Carbene adducts of dimethylcadmium

Article abstract of DOI:10.1515/znb-1999-1102

The first examples of carbene-cadmium complexes are reported from the reactions of a variety of imidazol-2-ylidenes or imidazolin-2-ylidenes with dimethylcadmium. Four new carbene complexes are characterized by NMR spectroscopy (¹H, ¹³C and ¹¹³Cd). The cadmium centers are strongly shifted downfield (100 -150 ppm) by interaction with the carbenes. X-ray structures are reported for three carbene-cadmium 1:1 adducts. The cadmium centers exhibit distorted trigonal-planar geometries in which the carbene ligands have an average 18.2 pm longer bond distance to cadmium compared to the methyl groups. The planes of cadmium coordination are twisted with respect to the plane of the imidazole ring. The more basic imidazolin-2-ylidene is shown to displace imidazol-2-ylidenes from the cadmium center.

Full text of DOI:10.1515/znb-1999-1102

Carbene Adducts of Dimethylcadmium
Anthony J. Arduengo, IIIa, Jens R. Goerlicha, Fredric Davidsonb,
and William J. Marshall5
a Institut für Anorganische und Analytische Chemie, der Technischen Universität
Carolo-Wilhelmina, D-38106 Braunschweig, Germany
b DuPont Science and Engineering Laboratory, Experimental Station,
Wilmington Delaware 19880, USA
Reprint requests to Prof. Dr. A. J. Arduengo
Z. Naturforsch. 54 b, 1350-1356 (1999); received June 16, 1999
Carbene, Cadmium, Ylide, Carbene Complex, Imidazol-2-ylidene
The first examples of carbene-cadmium complexes are reported from the reactions of a variety
of imidazol-2-ylidenes or imidazolin-2-ylidenes with dimethylcadmium. Four new carbene
complexes are characterized by NMR spectroscopy ('H , i?C and 1n Cd). The cadmium centers
are strongly shifted downfield (100 -150 ppm) by interaction with the carbenes. X-ray structures
are reported for three carbene-cadmium 1:1 adducts. The cadmium centers exhibit distorted
trigonal-planar geometries in which the carbene ligands have an average 18.2 pm longer bond
distance to cadmium compared to the methyl groups. The planes of cadmium coordination are
twisted with respect to the plane of the imidazole ring. The more basic imidazolin-2-ylidene is
shown to displace imidazol-2-ylidenes from the cadmium center.
Introduction
bonic anhydrases (retaining some enzymatic ac-
tivity) [2 1 ] and that cadmium can play a role in
epoxide/CC>2 copolymerizations [2 2 ], the coordina-
tion chemistry of cadmium has become more im-
portant. Organocadmium compounds, compared to
their zinc analogs have a much lower Lewis acidity,
and their complex-forming tendencies are consider-
ably decreased. Taking advantage of the high nucle-
ophilicity of imidazol-2 -ylidenes and imidazolin-2 -
ylidenes, we now report the first examples of zwit-
terionic carbene-cadmium complexes.
Since 1991 a number of structurally different
types of stable, nucleophilic carbenes have been
described, for example several 1,3-disubstituted
imidazol-2 -ylidenes [1 , 2 ], 1,3,4,5-tetrasubstituted
imidazol-2 -ylidenes [2-4], 1,3,4-triphenyl-1 ,2 ,4-
triazol-5-ylidene [5], 1,3-disubstituted imidazolin-
2-ylidenes [6 , 7], N,N,N',N'-tetraisopropylform-
amidinylidene [8 ], 3-(2,6-diisopropylphenyl)-4,5-
dimethylthiazol-2-ylidene [9], air-stable 4,5-di-
haloimidazol-2 -ylidenes [1 0 ], and most recently,
aminooxycarbenes [11]. A historical review of the
development of these stable nucleophilic carbenes
has recently appeared [1 2 ] and some of the chem-
istry of stable heterocyclic carbenes has been re-
viewed [13], Stable nucleophilic carbenes possess
high Lewis basicity and reveal a strong tendency to
react with even mild Lewis acids. As a consequence
of this reactivity, their reactions with both metallic
and non-metallic Lewis acids furnish many unusual
adducts [14].
Results and Discussion
When carbenes la-d were treated with dimethyl-
cadmium at room temperature, a smooth reaction
took place in which the cadmium complexes
2
a-
d were formed in good yields (eqs (1 ) and (2 )).
