Heteroditopic imino N-heterocyclic carbenes and their sulfur, selenium, and tungsten tetracarbonyl derivatives

Article abstract of DOI:10.1002/ejic.200400868

New heterditopic imino N-heterocyclic carbenes for use as chelating ligands in homogeneous catalysis are the focus of this contribution. The synthesis of the corresponding imidazolium precursors is accomplished in three steps by alkylation of imidazole wi

Full text of DOI:10.1002/ejic.200400868

FULL PAPER
Heteroditopic Imino N-Heterocyclic Carbenes and Their Sulfur, Selenium, and
Tungsten Tetracarbonyl Derivatives
Georg Steiner,[a] Holger Kopacka,[a] Karl-Hans Ongania,[b] Klaus Wurst,[a]
Peter Preishuber-Pflügl,[c] and Benno Bildstein*[a]
Keywords: Carbene ligands / N ligands / Selenium / Sulfur / Tungsten
New heterditopic imino N-heterocyclic carbenes for use as
chelating ligands in homogeneous catalysis are the focus of
this contribution. The synthesis of the corresponding imid-
ated ylides. In contrast, iminoisopropyl N-heterocyclic carb-
enes, where the acidic site of the methylene group is blocked
by two methyl groups, are stable in solution, as proven by 1H
azolium precursors is accomplished in three steps by alky- and 13C NMR spectroscopy. First derivatives of these new
lation of imidazole with ketoalkyl bromides, imination of the
carbonyl functionality with anilines, either by conventional
methods or by an aluminum-assisted condensation, and
methylation using highly electrophilic methyl triflate. Depro-
tonation of the imidazolium triflates with potassium hydride
gives a different outcome depending on the substitution
pattern of the iminomethyl moiety: iminomethyl N-heterocy-
clic carbenes containing a methylene group between the
imino moiety and the N-heterocycle are unstable because of
tautomerization to the corresponding methylene-deproton-
[N,C]-ligands include their sulfur and selenium oxidation
products (iminoisopropylimidazolin-2-thione and -selenone,
respectively) as well as a tungsten tetracarbonyl complex
with a six-membered [N,C] chelating moiety. All new prod-
ucts were fully characterized by multinuclear NMR (1H, 13C,
77Se, 183W) and IR spectroscopy, mass spectrometry, as well
as by X-ray single crystal structures.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
copolymerization.[1] In contrast, the use of NHC-derived
catalysts for olefin homopolymerizations[3] have met with
rather limited success so far. Established ligand lead struc-
tures in late transition metal olefin polymerization cataly-
sis[4] include, inter alia, 1,2-diimines containing bulky pe-
ripheral imine donors (type A, Scheme 1). We therefore set
out to explore new ligand architectures that combine the
steric bulk of appropriately substituted imine donors with
an electronically favorable NHC moiety.
In earlier work we showed that NHCs with a directly
N-bonded imine group of type B (Scheme 1) are unstable
because of a [1,2] rearrangement of the imidoyl moiety.[5]
To avoid this difficulty, we reasoned that an electronically
decoupled imine group with a spacer should be compatible
with an NHC carbon. Note that type B ligands should form
five-membered [N,C]-metal chelate rings, whereas type C li-
gands will form six-membered [N,C]-metal chelates due to
the C1 spacer unit. In this contribution we show that such
[N,C] ligands are indeed accessible provided that the meth-
ylene hydrogens of the C1 spacer are blocked by two ad-
ditional methyl groups (type D), and we report on their
group 6 metal carbonyl complexes and on their thio and
seleno derivatives. In a comparable approach, Tilset and co-
workers[6] as well as Coleman and coworkers[7] have recently
published similar chemistry of type C ligands focusing on
their monodentate silver and their labile κ1/κ2 palladium
complexes.
Introduction
The chemistry of N-heterocyclic carbenes (NHCs) and
their metal complexes[1] is of great current interest for appli-
cations in homogeneous catalysis. The advantages of NHCs
as steering ligands of catalytically active transition metal
complexes arise from their synthetic, thermodynamic, and
technical features. Synthetically, NHC ligands may be de-
signed and more or less easily synthesized in great struc-
tural variety, including multidentate and chiral representa-
tives. Thermodynamically, the metal–carbon bond of NHC
complexes is stronger than the metal–phosphorus bond of
phosphane complexes, which suggests that replacement of
phosphanes by NHC ligands will lead to catalysts with im-
proved stability and performance. Technically, NHC com-
plexes are often quite stable towards oxygen and thereby
allow catalytic reactions under noninert conditions without
catalyst degradation. Up to now, successful applications of
NHC catalysts include carbon-carbon cross-coupling reac-
tions, olefin metathesis,[2] hydrosilylation, and CO/ethylene
[a] Institute of General, Inorganic and Theoretical Chemistry, Uni-
versity of Innsbruck,
Innrain 52a, 6020 Innsbruck, Austria
E-mail: benno.bildstein@uibk.ac.at
[b] Institute of Organic Chemistry, University of Innsbruck,
Innrain 52a, 6020 Innsbruck, Austria
[c] BASF Aktiengesellschaft,
67056 Ludwigshafen, Germany
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B. Bildstein et al.
FULL PAPER
iminomethylimidazolium progenitors are therefore obvious
synthetic targets. Such compounds may be obtained in a
straightforward manner, as outlined in Scheme 2. First, a
simple alkylation of imidazole with α-bromoacetophenone
(1) afforded benzoylmethylimidazole 2 in a reasonable yield
of 48%; for simplicity, one additional equivalent of imid-
azole was used as the base to bind the hydrogen bromide
formed during the reaction. Secondly, conventional conden-
sation of the carbonyl moiety of 2 with 2,6-diisopropylani-
line with azeotropic removal of water gave iminomethyl-
imidazole 3 as a yellow, air-stable oil. Finally, alkylation by
the strongly electrophilic methyl trifluoromethanesulfonate
afforded air-sensitive imidazolium triflate 4 in 29% overall
yield starting from imidazole. Pertinent key NMR spectro-
scopic data of 4 include characteristic low-field signals for
the imidazolium C(2)-bonded hydrogen [δ(1H) = 9.17 ppm]
as well as for the imine carbon [δ(13C) = 161.2 ppm], obser-
vation of an imidazolium methyl group [δ(1H) = 3.94 ppm,
δ(13C) = 35.8 ppm] and of an acceptor-substituted imid-
azolium methylene group [δ(1H) = 5.85 ppm, δ(13C) =
64.9 ppm], and detection of diastereotopic methyl groups of
the isopropyl substituents [δ(1H) = 0.83 and 0.91 ppm,
δ(13C) = 21.7 and 23.5 ppm] due to hindered rotation of the
bulky 2,6-diisopropylphenyl substituent.
Scheme 1. Design concept for novel [N,C]-ligands.
Results and Discussion
N-Iminomethyl N-Heterocyclic Carbenes
In general, NHC ligands are generated most easily from
their corresponding azolium salts (e.g. imidazolium salts)
With the NHC precursor iminomethylimidazolium tri-
by deprotonation with suitable strong bases.[1] To get access flate 4 in hand, we anticipated that formation of the corre-
to imino NHCs of type C (Scheme 1), the corresponding sponding iminomethyl NHC would be easy to accomplish.
