Nickel(II), palladium(II) and rhodium(I) complexes of new NHC-thioether ligands: Efficient ketone hydrosilylation catalysis by a cationic Rh complex

Article abstract of DOI:10.1002/ejic.200700670

Five new, bifunctional imidazolium-thioether ligands of the general formula RS(CH₂)_n(imidazolium)⁺ArBr^- (n = 2 or 3, R = Et or tBu, Ar = 2,4,6-trimethylphenyl or 2,6-diisopropylphenyl) have been synthesised in good overall yields by a general method and used as N-heterocyclic carbene precursors for complexation studies on various transition metals (Ni^II, Pd^II and Rh^I). Sulfur does not coordinate the nickel centre, whereas the two functional groups bind the palladium centre to form a dinuclear compound. Cationic rhodium(I) complexes have also been prepared and preliminary catalytic tests show that they have good activity for the hydrosilylation of ketones. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700670

FULL PAPER
DOI: 10.1002/ejic.200700670
Nickel(II), Palladium(II) and Rhodium(I) Complexes of New NHC-Thioether
Ligands: Efficient Ketone Hydrosilylation Catalysis by a Cationic Rh Complex
Joffrey Wolf,[a] Agnès Labande,*[a] Jean-Claude Daran,[a] and Rinaldo Poli[a]
Keywords: N-Heterocyclic carbenes / S ligands / Nickel / Palladium / Rhodium
Five new, bifunctional imidazolium–thioether ligands of the
general formula RS(CH2)n(imidazolium)+ArBr– (n = 2 or 3, R
= Et or tBu, Ar = 2,4,6-trimethylphenyl or 2,6-diisopro-
tre, whereas the two functional groups bind the palladium
centre to form a dinuclear compound. Cationic rhodium(I)
complexes have also been prepared and preliminary cata-
pylphenyl) have been synthesised in good overall yields by lytic tests show that they have good activity for the hydro-
a general method and used as N-heterocyclic carbene pre- silylation of ketones.
cursors for complexation studies on various transition metals
(NiII, PdII and RhI). Sulfur does not coordinate the nickel cen-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
tive products of their complexation to various metals of
interest in catalysis: nickel(II), palladium(II) and rhodi-
um(I).
Introduction
N-Heterocyclic carbenes (NHC) have been thoroughly
studied over the last 15 years.[1] Whereas the high strength
of metal–NHC bonds has yielded new classes of robust cat-
alysts,[2–4] the combination of NHCs and less strongly bind-
ing heteroatom donors has been investigated in order to
combine robustness and activity in the corresponding com-
plexes. Thus NHC–phosphane[5–10] and NHC-N do-
nor[11,12] or NHC-O donor[13] ligands have been developed.
Thioethers are soft donor ligands and have been success-
fully used in catalysis, mostly in combination with other
donors such as phosphanes.[14] In combination with NHCs,
they could provide potentially useful catalytic properties. A
few NHC–thioether precursors have already been de-
scribed, but they have mainly been used as bioactive com-
pounds (antibacterials, fungicides)[15] or for heavy metal ex-
traction from water.[16] Few carbene–thioether complexes
have been isolated and characterised, respectively, by Seo et
al. in 2003[9] and Ros et al. recently[17,18] (Figure 1). NHC–
furan and NHC–thiophene ligands have also been de-
scribed, but only the NHC moiety coordinates the metal
centre.[19] We have recently described an efficient synthetic
pathway for phosphane–imidazolium compounds, using 1-
bromoalkyl-3-arylimidazolium bromides as key intermedi-
ates.[5,6] We have now extended this methodology to the syn-
thesis of NHC–thioether precursors and report here the
characterisation of these new ligands, as well as representa-
Figure 1. NHC–thioether complexes described in the literature. (A)
Seo et al.[9], (B) Ros et al.[17,18]
Results and Discussion
Ligand Syntheses
[a] Laboratoire de Chimie de Coordination, UPR CNRS 8241 (lié
par convention à l’Université Paul Sabatier et à l’Institut
National Polytechnique de Toulouse),
Compounds 5–7 were obtained from 1-(2-bromoethyl)-3-
arylimidazolium bromides 1 and 2, and compounds 8 and
9 from 1-(3-bromopropyl)-3-arylimidazolium bromides 3
and 4, by nucleophilic substitution with lithium alkylthiol-
ates (Scheme 1). An optimisation study has been carried out
on the reaction of compound 1 with lithium tert-butyl
205 route de Narbonne, 31077 Toulouse Cedex 4, France
Fax: +33-561553003
E-mail: agnes.labande@lcc-toulouse.fr
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 5069–5079
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J. Wolf, A. Labande, J.-C. Daran, R. Poli
FULL PAPER
Scheme 1. Nucleophilic substitution on 1–4 bromides by lithium alkylthiolate reagents.
thiolate (Table 1). Alcohols and water are commonly used
solvents for nucleophilic substitution reactions with thiol-
ates,[20] whereas acetone and DMF are employed with phe-
nolates.[21] Ethanol and DMF produced homogeneous mix-
tures with our substrates, contrary to acetone and dichloro-
methane. Our first attempt in ethanol at 60 °C, however,
gave 62% of an elimination product, E, and only 7% of the
expected compound. The temperature was lowered to 25 °C
in order to improve the selectivity in favour of the substitu-
tion product: compound 5 was obtained in 14% yield, but
again with 57% of elimination product (entry 1). A system-
atic study of the reaction conditions showed that the reac-
tion is highly solvent-dependent, ethanol and acetone lead-
ing to substantial amounts of elimination product E,
whereas dichloromethane and DMSO yield greater selectiv-
ity in favour of the substitution product but at slower rates.
The conversion was also greatly improved when the reac-
tions were carried out in more dilute media (entries 4 and
6). Under optimised reaction conditions (entry 6), 5 was
obtained in very good yields (Scheme 1). These conditions
were successfully applied to other substrates to afford thio-
ethers 6–9 in good yields.
Figure 2. ORTEP views of 5 (a) and 6 (b). Ellipsoids are shown at
the 30% probability level. All hydrogen atoms except H(1) and the
solvent molecule (CH2Cl2) which co-crystallised with 5 are omitted
for clarity.
Table 1. Solvent and concentration screening for ligand 5 synthe-
Nickel Complexes
sis.[a]
Preliminary complexation studies were carried out with
the catalytically relevant metals nickel, palladium and rho-
dium. Our previous studies of the coordination of phos-
phane-imidazolium salts to NiII complexes of type NiX2L2
led to the isolation of zwitterionic compounds of the for-
mula [NiX3(PPh2ImAr)], where ImAr is as defined in
Scheme 1.[5,6] The analogous reaction of 5 with 1 equiv. of
NiBr2(DME) did not give the corresponding zwitterionic
species with sulfur coordination. A NiBr42– species with two
imidazolium/thioether counterions, 10, was obtained in-
stead (Scheme 2). Deprotonation of 10 with tBuOK led to
Entry
Solvent
Solvent amount (mL)
1/E/5[b]
1
2
3
4
5
6
7
EtOH
Me2CO
DMSO
DMSO
CH2Cl2
CH2Cl2
CH2Cl2
2
2
2
3
2
3
4
29/57/14
38/50/12
85/00/15
60/00/40
74/07/19
03/03/94
30/01/69
[a] 1 (0.5 mmol), tBuSLi (0.55 mmol), 17 h at room temperature.
[b] Ratio determined by ethylene signal integration in 1H NMR
spectra of crude products.
1
The H NMR signals of the acidic imidazolium protons the biscarbene complex 11, with no sulfur coordination
are observed between 10.03 and 10.28 ppm for compounds onto the nickel centre. The alternative strategy consisting of
5, 6 and 8, and at δ = 9.87 ppm for compounds 7 and 9, initial deprotonation of ligand 5 with a strong base, fol-
which denotes a greater shielding effect of the bulky DIPP lowed by reaction of the resulting free carbene with
compared to the mesityl group. Compounds 5 and 6 were NiBr2(DME), also led to the same product. The absence
analysed by single-crystal X-ray diffraction. The structures of sulfur coordination has two possible explanations: the
(Figure 2) show hydrogen bonds, as is typically observed for bulkiness of the tert-butyl group prevents the coordination
imidazolium bromides,[22] between the bromide anion and on the nickel, or the sulfur donor power is insufficient to
the C1 proton (Br1···H1–C1 2.637 Å for 5, 2.624 Å for 6).
compete with bromide for coordination. In order to con-
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Efficient Ketone Hydrosilylation Catalysis
firm one of these hypotheses, we added 1 equiv. of 6, which Table 2. Comparison of the main structural parameters of 11 and
NiBr2(1,3-dicyclohexylimidazol-2-ylidene)2.
contains a less bulky ethyl substituent, to 1 equiv. of
[a]
NiBr2(MeCN)2. During the treatment, unreacted nickel
corresponding to half of the starting material was reco-
vered. This result would be more in favour of the second
hypothesis, although we have no further evidence to vali- Ni–C1
date it.
