Synthesis of benzannulated N-heterocyclic carbene ligands by a template synthesis from 2-nitrophenyl isocyanide

Article abstract of DOI:10.1002/chem.200400576

The reaction of 2-nitrophenyl isocyanide 2 with [M(CO)₅(thf)] (M = Cr, Mo, W) yields the isocyanide complexes [M(CO)₅(2)] (3: M = Cr; 4: M = Mo; 5: M = W). Complexes 3-5 react with elemental tin under reduction of the nitro function of the isocyanide ligand to give the complexes with the unstable 2-aminophenyl isocyanide ligand. The coordinated 2-aminophenyl isocyanide ligand in all three complexes reacts spontaneously under intramolecular nucleophilic attack of the primary amine at the isocyanide carbon atom to yield the complexes with the NH,NH-benzimidazol-2-ylidene ligand (6: M = Cr; 7: M = Mo; 8: M = W). An incomplete reduction of the nitro group in 3-5 is observed when hydrazine hydrate is used instead of tin. Here the formation of complexes with a coordinated 2-hydroxylamine-functionalized phenyl isocyanide [(CO)₅M-CN-C₆H_4--2-N(H)-OH] is postulated and this unstable ligand again undergoes intramolecular cyclization to give the NH,NOH-stabilized benzimidazol-2-ylidene complexes 9-11. The tungsten derivative 11 can be allylated stepwise by a deprotonation/ alkylation sequence first at the OH and then at the NH position to yield the monoallylated and diallylated species 12 and 13. The molecular structures of 3-5 and 12-13 were established by X-ray crystallography.

Full text of DOI:10.1002/chem.200400576

FULL PAPER
Synthesis of Benzannulated N-Heterocyclic Carbene Ligands by a Template
Synthesis from 2-Nitrophenyl Isocyanide
F.Ekkehardt Hahn,* CØsar García Plumed, Marco Münder, and Thomas Lügger [a]
Abstract: The reaction of 2-nitrophenyl
isocyanide 2 with [M(CO)5(thf)] (M=
Cr, Mo, W) yields the isocyanide com-
plexes [M(CO)5(2)] (3: M=Cr; 4: M=
Mo; 5: M=W). Complexes 3–5 react
with elemental tin under reduction of
the nitro function of the isocyanide
ligand to give the complexes with the
unstable 2-aminophenyl isocyanide
ligand. The coordinated 2-aminophenyl
isocyanide ligand in all three com-
plexes reacts spontaneously under in-
tramolecular nucleophilic attack of the
primary amine at the isocyanide
carbon atom to yield the complexes
with the NH,NH-benzimidazol-2-yli-
dene ligand (6: M=Cr; 7: M=Mo; 8:
M=W). An incomplete reduction of
the nitro group in 3–5 is observed
when hydrazine hydrate is used instead
of tin. Here the formation of com-
plexes with a coordinated 2-hydroxyl-
amine-functionalized phenyl isocyanide
[(CO)5M-CN-C6H4--2-N(H)-OH]
is
postulated and this unstable ligand
again undergoes intramolecular cycliza-
tion to give the NH,NOH-stabilized
benzimidazol-2-ylidene complexes 9–
11. The tungsten derivative 11 can be
allylated stepwise by a deprotonation/
alkylation sequence first at the OH and
then at the NH position to yield the
monoallylated and diallylated species
12 and 13. The molecular structures of
3–5 and 12–13 were established by
X-ray crystallography.
Keywords:
chromium
carbene ligands
· isocyanide ligands
·
·
molybdenum · tungsten
Introduction
the nucleophile and the isocyanide group are already linked
before coordination to the metal center. If suitably activated
by coordination to transition metals in higher oxidation
states these ligands spontaneously cyclize to form oxazoli-
din-2-ylidenes[6] allowing even the isolation of homoleptic
tetra-[7] and hexacarbene complexes.[8]
In b-functional aryl isocyanides the electrophilic isocya-
nide and the nucleophilic substituent are not only linked,
but are also suitably arranged in one plane for an intramo-
lecular cycloaddition reaction. This geometry together with
the aromaticity of the resulting cyclic carbene ligand could
lead to an even greater tendency to form heterocyclic yli-
denes. Contrary to aliphatic 2-hydroxyethyl isocyanide,[6–8]
free 2-hydroxyphenyl isocyanide is not stable and cyclizes to
give benzoxazole.[9] However, lithiation of benzoxazole and
subsequent reaction with Me3SiCl yields 2-(trimethylsiloxy)-
phenyl isocyanide,[10] a synthon for 2-hydroxyphenyl isocya-
nide. The O-protected 2-(trimethylsiloxy)phenyl isocyanide
can coordinate to transition metals and a series of com-
plexes of type A (Scheme 1) have been prepared.[11–16]
The nucleophilic attack at the carbon atom of a coordinated
isocyanide ligand is a standard method to generate metal–
carbene complexes.[1–3] Protic nucleophiles such as alcohols
and primary or secondary amines have been particularly
useful in this reaction. This carbene synthesis was first ap-
plied, although unintentionally, in 1915 when Tschugajeff
and Skanawy-Grigorjewa reacted tetrakis(methyl isocyani-
de)platinum(ii) with hydrazine.[4] The reaction products
were 50 years later recognized as carbene complexes.[5]
The addition of proton-containing bases HX to coordinat-
ed isocyanides usually leads to the formation of complexes
with acyclic carbene ligands. However, employment of func-
tional isocyanides, which contain both the isocyanide group
and the nucleophile in the same molecule, gives access to
complexes with heterocyclic carbene ligands through an in-
tramolecular 1,2-addition across the CꢀN triple bond. Fehl-
hammer et al. introduced readily available and stable 2-hy-
droxyalkyl isocyanides such as CꢀNCH2CH2OH, in which
ꢁ
Cleavage of the Si O bond in these complexes is best ach-
ieved by stirring in methanol with a catalytic amount of KF
under formation of complexes B with the 2-hydroxyphenyl
isocyanide ligand. Subsequently, complexes containing the
benzoxazol-2-ylidene ligand C can be formed by intramolec-
ular nucleophilic attack if the isocyanide is sufficiently acti-
vated (or insufficiently deactivated) towards intramolecular
[a] Prof. Dr. F. E. Hahn, C. García Plumed, Dr. M. Münder,
Dr. T. Lügger
Institut für Anorganische und Analytische Chemie
Westfälische Wilhelms-Universität Münster
Corrensstraße 36, 48149 Münster (Germany)
Fax : (+49)251-833-3108
E-mail: fehahn@uni-muenster.de
Chem. Eur. J. 2004, 10, 6285 – 6293
DOI: 10.1002/chem.200400576
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6285

FULL PAPER
known NR,NR-stabilized N-heterocyclic carbenes.[24] Free
saturated unsymmetrically substituted imidazolin-2-ylidenes
F[25] and benzannulated N-heterocyclic carbenes of type G[26]
show an interesting reactivity.[27] However, the synthesis of
the benzannulated free carbenes is difficult and time con-
suming.[26] Based on the template synthesis for NH,O-stabi-
lized carbene ligands presented in Scheme 1, we developed
the template-controlled synthesis of complexes with
NH,NH-stabilized (I) and NR,NR-stabilized carbene ligands
(J) starting from complexes with the 2-azidophenyl isocya-
nide ligand (H), which is a synthon for the unknown 2-ami-
nophenyl isocyanide (Scheme 2).[28] A similar method was
used by Michelin et al. for the preparation of N-heterocyclic
carbenes with a benzannulated six-membered N-heterocyclic
ring.[29]
Since 2-azidophenyl isocyanide is difficult to prepare and
explosive under certain circumstances, we searched for new
2-substituted phenyl isocyanide ligands that could be con-
Scheme 1. Template synthesis of NH,O-and NR,Os-tabilized carbene li-
gands from coordinated 2-(trimethylsiloxy)phenyl isocyanide.