Scheme 2. Synthetic route to N-iminomethyl NHC ligands. Conditions: (a) imidazole; (b) 2,6-diisopropylaniline, H+, reflux; (c) methyl
triflate; (d) potassium hydride; (e) tautomerization.
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Heteroditopic Imino-N-heterocyclic Carbenes
FULL PAPER
However, this is not the case. Upon reaction of 4 with one N-Iminoisopropyl N-Heterocyclic Carbenes
equivalent of potassium hydride as proton-abstracting rea-
The problems associated with the acidic methylene hy-
gent dihydrogen evolution was observed, as expected, and
a dark red solution was obtained, presumably containing
NHCs 5a–c. Hydrolysis of this solution followed by TLC
analysis showed that only the starting material 4 was pres-
ent, indicating that deprotonation must have occurred with-
out any decomposition, in contrast to earlier work[6] where
intractable reaction mixtures were obtained on attempted
deprotonation of iminomethylimidazolium salts. Closer in-
spection of the reactivity of this red solution indicated that
no NHC was present, but instead its formal tautomer 6a,b
and/or its ylidic enamine 6c,d must have been formed by
deprotonation of the methylene group instead of the imid-
azolium C(2)-hydrogen. The intense red color of this new
ylide is obviously due to the spread of charge over six unsat-
urated atoms, as indicated by formulas 6a–d. In retrospect,
this undesired deprotonation at the “wrong” site is not too
surprising because similar behavior has been reported for
some other imidazolium salts containing acidic methylene
groups.[6–8] Based on these results we conclude that the free
iminomethyl NHCs 5a–c are unstable or rearrange to their
tautomers. However, we note that such carbene ligands have
been successfully incorporated into some silver and palla-
dium complexes[6–8] using in situ deprotonation/complex-
ation procedures which avoid the free carbenes as interme-
diates.
drogens in NHCs of type C (Scheme 1) may be overcome
by the use of appropriate protecting groups. As the most
simple and sterically not too demanding groups we chose
two methyl groups for this purpose, selecting NHCs of type
D as our synthetic targets (Scheme 3). First, imidazole was
alkylated with 2-bromo-2-methylpropiophenone (7) under
reflux for three days in ethanolic solution to affording ben-
zoylisopropylimidazole (8) in 61% yield. The longer reac-
tion period and the increased temperature compared to the
preparation of 2 reflect the steric shielding imposed by the
two additional methyl groups. Besides the spectroscopic
data, which are in line with expectations, the identity of 8
was further corroborated by a single crystal structure analy-
sis (Table 2, Figure 1). In the second step, condensation of
the carbonyl moiety of 8 with anilines was necessary to in-
troduce the imine functionality. Attempts to perform this
conversion under common condensation conditions (pro-
ton-catalyzed azeotropic removal of water) failed com-
pletely, but applying an aluminum-assisted protocol that
was developed by us earlier for difficult substrates[9] worked
nicely also in this case, affording iminoisopropylimidazoles
9a and 9b in over 75% yield. In the third step, imidazoles
9a and 9b were alkylated with methyl triflate to give the
Scheme 3. Synthesis of N-iminoisopropyl NHC ligands and their derivatives. Conditions: (f) imidazole, reflux; (g) aniline or 2,6-diisopro-
pylaniline, trimethylaluminum, reflux; (h) methyl triflate; (i) potassium hydride; (j) elemental sulfur or selenium; (k) (CO)5W(THF), hν.
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B. Bildstein et al.
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imidazolium salts 10a and 10b in over 40% overall yield caused effervescence due to dihydrogen evolution and the
starting from imidazole.
initially yellow solution gradually changed color to orange,
which is notably different from the dark-red color of the
deprotonation product of 4. Performing this reaction on a
small scale in deuterated THF solution and analyzing the
outcome by NMR spectroscopy showed clearly that the de-
sired imino-N-heterocyclic carbene 11a–c had indeed been
1
formed in quantitative yield (Table 1): the H signal of the
imidazole-C(2)-bonded hydrogen is absent and the 13C reso-
nance of the imidazole-C(2) carbon is detected at low field
[δ(13C) = 216.3 ppm] in the typical range [δ(13C) = 205.9
to 231.5 ppm] of imidazolin-2-ylidene carbenes.[1e] All other
NMR signals, including the imine carbon resonance [δ(13C)
= 175.0 ppm], are more or less similar to those of the for-
mal conjugate acid 10a, thus proving that carbene 11a–c
exists in solution. Some attempts were undertaken to crys-
tallize NHC 11a–c, but so far no suitable single crystals for
an X-ray structure analysis have been obtained.
Figure 1. Molecular structure of 8. Selected bond lengths (pm):
C(5)–N(1) 135.24(17), C(5)–N(2) 131.1(2), N(1)–C(7) 137.36(17),
N(2)–C(6) 137.4(2), C(6)–C(7) 134.7(2), N(1)–C(2) 147.49(16),
C(2)–C(1) 154.95(17), C(1)–O(1) 121.61(15). Selected angles [°]:
N(1)–C(5)–N(2) 112.66(13), N(1)–C(2)–C(1) 109.73(9), C(3)–C(2)–
C(4) 109.52(11), C(2)–C(1)–O(1) 117.33(11).
N-Iminoisopropyl N-Heterocyclic Carbene Derivatives
Having achieved a clean synthesis of the first free imino
NHC 11a–c, we explored its chemistry (Scheme 3). Oxi-
Both imidazolium triflates 10a and 10b are yellow, dation with elemental sulfur afforded imidazolin-2-thione
slightly air-sensitive powders. Structurally, they differ only (12a) in 74% yield after workup. Spectroscopically, the sul-
in the substitution pattern of the N-bonded aryl group. Be- fur-carbon double bond is clearly evident from the 13C sig-
cause all further chemistry in this contribution was investi- nal at δ = 161.0 ppm (Table 1) and an intense IR absorption
gated with 10a as precursor (vide infra), we will discuss only (νC=S = 1224 cm–1). The carbon resonance of the imine
this triflate salt in more detail. Table 1 lists some key NMR functionality [δ(13C) = 173.3 ppm] is almost unshifted in
spectroscopic data in comparison to its derivatives dis- comparison to 11a–c, as expected. In addition, the C=N
cussed below. Imidazolium salt 10a shows a characteristic bond manifests itself by a strong IR band (νC=N
=
low-field resonance for the imidazolium C(2)-bonded hy- 1647 cm–1). Further structural proof for 12a was obtained
drogen [δ(1H) = 8.84 ppm] and an imine carbon signal from a single crystal structure analysis (Table 2, Figure 2);
[δ(13C) = 171.6 ppm] in the expected range. The two methyl relevant bond lengths and angles are given in the caption.