11
NiBr2L2
Bond lengths [Å]
Ni–Br
2.3113(5)
1.9186(17)
1.359(2)
1.354(2)
1.385(2)
1.395(2)
1.348(3)
2.3113(4)
1.908(3)
1.353(4)
1.347(4)
1.394(5)
1.390(5)
1.333(5)
C1–N1
C1–N2
N2–C4
N1–C3
C3–C4
Bond angles [°]
C1–Ni–C1i
180.00(9)
180.00
C1–Ni–Br1
C1–Ni–Br1i
89.48(5)
90.52(5)
89.41(10)
90.59(10)
Dihedral angles [°]
N1–C1–Ni–Br1
N2–C1–Ni–Br1i
N1–C1–C1i–N2i
74.43
75.41
0.98
[a] L = 1,3-dicyclohexylimidazol-2-ylidene.
are conformational isomers. In the crystalline compound,
the aryl and thioether alkyl chains of the two imidazol-2-
ylidene groups are mutually anti to afford a head-to-tail
arrangement, which minimises steric interactions. Strong
steric interactions between the N-substituents in a bis-
NHC-NiII complex have been observed for NiCl2[1,3-
bis(2,6-diisopropylphenyl)imidazol-2-ylidene]2, resulting in
a significant deviation from coplanarity for the two NHC
rings.[24] For our compound, it is possible to envisage that
the different N-substituents adopt a syn orientation in the
second isomer and that there is a significant barrier for the
180° rotation that is required to interconvert them. Recent
work by Gomes et al.[25] has shown that the energy barrier
for a 180° rotation of a N-heterocyclic carbene along the
C–Ni axis, in allyl NiII complexes, is 14–15 kcalmol–1
for NHCs bearing methyl substituents and becomes
Ͼ18 kcalmol–1 with tert-butyl substituents. In our case, the
imidazole-2-ylidene bears a bulky mesityl group on one side
and a functionalised alkyl chain on the other side. There-
fore it becomes possible to independently observe two con-
formational isomers.
Scheme 2. Nickel(II) complex synthesis.
The crystal structure of compound 11 has been resolved
by X-ray analysis (Figure 3). As the nickel atom is located
on an inversion centre, the geometry around it is perfectly
square-planar. The imidazol-2-ylidene ring is planar [maxi-
mum deviation of 0.005(1) Å for atom N2] and is approxi-
mately perpendicular [angle of 75.06(5)°] to the coordina-
tion plane, thus limiting steric interactions. This was already
observed for other previously described NiII–bis(NHC)
complexes.[23] The mesityl ring forms an angle of 77.63(6)°
with the NHC ring, and we can notice the existence of an
interaction between a hydrogen from methyl C119 and Br1
(C119···Br1i 2.75 Å). Selected bond lengths and angles are
listed in Table 2.
Palladium Complexes
Contrary to the nickel system, addition of ligands 5–9 to
PdBr2(COD) led to the expected coordination of the sulfur
and bromine atoms, leading to the zwitterionic complexes
12–16 in good yields (Scheme 3). A zwitterionic structure
for these complexes, with a coordinated thioether function
and a dangling imidazolium group, is suggested by the spec-
troscopic data. The typical signal of the acidic imidazolium
1
proton is still present in the H NMR spectra of all com-
Figure 3. An ORTEP view of compound 11. Ellipsoids are repre-
sented at the 50% probability level. Hydrogen atoms are omitted
for clarity.
plexes and is situated between 9.00 and 9.61 ppm. Likewise,
the elemental analyses of the complexes are in agreement
with the calculated values. Subsequent deprotonation of 13
Although only one isomer is present in the crystal, analy- (Scheme 3) led to NHC complex 17. The 1H and 13C NMR
sis by H and 13C NMR revealed a mixture of two distinct properties are consistent with the expected stoichiometry,
1
isomers in solution in a ratio of 1:1.27. We believe that these as for the related phosphane-carbene complexes previously
Eur. J. Inorg. Chem. 2007, 5069–5079
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J. Wolf, A. Labande, J.-C. Daran, R. Poli
FULL PAPER
Scheme 3. Synthesis of palladium(II) complexes.
described by Danopoulos et al.[7] and Lee et al.[26] The 13C
NMR signal of the carbene C atom is observed at δ =
155.75 ppm in the case of 17, and respectively at δ = 157.2
and 162.4 ppm for the above-mentioned phosphane-car-
1
bene complexes. Moreover, the H NMR spectrum of 17
only shows two protons for the imidazole cycle, appearing
as doublets, and a 2D HMBC NMR experiment confirms
the existence of a long-range coupling between these pro-
tons and the carbene C atom.
However, the X-ray structure (Figure 4) reveals that 17 is
a dinuclear complex where each palladium centre displays a
slightly distorted square-planar coordination environment.
The two square-planar moieties are located face to face and
the two NHC–thioether ligands span the metal centres in a
relative trans arrangement. Pd–C and Pd–S bond lengths
are comparable to the usual NHC–PdII and thioether–PdII
bonds.[7,26,27] A similar arrangement is adopted by related
NHC–oxazoline derivatives. Only three X-ray structures of
PdII complexes possessing a chelating NHC–thioether li-
gand have been described:[17,18] in these cases, the sulfur
atom is situated cis to the NHC moiety, with Pd–C and
Pd–S distances of, respectively, 2.036–2.063 Å and 2.326–
Figure 4. An ORTEP view of compound 17. Ellipsoids are repre-
sented at the 30% probability level. Hydrogen atoms and a co-
crystallised THF molecule are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd1–C1 1.990(4), Pd2–C2 1.983(4), Pd1–
S1 2.3731(9), Pd2–S2 2.3622(9), Br21–Pd2–Br22 175.50(2), C1–
Pd1–S1 173.10(12).
Rhodium Complexes
Addition of compounds 5–7 to [Rh(COD)Cl]2 in the
2.367 Å. Mass spectrometry analyses (FAB technique) con- presence of a strong base (Scheme 4) led, after halide ab-
firm the existence of a dinuclear compound. straction, to the formation of NHC derivatives 18–20. The
Scheme 4. Synthesis of rhodium(I) complexes.
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Efficient Ketone Hydrosilylation Catalysis
nature of these products, as salts of typical square-planar lecular distances: C5–C311 3.45(1) Å and H5–H31A
RhI complexes with cis chelating NHC–thioether ligands, is 2.36 Å; C6–C311 3.52(1) Å and H6–H31B 2.30 Å]. This
consistent with the spectroscopic characterisation. The 13C value is consistent with the previously reported data for
NMR signals of the carbene C atoms appear around similar complexes.[10,18,30] This distortion cannot be ob-
173 ppm, which is the expected value for cationic NHC– served in 18 and 19, which have a bulky tert-butyl substitu-
RhI complexes.[10,18,28] The sulfur coordination on rhodium ent on sulfur.
is suggested by the downfield shift (about 7 ppm) of the
quaternary carbon on sulfur for complexes 18 and 19, and
of the S–CH2CH3 carbon signal (about 6 ppm) for complex
20.[29]
Table 3. Comparison of the main structural parameters of 18–20
and of the RhI complex described by Seo et al. (A).
The square-planar coordination environment in com-
18
19
20
A[7]
plexes 18–20 was confirmed by X-ray diffraction studies
(Figure 5). Selected bond lengths and angles are listed in
Table 3. The structures reveal slightly shorter Rh1–C1 bond
lengths than in Seo’s NHC–thioether complex. Rh1–S1 dis-
tances are within the same range, except compound 20, for
which we observe a shorter bond of 2.351(2) Å. The Rh1–
C(COD) bonds trans to NHC are longer than the bonds
trans to sulfur, which indicates a stronger trans influence
of the NHC moiety. A boat-like conformation of the six-
membered metallacycle is a common feature for all these
structures. In the case of compound 20, the deviation from
the ideal 90° value of the C1–Rh1–S1 angle [82.5(2)°] could
be because of a close contact between the methylene of the
Bond lengths [Å]
Rh1–C1
Rh1–S1
Rh1–C11
Rh1–C12
Rh1–C15
Rh1–C16
C1–N1
2.032(4)
2.020(5)
2.042(7)
2.051(7)
2.394(2)
2.137(7)
2.148(9)
2.225(9)
2.236(8)
1.342(9)
1.319(9)
1.785(7)
1.802(7)
2.4076(10) 2.3940(18) 2.351(2)
2.145(4)
2.175(4)
2.199(4)
2.222(4)
1.351(5)
1.366(5)
1.827(4)
1.863(4)
2.127(6)
2.150(6)
2.191(6)
2.212(7)
1.341(7)
1.356(7)
1.791(8)
1.848(9)
2.149(6)
2.148(8)
2.175(6)
2.228(8)
1.360(9)
1.365(9)
1.806(9)
1.808(8)
C1–N2
S1–C5
S1–C6[a]
Bond angles [°]
C1–Rh1–S1
N1–C–1–N2
88.93(11)
104.0(3)
89.94(16) 82.5(2)
103.9(5) 104.1(6) 105.7(6)
89.0(2)
ethyl arm on sulfur (C311) and the COD ligand [intramo- [a] This carbon is labelled C111 for 19.
Figure 5. ORTEP views of the cations in complexes 18 (a), 19 (b) and 20 (c). Ellipsoids are represented at the 30% probability level.
Hydrogen atoms, the counterion (BF4) and a co-crystallised CDCl3 molecule 18 are omitted for clarity.
Eur. J. Inorg. Chem. 2007, 5069–5079
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J. Wolf, A. Labande, J.-C. Daran, R. Poli
FULL PAPER
Catalytic Hydrosilylation of Methyl Aryl Ketones
reaction. Finally, no reaction occurred when other silanes
(Et3SiH, MeEt2SiH and HSiCl3) were used with acetophe-
The catalysed hydrosilylation of ketones has attracted a none.
lot of attention for many decades as it is an efficient syn-
Table 4. Hydrosilylation of acetophenone.[a]
thetic alternative to the reduction of the carbonyl group by
main group hydrides and catalytic hydrogenation.[31] Rho-
dium is the favoured catalytic metal for this process, even
though other metals have been used. Neutral precatalysts
derived from RhCl(PPh3)3,[32,33] [RhCl(olefin)2]2 [olefin =
ethylene, cyclooctene; or (olefin)2 = 1,5-cyclooctadiene, nor-
bornadiene],[33–36] RhH(PPh3)4[37] or RhCl3L3[38] derivatives
have most commonly been used to generate the active cata-
lyst, but a few processes using cationic precursors have also
been reported.[39,40] It has also been reported that the assist-
ance of AgX (X = OSO2CF3, BF4) is required in some cases
to improve the catalytic activity,[38,41] presumably through
transformation into a more active cationic species. The typi-
cal supporting ligands, including chiral versions for the
enantioselective hydrosilylation of prochiral ketones, are
based on P or N donors. Although several catalysts have
shown outstanding activities,[36,41,42] the issue of catalyst
stability and deactivation may hamper extension to large-
scale production. As NHC ligands are likely to be solidly
anchored to the metal centre, they may be expected to im-
part activity and stability to the catalytic system. Previous
reports of ketone hydrosilylation using NHC ligands are
limited.[12,43,44] For these reasons, we considered it of inter-
est to test the catalytic activity of the cationic rhodium com-
plexes 18–20.
