An N-heterocyclic carbene ligand based on a β-cyclodextrin-imidazolium salt: Synthesis, characterization of organometallic complexes and Suzuki coupling

Article abstract of DOI:10.1039/c1nj20200f

A new ligand based on permethylated β-cyclodextrin bearing a methylimidazole group was synthesized. In the presence of this N-heterocyclic carbene ligand, silver or palladium complexes were generated. Interestingly, palladium species based on this ligand

Full text of DOI:10.1039/c1nj20200f

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PAPER
An N-heterocyclic carbene ligand based on a b-cyclodextrin–imidazolium
salt: synthesis, characterization of organometallic complexes and
Suzuki couplingwz
c
c
¸
ois-Xavier Legrand,yab Mickael Menand, Matthieu Sollogoub,
¨
´
Franc
´
ab
Sebastien Tilloy and Eric Monflier*ab
Received (in Victoria, Australia) 4th March 2011, Accepted 12th April 2011
DOI: 10.1039/c1nj20200f
A new ligand based on permethylated b-cyclodextrin bearing a methylimidazole group was
synthesized. In the presence of this N-heterocyclic carbene ligand, silver or palladium complexes
were generated. Interestingly, palladium species based on this ligand are more active than
palladium species based on TPP or IMes,Cl for a Suzuki cross-coupling reaction.
The first isolation of stable carbene by Bertrand et al.1
followed by the discovery of N-heterocyclic carbene (NHC)
by Arduengo et al. inspired the development of organometallic
and coordination chemistry of NHC ligands.2 NHCs have
emerged as stronger binding and less oxidizable alternative
ligands to classical phosphanes.3 The shape of NHCs signifi-
cantly differs from that of their phosphane counterparts. In the
case of transition-metal phosphane complexes, the phosphane
substituents point away from the metal center, forming a cone.
In transition-metal NHC complexes, the substituents bound to
the carbene nitrogen atom point toward the metal center and
thereby surround the metal. NHC ligands possessing bulky
groups are therefore particularly interesting. Indeed, successful
transformations often require low coordinated organometallic
complexes and the sterically demanding NHC ligands favour
the formation of such complexes.4
were prepared to be used as chiral selectors6 or linkers for a
CD dimer.7
We report herein, the first synthesis of an NHC-appended
CD, the study of the solubility, aggregation and recognition
properties of its imidazolium precursor as well as its coordina-
tion and catalytic behaviors.
PM-b-CD-MIM,Cl (1) was synthesized in two steps from
mono(6-O-tosyl)-b-CD (b-CD-OTs), which is easily prepared
by the tosylation of b-CD on a large scale.8 b-CD-OTs was
permethylated in the presence of methyl iodide and NaH to
give permethylated b-CD-OTs (PM-b-CD-OTs; yield: 50%).9
PM-b-CD-OTs and 1-methylimidazole (MIM) reacted in
DMF to give PM-b-CD-MIM,OTs. Attempts to precipitate
this product were unsuccessful, so a dialysis technique was
used to separate PM-b-CD-MIM,OTs from DMF and unreacted
MIM. To finish, PM-b-CD-MIM,OTs was converted to its
chloride salt (1) by being passed through an anion-exchange
resin. The compound 1 was obtained as a pale yellow solid
(yield: 48%) and fully characterized by mass (MALDI-TOF)
and NMR spectroscopies (see ESIz) (Scheme 1).
