Synthesis of chiral silver(I) diaminocarbene complexes from (R,R)-4,5-di-tert-butylimidazoline

Article abstract of DOI:10.1016/S0022-328X(01)01013-0

A preparation of chiral silver(I) diaminocarbene complexes was developed by treatment of imidazolinium salts derived from (R,R)-4,5-di-tert-butylimidazoline with silver(I) oxide. Complexes having the chirality on the heterocycle and methyl, benzyl or pico

Full text of DOI:10.1016/S0022-328X(01)01013-0

Journal of Organometallic Chemistry 631 (2001) 157–163
www.elsevier.com/locate/jorganchem
Synthesis of chiral silver(I) diaminocarbene complexes from
(R,R)-4,5-di-tert-butylimidazoline
Julien Pytkowicz, Sylvain Roland *, Pierre Mangeney
Laboratoire de Chimie des Organoe´le´ments, UMR 7611, Uni6ersite´ Pierre et Marie Curie, 4 Place Jussieu, tr. 44-45 2e`me e´t.,
75252 Paris Cedex 05, France
Received 10 April 2001; accepted 18 May 2001
Abstract
A preparation of chiral silver(I) diaminocarbene complexes was developed by treatment of imidazolinium salts derived from
(R,R)-4,5-di-tert-butylimidazoline with silver(I) oxide. Complexes having the chirality on the heterocycle and methyl, benzyl or
picolyl groups on the nitrogen atoms have been prepared. We also performed the synthesis of diaminocarbenes having in addition
the chiral (S)-1-phenylethyl moiety on the nitrogen atoms. X-ray structures of two of these carbenes (N,N%-dimethyl and
N,N%-dibenzyl) are presented. Several methods for the preparation of imidazolinium salts are described. © 2001 Elsevier Science
B.V. All rights reserved.
Keywords: Imidazolinium salts; Silver(I); Diaminocarbenes; Chiral ligands; Crystal structures
1. Introduction
were obtained by reaction of the free carbene with
silver triflate.
N-heterocyclic carbenes have recently emerged as an
important family of ligands with electronic characteris-
tics similar to those of the phosphines [1]. The use of
imidazol-2-ylidene, thiazol-2-ylidene and imidazolidin-
2-ylidene metal complexes rapidly showed an increased
interest since it was demonstrated that they are efficient
catalysts in important chemical transformations, such
as Ni and Pd carbon–carbon coupling reactions, CO–
ethylene copolymerisations, Ru-catalysed olefins
metathesis and Rh catalysed hydrosilylations. Initially,
the widespread use of catalysts with carbene ligands
was limited due to their relatively difficult preparation.
The first syntheses have utilised the free carbenes, ob-
tained by deprotonation of the corresponding azolium
salts, which are extremely air and moisture sensitive.
Recent investigations have demonstrated that the free
carbenes can be generated and directly trapped in situ
[2]. Silver(I) carbene complexes derived from imida-
zolium salts were synthesised and characterised for the
first time by Arduengo in 1993 [3]. These complexes
In our research to synthesise chiral imidazolidin-2-yl-
idene carbene complexes, we were particularly attracted
by an alternative method described by Wang and Lin
[4] in 1998. Indeed, these authors showed that a silver
benzimidazol-2-ylidene complex could be easily ob-
tained by treatment of the corresponding azolium salt
with Ag2O. Moreover, this silver carbene complex acts
as an effective carbene transfer agent for the synthesis
of palladium or gold carbene complexes. This method-
ology was applied recently with success by McGuinness
and Cavell [5] towards the synthesis of palladium imi-
dazol-2-ylidene complexes which are efficient catalysts
for C–C coupling reactions. Syntheses and structures of
N-fonctionalised silver(I) carbene complexes derived
from imidazolium salts were also reported by
Danopoulos et al. in 2000 [6]. Such an approach is mild
and compatible with the presence of acidic protons in
chains of the azolium salts. Especially if applicable to
the less acidic imidazolinium precursors, it could
provide a very convenient method for the formation of
chiral carbene complexes by overcoming many of the
difficulties arising from the use of strong bases.