Catalyst
(mol-%)
Solvent
(concentration)
Yield
(%)[b]
Entry
R
t (h)
1
2
3
4
5
6
7
H
H
H
H
H
H
H
18 (2)
18 (2)
18 (1)
18 (1)
19 (1)
19 (1)
20 (1)
CH2Cl2 (1 )
THF (1 )
THF (1 )
THF (2 )
THF (1 )
THF (2 )
THF (2 )
17
17
24
4
8
4
90
99
90
99
99
99
99
1
[a] Ketone (1 equiv.), diphenylsilane (1.1 equiv.), room temperature,
then hydrolysis with MeOH. [b] Determined by integration of sig-
1
nals in H NMR spectra of crude products.
Table 5. Hydrosilylation of acetophenone derivatives.[a]
Yield
Entry
R
Catalyst
Concentration
t (h)
(%)[b]
1
2
3
4
5
6
7
8
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
4-F
4-F
4-F
2-Me
2-Me
2-Me
18
18
19
19
20
18
19
20
18
19
20
1 
2 
1 
2 
2 
2 
2 
2 
2 
2 
2 
24
3
6
2.5
2
4
4.5
2
6
3.5
3.5
80
98
99
99
99
96
99
99
78[c]
99
99
9
10
11
Preliminary catalytic tests have shown that these com-
plexes are indeed active in the hydrosilylation of acetophe-
none and its derivatives (Tables 4 and 5, Scheme 5). The
reactions were followed by TLC and the silylated intermedi-
[a] Ketone (1 equiv.), diphenylsilane (1.1 equiv.), room temperature,
1 mol-% catalyst, THF, then hydrolysis with MeOH. [b] Deter-
mined by integration of signals in 1H NMR spectra of crude prod-
ucts. [c] The reaction was stopped before completion.
1
ate was hydrolysed with MeOH before H NMR analysis.
The reactions were first carried out with 2 mol-% of 18, in
dichloromethane or THF. The yield of the expected alcohol
reached 90% in dichloromethane in 17 h (Table 4, entry 1),
whereas it was quantitative in THF (Table 4, entry 2). The
catalyst loading was thus lowered to 1 mol-%. With a con-
centration of 1  in acetophenone in THF, the yield reached
90% after 24 h. However, working in a more concentrated
medium allowed us to get a total conversion of the sub-
Scheme 5. Hydrosilylation of acetophenone and its derivatives with
RhI complexes.
The activity of our complexes compares well with pre-
strate into the alcohol in only 4 h (entry 4). A similar result viously reported RhI systems bearing bifunctional NHC-
was obtained with complex 19 (Table 4, entries 5 and 6). oxazoline ligands. Thus, Bolm et al. obtain excellent yields
Finally, complex 20 proved to be the most active, with a of 1-phenylethanol with their system, using 2 mol-% of cat-
quantitative yield of alcohol in only 1 h at room tempera- alyst in THF at room temperature or at 0 °C.[44] Unfortu-
ture (Table 4, entry 7). The same trend was observed with 4- nately there is no indication of reaction times, which does
methoxyacetophenone (Table 5, entries 1–5): increasing the not allow a direct comparison with our results. On the other
concentration allowed us to get a total conversion of the hand, César et al. report the hydrosilylation of aceto-
substrate into the desired alcohol in a reduced time, while phenone with diphenylsilane using 1 mol-% catalyst in
20 showed a better activity than 18 and 19. Similar results dichloromethane at room temperature. In their case, the
were obtained with 4-fluoroacetophenone, bearing an elec- RhI complexes tested give from 70% to 93% yield in a
tron-withdrawing substituent (Table 5, entries 6–8). The in- maximum of 5 h.[12]
troduction of a methyl group ortho to the halide, however,
The higher catalytic activity observed at higher ketone
slowed the reaction down. As an example, the reaction with concentration is in agreement with previous reports of a
18 did not go to completion after 6 h, with only 78% con- saturation effect: the reaction was found to be first order in
version (Table 5, entry 9). Thus steric factors seem to have ketone at low concentrations, but eventually became
more influence than electronic factors on the issue of the [ketone] independent at high concentrations.[35,40]
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Efficient Ketone Hydrosilylation Catalysis
(125.8 MHz, CDCl3, 25 °C): δ = 141.26 [p-C (Mes)], 137.77 (N–
CH–N), 134.31 [o-C (Mes)], 130.66 [N–C (Mes)], 129.81 [CH
(Mes)], 124.13 (AlkN–CH=), 122.74 (MesN–CH=), 50.33 (N–
CH2), 43.33 [SC(CH3)3], 31.00 [SC(CH3)3], 29.32 (CH2S), 21.11 [p-
CH3 (Mes)], 17.66 [o-CH3 (Mes)] ppm. MS (ESI, positive mode):
m/z (%) = 303.35 (100) [C18H27N2S+]. MS (ESI, negative mode):
m/z (%) = 79 (100) [Br–].
Conclusions
In conclusion, we have described a general and simple
method for the preparation of new NHC–thioether precur-
sors and explored their coordination chemistry. The coordi-
nation of sulfur on nickel was not observed, yielding com-
plex 11 where the two ligands are monodentate through the
NHC function and the thioether function is dangling. In
the case of palladium(II), a dinuclear complex with trans
carbene and sulfur coordination, 17, was obtained. Rhodi-
um(I) complexes with chelating carbene/thioether ligands
were finally prepared in good yields. Preliminary catalytic
studies have shown that these complexes are very active for
the hydrosilylation of acetophenone and its derivatives. The
asymmetric version of this reaction, as well as other cata-
lytic reactions, is now under investigation, and the results
will be published in due course.
1-[2-(Ethylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazolium Bromide
(6): EtSLi (246 mg, 3.61 mmol) was added to a solution of 1
(1.125 g, 3.01 mmol) in CH2Cl2 (18 mL). The mixture was stirred
for one day at room temperature. CH2Cl2 (22 mL) was added and
the mixture was washed with water (2ϫ15 mL). The organic phase
was dried (MgSO4), filtered and concentrated under vacuum to
give a white hygroscopic solid. Yield 1.07 g (95%). X-ray quality
crystals were obtained by slow diffusion of diethyl ether in a
CH2Cl2 solution. M.p. 117 °C. C16H23BrN2S (355.36): calcd. C
54.08, H 6.52, N 7.88; found C 53.96, H 6.51, N 8.00. 1H NMR
(500 MHz, CDCl3, 25 °C): δ = 10.08 (s, 1 H, NCHN), 8.26 (s, 1 H,
MesNCH=), 7.16 (s, 1 H, AlkNCH=), 6.94 [s, 2 H, CH (Mes)],
4.90 (t, 3J = 6.0 Hz, 2 H, NCH2), 3.09 (t, 3J = 6.1 Hz, 2 H,
CH2SEt), 2.62 (q, 3J = 7.4 Hz, 2 H, SCH2CH3), 2.29 (s, 3 H, p-
Experimental Section
3
CH3), 2.02 (s, 6 H, o-CH3), 1.16 (t, J = 7.4 Hz, 3 H, SCH2CH3)
ppm. 13C NMR (125.8 MHz, CDCl3, 25 °C): δ = 141.11 [p-C
(Mes)], 137.97 (NCHN), 134.29 [o-C (Mes)], 130.67 [NC (Mes)],
129.73 [CH (Mes)], 123.98 (AlkNCH=), 122.93 (MesNCH=), 48.88
(NCH2), 32.14 (CH2SEt), 25.67 (SCH2CH3), 21.07 [p-CH3 (Mes)],
17.61 [o-CH3 (Mes)], 14.61 (SCH2CH3) ppm. MS (ESI, positive
mode): m/z (%) = 275.15 (100) [C16H23N2S+]. MS (ESI, negative
mode): m/z (%) = 79 (100) [Br–].
General Methods: Reactions involving air- or moisture-sensitive
reagents and products were carried out under dry argon using
Schlenk glassware and vacuum line techniques, and dry, purified
solvents. All other steps were done without particular precautions.
Elemental analyses were carried out by the Service d’Analyse du
Laboratoire de Chimie de Coordination in Toulouse. 1H and
13C{1H} NMR spectroscopic data were recorded with a Bruker AV-
500 spectrometer, operating at 500 MHz for 1H and 125.8 MHz for
13C and on a Bruker AV-200 spectrometer operating at 188 MHz
for 19F. The spectra were referenced internally using the signal from
the residual protiosolvent (1H), the signals of the solvent (13C) or
the signal of trifluoroacetic acid, 10% in C6D6 (19F). Mass spectra
(ESI) were obtained from acetonitrile or methanol solutions on a
TSQ 7000 (Thermo Electron) and (FAB) from DMSO or DMF
solutions on a Nermag R10-10 instrument. Electrospray high-reso-
lution mass spectra were performed by the Service de spectroscopie
de masse CESAMO de l’université de Bordeaux I. Chromato-
graphic work was performed on silica gel 60 Å. PdBr2(COD),[45] 1-
(2-bromoethyl)-3-(2,4,6-trimethylphenyl) imidazolium bromide 1,[6]
1-(2-bromoethyl)-3-(2,6-diisopropylphenyl)imidazolium bromide
2[6] and 1-(3-bromopropyl)-3-(2,4,6-trimethylphenyl)imidazolium
bromide 3[6] were prepared as described in the literature. Both lith-
ium alkylthiolates were prepared by action of methyllithium on the
corresponding thiols and used rapidly after their preparation.