“protecting” groups of the isopropyl moiety are regular,
Carbene 11a–c reacts analogously with elemental sele-
nonshielded alkyl groups [δ(1H) = 1.36 ppm, δ(13C) = nium to afford the corresponding air-stable imidazolin-2-
25.7 ppm] as intended, ruling out a deprotonation at this selenone (12b) in 43% isolated yield after workup. As ex-
site upon reaction with a strong base. The signals of the pected, the spectroscopic features of 12b are quite similar
imidazolium N-methyl group [δ(1H) = 3.33 ppm, δ(13C) = to those of its homologous thione 12a. Due to the spin-1/2
35.9 ppm] are similar in value to those observed for imi- 77Se isotope further structural proof by 77Se NMR spec-
nomethylmidazolium salt 4 containing a methylene spacer troscopy was possible [δ(13C)C=Se = 153.8 ppm, 1J(13C-77Se)
moiety (vide supra).
= 232 Hz; δ(77Se) = –1182 ppm; δ(13C)C=N = 172.8 ppm;
Imidazolium triflate 10a serves as the precursor for the νC=Se = 1222 cm–1; νC=N = 1644 cm–1]. These selenium
corresponding imino NHC 11a–c. Treatment of 10a with an NMR spectroscopic data compare well with those of the
equimolar amount of potassium hydride in THF solution few other known imidazolin-2-selenones.[10] In the solid
Table 1. Relevant NMR spectroscopic data for 10a, 11a–c, 12a, 12b, and 13.
Compound
10a
11a–c
12a
12b
13
Solvent
[D6]DMSO
149.3 ppm
[D8]THF
[D6]DMSO
161.0 ppm
[D6]DMSO
153.8 ppm
[D6]DMSO
192.4 ppm
δ(13C) of imidazole C(2)
216.3 ppm
1J(13C-77Se) = 232 Hz
δ(77Se) = –1182 ppm
1J(13C-183W) = 95 Hz
δ(183W) = –2569 ppm
δ of atom bonded to
imidazole C(2)
δ(1H) = 8.84 ppm
–
δ(33S): no data
δ(13C) of imine carbon
δ(1H) of N-CH3
171.6 ppm
3.33 ppm
35.9 ppm
1.36 ppm
25.7 ppm
66.7 ppm
175.0 ppm
3.69 ppm
38.2 ppm
1.83 ppm
28.4 ppm
64.8 ppm
173.3 ppm
3.49 ppm
34.5 ppm
1.83 ppm
26.3 ppm
64.6 ppm
172.8 ppm
3.59 ppm
36.5 ppm
1.91 ppm
26.7 ppm
65.7 ppm
184.2 ppm
3.84 ppm
overlapped by solvent signal
1.80 ppm
δ(13C) of N-CH3
δ(1H) of NЈ-C(CH3)2
δ(13C) of NЈ-C(CH3)2
27.6 ppm
64.4 ppm
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Heteroditopic Imino-N-heterocyclic Carbenes
FULL PAPER
However, because of the known sensitivity of such com-
pounds at room temperature and towards sunlight,[11] and
because of the obnoxious stench associated with organic
tellurium compounds in general, we refrained from at-
tempting this reaction. However, we note that both com-
pounds 12a and 12b represent new heteroditopic [N,S]- and
[N,Se]-ligands whose coordination chemistry remains unex-
plored at the moment.
As outlined in the introduction, carbene 11a–c was de-
signed as a member of a new family of heteroditopic [N,C]-
imino NHC ligands for application in homogeneous cataly-
sis. Consequently, it was of prime interest to study its coor-
dination chemistry. Reaction with simple metal halides
(PdCl2, CuCl, AgCl, NiCl2 etc.) gave, in general, polar
products that are obviously [N,C]-bound metal complexes.
Full characterization proved quite difficult, however, and
the growth of suitable crystals for an unambiguous struc-
tural proof by single crystal structure analysis has not yet
been possible. In contrast, the reaction with photochemi-
cally generated W(CO)5(THF) afforded the air-stable tung-
sten complex 13, which was fully characterized in solution
by a range of spectroscopic methods as well as in the solid
state by single crystal structure analysis. Its 13C NMR spec-
trum (Table 1) shows the carbene carbon signal at δ =
192.4 ppm, with a one-bond 13C-183W coupling constant of
95 Hz, thereby proving the direct connectivity of the NHC-
carbon to the metal center. The imine carbon is shifted to
low field [δ(13C) = 184.2 ppm] in comparison to the free
carbene 11a–c [δ(13C) = 175.0 ppm], thus reflecting the co-
ordination of the imine moiety to the tungsten metal center.
The four carbonyl groups are evident from their strong IR
absorptions and from three 13C signals with 183W satellites,
indicating two magnetically equivalent axial carbonyl
Figure 2. Molecular structure of 12a. Selected bond lengths (pm):
S(1)–C(5) 168.1(2), C(5)–N(2) 137.2(3), C(5)–N(3) 135.8(3), N(2)–
C(7) 138.4(3), N(3)–C(6) 137.9(3), C(6)–C(7) 133.4(3), N(3)–C(8)
145.8(3), N(2)–C(2) 148.1(3), C(2)–C(1) 153.5(3), C(1)–N(1)
127.3(3). Selected angles [°]: N(2)–C(5)–N(3) 105.46(17), N(2)–
C(2)–C(1) 108.49(16), C(3)–C(2)–C(4) 108.85(18), C(2)–C(1)–N(1)
116.60(18).
state, selenone 12b (Table 2, Figure 3) is isomorphous with
thione 12a; only some minor differences in bond lengths
and angles are observed. Most notable of these is the car-
bon-selenium bond length [184.0(2) pm] as compared to the
shorter C=S bond [168.1(2) pm] of thione 12a. The rather
long C=Se bond length is similar in value to that of an
imidazolinselenone published earlier[10] and suggests a re-
duced bond order due to significant contribution of the
zwitterionic C+-Se– valence structure.
1
groups [δ(13C) = 205.3 ppm, JC,W = 129 Hz] and two dif-
1
ferent equatorial CO ligands [δ(13C) = 210.1 ppm, JC,W
=
146 Hz; δ(13C) = 218.2 ppm, JC,W = 169 Hz] due to the
heteroditopic nature of the imino NHC ligand 11a–c. The
observation of only one 13C signal for the two axial CO
groups indicates rapid interconversion in solution of the
two possible boat conformations of the six-membered che-
late ring, which is further supported by the two isochronous
methyl groups of the isopropyl moiety [δ(13C) = 27.6 ppm,
δ(1H) = 1.80 ppm] (Table 1). Several NHC tungsten car-
bonyl complexes have been reported in the literature,[12] but
only for one (CO)5W(NHC) complex[12d] has a direct coup-
ling of the NHC-carbon to the tungsten metal center been
1
1
reported [δ(13C) = 176.4 ppm, JC,W = 99 Hz];[12d] these
data are in good agreement with ours. In addition, we were
able to detect for the first time the 183W chemical shift of an
NHC-tungsten complex: 13 shows a weak but nevertheless
significant 183W signal at δ = –2569 ppm vs. aqueous
Na2WO4 solution. In general, transition metal NMR spec-
troscopic data of tungsten metal complexes are very limited
due to the unfavorable receptivity of 183W (RC = 0.0589),
and only about 30 organometallic compounds have been
Figure 3. Molecular structure of 12b. Selected bond lengths (pm):
Se(1)–C(5) 184.0(2), C(5)–N(2) 136.7(2), C(5)–N(3) 135.4(3), N(2)–
C(7) 138.7(3), N(3)–C(6) 137.5(3), C(6)–C(7) 133.7(3), N(3)–C(8)
146.0(3), N(2)–C(2) 148.2(3), C(2)–C(1) 153.9(3), C(1)–N(1)
127.2(2). Selected angles [°]: N(2)–C(5)–N(3) 105.84(17), N(2)–
C(2)–C(1) 108.76(16), C(3)–C(2)–C(4) 108.55(17), C(2)–C(1)–N(1)
116.56(17).