In this context, the association of an NHC ligand with a
cyclodextrin (CD) moiety is promising, as it would bring
together steric crowding around the metal, water-solubility
and a spatially close recognition site.5 Although synthesis of
imidazolium CDs has been thoroughly reported in the literature,
they have never been used to generate an NHC and used in an
organometallic catalytic process. In fact, these compounds
First of all, solubility tests have shown that 1 is highly
soluble in organic solvents such as chloroform (450 mM at
20 1C), methanol (4100 mM at 20 1C), dichloromethane
(420 mM at 20 1C), dioxane (4100 mM at 20 1C), THF
(420 mM at 20 1C) or DMF (4100 mM at 20 1C) and in
water (440 mM at 20 1C). The compound 1 was firstly
characterized by NMR spectroscopy. NMR spectra recorded
in CDCl3 show that the chemical shifts of the three protons of
the imidazolium ring (H-2, H-4 and H-5) depend on the
concentration of 1 (Fig. 1). These concentration-dependent
shifts were already observed in the literature and were attributed
to p–p stacking interactions between the imidazolium rings.10
a Univ Lille Nord de France, F-59000 Lille, France
b UArtois, UCCS UMR CNRS 8181, rue Jean Souvraz,
F-62300 Lens, France. E-mail: eric.monflier@univ-artois.fr;
Fax: +33 3 21 79 17 55; Tel: +33 3 21 79 17 72
c
´
UPMC Univ Paris 06, Sorbonne Universites,
Institut Parisien de Chimie Moleculaire (UMR CNRS 7201),
´
FR 2769 C. 181, 4 place Jussieu, F-75005 Paris, France.
Fax: +33 1 47 27 55 04; Tel: +33 1 47 27 61 63
w Dedicated to Professor Didier Astruc on the occasion of his 65th
birthday.
1
z Electronic supplementary information (ESI) available. See DOI:
Moreover, H NMR spectra recorded in D2O displayed that
10.1039/c1nj20200f
deuterium exchange of the proton H-2 of the imidazolium ring
was observed as illustrated by the disappearance of the signal for
this proton (Fig. 2).11 This disappearance was also confirmed
y Present address: Commissariat a l’Energie Atomique et aux Energies
Alternatives, DSM/IRAMIS/SIS2M/LSDRM, UMR CEA/CNRS
3299, Centre de Saclay, 91191 Gif-sur-Yvette, France.
c
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Scheme 1 Synthetic pathway of the cyclodextrin-based imidazolium 1.
Reagents and conditions: (i) CH3I, NaH, anhyd. DMF, 6 h at 0 1C then
12 h at RT, 50%; (ii) (a) 1-methylimidazole, anhyd. DMF, 72 h at
80 1C; (b) dialysis; (c) ion exchange, 96%.
Fig. 2 Partial 1H NMR spectra (20 1C, 700.13 MHz, 2.0 mM, D2O)
of 1 recorded initially (a), after 2 h 30 min (b) and after 22 h (c).
Fig. 1 Partial 1H NMR spectra (20 1C, 700.13 MHz, CDCl3) of 1
recorded at (a) 1.5 mM; (b) 8.0 mM; (c) 40 mM.
by the modification of the H-4 and H-5 NMR signals. Initially,
the H-4 and H-5 protons appeared in the form of a pseudo-
singlet due to a 3J coupling between H-4 and H-5 protons and
a 4J coupling between H-2 and H-4 (or H-5) protons (Fig. 2a).
Indeed, after complete deuteriation of the acidic site of the
imidazolium cycle, the H-4 and H-5 imidazolium protons
appeared in the form of a doublet due to a 3J coupling between
H-4 and H-5 protons (Fig. 2c). In this case, a value of 1.77 Hz
was determinated for the 3JH-4/H-5 constant coupling. In order
to determine the rate constant for the hydrogen–deuterium
exchange reaction, 1H NMR spectra were also recorded at
repeated time intervals (see ESIz). The kH/D rate constant was
found to be equal to 4.53 ꢀ 10ꢁ3 minꢁ1 by considering a first
order kinetic (t1/2 = 2 h 30 min).