Other reagents were obtained from commercial sources and used
as received.
1-[2-(tert-Butylthio)ethyl]-3-(2,6-diisopropylphenyl)imidazolium Bro-
mide (7): tBuSLi (118 mg, 1.23 mmol) was added to a solution of
2 (410 mg, 0.99 mmol) in CH2Cl2 (6 mL). The mixture was stirred
for one day at room temperature. CH2Cl2 (14 mL) was added and
the mixture was washed with water (2ϫ4 mL). The organic phase
was dried (MgSO4), filtered and concentrated under vacuum to
give a pale yellow hygroscopic solid. Yield 387 mg (92%). M.p. 85–
90 °C. C21H33BrN2S (425.48). HRMS (ESI) m/z: calcd. 345.236446;
found 345.236823. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 9.87
(t, 4J = 1.7 Hz, 1 H, NCHN), 8.38 (t, 3,4J = 1.7 Hz, 1 H,
3
3
AlkNCH=), 7.47 [t, J = 7.8 Hz, 1 H, p-CH (DIPP)], 7.24 [d, J =
7.8 Hz, 2 H, m-CH (DIPP)], 7.16 [t, 3,4J = 1.7 Hz, 1 H, (DIPP)-
NCH=], 4.91 (t, J = 5.9 Hz, 2 H, NCH2), 3.16 (t, J = 5.9 Hz, 2
H, CH2StBu), 2.28 [h, J = 6.8, 6.9 Hz, 2 H, CH(CH3)2], 1.24 (s, 9
3
3
3
H, StBu), 1.15 [d, 3J = 6.9 Hz, 6 H, CH(CH3)2], 1.09 [d, 3J =
6.8 Hz, 6 H, CH(CH3)2] ppm. 13C NMR (125.8 MHz, CDCl3,
25 °C): δ = 145.42 [o-C (DIPP)], 137.94 (NCHN), 131.82 [p-CH
(DIPP)], 130.07 [NC (DIPP)], 124.60 [m-CH (DIPP)], 124.27
(AlkNCH=), 123.84 [(DIPP)NCH=], 50.10 (NCH2), 43.13
[SC(CH3)3)], 30.99 [SC(CH3)3], 29.39 (CH2S), 28.48 [CH(CH3)2],
24.40, 24.21 [CH(CH3)2] ppm. MS (ESI, positive mode): m/z (%)
= 345.50 (100) [C21H33N2S+]. MS (ESI, negative mode): m/z (%) =
81 (100) [Br–].
1-[2-(tert-Butylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazolium Bro-
mide (5): tBuSLi (170 mg, 1.77 mmol) was added to a solution of
1 (610 mg, 1.63 mmol) in CH2Cl2 (10 mL). The mixture was stirred
for one day at room temperature. CH2Cl2 (20 mL) was added and
the mixture was washed with water (10 + 5 mL). The organic phase
was dried (MgSO4), filtered and concentrated under vacuum to
give a white, hygroscopic solid. Yield 535 mg (86%). Suitable X-
ray colourless crystals were obtained by slow diffusion of diethyl
ether in a CH2Cl2 solution. M.p. 88–92 °C. C18H27BrN2S (383.42):
1-[3-(tert-Butylthio)propyl]-3-(2,4,6-trimethylphenyl)imidazolium
Bromide (8): tBuSLi (130 mg, 1.35 mmol) was added to a solution
of 3 (390 mg, 1.00 mmol) in CH2Cl2 (6 mL). The mixture was
stirred for one day at room temperature. CH2Cl2 (14 mL) was
added and the mixture was washed with water (2ϫ10 mL). The
1
HRMS (ESI) m/z: calcd. 303.189496; found 303.190467. H NMR
(500 MHz, CDCl3, 25 °C): δ = 10.03 (t, 4J = 1.6 Hz, 1 H, NCHN), organic phase was dried (MgSO4), filtered and concentrated under
8.13 (t, 3,4J = 1.5 Hz, 1 H, MesNCH=), 7.19 (t, 3,4J = 1.6 Hz, 1 H, vacuum to give a white, hygroscopic solid. Yield 290 mg (73%).
AlkN–CH=), 6.97 [s, 2 H, CH (Mes)], 4.89 (t, 3J = 6.0 Hz, 2 H,
M.p. 134–136 °C. C19H29BrN2S (397.42): HRMS (ESI) m/z: calcd.
3
NCH2), 3.17 (t, J = 6.1 Hz, 2 H, CH2StBu), 2.31 (s, 3 H, p-CH3),
317.205146; found 317.204589. 1H NMR (500 MHz, CDCl3,
2.06 (s, 6 H, o-CH3), 1.27 (s, 9 H, StBu) ppm. 13C NMR 25 °C): δ = 10.28 (t, 4J = 1.5 Hz, 1 H, NCHN), 7.93 (t, 3,4J =
Eur. J. Inorg. Chem. 2007, 5069–5079
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5075

J. Wolf, A. Labande, J.-C. Daran, R. Poli
FULL PAPER
1.7 Hz, 1 H, NCH=), 7.24 (t, 3,4J = 1.7 Hz, 1 H, =CHN), 6.98 [s,
CDCl3, 25 °C): δ = 169.34 (NCN), 137.51 [p-C (Mes)], 136.23 [o-
2 H, CH (Mes)], 4.81 (t, 3J = 6.9 Hz, 2 H, NCH2), 2.63 (t, 3J = C (Mes)], 135.56 [NC (Mes)], 129.09 [CH (Mes)], 123.21 (Mes-
6.9 Hz, 2 H, CH2StBu), 2.32 (q + s, 3J = 6.9 Hz, 5 H, p-CH3; NCH=), 121.90 (Alk-NCH=), 51.26 (NCH2), 42.95 [SC(CH3)3],
NCH2CH2), 2.06 (s, 6 H, o-CH3), 1.27 (s, 9 H, StBu) ppm. 13C 31.21 [SC(CH3)3], 29.43 (CH2S), 21.38 (p-CH3), 19.47(o-CH3) ppm.
NMR (125.8 MHz, CDCl3, 25 °C): δ = 141.27 [s, p-C (Mes)], MS (DCI[NH3]): m/z (%) = 743 (100) [C36H52BrN4S2Ni+].
137.99 (s, NCHN), 134.16 [s, o-C (Mes)], 130.67 [s, NC (Mes)],
{1-[2-(tert-Butylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazolium}-
129.86 [s, CH (Mes)], 123.42 (s, =CHN), 123.25 (s, =CH–N), 49.37
palladium Tribromide (12): PdBr2(COD) (146 mg, 0.39 mmol) was
(s, NCH2), 42.69 [s, SC(CH3)3], 30.83 [s, SC(CH3)3], 30.63 (s,
added to a solution of 5 (165 mg, 0.43 mmol) in THF (15 mL). The
mixture was stirred for 1 h at room temperature and filtered. The
orange solid obtained was washed with THF (15 mL), dichloro-
methane (10 mL) and dried in vacuo. Yield 223 mg (88%). M.p.
NCH2CH2), 24.66 (s, CH2S), 21.10 [s, p-CH3 (Mes)], 17.71 [s, o-
CH3 (Mes)] ppm. MS (ESI, positive mode): m/z (%) = 317.4 (100)
[C19H29N2S+]. MS (ESI, negative mode): m/z (%) = 81.0 (100) [Br–].
1-[3-(tert-Butylthio)propyl]-3-(2,6-diisopropylphenyl)imidazolium
Bromide (9): tBuSLi (130 mg, 1.35 mmol) was added to a solution
of 4 (450 mg, 1.05 mmol) in CH2Cl2 (6 mL). The mixture was
stirred for one day at room temperature. CH2Cl2 (14 mL) was
added and the mixture was washed with water (2ϫ15 mL). The
organic phase was dried (MgSO4), filtered and concentrated under
vacuum to give a pale yellow hygroscopic solid. Yield 318 mg
(69%). M.p. 103–104 °C. C22H35BrN2S (439.50): HRMS (ESI) m/z:
calcd. 359.252096; found 359.253029. 1H NMR (500 MHz, CDCl3,
25 °C): δ = 9.87 (s, 1 H, NCHN), 8.14 (t, 3,4J = 1.7 Hz, 1 H,
(dec.) 245 °C. C18H27Br3N2PdS (649.62): calcd. C 33.28, H 4.19, N
4.31; found C 33.26, H 4.35, N 4.98. 1H NMR (500 MHz, [D6]-
DMSO, 25 °C): δ = 9.46 (s, 1 H, NCHN), 8.12 (s, 1 H, MesNCH=),
7.91 (s, 1 H, AlkNCH=), 7.14 [s, 2 H, CH (Mes)], 4.44 (s, 2 H,
NCH2), 3.12 (s, 2 H, CH2StBu), 2.34 (s, 3 H, p-CH3), 2.04 (s, 6 H,
o-CH3), 1.28 (s, 9 H, StBu) ppm. 13C NMR (125.8 MHz, [D6]-
DMSO, 25 °C): δ = 140.78 [p-C (Mes)], 138.18 (NCHN), 134.8 [o-C
(Mes)], 131.57 [NC (Mes)], 129.73 [CH (Mes)], 124.34 (AlkNCH=),
123.68 (MesNCH=), 49.9 (NCH2), 43.22 [SC(CH3)3], 31.22
[SC(CH3)3], 28.31 (SCH2), 21.08 [p-CH3 (Mes)], 17.38 [o-CH3
(Mes)] ppm. MS (FAB, MNBA matrix): m/z (%) = 303 (100)
[ C 1 8 H 2 7 N 2 S + ] ; 4 8 9 ( 1 ) [ C 1 8 H 2 6 B r N 2 S P d + ] ; 5 6 9 ( 1 )
[C18H27Br2N2SPd+].
