Template synthesis of benzannulated N-heterocyclic carbene ligands

Article abstract of DOI:10.1002/chem.200390079

The reaction of 2-azidophenyl isocyanide (7) with [M(CO)₅(thf)] (M = Cr, W) yields the isocyanide complexes [M(CO)₅(7)] (M = Cr 8, M = W 9). Complexes 8 and 9 react with tertiary phosphines such as triphenylphosphane at the azido fun

Full text of DOI:10.1002/chem.200390079

FULL PAPER
Template Synthesis of Benzannulated N-Heterocyclic Carbene Ligands
F. Ekkehardt Hahn,*[a] Volker Langenhahn,[a] Nicole Meier,[a] Thomas L¸gger,[a] and
Wolf Peter Fehlhammer[b]
Abstract: The reaction of 2-azidophen-
yl isocyanide (7) with [M(CO)5(thf)]
(M ˆ Cr, W) yields the isocyanide com-
plexes [M(CO)5(7)] (M ˆ Cr 8, M ˆ W
9). Complexes 8 and 9 react with tertiary
phosphines such as triphenylphosphane
at the azido function of the isocyanide
ligand to give the 2-triphenylphosphin-
iminophenyl isocyanide complexes 10
(M ˆ Cr) and 11 (M ˆ W). The polar
triphenylphosphiniminophenyl function
in complexes 10 and 11 can be hydro-
lyzed with H2O/HBr to afford triphenyl-
phosphane oxide and the complexes
containing the unstable 2-aminophenyl
isocyanide ligand. This ligand spontane-
ously cyclizes by intramolecular nucleo-
philic attack of the primary amine at the
isocyanide carbon atom to yield the 2,3-
dihydro-1H-benzimidazol-2-ylidene
complexes 12 (M ˆ Cr) and 13 (M ˆ W).
Double deprotonation of the cyclic
NH,NH-carbene ligands in 12 and 13
with KOtBu and reaction with two
equivalents of allyl bromide yields the
N,N'-dialkylated benzannulated N-het-
erocyclic carbene complexes 14 (M ˆ
Cr) and 15 (M ˆ W). The molecular
structures of complexes 9 and 11 15
were confirmed by X-ray diffraction
studies.
Keywords:
chromium
carbene ligands
¥ isocyanide ligands
¥
¥
structure elucidation ¥ tungsten
While the addition of HX to coordinated isocyanides
usually leads to the formation of complexes with acyclic
carbene ligands, the use of functional isocyanides, which
contain both the isocyanide group and the nucleophile in the
same molecule, gives access to complexes with heterocyclic
carbene ligands through an intramolecular 1,2-addition across
Introduction
Nucleophilic attack at the carbon atom of a coordinated
isocyanide is a standard method to generate metal carbene
3]
complexes.[1
Protic nucleophiles such as alcohols and
primary or secondary amines have been particularly useful
in this reaction (Scheme 1). This carbene synthesis was first
discovered, although unintentionally, in 1915 by Tschugajeff
and Skanawy Grigorjewa who treated platinum(ii) tetrakis-
(methyl isocyanide) with hydrazine.[4] The reaction products
were only recognized as carbene complexes 50 years later.[5]
ꢀ
the C N bond. Fehlhammer et al. have introduced readily
available and stable 2-hydroxyalkyl isocyanides such as
ꢀ
C NCH2CH2OH, in which the nucleophile and the isocyanide
group are already linked before coordination to the metal
center. If suitably activated by coordination to transition
metals in high oxidation states, these ligands spontaneously
cyclize to form oxazolidin-2-ylidenes;[6] this even allows the
isolation of homoleptic tetra-[7] and hexacarbene complexes.[8]
In b-functionalized aryl isocyanides, the electrophilic iso-
cyanide and the nucleophilic substituent are not only linked,
but are also suitably oriented in one plane for an intra-
molecular cycloaddition reaction to occur. This geometry
together with the aromaticity of the resulting carbene ligand
could lead to an even greater tendency to form heterocyclic
Scheme 1. Carbene formation by nucleophilic attack on coordinated
isocyanides.
8]
ylidenes. Contrary to aliphatic 2-hydroxyethyl isocyanide,[6
[a] Prof. Dr. F. E. Hahn, Dr. V. Langenhahn,
Dipl.-Chem. N. Meier, Dr. T. L¸gger
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] which is a synthon for 2-hydroxyphenyl
isocyanide (Scheme 2).
Institut f¸r Anorganische und Analytische Chemie
Westf‰lische Wilhelms-Universit‰t M¸nster
Wilhelm-Klemm-Strasse 8, 48149 M¸nster (Germany)
Fax: ( ‡49)251-8333108
E-mail: fehahn@uni-muenster.de
The O-protected 2-(trimethylsiloxy)phenyl isocyanide can
[b] Prof. Dr. W. P. Fehlhammer
Deutsches Museum, Museumsinsel 1
80306 M¸nchen (Germany)
coordinate to transition metals and a series of such complexes
16]
have been prepared.[11 Cleavage of the Si O bond in these
À
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704 712
Scheme 2. Cyclization of 2-hydroxyphenyl isocyanide and synthesis of
2-(trimethylsiloxy)phenyl isocyanide from benzoxazole.
complexes is best achieved by stirring in methanol with a
catalytic amount of KF. Subsequently, complexes containing
the benzoxazol-2-ylidene ligand can form, if the isocyanide is
sufficiently activated (or insufficiently deactivated) towards
intramolecular nucleophilic attack by the hydroxyl group at
the isocyanide carbon atom. Different observations have been
made during the cyclization reaction depending on the nature
of the transition metal complexfragment. [17, 18] Strong M ! L
backbonding stabilizes the hydroxyphenyl isocyanide ligand,
while weak backbonding leads to the formation of the NH,O-
carbene complex(Scheme 3).
Scheme 4. N-Heterocyclic carbenes (top) and proposed template-control-
led cyclization of 2-azidophenyl isocyanide (bottom).
converted at a metal template into 2-aminophenyl isocyanide;
this allows the template-controlled cyclization of coordinated
2-aminophenyl isocyanide to an NH,NH-carbene ligand and
the double N,N'-alkylation of this ligand to give coordinated
carbenes of type D (Scheme 4).
Results and Discussion
Since free 2-aminophenyl isocyanide spontaneously cyclizes
to give benzimidazole, we searched for a synthon that would
allow the in situ generation of 2-aminophenyl isocyanide.
Benzimidazole cannot be opened with nBuLi to yield the 2-N-
lithiated phenyl isocyanide by analogy with the O-lithiation of
benzoxazole (Scheme 2). Thus, the preparation of an N-pro-
tected 2-aminophenyl isocyanide is not possible. However,
2-azidophenyl isocyanide (7) is a suitable synthon for
2-aminophenyl isocyanide. Isocyanide 7 can be activated at
the azido function; thus, reaction of 7 with triphenylphos-
phane leads to nitrogen liberation[25] and formation of an
unstable iminophosphorane which cyclizes with PPh3 migra-
tion to yield a benzimidazole derivative (Scheme 5).[26] We
have explored the reaction of metal-coordinated 7 with
tertiary phosphines with the intention of generating a
coordinated benzimidazol-2-ylidene.