Adducts 2a-d are colorless, air- and moisture-sensi-
tive solids which are soluble in aromatic hydro-
carbons and ethers. Although 2a, 2c, and 2d melt
within a rather narrow range of temperatures be-
tween 149 °C and 161 °C, a melting range of 280
Donor complexes of nucleophilic carbenes with - 285 °C was observed for 2b. Such high melting
points are often observed for adducts of 1,3-di-
been previously reported. Carbene-cadmium com- adamantylimidazol-2 -ylidene.
zinc [14, 15] or mercury [16-20] compounds have
Proton and carbon solution NMR spectra show
plexes remain unknown however. With the discov-
eries that cadmium can substitute for zinc in car- small chemical shift differences when the adducts
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A. J. Arduengo et al. ■Carbene Adducts of Dimethylcadmium
Table I. Selected bond
lengths (pm) and angles
(°) in carbene-cadmium
adducts 2b-d.
2d
Property
2b
2c
237.1 (7)
218.5 (8), 218.4 (8)
136.3 (8), 134.1 (8)
232.7 (2)
218.5 (4), 218.1 (4)
133.2 (4), 132.4 (4)
r(C2-Cd)
240.6 (4)
219.9 (4), 218.5 (4)
137.2(5), 136.5 (5)
r(Cd-CH3)
r(C -N ( )
r(N 1(3)-C5<4))
r(C4-C5)
6>(CPh-Cd-CHV)
<9(C2-Cd-CH3)
139.6 (6), 136.8 (6) 137.2(9), 137.7 (9) 148.7 (4), 147.5 (4)
136.4 (7)
138.8(2)
132.8(10)
140.0 (3)
153.0 (5)
136.2 (2)
109.9 (2), 114.0(1)
108.6 (3)
105.2(2), 116.0 (2) 111.2(3), 108.8(3)
104.0 (3)
<9(N'-C2-N3)
103.8(5)
110.8(6), 111.5 (6) 113.0(3), 113.9(3)
106.5 (4), 106.8(4) 107.1 (7), 106.7 (7) 102.2(3), 102.2(3)
/9(C2-N I(3)-C5(4))
6>(N1(3)-C5(4)-C4<5))
u;(imid<mpI)-Cd(C3~mpl)) 73.7
110.6(3), 112.1 (4)
69.7
86.8
of bis(trifluoromethyl)cadmium [24]. The ll3Cd
chemical shift changes observed for the formation
(1)
of a-d are intermediate between those of nucle-
2
ophilic solvent interactions with a cadmium center
and cadmate formation. With slightly varied sto-
ichiometries (carbene/CdMe2 i- 1), NMR spectra
of a-d exhibited averaged resonances suggesting
2
b: R1= 1-adamantyl, R2= H
that carbene exchanges with the adducts are fast
on the NMR time scale. However if different car-
benes are available, the dimethylcadmium moiety
is transferred to the most nucleophilic carbene cen-
ter and reverse exchange is no longer evident on
the NMR time scale. When a thf-d% solution of
c: R1= mesityl, R2= H
CH,
Cd(CH3)2
Cd;
(2)
toluene, 23 °C
CHg
the diadamantylimidazol-2 -ylidene adduct
mixed with the imidazolin-2 -ylidene carbene Id at
room temperature, only resonances for lb and
2
b was
2
d
2
d
R1= mesityl
1
d
were observed with no evidence of signal averaging.
Crystals of 2b-d suitable for single crystal X-ray
diffraction studies were grown by cooling saturated
toluene solutions to -20 °C. The adamantyl substi-
2
a-d are formed from the corresponding carbenes.
There is a 0.2 ppm upfield shift for the imidazole
ring protons (H4,5) in the dimethylcadmium adducts
2b and 2c compared to the respective carbenes. The
resonances for the imidazole C2 carbons in the cad-
mium adducts shift upfield by 14 - 18 ppm relative
to their positions in the free carbenes. These chem-
ical shift changes are similar to those reported for
the diethylzinc adducts of la and lb [15].
tuted adduct b crystallizes in the monoclinic space
2
group Cc (No. 9) with similar dimensions to the
corresponding diethylzinc derivative (both struc-
tures also include a toluene of crystallization) [15].
However, the two structures are not isomorphic.
The mesityl-substituted adducts 2c and 2d both
crystallize in the monoclinic P2j/c (No. 14) space
group but again the structures are not isomorphic
as has been found for other imidazolylidene-imid-
azolinylidene pairs [2, 7], Further details on the unit
cell parameters and data collection are found in the
experimental section.