In principal it would be interesting to synthesize the next investigated by this technique so far. Although the body of
higher homologue, iminoisopropylimidazolin-2-tellurone, 183W chemical shifts is therefore quite small for compara-
by oxidation of carbene 11a–c with elemental tellurium. tive purposes, the shift of 13 compares well with those of
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vinylidene-tungsten complexes [(dppe)CO]3W=C=CHR] NHC systems can be prepared by alkylation of imidazole
with signals in the range of δ = –2548 to –2596 ppm.[13]
with a ketoalkyl bromide, condensation of the carbonyl
In the solid state (Figure 4, Table 2), complex 13 shows group with anilines, alkylation of the iminoalkylimidazole
the expected κ2-coordination of the [N,C]-ligand in a boat with methyl trifluoromethanesulfonate, and deprotonation
conformation, with tungsten and the isopropylmethyl group of the N-iminoalkyl-NЈ-methylimidazolium triflate with po-
occupying the apical sites. Pertinent bond lengths and tassium hydride. For a successful generation of the imino
angles are given in the caption of Figure 4. Due to geomet- NHC it is necessary to block the methylene group between
rical constraints of the six-membered chelate ring, the coor- the heterocycle and the imine group by two methyl substitu-
dination angle at the formally octahedral tungsten center is ents, otherwise deprotonation at this undesired “wrong” site
only 78.0° as compared to the idealized normal angle. In occurs and an ylidic non-NHC product is observed. Spec-
addition, due to the steric requirements of the [N,C]-ligand, troscopically, the imino NHC ligand is characterized by a
the tungsten center shows a slightly distorted octahedron, typical low-field 13C chemical shift of the NHC-carbene
indicated by an “umbrella-like” back-bending of the four carbon together with an imine carbon signal. The chemical
carbonyl ligands. The W–N [226.5(8) pm] and W–C reactivity of the imino NHC comprises oxidation by ele-
[221.8(9) pm] bond lengths of the tungsten-coordinated mental sulfur and selenium to afford the corresponding im-
imino NHC ligand are in the normal range of other tung- idazolin-2-thione and selenone, which were fully charac-
sten-imino and tungsten-NHC complexes.[12] As a conse- terized by solid state structures and multinuclear NMR
quence of the boat conformation of the [N,C] six-membered spectroscopy, including 77Se spectroscopy. A first transition
chelate the two axial carbonyl groups at the tungsten center metal complex of the imino NHC ligand was obtained by
are inequivalent. However, this is just a solid-state effect; in treatment with tungsten hexacarbonyl; the resulting [N,C]
solution, a rapid ring flip process occurs as indicated by the W(CO)4 complex shows the anticipated six-membered me-
simplicity of the NMR spectra discussed above. Overall the tal [N,C] chelate in solution and in the solid state, as proven
X-ray structure of 13 shows the desired heteroditopic imino by an X-ray structure and by multinuclear NMR spec-
NHC chelate metal structure and indicates that steric tun- troscopy, including 183W spectroscopy.
ing will easily be possible in the future by altering the sub-
stitution pattern of the N-bonded aryl moiety.
Experimental Section
General: Commercially available starting materials were used as ob-
tained. Solvents were dried, deoxygenated, and saturated with ar-
gon according to standard procedures in organometallic chemistry.
Reactions of air-sensitive materials were performed in Schlenk
glassware under an atmosphere of argon using techniques common
in organometallic chemistry.
Imidazole 2 (CA registry no. 24155-34-8): A round-bottomed flask
was charged with imidazole (4.3 g, 62.8 mmol), α-bromoacetophe-
none (1; 5 g, 25.1 mmol), and 100 mL of THF. The yellow solution
was stirred overnight at ambient temperature to give a yellow sus-
pension of the product with precipitated imidazolium bromide.
Aqueous workup and recrystallization from methanol/diethyl ether
yielded pure, yellow 2 (2.24 g, 12 mmol, 48%). M.p.: 117–119 °C.
IR (KBr): ν = 2965 cm–1 (w), 2919 (w), 1696 (vs), 1597 (s), 1503
˜
(s), 1451 (s), 1360 (s), 1344 (m), 1288 (m), 1227 (vs), 1107 (s), 1074
1
(s), 1038 (s), 984 (s), 906 (s), 816 (s), 762 (s), 746 (vs), 692 (vs). H
Figure 4. Molecular structure of 13. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (pm): W(1)–C(5)
221.8(9), W(1)–N(1) 226.5(8), W(1)–C(01) 196.5(11), W(1)–C(02)
194.3(11), W(1)–C(03) 201.3(12), W(1)–C(04) 204.5(11), C(01)–
O(1) 116.3(13), C(02)–O(2) 119.0(13), C(03)–(O3) 115.0(13),
C(04)–O(4) 112.3(13), C(5)–N(2) 137.5(13), C(5)–N(3) 136.1(13),
N(2)–C(7) 137.4(13), N(3)–C(6) 138.1(14), C(6)–C(7) 131.2(17),
N(3)–C(8) 147.8(14), N(2)–C(2) 147.9(14), C(2)–C(1) 153.6(14),
C(1)–N(1) 129.8(12). Selected angles [°]: N(1)–W(1)–C(5) 78.0(3),
C(01)–W(1)–C(02) 88.3(4), C(03)–W(1)–C(04) 166.0(4), N(2)–
C(5)–N(3) 102.7(8), N(2)–C(2)–C(1) 111.3(8), C(3)–C(2)–C(4)
106.8(9), C(2)–C(1)–N(1) 120.7(9).
NMR (300 MHz, CD2Cl2): δ = 5.43 (s, 2 H, CH2), 6.94–7.99 (m,
8 H, C6H5, C3H3N2) ppm. 13C NMR (75.432 MHz, CD2Cl2): δ =
52.9 (CH2), 120.7, 128.2, 129.3, 134.6, and 138.5 (C6H5, C3H3N2),
192.4 (C=O) ppm.
Imidazole 3: A Dean–Stark apparatus was charged with 2 (940 mg,
5.05 mmol), 2,6-diisopropylaniline (2.80 mL, 15.1 mmol), p-tolu-
enesulfonic acid monohydrate (2.9 g, 15.1 mmol), and 100 mL of
toluene. The mixture was refluxed for 3 d, followed by aqueous
workup. Chromatography on alumina with diethyl ether/n-hexane
(v/v = 1:1) as eluent removed the excess of aniline, and elution with
methanol yielded pure 3 (1.07 g, 3.1 mmol, 61.4%) as a yellow oil.