Scheme 3. Template-controlled formation of NH,O-stabilized cyclic car-
bene ligands.
Various methods have been reported to shift the equili-
brium between the 2-hydroxyphenyl isocyanide complex and
the NH,O-carbene complexto either side. [17, 19] Finally, NH,O-
heterocarbene complexes are easily N-alkylated by NH-
deprotonation and reaction with alkyl halides.[12, 20] The
coordination chemistry and reactivity of coordinated 2-(tri-
methylsiloxy)phenyl isocyanide has recently been re-
viewed.[21]
NH,O- and NR,O-stabilized carbene ligands generated
according to Scheme 3 are not stable when liberated from the
metal center in contrast to the known NR,NR-stabilized
carbenes of types A C, [22], and D[23] (Scheme 4). The
benzannulated N,N'-stabilized carbenes of type D have inter-
esting reactivities[24] but their synthesis is difficult and time
consuming.[23] We therefore started a program to study the
preparation of coordinated carbenes of type D in a template
synthesis at suitable metal centers from coordinated b-
functionalized isocyanides based on the template synthesis
for N,O-stabilized carbene ligands presented in Scheme 3.
Our synthesis involves the template-based cyclization of
2-aminophenyl isocyanide to give the complexwith an
NH,NH-carbene ligand. However, 2-aminophenyl isocyanide
is not stable as a free molecule and cyclizes to give
benzimidazole. Here we report a synthon which can be
Synthesis of 2-azidophenyl isocyanide (7): The preparation of
2-azidophenyl isocyanide (7) has been mentioned in the
literature.[27] However, the briefly reported synthesis proved
Scheme 5. Reaction of 2-azidophenyl isocyanide with triphenylphosphane
leading to cyclization.
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705

F. E. Hahn et al.
FULL PAPER
irreproducible in our hands and no
analytical data for 7 were given. We
have therefore developed a synthesis
for 2-azidophenyl isocyanide derived
from the literature procedure as
shown in Scheme 6.
Thus, commercially available an-
thranilic acid (1) was treated with
NaNO2 to yield the diazonium salt 2.
Compound 2 was not isolated but
directly treated with NaN3 to give
2-azidobenzoic acid (3).[28] The acid 3
was converted with ethyl chlorofor-
mate into the mixed anhydride
which reacts with ammonia to give
2-azidobenzoic amide (4). The benz-
amide 4 was subjected to a Hof-
mann degradation[29] leading to the
azidoaniline 5. Reaction of 5 with
commercially available phenyl for-
mate gave N-formyl-2-azidoaniline
(6).[30] Compound 6 forms amido
imido tautomers in solution which
can be detected by NMR spectro-
Scheme 7. Synthesis of the carbene complexes 14 and 15 from the isocyanide complexes 8 and 9.
scopy; tautomer
6 is the major
The molecular structure of complex 9 was determined by
X-ray diffraction (Figure 1). The bond lengths and angles fall
into the range observed for carbonyl tungsten complexes with
phenyl isocyanide ligands in the trans position to CO (Fig-
ure 1).[3, 33] The tungsten atom in 9 is coordinated in a slightly
isomer (80%). 2-Azidophenyl isocyanide is finally obtained
from 6 by a classical Ugi isocyanide synthesis[31] by using
diphosgene and triethylamine for the dehydration. Isocyanide
7 is a low-melting (358C) crystalline solid with the typical bad
smell associated with phenyl isocyanides. It is light sensitive
ꢀ À
ꢀ
distorted octahedral fashion. The C N C group of the
isocyanide ligand has a linear geometry which is indicative
and should be stored in the dark. The N C stretching
frequency was observed in the infrared spectrum at
2142 cmÀ1, a value typical for O-functionalized phenyl iso-
cyanides.[3, 10] The signal for the isocyanide carbon atom
appears, as expected,[32] as a broad singlet at d ˆ 168.8 ppm in
the 13C NMR spectrum.
of weak W! C backbonding. This is corroborated by the
ꢀ
virtually unchanged wavenumber for the N C stretching
frequency upon coordination of 7 (Table 1). Clearly, the
isocyanide ligands in 8 and 9 are activated towards nucleo-
philic attack at the isocyanide carbon atom.[14, 17]
The azido function of the isocyanide ligand in 8 and 9 reacts
with triphenylphosphane in a Staudinger-type[25] reaction with
liberation of dinitrogen to give the complexes with an
iminophosphorane function[34] 10 and 11 (Scheme 7). The
new isocyanide complexes 10 and 11 can be easily identified
Template synthesis of carbene complexes: 2-Azidophenyl
isocyanide (7) reacted like other phenyl or alkyl isocyanides
with photochemically generated [Cr(CO)5(thf)] or
[W(CO)5(thf)] in THF to give the monoisocyanide complexes
[M(CO)5(7)] (M ˆ Cr 8, M ˆ W 9) in good yield (Scheme 7).
Both complexes are air stable and light sensitive.
ꢀ
by the strong IR absorptions caused by the C N stretching
ˆ
mode and by the characteristic IR absorptions for the P N
bond (1348 cmÀ1 for 10;
1350 cmÀ1 for 11). The conver-
sion of the azido function into
an iminophosphorane does not
ꢀ
significantly affect the N C
bond of the isocyanide as
judged by the minimal change
ꢀ
of wavenumber for the N C
stretching mode in the IR spec-
trum (Table 1). As in 9, all W
CO distances in 11 are shorter
than the W CN distance; this
means that CO is a better p
acceptor than phenyl isocya-
nide.
Scheme 6. Synthesis of 2-azidophenyl isocyanide (7).
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N-Heterocyclic Carbene Ligands
704 712
Figure 2. Molecular structure of complex 11 with the crystallographic
numbering scheme. Selected bond lengths [ä] and angles [8]: W C1
Figure 1. Molecular structure of complex 9 with the crystallographic
numbering scheme. Selected bond lengths [ä] and angles [8]: W C1
2.134(5),
W COcis 2.019(6) 2.043(6), W COtrans 2.009(6), C1 N1
1.147(5), N1 C2 1.400(6), C2 C3 1.403(6), C3 N2 1.376(5), N2
P
2.104(4),
W COcis 2.036(5) 2.062(5), W COtrans 2.025(4), C1 N1
1.564(4), P CPh 1.799(4) 1.815(4); C-W-C (cis) 87.0(2) 94.8(2), C-W-C
(trans) 174.7(2) 177.9(2), W-C1-N1 175.3(4), C1-N1-C2 173.6(4), C3-N2-P
129.7(3), N2(CPh)-P-CPh 105.3(2) 116.1(2).