The most dramatic chemical shift change for
adducts a-d is observed for the cadmium nucleus
2
which shifts to lower field by 100 - 155 ppm rela-
tive to dimethylcadmium. Nucleophilic interactions
with, or additions to, a dialkylcadmium center gen-
erally produce a downfield shift in the resonance
of the affected cadmium center. Dimethylcadmium
Selected bond lengths and angles in 2b-d are pre-
has been shown to be subject to rather large sol- sented in Table I and their structures are depicted
with the KANVAS [25] drawings in Figs 1 - 3. All
three structures show a planar 3-coordinated envi-
ronment at the cadmium centers although the co-
vent shifts (up to 65 ppm downfield) in nucleophilic
solvents like thf and diglyme [23]. The tris(trifluoro-
methyl)cadmate anion resonates 250 ppm downfield
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1352
A. J. Arduengo et al. ■Carbene Adducts of Dimethylcadmium
Fig. 3. KANVAS drawing of the solid state structure of
2d.
2b.
than the average C-Cd distance (224 pm) found
in the trimethylcadmate anion [26], The cadmium-
carbene distances are 240.6, 237.1 and 232.7 pm
for b-d and are an average 18.2 pm longer than the
2
cadmium-methyl bonds.
For all three structures the cadmium centers are
displaced from the idealized C2 vectors that pass
through the carbene centers. This distortion is great-
est for the dimesitylimidazol-2 -ylidene adduct c in
2
which the cadmium center lies 9.10 off the C2 vector
and rises 33.1 pm out of the plane of the imidazole
ring. In the corresponding saturated imidazolin-2-
ylidene adduct,
2
d, the distortion is minimal, and
the cadmium resides 9.3 pm out of the imidazole
plane and only 3.4° away from the C2 vector. The
adamantyl substituted derivative
2
b shows a 8 .1 °
deviation of the cadmium from the idealized imi-
dazole C2 axis and the cadmium is 33.8 pm out of
the imidazole plane. In 2d, the plane of the CdC3
grouping is twisted 8 6 .8 ° with respect to the imi-
dazoline plane. For 2b and 2c the inter-plane twists
are 73.7° and 69.7°, respectively. The various twists
of the cadmium coordination planes with respect to
the pendent imidazoles suggest that there are no
special p7r-d7r interactions between the imidazole
and cadmium centers.
Fig. 2. KANVAS drawing of the solid state structure of
2c.
ordination at cadmium is not trigonally symmet-
ric as found for the trimethylcadmate anion [26].
The deviations of the cadmium centers from the
plane of their three attached carbon atoms are only
0.6, 3.8 and 0.5 pm respectively for 2b-d. The va-
lence angles at cadmium show a pattern of one
large angle (136 - 140°) between the two methyl
groups and two smaller angles (105 - 116°) between
Following the successful coordination of car-
benes to dimethylcadmium, dimethylmercury was
briefly investigated as a potential Lewis acid partner
the methyl groups and the carbene moiety. The for carbenes la-d. However, no evidence of adduct
methyl-cadmium distances are all slightly shorter formation was detected with this dialkylmercury.
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1353
A. J. Arduengo et al. ■Carbene Adducts of Dimethylcadmium
Conclusions
NCH3); 13C NMR (C6D6): 6 -10.16 (s (br), Cd(CH3)2),
8.36 (s, CCH3), 34.57 (s, NCH3), 123.54 (s, C4’5), 196.78
(s (br), C2); ll3Cd NMR (C6D6): 6 155.0 (s).
Dialkylcadmium compounds form stable coor-
dination complexes with imidazol-2 -ylidenes and
imidazolin-2-ylidenes. These cadmium-carbene
Analysis for CgHigCd^ (266.7)
Calcd C 40.54 H 6.80 N 10.51%,
Found C 40.73 H6.91 N 10.74%.
