = 7.1 Hz), 89.6 (dd, JC-P = 7.1 Hz,
1
2
m), 7.52 (4H, br s), 7.07–6.98 (6H, m), 5.52 (1H, m), 5.36 (1H, dt,
1JC-Rh = 14.8 Hz), 48.3 (d, JC-P = 7.7 Hz), 35.5, 33.4, 33.2 (d,
3
2
3JH-H = 4.3 Hz, JH-H = 13.7 Hz), 4.10–4.03 (1H, m), 3.91 (1H, m),
2JC-P = 4.4 Hz), 30.2, 28.3, 28.0 (d, JC-P = 20.3 Hz), 26.8, 26.6, 26.1,
1
3.57 (1H, m), 2.70–0.88 (13H, m), 2.32 (3H, s), 2.28 (3H, s), 1.89
24.9, 23.3, 21.3, 16.4 (d, JC-P = 7.7 Hz). 31P NMR (121.5 MHz;
3
(3H, s), 0.84 (3H, m). 19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C
1
1
2
CDCl3): d 16.2 (d, JP-Rh = 151.5 Hz). MS (ESI+, m/z): 681.1 (39%),
NMR (75.5 MHz; CDCl3):
d 174.7 (dd, JC-Rh = 51.6 Hz, JC-P =
680.1 (42%), 679.1 ([MꢀBArF]+, 100%). MS (ESI-, m/z): 863.3
([BArF]ꢀ). IR (cmꢀ1): 2972, 1612, 1355, 1279, 1126, 887, 840,
744, 713, 682, 518. Elemental Anal. Calcd for C71H61BF24N2PRh:
C, 55.27; H, 3.98; N, 1.82. Found: C, 55.22; H, 4.09; N, 1.84.
Mp = decomposition from 70 °C.
1
13.2 Hz), 161.8 (q, JC-B = 49.8 Hz), 140.0, 135.6 (d, JC-P = 11.5 Hz),
135.5, 134.9 (br s), 134.8, 134.), 132.3 (d, JC-P = 2.2 Hz), 131.1 (d,
JC-P = 8.2 Hz), 130.5 (d, JC-P = 1.6 Hz), 129.9 (d, JC-P = 35.1 Hz),
4
4
1
2
3
129.8, 129.3–129.0, 129.0 (qq, JC-F = 31.3 Hz, JC-B = 2.9 Hz),
1
1
127.5, 126.6 (d, JC-P = 40.1 Hz), 124.7 (q, JC-F = 272.7 Hz), 120.3,
1
1
2
117.6, 99.5 (d, JC-Rh = 7.7 Hz), 97.0 (dd, JC-Rh = 5.5 Hz, JC-P
9.9 Hz), 90.0 (dd, JC-Rh = 6.6 Hz, JC-P = 14.8 Hz), 89.4 (d, JC-Rh
7.1 Hz), 48.1 (d, JC-P = 7.7 Hz), 35.6, 35.1 (d, JC-P = 20.3 Hz), 33.4
=
=
1
2
1
5.10.5. Complex Rh-1b-DiPP
3
1
Yield: 81%. Yellow solid. ½a D20
ꢁ
¼ þ20:9 (c 1.115, CHCl3). 1H NMR
2
3
2
(d, JC-P = 4.4 Hz), 30.6, 26.8 (d, JC-P = 2.7 Hz), 26.6, 23.4 (d, JC-P
=
(300 MHz; CDCl3): d 8.06 (2H, m), 7.73 (8H, br s), 7.59–7.02 (13H,
6.6 Hz), 21.0, 17.9, 12.8 (d, JC-P = 7.7 Hz). 31P NMR (121.5 MHz;
3
m), 7.53 (4H, br s), 5.54 (1H, m), 5.36 (1H, dt, JH-H = 4.1 Hz, 2JH-H
=
3
1
CDCl3): d 18.1 (d, JP-Rh = 152.9 Hz). MS (ESI+, m/z): 653.1 (11%),
13.4 Hz), 4.12–4.02 (3H, m), 3.64–3.46 (2H, m), 2.72–2.25 (2H, m),
652.1 (49%), 651.1 ([MꢀBArF]+, 100%). MS (ESI-, m/z): 863.3
([BArF]ꢀ). IR (cmꢀ1): 2927, 1611, 1355, 1279, 1129, 887, 839,
743, 715, 670, 518. Elemental Anal. Calcd for C69H57BF24N2PRh:
C, 54.71; H, 3.79; N, 1.85. Found: C, 54.81; H, 3.76; N, 1.77.