1.161(5), N1 C2 1.383(5), C2 C3 1.382(6), C3 N2 1.412(5), N2 N3
1.242(5), N3 N4 1.130(6); C-W-C (cis) 88.4(2) 92.7(2), C-W-C (trans)
176.6(2) 179.0(2), W-C1-N1 178.9(4), C1-N1-C2 175.6(4), C3-N2-N3
116.0(4), N2-N3-N4 172.6(5).
backbonding present. This assumption is backed by the slight
ꢀ
Table 1. Selected spectroscopic data for 7 and complexes 8 16.
increase of the wavenumber for the C N stretching mode in
10 and 11 compared to 8, 9, and the free ligand 7. The most
remarkable feature in the molecular structure of 11 is the
À1 [a]
ꢀ
Compound
nÄ(C N) [cm
]
13C NMR [d][b]
trans-CO
M
C
cis-CO
ˆ
ˆ
P N2 bond length of 1.565(4) ä. This value is typical for P N
7
8
9
10
11
12
13
14
15
16[c]
2142
2145
2141
2148
2147
168.8
179.1
158.9
167.1
148.7
200.6
182.8
206.2
193.2
196.9
ˆ
bonds and it is in good agreement with P N bond lengths
216.5
196.1
217.8
197.3
222.7
202.5
221.2
200.4
200.5
214.3
193.8
215.1
194.6
219.0
198.9
216.9
197.2
198.2
found in other aromatic-substituted triphenylphosphinimino-
phosphoranes with an sp2-hybridized nitrogen atom.[34] The
angle C3-N2-P of 129.7(3)8 is also consistent with an sp2-
hybridized nitrogen atom.
The 2-phosphiniminophenyl isocyanide ligand in 10 and 11
was hydrolyzed with aqueous methanol containing a catalytic
amount of HBr. This led to elimination of triphenylphosphane
oxide and formation of the 2-aminophenyl isocyanide com-
plex(Scheme 7). As with the corresponding 2-hydroxyphenyl
isocyanide complexes (Scheme 3); this complex is not stable.
The amino group of the coordinated 2-aminophenyl isocya-
nide ligand attacks the isocyanide carbon atom which leads to
the NH,NH-carbene complexes 12 and 13.
[a] Measured in CH2Cl2 solution (7) or as KBr pellets (8 11).
[b] 150.6 MHz for 7, 50.3 MHz for 8 15, 62.9 MHz for 16, measured in
[D6]DMSO (7), CDCl3 (8 11 and 14 16), or [D8]THF (12 13). [c] Data
for this carbene complex(Scheme 8) were taken from ref. [23].
The IR data of complexes 10 and 11 suggest that the
2-phosphiniminophenyl isocyanide ligand shows no tendency
for an intramolecular cyclization by attack of the negatively
polarized iminophosphorane nitrogen atom at the isocyanide
carbon atom. This contrasts the behavior of 2-phosphinimi-
nophenyl isocyanide, which is not stable in the free state but
instead spontaneously cyclizes by an intramolecular nucleo-
philic attack to give a benzimidazole derivative (Scheme 5).
Presently we do not know if the steric demand or electronic
factors (M ! L backbonding) of the W(CO)5 moiety are
responsible for the change in reactivity of coordinated
2-phosphiniminophenyl isocyanide compared with the free
ligand. This inertness towards intramolecular cyclization is
unequivocally demonstrated with the molecular structure of
11 (Figure 2). Complex 11 contains an essentially octahedrally
Carbene complexes 12 and 13 were initially characterized
spectroscopically. No absorptions due to an isocyanide
function could be detected in the IR spectra. The NH,NH-
carbene ligands have characteristic IR absorptions for the
N H bond (3463 cm for 12 and 3461 cmÀ1 for 13).[11, 12, 14
À1
16]
À
1
À
In the H NMR spectra, the strong deshielding of the N H
protons is confirmed by their resonance as broadened singlets
in the range d ˆ 11.9 12.15 ppm. The aromatic protons of the
2,3-dihydro-1H-benzimidazol-2-ylidene ligand in 12 and 13
give two multiplets in the range d ˆ 7.0 7.5 ppm. This is in
agreement with a system comprising an aromatic ring with
two identical substituents in the 1,2-positions.
Complexes 12 and 13 were crystallized and their molecular
structures were determined by X-ray diffraction (Figure 3).
The crystal structure analyses confirmed that 12 and 13
À
coordinated tungsten atom. The W CN bond is slightly
elongated and the C N bond is slightly shorter than in the
2-azidophenyl isocyanide complex 9. This indicates that the
isocyanide ligand in 11 is more electron-rich than the one in 9
and that it acts exclusively as a s donor with no W! C N
ꢀ
À
contain NH,NH-heterocyclic carbene ligands. The W C1
bond length in 13 is significantly longer than the W CN
distance in the isocyanide complexes 9 and 11. In the series
of formal CII ligands, CO is the strongest p acceptor
ꢀ
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F. E. Hahn et al.
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An important property of the carbene complexes 12 and 13
is their insolubility in solvents such as dichloromethane or
chloroform. However, they dissolve well in polar solvents
containing oxygen donor groups like diethyl ether or THF;
this is apparently caused by the ability of the NH protons to
form hydrogen bridges to oxygen atoms of the solvent.
The acidity of the NH protons in 12 and 13 facilitates the
generation of N-alkyl-substituted derivatives. In a typical
reaction, 12 or 13 were treated with KOtBu in DMF. The
resulting monodeprotonated intermediate was quenched with
allyl bromide and the deprotonation/quenching sequence was
repeated for a second time without isolation of the mono-
allylated product. The complexes with the dialkylated carbene
ligand 14 and 15 could be isolated in good yield. Complexes
with N-allylated carbene ligands are useful starting materials
for the preparation of carbene/olefin complexes, and the
substitution of a CO ligand by a carbene-bound allyl group
has been demonstrated with a W(CO)5 complexand an
N(allyl),O-carbene ligand.[20]
Figure 3. Molecular structure of complexes 12 (left) and 13 (right) with the
crystallographic numbering scheme. Starred atoms represent symmetry
equivalent positions. Complex 12 resides on a crystallographic mirror plane
and is bisected by a twofold axis along the Cr C1 vector. Complex 13 is
bisected by a twofold axis along the W C1 vector. Selected bond lengths
[ä] and angles [8] for 12 [13]: M C1 2.075(4) [2.203(4)], M COcis 1.887(3)
Complexes 14 and 15 were identified spectroscopically by
the lack of absorptions due to NH groups in the IR spectra
and by the characteristic coupling pattern of the allylic
protons in the 1H NMR spectra. In addition, both complexes
were characterized by X-ray diffraction (Figure 4).
[2.022(4) 2.029(4)],
M COtrans 1.853(5) [1.995(6)], C1 N1 1.343(4)
[1.356(4)], N1 C2 1.389(5) [1.376(4)], C2 C2* 1.336(7) [1.385(6)];
C-M-C (cis) 89.3(2) 90.7(2) [88.7(1) 90.3(1)], C-M-C (trans) 179.5(2)
180.0(1) [177.4(2) 180.0(1)], M-C1-N1 128.3(2) [128.6(2)], N1-C1-N1*
103.3(4) [102.8(4)], C1-N1-C2 112.2(3) [113.1(3)].