Fig. 3 Surface tension curves of an aqueous solution of 1 at 25 1C.
the CD moiety (see ESIz). These data clearly indicated that the
imidazolium ring is not included into the CD cavity. So, the
formation of aggregates are probably due to p–p stacking
interactions between imidazolium rings.13 As no self-inclusion
phenomenon was evidenced, the cavity should be able to
accommodate a guest. 1-Adamantol was selected to check
the inclusion properties because of its high affinity for the b-CD
cavity.14 An off-resonance ROESY experiment performed on
a mixture 1/1-adamantol displayed dipolar contacts between
1-adamantol and CD cavity protons proving that 1 is able to
include a guest (Fig. 4). Assuming a 1 : 1 stoichiometry, the
value of the association constant between 1-adamantol and 1
was determined by UV-vis spectroscopy and was found to be
equal to 5940 Mꢁ1 (see ESIz).
The surface active behavior of 1 was investigated by
measuring the evolution of the surface tension (g) versus the
concentration of 1 in water (Fig. 3). Surprisingly, the curve
exhibited two inflection points at 0.02 and 0.37 mM and a
plateau was observed at 1.5 mM. The inflection points are
characteristic of aggregation phenomena and the plateau
corresponds to the formation of micelles in water. In order
to have a better insight into the mechanism of aggre-
gates formation, off-resonance ROESY experiments were
performed.12 No dipolar contact was observed between the
protons of the imidazolium ring and the internal protons of
The coordination properties of the NHC complexes using 1
as a precursor were also studied. The silver complex (2) was
prepared in degassed CH2Cl2 by mixing 1 (2 eq.) with Ag2O
c
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Fig. 5 Partial 1H NMR spectra (20 1C, 300.13 MHz, 30 mM, CD2Cl2)
of (a) 1 and (b) 2.
Fig. 4 Partial contour plot of an off-resonance ROESY experiment
(15 1C, 599.94 MHz, D2O, effective angle: 54.71, mixing time: 300 ms)
recorded on a mixture of 1 (0.75 mM) and 1-adamantol (2.25 mM).
Horizontal part: 1-adamantol region; vertical part: cyclodextrine
region of the spectra.
Scheme 2 Proposed structures for 2.
(Scheme 2). 2 was sufficiently stable to be characterized by 1H
and 13C NMR spectroscopy. The 1H and 13C{1H} JMOD
NMR data reflect significant changes between the imidazolium
Fig. 6 Partial 13C{1H} JMOD NMR spectra (20 1C, 300.13 MHz,
30 mM, CD2Cl2) of (a) 1 and (b) 2.
1
salts and the carbene complex (Fig. 5 and 6). Indeed, the H
NMR spectrum showed the disappearance of the H-2 proton
resonance at 10.0 ppm together with a shielding of the
aromatic protons (Fig. 5). The formation of the silver(I)
carbene complex was confirmed in the 13C{1H} JMOD
NMR spectra by the disappearance of the C-2 resonance at
139.5 ppm for 1 and the appearance of the C-2 resonance at
171.4 ppm for 2 (Fig. 6). This value is similar to the chemical
shifts seen in other silver imidazolylidene complexes.15 However,
no coupling was observed between C-2 and the silver atom.
The lack of coupling may be due to reversible coordination of
the carbene to the silver center in solution.16 By analogy with
the characterized structures of silver complexes described in
the literature, complex 2 can be assigned to a mono or a bis-
(imidazol-2-ylidene)silver structure. Unfortunately, attempts
to obtain the exact structure were unsuccessful. Indeed, the
electrospray mass spectrum of 2 only showed the signal of 1
probably due to the poor stability of the complex under the
ESIz conditions. Moreover, no X-ray structure was obtained
because of difficulties to obtain the crystallisation of 2.