Mp = 160–162 °C.
3
2.08–1.65 (7H, m), 1.60–0.82 (5H, m), 1.17 (3H, d, JH-H = 6.8 Hz),
3
3
1.07 (3H, d, JH-H = 6.8 Hz), 1.06 (6H, d, JH-H = 6.8 Hz), 0.89–0.82
(3H, m). 19F NMR (282.4 MHz; CDCl3):
(75.5 MHz; CDCl3): d 177.4 (dd, JC-Rh = 51.6 Hz, JP-C = 12.1 Hz),
161.8 (q, JC-B = 49.8 Hz), 146.2, 144.6, 135.8, 135.6 (d, JC-P
11.5 Hz), 134.9 (br s), 132.4 (d, JC-P = 2.2 Hz), 130.8 (d, JC-P
d
ꢀ62.3. 13C NMR
1
2
1
=
=
=
4
2
8.8 Hz), 130.7, 130.5, 130.0, 129.7–129.0, 129.0 (qq, JC-F
5.10.3. Complex Rh-1c-Mes
3
1
31.3 Hz, JC-B = 2.7 Hz), 126.7 (d, JC-P = 38.4 Hz), 125.1, 124.7 (q,
Yield: 84%. Yellow solid. ½a D20
ꢁ
¼ þ16:2 (c 0.1, CHCl3). 1H NMR
1JC-F = 272.5 Hz), 123.9, 119.8, 117.6, 99.7 (d, JC-Rh = 7.7 Hz), 96.2
1
(300 MHz; CDCl3): d 7.93 (2H, m), 7.72 (8H, br s), 7.58–7.43
2
1
1
(dd, JC-P = 5.5 Hz, JC-Rh = 9.9 Hz), 89.9 (d, JC-Rh = 7.1 Hz), 90.0–
89.7 (m), 48.1 (d, JC-P = 7.7 Hz), 35.5 (d, JC-P = 19.8 Hz), 35.5, 33.2
(d, JC-P = 3.8 Hz), 30.5, 30.3, 28.2, 26.9 (d, JC-P = 2.7 Hz), 26.6,
26.1, 24.6, 23.5 (d, JC-P = 7.7 Hz), 23.3, 21.4, 13.0 (d, JC-P
3
(6H, m), 7.53 (4H, br s), 7.29–7.22 (2H, m), 7.09 (1H, d, JH-H
=
3
1
3
1.9 Hz), 7.03 (1H, d, JH-H = 1.9 Hz), 6.96 (2H, s), 5.60 (1H, dt,
2
3
2
3
3JH-H = 4.3 Hz, JH-H = 13.7 Hz), 5.34 (1H, m), 4.26 (1H, dd, JH-H
=
2
3
=
2
6.4 Hz, JH-H = 14.3 Hz), 4.12 (1H, m), 3.84–3.75 (1H, m), 3.73–
7.7 Hz). 31P NMR (121.5 MHz; CDCl3): d 17.8 (d, JP-Rh = 153.0 Hz).
MS (ESI+, m/z): 695.1 (9%), 694.1 (40%), 693.1 ([MꢀBArF]+, 100%).
MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2973, 1612, 1355,
1278, 1126, 889, 839, 744, 713, 682, 670, 520. Elemental Anal.
Calcd for C72H63BF24N2PRh: C, 55.54; H, 4.08; N, 1.80. Found: C,
54.60; H, 4.19; N, 1.63. Mp = decomposition from 70 °C.
1
3.64 (1H, m), 2.63–1.21 (12H, m), 2.32 (3H, s), 2.03 (3H, s), 1.88
3
3
(3H, s), 0.86 (3H, d, JH-H = 7.0 Hz), 0.29 (3H, d, JH-H = 6.8 Hz).