À ꢀ
followed by R N C, and the N-heterocyclic carbene is the
weakest one. This order of p-acceptor capability has been
demonstrated previously with tungsten complexes containing
CO, isocyanides, and carbene ligands.[35] On the other hand,
the NH,NH-carbene ligand is a better s donor than the
isocyanide. In 12 and 13 this causes a significant shortening of
the M CO distance for the trans-CO ligand compared with
the cis-CO ligands. In the isocyanide complexes 9 and 11 the
M
CO distances of the cis and trans carbonyls are identical
within experimental error.
In 13 the W C1 bond length is longer than in the related
complexwith an NH,O-stabilized heterocyclic annulated
carbene ligand (2.185(10) ä, Scheme 3).[12] Owing to the
higher electronegativity of oxygen, the carbene carbon atom
of the latter ligand is not as efficiently stabilized by pp pp
N ! C interactions as the NH,NH-carbene ligand in 13. On
the other hand, the efficient pp pp donation of the nitrogen
atoms in the carbene ligand of 13 prevents any significant
backdonation from the metal center to the carbene carbon
atom. This electronic situation manifests itself in the 13C NMR
spectra, in which the C2 resonance for the coordinated NH,O-
carbene ligand (d ˆ 211.6 ppm) is shifted to lower field by
about 30 ppm relative to the C2 resonance for 13 (d ˆ
182.8 ppm).[36]
Figure 4. Molecular structure of complexes 14 (left) and 15 (right) with the
crystallographic numbering scheme. Selected bond lengths [ä] and angles
[8] for 14 [15]: M C1 2.135(2) [2.256(3)], M COcis 1.880(2) 1.918(2)
[2.017(3) 2.061(3)],
M COtrans 1.856(2) [2.002(3)], C1 N1 1.372(3)
[1.375(4)], C1 N2 1.365(3) [1.372(3)], N1 C2 1.387(3) [1.390(4)], N2
C3 1.386(3) [1.384(4)], C2 C3 1.376(3) [1.388(4)], N1 C8 1.460(3)
[1.458(4)], N2 C11 1.459(3) [1.456(4)]; C-M-C (cis) 86.85(10) 95.15(9)
[87.01(13) 94.75(13)], C-M-C (trans) 174.79(9) 178.87(9) [174.99(11)
179.37(11)], M-C1-N1 128.26(14) [128.8(2)], M-C1-N2 127.76(14)
[127.1(2)], N1-C1-N2 103.9(2) [104.0(2)], C1-N1-C2 111.50(2) [111.7(2)],
C1-N1-C8 127.6(2) [126.9(2)], C2-N1-C8 120.8(2) [121.3(2)], C1-N2-C3
112.0(2) [111.8(2)], C1-N2-C11 127.3(2) [126.8(3)], C3-N2-C11 120.6(2)
[121.4(2)].
The intramolecular cyclization of 2-hydroxyphenyl isocya-
nide at the W(CO)5 complexfragment leads to a mixture of
The carbene carbon atoms in both complexes are stabilized
by strong pp pp N ! C interactions from the essentially
planar ring nitrogen atoms (sum of angles at N for both 14 and
15 is 359.98). The NR,NR-carbene ligands are even stronger s
donors than the carbene ligands in 12 and 13. This leads to a
further elongation of the M C1 bond length (2.135(2) ä for
14, 2.256(3) ä for 15) compared with the complexes with the
NH,NH-carbene ligands in 12 and 13. In addition, the
the isocyanide complex(15%) and the NH,O-carbene com-
[17]
plex(85%).
Due to the enhanced nucleophilicity of the
amino group in 2-aminophenyl isocyanide compared with the
hydroxyl group in 2-hydroxyphenyl isocyanide, no equilibri-
um between the isocyanide complexand the NH,NH-carbene
complexwas observed by NMR spectroscopy during the
hydrolysis and cyclization of complexes 10 and 11.[17, 19]
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N-Heterocyclic Carbene Ligands
704 712
13C NMR spectra of complexes 14 and 15 have the largest Dd
differences between the trans- and cis-CO resonances of all
complexes reported here.
2-azidophenyl isocyanide at RuII[41] and of polycarbene
ligands by bridging alkylation of the carbene ligands in
poly(NH,NH-carbene) complexes. While it is known that free
benzannulated N-heterocyclic carbenes exhibit different
properties to ™Arduengo-type∫ N-heterocyclic carbenes (A
in Scheme 4),[23, 24] the pentacarbonyl tungsten complexof a
typical ™Arduengo-carbene∫[40] exhibits structural parameters
which are quite similar to 15 and 16.
The W C1 distance in 15 compares well with the equi-
valent distance in a reported tungsten complexwith a
benzannulated NR,NR-heterocyclic carbene ligand (2.229(7)
and 2.216(7) ä.[37] The W C1 distance in 15 is shorter than
the equivalent distance in complex 16 (2.27(1) and 2.29(1) ä)
which also contains a benzannulated NR,NR-carbene ligand
(Scheme 8).[23] However, the carbene ligand in complex 16 is
N,N'-substituted with sterically very demanding substituents
which even force the metal out of the plane of the carbene
ligand.
Experimental Section
General: All operations were performed in an atmosphere of dry argon by
using Schlenk and vacuum techniques. Solvents were dried by standard
methods and distilled prior to use. NMR spectra were recorded on a Bruker
AC 200 (200 MHz) or a Varian U 600 spectrometer (600 MHz) and are
reported relative to TMS as internal standard. IR spectra were recorded on
À
The C N bond lengths within the carbene ring in 14 and 15
fall in a narrow range (1.365(3) 1.390(4) ä) and are indica-
tive of pp pp N ! C interactions between the nitrogen and
À
carbon atoms. As expected, these C N bonds are significantly
a
Bruker Vector 22 or on a Beckman IR 12 double-beam infrared
À
shorter than the N CH2 bonds (range 1.456(4) 1.460(3) ä).
spectrometer. Mass spectra (EI, 70 eV and 80 eV) were recorded on
Finnigan MAT 711 or Varian MAT 212 instruments. Elemental analyses
(C,H,N) were performed on a Heraeus CHN-Rapid elemental analyzer or
a Vario EL III elemental analyzer.
À À
The N C N bond angles at the carbene carbon atom are
almost identical in both complexes (103.9(2)8 and 104.0(2)8)
and are typical for benzimidazol-2-ylidene complexes.
