Synthesis of chiral imino- and amino-imidazolium salts and of chelating amino-N-heterocyclic carbene palladium(II) complexes

Article abstract of DOI:10.1016/j.jorganchem.2006.04.038

A new preparation of chiral imino-imidazolium salts has been developed by condensation of chiral primary amines with 1-(2-oxo-2-phenyl-ethyl)-imidazolium salts in chloroform. This reaction gave the (E)-imino-imidazolium salts with stereoselectivities superior to 95:5. The structure of the imines were determined by NMR analyses. Reduction of the chiral (E)-imino-imidazolium salts with NaBH₄ in MeOH led to amino-imidazolium salts as a mixture of diastereomers with selectivities ranging from 84:16 to 90:10. The major diastereoisomer could be purified in some cases by crystallization and the absolute configurations were determined by X-ray diffraction. Chelating amino-N-heterocyclic carbene dichloro palladium(II) complexes were obtained in two steps via formation of the corresponding silver(I) complexes and reaction of these latters with bis(acetonitrile)dichloropalladium. Crystal structure details of a cis-dichloro amino-imidazol-2-ylidene palladium complex are presented and confirmed the formation of a six-membered Pd-metallocycle.

Full text of DOI:10.1016/j.jorganchem.2006.04.038

Journal of Organometallic Chemistry 691 (2006) 3498–3508
www.elsevier.com/locate/jorganchem
Synthesis of chiral imino- and amino-imidazolium salts and of
chelating amino-N-heterocyclic carbene palladium(II) complexes
a
b
a,
a
Alexandre Flahaut , Jean-Pierre Baltaze , Sylvain Roland *, Pierre Mangeney
a
Universite´ Pierre et Marie Curie-Paris 6, Laboratoire de Chimie Organique, UMR 7611, Institut de chimie mole´culaire (FR 2769), 4, place Jussieu,
tr. 44-45 2e`me e´t., 75252, Paris Cedex 05, France
b
Universite´ Paris-Sud, Laboratoire de Chimie, Structurale Organique, I.C.M.M.O. UMR 8182, 91405 Orsay Cedex, France
Received 4 April 2006; accepted 28 April 2006
Available online 13 May 2006
Abstract
A new preparation of chiral imino-imidazolium salts has been developed by condensation of chiral primary amines with 1-(2-oxo-2-
phenyl-ethyl)-imidazolium salts in chloroform. This reaction gave the (E)-imino-imidazolium salts with stereoselectivities superior to
95:5. The structure of the imines were determined by NMR analyses. Reduction of the chiral (E)-imino-imidazolium salts with NaBH4
in MeOH led to amino-imidazolium salts as a mixture of diastereomers with selectivities ranging from 84:16 to 90:10. The major diaste-
reoisomer could be purified in some cases by crystallization and the absolute configurations were determined by X-ray diffraction. Che-
lating amino-N-heterocyclic carbene dichloro palladium(II) complexes were obtained in two steps via formation of the corresponding
silver(I) complexes and reaction of these latters with bis(acetonitrile)dichloropalladium. Crystal structure details of a cis-dichloro
amino-imidazol-2-ylidene palladium complex are presented and confirmed the formation of a six-membered Pd-metallocycle.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Chiral imino- and amino-imidazolium salts; Chelating amino-N-heterocyclic carbenes; Palladium(II)-metallocycles
1. Introduction
ligands [9–16]. Such ligands gave good results particularly
in the iridium catalyzed hydrogenation of alkenes
[10,11,14] and the rhodium catalyzed hydrosilylation of
ketones [13]. The best enantioselectivities in palladium cat-
alyzed reactions were also obtained using heteroditopic
NHC–imino palladium(II) complexes, reported in 2003
by Douthwaite [17]. These complexes led to ee up to 92%
in the asymmetric allylic alkylation reaction.
Several other achiral or chiral racemic palladium(II)
complexes with chelating NHC–N ligands have been
reported, including NHC–pyridyl [18–23], NHC–amino
[23,24], NHC–amido [24], NHC–imino [25–28] and
NHC–enamino complexes [29].
We wish to report here a straightforward synthesis of
chiral imino-imidazolium salts from 1-(2-oxo-ethyl)-imi-
dazolium salts. The diastereoselective reduction of the chi-
ral imines afforded amino-imidazoliums salts. The
synthesis of chelating NHC–amino Pd(II) complexes from
these azoliums as well as the structure of one of these com-
plexes are presented.
N-heterocyclic carbenes (NHC) have emerged as an
important family of ligands with strong r-donor electronic
properties and have now been used in a wide range of cat-
alytic reactions [1–4].
Lappert and coworkers were the first to report in 1983,
the synthesis of chiral Rh(I) and Co(I) imidazolinylidene
complexes [5]. In the last 10 years, many efforts have been
made to synthesize novel chiral NHC ligands and their cor-
responding metal complexes. Some of these complexes
have been tested in asymmetric catalysis and excellent
levels of enantioselectivity could be reached (up to >99%)
[6–8]. Among these chiral ligands, some heteroditopic
NHC–N ligands were reported. Several research groups
have described the synthesis and use of NHC–oxazoline
*
Corresponding author. Tel.: +33 1 44275567; fax: +33 1 44277567.
E-mail address: sroland@ccr.jussieu.fr (S. Roland).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.04.038

A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
3499
X–
Ph
Table 1
X–
X–
+
Br–
R1
Ph
Formation of imino-imidazolium salts
+
+
N
N
N
N
N
R
N
N
R1
X
Yield (%)
R
Imine
R
Ar
R1
N
N
+
N
Ar
N
O
9
10
11
12
13
14
15
Mes
Ph
Me
Me
Me
Me
Et
Cl
Cl
Cl
Cl
Cl
Cl
Br
87
70
92
70
78
88
76
R2
R2
i-Pr
1
2
3
4
Mes
p-Cl-C6H4
2,6-(i-Pr)2C6H3
2,6-(i-Pr)2C6H3
2,6-(i-Pr)2C6H3
t-Bu
Ph
p-Cl-C6H4
Fig. 1. Imino-imidazolium salts.
Ph
Ph
Ph
Me
Me
2. Results and discussion
2.1. Synthesis of chiral imino-imidazolium salts
t-Bu
tion of CHCl3 under prolonged heating. This chlorhydrate
could not be separated from the imidazolium salts after
precipitation. Thus, the reaction solution must be carefully
neutralized by stirring with solid NaHCO3 for 1 h before
precipitation and washing of the salts.
Several imino-imidazolium salts have been reported in
the literature (Fig. 1). Chiral salts 1 were obtained by Dou-
thwaite by reaction of the corresponding primary amine
with an excess of aldehyde (R1 = H) or with acetone
(R1 = R2 = Me) in the presence of MgSO4 or molecular
sieves [17]. For the synthesis of imino-imidazolium salts 2,
the condensation of a-chloroimines with monosubtituted
imidazoles was found to be an efficient procedure [25,29].
Alternatively, imidazoliums of type 2 were obtained by con-
densation of 1-(2-oxo-ethyl)-imidazoles with amines fol-
lowed by alkylation of the imidazole with methyl
trifluoromethanesulfonate to form the azolium [30]. The
direct condensation of 1-(2-oxo-ethyl)-imidazolium 3 with
amines was reported to give undesired decomposition reac-
tions [25]. Imidazolium salts 4 were prepared by reaction of
iminoyl chlorides with imidazoles [26,27,31,32].
Looking for a straightforward method to synthesize var-
ious chiral imino-imidazolium salts, we first tested the con-
densation of 1-(2-oxo-ethyl)-imidazolium salt 5 with chiral
amines in benzene or toluene. This reaction gave poor or
no conversion, one of the main problem being the low sol-
ubility of 5 in these apolar solvents, even at high tempera-
ture. These solvents are generally necessary to remove the
water formed by azeotropic distillation and to displace
the equilibrium. Looking for a solvent capable of forming
an azeotrope with water and in which the salts 5–8 are sol-
uble, we found that chloroform could be appropriate [33].
The reaction of salts 5–8 with 3 equivalents of a chiral
amine in CHCl3 for 60 h at 90 °C effectively afforded
cleanly the corresponding imino-imidazolium salts 9–15
in 70–92% yields after precipitation (Scheme 1 and Table 1).
The excess of amine is removed by washing the salt with
Et2O or THF. The main impurity formed in the reaction
is the chlorhydrate of the starting amine and is probably
due to the generation of hydrochloric acid by decomposi-
1
The H NMR of these imino-salts showed the presence
of one isomer highly predominant (>95:5). Only traces of
the minor isomer could be detected in some spectra. The
stereochemistry of the major isomer was determined by
nOe experiments on 10, after determination of 1H and
13C assignments using COSY, HMBC and HMQC experi-
ments and was found to be (E) according to the CIP rules
(Fig. 2). The phenyl group of the imine and the alkyl group
on the nitrogen atom are in a cis position. Such a geometry
may be highly favoured by a strong intramolecular hydro-
gen bond between the nitrogen of the imine and the acidic
hydrogen of the azolium salt. The same type of favoured
geometry was reported by Palmieri and coworkers for the
imine 16 [34].