* Corresponding author. Tel.: +33-1-4427-5567; fax: +33-1-4427-
7567.
E-mail address: sroland@ccr.jussieu.fr (S. Roland).
Synthesis of chiral diaminocarbene complexes re-
mains an important challenge for organic chemists and
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01013-0

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J. Pytkowicz et al. / Journal of Organometallic Chemistry 631 (2001) 157–163
only a few catalysts have been reported [7]. We report
here a versatile access to chiral imidazolin-2-ylidene
silver(I) carbene complexes and X-ray structures of two
of these compounds. The synthesis of the precursor
imidazolinium salts from (R,R)-4,5-di-tert-butylimida-
zolidine is also reported.
showed the characteristic peak of the 2H-imidazolin-
ium proton around 10–11 ppm (1H-NMR). However,
we were also particularly attracted by the development
of a methodology that allows us to oxidise the aminal
ring with preservation of the chiral moieties on the
nitrogen atoms. In order to perform this reaction, we
first tried the treatment of the imidazolidine 1 with 10%
Pd/C in refluxing ethanol and no hydrogen donor. A
slow reaction occurred, giving within 20 h the imidazo-
line 4 (90%) and a small amount (10%) of the expected
salt 3d. Addition of an excess of acetic acid gave the
best results leading to a mixture of 3d (75%) and 4
(25%). After neutralization, precipitation by addition of
Et2O, filtration and drying under vacuum (0.5 mmHg)
for 12 h at 100 °C to remove residual acetic acid, the
expected salt 3d was isolated in 61% yield. The charac-
terization of the counterion in 3d was quite difficult.
We first considered that it may be an acetate ion since
the elemental analysis of 3d was in accordance with the
calculated values of the monohydrate of the acetate salt
(see Section 4). This hypothesis could be confirmed by
the 1H-NMR spectrum that showed (after drying) a
signal at 2.12 ppm (3H) and no detectable acidic proton
characteristic of a carboxylic acid. Nevertheless, the
13C-NMR spectrum of 3d exhibited signals which chem-
ical shifts (20.9 and 177.2 ppm) were more consistent
with the presence of one molecule of acetic acid than an
acetate ion. For these reasons, the exact nature of the
counterion (hydroxide or acetate) remains uncertain
although this has no effect of the further reactions of
the salt.
2. Results and discussion
2.1. Synthesis of imidazolinium salts
We recently performed the synthesis of (R,R)-4,5-di-
tert-butylimidazolidine (2) from the aminal 1 [8] by a
one step palladium-mediated hydrogenolysis and oxida-
tion procedure [9]. This imidazoline 2 appeared to be
an interesting precursor for the synthesis of imidazolin-
ium salts (Scheme 1).
Indeed, 2 was easily alkylated in CH2Cl2 at 20 °C
using various halides. Precipitation with Et2O and pen-
tane and filtration led with 85–95% yields to the ex-
pected compounds 3a–c. All these imidazolinium salts
More recently, we found that a reported procedure
using iodine and NaHCO3 in CH2Cl2 was also efficient
to perform this oxidation [10] (Scheme 2). This reaction
seemed quantitative since no aminal 1 was detected in
the crude by TLC. The imidazolinium salt 3e has a very
low solubility in most organic solvents and was isolated
in 58% yield after dilution of the organic layer with
Et2O, stirring with an aqueous solution of sodium
Scheme 1. Preparation of imidazolinium salts from (R,R)-4,5-di-tert-
butylimidazolidine (2).
1
bisulfit and filtration. H-NMR spectroscopy (CDCl3)
of this compound showed the characteristic peak of the
2H-imidazolinium proton at 10.21 ppm. Nevertheless,
because of its low solubility and very high melting point
(m.p.\290 °C), we were unable to perform comple-
mentary analyses of 3e [11].