2-Azidobenzoic acid (3): A suspension of anthranilic acid (1) (100 g,
0.73 mol) in water (500 mL) and concentrated hydrochloric acid (185 mL)
was cooled to À58C, and a solution of sodium nitrite (52.6 g, 760 mmol)
dissolved in water (150 mL) was added dropwise. The resulting solution
was stirred for 30 min at À58C. The diazonium salt 2 was not isolated, but
the reaction mixture was poured into a mixture of sodium azide (53 g,
820 mmol) dissolved in water (150 mL) and ice (1000 g). A pale yellow
precipitate formed immediately. The reaction mixture was set aside
overnight. By then, the development of nitrogen had ceased. A pale
yellow precipitate was isolated by filtration. The precipitate was washed
with water and dried in vacuo to afford compound 3 (117 g, 98%). 1H NMR
([D6]DMSO, 600 MHz): d ˆ 13.12 (s, 1H; OH), 7.76 7.24 (m, 4H; Ar-H);
13C{1H} NMR ([D6]DMSO, 150.6 MHz): d ˆ 166.4 (CO), 138.7, 133.1, 131.1,
124.9, 124.0, 120.8 (Ar-C); IR (KBr pellet): nÄ ˆ 3000 2500 (m, OH), 2128,
Conclusion
Previously we have demonstrated that pentacarbonyl metal
complexes with a benzannulated N-heterocyclic carbene
ligand are accessible by substitution of a CO ligand in
hexacarbonyl metal complexes (preparation of 16 in
Scheme 8).[23] Similar complexes can be generated by the
reaction of N,N'-dialkylbenzimidazolium salts with metal salts
39]
containing basic anions[37 or by the opening of dibenzote-
2107, 2083 (vs, N3), 1692 (s, C O) cmÀ1; MS (80 eV, EI): m/z (%): 163 (74)
traazafulvalenes by electrophilic metal centers.[24a] All these
methods utilize free or in situ generated benzimidazol-2-
ylidenes in a substitution-type reaction. Here, we present for
the first time a method to generate the benzannulated
N-heterocyclic carbene ligand at a template metal starting
from a b-functionalized phenyl isocyanide ligand (preparation
of 15 in Scheme 8).
ˆ
‡
‡
‡
[M] , 135 (100) [M À N2] , 119 (72) [M À CO2] ; elemental analysis calcd
(%) for C7H5N3O2 (163.13): C 51.54, H 3.09, N 25.76; found: C 51.36, H
2.90, N 25.71.
2-Azidobenzoic amide (4): A three-necked flask equipped with a mechan-
ical stirrer, thermometer, and dropping funnel was charged with 3 (117 g,
0.72 mol), dichloromethane (1000 mL), and triethylamine (105 mL,
830 mmol). The resulting suspension was cooled to À158C and ethyl
chloroformate (72 mL, 0.75 mol) was added dropwise; the temperature
must not exceed 08C during the addition. A precipitate of triethylammo-
nium chloride formed during the addition. After completion of the
addition, the reaction mixture was stirred for 1 h at 08C. Subsequently, the
reaction mixture was cooled to À358C and gaseous ammonia was added for
about 40 min. The resulting pale yellow suspension was stirred overnight.
Removal of the solvent afforded a solid, which was washed with water
(400 mL) and dried in vacuo to give 4 (113 g, 97%) as pale yellow needles.
1H NMR ([D6]DMSO, 600 MHz): d ˆ 8.38 7.70 (m, 4H; Ar-H), 7.51 (brs,
2H; NH2); 13C{1H} NMR ([D6]DMSO, 150.6 MHz): d ˆ 176.6 (CO), 148.0,
142.7, 141.8, 137.0, 135.3, 129.7 (Ar-C);
This new method offers several advantages. It gives access
to complexes with the NH,NH-heterocyclic carbenes, a ligand
type which is not stable in the free state. The NH,NH-carbene
ligand can be alkylated stepwise to give access to unsym-
metrically N,N'-substituted carbene ligands. The generation of
a benzannulated N-heterocyclic carbene ligand from a
coordinated 2-azidophenyl isocyanide might allow the gen-
eration of new Grubbs-type catalysts by cyclization of
IR (KBr pellet): nÄ ˆ 3375, 3163 (m,
NH), 2131, 2101 (vs, N3), 1654
(C O) cmÀ1; elemental analysis calcd
ˆ
(%) for C7H6N4O (162.15): C 51.85, H
3.73, N 34.55; found: C 51.61, H 3.41, N
34.57.
2-Azidoaniline (5): Freshly prepared
aqueous NaOCl (1.0 L, 1.1m) was
added to a suspension of 4 (113 g,
0.70 mol) in an aqueous NaOH solu-
tion (200 mL, 10%) at 08C. The re-
Scheme 8. Synthesis of complexes with benzannulated N-heterocyclic carbene ligands by substitution (right) and
by template-controlled generation of a carbene ligand (left).
action mixture was stirred for 6 h
during which the temperature was
Chem. Eur. J. 2003, 9, No. 3
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709

F. E. Hahn et al.
FULL PAPER
kept below 208C. The resulting dark brown solution was stirred overnight
at room temperature. The reaction mixture was then filtered to remove
unreacted 4. Compound 5 was precipitated from the filtrate by addition of a
saturated aqueous solution of ammonium chloride (100 mL) and isolated
by filtration. Purification was achieved by redissolving in diethyl
ether together with activated charcoal. A brown solution was isolated
Pentacarbonyl(2-triphenylphosphiniminophenyl isocyanide)chromium(0)
(10): Triphenylphosphane (1060 mg, 4.04 mmol) in THF (10 mL) was
added to a solution of 8 (1341 mg, 4 mmol) in THF (200 mL). The yellowish
solution was stirred for 6 h at ambient temperature until the evolution of
dinitrogen ceased. The solvent was stripped in vacuo and the resulting dark
yellow residue was purified by column chromatography (neutral Al2O3,
4% H2O) with diethyl ether/nhexane (1:1) as eluent. The second pale
yellow fraction was collected and the solvent mixture was removed in
vacuo. Recrystallization of the remaining residue (diethyl ether/nhexane
2:1) at À208C yielded 10 (1825 mg, 80%) as pale yellow, air-stable crystals.
1H NMR (CDCl3, 200.1 MHz): d ˆ 7.65 6.36 (m, 19H; Ar-H); 13C{1H}
NMR (CDCl3, 50.3 MHz): d ˆ 217.8 (trans-CO), 215.1 (cis-CO), 167.1
after filtration. Removal of the diethyl ether solvent yielded
5
(48.6 g, 52%) as brownish microcrystals. 1H NMR ([D6]DMSO,
600 MHz): d ˆ 7.47 7.14 (m, 4H; Ar-H), 5.02 (brs, 2H; NH2); 13C{1H}
NMR ([D6]DMSO, 150.6 MHz): d ˆ 150.3, 136.2, 134.5, 128.8, 128.1, 125.9
(Ar-C); IR (KBr pellet): nÄ ˆ 3387, 3295, 3188 (m, NH), 2129 (vs, N3), 2080
(m, N3) cmÀ1. Compound 5 was fully characterized by NMR and IR
spectroscopy.