MS (EI): m/z = 345.3 [M]+. 1H NMR (300 MHz, CD2Cl2): δ =
0.87–1.23 (m, 12 H, CH3), 2.67 (m, 2 H, CH), 4.90 (s, 2 H, CH2),
6.64–7.88 (m, 11 H, C6H5, C6H3, C3H3N2) ppm. 13C NMR
(75.432 MHz, CD2Cl2): δ = 22.1, 23.7, and 28.8 [CH(CH3)2], 44.7
(CH2), 119.4, 120.2, 123.2, 123.5, 124.2, 124.7, 127.6, 128.7, 129.1,
Conclusions
New heteroditopic ligands combining the advantageous
properties of N-heterocyclic carbenes and imine donors
with N-aryl groups have been investigated. Such imino 129.7, 130.2, 131.3, 135.7, 136.1, 136.9, 137.8, 138.2, and 145.1
1330 © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2005, 1325–1333

Heteroditopic Imino-N-heterocyclic Carbenes
(C6H5, C6H3, C3H3N2), 162.2, 162.9 (C=N) ppm. C23H27N3 and 63.1 [C(CH3)2], 117, 8, 120.2, 123.6, 127.8, 128.1, 128.5, 128.7,
FULL PAPER
(345.48): calcd. C 79.96, H 7.88, N 12.16; found C 80.11, H 7.86,
N 12.13.
129.6, 134.6, 135.6, and 150.3 (C6H5, C3H3N2), 173.0 (C=N) ppm.
C19H19N3 (289.37): calcd. C 78.86, H 6.62, N 14.52; found C 78.99,
H 6.59, N 14.48.
Imidazolium Triflate 4: A Schlenk tube was charged with 3 (392 mg,
1.13 mmol) and dry dichloromethane (40 mL). The solution was
cooled to –80 °C and methyl trifluoromethanesulfonate (124 μL,
1.13 mmol) was added from a syringe. After 90 min stirring at
–80 °C, the cooling bath was removed and the mixture was stirred
for a further 90 min. Workup: all volatile materials were removed
on a vacuum line, the solid yellow residue was washed with two
portions of dry diethyl ether, and dried in vacuo to afford 570 mg
of 4 as a yellow, air-sensitive powder in 99% yield. MS (FAB):
m/z = M of cation not observed due to hydrolysis. 1H NMR
Imidazole 9b: A Schlenk tube was charged with 2,6-diisopropylani-
line (2.96 mL, 15.7 mmol), 40 mL of toluene, and 7.84 mL of a
2.0 m toluene solution of trimethylaluminum (15.7 mmol). The
stirred solution was heated to 80 °C. After 90 min methane evol-
ution was complete and the solution was cooled to ambient tem-
perature. Under protection from air, imidazole
8 (1.12 g,
5.23 mmol) was added in one portion. The mixture was stirred
overnight at ambient temperature and heated to 80 °C for a further
three hours to afford a bright-yellow solution. Workup as described
above for 9a afforded 1.46 g of pure 9b in 75% yield as a yellow
oil. MS (EI): m/z = 373.3 [M]+. 1H NMR (300 MHz, CD2Cl2): δ =
1.06 [d, 3JH,H = 6.94 Hz, 6 H, CH(CH3)2], 1.14 [d, 3JH,H = 6.61 Hz,
6 H, CH(CH3)2], 2.74 [m, 2 H, 2×CH(CH3)2], 6.38–7.49 (m, 11 H,
C6H5, C6H3, C3H3N2) ppm. 13C NMR (75.432 MHz, CDCl3): δ =
21.3, 23.9, and 28.7 [CH(CH3)2], 27.3 and 63.4 [C(CH3)2], 117.8,
122.7, 126.4, 127.6, 128.0, 128.8, 129.5, 134.7, 135.5, 136.9, and
145.0 (C6H5, C6H3, C3H3N2), 170.4 (C=N) ppm. C25H31N3
(373.53): calcd. C 80.39, H 8.37, N 11.25; found C 80.52, H 8.34,
N 11.20.
3
[300 MHz, (CD3)2SO]: δ = 0.83 [d, JH,H = 6.9 Hz, 6 H, CH-
3
(CH3)2], 0.91 [d, JH,H = 6.6 Hz, 6 H, CH(CH3)2], 2.65 [m, 2 H,
2×CH(CH3)2], 3.94 (s, 3 H, CH3), 5.85 (s, 2 H, CH2), 6.95–7.82
(m, 10 H, C6H5, C6H3, C3H3N2), 9.17 (s, 1 H, C3H3N2) ppm. 13C
NMR [75.432 MHz, (CD3)2SO]: δ = 21.7, 23.5, and 27.4 [CH-
(CH3)2], 35.8 (N-CH3), 64.9 (CH2), 118.6, 122.6, 122.8, 123.2,
123.8, 124.1, 127.2, 128.5, 128.8, 130.4, 133.6, 134.8, 137.8, and
144.0 (C6H5, C6H3, C3H3N2), 161.2 (C=N) ppm. The weak 13C
signals for the triflate anion [δ = 121 ppm, q, 1J(13C-19F) = 322 Hz]
were not observed due to insufficient concentration and/or too
short an acquisition period. C25H30F3N3O3S (509.59): calcd. C
58.92, H 5.93, N 8.25; found C 58.69, H 5.95, N 8.22.
Imidazolium Triflate 10a: A Schlenk tube was charged with 9a
(650 mg, 2.25 mmol) and dry dichloromethane (40 mL). The solu-
tion was cooled to –80 °C and methyl trifluoromethanesulfonate
(246 μL, 2.25 mmol) was added with a syringe. After 90 min stir-
ring at –80 °C, the cooling bath was removed and the mixture was
stirred for a further 90 min. Workup: all volatile materials were
removed on a vacuum line, the solid yellow residue was washed
with two portions of dry diethyl ether, and dried in vacuo to afford
920 mg of 10a as a yellow, slightly air-sensitive powder in 90%
yield. MS (FAB): m/z = 304.1 [M]+ of cation. 1H NMR [300 MHz,
(CD3)2SO]: δ = 1.36 (s, 6 H, CH3), 3.33 (s, 3 H, CH3), 6.03–7.54
(m, 12 H, C6H5, C3H3N2), 8.84 (s, 1 H, C3H3N2) ppm. 13C NMR
[75.432 MHz, (CD3)2SO]: δ = 25.7 and 66.7 [C(CH3)2], 35.8 (N-
CH3), 119.4, 121.6, 121.8, 123.3, 123.6, 123.8, 127.8, 127.9, 128.3,
Imidazole 8: A round-bottomed flask was charged with imidazole
(3.40 g, 49.9 mmol), 2-bromo-2-methylpropiophenone (7; 4 mL,
23.8 mmol), and 40 mL of ethanol. The yellow solution was re-
fluxed for 3 d. Aqueous workup yielded a yellow oil which crys-
tallized in the freezer. Recrystallization from dichloromethane/n-
hexane (1:2) afforded pure, colorless 8 (3.11 g, 14.5 mmol, 61%).