Finally, catalytic behaviour of the system was probed. The
palladium catalyzed Suzuki coupling reaction of phenyl bro-
mide with phenylboronic acid was chosen as model reaction to
evaluate the capacity of 1 to stabilize active catalytic species.17
All reactions were carried out with Pd(OAc)2 as a palladium
source and Cs2CO3 as a base. No catalytic activity was
observed without the ligand in
a control experiment
(Table 1, entry 1). For the following experiments, the catalyst
was formed in situ from 1 (or other ligand) and Pd(OAc)2 in
the presence of Cs2CO3. A first set of reactions was performed
in 1,4-dioxane (entries 1–7), THF being a less suitable solvent
c
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Table 1 Suzuki cross-coupling of phenylbromide and phenylboronic
acid to yield biphenyla
due to the unstability of this carbene in the presence of labile
protons. Work is currently in progress to synthesize isolable
NHC appended to CDs for organometallic catalysis.
Experimental
Entry
Solvent
Ligand
L/Pd
Yieldb (%)
Synthesis of 6A-deoxy-6A-(3-N-methylimidazolium)-
2A,2B,2C,2D,2E,2F,2G,3A,3B,3C,3D,3E,3F,3G,6B,6C,6D,6E,6F,6G-
eicosa-O-methyl-b-cyclodextrin chloride salt 1
1
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
THF
(–)
1
1
1
1
TPP
IMes,Cl
1
1
1
1
(–)
1
1
2
2
5
2
2
2
0
52
60
39
99
17
25
22
1
2
3c
4
N-Methylimidazole (2.63 g i.e. 2.55 mL, 32 mmol) was added
under an inert atmosphere to a stirred solution of dried PM-b-
CD-OTs (5.0 g, 3.2 mmol) in dry DMF (10 mL). The reaction
mixture was stirred for 72 h at 80 1C under nitrogen. After
evaporation of most of the solvent under reduced pressure, the
residual syrup was then purified by dialysis (MWCO 1000 Da,
Spectra/Pors 7 dialysis membrane, Spectrum Laboratories)
against 5 L deionized water while stirring at 20 1C. The water
was changed after 2 h followed by an additional 2 h of dialysis.
The last step was repeated all five times to give after evapora-
tion under reduced pressure the tosylate salt of 1 as a yellow
powder. Finally, this powder was dissolved in deionised water
and replacement of tosylate by chloride was performed by
using an Amberlites IRA-900 Cl resin. The solution was
filtered and the corresponding filtrate was collected and the
solvent was removed by evaporation under reduced pressure
to give the desired product, chloride salt 1 as a yellow
amorphous solid (4.45 g, 96%).
5c
6d
7
8
9
10
11
12
Water
Dioxane/watere
Toluene/waterf
Dioxane
2
2
2
15
5
2
b-CD-MIM,Cl
a
Experimental conditions: Pd(OAc)2 (2.22 ꢀ 10ꢁ2 mmol), solvent
(5 mL), bromobenzene (3.34 mmol), phenylboronic acid (4.01 mmol),
b
Cs2CO3 (6.68 mmol), T: 50 1C; time: 6 hours. Yield calculated from
c
d
bromobenzene. Time: 16 hours. For a ratio Pd/TPP inferior to 5,
the catalytic system was unstable (presence of black palladium
e
precipitate). v(dioxane)/v(water) = 75/25. v(toluene)/v(water) =
f
50/50.
(entries 4 vs. 8). Although the kinetics of the reaction is faster
during the first 6 hours using one equivalent of 1, two
equivalents lead to a better stabilization of the catalytic species
(compare entries 2 and 4) and allow a total conversion after
16 hours (compare entries 3 and 5).18
[a]D = +267.51 (c 2.0, H2O); 1H NMR (700.13 MHz,
20
CDCl3, 293.0 K): d = 9.85 (ps, 1H, N–CHQN), 7.64 (ps, 1H,
CH2–N–CHQCH), 7.32 (ps, 1H, CH3–N–CHQCH), 5.15 (d,
1H, JH –H = 3.3 Hz, H1sub), 5.13 (d, 1H, JH –H = 3.6 Hz,
Two comparison experiments were conducted in the presence
of the classical ligand triphenylphosphane (TPP) and the typical
NHC ligand 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride
(IMes,Cl). Interestingly, the catalytic activity observed in the
presence of 1 is 1.5 and 2-fold higher than in the presence of
IMes,Cl and TPP, respectively (compare entry 4 with entries 6
and 7). As 1 is water-soluble, the catalytic activity of Pd–NHC
complexes derived from 1 was also evaluated in water. Indeed,
only few hydrophilic metal–NHC complexes have been used
during organometallic catalytic processes.19 In pure water, the
catalytic activity dramatically decreased (entry 9). The same
tendency was also observed in a mixture of dioxane/water or
toluene/water (entries 10 and 11). From these results, it appears
that the catalytic system is unstable in water. An experiment
performed in dioxane by replacing 1 by its hydroxylated
equivalent (b-CD-MIM,Cl; the hydroxyl groups of CD are
not methylated) confirmed that the presence of labile protons
has a disastrous influence on the catalytic activity (entry 12).