Surprisingly, prolonging standing of the salts 10 and 12
(R1 = p-ClC6H4) in CDCl3 (NMR tube, 16 h) led to 80%
(R = Mes) and 66% (R = 2,6-iPrC6H3) deuteration of the
imine a-methylene position and of the N–CH@N acidic
position of the imidazolium ring (Scheme 2). These deuter-
ations show that an imine–enamine equilibrium occurs but
also that a free carbene may be generated during the pro-
cess. Stirring the imino-imidazolium salt 10 with 5 equiva-
lent of K2CO3 in CDCl3 led to incorporation of 97–98%
Cl–
R1
+
N
H
R
N
N
N
H
X–
Mes
H
Ph
N
O
R2
Ph
N
(E)
H3C
N
Ph
H
H
+
(E)
(E)
Cl
16
9-15
Observed n.O.e for 10
Fig. 2. Favoured structure of imino-imidazolium salts.
X–
X–
+
Ar
+
CHCl3, 90 ˚C, 60 h
70-92%
N
N
N
N
R
+
H2N
R
R1
Db
N
Cl–
Cl–
Ha
N
Da
+
Hb
N
Ph
Ph
Ar
O
N
Ph
Ph
(3 equiv.)
N
CDCl3 (K2CO3)
CHCl3 (K2CO3)
R1
5 : R = Mes, X = Cl
Ar
Ar
N
Mes
N
Mes
Dc
Hc
10
6 : R = 2,6-(i-Pr)2C6H3, X = Cl
7 : R = t-Bu, X = Cl
9-15
8 : R = t-Bu, X = Br
(E) / (Z) > 95 : 5
Scheme 1.
Scheme 2.

3500
A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
deuterium in the three positions after 7 h. Each deuterium
(Da, Db, Dc) is incorporated within nearly the same rate
during the reaction. Thus, deuteration of imine a-position
is two times faster than deuteration of the azolium ring.
The reaction is reversible: the protonation of the D3-salt
by CHCl3 in the presence of K2CO3 was also effective
but slower than the initial deuteration (50–60% hydrogen
incorporation after 7 h).
amino-imidazolium salts 17 and 19 were obtained respec-
tively in 36% and 46% yield without detectable trace of
the minor isomer. Crystals of 18 suitable for X-ray analysis
were grown by the same method. The molecular structure
of this salt allowed us to assign the (S,S) configuration to
the major diastereomer. The stereochemical outcome of
this reduction is in accordance with the model proposed
for the reduction of chiral imines resulting from the con-
densation of acetophenone with a-methylbenzylamine [35]
(Scheme 4).
2.2. Synthesis of chiral amino-imidazolium salts
The reduction of the imino salts using NaBH4 in MeOH
gave the corresponding amino-imidazolium salts 17–20 in
65–99% yield and with d.r. ranging from 84:16 to 90:10
(Scheme 3 and Table 2). The addition of NaBH4 was per-
formed at ꢀ70 °C and the mixture was allowed to warm to
ambient temperature. No significant change in the diastere-
oselectivity was observed when the addition is performed at
0 °C but the procedure at ꢀ70 °C led to cleaner crude prod-
ucts and enhanced yields. Surprisingly, the same reaction
performed in EtOH led only to degradation products.
The use of sodium borohydride in the reduction of chiral
imines resulting from the condensation of acetophenone
with a-methylbenzylamine or similar chiral amines was
already reported [35]. However, the most frequently used
method is the hydrogenation catalyzed by Pd/C [36–38].
Our attempts to reduce the imino-imidazolium salt by this
procedure led to amino-imidazolium salts with low d.r. in
the presence of several by-products. No improvement of
the diastereoselectivity was obtained by using zinc borohy-
dride that was reported to give better results than the
NaBH4/MeOH system in the reduction of similar enantio-
pure imines [34].
2.3. Synthesis of amino-NHC palladium(II) complexes
Palladium(II) complexes with achiral tridentate amino-
NHC-amino ligands were reported by Cavell and cowor-
kers in 2001 [23]. Douthwaite also described in 2004 the
synthesis of a Pd(II) complex with an achiral tridentate
chelating NHC-amino-NHC ligand [24]. In these two cases,
the complexes were prepared from the azolium salt by prior
formation of the silver(I) complex, then transfer of the car-
bene ligand to the precursor palladium complex. Ag(I)
complexes bearing bidentate amino-NHC ligands were also
reported by Arnold [39]. These complexes were obtained by
treatment of the azolium salt with Ag2O. Tridentate
amino-NHC-amino ligands could also be generated by
deprotonation of the imidazolium salt with KHMDS
[40]. The use of Ag2O to generate silver NHC complexes,
initially reported by Lin and co-workers [41], and the trans-
fer of the NHC ligands from silver to a transition metal is
one of the widely used method to form NHC complexes [1–
4,6–8,42,43].
The amino-NHC silver complexes 21 and 22 were
obtained respectively in 73% and 80% yield by treatment
of the corresponding azolium salts 17 and 19 with 0.55
equivalent of Ag2O in CH2Cl2 at 20 °C for 16 h (Scheme 5).
The reaction was performed with exclusion of light. The
carbene carbon was not detectable in the 13C NMR spec-
trum of complex 21, but appeared as a doublet of doublet
at 181 ppm in complex 22 with two coupling constants of
272 Hz (J1 109Ag–13C) and 236 Hz (J1 107Ag–13C).
Dichloro palladium(II) complexes 23 and 24 were obtained
by stirring a solution of the silver complexes in CH2Cl2
with 1 equivalent of bis(acetonitrile)dichloropalladium for
1 h. The complexes 23 and 24 were respectively isolated
in 50% and 53% yield after filtration of the silver salts, con-
centration, dissolution of the crude in CHCl3 or CH2Cl2
and precipitation with Et2O.
The separation of the major diastereomer could be
performed by several crystallisations in a mixture of dichlo-
romethane, acetone and ether. By this procedure, the
Cl–
Cl–
+
+
N
N
N
N
R
R
NaBH4, MeOH
major
(S,S)
Ph
Ar
Ph
N
–70 to 20 ˚C, 16 h
HN
R1
(S)
Ar
R1
17-20
Scheme 3.
Table 2
NaBH4 reduction of imino-imidazolium salts
Amine
R
Ar
R1
Yield (%)
drb
Cl–
Cl–
H–
+
+
91 (36a)
87
99 (46a)
65
90:10 (>98:2c)
86:14
85:15 (>98:2c)
85:15
N
N
N
N
17
18
19
20
a
Mes
Ph
Ph
Ph
Ph
Me
Me
Et
R
R
favoured
2,6-(i-Pr)2C6H3
2,6-(i-Pr)2C6H3
t-Bu
(S,S)
Ph
Ph
Ar
(Z)
Ar
N
HN
R1
Me
H
Yield of pure major diastereomer isolated by crystallisation.
Ratio determined by 1H NMR (400 MHz).
R1
b
c
Diastereomeric excess after recrystallisation.
Scheme 4.

A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
3501
Cl–
+
N
N
N
N
N
N
PdCl2(CH3CN)2
CH2Cl2, 20 ˚C
Ag2O (0.55 equiv)
CH2Cl2, 20 ˚C
R
R
R
Ph
Ph
Ph
Ph
Ag
Cl Pd
Cl
NH
NH
HN
R1
Cl
Ph
R1
Ph
R1
21: R = Mes, R1 = Me (73%)
22: R = 2,6-(i-Pr)2C6H3, R1 = Et (80%)
23: R = Mes, R1 = Me (50%)
24: R = 2,6-(i-Pr)2C6H3, R1 = Et (53 %)
Scheme 5.
Fig. 3. Molecular structure of palladium complex 23. Hydrogen atoms are omitted for clarity.
Yellow single crystals suitable for X-ray analysis were
obtained by cooling at 4 °C a concentrated solution of
the crude complex 23 in CHCl3. The complex crystallises
together with three molecules of CHCl3. The structure of
23 is presented in Fig. 3. The crystallographic data are
shown in Table 3. Selected bond lengths and angles are
given in Table 4.
2.5. Synthesis of imino-NHC complexes
Since we have developed a method to synthesize various
chiral imino-imidazolium salts, it was also of interest to
acceed to the corresponding imino-NHC complexes. Sev-
eral metal complexes (Pd, Pt, Rh, Ni) with non enolisable
imino-NHC ligands have been reported [17,26,28,32,44].
Such complexes could be synthesized either from the corre-
sponding silver complex or from the free carbene obtained
by treatment of the imidazolium salt with an appropriate
base [28,44]. Most of these complexes were obtained from
iminoylimidazolium salts 4 (Fig. 1) [26,28,32] or from aro-
matic aldimines [44]. By contrast, complexes with enolisa-
ble imino-NHC ligands, derived from azolium salts of
type 2 (Fig. 1), could not be synthesized through the free
carbene. Several of these complexes have been obtained
by prior formation of the silver complex [23,26].
Treatment of the imino-imidazolium salt 9 with Ag2O in
CH2Cl2 afforded the silver complex 25 in 80% yield. The IR
spectrum of 25 shows a mC@N absorption at 1647 cmꢀ1
which is essentially unchanged compared to that seen for
the corresponding imidazolium salt 9 (1657 cmꢀ1). This
suggests, as already observed [23], that the imino-NHC is
bonded in a monodentate fashion to silver through the
carbene carbon. Unfortunately, reaction of 25 with
PdCl2(CH3CN)2 in CH2Cl2 at 20 °C led to untractable
reaction mixtures and no improvement was observed at
lower temperatures.
This structure confirmed the formation of a cis-dichloro
palladium(II) complex with a chelating amino-NHC
ligand, the six-membered Pd-metallocycle having a boat-
like conformation. It also showed a distorted square–
planar coordination around the palladium center. The
˚
palladium–carbene bond length is of about 1.975 A. The
Pd–Cl bond length trans to the NHC ligand is longer than
the Pd–Cl bond trans to the amine due to the strongly r-
donating effect of the carbene. The structure of this com-
plex is more or less similar to the one of a six-membered
chelating imino–NHC palladium(II) complex reported by
Douthwaite and co-workers in 2003 [17].