MS (EI): m/z = 214.1 [M]+. IR (KBr): ν = 3145 cm–1 (w), 3000(w),
˜
1672(vs), 1599(m), 1576(w), 1493(m), 1470(m), 1451(m), 1393(w),
1375(m), 1339(w), 1285(w), 1261(s), 1240(vs), 1177(s), 1167(s),
1
1153(m), 1082(s), 1013(s), 976(s), 906(s), 893(s), 820(s), 750(s). H
NMR [300 MHz, (CD3)2SO]: δ = 1.80 (s, 6 H, CH3), 6.94–7.87 (m,
8 H, C6H5, C3H3N2) ppm. 13C NMR [75.432 MHz, (CD3)2SO]: δ
= 26.6 and 64.7 [C(CH3)2], 118.1, 128.0, 128.5, 129.1, 132.6, 134.8,
and 135.6 (C6H5, C3H3N2), 199.3 (C=O) ppm. C13H14N2O
(214.26): calcd. C 72.87, H 6.59, N 13.07; found C 72.95, H 6.57,
N 13.03.
128.5, 128.6, 128.8, 133.4, 136.5, and 149.3 (C6H5, C3H3N2), 171.6
1
(C=N), 120.7 (q, JC,F
= 322 Hz, CF3 of triflate) ppm.
C21H22F3N3O3S (453.48): calcd. C 55.62, H 4.89, N 9.27; found C
55.34, H 4.91, N 9.24.
Imidazolium Triflate 10b: A Schlenk tube was charged with 9b
(1.47 g, 3.94 mmol) and dry dichloromethane (40 mL). The solu-
tion was cooled to –80 °C and methyl trifluoromethanesulfonate
(432 μL, 3.94 mmol) was added with a syringe. After 90 min stir-
ring at –80 °C, the cooling bath was removed and the mixture was
stirred for a further 90 min. Workup: all volatile materials were
removed on a vacuum line, the solid yellow residue was washed
with two portions of dry diethyl ether, and dried in vacuo to afford
2.00 g of 10b as a yellow, slightly air-sensitive powder in 95% yield.
MS (FAB): m/z = 388.4 [M]+ of cation. 1H NMR [300 MHz,
Imidazole 9a: A Schlenk tube was charged with aniline (524 μL,
5.75 mmol), 40 mL of toluene, and 2.87 mL of a 2.0 m toluene solu-
tion of trimethylaluminum (5.75 mmol). The stirred solution was
heated to 80 °C. After 90 min methane evolution was complete and
the solution was cooled to ambient temperature. Under protection
from air, imidazole 8 (560 mg, 2.61 mmol) was added in one por-
tion. The mixture was stirred overnight at ambient temperature and
then heated to 80 °C for a further three hours to afford a bright-
yellow solution. Workup: the solution was cooled to 0 °C, the mix-
ture was carefully hydrolyzed with crushed ice, the organic product
was extracted with three portions of dichloromethane, the com-
bined organic layers were washed with three portions of a 5% aque-
ous NaOH solution, the dichloromethane solution was washed
with two portions of water, the organic phase was dried with
Na2SO4, and all volatile materials were removed in vacuo on a
rotary evaporator to afford the crude product together with aniline.
Chromatography on alumina with diethyl ether/n-hexane (v/v, 1:1)
as eluent followed by methanol afforded 651 mg of pure 9a in 86%
3
(CD3)2SO]: δ = 0.91 [d, JH,H = 6.61 Hz, 6 H, CH(CH3)2], 1.05 [d,
3JH,H = 6.93 Hz, 6 H, CH(CH3)2], 2.00 [s, 6 H, C(CH3)2], 2.65 [m,
2 H, 2×CH(CH3)2], 3.87 (s, 3 H, CH3), 6.82–8.10 (m, 10 H, C6H5,
C6H3, C3H3N2), 8.94 (s, 1 H, C3H3N2) ppm. 13C NMR [75.432
MHz, (CD3)2SO]: δ = 21.2, 23.6, and 27.7 [CH(CH3)2], 26.1 and
66.9 [C(CH3)2], 35.8 (N-CH3), 121.7, 122.2, 123.4, 123.8, 126.1,
126.8, 127.3, 127.5, 128.0, 129.1, 133.6, 134.6, 136.8, 143.7, and
1
143.8 (C6H5, C6H3, C3H3N2), 170.5 (C=N), 120,7 (q, JC,F
=
322 Hz, CF3 of triflate) ppm. C27H34F3N3O3S (537.64): calcd. C
60.32, H 6.37, N 7.82; found C 60.04, H 6.40, N 7.78.
1
yield as a yellow oil. MS (FAB): m/z = 290.2 [M + H]+. H NMR
(300 MHz, CD2Cl2): δ = 1.85 (s, 6 H, CH3), 6.39–7.53 (m, 13 H, Imino N-Heterocyclic Carbene 11a–c: A small Schlenk tube was
C6H5, C3H3N2) ppm. 13C NMR (75.432 MHz, CD2Cl2): δ = 26.7 charged with imidazolium triflate 10a (50 mg, 0.110 mmol) dis-
Eur. J. Inorg. Chem. 2005, 1325–1333
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1331

B. Bildstein et al.
FULL PAPER
solved in 1 mL of dry, deuterated THF. Under protection from air,
potassium hydride (4.4 mg, 0.110 mmol) was added in one portion.
The mixture was stirred at ambient temperature for 2 h. Dihydro-
gen evolution was observed and a white precipitate of potassium
triflate formed during this period. The orange suspension was
transferred under an atmosphere of argon to an NMR tube and
analyzed spectroscopically: 1H NMR (300 MHz, [D8]THF): δ =
1.83 (s, 6 H, CH3), 3.69 (s, 3 H, CH3), 6.55–7.12 (m, 12 H, C6H5,
C3H2N2) ppm. 13C NMR (75.432 MHz, [D8]THF): δ = 28.4 and
64.8 [C(CH3)2], 38.2 (N-CH3), 118.1, 120.7, 121.0, 123.3, 127.8,
128.2, 128.7, 129.4, 136.7, and 151.9 (C6H5, C3H2N2), 175.0
(C=N), 216.3 (carbene C) ppm.
C3H2N2), 161.0 (C=S), 173.3 (C=N) ppm. C20H21N3S (335.47):
calcd. C 71.61, H 6.31, N 12.53; found C 71.34, H 6.33, N 12.48.