complexes are novel examples of
a hitherto
unknown type of cadmium-carbon bond. The
dimethylcadmium adducts 2a-d are stable in the
solid state and in solution where they show a ten-
dency for carbene ligand exchange in the presence
of excess carbene. The geometry at cadmium in
these 1 : 1 adducts is cadmate-like but the trigonal
aspect of the coordination is not as fully developed
as it is in simple cadmates like Cd(CH3)3 ~ [26], The
carbene-metal bonding appears weaker in 2b and
2c compared to the analogous diethyl zinc deriva-
tives [15]. There is no evidence for p7r-d7r interac-
1,3-D i-l-adamantylimidazol-2-ylidene ■dimethyl-
cadmium (2b)
To a solution of 0.168 g (0.5 mmol) of 1,3-di-l-ada-
mantylimidazol-2-ylidene (lb) in a mixture of 10 ml of
toluene, and 5 ml of thf at 23 °C was added a solution
of 0.071 g (0.5 mmol) of dimethylcadmium in 5 ml of
toluene. Immediately a colorless solid precipitated. The
mixture was stirred for 16 h at 23 °C and subsequently
evaporated to give 2b as a colorless solid. Recrystalliza-
tion from toluene at -20 °C furnished colorless crystals.
tion between the cadmium and carbene centers. The Yield: 0.192 g (80%); m. p. 280 - 285 °C (dec.);1H NMR
(C6D6): 6 -0.02 (s + d, / CdH = 46.8 Hz, 6 H, Cd(CH3)2),
1.47 (m, 12 H, Ad4'6'10), 1.91 (s, 6 H, Ad3-5-7), 2.12 (s,
12 H, Ad2-8-9), 6.72 (s, 2 H, H4’5); l3C NMR (C6D6): 6
-6.03 (s, Cd(CH3)2), 29.89 (s, Ad3-5’7), 35.99 (s, Ad4-6’10),
44.46 (s, Ad2’8’9), 57.01 (s, Ad1), 114.92 (s, C4’5), 201.78
(s, C2); ll3Cd NMR (C6D6): 6 102.6 (s).
cadmium-carbene bond is best described as a sim-
ple cr-interaction. There is no evidence of complex
formation between dimethylmercury and carbenes
la-d. Mercuric chloride and mercury(II) ions are
however known to form complexes with imidazole-
derived carbenes [16 - 2 0 ].
Analysis for C25H38CdN2 (479.0)
Calcd C 62.69 H 8.00 N 5.85%,
Found C 63.15 H 7.98 N 5.54%.
Experimental
Reactions and manipulations were carried out under
an atmosphere of dry nitrogen, either in a Vacuum Atmo-
spheres dry box or using standard Schlenk techniques.
Solvents were dried (using standard procedures) [27],
distilled, and deoxygenated prior to use. Glassware was
oven-dried at 160 °C overnight. Proton NMR spectra were
recorded on a General Electric QE-300 spectrometer. The
l3C and " 3Cd spectra were recorded on a GE Omega
300WB spectrometer. NMR references are (CH .^Si ('H,
l3C), and Cd(CH3)2 [via external 0.1 M CdCl2] (ll3Cd).
Melting points were obtained on a Thomas-Hoover capil-
lary apparatus and were not corrected. Elemental analyses
were performed by Schwarzkopf Microanalytical Labo-
ratory, Inc., Woodside, NY.
X-ray structure determination o f 2b
Crystals of 2b were grown from a solution in toluene at
-20 °C. Crystal data for 2b at -114 °C with MoKq radia-
tion: a = 1593.7(1), b = 1387.6(1), c = 1291.0(1) pm, ß =
102.61(1)°, monoclinic, Cc, Z = 4, //(Mo) = 8.01 cm-1 .
The data were collected using a Rigaku RU300 R-AXIS
image plate area detector. Filament size 10.0 x 0.5 mm,
anode power 55 Kv x 200 ma, crystal to plate distance
8.5 mm, 105 n pixel raster, 45 frames, oscillation range
4.0 °/frame, exposure 17 min/frame, box sum integration,
7221 data collected 7.4° = 20 = 48.2°, maximum h, k, I
18 15 14, no absorption correction. 2390 duplicates, 1.3%
R-merge, 2026 unique reflections with I > 3.0 <r(I). The
structure was solved by direct methods (MULTAN) and
refined by full-matrix least-squares on F. Carbon, nitro-
gen, and cadmium were refined with anisotropic thermal
parameters. Because the refinement gave large thermal
1,3,4,5-Tetramethylimidazol-2-ylidene ■dimethyl-
cadmium (2a)
To a solution of 0.124 g (1 mmol) of 1,3,4,5-tetrame-
thylimidazol-2-ylidene (la) in 20 ml of toluene at 23 °C parameters for some of the hydrogens, all hydrogens were
was added a solution of 0.142 g (1 mmol) of dimethylcad- idealized close to their previously refined positions. The
mium in 5 ml of toluene. The mixture was stirred for 2 h largest residual electron density in the final difference