As a summary, we have prepared a new CD-appended
imidazolium salt ligand (1), which is soluble in water and in
organic solvents and displays aggregation properties depending
on concentration. Its cavity is however available for inclusion
of a hydrophobic guest. Silver complexes could also be
generated with 1. Furthermore, a Suzuki cross-coupling reac-
tion was performed using 1 generating catalytic active species
with a palladium precursor. It is important to underline that
palladium species based on 1 are more active than those based
on the classical ligand such as TPP or IMes,Cl. Unfortunately,
the catalytic experiments performed in water failed probably
3
3
1
2
1
2
H1), 5.10 (d, 1H, 3JH –H = 3.4 Hz, H1), 5.08 (d, 1H, 3JH –H
=
1
2
1
2
3
3.4 Hz, H1), 5.05 (d, 1H, JH –H = 3.3 Hz, H1), 5.05 (vt, 2H,
1
2
JH –H = 4.5 Hz, H1), 4.79 (dd, 1H, 3JH –H = 2.8 Hz, JH –H
14.7 Hz, H6 sub), 4.57 (dd, 1H, 3JH –H = 2.7 Hz, 2JH –H = 14.7
3
2
0
0
=
1
2
5
6
6
6
0
0
6
5
6
6
0
Hz, H6 sub), 4.16 (s, 3H, N–CH3), 4.12 (m, 1H, H5sub), 3.98–3.22
0
(m, 91H, H3sub, H3, H4, H5, H6, H6 , Me2, Me3, Me6), 3.21–3.12
(m, 6H, H2), 3.00 (dd, 1H, 3JH –H = 3.3 Hz, 3JH –H = 10.3 Hz,
1
2
2
3
H
2sub), 2.98 (t, 1H, 3JH –H E 3JH –H = 9.5 Hz, H4sub); 13C NMR
3 4 4 5
(176.06 MHz, CDCl3, 293.0 K): 139.51 (1 ꢀ N–CHQN), 123.83
(1 ꢀ CH2–N–CHQCH), 122.66 (1 ꢀ CH3–N–CHQCH), 100.42,
100.22, 99.30, 99.19, 99.12 (6 ꢀ C1), 98.02 (1 ꢀ C1sub), 82.48,
82.34, 82.25, 82.09, 81.85, 81.78, 81.73, 81.45, 81.42, 81.28, 81.08,
80.84, 80.78, 80.58, 80.04, 79.87 (7 ꢀ C2, 7 ꢀ C3, 7 ꢀ C4),
72.75, 71.99, 71.53, 71.42, 71.39, 71.35, 71.18, 71.15, 71.03
(6 ꢀ C5, 6 ꢀ C6), 68.77 (1 ꢀ C5sub), 61.92, 61.72, 61.65,
61.59, 61.54, 61.32 (6 ꢀ Me6), 60.11, 59.42, 59.24, 59.12, 59.06,
58.80, 58.59, 58.54, 58.47 (7 ꢀ Me2, 7 ꢀ Me3), 49.92 (1 ꢀ C6sub),
37.21 (1 ꢀ N–CH3); MALDI-TOF-MS: m/z = 1479.576
(calcd. 1479.733 for [C66H115O34N2Cl–Cl]+); UV-vis (water,
293.15 K); lmax = 211 nm, log e = 3.71.
Synthesis of silver(I)–carbene complex 2
The silver(I)–carbene complex 2 was synthesised from 1 via a
procedure adapted from the literature.20 Briefly, Ag2O (6 mg,