Scheme 2. Preparation of imidazolinium salts by oxidation of aminal
1.
2.2. Synthesis of sil6er(I) diaminocarbenes
Synthesis of silver(I) diaminocarbenes was very effi-
cient using the Wang and Lin procedure. Treatment of
the imidazolinium salts 3a–e with 0.5 equivalents of
silver oxide in CH2Cl2 afforded quantitavely after few
hours the expected carbenes 5a–e (Scheme 3). This
experiment was easily followed since Ag2O is insoluble
in CH2Cl2 and slowly disappeared in the course of the
reaction.
Scheme 3. Synthesis of Ag(I) carbene complexes.

J. Pytkowicz et al. / Journal of Organometallic Chemistry 631 (2001) 157–163
159
the 13C-NMR studies of carbenes 5a–c and 5e. How-
ever, in 5d, two doublets centered at 194.6 ppm were
observed for the carbene signal. This multiplicity is
probably due to the 13C–109Ag/107Ag couplings with
coupling constants of 268 and 232 Hz. Two other
signals corresponding to Ph–CH–N at 72.6/72.8 ppm
and to CH3–CH–Ph at 22.1/22.2 ppm, are also dou-
bled. We could not determine if this phenomena was
1
These carbenes were fully characterised by H-NMR
(CDCl3 or DMSO-d6). 1H-NMR spectra of all these
compounds showed the complete disappearance of the
2H-imidazolinium proton. The complexes 5a, 5b and 5d
gave only one signal for each group of equivalent
protons. In 5c and 5e, two sets of similar peaks, charac-
teristic of two compounds with a C2 symmetry, were
observed. The ratio of these two similar forms was
variable (from 2:1 to 9:1). The same phenomena was
observed by Danopoulos et al. with some of their
complexes [6] and the exact structure of these two
forms could not be determined. However, we noticed
that the NMR peaks of the minor form in 5c and 5e,
had chemical shifts similar to those of the precursor
salts but with no 2H-imidazolinium proton signal de-
tectable. Moreover, stirring a mixture of the two forms
of 5c in CH2Cl2, in the presence of Ag2O, gave back to
only one compound. From these observations, we de-
duced that the minor compound observed in some
cases, may be the 2D-imidazolinium salt obtained by
deuteration of the carbene by the NMR solvent [12]. In
compounds 5a–e, the carbon between the two nitro-
gens atoms showed characteristic high chemical shifts
of carbene signals in 13C-NMR (213.7 ppm for 5a, 206
ppm for 5b, 197.2 ppm for 5c, 194.6 ppm for 5d).
Nevertheless, these chemical shifts are significantly
higher than those described previously by Arduengo
(183.6 ppm), Lin (188–189 ppm), Cavell (182 ppm) and
Danopoulos on silver carbenes derived from imida-
zolium salts. No 13C–107,109Ag coupling was observed in
3
4
due to a J or JC–Ag coupling or to a desymmetrisa-
tion of the molecule.
2.3. Structures of sil6er(I) diaminocarbenes
Structures of 5a and 5b were determined by X-ray
spectroscopy. Figs. 1 and 3 show the ORTEP diagram of
these two complexes. The crystallographic data for 5a
and 5b are shown, respectively, in Tables 1 and 2.
Selected bond lengths and angles are given in Table 3.
The structure of 5a showed a dimer of a carbene–
Ag–I unit, the two silver atoms beeing bridged by two
iodides (Fig. 2). On the contrary, Lin and Arduengo
have reported structures, for complexes derived from
imidazolium or benzimidazolium salts, having two car-
benes for one silver atom, this latter being associated
with one molecule of AgX2. Nevertheless, Lin already
postulated in 1998 that an equilibrium should occur in
solution between these two forms. More recently,
Danopoulos et al. have reported that silver carbene
complexes derived from imidazolium salts can adopt
various structures in the solid state and also described
Fig. 1. ORTEP view of the dimeric structure of silver(I) diaminocarbene 5a.