2.4. Catalysis – Allylic alkylation with a chelating amino-
NHC ligand
The potential application of these chelating chiral
ligands was tested on the asymmetric allylic alkylation of
(E)-1,3-diphenylprop-3-en-yl acetate with dimethyl malon-
ate (Scheme 6). A test reaction was performed at 20 °C
using 7 mol. % of silver complex 21 and 3 mol. % of [Pd(al-
lyl)Cl]2. After 16 h at 20 °C, the product was isolated in
41% yield and 60% ee. The conditions were not optimised.
Direct reactions of imidazolium salts with basic transi-
tion metal salts were also frequently used to generate

3502
A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
Table 3
NHC complexes [1–4,6–8]. Reaction of imino-imidazolium
Crystallographic data for compound 23
salt 13 with Pd(OAc)2 in refluxing THF led after work-up
1
Compound
23
to a brown solid. The H NMR spectrum of this solid in
CDCl3 was unexploitable. The same reaction performed
at 20 °C in the presence of bases also led to the same result.
We observed then that the treatment of salts 9–14 with 1
equivalent of Pd(OAc)2 and 4 equivalent of LiCl in THF
at 0 °C led in 87–100% yield to new complexes from which
Formula
Fw
C31H34Cl11N3Pd
945.01
Crystal system
Orthorhombic
10.6921 (15)
˚
a (A)
˚
b (A)
16.4551 (18)
˚
c (A)
23.849 (3)
90
1
structure could not be exactly determined. The H NMR
a (°)
b (°)
c (°)
90
spectra of these complexes are well defined and show that
the diastereotopic methylene protons are shifted to low-
field compared to those of the corresponding salts. For
example, signals corresponding to the methylene protons
of 14 (two doublets at 5.77 and 5.94 ppm) are shifted to
7.79 and 7.88 ppm in the complex. Moreover, the IR spec-
trum shows a mC@N absorption at 1628 cmꢀ1 instead of
1663 cmꢀ1 for the imidazolium salt 14. This suggests that
an imino-Pd complex is formed. However, for most of
90
3
˚
V (A )
1495.9 (8)
4
Z
Space group
Crystal shape
Crystal colour
Linear absorption coefficient l (cmꢀ1
Density q (g cm3)
P212121
Parallelepiped
Yellow
11.68
)
1.50
Diffractometer
KAPPACCD-Enraf Nonius
˚
Radiation
Temperature (K)
Mo Ka (k = 0.71073 A)
250
1
these complexes, the H NMR spectra still showed three
h Limits (°)
Octants collected
Number of data collected
Number of unique data collected
Number of unique data used for refinement 7327(Fo)2 > 3r(Fo)2
2–30
singlet resonance that integrate each for one hydrogen
and may fit with the three protons of the imidazolium ring.
Treatment of these complexes with NEt3 in THF led to the
starting imidazolium salts. These observations suggested
that these complexes are probably imino-imidazolium
PdCl2 complexes and not imino-NHC complexes. The
enamine form, observed by Coleman and co-workers after
reaction of an imino-NHC silver complex with
PdCl(CH3CN)2 [26], was not detected. 13C NMR spectra
could not be obtained with acceptable resolution since
the complexes are poorly stable in solution. Mass spectros-
copy analyses confirmed the formation of palladium com-
plexes but did not allowed us to make a distinction
between an azolium salt and a free carbene. Finally, reac-
tion of these palladium complexes with t-BuOK in THF
also led to degradation products and not to the expected
imino-NHC complexes or enamino-NHC complexes. All
these observations and the results of the deuteration exper-
iments showed in Scheme 2, underline that in the case of
enolisable imino-imidazoliums salts 9–15, the methylene
protons are more acidic than the N–CH@N proton of
the imidazolium ring. A similar observation was reported
by Bilstein after unsuccessful attempts to generate NHC
from 2-imino-2-phenyl ethyl imidazolium salts of type 2
(Fig. 1, R1 = Ph) [30] (see Scheme 7).
ꢀ14, 15; ꢀ23, 22; ꢀ33, 22
27,539
11,724
Merging R
0.032
0.0684
0.0706
SADABS
None
1.075
357
P
P
R = jjFoj ꢀ jFcjj/ jFoj
P
P
2 1/2
]
Rwa = [ w(jjFoj ꢀ jFc jj)2/ wFo
Absorption correction
Secondary extinction coefficient
Goodness of fit
Nb of variables
3
˚
Dqmin (e/A )
ꢀ2.24
2.61
3
˚
Dqmax (e/A )
a
Weighting scheme of the form w = w0[1 ꢀ ((jj Foj ꢀ jFcjj)/6r(Fo))2]2
with w0 = 1/RrArTr(X) with coefficients 1.10, ꢀ1.53, 0.0762, ꢀ0.770 and
ꢀ0.481 for a Chebyshev serie for which X = Fc/Fc(max).
Table 4
˚
Selected bond lengths (A) and angles (°) for 23
Compound
23
Bond lengths
Pd(1)–Cl(1)
Pd(1)–Cl(2)
Pd(1)–C(5)
Pd(1)–N(3)
C(5)–N(1)
C(5)–N(2)
C(3)–N(1)
C(4)–N(2)
C(4)–C(3)
2.3690(18)
2.3008(17)
1.975(5)
2.117(5)
1.349(7)
1.365(8)
1.369(8)
1.407(8)
1.332(11)
3. Conclusion
Bond angles
We have developed an efficient procedure for the synthe-
sis of a new class of chiral imino-imidazolium salts. The
diastereoselective reduction of these compounds led to
amino-imidazolium salts. Pure diastereomers could be
obtained by recrystallisation. New chiral amino–NHC sil-
ver(I) and palladium(II) complexes were synthesized from
these azoliums. The preparation of a range of chiral ligands
can be envisaged by this methodology. Amino–NHC
ligands can be used in asymmetric allylic alkylation reac-
tion. Currently, moderate results were obtained in this
C(5)–Pd(1)–N(3)
Cl(1)–Pd(1)–Cl(2)
C(5)–Pd(1)–Cl(2)
N(3)–Pd(1)–Cl(1)
N(3)–Pd(1)–Cl(2)
C(5)–Pd(1)–Cl(1)
Pd(1)–N(3)–C(1)
Pd(1)–C(5)–N(1)
Pd(1)–C(5)–N(2)
Pd(1)–N(3)–C(15)
C(1)–N(3)–C(15)
88.7(2)
91.88(7)
92.75(17)
86.82(15)
178.35(15)
169.23(19)
117.5(4)
118.2(4)
136.5(4)
110.7(4)
111.0(5)

A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
3503
[Pd(allyl)Cl]2, 3 mol. %
NHC–AgCl 21, 7 mol. %
MeO2C
Ph
CO2Me
Ph
N
N
OAc
Ph
Mes
Ph
Ag
dimethyl malonate (3 equiv.)
NaH (2.7 equiv.), THF, 20 ˚C
Ph
NH
Cl
41%, ee 60% (R)
Ph
21
Me
Scheme 6.
Cl–
+
N
Ag
N
N
N
Mes
Mes
PdCl2(CH3CN)2
CH2Cl2, 20 ˚C
Ag2O (0.6 equiv)
CH2Cl2, 20 ˚C
80%
Degradation
Ph
Ph
Ph
Ph
N
N
Cl
9
25
Scheme 7.
reaction with the ligand tested. The optimisation of this
reaction and the use of these chelating chiral amino–
NHC ligands in other reactions in asymmetric catalysis
are under investigation.
1H, J = 8 Hz), 7.74 (t, 1H, J = 1.5 Hz), 8.19 (d, 2H,
J = 8 Hz), 10.40 (s, 1H, N–CH@N). 13C NMR
(100 MHz, CDCl3) d 17.5, 21.1, 56.1 (CH2), 122.1, 125.1,
128.6, 129.0, 129.7, 130.7, 133.7, 134.3, 134.4, 139.1 (N–
CH@N), 141.2, 191.2 (C@O). Anal. Calc. for
C20H21ClN2O (MW = 340.85) C, 70.48; H, 6.21; N, 8.22.
Found: C, 70.29; H, 6.26; N, 8.21%. IR (ATR diamond)
4. Experimental
All experiments were performed under argon using stan-
dard Schlenk techniques unless stated otherwise. Solvents
were dried over the appropriate drying agent and distilled
under dinitrogen. Sodium benzophenone ketyl (THF,
Et2O), CaH2 (CH2Cl2). EtOH, MeOH and CHCl3 of ana-
lytical grade type were used without special drying or dis-
tillation. All reagents were purchased from Acros or
Aldrich and used as received unless otherwise stated.
1-Mesitylimidazole and 1-(2,6-i-Pr2C6H3)-imidazole were
prepared according to Zhang [45]. In the case of 1-mesity-
limidazole, the purification by chromatography described
was replaced by several recrystallisations in cyclohexane
to give the pure product in 35% yield. 1-(2,6-i-Pr2C6H3)-
Imidazole can also be recrystallised in n-pentane. 1-
tert-Butyl-imidazole was prepared according to Gridnev
[46]. Microanalyses were performed by the microanalytical
service ICSN (CNRS). NMR spectra were recorded on a
Bruker ARX 400 or AC 200 Q instrument, in CDCl3,
CD2Cl2 or CD3OD as the solvent. Optical rotations were
measured on a Perkin–Elmer 343.
mC@O 1703 cmꢀ1
.