0.025 mmol) was added to a degassed solution of 1 (76 mg,
0.05 mmol) in anhydrous dichloromethane (1 mL). The reaction
mixture was stirred at room temperature in the dark,
c
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by recovering the Schlenk flask with aluminium foil, until
discoloration of the dark solution. After this stirring period,
the mixture was filtered through Celites to give a pale yellow
filtrate. The solvent was removed under reduced pressure and
the resulting solid was dried under reduced pressure to afford a
pale yellow material (97% yield).
1H NMR (300.13 MHz, CD2Cl2, 295.1 K): d = 7.30 (d, 1H,
3JH–H = 1.6 Hz, CH2–N–CHQCH), 7.03 (d, 1H, 3JH–H = 1.6
Hz, CH3–N–CHQCH), 5.14–5.08 (m, 4H, H1), 5.07 (d, 1H,
3JH1–H2=3.5 Hz, H1), 5.03 (d, 1H, 3JH1–H2=3.3 Hz, H1), 5.00
5 For cyclodextrin-phosphane used during organometallic catalytic
processes, see: M. T. Reetz and S. R. Waldvogel, Angew. Chem.,
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R. Marchelli and G. Vecchio, Electrophoresis, 1997, 18, 905;
T. T. Ong, T. Weihua, W. Muderawan, S. C. Ng and H. Sze On
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(d, 1H, 3JH –H = 3.5 Hz, H1), 4.81 (dd, 1H, 3JH –H = 1.5 Hz,
0
1
2
5
6
2
3
JH –H = 13.9 Hz, H6 sub), 4.43 (dd, 1H, JH –H = 1.9 Hz,
0
0
6
6
5
6
2
0
0
JH –H = 13.9 Hz, H6 sub), 4.06–2.96 (m, 103H, N–CH3, H2,
6
6
H3, H4, H5, H6, H6 , Me2, Me3, Me6); 13C NMR (75.49 MHz,
CD2Cl2, 295.1 K): 171.38 (1 ꢀ N–C(Ag)QN), 122.59 (1 ꢀ
CH2–N–CHQCH), 122.31 (1 ꢀ CH3–N–CHQCH), 99.76,
99.73, 99.45, 99.08, 98.98, 98.94, 98.45 (7 ꢀ C1), 84.21,
82.77, 82.72, 82.67, 82.61, 82.51, 82.47, 82.40, 82.36, 82.21,
82.08, 80.83, 80.62, 80.47, 80.36, 80.33, 79.73 (7 ꢀ C2, 7 ꢀ C3,
7 ꢀ C4), 73.12, 72.32, 72.13, 71.90, 71.81, 71.70, 71.63, 71.61,
71.39, 71.25, 71.00 (7 ꢀ C5, 6 ꢀ C6), 62.03, 61.80, 61.70, 61.65,
61.52, 61.41 (6 ꢀ Me6), 59.65, 59.54, 59.50, 59.44, 59.33, 59.19,
59.18, 58.98, 58.90, 58.80, 58.59, 58.44 (7 ꢀ Me2, 7 ꢀ Me3),
53.8 (1 ꢀ C6sub, resonance overlapped by solvent signals),
39.24 (1 ꢀ N–CH3).
0
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Organometallics, 2006, 25, 5151.