Fourier map was 0.37 e/° 3. The data/parameter ratio was
6.42. The final R factors were R = 0.027 and Rw = 0.035.
Crystallographic data for the structure of 2b have been de-
posited with the Cambridge Crystallographic Data Centre
at 23 °C and subsequently evaporated to give a colorless
solid that was recrystallized from toluene at -20 °C. Yield:
0.198 g (74%); m.p. 152 - 154 °C; 'H NMR (C6D6): 6
0.11 (s, 6 H, Cd(CH3)2), 1.39 (s, 6 H, CCH3), 3.44 (s, 6 H,
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1354
A. J. Arduengo et al. • Carbene Adducts of Dimethylcadmium
(ref. Nr. 127341). Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: int. code
+(1223)336-033; e-mail: teched@chemcrys.cam.ac.uk).
Copies of the data can be obtained free of charge from
the address listed under 2b.
1,3-Dimesitylimidazolin-2-ylidene ■dimethyl-
cadmium (2d)
1,3-Dimesitylimidazol-2-ylidene ■dimethylcadmium (2c)
A solution of 0.142 g (1 mmol) of dimethylcadmium
in 5 ml of toluene was added to a solution of 0.153 g
(0.5 mmol) of l,3-dimesitylimidazolin-2-ylidene (Id) in
20 ml of hexane at 23 °C. Immediately a colorless solid
precipitated. The mixture was stirred for 1 h at 23 °C,
and subsequently evaporated to give 2d as a colorless
solid. Recrystallization from toluene at -20 °C furnished
colorless crystals suitable for X-ray diffraction. Yield:
0.176 g (78%); m.p. 161 - 164 °C; 'H NMR (C6D6): 6
-0.43 (s (br), 6 H, Cd(CH3)2), 2.03 (s, 6 H, p-CH3), 2.24
(s, 12 H, o-CH3), 3.08 (s, 4 H, H4 5), 6.72 (s, 2 H, m-CH);
A solution of 0.071 g (0.5 mmol) of dimethylcadmium
in 5 ml of toluene was added to a solution of 0.152 g
(0.5 mmol) of l,3-dimesitylimidazol-2-ylidene (lc) in a
mixture of 10 ml of toluene and 5 ml of thf at 23 °C .
The mixture was stirred for 16 h at 23 °C, and subse-
quently evaporated to give 2c as a colorless solid. Recrys-
tallization from toluene at -20 °C afforded colorless crys-
tals suitable for X-ray diffraction. Yield: 0.170 g (76%);
m.p. 149 - 151 °C; 'H NMR (C6D6): 6 -0.41 (s, 6 H,
Cd(CH3)2), 2.08 (s, 18 H,
0
-CH + p-CH3), 6.23 (s, 2 H,
3
l3C NMR (C6D6): <5-7.67 (s (br), Cd(CH3)2), 17.86 (s,
0 -C H 3), 20.96 (s, p-CH3), 50.78 (s, C*'5), 129.68 (s, m-
O , 136.09 (s, o-Q , 136.12 (s, ipso-C), 137.99 (s, p-Q ,
226.09 (s, C2); " 3Cd NMR (C6D6): «5 142.0 (s).
H4’5), 6.74 (s, 4 H, m-CH); ,3C NMR (C6D6): 6 -7.7 (s
(br), 6 H, Cd(CH3)2), 17.61 (s, o-CH3), 20.98 (s, p-CH3),
121.36 (s, C4’5), 129.32 (s, m-C), 135.12 (s, o-Q , 136.45
(s, ipso-C), 138.64 (s, p-C), 202.82 (s (br), C2); ll3Cd
NM R(C6D6): 6 152.6 (s).
Analysis for C2
3
H3 2CdN2 • ('/2 C?Hg) (483.0)
Calcd C 63.41 H7.51 N 5.80%,
Found C 63.51 H 7.68 N5.71%.
Analysis for C2 3 H3oCdN2 (446.9)
Calcd C 61.81 H 6.77 N 6.27%,
Found C 60.62 H 6.94 N 6.29%.