160
J. Pytkowicz et al. / Journal of Organometallic Chemistry 631 (2001) 157–163
Table 1
the two metals. The structure of 5b showed the same
carbene–Ag–X unit but this complex crystallised as a
monomer.
Crystallographic data for compound 5a
Compound
Formula
Colour
Crystal class
Space group
Z
5a
C
26H52Ag2I2N4
Colourless
Tetragonal
P42
Table 3
,
Selected bond lengths (A) and bond angles (°) for 5a and 5b
4
5a
5b
Unit cell parameters
,
a (A)
14.435 (3)
14.435 (3)
8.364 (2)
1742.8 (6)
Mo Ka
0.71069
1.70
Bond lengths
Ag(1)–C(2)
N(1)–C(2)
,
b (A)
2.120(8)
1.324(13)
1.31(1)
3.0196(14)
2.6251(8)
–
2.089(17)
1.28(2)
1.32(2)
–
,
c (A)
V
N(3)–C(2)
Radiation type
Wavelength (A)
Ag(1)–Ag(1%)
Ag(1)–I(1)
Ag(1)–Br(1)
,
–
Density
2.401(3)
M (g mol−1
)
890.28
29.14
v (cm−1
)
Bond angles
N(1)–C(2)–N(3)
Ag(1)–C(2)–N(1)
Ag(1)–C(2)–N(3)
I(1)–Ag(1)–C(2)
Br(1)–Ag(1)–C(2)
C(2)–N(3)–C(4)
C(2)–N(1)–C(5)
108.8(7)
123.2(6)
127.4(6)
166.3(2)
–
109.5(15)
123.2(12)
126.9(13)
–
175.2(5)
114.5(15)
113.7(14)
Temperature (K)
Size
Shape
Diffractometer
Reflections measured
Independent reflections
Rint
295
0.2×0.2×0.4
Stick
Enraf–Nonius Cad-4
1793
1651
113.5(6)
112.8(6)
0.03
Table 2
Crystallographic data for compound 5b
Compound
Formula
Colour
Crystal class
Space group
Z
5b
C25H34AgBrN2
Colourless
Orthorhombic
P212121
4
Fig. 2. Dimeric and monomeric structures of 5a.
Unit cell parameters
,
a (A)
9.603 (5)
15.778 (7)
16.607 (7)
2516 (2)
Mo–Ka
,
b (A)
,
c (A)
V
Radiation type
,
Wavelength (A)
0.71069
1.45
550.33
24
Density
M (g mol−1
)
v (cm−1
)
Temperature (K)
Size
Shape
Diffractometer
Reflections measured
Independent reflections
295
0.2×0.3×0.3
Parallelepiped
Enraf–Nonius Cad-4
2540
2515
carbenes complexes having structures similar to 5a,
with a weak Ag–Ag interaction. The Ag–C(1) bond
,
distance in 5a (2.12 A) is comparable but a bit longer
,
than the one found by Lin (2.073 and 2.052 A) and
,
Danopoulos (2.06–2.1 A). The Ag(1)–I(1)–Ag(1%)–
I(1%) structure is not planar and the Ag-Ag distance of
,
3.02 A can be attributed to a weak interaction between
Fig. 3. ORTEP view of silver(I) diaminocarbene 5b.

J. Pytkowicz et al. / Journal of Organometallic Chemistry 631 (2001) 157–163
161
3. Conclusion
4.2.2. (4R,5R)-1,3-Dibenzyl-4,5-di-tert-butylimidazo-
linium bromide (3b)
This work provides a convenient method for the
synthesis of various chiral Ag(I) carbene complexes
from imidazolinium salts. X-ray structures of 5a and 5b
clearly show a monomeric carbene–Ag–X unit. Fur-
ther utilisation of these compounds for the preparation
of transition metal carbene complexes and their use in
catalytic reactions is under investigation.
M.p. 249–250 °C. [h]2D0= −114.3 (c 1.6, CHCl3).