General procedure for the Suzuki–Miyaura
cross-coupling reaction
The first step was the preparation of the catalytic solutions
under nitrogen using standard Schlenk techniques. In a typical
experiment, Pd(OAc)2 (2.22 ꢀ 10ꢁ2 mmol), 1 (4.44 ꢀ 10ꢁ2 mmol)
and caesium carbonate (6.68 mmol) were dissolved in 10 mL
of deoxygenated 1,4-dioxane and stirred for about one hour at
1250 rpm. Then, after this incubation step, the catalytic
solution was added to degassed bromobenzene (3.34 mmol)
and phenylboronic acid (4.01 mmol). The glass reactor
was then heated at 50 1C, stirred with a magnetic stirrer at
1250 rpm. For kinetic measurements the time corresponding
to the desired temperature was considered as the beginning of
the reaction. The reaction medium was sampled during the
reaction by GC analyses.
17 For reviews, see: N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95,
2457; S. P. Stanforth, Tetrahedron, 1998, 54, 263; A. Suzuki,
J. Organomet. Chem., 1999, 576, 147.
18 Black palladium precipitate is observed after 6 hours of reaction with
one equivalent of 1 explaining the decrease in catalytic activity.
19 For examples, see: W. A. Herrmann, M. Elison, J. Fischer and
C. Kocher, US Pat. 5 663 451, 1997; I. Ozdemir, B. Yigit,
B. Cetinkaya, D. Ulku, M. N. Tahir and C. Arici, J. Organomet.
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D. Schonfelder, O. Nuyken and R. Weberskirch, J. Organomet.
Chem., 2005, 690, 4648; D. Schonfelder, K. Fischer, M. Schmidt,
O. Nuyken and R. Weberskirch, Macromolecules, 2005, 38, 254;
J. P. Gallivan, J. P. Jordan and R. H. Grubbs, Tetrahedron Lett.,
2005, 46, 2577; S. H. Hong and R. H. Grubbs, J. Am. Chem. Soc.,
2006, 128, 3508; J. W. Kim, J. H. Kim, D. H. Lee and Y. S. Lee,
Tetrahedron Lett., 2006, 47, 4745; C. Fleckenstein, S. Roy,
S. Leuthaußer and H. Plenio, Chem. Commun., 2007, 2870;
J. P. Jordan and R. H. Grubbs, Angew. Chem., Int. Ed., 2007,
46, 5152; F. Tewes, A. Schlecker, K. Harms and F. Glorius,
J. Organomet. Chem., 2007, 692, 4593; H. Ohta, T. Fujihara and
Y. Tsuji, Dalton Trans., 2008, 379; M. Meise and R. Haag,
ChemSusChem, 2008, 1, 637; J. Mesnager, P. Lammel,
E. Jeanneau and C. Pinel, Appl. Catal., A, 2009, 368, 22;
J. Mesnager, C. Quettier, A. Lambin, F. Rataboul, A. Perrard
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A. C. Benyei and F. Joo, Organometallics, 2010, 29, 2484; S. Roy
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Acknowledgements
One of us (F.-X. L.) is thankful to Drs P. Berthault and
G. Huber (CEA/DSM/IRAMIS/SIS2M/LSDRM) for the
high-resolution NMR facility and to Dr B. Rousseau and
D.-A. Buisson (CEA/DSV/IBITEC-S/SCBM) for the use of
their analytical platform. Roquette Freres (Lestrem, France) is
gratefully acknowledged for generous gifts of b-cyclodextrin.
Notes and references
1 A. Igau, H. Grutzmacher, A. Baceiredo and G. Bertrand, J. Am.
Chem. Soc., 1988, 110, 6463.
2 A. J. Arduengo, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1991, 113, 361.
3 S. Leuthausser, D. Schwarz and H. Plenio, Chem.–Eur. J., 2007, 13,
7195; A. Azua, S. Sanz and E. Peris, Organometallics, 2010, 29, 3661.
4 S. Wurtz and F. Glorius, Acc. Chem. Res., 2008, 41, 1523.
20 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, 972.
c
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New J. Chem., 2011, 35, 2061–2065 2065