À À ˆ
À À
(CNR), 148.4 (Ar C N P), 132.5, 132.3, 132.0 (P Ar C), 130.8
À
À
À À
(CN Ar C), 129.0, 128.8, 128.5 (P Ar C), 127.2, 121,8, 121.6, 116.6
N-Formyl-2-azidoaniline (6): Azide 5 (6.5 g, 0.05 mol) was dissolved in
diethyl ether (100 mL) and cooled to 08C. Phenyl formate (7.14 mL,
0.065 mol) was then added dropwise at this temperature. The solution was
then stirred at room temperature overnight. The solvent and phenol
formed were removed in vacuo. The crude oily product was purified by
recrystallization from dichloromethane/methanol (3:1) to give 6 (5.97 g,
76%) as brownish crystals. 1H NMR ([D6]DMSO, 600 MHz): d ˆ 9.67 (s,
(CN Ar C); 31P{1H} NMR (CDCl3, 81 MHz): d ˆ 8.02 (s); IR (KBr
À
À
pellet): nÄ ˆ 2148 (s, CN), 2059, 1990, 1937 (vs, CO), 1348 (s, P N) cmÀ1; MS
ˆ
‡
‡
(80 eV, EI): m/z (%): 570 (3) [M] , 514 (5) [M À 2CO] , 486 (2) [M À
‡
‡
‡
3CO] , 458 (16) [M À 4CO] , 430 (100) [M À 5CO] ; elemental analysis
calcd (%) for C30H19N2CrO5P (570.31): C 63.15, H 3.33, N 4.91; found: C
62.78, H 3.60, N 4.84.
Pentacarbonyl(2-triphenylphosphiniminophenyl
isocyanide)tungsten(0)
ˆ
1H; NH, major tautomer 80%), 8.48 (s, 1H; N CH(OH), minor
(11): Complex 11 was prepared as described for 10 from 9 (1872 mg,
4 mmol) and triphenylphosphane (1060 mg, 4.04 mmol). Compound 11
(2100 mg, 75%) was obtained as yellow, air-stable crystals. 1H NMR
(CDCl3, 200.1 MHz): d ˆ 7.85 6.51 (m, 19H; Ar-H); 13C{1H} NMR
(CDCl3, 50.3 MHz): d ˆ 197.3 (trans-CO), 194.6 (cis-CO), 148.7 (CNR
tautomer), 8.30 (d, 1H; C(O)H, major tautomer), 8.10 7.13 (m, 4H; Ar-
H, both tautomers), 3.41 (brs; N C OH, minor tautomer); 13C{1H} NMR
ˆ À
ˆ À
À ˆ
([D6]DMSO, 150.6 MHz): d ˆ 168.7 (N C OH), 165.3 (N C O), 134.0,
133.9, 130.4, 130.1, 127.2, 124.2 (Ar-C); IR (KBr pellet): nÄ ˆ 3000 2500
(brm, NH and OH), 2107 (vs, N3), 1692 (s, C O) cmÀ1; elemental analysis
ˆ
À À ˆ
À
À
À
À
and Ar C N P), 132.5, 132.4, 132.1 (P Ar C), 130.7 (CN Ar C), 129.3,
calcd (%) for C7H6N4O (162.15): C 51.85, H 3.73, N 34.55; found: C 51.73, H
3.47, N 34.34.
128.9, 128.6 (P Ar C), 127.4, 121,9, 121.7, 116.8 (CN Ar C); 31P{1H} NMR
(CDCl3, 81 MHz): d ˆ 5.09 (s); IR (KBr pellet): nÄ ˆ 2147 (s, CN), 2065,
À
À
À
À
1993, 1942 (vs, CO), 1350 (s, P N) cmÀ1; MS (80 eV, EI): m/z (%): 702 (5)
2-Azidophenyl isocyanide (7): Compound 6 (3.0 g, 18.5 mmol) and triethyl-
amine (10.3 mL, 74 mmol) were dissolved in dichloromethane (50 mL).
The solution was cooled to 08C and diphosgene (1.2 mL, 10 mmol) was
added dropwise with a syringe. The reaction mixture was stirred for 1 h at
08C and then at ambient temperature overnight. The brown solution was
then poured into a saturated aqueous potassium carbonate solution
(100 mL) and the mixture was stirred for 30 min. The organic layer was
separated, washed several times with water, and dried over sodium sulfate.
Removal of the solvent gave 7 as a brown oil. This was purified by
chromatography on neutral Al2O3 (4% H2O) with diethyl ether as the
eluent to give 7 (2.0 g, 74.9%) as brownish crystals. Isocyanide 7 should be
ˆ
‡
‡
‡
‡
[M] , 646 (7) [M À 2CO] , 618 (3) [M À 3CO] , 590 (10) [M À 4CO] , 562
‡
(64) [M À 5CO] ; elemental analysis calcd (%) for C30H19N2O5PW
(702.16): C 51.31, H 2.70, N 3.98; found: C 51.74, H 3.01, N 4.08.
Pentacarbonyl(2,3-dihydro-1H-benzimidazol-2-ylidene)chromium(0) (12):
Aqueous HBr (0.1 mL, 47%) was added to a solution of 10 (1140 mg,
2 mmol) in a mixture of methanol (10 mL) and water (1 mL). After stirring
the reaction mixture for 24 h, a saturated aqueous NaHCO3 solution
(1 mL) was added. The solvents were stripped in vacuo. The remaining
residue was suspended several times in water (25 mL) to remove the
inorganic salts. The organic residue was filtered, dissolved in diethyl ether
(20 mL), and dried over Na2SO4. The salt was removed by filtration and the
filtrate was evaporated to dryness. Complex 12 was purified by column
chromatography (silica gel 60, 4% H2O) with diethyl ether/methanol (25:1)
as the eluent. Removal of the solvent yielded 12 as an off-white solid.
Recrystallization from diethyl ether/nhexane (1:1) at À208C yielded 12
(527 mg, 85%) as pale yellow, air-stable crystals. 1H NMR ([D8]THF,
200.1 MHz): d ˆ 11.90 (s, 2H; NH), 7.21 (m, 2H; Ar-H), 7.02 (m, 2H; Ar-
H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d ˆ 222.7 (trans-CO), 219.0 (cis-
CO), 200.6 (NCN), 135.3, 123.7, 110.8 (Ar-C); IR (KBr pellet): nÄ ˆ 3463 (m,
1
stored in the dark at low temperature. M.p. 358C; H NMR ([D6]DMSO,
600 MHz): d ˆ 7.58 (dd, 1H; H-6), 7.53 (dt, 1H; H-4), 7.46 (dd, 1H; H-3)
7.24 (dt, 1H; H-5); 13C{1H} NMR ([D6]DMSO, 150.6 MHz): d ˆ 168.8 (br,
ꢀ
À
N C), 136.1 (C N3), 131.0 (C-4), 127.9 (C-6), 125.5 (C-5), 120.1 (C-3), 116.6
(C-1); IR (CH2Cl2 solution): nÄ ˆ 2142 (s, C N), 2121, (s, N3) cmÀ1. Due to
ꢀ
the light sensitivity of 7, no elemental analysis was performed.
Pentacarbonyl(2-azidophenyl isocyanide)chromium(0) (8): A solution of
[Cr(CO)6] (880 mg, 4 mmol) in THF (300 mL) was irradiated for 8 h in a
photoreactor (high-pressure mercury vapor lamp). A solution of 7 (560 mg,
3.9 mmol) in toluene (4 mL) was added with a syringe to the resulting
orange solution and this then stirred overnight with the exclusion of light.