Anal. Calc. for C25H35BrN2 (MW=443.46): C, 67.71;
H, 7.96; N, 6.32. Found: C, 66.55; H, 7.79; N, 6.15.
1H-NMR (200 MHz, CDCl3): l 0.68 (s, 18H, C(CH3)3),
3.38 (s, 2H, CH–N), 4.47 (d, 2H, J 14 Hz, Ph–
C(H%)H–N), 5.53 (d, 2H, J 14 Hz, Ph–C(H)H%–N)
7.38–7.43 (m, 6H, Ph), 7.54–7.56 (m, 4H, Ph), 11.12
(s, 1H, N–CHꢀN+). 13C-NMR l 26.5, 35.8, 53.5, 69.7,
129.4, 130, 132.9, 159.6.
4. Experimental
4.2.3. (4R,5R)-1,3-Dipicolyl-4,5-di-tert-butylimidazo-
linium chloride (3c)
All experiments were carried out under argon. Sil-
ver(I) oxide 99+% was purchased from Acros. Sol-
vents were of analytical grade type and used without
special drying or distillation. NMR spectra were
recorded on a Brucker ARX 400 or AC 200 Q instru-
ment, in CDCl3 or DMSO-d6 as the solvent. Optical
rotations were measured on a Perkin–Elmer 343.
M.p. 148–149 °C. [h]2D0= −52 (c 1, CH2Cl2). Anal.
Calc. for C23H33ClN4 (MW=400.99): C, 68.89; H,
8.30; N, 13.97. Found: C, 66.42; H, 8.56; N, 13.44.
1H-NMR (200 MHz, DMSO-d6): l 0.72 (s, 18H,
C(CH3)3), 3.82 (s, 2H, CH–N), 4.67 (d, 2H, J 14.5 Hz,
Ar–C(H%)H–N), 5.45 (d, 2H, J 14.5 Hz, Ar–C(H)H%–
N) 7.23–7.33 (m, 2H, Ar), 7.69–7.87 (m, 4H, Ar), 8.55
(d, 2H, J 5 Hz, Ar), 10.71 (s, 1H, N–CH=N+).
13C–NMR (DMSO-D6): l 26.1, 36.3, 54, 71.5, 124.5,
124.7, 138.4, 150.3, 154.4, 160.5.
4.1. Synthesis of imidazoline (2)
To a solution of imidazolidine 1 [8] (1 mmol) in
EtOH (20 ml), were added Pd(OH)2/C (0.1 mmol) and
ammonium formate (10 mmol). The mixture was
refluxed for 6 h, filtered and concentrated. To the
residue were added Et2O (15 ml) and K2CO3 (0.5 g) and
the suspension was stirred for 1 h, filtered and concen-
4.2.4. (4R,5R)-1,3-[(S)-1-phenylethyl]-4,5-di-tert-
butylimidazolinium acetate (3d)
A mixture of aminal 1 (1 mmol), acetic acid (4 mmol)
and Pd/C (0.1 mmol.) in iPrOH (20 ml) was refluxed for
20 h, filtered through Celite and concentrated. The
residue was taken off in CH2Cl2 (15 ml) and solid
K2CO3 was added. The suspension was stirred for 0.5
h, filtered and concentrated. The residue was taken off
in Et2O (15 ml). The white precipitate formed was
filtered, washed several times with pentane and dried
under vacuum (0.1 mmHg) at 100 °C to give 275 mg
(61%) of 3d. Recrystallisation in ethylacetate and a
small amount of CHCl3 led to small, thin, colourless
needles.
1
trated to give the imidazoline 2 as a white solid. H
NMR (CDCl3): l 0.86 (s, 18H), 3.27 (s, 2H), 4,8 (s,
1H), 7,05 (s, 1H). 13C NMR: l 24.5, 33.2, 69.1, 150.7.