nucleophilic attack by the hy-
droxy group at the isocyanide
carbon atom. Different obser-
vations are made during the
cyclization reaction depending
on the nature of the transition-
metal
complex
fragment
MLx.[17,18] Strong M!L back-
bonding stabilizes the hydroxy-
phenyl isocyanide ligand (B),
whereas weak backbonding
leads to the formation of the
complex C with an NH,O-stabi-
lized
carbene
ligand
(Scheme 1).
Various methods have been
reported to shift the equilibri-
um between the 2-hydroxy- Scheme 2. Template-controlled synthesis of complexes with N-heterocyclic carbene ligands.
phenyl isocyanide complex B
and the NH,O-carbene complex C to either one side.[17,19] Fi-
nally, the NH,O-heterocarbene complexes C are easily N-al-
kylated by NH-deprotonation and reaction with alkyl hal-
ides to give ylidene complexes of type D.[12,20] The cycliza-
tion reaction A!B!C is of general nature and has recently
been employed to generate benzoxazin-2-ylidene complexes
E in which the carbene carbon atom is part of a six-mem-
bered ring.[21] General methods
verted into NH,NH-stabilized carbene ligands in a template
reaction. Here we present the preparation of 2-nitrophenyl
isocyanide, its pentacarbonyl metal complexes, and the re-
duction of the nitro group in the coordinated ligand to give
different carbene complexes depending on the reducing
agent used (Scheme 3).
for the template-controlled
preparation of N-heterocyclic
carbenes from coordinated iso-
cyanides[22] and the the coordi-
nation chemistry and reactivity
of coordinated 2-(trimethylsil-
oxy)phenyl isocyanide have re-
cently been reviewed.[23]
NH,O and NR,O-stabilized
carbene ligands generated as
depicted in Scheme 1 are not
stable when liberated from the
metal center, in contrast to the Scheme 3. Reduction of the nitro group in complexes with the 2-nitrophenyl isocyanide ligand.
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6286

Benzannulated N-Heterocyclic Carbene Ligands
6285 – 6293
Results and Discussion
Coordinated 2-hydroxyphenyl isocyanide (B in Scheme 1)
cyclizes spontaneously to give the NH,O-stabilized carbene
ligand. To generate NH,NH-stabilized carbene ligands it ap-
pears neccessary to generate, at least in situ, the complex
with the freely unknown 2-aminophenyl isocyanide ligand
which is supposed to immediately cyclize by intramolecular
nucleophilic attack of the amine group at the isocyanide
carbon atom. We intended to generate the 2-aminophenyl
isocyanide ligand from coordinated 2-nitrophenyl isocyanide
by reduction of the nitro group of the coordinated ligand.
Synthesis of 2-nitrophenyl isocyanide 2 and of complexes
[M(CO)5(2)] (3: M=Cr; 4: M=Mo; 5: M=W): Ligand 2
was prepared by reaction of commercially available nitro-
aniline with acetyl formate to yield 2-nitrophenyl formamide
1 (Scheme 4). Dehydration of 1 with diphosgene in basic so-
lution[30] gives the isocyanide 2 in about 90% yield.
Figure 1. Molecular structure of 5 (the Cr and Mo derivatives 3 and 4, re-
spectively, are isostructural).
bility of the nitro group com-
pared to the azido group lead-
ing to a slightly stronger W!C
backbonding.
In general, the IR spectro-
scopic data for complexes 3–5
are indicative of only weak
Scheme 4. Preparation of 2-nitrophenyl isocyanide 2.
M!C backbonding. This is cor-
roborated by the virtually un-
Isocyanide 2 is an off-white solid with the typical smell of
phenyl isocyanides. The NꢀC stretching frequency in 2 is ob-
served in the IR spectrum at
changed wavenumber for the NꢀC stretching frequency
upon coordination of 2 (Table 2). Clearly, the isocyanide li-
n˜ =2129 cmꢁ1, slightly lower
Table 1. Selected bond lengths [Š] and angles [8] for complexes 3–5.
than reported for 2-azidophenyl
isocyanide
The resonance of the isocyanide
carbon atom in 13C NMR spec-
(n˜ =2142 cmꢁ1).[28]
3
4
5
ꢁ
M CN
1.953(3)
1.903(4)
1.905(4)–1.910(4)
1.159(4)
1.377(4)
1.466(4)
88.66(13)–90.82(14)
178.18(14)
176.7(3)
171.3(3)
2.090(4)
2.073(5)
ꢁ
M COtrans
2.043(4)
2.038(5)
ꢁ
M COcis
2.045(5)-2.062(5)
1.166(4)
2.036(6)–2.073(5)
1.157(6)
trum appears as
signal[31] at d=173.6 ppm.