Imidazolin-2-selenone 12b: A Schlenk tube was charged with imid-
azolium triflate 10a (220 mg, 0.485 mmol), 40 mL of THF, and po-
tassium hydride (20 mg, 0.485 mmol). The mixture was stirred for
2 h at ambient temperature. Dihydrogen evolution occurred during
this period and the mixture gradually changed in color from yellow
to orange. Elemental selenium (40 mg, 0.507 mmol) was added to
the stirred mixture and the reaction was allowed to proceed over-
night at ambient temperature. Chromatography on alumina with
diethyl ether/n-hexane (v/v, 1:1) and methanol as eluents afforded
air-stable, yellow 12b (80 mg, 0.209 mmol, 43%). MS (FAB): m/z =
Imidazolin-2-thione 12a: A Schlenk tube was charged with imid-
azolium triflate 10a (165 mg, 0.364 mmol), 40 mL of THF, and
potassium hydride (15 mg, 0.364 mmol). The mixture was stirred
for 2 h at ambient temperature. Dihydrogen evolution occurred
during this period and the mixture gradually changed in color from
yellow to orange. Elemental sulfur (93 mg, 0.364 mmol) was added
to the stirred mixture and the reaction was allowed to proceed over-
night at ambient temperature. Chromatography on alumina with
diethyl ether/n-hexane (v/v, 1:1) and methanol as eluents afforded
air-stable, yellow 12a (90 mg, 0.268 mmol, 74%). MS (FAB): m/z =
383.1 [M]+. IR (KBr): ν = 3141 cm–1 (w), 3072 (w), 2979 (w), 1644
˜
(vs) (νC=N), 1591 (s), 1478 (s), 1452 (vs), 1377 (vs), 1296 (s), 1222
1
(vs) (νC=Se), 1131 (s), 938 (m), 778 (s), 733 (m), 697 (vs). H NMR
[300 MHz, (CD3)2SO]: δ = 1.91 (s, 6 H, CH3), 3.59 (s, 3 H, CH3),
6.70–7.48 (m, 12 H, C6H5, C3H2N2) ppm. 13C NMR [75.432 MHz,
(CD3)2SO]: δ = 26.7 and 65.7 [C(CH3)2], 36.5 (CH3), 118.2, 119.6,
119.8, 122.3, 127.4, 127.9, 128.8, 135.5, and 150.8 (C6H5, C3H2N2),
153.8 (1JC,Se = 232 Hz, C=Se), 172.8 (C=N) ppm. 77Se NMR
(57.203 MHz, (CD3)2SO, vs. H2SeO3): δ = –1182 (C=Se) ppm.
C20H21N3Se (382.36): calcd. C 62.82, H 5.54, N 10.99; found C
62.62, H 5.56, N 10.95.
335.0 [M]+. IR (KBr): ν = 3140 cm–1 (w), 3071 (w), 2979 (w), 2928
˜
(w), 1647 (vs) (νC=N), 1591 (s), 1478 (s), 1453 (s), 1403 (s), 1386
(vs), 1362 (s), 1292 (m), 1265 (m), 1224 (vs) (νC=S), 1149 (m), 989 Tungsten Complex 13: A Schlenk tube was charged with imidazol-
(m), 778 (s), 704 (s), 697 (vs), 670 (vs). 1H NMR [300 MHz, ium triflate 10a (768 mg, 1.69 mmol), 50 mL of THF, and potas-
(CD3)2SO]: δ = 1.83 (s, 6 H, CH3), 3.49 (s, 3 H, CH3), 6.62–7.37 sium hydride (86 mg, 1.69 mmol). The mixture was stirred for 2 h
(m, 12 H, C6H5, C3H2N2) ppm. 13C NMR [75.432 MHz, at ambient temperature. Dihydrogen evolution occurred during this
(CD3)2SO]: δ = 26.3 and 64.6 [C(CH3)2], 34.5 (CH3), 115.6, 117.9, period and the mixture gradually changed in color from yellow to
119.6, 122.4, 127.5, 128.0, 128.1, 128.6, 135.6, and 150.9 (C6H5, orange. Tungsten hexacarbonyl (596 mg, 1.69 mmol) was added to
Table 2. Crystallographic data for 8, 12a, 12b, and 13.
Compound
8
12a
12b
13
Molecular formula
Molecular mass
Crystal system
Space group
a [pm]
b [pm]
c [pm]
α [°]
β [°]
C13H14N2O
214.26
triclinic
C20H2N3S
335.46
C20H21N3Se
382.36
C24H21N3O4W
599.29
triclinic
monoclinic
C2/c (no. 15)
3330.04(5)
673.30(2)
1626.7(2)
90
101.313(6)
90
8
monoclinic
C2/c (no. 15)
3344.67(2)
680.17(4)
1622.54(5)
90
101.519(2)
90
8
P1 (no. 2)
626.64(3)
792.77(4)
1238.73(6)
97.332(2)
91.089(2)
112.391(3)
2
P1 (No. 2)
856.58(2)
1363.90(5)
2014.61(7)
82.654(2)
79.147(2)
89.959(2)
4
γ [°]
Z
V [nm3]
0.56279(5)
1.264
3.5764(5)
1.246
3.6168(2)
1.404
2.29187(13)
1.737
ρcalcd [Mgm–3
]
Temp. [K]
233(2)
0.082
228
233(2)
0.187
1424
233(2)
2.082
1568
233(2)
5.075
1168
Absorption coeff. [mm–1
F000
]
Color, habit
Crystal size
θ range for data collection
colorless prism
0.4×0.2×0.15 mm
1.66° to 24.00°
0 Յ h Յ 7
–9 Յ k Յ 8
–14 Յ l Յ 14
2780
colorless plate
0.4×0.2×0.05 mm
2.49° to 22.50°
0 Յ h Յ 35
–7 Յ k Յ 7
–17 Յ l Յ 16
7515
colorless plate
0.35×0.15×0.07 mm
2.49° to 25.00°
0 Յ h Յ 39
–8 Յ k Յ 8
–19 Յ l Յ 18
10789
yellow plate
0.25×0.11×0.04 mm
1.51° to 23.00°
–9 Յ h Յ 0
–14 Յ k Յ 14
–22 Յ l Յ 21
10971
Index ranges
Reflections collected
Independent reflections
Reflections with I Ͼ 2σ(I)
Absorption correction
Refinement method
1754 (Rint = 0.0143)
1593
2333 (Rint = 0.0293)
1909
none
3180 (Rint = 0.0286)
2698
none
6341 (Rint = 0.0370)
5407
none
none
full-matrix least squares on F2 full-matrix least squares on F2 full-matrix least squares on F2 full-matrix least squares on F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
1754/0/146
1.065
2333/0/219
1.028
3180/0/219
1.040
6341/0/581
1.025
R1 = 0.0341
wR2 = 0.0874
R1 = 0.0379
wR2 = 0.0899
0.171(18)
R1 = 0.0385
wR2 = 0.0957
R1 = 0.0518
wR2 = 0.1017
0.0017(3)
R1 = 0.0274
wR2 = 0.0640
R1 = 0.0365
wR2 = 0.0671
0.00029(11)
191 and –301 enm–3
R1 = 0.0542
wR2 = 0.1352
R1 = 0.0630
wR2 = 0.1405
0.0043(10)
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
176 and –149 enm–3
168 and –200 enm–3
6779 and –1654 enm–3
1332
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 1325–1333

Heteroditopic Imino-N-heterocyclic Carbenes
FULL PAPER
Chem. 2002, 114, 1343; Angew. Chem. Int. Ed. 2002, 41, 1290;
c) W. A. Herrmann, T. Weskamp, V. P. W. Böhm, Adv. Or-
ganomet. Chem. 2001, 48, 1; d) C. J. Carmalt, A. H. Cowley,
Adv. Inorg. Chem. 2000, 50, 1; e) D. Bourissou, O. Guerret,
F. P. Gabbai, G. Bertrand, Chem. Rev. 2000, 100, 39; f) A. J.
Arduengo, Acc. Chem. Res. 1999, 32, 913; g) W. A. Herrmann,
C. Köcher, Angew. Chem. 1997, 109, 2257; Angew. Chem. Int.
Ed. Engl. 1997, 36, 2163.
a) T. Weskamp, F. J. Kohl, W. A. Herrmann, J. Organomet.