The solvent was removed in vacuo, and the resulting dark yellow residue
was purified by column chromatography (neutral Al2O3, 4% H2O) with
dichloromethane as eluent. The second pale yellow fraction was collected
and the solvent was removed. Recrystallization of the yellow residue
(diethyl ether/nhexane 2:1) at À208C yielded 8 (0.865 mg, 65%) as yellow,
light-sensitive crystals. 1H NMR (CDCl3, 200.1 MHz): d ˆ 7.52 7.12 (m,
4H; Ar-H); 13C{1H} NMR (CDCl3, 50.3 MHz): d ˆ 216.5 (trans-CO), 214.3
(cis-CO), 179.1 (CNR), 137.4, 129.8, 129.5, 126.9, 125.2, 119.4 (Ar-C); IR
‡
NH), 2058, 1951 (vs, CO) cmÀ1; MS (80 eV, EI): m/z (%): 310 (10) [M] , 282
‡
‡
‡
(3) [M À CO] , 254 (5) [M À 2CO] , 226 (5) [M À 3CO] , 198 (12) [M À
‡
‡
4CO] , 170 (100) [M À 5CO] ; elemental analysis calcd (%) for
C12H6N2CrO5 (310.14): C 46.47, H 1.94, N 9.03; found: C 46.85, H 2.12, N
9.16.
Pentacarbonyl(2,3-dihydro-1H-benzimidazol-2-ylidene)tungsten(0) (13):
Complex 13 was prepared as described for 12 from 11 (1404 mg, 2 mmol).
Complex 13 (689 mg, 78%) was obtained as yellow, air-stable crystals.
1H NMR ([D8]THF, 200.1 MHz): d ˆ 12.15 (s, 2H; NH), 7.45 (m, 2H; Ar-
H), 7.20 (m, 2H; Ar-H); 13C{1H} NMR ([D8]THF, 50.3 MHz): d ˆ 202.5
(trans-CO), 198.9 (cis-CO), 182.8 (NCN), 135.1, 121.6, 111.2 (Ar-C); IR
(KBr pellet): nÄ ˆ 3461 (m, NH), 2064, 1869 (vs, CO) cmÀ1; MS (80 eV, EI):
(CH2Cl2 solution): nÄ ˆ 2145 (s, CN), 2126 (s, N3), 2054, 1958 (vs, CO) cmÀ1
;
elemental analysis calcd (%) for C12H4N4CrO5 (335.18): C 42.87, H 1.20, N
16.67; found: C 42.90, H 1.30, N 17.24.
‡
‡
‡
m/z (%): 442 (71) [M] , 414 (11) [M À CO] , 386 (6) [M À 2CO] , 358 (18)
‡
‡
‡
[M À 3CO] , 330 (27) [M À 4CO] , 302 (100) [M À 5CO] ; elemental
analysis calcd (%) for C12H6N2O5W (441.99): C 32.60, H 1.35, N 6.33;
found: C 32.69, H 1.78, N 6.42.
Pentacarbonyl(2-azidophenyl isocyanide)tungsten(0) (9): Complex 9 was
prepared as described for 8 from [W(CO)6] (1410 mg, 4 mmol) and 7
(560 mg, 3.9 mmol). Complex 9 (1179 mg, 63%) was obtained as yellow,
light-sensitive crystals. 1H NMR (CDCl3, 200.1 MHz): d ˆ 7.47 7.14 (m,
4H, Ar-H); 13C{1H} NMR (CDCl3, 50.3 MHz): d ˆ 196.1 (trans-CO), 193.8
(cis-CO), 158.9 (CNR), 137.6, 130.1, 127.2, 125.2, 119.3, 118.9 (Ar-C); IR
Pentacarbonyl(1,3-bisallylbenzimidazol-2-ylidene)chromium (14): Potassi-
um tert-butanolate (245 mg, 2.2 mmol) was added to a solution of 12
(620 mg, 2 mmol) in DMF (10 mL) and at À208C. After stirring for 4 h at
room temperature, allyl bromide (1.8 mL, 2.1 mmol) was added and the
solution was stirred overnight. This procedure was repeated as described
above to achieve the second alkylation. The solvent was stripped in vacuo,
(CH2Cl2 solution): nÄ ˆ 2141 (s, CN), 2122 (s, N3), 2056, 1953 (vs, CO) cmÀ1
;
elemental analysis calcd (%) for C12H4N4O5W (468.03): C 30.79, H 0.86, N
11.97; found: C 30.81, H 0.85, N 11.92.
710
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0903-0710 $ 20.00+.50/0
Chem. Eur. J. 2003, 9, No. 3

N-Heterocyclic Carbene Ligands
704 712
and the oily brownish residue was dissolved in diethyl ether. The inorganic
salt was filtered off, and column chromatography (neutral Al2O3, 4% H2O)
with nhexane/CH2Cl2 (10:1) as eluent gave complex 14 (507 mg, 65%) as a
pale yellow solid. Recrystallization from nhexane/diethyl ether (3:1) at
À208C afforded yellow, air-stable crystals of 14. 1H NMR (CDCl3,
crystallographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (‡44)1223-336033; or deposit@ccdc.cam.uk).
3
200.1 MHz): d ˆ 7.27 7.11 (m, 4H; Ar-H), 6.0 (ddt, J ˆ 16, 10, 4 Hz, 2H;
CH2 CH CH2), 5.32 5.29 (m, 4H; CH CH2), 5.02 (d, 3J ˆ 4 Hz, 4H;
À
ˆ
ˆ
N CH2); 13C{1H} NMR (CDCl3, 50.3 MHz): d ˆ 221.2 (trans-CO), 216.9
À
Acknowledgement
À
ˆ
(cis-CO), 206.2 (NCN), 135.2 (Ar-C), 132.3 (CH2 CH CH2), 122.9
À
À
ˆ
À
(Ar C), 117.9 (CH2 CH CH2), 110.9 (Ar-C), 51.5 (N CH2); IR (KBr):
We thank the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie for financial support.
‡
nÄ ˆ 2057, 1980, 1903 (vs, CO) cmÀ1; MS (80 eV, EI): m/z (%): 390 (8) [M] ,
‡
‡
‡
362 (11) [M À CO] , 334 (15) [M À 2CO] , 306 (12) [M À 3CO] , 278 (21)
‡
‡
[M À 4CO] , 250 (100) [M À 5CO] ; elemental analysis calcd (%) for
C18H14N2CrO5 (390.20): C 55.40, H 3.58, N 7.15; found: C 55.85, H 4.11, N
7.52.
[1] a) K. H. Dˆtz, H. Fischer, P. Hofmann, F. R. Kreissl, U. Schubert, K.
Weiss, Transition Metal Carbene Complexes, Verlag Chemie, Wein-
heim, 1983; b) B. Crociani, in Reactions of Coordinated Ligands, Vol. 1
(Ed.: P. S. Braterman), Plenum, New York, 1986, p. 553.
[2] Reviews on coordination chemistry of isocyanides: a) E. Singleton,
H. E. Oosthuizen, Adv. Organomet. Chem. 1983, 22, 209; b) P. M.
Treichel, Adv. Organomet. Chem. 1973, 11, 21.