Coordination of 2 to photo-
chemically generated
a
broad
ꢁ
C1 N1
ꢁ
N1 C2
1.385(4)
1.382(6)
ꢁ
N2 C3
1.459(5)
1.454(7)
C1-M-COcis
C1-M-COtrans
M-C1-N1
88.21(15)–90.70(15)
88.7(2)–90.9(2)
178.02(15)
176.5(3)
172.8(4)
178.0(2)
177.3(4)
171.6(5)
[M(CO)5(thf)] (M=Cr, Mo, W)
in THF gives the isocyanide
complexes [M(CO)5(2)] (3: M=
Cr; 4: M=Mo; 5: M=W) as
red solids in good yield. Com-
C1-N1-C2
plexes 3–5 are air-stable but light sensitive. The molecular
structures of complexes 3–5 were determined by X-ray dif-
fraction (Figure 1).
gands in 3–5 are activated for a nucleophilic attack at the
isocyanide carbon atom.[23]
Bond lengths and angles in 5 fall in the range observed
for carbonyl tungsten complexes with a phenyl isocyanide
ligand in the trans position to CO (Table 1).[3,26,28,32] The
tungsten atom is coordinated in a slightly distorted octahe-
Reduction of the nitro group in 3–5 with Sn/HCl: Com-
plexes 3–5 react in diethyl ether with tin and aqueous hydro-
chloric acid to give the complexes 6–8 with an NH,NH-sta-
bilized carbene ligand (Scheme 5). We propose the com-
plexes with a 2-aminophenyl isocyanide ligand as an inter-
mediate in this reaction. Intramolecular nucleophilic attack
of the amine group at the isocyanide carbon atom leads to
the NH,NH-carbene ligand. We have obtained complexes 6
and 8 previously by Staudinger reaction followed by hydro-
ꢁ
dral fashion. The CꢀN C group of the isocyanide ligand ex-
hibits an almost linear geometry. It deviates, however, more
from linearity than observed for the pentacarbonyl tungsten
complex with the 2-azidophenyl isocyanide ligand.[28] This
can be attributed to the stronger electron-withdrawing capa-
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F. E. Hahn et al.
FULL PAPER
Table 2. Selected spectroscopic data for 2 and complexes 3–14.
ꢁ
The cleavage of the O SiMe3 bond in M(CO)5 complexes
the 2-(trimethylsiloxy)phenyl isocyanide ligand
[a]
n˜ [cmꢁ1
]
ꢁ
N H
13C NMR[d][b]
trans-CO
of
Compound
ꢁ
O H
ꢁ
M C
CꢀN
cis-CO
(Scheme 1) leads to a mixture of the isocyanide complex B
and the NH,O-carbene complex C.[17] Owing to the en-
hanced nucleophilicity of the amine group in 2-aminophenyl
isocyanide compared with the hydroxy group in 2-hydroxy-
phenyl isocyanide no such equilibrium is observed upon re-
duction of the nitro group in complexes 3–5. However, the
reduction/cyclization reaction of complex 3 to give complex
6 is particularly slow and the transient 2-aminophenyl isocy-
anide complex (1H NMR: d=4.90 ppm NH2; IR: n˜ =
2151 cmꢁ1 for the transient 2-aminophenyl isocyanide com-
plex versus n˜ =2134 cmꢁ1 for 3) can be observed together
with the carbene complex 6 after a reaction time of only 6 h.
After 17 h complete conversion to the NH,NH-carbene
complex 6 has occurred.
2
3
4
5
2129
2134
2133
2134
173.6[c]
183.9
174.0
163.2
200.8
194.1
182.8
198.1
191.7
182.5
182.7
187.7
200.5
215.8
205.6
195.4
222.9
213.1
202.6
223.4
219.3
203.5
202.7
201.2
198.2
213.9
203.1
193.3
219.3
208.3
199.0
219.1
213.3
199.4
199.2
197.6
6[d]
7
3466
3467
3463
3460
3462
3458
3413
8[d]
9
3623
3626
3623
10
11
12
13
14[e]
196.9
[a] Measured as KBr pellets. [b] 50.3 MHz, measured in CDCl3 (for 2–5
and 13) or [D8]THF (for 6–12). [c] Data for the free isocyanide ligand.
[d] The spectroscopic data for 6 and 8 are identical within experimental
error to those reported for identical complexes obtained from 2-azido-
phenyl isocyanide complexes.[28] [e] Data for 14 (Scheme 8, 62.9 MHz,
CDCl3) were taken from reference.[26]
Reduction of the nitro group in 3–5 with hydrazine/Raney
nickel: The reaction of complexes 3–5 in methanol with hy-
drazine hydrate and a small amount of Raney nickel does
not yield the NH,NH-carbene complexes 6–8. Instead com-
plexes 9–11 are obtained. They exhibit the resonance typical
for the carbene-carbon atom (d=182.5–198.1 ppm) in their
13C NMR spectra. Surprisingly, the 13C NMR spectra show
six resonances for the benzene ring instead of the expected
three resonances for a C2-symmetrical carbene ligand. In ad-
dition both an NH and one OH absorption are observed in
the IR spectra (Table 2). Mass spectra showed molecular
weights that were always 16 amu higher than those found
for complexes 6–8. The analytical data strongly indicate that
complexes 9–11 contain an unsymmetrically NH,NOH-sub-
stituted carbene ligand (Scheme 6). All analytical data are
in agreement with the representation of 9–11 in Scheme 6.
The chemical shifts for the carbene carbon atoms in 9–11
Scheme 5. Preparation of carbene complexes 6–8 by reduction of the
nitro group in complexes 3–5.
lysis from complexes with an 2-
azidophenyl isocyanide ligand
(Scheme 2).[28] The method pre-
sented here appears superior,
since the 2-nitrophenyl isocya-
nide is much easier to synthe-
size than 2-azidophenyl isocya-
nide and the reduction is a
simple conversion compared to
the Staudinger reaction.
The carbene complexes 6–8
were characterized by spectros-
copy (Table 2). No absorptions
due to an isocyanide function
could be detected in the IR
Scheme 6. Preparation of carbene complexes 9–11 by reduction of the nitro group in complexes 3–5 with hy-
drazine hydrate/Raney nickel.
spectra. The NH,NH-carbene ligands show the characteristic
compare well to the equivalent parameters in the complexes
with NH,NH-stabilized carbene ligands 6–8 (Table 2). Com-
ꢁ1 [28]
ꢁ
IR absorption for the N H bond around 3465 cm .
In
1
ꢁ
ꢁ
the H NMR spectra the strong deshielding of the N-H pro-
tons is confirmed by their resonance as broadened singlets
around d=12 ppm. The spectroscopic data for 6 and 8 are
identical within experimental error to those reported for the
same compounds obtained from the 2-azidophenyl isocya-
nide complexes (Scheme 2).[28]
plexes 9–11 show one N H and one O H absorption each
in the IR spectrum (Table 2). While the wavenumbers for
ꢁ
the N H absorptions is similar to those for the complexes
ꢁ
with NH,NH-stabilized carbene ligands, the O H absorption
appears at a much higher wavenumber around n˜ =3620 cmꢁ1
(Table 2).
6288
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Benzannulated N-Heterocyclic Carbene Ligands
6285 – 6293
Apparently, the reduction of the nitro groups in com-
plexes 6–8 proceeds via an unstable hydroxylamine deriva-
tive (Scheme 6) that can undergo an intramolecular cycliza-
tion to give the carbene complexes 9–11. This behavior was
not observed upon reduction with the stronger reducing
agent Sn/HCl.