4.1.2. 3-(2,6-Diisopropylphenyl)-1-(2-oxo-2-phenyl)ethyl
imidazolium chloride (6)
A
solution of 1-(2,6-diisopropylphenyl)imidazole
(4.43 g, 19.4 mmol) and 2-chloroacetophenone (8.96 g,
58.2 mmol) in dry THF (20 mL) was stirred for 6 h at
reflux. After cooling, Et2O was added and the precipitate
formed was filtered, washed with Et2O and dried to give
6.4 g (94%) of a white solid. M.p. 98 °C. 1H NMR
(400 MHz, CDCl3) d 1.12 (d, 6H, J = 6.6 Hz), 1.19 (d,
6H, J = 6.6 Hz), 2.34 (m, 2H, J = 6.6 Hz), 6.77 (s, 2H,
CH2C@O), 7.14 (s, 1H), 7.26 (d, 2H, J = 8 Hz), 7.45–
7.51 (m, 3H), 7.58 (t, 1H, J = 7.5 Hz), 7.85 (d, 1H,
J = 8.3 Hz), 8.11 (d, 2H, J = 7.5 Hz), 10.20 (s, 1H, N–
CH@N). 13C NMR (100 MHz, CDCl3) d 24.3, 28.7,
56.1 (CH2), 123.2, 124.7, 128.8, 129.2, 130.1, 132.0,
133.5, 134.8, 139.8 (N–CH@N), 145.53, 191.0 (C@O).
Exact MS (ESI+ in MeOH sens = 1.00e8) m/e = 348.26
for C23H27N2O (M+–Cl). IR (ATR diamond) mC@O
1696 cmꢀ1
.
4.1. Preparation of 1-(2-oxo-2-phenyl)ethyl imidazolium
salts
4.1.3. 3-tert-Butyl-1-(2-oxo-2-phenyl)ethyl imidazolium
chloride (7)
4.1.1. 3-Mesityl-1-(2-oxo-2-phenyl)ethyl imidazolium
chloride (5)
A solution of 1-tert-butylimidazole (2 g, 16.1 mmol) and
2-chloroacetophenone (2.97 g, 19.2 mmol) in dry THF
(18 mL) was stirred for 16 h at 20 °C then heated at reflux
for 2 h. After cooling, the precipitate formed was filtered,
washed with Et2O and dried to give 4.46 g (99%) of a white
A solution of 1-mesitylimidazole (3 g, 16.1 mmol) and
2-chloroacetophenone (2.98 g, 19.3 mmol) in dry THF
(20 mL) was stirred for 16 h at 20 °C then heated at reflux
for 3 h. After cooling, the precipitate formed was filtered,
washed with Et2O and dried to give 3.39 g (62%) of an
1
solid. M.p. 250 °C. H NMR (400 MHz, CDCl3) d 1.76 (s,
9H), 6.49 (s, 2H, CH2C@O), 7.35 (s, 1H), 7.43 (s, 1H), 7.57
(dd, 2H, J = 8.1 and 7.3 Hz), 7.69 (t, 1H, J = 7.3 Hz), 8.15
(d, 2H, J = 8.1 Hz), 11,03 (s, 1H, N–CH@N). 13C NMR
(100 MHz, CD3OD, the salt is little soluble in CDCl3) d
1
off white solid. M.p. 207 °C. H NMR (400 MHz, CDCl3)
d 2.15 (s, 6H), 2.38 (s, 3H), 6.82 (s, 2H, CH2C@O), 7.05 (s,
2H), 7.21 (t, 1H, J 1.5 Hz), 7.57 (t, 2H, J = 8 Hz), 7.67 (t,

3504
A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
30.7, 57.4 (CH2), 62.3, 121.8, 126.5, 130.2, 131.0, 136.0,
136.5, 138.0 (N–CH@N), 193.1 (C@O). Anal. Calc. for
C15H19ClN2O (MW = 278.78) C, 64.63; H, 6.87; N, 10.05.
Found: C, 64.31; H, 7.17; N, 9.83%. IR (ATR diamond)
128.8, 129.5, 129.6, 131.1, 134.2, 134.6, 139.6 (N–C@N),
141.0, 141.6, 145.3, 162.2 (CH2C@N). Exact MS (ESI+
in MeOH sens = 4.10e6): m/e = 408.23 for C28H30N3
(M+–Cl). IR (ATR diamond) mC@N 1657 cmꢀ1
.
mC@O 1694 cmꢀ1
.
4.2.2. 3-Mesityl-1-[2-{(S)-1-(p-chlorophenyl)ethylimino}-
2- phenyl ethyl] imidazolium chloride (10)
4.1.4. 3-tert-Butyl-1-(2-oxo-2-phenyl)ethyl imidazolium
bromide (8)
20
Yield 70%, off white solid. M.p. 121 °C. ½aꢁD ¼ ꢀ24 (c
1
A solution of 1-tert-butylimidazole (1.68 g, 13.5 mmol)
and 2-bromoacetophenone (2.67 g, 13.5 mmol) in dry
THF (15 mL) was stirred for 16 h at 20 °C. The precipitate
formed was filtered, washed with Et2O and dried to give
4.06 g (93%) of a white solid. M.p. 225 °C. 1H NMR
(400 MHz, CDCl3) d 1.80 (s, 9H), 6.22 (s, 2H, CH2C@O),
7.43 (s, 2H), 7.60 (t, 2H, J = 8 Hz), 7.72 (t, 1H, J = 8 Hz),
8.13 (d, 2H, J = 8 Hz), 9,61 (s, 1H, N–CH@N). 13C NMR
(100 MHz, CD3OD, the salt is little soluble in CDCl3) d
30.7, 57.5 (CH2), 62.3, 121.8, 126.5, 130.2, 131.0, 136.0,
136.5, 137.9 (N–CH@N), 193.0 (C@O). Anal. Calc. for
C15H19BrN2O (MW = 323.23) C, 55.74; H, 5.92; N, 8.67.
Found: C, 55.56; H, 6.01; N, 8.53%. IR (ATR diamond)
1.2, CHCl3). H NMR (400 MHz, CDCl3) d 1.24 (d, 3H,
J = 6.3 Hz), 1.98 (s, 3H), 2.07 (s, 3H), 2.35 (s, 3H), 4.56
(q, 1H, J = 6.3 Hz), 5.72 (d, 1H, J = 17.3 Hz, CHH–
C@N), 6.27 (d, 1H, J = 17.3 Hz, CHH–C@N), 6.99 (s,
2H), 7.07 (d, 2H, J = 8.5 Hz, meta position of the chloride
in C6H4Cl), 7.12 (s, 1H, CH@CH), 7.23 (d, 2H, J = 8.5 Hz,
ortho position of the chloride in C6H4Cl), 7.40–7.53 (m,
5H), 7.70 (s, 1H, CH@CH), 10.49 (s, 1H, N–CH@N).
13C NMR (100 MHz, CD2Cl2) d 17.6, 17.7, 25.0, 56.3
(CH2), 59.9 (CH3–CH–N), 122.4 (Mes-N-CH@CH),
125.0 (CH@CH–N–CH2), 127.7, 128.1, 128.8, 129.2,
130.0, 131.4, 132.5, 134.5, 134.9, 140.2 (N–C@N), 141.5,
144.2, 163.2 (CH2C@N). Exact MS (ESI+ in MeOH
sens = 3.72e7): m/e = 442.2 for C28H29N3Cl (M+–Cl). IR
mC@O 1697 cmꢀ1
.
(ATR diamond) mC@N 1662 cmꢀ1
.
4.2. General procedure for the preparation of
imino-imidazolium salts
4.2.3. 3-(2,6-Diisopropylphenyl)-1-[2-{(S)-1-(phenyl)-
ethylimino}-2-phenyl ethyl] imidazolium chloride (11)
20
In a screw-cap tube flushed with argon were added the 1-
(2-oxo-2-phenyl)ethyl imidazolium salt 5–8 (1 mmol), the
chiral amine (3 mmol) and 2 mL of CHCl3. A paper trap
Yield 92%, yellow solid. M.p. 125 °C. ½aꢁD ¼ þ4 (c 1.1,
CHCl3). 1H NMR (400 MHz, CDCl3) d 1.14 (d, 3H,
J = 6.8 Hz), 1.18 (d, 3H, J = 6.8 Hz), 1.22 (d, 3H, J =
6.8 Hz), 1.24 (d, 3H, J = 6.8 Hz), 1.29 (d, 3H,
J = 6.3 Hz), 2.33 (m, 1H, J = 6.8 Hz), 2.49 (m, 1H, J =
6.8 Hz), 4.66 (q, 1H, J = 6.3 Hz), 5.58 (d, 1H,
J = 17.4 Hz, CHH–C@N), 6.56 (d, 1H, J = 17.4 Hz,
CHH–C@N), 7.12–7.40 (m, 8H), 7.45–5.57 (m, 6H), 7.65
(s, 1H), 10.60 (s, 1H, N–CH@N). 13C NMR (100 MHz,
CD2Cl2) d 23.9, 24.1, 24.2, 24.8, 28.4, 28.5, 55.9 (CH2),
60.0, 123.0, 124.5, 124.9, 126.1, 126.6, 127.5, 128.4, 128.7,
129.4, 130.6, 131.6, 134.4, 140.0 (N–C@N), 145.4, 145.6,
162.5 (CH2C@N). Exact MS (ESI+ in MeOH
sens = 2.09e6): m/e = 450.25 for C31H36N3 (M+–Cl). IR
˚
filled with molecular sieves 4 A was placed at the top of
the tube before closing. The mixture was stirred under
argon at 90 °C (oil bath) for 60 h. After cooling, CH2Cl2
(2 mL) and NaHCO3 (300 mg, 3.5 mmol) were added and
the mixture was stirred vigorously for 1 h, filtered under
dinitrogen and concentrated. Imino-imidazolium salts
9–13 were precipitated from the crude by several washing
of the residue with dry Et2O. Imino-imidazolium salts
14–15 were precipitated in THF and washed with the same
solvent. The reaction could be performed on a 3 mmol
scale. In this case the precipitation of the imino-imidazo-
lium salts 9–13 was more difficult and after addition of
dry Et2O the reaction vessel was placed in an ultrasonic
bath for 5 min. Et2O was removed. The procedure was
repeated several times until the solid precipitate.