4.2. Typical procedure for the synthesis of
imidazolinium salts (3a–c)
To a solution of imidazoline 2 (1 mmol.) in CH2Cl2
(5 ml) were added K2CO3 (0.5 g) and the halide (2.1
mmol.). The solution was stirred for 12 h at 20 °C,
filtered through Celite and concentrated. The residue
was taken off in Et2O or pentane (15 ml). The white
precipitate formed was filtered, washed several times
with pentane and dried under vacuum to afford the
expected salts (85–95%) as white solids.
[h]2D0= −163 (c 1.77, CHCl3). Anal. Calc. for
C29H42N2O2 (MW=450.66): C, 77.29; H, 9.39; N, 6.22.
Calc. for C29H42N2O2.H2O: C, 74.32; H, 9.46; N, 5.98.
1
Found: C, 74.02; H, 9.12; N, 6.06. H-NMR (CDCl3) l
0.59 (s, 18H, C(CH3)3), 2.12 (s, 3H, CH3CO−2 ), 2.20 (d,
6H, J 7.4 Hz, CH3–CH), 3.29 (s, 2H, tBu–CH–N),
4.61 (q, 2H, J 7.4 Hz, CH–CH3), 7.30–7.71 (m, 10H,
Ph), 11.25 (s, 1H, N–CHꢀN+). 13C-NMR (CDCl3): l
20.9, 24.3, 27.1, 36.4, 62.3, 71.9, 128.6, 130.1, 130.4,
139.8, 157.5, 177.2.
4.2.1. (4R,5R)-1,3-Dimethyl-4,5-di-tert-butylimidazo-
linium iodide (3a)
M.p. 270–271 °C. [h]2D0= −54.4 (c 2.02, CHCl3).
Anal. Calc. for C13H27IN2 (MW=338.27): C, 46.16; H,
8.05; N, 8.28. Found: C, 45.47; H, 8.36; N, 7.98.
1H-NMR (400 MHz, CDCl3): l 1.02 (s, 18H, C(CH3)3),
3.38 (s, 2H, CH–N), 3.45 (s, 6H, CH3–N), 10.07 (s,
1H, N–CHꢀN+). 13C-NMR (100 MHz, CDCl3): l
27.5, 37.2, 38.7, 75.5, 160.6.
4.2.5. (4R,5R)-1,3-[(S)-1-phenylethyl]-4,5-di-tert-
butylimidazolinium iodide (3e)
To a mixture of aminal 1 (1 mmol.) and NaHCO3 (1
mmol) in CH2Cl2 (5 ml) was added dropwise a solution
of iodine (1 mmol) in CH2Cl2 (5 ml). The mixture was
stirred 24 h at 20 °C. Et2O (50 ml) and sodium bisulfit

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J. Pytkowicz et al. / Journal of Organometallic Chemistry 631 (2001) 157–163
(aqueous solution) was added. The suspension was
stirred until decoloration and appearance of a white
precipitate in the organic phase. The solution was
filtered and the precipitate was washed with Et2O and
dried to afford 290 mg (58%) of the expected com-
pound as a white solid.
4.3.4. (4R,5R)-1,3-bis-[(S)-1-Phenylethyl]-4,5-di-tert-
butylimidazolin-2-ylidene sil6er(I) acetate (5d)
[h]2D0= −71 (c 0.5, CH2Cl2). Anal. Calc. for
C29H41AgN2O2 (MW=557.5): C, 62.48; H, 7.41; N,
1
5.02. Found: C, 61.35; H, 7.88; N, 4.94%. H-NMR
(CDCl3) l 0.60 (s, 18H, C(CH3)3), 2.17 (d, 6H, J 7 Hz,
t
1H-NMR (CDCl3): l 0.60 (s, 18H, C(CH3)3), 2.28 (d,
CH3–CH), 2.18 (s, 3H, CH3CO2Ag), 3.15 (s, 2H, Bu–
t
6H, J 7.4 Hz, CH3–CH), 3.35 (s, 2H, Bu–CH–N),
CH–N), 4.65 (q, 2H, J 7 Hz, CH–CH3), 7.22–7.61 (m,
10H, Ph). 13C-NMR l 22.1, 22.2 (CH3–CH–Ph), 23.2,
26.6, 35.1, 59.6 (tBu–CH–N), 72.6, 72.9 (Ph–CH–N),
127.9, 128.2, 128.7, 140.8, 178.7, 194.6 (d+d, J 232
and 268 Hz, N–C–N).