19F NMR (282.4 MHz; CDCl3): d ꢀ62.3. 13C NMR (75.5 MHz;
1
2
CDCl3): d 174.6 (dd, JC-Rh = 51.6 Hz, JC-P = 13.2 Hz), 161.8 (q,
1JC-B = 49.8 Hz), 140.1, 135.2, 134.9 (br s), 134.8, 134.6, 134.6 (d,
3
3
JC-P = 8.8 Hz), 132.4 (d, JC-P = 9.3 Hz), 132.2 (d, JC-P = 2.2 Hz)
3
130.9 (d, JC-P = 1.6 Hz), 129.7, 129.5, 129.3–129.0, 129.0 (qq,
2JC-F = 31.3 Hz, JC-B = 2.7 Hz), 127.9, 127.5, 124.7 (q, JC-F
=
3
1
5.10.6. Complex Rh-1c-DiPP
Yield: 85%. Yellow solid. ½a D20
ꢁ
¼ þ24:0 (c 1.00, CHCl3). 1H NMR
1
272.7 Hz), 120.2, 117.6 (m), 97.9 (d, JC-Rh = 7.7 Hz), 95.7 (dd,
1JC-Rh = 5.5 Hz, JC-P = 9.3 Hz), 91.0 (d, JC-Rh = 7.1 Hz), 89.8 (dd,
2
1
(300 MHz; CDCl3): d 8.00 (2H, m), 7.73 (8H, br s), 7.59–7.49 (6H,
3
1JC-Rh = 7.7 Hz, JC-P = 14.3 Hz), 48.6 (d, JC-P = 7.7 Hz), 38.9 (d,
2
3
m), 7.53 (4H, br s), 7.47 (1H, t, JH-H = 8.3 Hz), 7.29–7.12 (6H, m),
5.60 (1H, dt, 3JH-H = 3.6 Hz, 2JH-H = 13.7 Hz), 5.41 (1H, m), 4.33–4.20
(2H, m), 4.06–3.93 (1H, m), 3.62–3.52 (1H, m), 3.33–3.25 (1H, m),
2.63–2.52 (1H, m), 2.31–2.12 (2H, m), 2.05–1.00 (11H, m), 1.16
1JC-P = 19.8 Hz), 35.2, 33.1 (d, JC-P = 3.8 Hz), 27.1 (d, JC-P = 2.7 Hz),
2
3
3
3
26.9 (d, JC-P = 6.0 Hz), 26.7, 25.5, 24.8 (d, JC-P = 8.2 Hz),
21.0, 20.7, 18.0, 17.9. 31P NMR (121.5 MHz; CDCl3): d 17.6 (d,

J. Passays et al. / Tetrahedron: Asymmetry 22 (2011) 562–574
573
3
3
(3H, d, JH-H = 6.6 Hz), 1.07 (3H, d, JH-H = 6.8 Hz), 1.02 (3H, d,
References
3JH-H = 6.8 Hz), 0.90 (3H, d, JH-H = 6.8 Hz), 0.86 (3H, d, JH-H = 6.7
3
3
Hz), 0.23 (3H, d, JH-H = 6.8 Hz). 19F NMR (282.4 MHz; CDCl3): d
3
1. For recent reviews see: (a) Perry, M. C.; Burgess, K. Tetrahedron: Asymmetry
2003, 14, 951–961; (b) Herrmann, W. A.; Köcher, C. Angew. Chem., Int. Ed. 1997,
36, 2162–2187; (c) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–
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100, 39–92; (e) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248, 2247–
2273; (f) Nolan, S. P. N-Heterocyclic Carbenes in Synthesis; Wiley-VCH:
Weinheim, Germany, 2006; (g) Glorius, F. N-Heterocyclic Carbenes in
Transition Metal Catalysis; Springer-Verlag: Heidelberg, Germany, 2007; (h)
Normand, A. T.; Cavell, K. J. Eur. J. Inorg. Chem. 2008, 2781–2800; (i) Würtz, S.;
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ꢀ62.3. 13C NMR (75.5 MHz; CDCl3): d 177.7 (dd, JC-Rh = 51.6 Hz,
1
2JP-C = 12.6 Hz), 161.9 (q, 1JC-B = 50.0 Hz), 146.2, 144.7, 135.5, 135.0,
4
134.9 (br s), 132.4 (d, JC-P = 2.2 Hz), 131.2 (d, JC-P = 8.2 Hz), 130.7,
130.5, 130.1, 129.7–129.2, 129.0 (qq, JC-F = 31.8 Hz, JC-B = 2.7 Hz),
127.4 (d, JC-P = 36.2 Hz), 125.1, 124.7 (q, JC-F = 272.7 Hz), 123.9,
2
3
1
1
1
2
119.6, 117.6, 99.4 (d, JC-Rh = 7.7 Hz), 94.9 (dd, JC-P = 5.5 Hz,
1JC-Rh = 9.9 Hz), 91.2 (d, JC-Rh = 7.1 Hz), 88.6 (dd, JC-P = 7.7 Hz,
1
2