Complexes 12 and 13 were identified spectroscopically by
ꢁ
ꢁ
the lack of absorptions due to O H and N H and groups in
the IR spectra and by the characteristic coupling pattern of
1
the allylic protons in the H NMR spectra. In addition, both
complexes were characterized by X-ray diffraction. The mo-
lecular structure of complex 12 is shown in Figure 2. It con-
firms that indeed the monoalkylated O-allylated species has
formed upon reaction of 11 with one equivalent of base and
one equivalent of allyl bromide.
Bond parameters in 12 are comparable to equivalent pa-
rameters found for W(CO)5 complexes of NR,NR-[26] and
NH,NH-stabilized[28] benzannulated N-heterocyclic carbenes.
The carbene-carbon atom is efficiently stabilized by (p-
p)pN!C donation. The nitrogen atoms of the N-heterocy-
clic ring are almost perfectly planar and the bond lengths
Alkylation of complexes 9–11: Complexes with NH,NH-sta-
bilized carbene ligands such as 6–8 can be deprotonated and
alkylated at the nitrogen atoms.[28] The carbene ligands in
complexes 9–11 contain two functional groups (NH and
OH) that both possess acidic protons and that both can be
alkylated. Previous studies with complexes containing the 4-
hydroxybenzoxazol-2-ylidene ligand have shown, that step-
wise alkylation yields first the N-and then the Oa-lkylation
product.[19,33]
within the five-membered ring fall in
a small range
ꢁ
ꢁ
The tungsten complex 11 reacts with one equivalent of
nBuLi and subsequently with one equivalent of allyl bro-
mide to give exclusively the O-alkylated complex 12. If the
deprotonation/alkylation procedure is repeated, the N,O-di-
alkylated complex 13 is obtained (Scheme 7).
(1.348(4)–1.396(5) Š). The C1 N1 and C1 N2 separations
are almost equidistant indicating that the type of substituent
ꢁ
at the nitrogen atoms is not significant for the N C bond
lengths within the N-heterocyclic ring.
The molecular structure of complex 13 is shown in
Figure 3. Here both the nitrogen atom and the oxygen atom
are substituted with allyl
groups. Equivalent bond pa-
rameters do not differ signifi-
cantly between 12 and 13.
Again both nitrogen atoms are
almost planar (sum of angles
359.68 for N1 and 360.08 for
N2). The N-C-N angle at the
carbine-carbon atom C1 is
almost identical for 12 and 13.
Scheme 7. Stepwise O-and N -alkylation of the carbene ligand in complex 11.
The order of alkylation in 11
and 12 (first O-alkylation,
Figure 2. Molecular structure of complex 12. Selected bond lengths [Š]
Figure 3. Molecular structure of complex 13. Selected bond lengths [Š]
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
and angles [8]: W C1 2.232(4), W COcis 2.036(4)–2.047(4), W COtrans
and angles [8]: W C1 2.242(3), W COcis 2.023(4)–2.047(4), W COtrans
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
1.983(4), N1 C1 1.357(5), N1 C2 1.394(5), N2 C1 1.348(4), N2 C3
2.001(4), N1 C1 1.352(4), N1 C2 1.388(4), N2 C1 1.370(4), N2 C3
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
1.396(5), C2 C3 1.382(5), N1 O1 1.374(4), O1 C8 1.471(5); C-W-Ccis
85.83(15)–91.98(14), C-W-Ctrans 174.31(15)–178.0(2), W-C1-N1 132.0(3),
W-C1-N2 124.7(3), N1-C1-N2 103.3(3), C1-N1-C2 113.0(3), C1-N1-O1
125.4(3), C2-N1-O1 121.1(3), C1-N2-C3 112.9(3), N1-O1-C8 111.3(3).
1.391(4), C2 C3 1.382(5), N1 O1 1.380(3), O1 C8 1.468(4), N2 C11
1.457(4); C-W-Ccis 86.3(2)–93.5(1), C-W-Ctrans 175.0(2)–176.2(2), W-C1-N1
126.3(2), W-C1-N2 130.8(2), N1-C1-N2 102.9(3), C1-N1-C2 114.6(3), C1-
N1-O1 122.8(3), C2-N1-O1 122.4(3), C1-N2-C3 111.3(3), C1-N2-C11
126.2(3), C3-N2-C11 122.5(3), N1-O1-C8 110.3(2).
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F. E. Hahn et al.
FULL PAPER
second N-alkylation) is inverted compared to that for com-
plexes with the 4-hydroxybenzoxazol-2-ylidene ligand. Obvi-
ously, the hydroxy group in the hydroxylamine derivative 11
is more nucleophilic and thus much more easily alkylated
than a hydroxy group bound to the aromatic ring. This be-
havior allows the stepwise alkylation and the preparation of
unsymmetrically substituted NR,NOR-stabilized carbene li-
gands in a template synthesis.
cyanide ligand to give the complex with an NH,NH-stabi-
lized carbene ligand. Such complexes were previously pre-
pared by Staudinger reaction followed by template-control-
led cyclization of 2-azidophenyl isocyanide.[28] The reaction
starting from 2-nitrophenyl isocyanide has the advantage
that this ligand is easily prepared and that the reduction re-
action with Sn/HCl is straightforward compared to the Stau-
dinger reaction of 2-azidophenyl isocyanide. The NH,NH-
stabilized carbene ligand can be alkylated to give the com-
plex with an NR,NR-stabilized carbene, a carbene ligand
that is stable in the free state for certain substituents R.
Pentacarbonyl metal complexes of 2-nitrophenyl isocya-
nide also react with hydrazine hydrate/Raney nickel under
incomplete reduction of the nitro group. After cyclization
complexes with an unsymmetrically substituted NH,NOH-
stabilized carbene ligand are obtained. Such complexes can
be alkylated in a stepwise fashion first under O-alkylation
and then under N-alkylation (Scheme 8).
Conclusion
Previously we have demonstrated that pentacarbonyl metal
complexes with a benzannulated N-heterocyclic carbene
ligand are accessible by substitution of a CO ligand for a
stable N-heterocyclic carbene ligand in hexacarbonyl metal
complexes (preparation of 14 in Scheme 8)[26] or by addition
of the stable carbenes to metal salts.[34] Similar complexes
can be generated by the reaction of N,N’-dialkylbenzimida-
zolium salts with metal salts containing basic anions[35,36] or
in the presence of an external base.[37] Alternatively, the
The template-controlled formation of NH,NH- and
NH,NOH-stabilized carbene ligands allows the preparation
of complexes with carbene ligands that are not stable in the
free state. These ligands can be
alkylated and thus carbene li-
gands that are stable without
coordination to
a transition
metal can be obtained. Even
when the carbene ligand ob-
tained by template synthesis is
not stable in the free state it
can still be transferred to other
metals by ligand transfer reac-
tions.[39] In summary: the tem-
plate reaction described here
gives access to transition-metal
complexes bearing carbene li-
gands that do not exist in the
free state.