X-ray structure determination o f 2d
Crystals of 2d were grown from a saturated solution
in toluene at -20 °C. Crystal data for 2d at -114 °C
with MoKct radiation: a = 1795.2(2), b = 907.6(1), c =
1708.7(2) pm, ß = 112.83(1)°, monoclinic, P2]/c, Z = 4,
p(Mo) = 8.60 cm-1 . The data were collected using a
Rigaku RU300 R-AXIS image plate area detector. Fil-
X-ray Structure Determination o f (2c)
Crystals of 2c were grown from a solution in toluene at
-20 °C. Crystal data for 2c at - 1 15 °C with Mo Ka radi-
ation: a = 825.9(1), b = 1580.7(1), c = 1714.6(1) pm, ß =
92.26 (1)°, monoclinic, P2i/n, Z = 4, p(Mo) = 9.79 cm-1.
The data were collected using a Rigaku RU300 R-AXIS
image plate area detector. Filament size 10.0 x 0.5 mm,
anode power 55 Kv x 200 ma, crystal to plate distance
8.5 mm, 105 p pixel raster, 45 frames, oscillation range
4.0 °/frame, exposure 15 min/frame, box sum integration,
ament size 10.0
x 0.5 mm, anode power 55 Kv x
180 ma, crystal to plate distance 8.5 mm, 105 p pixel
raster, 45 frames, oscillation range 4.0 “/frame, exposure
17 min/frame, box sum integration, 11647 data collected
4.8° = 26 = 48.2°, maximum h, k,l 20 9 19, no absorption
9961 data collected 3.5° = 29 = 48.2°, maximum h, k, I correction. 3341 duplicates, 1.7% R-merge, 3037 unique
9 18 19, no absorption correction. 2889 duplicates, 2.6%
R-merge, 1907 unique reflections with I > 3.0 a(I). The
structure was solved by direct methods (SHELXS) and
refined by full-matrix least-squares on F. Carbon, nitro-
gen, and cadmium were refined with anisotropic thermal
parameters. Because the refinement gave large thermal
parameters for some of the methyl hydrogens, all hydro-
gens except H4-5 were idealized close to their previously
refined positions. The largest residual electron density in
the final difference Fourier map was 0.46 e/°3 near Cl.
The data/parameter ratio was 7.83. The final R factors
were R = 0.052 and /?„ = 0.056. Crystallographic data
for the structure of 2c have been deposited with the Cam-
bridge Crystallographic Data Centre (ref. Nr. 127342).
reflections with I > 3.0 cr(I). The structure was solved
by automated Patterson analysis (PHASE) and refined by
full-matrix least-squares on F. Carbon, nitrogen, and cad-
mium were refined with anisotropic thermal parameters.
Because the refinement gave large thermal parameters for
some of the methyl hydrogens, all hydrogens were ideal-
ized close to their previously refined positions. The largest
residual electron density in the final difference Fourier
map was 0.45 e/°3. The data/parameter ratio was 10.82.
The final R factors were R =0.039 and Rn =0.046. Crystal-
lographic data for the structure of 2c have been deposited
with the Cambridge Crystallographic Data Centre (ref.
Nr. 127343). Copies of the data can be obtained free of
charge from the address listed under
2b.
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1355
A. J. Arduengo et al. •Carbene Adducts of Dimethylcadmium
Reaction of 2b with Id Acknowledgements
To
5
a
solution of 0.048
g
(0.1 mmol) of 2b
A .J.A . gratefully acknowledges the support of the
Alexander von Humboldt Foundation for a Senior Re-
search Prize that enabled this research. J. R. G. thanks the
DuPont Company for their support of a Visiting Research
Scientist appointment (1996-7). The authors dedicate this
work to Professor Dr. Reinhard Schmutzler on the occa-
sion of his 65th birthday.
in
ml of thf-dg were added at 23 °C 0.031
g
(0.1 mmol) of Id. The mixture was stirred at 23 °C
for 1 h, and investigated by ‘H NMR which indi-
cated that Id had completely replaced the di-l-ada-
matylimidazol-2-ylidene in
and lb.
2
b, giving a solution of d
2
g) A. J. Arduengo, III, C. J. Carmalt, J. A. C.
Clyburne, A. H. Cowley, R. Pyati, J. Chem. Soc.,
Chem. Commun. (1997);
h) W. A. Herrmann, L. J. Goossen, G. R. J. Artus,
C. Köcher, Organometallics 16, 2472-7 (1997);
i) A. J. Arduengo, III, S. F. Gamper, M. Tamm, J. C.
Calabrese, F. Davidson, H. A. Craig, J. Am. Chem.
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