(ATR diamond) mC@N 1662 cmꢀ1
.
4.2.4. 3-(2,6-Diisopropylphenyl)-1-[2-{(S)-1-(p-chloro-
phenyl)ethylimino}-2-phenyl ethyl] imidazolium chloride
(12)
20
4.2.1. 3-Mesityl-1-[2-{(S)-1-(phenyl)ethylimino}-2-phenyl
ethyl] imidazolium chloride (9)
Yield 70%, pale orange solid. M.p. 131 °C. ½aꢁD ¼ ꢀ20 (c
1
1.3, CHCl3). H NMR (400 MHz, CD2Cl2) d 1.03 (d, 3H,
20
Yield 87%, pale orange powder. M.p. 83 °C. ½aꢁD ¼ ꢀ5
J = 6.5 Hz), 1.05 (d, 3H, J = 6.5 Hz), 1.07 (d, 3H, J =
6.5 Hz), 1.09 (d, 3H, J = 6.5 Hz), 1.17 (d, 3H, J = 6.5 Hz),
2.24 (m, 1H, J = 6.5 Hz), 2.35 (m, 1H, J = 6.5 Hz), 4.50
(q, 1H, J = 6.5 Hz), 5.65 (d, 1H, J = 17.4 Hz, CHH–
C@N), 6.21 (d, 1H, J = 17.4 Hz, CHH–C@N), 7.05 (d,
2H, J = 8.5 Hz), 7.13 (s, 1H), 7.17 (d, 2H, J = 8.5 Hz),
7.25 (dd, 2H, J = 8 and 2 Hz), 7.32–7.36 (m, 3H), 7.43–
7.51 (m, 3H), 7.81 (s, 1H), 10.60 (s, 1H, N–CH@N). 13C
NMR (100 MHz, CD2Cl2) d 24.3, 24.4, 24.5, 25.1, 28.8,
28.9, 56.4 (CH2), 59.8, 123.4, 124.8, 125.0, 127.8, 128.0,
1
(c 1.1, CHCl3). H NMR (400 MHz, CDCl3) d 1.26 (d,
3H, J = 6.6 Hz), 2.00 (s, 3H), 2.10 (s, 3H), 2.35 (s, 3H),
4.60 (q, 1H, J = 6.6 Hz), 5.66 (d, 1H, J = 17.4 Hz, CHH–
C@N), 6.32 (d, 1H, J = 17.4 Hz, CHH–C@N), 6.99 (s,
2H), 7.12–7.15 (m, 3H), 7.20–7.29 (m, 3H), 7.42–7.55 (m,
5H), (t, 1H, J = 1.5 Hz), 7.67 (t, 1H, J = 1.5 Hz), 10.47
(s, 1H, N–CH@N). 13C NMR (100 MHz, CD2Cl2) d
17.3, 17.4, 20.9, 24.8, 55.9 (CH2), 60.2 (CH3CHN), 122.1
(CH@CH), 124.8 (CH@CH), 126.2, 126.7, 127.4, 128.4,

A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
3505
128.8, 129.2, 130.0, 130.8, 132.1, 132.5, 134.4, 140.6 (N–
4.3. General procedure for the NaBH4 reduction of imino-
imidazolium salts
C@N), 144.3, 145.9, 163.4 (CH2C@N). Exact MS (ESI+
in MeOH sens = 4.14e7): m/e = 484.3 for C31H35N3Cl
(M+–Cl). IR (ATR diamond) mC@N 1663 cmꢀ1
.
The imino-imidazolium salt (0.22 mmol) was dissolved
in MeOH (5 mL) under argon. The solution was cooled
to –70 °C and NaBH4 (33 mg, 0.88 mmol) was added by
portions. The mixture was stirred overnight, during which
period it was allowed to gradually warm to 20 °C. A satu-
rated aqueous NH4Cl solution (5 mL) was added and the
mixture was stirred vigorously for 10 min. Solid K2CO3
was added and the mixture was stirred for 10 min. The
methanol was evaporated and the resulting mixture was
extracted with CH2Cl2. The organic layer was dried over
Na2SO4 and concentrated. The product was washed with
Et2O and dried under vacuum.
4.2.5. 3-(2,6-Diisopropylphenyl)-1-[2-{(S)-1- (phenyl)-
propylimino}-2-phenyl ethyl] imidazolium chloride (13)
20
Yield 78%, white solid. M.p. 241 °C. ½aꢁD ¼ ꢀ17 (c 1.0,
CHCl3). 1H NMR (400 MHz, CDCl3) d 0.68 (t, 3H,
J = 7.3 Hz), 1.15 (d, 3H, J = 6.8 Hz), 1.22 (d, 3H, J =
6.8 Hz), 1.25 (d, 3H, J = 6.8 Hz), 1.28 (d, 3H,
J = 6.8 Hz), 1.60 (dq, 1H, J = 7.3 and 6.6 Hz, CH3CHH),
1.64 (dq, 1H, J = 7.3 and 6.6 Hz, CH3CHH), 2.33 (m,
1H, J = 6.8 Hz), 2.53 (m, 1H, J = 6.8 Hz), 4.36 (t, 1H,
J = 6.6 Hz), 5.45 (d, 1H, J = 17.4 Hz, CHH–C@N), 6.76
(dd, 1H, J = 17.4 and 2 Hz, CHH–C@N), 7.14–7.19 (m,
3H), 7.22–7.36 (m, 5H), 7.43–7.62 (m, 7H), 10.75 (s, 1H,
4.3.1. 3-Mesityl-1-[(2S)-2-{(S)-1-(phenyl)ethylamino}-2-
phenyl ethyl] imidazolium chloride (17)
N–CH@N). 13C NMR (100 MHz, CDCl3)
d 10.9
Yield 91%, pale orange solid. 90:10 Mixture of diastereo-
mers. The major diastereomer was separated by crystallisa-
tion. The crude was dissolved in a minimum of CH2Cl2 and
diluted with acetone. Et2O was then added until the mixture
becomes cloudy and the mixture was cooled at 4 °C for
16 h. This procedure afforded 52% of small colorless needles
with a dr of 94:6. A second crystallisation in the same con-
ditions led to 36% of the major diastereomer with a dr >98:2
(the minor isomer was not detectable in the NMR spec-
(CH2CH3), 24.0, 24.3, 24.4, 24.7, 28.3, 28.6, 32.5
(CH2CH3), 56.2 (CH2C@N), 66.9, 123.0, 124.3, 124.5,
124.6, 126.4, 126.6, 126.9, 127.3, 127.6, 128.5, 128.8,
129.6, 130.3, 131.7, 133.8, 139.9 (N–C@N), 144.3, 145.4,
145.5, 162.6 (CH2C@N). Exact MS (ESI+ in MeOH
sens = 5.28e7): m/e = 464.3 for C32H38N3 (M+–Cl). IR
(ATR diamond) mC@N 1664 cmꢀ1
.
20
4.2.6. 3-tert-Butyl-1-[2-{(S)-1-(phenyl)ethylimino}-2-
phenyl ethyl] imidazolium chloride (14)
trum). White powder, M.p. 113 °C. ½aꢁD ¼ þ 101 (c 1,
CHCl3). 1H NMR (400 MHz, CDCl3) d 1.36 (d, 3H,
J = 6.5 Hz), 1.95 (s, 3H), 2.03 (s, 3H), 2.36 (s, 3H), 2.79
(br s, 1H, NH), 3.80 (q, 1H, J = 6.5 Hz), 4.33 (dd, 1H,
J = 6 and 5 Hz, CH2–CH–NH), 4.98 (dd, 1H, J = 13.6
and 6 Hz, CHH–CH–NH), 5.15 (dd, 1H, J = 13.6 and
5 Hz, CHH–CH–NH), 6.92 (t, 1H, J = 1.5 Hz, CH@CH),
6.99 (br s, 2H), 7.11 (t, 1H, J = 1.5 Hz, CH@CH) 7.19–
7.33 (m, 10H), 10.42 (t, 1H, J = 1.5 Hz, N–CH@N). 13C
NMR (100 MHz, CD2Cl2) d 17.3, 17.5, 21.0, 22.7 (CH3–
CH), 54.5 (CH3–CH–NH), 54.7 (CH2), 59.7 (CH2–CH–
NH), 121.6 (CH@CH), 123.3 (CH@CH), 126.5, 126.7,
127.4, 127.8, 128.1, 128.3, 128.9, 129.7, 130.7, 134.3, 139.3
(N–CH@N), 141.1, 145.5. Exact MS (ESI+ in CH3CN
sens = 4.17e6): m/e = 410.2 for C28H32N3 (M+–Cl).