Experimental Section
General: All operations were per-
formed in an atmosphere of dry argon
by using Schlenk and vacuum techni-
ques. Solvents were dried by standard
methods and distilled prior to use. 1H
and 13C NMR spectra were recorded
on a Bruker AC 200 (200 MHz) or a
Varian U 600 (600 MHz) spectrometer
and are reported relative to TMS as
internal standard. IR spectra were re-
Scheme 8. Preparation of benzannulated N-heterocyclic carbene ligands by template synthesis.
opening of dibenzotetraazafulvalenes by electrophilic metal
corded on a Bruker Vector 22 FT spectrometer. Mass spectra were taken
on Varian MAT 212 (EI, 70 eV), Varian MAT 8200 (EI, 70 eV) or Quat-
tro LCZ (ESI, 50 eV) instruments. Elemental analyses were obtained
with a Vario EL III Elemental Analyzer at the Institut für Anorganische
und Analytische Chemie, Westfälischen Wilhelms-Universität Münster.
centers yields carbene complexes.[27a,38] All these methods
utilize free or in situ generated benzimidazol-2-ylidenes in a
substitution-type reaction. Here we present a method to
generate the benzannulated N-heterocyclic carbene ligand
at a metal template starting from 2-nitrophenyl isocyanide
ligand (Scheme 8).
Nitrophenyl formamide (1): Sodium formate (19.7 g, 0.29 mol) was dried
at 608C under vacuum for 8 h. After cooling to room temperature it was
suspended in diethyl ether (100 mL) and acetyl chloride (10.3 mL,
0.145 mol) was added. The suspension was stirred for 12 h at ambient
temperature. The resulting acetyl formate was added to nitroaniline
(10.0 g, 72 mmol) and the resulting mixture was stirred for 0.5 h at ambi-
This method involves the reduction of the nitro group in
coordinated 2-nitrophenyl isocyanide with Sn/HCl and the
cyclization of the intermediate, unstable 2-aminophenyl iso-
6290
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 6285 – 6293

Benzannulated N-Heterocyclic Carbene Ligands
6285 – 6293
ent temperature. Removal of the solvent at reduced pressure afforded a
yellow solid, which was washed with acetone and dried in vacuum to give
1 (11.8 g, 98%) as a yellow powder. 1H NMR (CDCl3, 200.1 MHz): d=
10.30 (br s, 1H; NH), 8.79 (d, 1H; Ar-H), 8.58 (s, 1H; NC(O)H), 8.26–
7.27 ppm (m, 3H; Ar-H); 13C{1H} NMR (CDCl3, 50.3 MHz): d=159.5
(CO) 136.0, 133.6, 125.8, 123.9, 122.9 ppm (Ar-C) (only five of the six ex-
pected Ar-C signals could be resolved); IR (KBr pellet): n˜ =3285 (s,
NH), 1684 (vs, CO), 1507 (vs, NO2), 1337 cmꢁ1 (s, NO2); elemental analy-
sis calcd (%) for C7H6N2O3 (166.14): C 50.61, H 3.64, N 16.86; found: C
50.62, H 3.70, N 16.31.
emental analysis calcd (%) for C12H4WN2O7 (472.02): C 30.53, H 0.85, N
5.93; found: C 30.89, H 1.00, N 5.93.
Pentacarbonyl(benzimidazol-2-ylidene)chromium(0) (6): Tin powder
(3.250 g, 27 mmol) was added to a solution of 3 (1.323 g, 3.9 mmol) in di-
ethyl ether (90 mL). The solution was cooled to 08C and aqueous (37%)
HCl (7.6 mL) was added. After the reaction mixture was stirred for 1 h
at 08C and for 16 h at ambient temperature, the yellow solution was fil-
tered. The solvent was removed under reduced pressure, and the yellow
residue was purified by column chromatography on neutral silica gel
(4% H2O) with ethyl acetate/n-hexane (1:4, v/v) as eluent. The light
yellow fraction was collected and the solvents were stipped in vacuo to
2-Nitrophenyl isocyanide (2): A solution of 1 (3.39 g, 20.4 mmol) in
CH2Cl2 (140 mL) was treated with triethylamine (11.0 mL, 78.2 mmol)
and then cooled down to 08C. Diphosgene (2.5 mL, 20.7 mmol) was
added dropwise. The reaction mixture was stirred at 08C for 0.5 h and
then at room temperature for 2 h. The brown solution was poured into a
saturated aqueous potassium carbonate solution (100 mL). The organic
layer was separated, and washed several times with the potassium car-
bonate solution and subsequently with water. The organic phase was
dried over magnesium sulfate and the solvent was removed in vacuo. The
resulting oily product was purified by column chromatography on neutral
Al2O3 (4% H2O) with ethyl acetate/n-hexane (1:4, v/v) as eluent to give
2 (2.70 g, 89%) as a brownish solid. 1H NMR (CDCl3, 200.1 MHz): d=
8.14 (m, 1H; Ar-H), 7.79–7.63 ppm (m, 3H; Ar-H); 13C{1H} NMR
(CDCl3, 50.3 MHz): d=173.6 (br; Ar-C-NC), 144.1 (Ar-C-NC), 136.0,
134.5, 130.3, 129.8, 125.5 ppm (Ar-C); IR (KBr pellet): n˜ =2129 (vs, NC),
1532, 1345 cmꢁ1 (vs, NO2); elemental analysis calcd (%) for C7H4N2O2
(148.12): C 56.76, H 2.72, N 18.91; found: C 56.76, H 2.97, N 18.61.
yield
6
(1.082 g, 89%) as pale yellow powder. 1H NMR ([D8]THF,
200.1 MHz): d=12.07 (s, 2H; NH), 7.38 (m, 2H; Ar-H), 7.20 ppm (m,
2H; Ar-H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d=222.9 (trans-CO),
219.3 (cis-CO), 200.8 (NCN), 135.6 (Ar-C-N), 123.5, 111.1 cmꢁ1 (Ar-C);
IR (KBr pellet): n˜ =3466 (s, NH), 2059 (vs, CO), 1919 (vs, CO),
1889 cmꢁ1 (vs, CO); MS (70 eV, EI): m/z (%): 310 (25) [M]+, 282 (6)
[MꢁCO]+, 254 (8) [Mꢁ2CO]+, 226 (13) [Mꢁ3CO]+, 198 (17)
[Mꢁ4CO]+, 170 (100) [Mꢁ5CO]+; elemental analysis calcd (%) for
C12H6N2CrO5 (310.19): C 46.47, H 1.95, N 9.03; found: C 46.64, H 1.83, N
8.86. The spectroscopic and microanalytical data for 6 are identical
within experimental error to those reported for 6 obtained from the 2-
azidophenyl isocyanide complex.[28]
Pentacarbonyl(benzimidazol-2-ylidene)molybdenum(0) (7): Complex
7
was prepared as described for 6 from 4 (316 mg, 0.8 mmol), tin powder
(685 mg, 5.8 mmol) and aqueous (37%) HCl (1.65 mL) in diethyl ether
(40 mL). Complex 7 was obtained as a pale yellow solid (122 mg, 42%).