3
3
AlkNCH=), 7.39 [t, J = 7.8 Hz, 1 H, p-CH (DIPP)], 7.25 [d, J =
7.9 Hz, 2 H, m-CH (DIPP)], 7.23 [t, 3,4J = 1.7 Hz, 1 H, (DIPP)
3
3
NCH=], 4.84 (t, J = 6.8 Hz, 2 H, NCH2), 2.61 (t, J = 7.1 Hz, 2
3
H, CH2StBu), 2.30 (q, J = 6.9; 7.0 Hz, 2 H, NCH2CH2), 2.25 [h,
3J = 6.9 Hz, 2 H, CH(CH3)2], 1.26 (s, 9 H, StBu), 1.17 [d, 3J =
6.8 Hz, 6 H, CH(CH3)2], 1.10 [d, 3J = 6.8 Hz, 6 H, CH(CH3)2]
ppm. 13C NMR (125.8 MHz, CDCl3, 25 °C): δ = 145.29 [s, o-C
(DIPP)], 138.08 (s, NCHN), 131.85 [s, p-CH (DIPP)], 130.13 [s, NC
(DIPP)], 124.63 [s, m-CH (DIPP)], 124.30 (s, AlkNCH=), 123.75
[s, (DIPP)NCH=], 49.43 (s, NCH2), 42.61 [s, SC(CH3)3], 30.90 [s,
SC(CH3)], 30.82 (s, NCH2CH2), 28.67 [s, CH(CH3)2], 24.59 (s,
CH2S), 24.40, 24.19 [s, CH(CH3)2] ppm. MS (ESI, positive mode):
m/z (%) = 359.4 (100) [C22H35N2S+]. MS (ESI, negative mode): m/z
(%) = 80.8 (100) [Br–].
{1-[2-(Ethylthio)ethyl]-3-(2,4,6-trimethylpenyl)imidazolium}-
palladium Tribromide (13): PdBr2(COD) (170 mg, 0.44 mmol) was
added to a suspension of 6 (145 mg, 0.4 mmol) in THF
(2ϫ10 mL). The mixture was stirred for 2 h at room temperature
and filtered. The orange solid obtained was washed with THF
(15 mL) and dried in vacuo. Yield 250 mg (99%). M.p. 177–179 °C.
C16H23Br3N2PdS (621.57): calcd. C 30.92, H 3.73, N 4.51; found
C 30.58, H 3.57, N 4.56. 1H NMR (500 MHz, [D6]Me2CO, 25 °C):
4
δ = 9.00 (t, J = 1.7 Hz, 1 H, NCHN), 7.84 (t, 3,4J = 1.7 Hz, 1 H,
MesNCH=C), 7.50 (t, 3,4J = 1.8 Hz, 1 H, AlkNCH=C), 7.13 [s, 2
H, CH (Mes)], 4.88 (t, 3J = 4.3 Hz, 2 H, NCH2), 3.49 (t, 3J =
Bis{1-[2-(tert-butylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazol-2-
ylidene}nickel Dibromide (11): NiBr2(MeCN)2 (140 mg, 0.47 mmol)
and 3 (383 mg, 1.00 mmol) were placed in a Schlenk tube and THF
(15 mL) was added. After stirring for 5 min, a homogeneous blue-
green solution was obtained. A freshly prepared KN(SiMe3)2 solu-
tion (5 mL, 0.2  in THF) was added over 5 min during which the
mixture colour became darker and changed to deep pink-red. The
mixture was stirred at room temperature for 15 min and the solvent
was removed under vacuum. The residue was washed with diethyl
ether (20 mL) and filtered. The filtrate was concentrated (about
5 mL), precipitated in pentane (50 mL) and filtered. The solution
was concentrated to give a pink-red solid. Yield 217 mg (57%). X-
ray quality crystals were obtained by slow evaporation of a pentane
solution. M.p. (dec.) 195–200 °C. C36H52Br2N4NiS2 (823.47): calcd.
C 52.51, H 6.37, N 6.80; found C 52.45, H 6.39, N 6.56. NMR
shows signals for two isomers, 1.27:1 ratio. Major isomer: 1H NMR
3
4.3 Hz, 2 H, CH2SEt), 3.00 (q, J = 7.2 Hz, 2 H, SCH2CH3), 2.35
(s, 3 H, p-CH3), 2.06 (s, 6 H, o-CH3), 1.16 (t, 3J = 7.3 Hz, 3 H,
SCH2CH3) ppm. 13C NMR (125.8 MHz, [D6]Me2CO, 25 °C): δ =
141.30 [p-C (Mes)], 137.10 (NCHN), 134.86 [o-C (Mes)], 130.87
[NC (Mes)], 129.45 [CH (Mes)], 124.16 (AlkNCH=), 123.42
(MesNCH=), 47.94 (NCH2), 36.11 (CH2SEt), 32.26 (SCH2CH3),
20.17 [p-CH3 (Mes)], 16.90 [o-CH3 (Mes)], 12.63 (SCH2CH3) ppm.
MS (FAB, MNBA matrix): m/z (%) = 275 (100) [C16H23N2S+]; 461
(1) [C16H22BrN2PdS+]; 543 (0.9) [C16H23Br2N2PdS+].
{1-[2-(tert-Butylthio)ethyl]-3-(2,6-diisopropylphenyl)imidazolium}-
palladium Tribromide (14): PdBr2(COD) (374 mg, 1.00 mmol) was
added to a solution of 7 (400 mg, 0.94 mmol) in THF (15 mL). The
mixture was stirred for 2 h at room temperature and filtered. The
orange solid obtained was washed with THF (2 ϫ 15 mL),
CH2Cl2 (15 mL) and dried in vacuo. Yield 579 mg (89 %). M.p.
(500 MHz, CDCl3, 25 °C): δ = 7.09 [s, 4 H, CH (Mes)], 6.97 (s, 2 210–212 °C. C21H33Br3N2PdS (691.70): calcd. C 36.47, H 4.81, N
H, AlkNCH=), 6.60 (s, 2 H, MesNCH=), 4.92 (s, 4 H, NCH2), 4.05; found C 36.60, H 4.49, N 3.87. 1H NMR (500 MHz, [D6]-
3.18 (s, 4 H, CH2S), 2.45 [s, 6 H, p-CH3 (Mes)], 2.23 [s, 12 H, o- DMSO, 25 °C): δ = 9.59 (s, 1 H, NCHN), 8.16 [s, 1 H, (DIPP)-
3
CH3 (Mes)], 1.30 (s, 18 H, StBu). 13C NMR (125.8 MHz, CDCl3,
NCH=C], 8.10 (s, 1 H, AlkNCH=C), 7.64 [t, J = 7.8 Hz, 1 H, p-
3
25 °C): δ = 169.74 (NCN), 138.41 [p-C (Mes)], 136.95 [o-C (Mes)], CH (DIPP)], 7.47 [d, J = 7.8 Hz, 2 H, m-CH (DIPP)], 4.47 (t, 2
136.03 [NC (Mes)], 129.03 [CH (Mes)], 122.66 (MesNCH=), 122.53
H, NCH2), 3.13 (t, 2 H, CH2StBu), 2.51 [h, 3J = 6.8 Hz, 2 H,
(AlkNCH=), 50.94 (NCH2), 42.68 [SC(CH3)3], 31.05 [SC(CH3)3], CH(CH3)2], 1.28 (s, 9 H, StBu), 1.16 [d, 3J = 6.9 Hz, 6 H, CH-
29.24 (CH2S), 21.27 (p-CH3), 19.99 (o-CH3) ppm. Minor isomer:
1H NMR (500 MHz, CDCl3, 25 °C): δ = 7.01 (s, 2 H, AlkNCH=),
6.90 [s, 4 H, CH (Mes)], 6.53 (s, 2 H, MesNCH=), 5.37 (s, 4 H,
NCH2), 3.62 (s, 4 H, CH2S), 2.54 [s, 6 H, p-CH3 (Mes)], 1.94 [s, 12
H, o-CH3 (Mes)], 1.42 (s, 18 H, StBu) ppm. 13C NMR (125.8 MHz,
(CH3)2], 1.14 [d, 3J = 6.9 Hz, 6 H, CH(CH3)2] ppm. 13C NMR
(125.8 MHz, [D6]DMSO, 25 °C): δ = 145.64 [o-C (DIPP)], 138.71
(NCHN), 131.98 [p-CH (DIPP)], 130.98 [NC (DIPP)], 125.69
[(DIPP)NCH=], 124.91 [m-CH (DIPP)], 123.60 (AlkNCH=), 49.84
(NCH2), 43.07 [SC(CH3)3], 31.17 [SC(CH3)3], 28.48 (CH2S), 28.40
5076
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5069–5079

Efficient Ketone Hydrosilylation Catalysis
[CH(CH3)2], 24.33, 24.30 [CH(CH3)2] ppm. MS (FAB, MNBA ma-
t r i x ) : m / z ( % ) = 3 4 5 ( 1 0 0 ) [ C 2 1 H 3 3 N 2 S + ] ; 6 1 1 ( 1 )
[C21H33Br2N2SPd+].
(CH2SEt), 20.88 [p-CH3 (Mes)], 19.10 [o-CH3 (Mes)], 14.00
(SCH2CH3) ppm. MS (FAB, MNBA matrix): m/z (%) = 245 (100)
[C14H17N2S+]; 275 (47) [C16H23N2S+]; 461 (7) [C16H22BrN2SPd+];
1001 (3) [C32H44Br3N4S2Pd2+].