Chem. 1999, 582, 362; b) T. Weskamp, W. C. Schattenmann,
M. Spiegler, W. A. Herrmann, Angew. Chem. 1998, 110, 2631;
Angew. Chem. Int. Ed. 1998, 37, 2490; c) C. W. Bielawski, R. H.
Grubbs, Angew. Chem. 2000, 112, 3025; Angew. Chem. Int. Ed.
2000, 39, 2903; d) Review: M. R. Buchmeiser, Well-Defined
Transition Metal Catalysts for Metathesis Polymerization, in,
Late Transition Metal Polymerization Catalysis (Eds.: B. Ri-
eger, L. S. Baugh, S. Kacker, S. Striegler), Wiley-VCH,
Weinheim, 2003, chapter 5, p. 155.
the mixture and the reaction was stirred overnight at room tem-
perature followed by irradiation at 0 °C with a 150 W high pressure
mercury lamp for the period of 3 h. Chromatography on alumina
with diethyl ether/n-hexane (v/v, 1:1) and methanol as eluents af-
forded air-stable, yellow 13 (253 mg, 0.422 mmol, 25%). M.p.
169 °C. MS (FAB): m/z = 600.9 [M]+. IR (KBr): ν = 3206 cm–1 (w),
˜
3057(w), 1990(vs), 1865 (vs), 1854 (vs), 1819 (vs), 1576 (m), 1466
(m), 1440 (s), 1390 (m), 1360 (s), 1287 (m), 1216 (s), 1125 (m), 1077
(m), 990 (m), 719 (s), 704 (s), 694 (s), 683 (s). 1H NMR [300 MHz,
(CD3)2SO]: δ = 1.80 (s, 6 H, CH3), 3.84 (s, 3 H, CH3), 6.69–7.19
[2]
3
3
(m, 10 H, C6H5), 7.54 (d, J = 1.6 Hz, 1 H, C3H2N2), 7.67 (d, J
= 1.6 Hz, 1 H, C3H2N2) ppm. 13C NMR [75.432 MHz, (CD3)2SO]:
δ = 27.6 and 64.4 [C(CH3)2], 119.6, 121.2, 122.7, 124.3, 127.1,
127.4, 127.7, 128.1, 136.1, and 155.5 (C6H5, C3H2N2), 184.2
(C=N), 192.4 (1JC,W = 95 Hz, carbene C), 205.3 [1JC,W = 129 Hz,
W(CO)axial], 210.1 [1JC,W = 146 Hz, W(CO)equatorial], 218.2 [1JC,W
=
169 Hz, W(CO)equatorial]
ppm. 183W NMR [12.483 MHz,
[3]
[4]
a) D. S. McGuiness, V. C. Gibson, D. F. Wass, J. W. Steed, J.
Am. Chem. Soc. 2003, 125, 12 716; b) M. Tilset, O. Andell, A.
Dhindsa, M. Froseth (Borealis Technology Oy, Finland), WO
2002049758; Chem. Abstr. 2002, 137, 63615.
(CD3)2SO, vs. saturated aqueous Na2WO4]: δ = –2569 [W(CO)4]
ppm. C24H21N3O4W (599.28): calcd. C 48.10, H 3.53, N 7.01;
found C 47.97, H 3.52, N 6.97.
Recent reviews: a) Late Transition Metal Polymerization Catal-
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Crystallography: Crystallographic data for 8, 12a, 12b, and 13 are
given in Table 2. The data collection was performed on a Nonius
Kappa-CCD equipped with graphite-monochromated Mo-Kα radi-
ation (λ = 0.71073 Å) and a nominal crystal-to-area-detector dis-
tance of 36 mm. Intensities were integrated using DENZO and
scaled with SCALEPACK.[14] Several scans in φ and ω direction
were made to increase the number of redundant reflections, which
were averaged in the refinement cycles. This procedure replaces an
empirical absorption correction. The structures were solved by di-
rect methods (SHELXS-86) and refined against F2 (SHELX-97).[15]
Hydrogen atoms at carbon atoms were added geometrically and
refined using a riding model. All non-hydrogen atoms were refined
with anisotropic displacement parameters.
The structure determination of 13 was complicated by two crystal-
lographic characteristics. First, several crystals were examined and
showed systematic twinning. The best crystal was measured and
the 20 worst overlying reflections were omitted in the refinement.
Second, the correct determination of the space group because of a
possible transformation to bravais lattice higher in symmetry. In
the triclinic space group were two identical molecules, which can
be transferred into each other by refinement in the monoclinic
space group C2/c. Nevertheless, the space group C2/c was excluded
because the Rint value of 0.176 for 8154 symmetry-equivalent reflec-
tions is much higher than the Rint value of 0.038 for 4919 reflections
in the triclinic space group. In addition, the conventional R1 value
of 0.0750 is also higher (0.0542). The unit cell constants of the
transformed C-centered lattice are 3958.4, 856.6, 136.39 pm and
90.04, 97.48, 91.42°. The deviation of the angle γ from over 1° to
the correct 90° angle is also too high for this monoclinic space
group.
[5]
[6]
[7]
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Chem. 1998, 552, 45; c) W. A. Herrmann, L. J. Goossen,
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Chem. Eur. J. 1996, 2, 1627; e) W. A. Herrmann, L. J. Goossen,
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498, 1.
CCDC-252740 (for 8), -252741 (for 12a), -252742 (for 12b), and
-252743 (for 13) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[13] R. J. Carbajo, L. Zhang, F. Lopez-Ortiz, Magn. Reson. Chem.
1998, 36, 807.
Acknowledgments
[14] Processing of X-ray diffraction data collected in oscillation
mode: Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276,
307.
Support from BASF Aktiengesellschaft, Ludwigshafen, Germany,
is gratefully acknowledged.
[15] G. M. Sheldrick, Program package SHELXTL V.5.1, Bruker
Analytical X-ray Instruments Inc., Madison, USA, 1997.
Received: October 14, 2004
[1] Reviews: a) Carbene Chemistry (Ed.: G. Bertrand), Marcel
Dekker, Inc., New York, 2002; b) W. A. Herrmann, Angew.
Eur. J. Inorg. Chem. 2005, 1325–1333
www.eurjic.org
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