1H NMR ([D8]THF, 200.1 MHz): d=11.96 (s, 2H; NH), 7.38 (m, 2H; Ar-
H), 7.18 ppm (m, 2H; Ar-H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d=
213.1 (trans-CO), 208.3 (cis-CO), 194.1 (NCN), 135.5 (Ar-C-N), 124.0,
111.5 ppm (Ar-C); IR (KBr pellet): n˜ =3467 (s, NH), 2066 (vs, CO), 1922
(vs, CO), 1889 (vs, CO).
Pentacarbonyl(2-nitrophenyl isocyanide)chromium(0) (3): A solution of
[Cr(CO)6] (2.03 g, 9.2 mmol) in THF (150 mL) was irradiated for 6 h in a
photoreactor (high-pressure mercury vapour lamp) to give
[Cr(CO)5(thf)]. Isocyanide
2 (1.30 g, 8.8 mmol) dissolved in toluene
(10 mL) was added to the [Cr(CO)5(thf)] solution with a syringe. The re-
sulting orange solution was stirred overnight at ambient temperature.
The solvent was removed under reduced pressure and the dark red resi-
due was purified by column chromatography on neutral Al2O3 (4% H2O)
with dichloromethane/petrol ether (1:3, v/v) as eluent. The deep red frac-
tion was collected and the solvents were removed to yield 3 (1.93 g,
65%) as a red solid. 1H NMR (CDCl3, 200.1 MHz): d=8.19 (d, 1H; Ar-
H), 7.75–7.50 ppm (m, 3H; Ar-H); 13C{1H} NMR (CDCl3, 50.3 MHz): d=
215.8 (trans-CO), 213.9 (cis-CO), 183.9 (br, Ar-C-NC), 144.2 (Ar-C-NC),
134.7, 129.2, 129.1, 126.1 ppm (Ar-C) (only five of the expected six Ar-C
resonances could be resolved); IR (KBr pellet):n˜ =2134 (s, CN), 2046 (vs,
CO), 2000 (sh, CO), 1934 (vs, CO), 1530 (s, NO2), 1332 cmꢁ1 (s, NO2);
MS (70 eV, EI): m/z (%): 340 (54) [M]+, 284 (8) [Mꢁ2CO]+, 256 (19)
[Mꢁ3CO]+, 228 (44) [Mꢁ4CO]+, 200 (42) [Mꢁ5CO]+; elemental analy-
sis calcd (%) for C12H4N2CrO7 (340.17): C 42.37, H 1.19, N 8.24; found:
C 42.33, H 1.47, N 8.16.
Pentacarbonyl(benzimidazol-2-ylidene)tungsten(0) (8): Complex 8 was
prepared as described for
6 from 5 (492 mg, 1 mmol), tin powder
(890 mg, 7.5 mmol) and aqueous (37%) HCl (2.2 mL) in diethyl ether
(45 mL). Complex 8 was obtained as a pale yellow solid (402 mg, 87%).
1H NMR ([D8]THF, 200.1 MHz): d=11.97 (s, 2H; NH), 7.31 (m, 2H; Ar-
H), 7.12 ppm (m, 2H; Ar-H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d=
202.6 (trans-CO), 199.0 (cis-CO), 182.8 (NCN), 135.1 (Ar-C-N), 123.8,
111.3 ppm (Ar-C); IR (KBr pellet): n˜ =3463 (s, NH), 2065 (vs, CO), 1921
(vs, CO), 1895 cmꢁ1 (vs, CO); MS (70 eV, EI): m/z (%): 442 (82) [M]+,
414 (65) [MꢁCO]+, 386 (100) [Mꢁ2CO]+, 358 (92) [Mꢁ3CO]+, 330
(73) [Mꢁ4CO]+, 302 (86) [Mꢁ5CO]+. The spectroscopic data for 8 are
identical within experimental error to those reported for 8 obtained from
the 2-azidophenyl isocyanide complex.[28]
Pentacarbonyl(1-hydroxy-3-hydro-benzimidazol-2-ylidene)chromium(0)
(9): To obtain complex 9 the reduction of the nitro group in 3 was carried
out with hydrazine hydrate instead of tin powder. N2H4·H2O (1.65 mL,
34 mmol) and a small amount of Raney nickel (ca. 15 mg) were added to
a solution of 3 (825 mg, 2.6 mmol) in methanol (50 mL). The mixture was
stirred 0 C for 1 h and then at room temperature for 3 h. The cloudy red
solution was filtered and the solvent was removed under reduced pres-
sure. The dark red residue obtained was purified by column chromatog-
raphy on neutral silica gel (4% H2O) with ethyl acetate/n-hexane (1:4,
v/v) as eluent. The pale yellow fraction was collected and the solvents
Pentacarbonyl(2-nitrophenyl isocyanide)molybdenum(0) (4): Complex 4
was prepared as described for 3 from [Mo(CO)6] (3.06 g, 11.6 mmol) and
2 (1.55 g, 10.5 mmol). Complex 4 was obtained as a red, light-sensitive
powder (2.61 g, 65%). 1H NMR (CDCl3, 200.1 MHz): d=8.18 (d, 1H;
Ar-H), 7.73–7.56 ppm (m, 3H; Ar-H); 13C{1H} NMR (CDCl3, 50.3 MHz):
d=205.6 (trans-CO), 203.1 (cis-CO), 174.0 (br; Ar-C-NC), 144.3 (Ar-C-
NC), 134.7, 129.4, 129.4, 126.1 ppm (Ar-C) (only five of the six expected
Ar-C resonances could be resolved); IR (KBr pellet): n˜ =2133 (s, CN),
2048 (vs, CO), 2005 (sh, CO), 1938 (vs, CO), 1531 (s, NO2), 1335 cmꢁ1 (s,
NO2); MS (70 eV, EI): m/z (%): 384 (33) [M ]+, 356 (20) [MꢁCO]+, 328
(6) [Mꢁ2CO]+, 300 (6) [Mꢁ3CO]+, 272 (11) [Mꢁ4CO]+, 244 (66)
[Mꢁ5CO]+; elemental analysis calcd (%) for C12H4N2MoO7 (384.11): C
37.52, H 1.05, N 7.29; found: C 37.58, H 1.27, N 7.50.