{1-[3-(tert-Butylthio)propyl]-3-(2,4,6-trimethylphenyl)imidazolium}-
palladium Tribromide (15): PdBr2(COD) (141 mg, 0.38 mmol) was {1-[2-(tert-Butylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazol-2-ylid-
added to a solution of 8 (180 mg, 0.45 mmol) in THF (10 mL). The
mixture was stirred for 2 h at room temperature and filtered. The
orange solid obtained was washed with THF (2ϫ10 mL) and dried
in vacuo. Yield 206 mg (82%). M.p. 200–202 °C. C19H29Br3N2PdS
(663.65): calcd. C 34.39, H 4.40, N 4.22; found C 35.21, H 4.34, N
ene-1,4-cyclooctadienyl}rhodium(I) Tetrafluoroborate (18):
[Rh(COD)Cl]2 (77.2 mg, 0.16 mmol) was stirred for 15 min at room
temperature with tBuOK (38.6 mg, 0.34 mmol) in THF (4 mL).
The dark yellow solution was slowly added to a solution of 5
(120.0 mg, 0.31 mmol) in THF (4 mL). The mixture was stirred
3.92. 1H NMR (500 MHz, [D6]DMSO, 25 °C): δ = 9.45 (s, 1 H, overnight at room temperature and the solvent was removed under
NCHN), 8.13 (s, 1 H, MesNCH=C), 7.95 (s, 1 H, AlkNCH=C), vacuum. AgBF4 (122.0 mg, 0.63 mmol) and CH2Cl2 (10 mL) were
3
7.16 [s, 2 H, CH (Mes)], 4.38 (s, J = 6.7 Hz, 2 H, NCH2), 2.55 (s,
3J = 6.8 Hz, 2 H, CH2StBu), 2.30 (s, 3 H, p-CH3), 2.17 (t, 3J =
7.0 Hz, 2 H, NCH2CH2), 2.04 (s, 6 H, o-CH3), 1.27 (s, 9 H, StBu)
ppm. 13C NMR (125.8 MHz, [D6]DMSO, 25 °C): δ = 140.74 [s, p-
added to the residue and the reaction was stirred at room tempera-
ture for two additional hours. The mixture was filtered through
Celite, concentrated under vacuum and purified by column
chromatography on silica gel (eluent: CH2Cl2/Me2CO, 17:3) to give
C (Mes)], 137.87 (s, NCHN), 134.76 [s, o-C (Mes)], 131.63 [s, NC a yellow-orange hygroscopic solid (152 mg, 81%). Suitable X-ray
(Mes)], 129.73 [s, CH (Mes)], 124.51 (s, AlkNCH=), 123.73 (s,
MesNCH=), 49.35 (s, NCH2), 42.64 [s, SC(CH3)3], 31.08 [s,
SC(CH3)3], 29.96 (s, NCH2CH2), 24.81 (s, CH2S), 21.09 [s, p-CH3
crystals were obtained by layer diffusion of pentane into a CDCl3
solution. M.p. 99–101 °C. C26H38BF4N2RhS (600.38): calcd. C
52.01, H 6.38, N 4.67; found C 51.67, H 5.86, N 4.54. 1H NMR
(Mes)], 17.41 [s, o-CH3 (Mes)] ppm. MS (FAB, MNBA matrix): (500 MHz, [D6]DMSO, 80 °C): δ = 7.64 (d, 3J = 1.8 Hz, 1 H,
m/z (%) = 317 (100) [C19H29N2S+]; 503 (1) [C19H28BrN2SPd+]; 583 AlkNCH=), 7.34 (d, J = 1.7 Hz, 1 H, MesNCH=), 7.13 [s, 2 H,
3
(1) [C19H29Br2N2SPd+].
CH (Mes)], 4.85 [s, 2 H, CH (COD)], 4.62 (t, 3J = 5.3 Hz, 2 H,
CH2N), 3.90 [br. s, 2 H, CH (COD)], 2.97 (t, 3J = 5.3 Hz, 2 H,
CH2StBu), 2.36 (s, 3 H, p-CH3), 2.11–2.26 [m + s, 8 H, o-CH3;
CH2 (COD)], 1.82–2.06 [br. m, 6 H, CH2 (COD)], 1.25 (s, 9 H,
StBu) ppm. 13C NMR (125.8 MHz, [D6]DMSO, 80 °C): δ = 173.63
{1-[3-(tert-Butylthio)propyl]-3-(2,6-diisopropylphenyl)imidazolium}-
palladium Tribromide (16): PdBr2(COD) (374 mg, 1.00 mmol) was
added to a solution of 9 (505 mg, 1.15 mmol) in THF (20 mL). The
mixture was stirred for 2 h at room temperature and filtered. The
orange solid obtained was washed with THF (2ϫ15 mL), CH2Cl2
(15 mL) and dried in vacuo. Yield 642 mg (91%). M.p. 184–186 °C.
C22H35Br3N2PdS (705.73): calcd. C 37.44, H 5.00, N 3.97; found
1
(d, JRh–C = 49.8 Hz, NCN), 139.41 [p-C (Mes)], 135.88 [NC
(Mes)], 135.37 [o-C (Mes)], 129.46 [CH (Mes)], 125.54
(MesNCH=), 123.10 (AlkNCH=), 96.86, 81.86 [CH (COD)], 51.11
[SC(CH3)3], 50.06 (NCH2), 31.90, 29.38 [CH2 (COD)], 30.01
[SC(CH3)3], 27.54 (SCH2), 20.88 [p-CH3 (Mes)], 19.11 [o-CH3
(Mes)] ppm. 19F NMR (188 MHz, CDCl3, 25 °C): δ = –76.73 (s,
BF4) ppm. MS (ESI): m/z (%) = 513.3 (100) [C26H38N2RhS+].
1
C 37.79, H 4.79, N 3.99. H NMR (500 MHz, [D6]DMSO, 20 °C):
δ = 9.61 (s, 1 H, NCHN), 8.18 (s, 1 H, AlkNCH=), 8.12 [s, 1 H,
(DIPP)NCH=], 7.63 [s, 1 H, p-CH (DIPP)], 7.46 [s, 2 H, m-CH
(DIPP)], 4.42 (s, 2 H, NCH2), 2.53 (s, 2 H, CH2StBu), 2.28 [s, 2 H,
CH(CH3)2], 2.17 (s, 2 H, NCH2CH2), 1.27 (s, 9 H, StBu), 1.14 [s, {1-[2-(tert-Butylthio)ethyl]-3-(2,6-diisopropylphenyl)imidazol-2-ylid-
12 H, CH(CH3)2] ppm. 13C NMR (125.8 MHz, [D6]DMSO, 20 °C):
δ = 145.56 [s, o-C (DIPP)], 138.12 (s, NCHN), 130.96 [s, NC
ene-1,4-cyclooctadienyl}rhodium(I) Tetrafluoroborate (19): Com-
pound 19 was prepared using the same procedure as for 18, from
(DIPP)], 131.97 [s, p-CH (DIPP)], 125.73 [s, (DIPP)NCH=], 124.90 compound 7 (95.0 mg, 0.22 mmol), [Rh(COD)Cl]2 (55.0 mg,
[s, m-CH (DIPP)], 124.00 (s, AlkNCH=), 49.52 (s, NCH2), 42.58 0.11 mmol), tBuOK (27.6 mg, 0.25 mmol) and AgBF4 (87.0 mg,
[s, SC(CH3)3], 31.05 [s, SC(CH3)3], 29.92 (s, NCH2CH2), 28.53 [s,
0.45 mmol). After purification, the product was recovered as a yel-
CH(CH3)2], 24.76 (s, CH2S), 24.34, 24.27 [s, CH(CH3)2] ppm. MS low-orange solid (113 mg, 79%). Suitable X-ray crystals were ob-
(FAB, MNBA matrix): m/z (%) = 359 (100) [C22H35N2S+]; 545 (1) tained by slow evaporation of a saturated ether solution. M.p. (slow
[C22H34BrN2SPd+]; 625 (1) [C22H35Br2N2SPd+].
dec.) Ͼ150 °C. C29H44BF4N2RhS (642.46): calcd. C 54.22, H 6.90,
1
N 4.36; found C 54.46, H 6.64, N 4.48. H NMR (500 MHz, [D6]-
{1-[2-(Ethylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazol-2-ylidene}-
palladium Dibromide Dimer (17): A solution of tBuOK (42 mg,
0.38 mmol) in THF (15 mL) was slowly added to a suspension of
13 (117 mg, 0.19 mmol) in THF (15 mL). The mixture was stirred
for 2 h at room temperature and the solvent removed in vacuo. The
resulting solid was dissolved in CH2Cl2 and filtered through Celite.
The product was purified by column chromatography on silica gel
(eluent: CH2Cl2/acetone, 9:1). The product was crystallised by layer
diffusion of diethyl ether into a THF solution to give yellow orange
crystals. Yield 64 mg (63%). M.p. (dec.) 240 °C. C32H44Br4N4Pd2S2
(1081.3): calcd. C 35.54, H 4.10, N 5.18; found C 36.14, H 4.04, N
5.03. 1H NMR (500 MHz, CD2Cl2, 25 °C): δ = 7.28 (d, 3J = 1.9 Hz,
3
DMSO, 80 °C): δ = 7.67 (s, 1 H, AlkNCH=), 7.57 [t, J = 7.8 Hz,
1 H, p-CH (DIPP)], 7.43 [s, 1 H, (DIPP)NCH=], 7.41 [d, 3J =
7.8 Hz, 2 H, m-CH (DIPP)], 4.87 [s, 2 H, CH (COD)], 4.68 (s, 2
H, CH2N), 3.92 [br. s, 2 H, CH (COD)], 3.01 (s, 2 H, CH2StBu),
2.5–2.6 [br. s, 2 H, CH(CH3)2], 2.14–2.24 [m, 2 H, CH2 (COD)],
1.90–2.04 [m, 4 H, CH2 (COD)], 1.80–1.90 [m, 2 H, CH2 (COD)],
3
1.35 [d, J = 4.1 Hz, 6 H, CH(CH3)2], 1.28 (s, 9 H, StBu), 1.08 [d,
3J = 6.7 Hz, 6 H, CH(CH3)2] ppm. 13C NMR (125.8 MHz, [D6]-
1
DMSO, 80 °C): δ = 173.02 (d, JRh–C = 50 Hz, NCN), 146.04 [o-C
(DIPP)], 135.06 [NC (DIPP)], 130.76 [p-CH (DIPP)], 127.06
[(DIPP)NCH=], 124.51 [m-CH (DIPP)], 122.84 (AlkNCH=),
96.71, 81.21 [CH (COD)], 50.95 [SC(CH3)3], 50.33 (NCH2), 31.73,
29.36 [CH2 (COD)], 30.00 [SC(CH3)3], 28.44 [CH(CH3)2], 27.74
(SCH2), 25.62, 23.51 [CH(CH3)2] ppm. 19F NMR (188 MHz,
CDCl3, 25 °C): δ = –76.83 (s, BF4) ppm. MS (FAB, MNBA ma-
trix): m/z (%) = 555 (100) [C29H44N2RhS+].