1JC-Rh = 15.4 Hz), 48.6 (d, JC-P = 7.1 Hz), 38.3 (d, JC-P = 17.0 Hz),
3
1
2
3
35.4, 33.1 (d, JC-P = 4.4 Hz), 30.1, 28.3, 26.9 (d, JC-P = 2.7 Hz), 26.7
(d, 3JC-P = 7.1 Hz), 26.6, 26.2, 25.4, 25.1 (d, 2JC-P = 8.2 Hz), 24.6, 23.3,
21.1, 18.1. 31P NMR (121.5 MHz; CDCl3): d 17.5 (d, 1JP-Rh = 150.0 Hz).
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+
, 100%).
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MS (ESI-, m/z): 863.3 ([BArF]ꢀ). IR (cmꢀ1): 2975, 1611, 1356, 1279,
1126, 887, 840, 744, 713, 682, 670, 512. Elemental Anal. Calcd for
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4.02; N, 1.77. Mp = decomposition from 70 °C.
5.11. General procedure for asymmetric hydrogenation
experiments
The substrate, metal complex and dry, degassed dichlorometh-
ane were introduced in a 100-mL autoclave with a glass insert and
a magnetic stirrer bar. The charged autoclave was purged three
times with 5 bar of H2 and then pressurized to 20–50 bar of hydro-
gen. After stirring for the indicated time (see Tables) at the appro-
priate temperature, the reaction vessel was vented (if necessary, it
was cooled to room temperature before venting). Reaction times
were not optimized. After evaporation of the solvents, conversions
and ee’s were determined by, respectively,1H NMR and HPLC or GC
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0.45 lm, GRACE), (an addition of iPrOH to the sample was neces-
sary to improve solubility without disturbing the retention times)
and the filtrate was directly analyzed by chiral HPLC to determine
the ee.
HPLC analysis: 2-methylsuccinic acid dimethyl ester 9: Chiral-
cel OD-H column, 215 nm, 20 °C, 1.0 mL minꢀ1, n-heptane/iso-pro-
panol, 96:4, retention times (in min) = 7.1 (R), 10.5 (starting
material), 11.3 (S).8d 2-(4-Methoxyphenyl)butane 11: Daicel Chi-
ralcel OD-H column, 254 nm, 20 °C, 0.5 mL minꢀ1, n-heptane/iso-
propanol, 99.99:0.01, retention times (in min) = 12 (S), 13 (R).8d
1,2-Diphenylpropane 13: Chiralcel OJ-H column, 220 nm, 20 °C,
1.0 mL minꢀ1, n-heptane/iso-propanol, 99:1, retention times (in
min) = 8 (R), 14 (S), 16 (starting material).8d N-Acetylphenylalanine
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methyl ester 16: Chiral ADH column, 220 nm, 20 °C, 1.0 mL minꢀ1
,
n-heptane/iso-propanol, 90:10, retention times (in min) = 10.0 (R),
13.9 (S).8d GC analysis: Alanine methyl ester 17: chiral b-cyclodex-
trine 25 m ꢂ 0.25 mm, 0.25
lm coated, isotherm 100 °C, gas carrier
1 mL mnꢀ1, retention times (in min): 17 (starting material), 24 (S),
25 (R).22
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Acknowledgements
This work is part of the CRUNCH program (grant to J.P.), and we
thank the Conseil Régional de Haute-Normandie for their financial
support.

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