were removed to give
9
as yellow solid (200 mg, 25%). 1H NMR
([D8]THF, 200.1 MHz): d=11.85 (s, 1H; NH), 10.92 (s, 1H; OH), 7.45–
7.34 ppm (m, 4H; Ar-H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d=223.4
(trans-CO), 219.1 (cis-CO), 198.1 (NCN), 133.6 (Ar-C-N), 133.4 (Ar-C-
N), 124.2, 123.6, 111.5, 109.1 ppm (Ar-C); IR (KBr pellet): n˜ =3623 (s,
OH), 3460 (s, NH), 2058 (vs, CO), 1943 (sh, CO), 1888 cmꢁ1 (vs, CO);
MS (70 eV, EI): m/z (%): 326 (22) [M]+, 270 (11) [Mꢁ2CO]+, 242 (13)
[Mꢁ3CO]+, 214 (24) [Mꢁ4CO]+, 186 (100) [Mꢁ5CO]+.
Pentacarbonyl(2-nitrophenyl isocyanide)tungsten(0) (5): Complex 5 was
prepared as described for 3 from [W(CO)6] (2.74 g, 7.8 mmol) and 2
(1.10 g, 7.4 mmol). Complex 5 was obtained as a red, light-sensitive
powder (2.86 g, 82%). 1H NMR (CDCl3, 200.1 MHz): d=8.18 (d, 1H;
Ar-H), 7.82–7.55 ppm (m, 3H; Ar-H); 13C{1H} NMR (CDCl3, 50.3 MHz):
d=195.4 (trans-CO), 193.3 (cis-CO), 163.2, (br; Ar-C-NC), 144.1 (Ar-C-
NC), 134.5, 129.2, 129.2, 125.9 ppm (Ar-C) (only five of the six expected
Ar-C resonances could be resolved); IR (KBr pellet): n˜ =2134 (s, CN),
2044 (vs, CO), 1995 (sh, CO), 1928 (vs, CO), 1530 (s, NO2), 1334 cmꢁ1 (s,
NO2); MS (70 eV, EI): m/z (%): 472 (50) [M]+, 332 (100) [Mꢁ5CO]+; el-
Pentacarbonyl(1-hydroxy-3-hydro-benzimidazol-2-ylidene)
num(0) (10): The complex was obtained as described for the synthesis of
from N2H4·H2O (0.70 mL, 14 mmol), Raney nickel (15 mg) and 4
molybde-
9
(398 mg, 1 mmol) in methanol (50 mL). Complex 10 was isolated as a
1
yellow powder (276 mg, 72%). H NMR ([D8]THF, 200.1 MHz): d=11.79
(s, 1H; NH), 10.88 (s, 1H; OH), 7.49–7.25 ppm (m, 4H; Ar-H); 13C{1H}
NMR ([D8]THF, 50.3 MHz): d=219.3 (trans-CO), 213.3 (cis-CO), 191.7
Chem. Eur. J. 2004, 10, 6285 – 6293
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6291

F. E. Hahn et al.
FULL PAPER
(NCN), 133.6 (Ar-C-N), 133.0 (Ar-C-N), 124.4, 123.8, 111.9, 109.6 ppm
(Ar-C); IR (KBr pellet): n˜ =3626 (s, OH), 3462 (s, NH), 2066 (vs, CO),
1938 (sh, CO), 1888 cmꢁ1 (vs, CO); MS (70 eV, EI): m/z (%): 371 (100)
[MꢁH]+, 343 (30) [MꢁCOꢁH]+, 325 (31) [MꢁCOꢁH2O]+, 314 (31)
[Mꢁ2COꢁH]+, 259 (62) [Mꢁ4COꢁH]+.
Ar-H), 6.26 (m, 1H, O-CH2-CH=CH2), 6.06 (m, 1H, N-CH2-CH=CH2),
5.66 ꢁ5.63 (m, 2H, O-CH2-CH=CH2), 5.35–5.14 (m, 2H, N-CH2-CH=
CH2), 5.20 (m, 2H, N-CH2), 4.87 ppm (m, 2H, O-CH2); 13C NMR
(CDCl3, 150.6 MHz): d=201.2 (trans-CO), 197.6 (cis-CO), 187.7 (NCN),
132.5, 132.0 (Ar-C-N), 130.5, 129.7 (CH2-HC=CH2), 124.1, 123.9 (Ar-C),
122.1 (O-CH2-HC=CH2), 118.4 (N-CH2-HC=CH2), 111.5, 109.3 (Ar-C),
79,0 (O-CH2), 52.6 ppm (N-CH2); IR (KBr pellet): n˜ =2064 (vs, CO),
1965 (vs, CO), 1909 cmꢁ1 (vs, CO); MS (70 eV, EI): m/z (%): 538 (53)
[M]+, 510 (17) [MꢁCO]+, 454 (34) [Mꢁ3CO]+, 426 (52) [Mꢁ4CO]+,
398 (54) [Mꢁ5CO]+; elemental analysis calcd (%) for C18H14N2O6W
(538.17): C 40.17, H 2.62, N 5.21; found: C 40.54, H 2.41, N 5.22.
Pentacarbonyl(1-hydroxy-3-hydro-benzimidazol-2-ylidene)tungsten(0)
(11): Complex 11 was prepared as described for 9 from 5 (1.202 g,
2.5 mmol), N2H4·H2O (1.73 mL, 36 mmol) and Raney nickel (15 mg) in
methanol (50 mL). After column chromatography complex 11 was ob-
tained as
a
pale yellow solid (835 mg, 73%). 1H NMR ([D8]THF,
200.1 MHz): d=11.87 (s, 1H; NH), 10.94 (s, 1H; OH), 7.49–7.25 ppm (m,
4H; Ar-H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d=203.5 (trans-CO),
199.4 (cis-CO), 182.5 (NCN), 134.0 (Ar-C-N), 133.0 (Ar-C-N), 124.4,
123.8, 111.9, 109.6 ppm (Ar-C); IR (KBr pellet): n˜ =3623 (s, OH), 3458
(s, NH), 2065 (vs, CO), 1908 (vs, CO), 1884 cmꢁ1 (vs, CO); MS (50 eV,
ESI): m/z (%): 457 (100) [MꢁH]+, 429 (14) [MꢁCOꢁH]+, 401 (7)
[Mꢁ2COꢁH]+, 347 (17) [Mꢁ3COꢁH]+; elemental analysis calcd (%)
for C12H6N2O6W (458.04): C 31.47, H 1.32, N 6.12; found: C 31.82, H
1.48, N 6.00.