3
2 H, NCH=), 7.05 [s, 4 H, CH (Mes)], 6.96 (d, J = 1.8 Hz, 2 H,
MesNCH=), 4.60 (br. s, 4 H, CH2N), 3.35 (br. s, 4 H, SCH2CH3),
2.75 (br. s, 4 H, CH2SEt), 2.39 [s, 6 H, p-CH3 (Mes)], 2.24 [s, 12
3
H, o-CH3 (Mes)], 1.53 (t, J = 7.3 Hz, 6 H, SCH2CH3) ppm. 13C
NMR (125.8 MHz, CD2Cl2, 25 °C): δ = 155.75 (NCN), 139.28 [p-C
(Mes)], 135.69 [NC (Mes)], 134.79 [o-C (Mes)], 129.09 [CH (Mes)],
125.09, 121.56 (NCH=), 51.67 (NCH2), 35.81 (SCH2CH3), 32.62
{1-[β-(Ethylthio)ethyl]-3-(2,4,6-trimethylphenyl)imidazol-2-ylidene-
1,4-cyclooctadienyl}rhodium(I) Tetrafluoroborate (20): Compound
Eur. J. Inorg. Chem. 2007, 5069–5079
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5077

J. Wolf, A. Labande, J.-C. Daran, R. Poli
FULL PAPER
[7]
[8]
N. Tsoureas, A. A. Danopoulos, A. A. D. Tulloch, M. E. Light,
Organometallics 2003, 22, 4750–4758.
C. L. Yang, H. M. Lee, S. P. Nolan, Org. Lett. 2001, 3, 1511–
1514; T. Focken, G. Raabe, C. Bolm, Tetrahedron: Asymmetry
2004, 15, 1693–1706.
H. Seo, H.-J. Park, B. Y. Kim, J. H. Lee, S. U. Son, Y. K.
Chung, Organometallics 2003, 22, 618–620.
L. D. Field, B. A. Messerle, K. Q. Vuong, P. Turner, Organome-
tallics 2005, 24, 4241–4250.
L. G. Bonnet, R. E. Douthwaite, R. Hodgson, J. Houghton,
B. M. Kariuki, S. Simonovic, Dalton Trans. 2004, 3528–3535;
W. A. Herrmann, L. J. Gooßen, M. Spiegler, Organometallics
1998, 17, 2162–2168; D. S. McGuinness, K. J. Cavell, Organo-
metallics 2000, 19, 741–748.
20 was prepared using the same procedure as for 18, from com-
pound 6 (40.0 mg, 0.11 mmol), [Rh(COD)Cl]2 (27.8 mg,
0.06 mmol), tBuOK (13.9 mg, 0.12 mmol) and AgBF4 (48.0 mg,
0.25 mmol). After purification, the product was recovered as a yel-
l ow- ora n g e s o l i d ( 4 9 m g , 7 6 % ) . M. p. ( d ec . ) Ͼ7 0 ° C.
C24H34BF4N2RhS (572.32): calcd. C 50.37, H 5.98, N 4.89; found
C 48. 89, H 5. 59, N 4. 57. HRMS (ESI) m/z: calcd. for
[9]
[10]
[11]
C
24H34N2RhS 485.1498; found 485.1512. 1H NMR (500 MHz,
[D6]DMSO, 80 °C): δ = 7.65 (d, 3J = 1.8 Hz, 1 H, AlkNCH=), 7.34
3
(d, J = 1.8 Hz, 1 H, MesNCH=), 7.12 [s, 2 H, CH (Mes)], 4.72 [s,
3
2 H, CH (COD)], 4.65 (t, J = 5.3 Hz, 2 H, CH2N), 3.97 [br. s, 2
3
3
H, CH (COD)], 2.93 (t, J = 5.3 Hz, 2 H, CH2SEt), 2.65 (q, J =
7.3 Hz, 2 H, SCH2CH3), 2.36 (s, 3 H, p-CH3), 2.07–2.23 [m + s, 8
H, o-CH3; CH2 (COD)], 1.86–2.05 [br. m, 6 H, CH2 (COD)], 1.30
(t, 3J = 7.3 Hz, 3 H, SCH2CH3) ppm. 13C NMR (125.8 MHz, [D6]-
[12]
[13]
L. H. Gade, V. César, S. Bellemin-Laponnaz, Angew. Chem. Int.
Ed. 2004, 43, 1014–1017; V. César, S. Bellemin-Laponnaz, H.
Wadepohl, L. H. Gade, Chem. Eur. J. 2005, 11, 2862–2873.
P. L. Arnold, A. C. Scarisbrick, A. J. Blake, C. Wilson, Chem.
Commun. 2001, 2340–2341; P. L. Arnold, M. Rodden, C. Wil-
son, Chem. Commun. 2005, 1743–1745; P. L. Arnold, C. Wil-
son, Inorg. Chim. Acta 2007, 360, 190–196; A. R. Chianese,
R. H. Crabtree, Organometallics 2005, 24, 4432–4436; E. Mas-
Marzá, M. Poyatos, M. Sanaú, E. Peris, Organometallics 2004,
23, 323–325; D. J. Nielsen, K. J. Cavell, B. W. Skelton, A. H.
White, Inorg. Chim. Acta 2003, 352, 143–150; S. Prühs, C. W.
Lehmann, A. Fürstner, Organometallics 2004, 23, 280–287; J. J.
Van Veldhuizen, S. B. Garber, J. S. Kingsbury, A. H. Hoveyda,
J. Am. Chem. Soc. 2002, 124, 4954–4955.
J. C. Bayón, C. Claver, A. M. Masdeu-Bultó, Coord. Chem.
Rev. 1999, 193–195, 73–145; L. Routaboul, S. Vincendeau, J.-
C. Daran, E. Manoury, Tetrahedron: Asymmetry 2005, 16,
2685–2690; R. Malacea, E. Manoury, L. Routaboul, J.-C. Da-
ran, R. Poli, J. P. Dunne, A. C. Whitwood, C. Godard, S. B.
Duckett, Eur. J. Inorg. Chem. 2006, 1803–1816; R. Malacea, J.-
C. Daran, S. B. Duckett, J. P. Dunne, C. Godard, E. Manoury,
R. Poli, A. C. Whitwood, Dalton Trans. 2006, 3350–3359.
J. Pernak, A. Skrzypczak, Eur. Med. Chem. 1996, 31, 901–903;
G. Nalecz-Jawecki, E. Grabinska-Sota, P. Narkiewicz, Ecotox-
icol. Environ. Saf. 2003, 54, 87–91.
A. E. Visser, R. P. Swatloski, W. M. Reichert, R. Mayton, S.
Sheff, A. Wierzbicki, J. H. Davis Jr, R. D. Rogers, Chem. Com-
mun. 2001, 135–136; A. E. Visser, R. P. Swatloski, W. M. Reich-
ert, R. Mayton, S. Sheff, A. Wierzbicki, J. H. Davis Jr, R. D.
Rogers, Environ. Sci. Technol. 2002, 36, 2523–2529.
A. Ros, D. Monge, M. Alcarazo, E. Álvarez, J. M. Lassaletta,
R. Fernández, Organometallics 2006, 25, 6039–6046.
S. J. Roseblade, A. Ros, D. Monge, M. Alcarazo, E. Alvarez,
J. M. Lassaletta, R. Fernandez, Organometallics 2007, 26,
2570–2578.
D. J. Nielsen, K. J. Cavell, M. S. Viciu, S. P. Nolan, B. W. Skel-
ton, A. H. White, J. Organomet. Chem. 2005, 690, 6133–6142.
D. S. Tarbell, W. E. Lovett, J. Am. Chem. Soc. 1956, 78, 2259–
2264; M. Zaidlewicz, J. V. B. Kanth, H. C. Brown, J. Org.
Chem. 2000, 65, 6697–6702.
1
DMSO, 80 °C): δ = 173.72 (d, JRh–C = 50.3 Hz, NCN), 139.38 [p-
C (Mes)], 135.85 [NC (Mes)], 135.28 [o-C (Mes)], 129.33 [CH
1
(Mes)], 125.13 (MesNCH=), 122.99 (AlkNCH=), 94.36 [d, JRh–C
= 7.3 Hz, CH (COD)], 83.56 [br. s, CH (COD)], 51.88 (NCH2),
32.00 (SCH2CH3), 31.91 (CH2SEt), 31.78, 29.61 [CH2 (COD)],
27.54 (SCH2), 20.92 [p-CH3 (Mes)], 18.45 [o-CH3 (Mes)], 14.49
(SCH2CH3) ppm. 19F NMR (188 MHz, CDCl3): δ = –76.08 (BF4)
ppm. MS (ESI): m/z (%) = 485.7 (100) [C24H34N2RhS+].
CCDC-631917 to -631922 and -637108 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/datarequest/cif.
[14]
Supporting Information (see footnote on the first page of this
article): Synthesis and characterization of compounds 21 and 4;
crystallographic data for compounds 5, 6, 11, 17–20.