4.64 (q, 2H, J 7.4 Hz, CH–CH3), 7.25–7.77 (m, 10H,
Ph), 10.21 (s, 1H, N–CHꢀN+).
4.3. Typical procedure for the synthesis of 5a–e
To a solution of imidazolinium salt 3a–e (1 mmol) in
CH2Cl2 (15 ml) was added Ag2O (0.5 mmol). The
mixture was stirred at 20 °C until complete consump-
tion of the precipitate (4–20 h), filtered through Celite
and concentrated to give quantitatively the expected
compounds as crystalline solids.
4.3.5. (4R,5R)-1,3-bis-[(S)-1-Phenylethyl]-4,5-di-tert-
butylimidazolin-2-ylidene sil6er(I) iodide (5e)
1H-NMR (CDCl3): l 0.61 (s, 18H, C(CH3)3), 2.15 (d,
t
6H, J 7.4 Hz, CH3–CH–N), 2.02 (s, 2H, Bu–CH–N),
4.66 (q, 2H, J 7.4 Hz, CH3–CH–N), 7.23–7.72 (m,
10H). 13C-NMR (DMSO-D6) l 22.1, 26, 34.9, 58.2,
72.1, 127.9, 128.4, 141.3. The carbene carbon was not
observed.
4.3.1. (4R,5R)-1,3-Dimethyl-4,5-di-tert-
butylimidazolin-2-ylidene sil6er(I) iodide (5a)
[h]2D0= −93 (c 1, CHCl3). Anal. Calc. for
C13H26AgIN2 (MW=445.1): C, 35.08; H, 5.89; N, 6.29.
5. Supplementary material
1
Found: C, 36.89; H, 6.60; N, 6.37%. H–NMR (400
MHz, DMSO-d6) l 0.87 (s, 18H, C(CH3)3), 3.21 (s, 6H,
CH3–N), 3.34 (s, 2H, CH–N). 13C-NMR (DMSO-d6) l
32.9, 41.7, 45.8, 80.5, 213.7 (N–C–N). The single crys-
tals of 5a suitable for X-ray diffraction analysis were
obtained by recrystallisation from CH2Cl2, Et2O and
pentane mixture.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 160043 for compound 5a and
160044 for 5b. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44-
1233-336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
4.3.2. (4R,5R)-1,3-Dibenzyl-4,5-di-tert-
butylimidazolin-2-ylidene sil6er(I) bromide (5b)
[h]2D0= −57 (c 0.68, CH2Cl2). Anal. Calc. for
C25H34AgBrN2 (MW=550.3): C, 54.56; H, 6.23; N,
Acknowledgements
1
5.09. Found: C, 55.24; H, 6.42; N, 4.89%. H-NMR
(200 MHz, CDCl3) l 0.68 (s, 18H, C(CH3)3), 3.24 (s,
2H, CH–N), 4.50 (d, 2H, J 14.5 Hz, Ph–C(H%)H–N),
5.12 (d, 2H, J 14.5 Hz, Ph–C(H)H%–N) 7.3–7.42 (m,
10H, Ph). 13C-NMR (CDCl3) l 27.3, 35.7, 56.5, 71.2,
128.8, 129.2, 129.7, 135.4, 206 (N–C–N).
J. Pytkowicz thanks the MESR for a grant. We
thank C. Guyard-Duhayon (Centre de Resolution de
Structures, Laboratoire de Chimie Inorganique et Ma-
te´riaux Mole´culaires, Universite´ P. et M. Curie) for
X-ray structures.
The single crystals of 5b suitable for X-ray diffrac-
tion analysis were obtained by recrystallisation from
CH2Cl2 and hexane mixture.
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1
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.