X-ray crystallography: Single crystals suitable for X-ray analysis were ob-
tained by recrystallization from acetone at 08C (3–5) or from ethyl ace-
tate at 08C (12,13). They were mounted on glass fibers using two-compo-
nent glue or mineral oil. X-ray intensities were measured by using a
Bruker AXS Apex system equipped with a rotating anode. All data were
measured with MoKa radiation (l=0.71073 Š). Data reduction was per-
formed with the Bruker SMART[40] program package. For further crystal
and data collection details see Table 3. All crystal structures were solved
by using SHELXS-97[41] by heavy-atom methods and refined with
SHELXL-97[42] using anisotropic thermal parameters for all none hydro-
gen atoms. Hydrogen positions were calculated and thermally fixed to
1.3 Ueqv of the parent atom (exception atom H(2N) in 12 whose position-
al parameters were identified from a difference Fourier map and which
were refined). The C=C portion of one of the allyl groups in 13 is disor-
dered. Ortep-3 for Windows[43] has been used for all plots. CCDC-197035
(3), CCDC-235843 (4), CCDC-197036 (5), CCDC-235844 (12), and
CCDC-235845 (13) contain the supplementary crstallographic data for
this paper. These data can be free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge, CB2 1EZ, UK; fax: (+44)1223-
336033; or deposit@ccdc.ac.uk).
Pentacarbonyl(1-allyloxy-3-hydro-benzimidazol-2-ylidene)tungsten(0)
(12): Complex 11 (416 mg, 0.9 mmol) in THF (20 mL) was deportonated
with nBuLi (0.43 mL of a 2.5m solution in nhexane) at ꢁ788C. After the
reaction mixture had been stirred for 2 h, allyl bromide (0.09 mL,
1.1 mmol) was added at 08C and the solution was stirred overnight. The
solvent was removed under reduced pressure and the oily brownish resi-
due was dissolved in diethyl ether. The insoluble LiBr was separated by
filtration and the soluble fraction was purified by column chromatogra-
phy on neutral Al2O3 (4% H2O) with ethyl acetate/n-hexane (1:16, v(v)
as eluent to yield 12 as a pale yellow solid (402 mg, 89%). 1H NMR
([D8]THF, 200.1 MHz): d=12.22 (s, 1H; NH), 7.37 (m, 4H; Ar-H), 6.23
(m, 1H, CH=CH2), 5.50 (m, 2H, CH=CH2), 4.87 ppm (m, 2H, O-CH2);
13C NMR ([D8]THF, 50.3 MHz): d=202.7 (trans-CO), 199.2 (cis-CO),
182.7 (NCN), 134.0 (Ar-C-N), 131.9 (Ar-C-N), 131.2 (HC=CH2), 125.3
(Ar-C), 124.6 (Ar-C), 122.6 (HC=CH2), 112.6 (Ar-C), 110.3 (Ar-C),
80.3 ppm (O-CH2); IR (KBr pellet): n˜ =3413 (s, NH), 2066 (vs, CO),
1919 (vs, CO), 1879 (vs, CO), 1863 cmꢁ1 (vs, CO); MS (70 eV, EI): m/z
(%): 498 (37) [M]+, 442 (7) [Mꢁ2CO]+, 414 (11) [Mꢁ3CO]+, 386 (8)
[Mꢁ4CO]+, 358 (94) [Mꢁ5CO]+.
Acknowledgement
Pentacarbonyl(1-allyloxy-3-allyl-benzimidazol-2-ylidene)tungsten(0) (13):
The alkylation procedure to prepare 12 from 11 was repeated with the 12
obtained in the previous reaction. Complex 13 was obtained as a yellow
powder (381 mg, 78%). 1H NMR (CDCl3, 600 MHz): d=7.38 (m, 4H;
We thank the Deutsche Forschungsgemeinschaft (IGK 673) and the
NRW International Graduate School of Chemistry in Münster for finan-
cial support.
Table 3. Selected crystal and data collection details for 3–5 and 12–13.
3
4
5
12
13
formula
Mr
C12H4N2CrO7
340.17
C12H4N2MoO7
384.11
C12H4N2O7W
472.02
C15H10N2O6W
498.10
C18H14N2O6W
538.16
a [Š]
b [Š]
c [Š]
a [8]
6.2511(3)
26.5422(12)
8.0857(4)
90.0
6.5466(7)
27.944(3)
7.6700(8)
90.0
6.4755(4)
27.633(2)
7.6282(5)
90.0
6.8366(4)
19.1135(12)
12.1643(7)
90.0
10.5020(10)
9.7299(10)
18.491(2)
90.0
b [8]
g [8]
95.749(2)
90.0
92.409(3)
90.0
92.9130(10)
90.0
99.2400(10)
90.0
94.576(2)
90.0
V [Š3]
T [K]
1calcd [gcmꢁ3
space group
Z
1334.81(11)
153(2)
1.693
P21/c
4
1401.9(3)
153(2)
1.820
P21/c
4
1363.22(15)
123(2)
2.300
P21/c
4
1568.9(2)
173(2)
2.109
P21/c
4
1883.4(3)
173(2)
1.898
P21/c
4
]
m [mmꢁ1
]
0.895
0.972
8.511
7.397
6.170
theta limits [8]
unique data
5.2ꢂ2qꢂ50.0
5.5ꢂ2qꢂ55.1
3.0ꢂ2qꢂ50.0
5.4ꢂ2qꢂ60.0
4.4ꢂ2qꢂ60.1
2329
3212
2386
4557
5475
obs data [I>2s(I)]
R1 (obs) [%]
R2 (all) [%]
2120
2451
2243
4046
4413
5.11, wR1=10.30
5.90, wR2=10.59
1.267
4.70, wR1=9.24
7.16, wR2=9.98
1.066
2.77, wR1=5.11
3.12, wR2=5.20
1.337
3.02, wR1=6.36
3.68, wR2=6.58
1.118
3.15, wR1=5.80
4.67, wR2=6.21
1.015
GOF
no. of variables
res. el. density [eŠ
199
0.368/ꢁ0.221
199
0.779/ꢁ0.296
199
0.883/ꢁ0.605
221
1.677/ꢁ1.413
263
1.343/ꢁ0.930
ꢁ3
]
6292
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 6285 – 6293

Benzannulated N-Heterocyclic Carbene Ligands
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Received: June 8, 2004
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Published online: November 3, 2004
Chem. Eur. J. 2004, 10, 6285 – 6293
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6293