[15]
[16]
Acknowledgments
We thank the Centre National de la Recherche Scientifique
(C.N.R.S.) for support of this work, the Fonds Social Européen
(F.S.E.) for a Ph.D. fellowship to J. W., and Yannick Coppel for
NMR analysis of the rhodium complexes.
[17]
[18]
[1] D. Bourissou, O. Guerret, F. P. Gabbaï, G. Bertrand, Chem.
Rev. 2000, 100, 39–91; W. A. Herrmann, Angew. Chem. Int. Ed.
2002, 41, 1290–1309; N. M. Scott, S. P. Nolan, Eur. J. Inorg.
Chem. 2005, 1815–1828; F. E. Hahn, Angew. Chem. Int. Ed.
2006, 45, 1348–1352.
[2] M. Scholl, T. M. Trnka, J. P. Morgan, R. H. Grubbs, Tetrahe-
dron Lett. 1999, 40, 2247–2250; L. Jafarpour, H.-J. Schanz,
E. D. Stevens, S. P. Nolan, Organometallics 1999, 18, 5416–
5419; S. Díez-González, N. M. Scott, S. P. Nolan, Organome-
tallics 2006, 25, 2355–2358.
[3] V. P. W. B öhm, T. Weskamp, C. W. K. Gstöttmayr, W. A.
Herrmann, Angew. Chem. Int. Ed. 2000, 39, 1602–1604; N.
Gürbüz, I. Özdemir, S. Demir, B. Çetinkaya, J. Mol. Catal. A
2004, 209, 23–28; A. C. Hillier, G. A. Grasa, M. S. Viciu, H. M.
Lee, C. Yang, S. P. Nolan, J. Organomet. Chem. 2002, 653, 69–
82; N. Hadei, E. A. B. Kantchev, C. J. O’Brien, M. G. Organ,
Org. Lett. 2005, 7, 3805–3807.
[4] E. Mas-Marzá, E. Peris, I. Castro-Rodríguez, K. Meyer, Orga-
nometallics 2005, 24, 3158–3162; I. Özdemir, S. Demir, B. Çet-
inkaya, J. Mol. Catal. A 2004, 215, 45–48; C. Rivera, R. H.
Crabtree, J. Mol. Catal. A 2004, 222, 59–73; F. Hanasaka, K.-
i. Fujita, R. Yamaguchi, Organometallics 2005, 24, 3422–3433.
[5] J. Wolf, A. Labande, J.-C. Daran, R. Poli, J. Organomet. Chem.
2006, 691, 433–443.
[19]
[20]
[21]
L. A. Sayyed, V. V. Thakur, M. D. Nikalje, G. K. Dewkar, S. P.
Kotkar, A. Sudalai, Tetrahedron 2005, 61, 2831; W. Kurosawa,
T. Kan, T. Fukuyama, J. Am. Chem. Soc. 2003, 125, 8112–
8113.
[22]
[23]
T. Welton, Chem. Rev. 1999, 99, 2071–2084.
W. A. Herrmann, G. Gerstberger, M. Spiegler, Organometallics
1997, 16, 2209–2212; D. S. McGuinness, W. Mueller, P. Wasser-
scheid, K. J. Cavell, B. W. Skelton, A. H. White, U. Englert,
Organometallics 2002, 21, 175–181.
A. L. MacKinnon, M. C. Baird, J. Organomet. Chem. 2003,
683, 114–119.
L. C. Silva, P. T. Gomes, L. F. Veiros, S. I. Pascu, M. T. Duarte,
S. Namorado, J. R. Ascenso, A. R. Dias, Organometallics 2006,
25, 4391–4403.
H. M. Lee, P. L. Chiu, J. Y. Zeng, Inorg. Chim. Acta 2004, 357,
4313–4321.
[24]
[25]
[26]
[6] J. Wolf, A. Labande, M. Natella, J.-C. Daran, R. Poli, J. Mol.
Catal. A 2006, 259, 205–212.
5078
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5069–5079

Efficient Ketone Hydrosilylation Catalysis
[27] D. Enders, R. Peters, J. Runsink, J. W. Bats, Org. Lett. 1999,
1, 1863–1866; D. A. Evans, K. R. Campos, J. S. Tedrow, F. E.
[35] C. Reyes, A. Prock, W. P. Giering, Organometallics 2002, 21,
546–554.
Michael, M. R. Gagné, J. Am. Chem. Soc. 2000, 122, 7905– [36] T. Hayashi, C. Hayashi, Y. Uozumi, Tetrahedron: Asymmetry
7920.
1995, 6, 2503–2506.
[28] B. A. Messerle, M. J. Page, P. Turner, Dalton Trans. 2006, 3927–
3933; V. César, S. Bellemin-Laponnaz, L. H. Gade, Eur. J. In-
org. Chem. 2004, 3436–3444.
[37] T. H. Chan, G. Z. Zheng, Tetrahedron Lett. 1993, 34, 3095–
3098; G. Z. Zheng, T. H. Chan, Organometallics 1995, 14, 70–
79.
[29] The influence of the deuterated solvent on 13C NMR chemical
shifts is negligible compared to the difference in 13C NMR
chemical shifts observed between compounds 5 and 18. For 18,
the SC(CH3)3 signal is at δ = 51.11 ppm in [D6]DMSO and at
δ = 50.5 ppm in CDCl3.
[38] H. Nishiyama, H. Sakaguchi, T. Nakamura, M. Horihata, M.
Kondo, K. Itoh, Organometallics 1989, 8, 846–848; H. Nishi-
yama, M. Kondo, T. Nakamura, K. Itoh, Organometallics
1991, 10, 500–508; H. Nishiyama, S. B. Park, K. Itoh, Tetrahe-
dron: Asymmetry 1992, 3, 1029–1034; D. Cuervo, M. P. Gam-
asa, J. Gimeno, J. Mol. Catal. A 2006, 249, 60–64.
[39] T. Hayashi, K. Yamamoto, K. Kasuga, H. Omizu, M. Kum-
ada, J. Organomet. Chem. 1976, 113, 127–137; M. Sawamura,
R. Kuwano, Y. Ito, Angew. Chem. Int. Ed. Engl. 1994, 33, 111–
113; T. Imamoto, T. Itoh, Y. Yamanoi, R. Narui, K. Yoshida,
Tetrahedron: Asymmetry 2006, 17, 560–565.
[40] I. Kolb, J. Hetflejs, Collect. Czech. Chem. Commun. 1980, 45,
2808–2816; T. E. Waldman, G. Schaefer, D. P. Riley, ACS
Symp. Ser. 1993, 517, 58–74.
[41] H. Nishiyama, S. Yamaguchi, M. Kondo, K. Itoh, J. Org.
Chem. 1992, 57, 4306–4309.
[30] G. Esquius, J. Pons, R. Yáñez, J. Ros, R. Mathieu, B. Donnad-
ieu, N. Lugan, Eur. J. Inorg. Chem. 2002, 2999–3006.
[31] I. Ojima, Z. Li, J. Zhu in The Chemistry of Organic silicon
Compounds (Eds.: Z. Rappoport, Y. Apeloig), Wiley, New
York, 1998, vol. 2, p. 1687.
[32] I. Ojima, M. Nihonyanagi, Y. Nagai, J. Chem. Soc. Chem.
Commun. 1972, 938; R. J. P. Corriu, J. J. E. Moreau, J. Or-
ganomet. Chem. 1975, 91, C27–C30; I. Ojima, M. Nihonyanagi,
T. Kogure, M. Kumagai, S. Horiuchi, K. Nakatsugawa, J. Or-
ganomet. Chem. 1975, 94, 449–461.
[33] I. Ojima, T. Kogure, Organometallics 1982, 1, 1390–1399.
[34] W. Dumont, J. C. Poulin, P. Dang Tuan, H. B. Kagan, J. Am. [42] D. A. Evans, F. E. Michael, J. S. Tedrow, K. R. Campos, J. Am.
Chem. Soc. 1973, 95, 8295–8299; M. E. Wright, S. A. Svejda,
Polyhedron 1991, 10, 1061–1068; H. Brunner, G. Riepl, H.
Weitzer, Angew. Chem. 1983, 95, 326; H. Brunner, R. Becker,
G. Riepl, Organometallics 1984, 3, 1354–1359; H. Brunner, B.
Reiter, G. Riepl, Chem. Ber. 1984, 117, 1330–1354; H. Brunner,
A. Kürzinger, J. Organomet. Chem. 1988, 346, 413–424; T. Kog-
Chem. Soc. 2003, 125, 3534–3543.
[43] M. F. Lappert, R. K. Maskell, J. Organomet. Chem. 1984, 264,
217–228; W.-L. Duan, M. Shi, G.-B. Rong, Chem. Commun.
2003, 2916–2917; Q. Xu, X. Gu, S. Liu, Q. Dou, M. Shi, J.
Org. Chem. 2007, 72, 2240–2242; J. W. Faller, P. P. Fontaine,
Organometallics 2006, 25, 5887–5893.
ure, I. Ojima, J. Organomet. Chem. 1982, 234, 249–256; B. Tao, [44] Y. Yuan, G. Raabe, C. Bolm, J. Organomet. Chem. 2005, 690,
G. C. Fu, Angew. Chem. Int. Ed. 2002, 41, 3892–3894; R. Cor-
riu, J. J. E. Moreau, J. Organomet. Chem. 1975, 85, 19–33; I.
Ojima, T. Kogure, M. Kumagai, S. Horiuchi, T. Sato, J. Or-
ganomet. Chem. 1976, 122, 83–97.
5747–5752.
[45] D. Drew, J. R. Doyle, Inorg. Synth. 1972, 13, 47–55.
Received: June 28, 2007
Published Online: September 20, 2007
Eur. J. Inorg. Chem. 2007, 5069–5079
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