[3] F. E. Hahn, Angew. Chem. 1993, 105, 681; Angew. Chem. Int. Ed. Engl.
1993, 32, 650.
[4] a) L. Tschugajeff, M. J. Skanawy Grigorjewa, J. Russ. Chem. Soc.
1915, 47, 776; b) L. Tschugajeff, M. Skanawy Grigorjewa, A. Posnjak,
Z. Anorg. Chem. 1925, 148, 37.
[5] a) A. Burke, A. L. Balch, J. H. Enemark, J. Am. Chem. Soc. 1970, 92,
2555; b) W. M. Butler, J. H. Enemark, Inorg. Chem. 1971, 10, 2416;
c) W. M. Butler, J. H. Enemark, J. Parks, A. L. Balch, Inorg. Chem.
1973, 12, 451.
[6] a) W. P. Fehlhammer, H. Hoffmeister, H. Stolzenberg, B. Boyadjiev,
Z. Naturforsch. 1989, 44b, 419; b) W. P. Fehlhammer, H. Hoffmeister,
B. Boyadjiev, T. Kolrep, Z. Naturforsch. 1989, 44b, 917; c) U.
Kernbach, W. P. Fehlhammer, Inorg. Chim. Acta 1995, 235, 299;
d) W. P. Fehlhammer, K. Bartel, B. Weinberger, U. Plaia, Chem. Ber.
1985, 118, 2220.
Pentacarbonyl(1,3-bisallylbenzimidazol-2-ylidene)tungsten(0) (15): Com-
plex 15 was prepared as described for 14 from 13 (882 mg, 2 mmol).
Complex 15 (678 mg, 65%) was obtained as yellow, air-stable crystals.
1H NMR (CDCl3, 200.1 MHz): d ˆ 7.41 7.26 (m, 4H; Ar-H), 6.02 (ddt,
3
À
ˆ
ˆ
J ˆ 16, 10, 4 Hz, 2H; CH2 CH CH2), 5.34 5.23 (m, 4H; CH CH2), 5.09
(d, J ˆ 4 Hz, 4H; N CH2); 13C{1H} NMR (CDCl3, 50.3 MHz): d ˆ 200.4
3
À
(trans-CO), 197.2 (cis-CO), 193.2 (NCN), 134.6 (Ar-C), 132.1
À
ˆ
À
ˆ
(CH2 CH CH2), 123.3 (Ar-C), 118.0 (CH2 CH CH2), 111.3 (Ar-C), 52.9
(N CH2); IR (KBr pellet): nÄ ˆ 2063, 1977, 1900 (vs, CO) cmÀ1; MS (70 eV,
À
‡
‡
‡
EI): m/z (%): 522 (26) [M] , 494 (16) [M À CO] , 466 (15) [M À 2CO] ,
‡
‡
‡
438 (22) [M À 3CO] , 410 (100) [M À 4CO] , 382 (63) [M À 5CO] ;
elemental analysis calcd (%) for C18H14N2O5W (522.16): C 41.40, H 2.70, N
5.36; found: C 41.37, H 2.61, N 5.17.
X-ray crystallography: Single crystals suitable for X-ray analysis were
mounted on glass fibers by using two-component glue or mineral oil. X-ray
intensities were measured at room temperature (11 14) with a Nonius
CAD-4 equipped with a seal tube or at 153 K by using a Bruker AXS Apex
system equipped with a rotating anode (9, 15). All data were measured with
MoKa radiation (l ˆ 0.71073 ä). Data reduction was performed with either
X-CAD[42] or the Bruker SMART[43] program packages, respectively. For
further crystal and data collection details see Table 2. All crystal structures
were solved with SHELXS-97[44] by heavy atom methods and were refined
with SHELXL-97[45] by using anisotropic thermal parameters for all non-
hydrogen atoms. With the exception of 12, all hydrogen positions were
determined by Fourier techniques and were refined with isotropic thermal
parameters. Hydrogen positions in 12 were calculated and thermally fixed
to 1.3 Ueqv of the parent atom. Ortep3 for Windows[46] was used for all
plots. Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre: CCDC-192094 192099 contain the supplementary
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Table 2. Selected crystal and data collection details for 9 and 11 15.
9
11
12
13
14
15
formula
Mr
C12H4N4O5W
468.04
C30H19N2O5PW
702.29
C12H6NCrO5
310.19
C12H6N2O5W
442.04
C18H14N2O5Cr
390.31
C18H14N2O5W
522.16
a [ä]
b [ä]
c [ä]
a [8]
b [8]
g [8]
V [ä]3
T [K]
1calcd [gcmÀ1
space group
Z
m [mmÀ1
unique data
7.0986(5)
16.7591(12)
11.9553(9)
90.0
93.713(2)
90.0
1419.3(2)
153(2)
2.190
P21/c
4
8.168
4092
9.4320(10)
23.547(2)
12.678(2)
90.0
98.1300(10)
90.0
2787.4(6)
293(2)
1.673
P21/n
4
4.243
4875
11.768(3)
14.794(2)
7.318(2)
90.0
90.0
90.0
1274.0(5)
293(2)
1.617
Cmcm
4
11.909(3)
14.940(3)
7.517(2)
90.0
92.18(2)
90.0
1336.5(6)
293(2)
2.197
C2/c
4
8.662
1164
8.7850(10)
9.842(2)
8.825(4)
9.800(4)
10.672(4)
99.88(3)
102.68(3)
90.13(4)
886.3(6)
153(1)
10.748(2)
80.0200(10)
77.4100(10)
89.4600(10)
892.8(3)
293(2)
]
1.452
1.957
≈
≈
P1
P1
2
2
]
0.918
637
0.671
3127
6.548
5056
obs data [I > 2s(I)]
R1 (obs.) [%]
R2 (all) [%]
3617
3873
501
1037
2678
4794
3.51, wR1 ˆ 9.10
4.03, wR2 ˆ 9.44
1.041
2.84, wR1 ˆ 7.13
4.73, wR2 ˆ 7.75
0.994
3.34, wR1 ˆ 8.28
5.09, wR2 ˆ 8.95
1.091
1.30, wR1 ˆ 3.18
1.69, wR2 ˆ 3.26
1.066
3.43, wR1 ˆ 9.09
4.49, wR2 ˆ 9.75
1.087
2.59, wR1 ˆ 5.86
2.74, wR2 ˆ 5.91
1.016
GOF
no. of variables
res. el. density [eäÀ3
215
2.544/ À 2.777
352
0.940/ À 0.811
68
105
0.398/ À 0.507
292
0.317/ À 0.202
291
2.113/ À 1.679
]
0.344/ À 0.329
Chem. Eur. J. 2003, 9, No. 3
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0903-0711 $ 20.00+.50/0
711

F. E. Hahn et al.
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Received: August 26, 2002 [F4371]
712
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0947-6539/03/0903-0712 $ 20.00+.50/0
Chem. Eur. J. 2003, 9, No. 3