20
Yield 88%, white solid. M.p. 64 °C. ½aꢁD ¼ ꢀ36 (c 1,
CH2Cl2). 1H NMR (400 MHz, CDCl3) d 1.27 (d, 3H,
J = 6.3 Hz), 1.72 (s, 9H), 4.57 (q, 1H, J = 6.3 Hz), 5.46
(d, 1H,J = 17.4 Hz, CHH–C@N), 5.94 (d, 1H,
J = 17.4 Hz, CHH–C@N), 7.10–7.13 (m, 2H), 7.22–7.30
(m, 3H), 7.33–7.36 (m, 2H), 7.40–7.50 (m, 5H), 10.96 (s,
1H, N–CH@N). 13C NMR (100 MHz, CDCl3) d 25.2,
30.0, 55.7 (CH2), 59.9 (C(CH3)), 60.4 (N–CH–CH3),
118.2, 123.8, 126.1, 126.8, 127.2, 128.4, 128.9, 129.5,
133.8, 137.5 (N–C@N), 145.2, 161.6 (CH2C@N). Anal.
Calc. for C23H28ClN3 Æ H2O (MW = 399.96) C, 69.07; H,
7.56; N, 10.51. Found: C, 69.15; H, 7.27; N, 10.41%. IR
(ATR diamond) mC@N 1663 cmꢀ1
.
4.2.7. 3-tert-Butyl-1-[2-{(S)-1-(phenyl)ethylimino}-2-
phenyl ethyl] imidazolium bromide (15)
4.3.2. 3-(2,6-Diisopropylphenyl)-1-[(2S)-2-{(S)-1-
(phenyl)ethylamino}-2-phenyl ethyl] imidazolium chloride
(18)
20
Yield 76%, white solid. M.p. 80 °C. ½aꢁD ¼ ꢀ39 (c 1.3,
CH2Cl2). 1H NMR (400 MHz, DCl3) d 1.27 (d, 3H,
J = 6.6 Hz), 1.73 (s, 9H), 4.57 (q, 1H, J = 6.6 Hz), 5.45
(d, 1H, J = 17.4 Hz, CHH–C@N), 5.92 (dd, 1H, J = 17.4
and 4.5 Hz, CHH–C@N), 7.10–7.12 (m, 2H), 7.15–7.50
(m, 10H), 10.69 (br s, 1H, N–CH@N). 13C NMR
Yield 87%, yellow solid. 86:14 Mixture of diastereomers.
1
Major diastereomer: H NMR, (400 MHz, CDCl3) d 1.07–
1.12 (m, 9H), 1.21 (d, 3H, J = 6.6 Hz), 1.36 (d, 3H,
J = 6.1 Hz), 2.16–2.31 (m, 2H), 3.79 (q, 1H, J = 6.6 Hz),
4.29 (dd, 1H, J = 6.3 and 4.5 Hz), 4.90 (dd, 1H, J = 13.6
and 6.3 Hz), 5.17 (dd, 1H, J = 13.6 and 4.5 Hz), 6.86 (s,
1H), 6.96–7.51 (m, 14H), 10.33 (s, 1H). 13C NMR
(100 MHz, CDCl3) d 22.9, 24.0, 24.1, 24.2, 24.4 (CH3),
28.5 (CH(CH3)2), 54.7 (N–CH–CH3), 54.9 (CH2), 59.6
(CH2–CH–Ph), 122.8, 123.7, 124.4, 124.5, 126.4, 126.7,
127.4, 128.0, 128.3, 128.7, 130.3, 131.6, 139.3 (N–CH@N),
(100 MHz, CDCl3)
d 25.2, 30.1, 55.8 (CH2), 60.1
(C(CH3)), 60.4 (N–CH–CH3), 118.1, 123.9, 126.1, 126.8,
127.2, 128.4, 128.9, 129.6, 133.7, 137.2 (N–C@N), 145.1,
161.4 (CH2C@N). Anal. Calc. for C23H28BrN3 (MW
426.39) C, 64.79; H, 6.62; N, 9.85. Found: C, 64.67; H,
6.79; N, 9.67%. IR (ATR diamond) mC@N 1663 cmꢀ1
=
.

3506
A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
139.8, 145.3, 145.5. Exact MS (ESI+ in CH3CN sens =
2.09e6): m/e = 452.3 for C31H38N3 (M+–Cl). The crude salt
was recrystallised twice in CH2Cl2/acetone/Et2O to give
colorless needles suitable for X-ray diffraction analysis.
The NMR spectrum of the crystals obtained showed the
presence of the major diastereomer only.
tered through celite, concentrated under reduced pressure
and dried under vaccum.
4.4.1. 3-Mesityl-1-[(2S)-2-{(S)-1-(phenyl)ethylamino}-2-
phenyl ethyl] imidazol-2-ylidene AgCl (21)
20
Yield 73% from 17, white solid. M.p. 82 °C. ½aꢁD ¼ ꢀ33
(c 0.3, CHCl3). 1H NMR (400 MHz, CDCl3) d 1.28 (d, 3H,
J = 6.6 Hz), 1.71 (s, 3H), 1.81 (s, 3H), 2.22 (s, 3H), 3.76 (q,
1H, J = 6.6 Hz, CH3–CH–N), 4.00 (dd, 1H, J = 6 and
7 Hz, CH2–CH–NH), 4.31 (dd, 1H, J = 13.4 and 7 Hz,
CHH–CH–NH), 4.38 (dd, 1H, J = 13.4 and 6 Hz
CHHCH–NH), 6.71 (d,1H, J = 1.5 Hz, CH@CH), 6.82
(s, 1H, CH Mes), 6.83 (s, 1H, CH Mes), 6.89 (s br, 1H,
CH@CH), 7.10 (m, 2H), 7.15–7.26 (m, 8H). 13C NMR
(100 MHz, CDCl3) d 17.6, 17.7, 21.0, 23.0, 55.2 (NH–
CH–CH3), 57.3 (CH2), 61.2 (CH2CH–NH), 121.8
(CH@CH), 122.1 (CH@CH), 126.5, 127.1, 127.3, 128.2,
128.7, 129.2, 129.3, 134.5, 134.6, 135.2, 139.4, 139.7,
145.0, the carbene carbon was not detected. Anal. Calc.
for C28H31AgClN3 (MW = 552.89) C, 60.83; H, 5.65; N,
7.60. Found: C, 60.79; H, 5.46; N, 7.55%.
4.3.3. 3-(2,6-Diisopropylphenyl)-1-[(2S)-2-{(S)-1-
(phenyl)propylamino}-2-phenyl ethyl] imidazolium chloride
(19)
Yield 99%, yellow solid. Mixture of diastereomers 85:15.
The same procedure was followed for the separation of the
major diastereomer by crystallisation. The first crystallisa-
tion afforded 62% of small colorless needles with a dr of
97:3. A second crystallisation in the same conditions led
to 46% of the major diastereomer with a dr >98:2 (the minor
isomer was not detectable in the NMR spectrum). White
20
powder. M.p. 245 °C. ½aꢁD ¼ þ31:6 (c 2, CHCl3). 1H
NMR (400 MHz, CDCl3) d 0.74 (t, 3H, J = 7.5 Hz), 1.06–
1.10 (m, 9H), 1.20 (d, 3H, J = 6.8 Hz), 1.65 (m, 1H,
CHH–CH3), 1.84 (m, 1H, CHH–CH3), 2.16 (m, 1H,
J = 7 Hz, CH(CH3)2), 2.23 (m, 1H, J = 7 Hz, CH(CH3)2),
2.72 (br s, 1H, NH), 3.56 (dd, 1H, J = 8.3 and 4.8 Hz, Et-
CH–N), 4.32 (dd, 1H, J = 6 and 4.5 Hz, N–CH2–CH–
NH), 5.00 (dd, 1H, J = 6 and 13.9 Hz, N–CHH–CH–NH),
5.16 (dd, 1H, J = 4.5 and 13.9 Hz, N–CHH–CH–NH),
6.95 (t, 1H, J = 1.5 Hz, CH@CH), 7.13–7.32 (m, 10H),
7.38 (t, 1H, J = 1.5 Hz), 7.50 (t, 1H, J = 7.8 Hz), 10.37 (s,
1H, N–CH@N). 13C NMR (100 MHz, CD2Cl2) d 10.4
(CH3–CH2), 24.0, 24.1, 24.3, 24.5, (CH(CH3)2), 28.5
(CH(CH3)2), 29.5 (CH2–CH3), 54.4 (CH2–N), 59.7 (N–
CH2–CH–N), 61.3 (Et-CH–N), 122.6 (CH@CH), 123.3
(CH@CH), 124.5, 124.6, 126.7, 127.2, 127.3, 128.0, 128.3,
128.7, 130.3, 131.7, 139.3, 139.6 (N–CH@N), 143.5, 145.3.
Anal. Calc. for C32H40ClN3 (MW = 502.13) C, 76.54; H,
8.03; N, 8.37. Found: C, 76.53; H, 8.12; N, 8.35%.
4.4.2. 3-(2,6-Diisopropylphenyl)-1-[(2S)-2-{(S)-1-
(phenyl)propylamino}-2-phenyl ethyl] imidazol-2-ylidene
AgCl (22)
20
Yield 80% from 19, white solid. M.p. 75 °C. ½aꢁD
¼
1
ꢀ18:4 (c 1, CHCl3). H NMR (400 MHz, CDCl3) d 0.80
(t, 3H, J = 7.3 Hz), 1.02 (d, 3H, J = 6.8 Hz), 1.06 (d, 3H,
J = 6.8 Hz), 1.10 (d, 3H, J = 6.8 Hz), 1.14 (d, 3H, J =
6.8 Hz), 1.65 (m, 1H, CHH–CH3), 1.76 (dd, 1H, J = 6.8
and 6 Hz, NH), 1.83 (m, 1H, CHH–CH3), 2.10 (m, 1H,
J = 6.8 Hz, CH(CH3)2), 2.19 (m, 1H, J = 6.8 Hz, CH-
(CH3)2), 3.65 (m, 1H, Et-CH–N), 4.03 (m, 1H, N–CH2-
CH–N), 4.43 (dd, 1H, J = 6.8 and 13.8 Hz, N–CHH–
CH–NH), 4.47 (dd, 1H, J = 6.3 and 13.8 Hz, N–CHH–
CH–NH), 6.80 (s, 1H, CH@CH), 6.94 (s, 1H, CH@CH),
7.14-7.34 (m, 10H), 7.41 (t, 1H, J = 7.8 Hz). 13C NMR
(100 MHz, CDCl3) d 9.6 (CH3–CH2), 23.30, 23.37, 23.41,
23.47, 27.01, 27.04, 28.9 (CH2–CH3), 55.8 (CH2–N), 60.1
(N–CH2–CH–N), 61.1 (Et-CH–N), 120.5 (d, J3(Ag–13C)
7 Hz), 122.4 (d, J3(Ag–13C) 8 Hz), 123.1, 126.1, 126.2,
127.1, 127.6, 128.0, 129.4, 133.5, 138.8, 142.2, 144.5,
181.0 (dd, J1(109Ag–13C) 272 Hz and J1(107Ag–13C)
236 Hz, Ccarbene). Anal. Calc. for (C32H39ClN3Ag)6(AgCl)5
(MW = 4370.56) C, 52.76; H, 5.40; N, 5.77. Found: C,
52.77; H, 5.69; N, 5.17%.
4.3.4. 3-tert-butyl-1-[(2S)-2-{(S)-1-(phenyl)ethylamino}-
2-phenyl ethyl] imidazolium chloride (20)
Yield 65%, white solid. 85:15 Mixture of diastereomers.
1
Major diastereomer: H NMR, (400 MHz, CDCl3) d 1.28
(d, 3H, J = 6.6 Hz), 1.66 (s, 9H), 3.77 (q, 1H, J =
6.6 Hz), 4.17 (dd, 1H, J = 7 and 5.3 Hz), 4.69 (dd, 1H,
J = 13.8 and 5.3 Hz), 4.75 (dd, 1H, J = 13.8 and 7 Hz),
6.96 (br s, 1H), 7.12 (t, 1H, J = 1.8 Hz), 7.15–7.39 (m,
10H), 10.82 (br s, 1H). 13C NMR (100 MHz, CDCl3). d
23.0, 30.0, 54.3 (CH2), 54.6, 59.8, 118.3, 122.9, 126.4,
126.8, 127.2, 128.0, 128.3, 128.8, 137.1 (N–CH@N),
139.5, 145.6. Exact MS (ESI+ in CH3CN sens = 6.37e6):
m/e = 348.3 for C23H30N3 (M+–Cl).
4.4.3. 3-Mesityl-1-[(2S)-2-{(S)-1-(phenyl)ethylamino}-2-
phenyl ethyl] imidazol-2-ylidene PdCl2 (23)
A solution of Ag(I) complex 21 (88 mg, 0.16 mmol) and
PdCl2(CH3CN)2 (41.7 mg, 0.16 mmol) in CH2Cl2 (1.5 mL)
was stirred at 20 °C for 1 h with exclusion of light, filtered
through celite and concentrated under reduced pressure to
give 97 mg (100%) of a brown yellow solid. The crude
was dissolved in CHCl3 (1 mL) and the complex was pre-
cipitated by addition of Et2O. Yield 50% (47 mg) of a pale
yellow solid. M.p. 270 °C. Single crystals suitable for X-ray
4.4. Preparation of amino-imidazol-2-ylidene silver (I)
complexes
To a solution of imidazolium salt (1 mmol) in dry
CH2Cl2 (15 mL) was added Ag2O (0.55 mmol). The mix-
ture was stirred at 20 °C for 16 h with exclusion of light, fil-

A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
3507
analysis were obtained by cooling a concentrated solution
of the crude complex in CHCl3 at 4 °C. The complex
obtained contains one molecule of CHCl3 and is then little
CHCl3). 1H NMR (400 MHz, CD2Cl2) d 1.33 (d, 3H,
J = 6.5 Hz), 1.83 (s, 3H), 1.92 (s, 3H), 2.31 (s, 3H), 4.52
(q, 1H, J = 6.5 Hz), 5.20 (d, 1H, J = 16.4 Hz, CHH–
C@N), 5.23 (d, 1H, J = 16.4 Hz, CHH–C@N), 6.93 (d,
1H, J = 1.8 Hz), 6.95 (s, 2H), 7.10–7.50 (m, 9H). 13C
NMR (100 MHz, CDCl3) d 17.5, 17.6, 21.0, 25.0, 59.5
(CH2), 61.1 (N–CH–CH3), 121.8, 122.7, 126.4, 126,7,
126.9, 128.5, 129.1, 129.3, 129.4, 134.3, 134.6, 134.7,
135.2, 139.5, 145.0, 163.8, the carbene carbon was not
detected. Anal. Calc. for C28H30AgClN3 (MW = 551.88)
C, 60.94; H, 5.48; N, 7.61. Found: C, 60.66; H, 5.91; N,
20
soluble in this solvent. ½aꢁD ¼ ꢀ19 (c 0.5, CHCl3). 1H
NMR (400 MHz, CDCl3) d 2.13 (s, 3H), 2.18 (d, 3H,
J = 6.6 Hz), 2.31 (s, 3H), 2.34 (s, 3H), 3.31 (dq, 1H,
J = 11.6 and 6.6 Hz, CH3–CH–NH), 3.58 (ddd, 1H, J =
11.9, 4.3 and 4 Hz, CH2–CH–NH), 4.16 (dd, 1H,
J = 14.3 and 4.3 Hz, CHH–CH–N), 5.17 (dd, 1H, J =
14.3 and 11.9 Hz, CHH–CH–N), 5.74 (dd, 1H, J = 11.6
and 4 Hz, NH), 6.89 (d, 1H, J = 2 Hz), 6.94–6.96 (m,
3H), 7.03–7.12 (m, 5H), 7.17–7.25 (m, 4H), 7.43 (d, 1H,
J = 2 Hz). 13C NMR (100 MHz, CDCl3) d 17.6, 18.8,
21.1, 27.1 (CH3–CH–N), 58.2 (CH2), 62.9 (CH2–CH–N),
68.6 (CH3ACH), 121.3 (CH@CH), 124.3 (CH@CH),
126.7, 127.2, 128.5, 128.7, 128.8, 129.2, 129.3, 133.1,
134.5, 137.0, 137.1, 139.4, 139.7, 153.3 (Ccarbene). Anal.
Calc. for (C28H31Cl2N3Pd)7(CHCl3)4 (MW = 4585.75) C,
52.38; H, 4.86; N, 6.41. Found: C, 52.28; H, 4.66; N,
6.24%. CHCl3 was difficult to remove totally from the solid
complex (MW of the complex = 686.89).
7.35%. IR (ATR diamond) mC@N 1647 cmꢀ1
.
4.6. Allylic alkylation
A mixture of [Pd(g3-C3H5)Cl]2 (4.3 mg, 0.012 mmol) and
silver complex 21 (15.3 mg, 0.028 mmol) in THF (2 mL)
was stirred for 1 h at 20 °C under argon. The mixture was
filtered and added to a solution of (E)-1,3-diphenylprop-
3-en-yl acetate (100 mg, 0.396 mmol) in THF (1 mL).
After 10 min, a solution of dimethyl malonate (138 lL,
1.188 mmol) and NaH (1.07 mmol) in THF (1 mL) was
added dropwise. After 16 h at 20 °C, brine (3 mL) was
added and the mixture was extracted with Et2O. The
organic layer was dried over Na2SO4, filtered and concen-
trated. The residue was purified by column chromatogra-
phy (SiO2, pentane/Et2O;9/1) to afford 53 mg (41% yield).
Enantiomeric excess (60 % (R)) was determined by 1H
NMR with a chiral shift reagent Eu(hfc)3.
4.4.4. 3-(2,6-Diisopropylphenyl)-1-[(2S)-2-{(S)-1-(phenyl)
propylamino}-2-phenyl ethyl] imidazol-2-ylidene PdCl2 (24)
A solution of Ag(I) complex 22 (50 mg, 0.082 mmol)
and PdCl2(CH3CN)2 (21.5 mg, 0.082 mmol) in CH2Cl2
(1 mL) was stirred at 20 °C for 1 h with exclusion of light,
filtered through celite and concentrated under reduced
pressure to give 45 mg (85%) of an orange solid. The crude
was dissolved in CH2Cl2 (1 mL) and the complex was pre-
cipitated by addition of Et2O. Yield 53% (28 mg) of a pale
5. Supplementary material
20
orange solid. M.p. 209 °C. ½aꢁD ¼ þ187 (c 1.8, CHCl3). 1H
NMR (400 MHz, CDCl3) d 0.59 (t, 3H, J = 7.3 Hz), 1.11
(d, 3H, J = 6.8 Hz), 1.12 (d, 3H, J = 6.8 Hz), 1.36 (d, 3H,
J = 6.6 Hz), 1.61 (d, 3H, J = 6.8 Hz), 2.29 (m, 2H, CH2–
CH3), 3.08 (dt, 1H, J = 11 and 4.6 Hz, Et-CH–NH), 3.30
(m, 1H), 3.45 (m, 1H), 3.60 (dt, 1H, J = 11.7 and 4.5
Hz, N–CH2–CH–NH), 4.08 (dd, 1H, J = 14.2 and
4.5 Hz, CHH–CH–N), 5.22 (dd, 1H, J = 14.2 and
11.7 Hz, CHH–CH–N), 5.74 (dd, 1H, J = 11 and 4.5 Hz,
NH), 6.90–6.92 (m, 2H), 6.95 (d, 1H, J = 1.8 Hz), 7.00–
7.37. (m, 11H), 7.48 (t, 1H, J = 7.6 Hz). 13C NMR
(100 MHz, CDCl3) d 11.8 (CH3–CH2), 22.3, 23.0, 25.7,
26.2 (CH3, i-Pr), 28.8, 29.0 (CH, i-Pr), 32.O (CH3ACH2),
58.1 (N–CH2), 62.6 (N–CH2–CH–Ph), 74.5 (Et-CH–Ph),
121.7, 123.0, 124.1, 126.1, 126.6, 127.9, 128.3, 128.4,
128.6, 129.0, 129.9, 134.8, 137.8, 137.9, 143.4, 147.1,
Crystallographic data for the structures reported in this
paper have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC No. 288055 for compound
19 and No. 288056 for complex 23. Copies of this informa-
tion may be obtained free of charge from the Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax:
+44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk).
Acknowledgements
A. Flahaut thanks Clariant France for a grant. We
´
thank P. Herson (Centre de resolution de structures – Lab-
´
´
oratoire de chimie inorganique et materiaux moleculaires,
´
universite P. et M. Curie) for X-ray structures.
151.4. Anal. Calc. for (C32H39Cl2N3Pd)7(CHCl3)4 (MW
=
5195.58) C, 52.95; H, 5.39; N, 5.64. Found: C, 52.97; H,
5.33; N, 5.54%. CHCl3 was difficult to remove totally from
the solid complex (MW of the complex = 643.00).
References
[1] D. Bourrissou, O. Guerret, F.P. Gabba¨ı, G. Bertrand, Chem. Rev.
100 (2000) 39.
[2] W.A. Herrmann, C. Ko¨cher, Angew. Chem., Int. Ed. Engl. 36 (1997)
2162.
[3] W.A. Herrmann, Angew. Chem., Int. Ed. Engl. 41 (2002) 1290.
[4] L. Jafarpour, S.P. Nolan, Adv. Organomet. Chem. 46 (2001) 181.
[5] A.W. Coleman, P.B. Hitchcock, M.F. Lappert, R.K. Maskell, J.H.
4.5. 3-Mesityl-1-[2-{(S)-1-(phenyl)ethylimino}-2-phenyl
ethyl] imidazol-2-ylidene AgCl (25)
The procedure was the same as for 21 and 22. Yield 83%
20
Muller, J. Organomet. Chem. 250 (1983) C9–C14.
¨
from 9, off white solid. M.p. 89 °C. ½aꢁD ¼ ꢀ54 (c 0.3,

3508
A. Flahaut et al. / Journal of Organometallic Chemistry 691 (2006) 3498–3508
[6] M.C. Perry, K. Burgess, Tetrahedron: Asymmetry 14 (2003) 951.
[26] M. Frøseth, K.A. Netland, C. Rømming, M. Tilset, J. Organomet.
Chem. 690 (2005) 6125.
´
[7] V. Cesar, S. Bellemin-Laponnaz, L.H. Gade, Chem. Soc. Rev. 33
(2004) 619.
[27] M. Frøseth, K.A. Netland, K.W. To¨rnroos, A. Dhindsa, M. Tilset,
J. Chem. Soc., Dalton Trans. (2005) 1164.
[28] S. Dastgir, K.S. Coleman, A.R. Cowley, M.L.H. Green, Organomet-
allics 25 (2006) 300.
[8] S. Roland, P. Mangeney, in: M. Lemaire, P. Mangeney (Eds.), Top.
Organomet. Chem., vol. 15, Springer Verlag, Berlin, Heidelberg,
2005, p. 191.
[9] W.A. Herrmann, L.J. Goossen, M. Spiegler, Organometallics 17
(1998) 2162.
[10] M.T. Powell, D.-R. Hou, M.C. Perry, X. Cui, K. Burgess, J. Am.
Chem. Soc. 123 (2001) 8878.
[29] K.S. Coleman, H.T. Chamberlayne, S. Tuberville, M.L.H. Green,
A.R. Cowley, J. Chem. Soc., Dalton Trans. (2003) 2917.
[30] G. Steiner, H. Kopacka, K.-H. Ongania, K. Wurst, P. Preishuber-
Pflugl, B. Bildstein, Eur. J. Inorg. Chem. (2005) 1325.
¨
[11] M.C. Perry, X. Cui, M.T. Powell, D.-R. Hou, J.H. Reibenspies, K.
Burgess, J. Am. Chem. Soc. 125 (2003) 113.
[31] G. Steiner, A. Krajete, H. Kopacka, K.-H. Ongania, K. Wurst,
P. Preishuber-Pflugl, B. Bildstein, Eur. J. Inorg. Chem. (2004)
¨
´
[12] V. Cesar, S. Bellemin-Laponnaz, L.H. Gade, Organometallics 21
2827.
(2002) 5204.
[32] K.S. Coleman, S. Dastgir, G. Barnett, M.J.P. Alvite, A.R. Cowley,
M.L.H. Green, J. Organomet. Chem. 690 (2005) 5591.
[33] Azeotrope CHCl3/H2O: 97/3 (%).
´
[13] L.H. Gade, V. Cesar, S. Bellemin-Laponnaz, Angew. Chem., Int. Ed.
Engl. 43 (2004) 1014.
[14] T. Focken, G. Raabe, C. Bolm, Tetrahedron: Asymmetry 15 (2004)
1693.
[34] C. Cimarelli, G. Palmieri, Tetrahedron: Asymmetry 11 (2000)
2555.
[15] N. Schneider, V. Ce´sar, S. Bellemin-Laponnaz, L.H. Gade, J.
Organomet. Chem. 690 (2005) 5556.
[35] J.C.G. Van Niel, U.K. Pandit, Tetrahedron 41 (1985) 6011.
[36] C.G. Overberger, N.P. Marullo, R.G. Hiskey, J. Am. Chem. Soc. 83
(1961) 1374.
[37] G. Uccello-Barretta, R. Bernardini, F. Balzano, P. Salvadori, J. Org.
Chem. 66 (2001) 123.
[38] A. Alexakis, S. Gille, F. Prian, S. Rosset, K. Ditrich, Tetrahedron
Lett. 45 (2004) 1449.
[39] I.S. Edworthy, M. Rodden, S.A. Mungur, K.M. Davis, A.J. Blake,
C. Wilson, M. Schro¨der, P.L. Arnold, J. Organomet. Chem. 690
(2005) 5710.
[16] Y. Yuan, G. Raabe, C. Bolm, J. Organomet. Chem. 690 (2005) 5747.
[17] L.G. Bonnet, R.E. Douthwaite, Organometallics 22 (2003) 4187.
[18] D.S. McGuinness, K.J. Cavell, Organometallics 19 (2000) 741.
[19] A.A.D. Tulloch, A.A. Danopoulos, R.P. Tooze, S.M. Cafferkey, S.
Kleihenz, M.B. Hursthouse, Chem. Commun. (2000) 1247.
[20] A.A.D. Tulloch, A.A. Danopoulos, G.J. Tizzard, S.J. Colles, M.B.
Hursthouse, R.S. Hay-Motherwell, W.B. Motherwell, Chem. Com-
mun. (2001) 1270.
[21] P.L. Chiu, C.-L. Lai, C.-F. Chang, C.-H. Hu, H.M. Lee, Organo-
metallics 24 (2005) 6169.
[22] F.E. Hahn, M.C. Jahnke, V. Gomez-Benitez, D. Morales-Morales,
T. Pape, Organometallics 24 (2005) 6458.
[40] L.P. Spencer, M.D. Fryzuk, J. Organomet. Chem. 690 (2005) 5788.
[41] H.M. Wang, I.J.B. Lin, Organometallics 17 (1998) 972.
[42] J.C. Garrisson, W.J. Youngs, Chem. Rev. 105 (2005) 3978.
´
[43] P. de Fremont, N.M. Scott, E.D. Stevens, T. Ramnial, O.C.
[23] A.M. Magill, D.S. McGuinness, K.J. Cavell, G.J.P. Britovsek, V.C.
Gibson, A.J.P. White, D.J. Williams, A.H. White, B.W. Skelton, J.
Organomet. Chem. 617–618 (2001) 546.
[24] R.E. Douthwaite, J. Houghton, B. Kariuki, Chem. Commun. (2004)
698.
Lightbody, C.L.B. Macdonald, J.A.C. Clyburne, C.D. Abernethy,
S.P. Nolan, Organometallics 24 (2005) 6301.
[44] W. Li, H. Sun, M. Chen, Z. Wang, D. Hu, Q. Shen, Y. Zhang,
Organometallics 24 (2005) 5925.
[45] J. Liu, J. Chen, J. Zhao, Y. Zhao, L. Li, H. Zhang, Synthesis (2003)
2661.
[46] A.A. Gridnev, I.M. Mihaltseva, Synth. Commun. 24 (1994) 1547.
[25] M. Frøseth, A. Dhindsa, H. Røise, M. Tilset, J. Chem. Soc., Dalton
Trans. (2003) 4516.