N-Heterocyclic carbenes with N-ferrocenyl-N′-methyl-substitution: Synthesis, reactivity, structure and electrochemistry

Article abstract of DOI:10.1016/S0022-328X(98)00943-7

Benzimidazolium salts with one N-ferrocenyl substituent and with one N-methyl substituent are prepared by a synthetic sequence involving coupling of the metallocenyl group to a non-cyclic orthophenylene-diamine precursor, ring closure, and oxidation. From these carbene progenitors a range of carbene derivatives are synthesized, including thiourea, azine, and metal complexes with W(0), Pd(II) and Hg(II). Spectroscopic, structural and electrochemical properties in this series of compounds are compared with those of recently published analogous but methylene-spacered benzimidazoline-2-ylidene derivatives, indicating significant electronic communication between the carbene moiety and the N-ferrocenyl substituent.

Full text of DOI:10.1016/S0022-328X(98)00943-7

Journal of Organometallic Chemistry 572 (1999) 177–187
N-Heterocyclic carbenes with N-ferrocenyl-N%-methyl-substitution:
synthesis, reactivity, structure and electrochemistry
Benno Bildstein a,*, Michael Malaun a, Holger Kopacka a, Karl-Hans Ongania b, Klaus Wurst a
a Institut fu¨r Allgemeine, Anorganische, und Theoretische Chemie Uni6ersita¨t Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria
b Institut fu¨r Organische Chemie Uni6ersita¨t Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria
Accepted 17 August 1998
Abstract
Benzimidazolium salts with one N-ferrocenyl substituent and with one N-methyl substituent are prepared by a synthetic
sequence involving coupling of the metallocenyl group to a non-cyclic orthophenylene-diamine precursor, ring closure, and
oxidation. From these carbene progenitors a range of carbene derivatives are synthesized, including thiourea, azine, and metal
complexes with W(0), Pd(II) and Hg(II). Spectroscopic, structural and electrochemical properties in this series of compounds are
compared with those of recently published analogous but methylene-spacered benzimidazoline-2-ylidene derivatives, indicating
significant electronic communication between the carbene moiety and the N-ferrocenyl substituent. © 1999 Elsevier Science S.A.
All rights reserved.
Keywords: Carbene; Benzimidazoline-2-ylidene; Ferrocene; Azine; Iron; Tungsten; Palladium; Mercury; X-ray structure; Electro-
chemistry
1. Introduction
electron-deficient carbene moiety. We have previously
reported the synthesis, structural properties, and co-
ordination chemistry of imidazoline-2-ylidenes with
pendant ferrocenyl substituents [3]. In these systems
with remote metallocenyl groups the electronic influ-
ence of the ferrocenyl donor is almost negligible, as
expected, due to the saturated spacer between the
pendant ferrocenyl substituent and the central car-
bene moiety. The subject of this paper is to study
analogous systems with non-spacered directly at-
tached ferrocenyl groups which should transfer elec-
tron density onto the carbene moiety and further to
coordinated metal fragments. Because of synthetic
reasons—as outlined below—we first report on benz-
imidazoline-2-ylidenes with one N-metallocenyl group
and one N%-alkyl group; results on symmetric N,N%-
diferrocenyl carbenes will be published in due course
[4].
N-Heterocyclic carbenes are of current interest due
to their anticipated advantageous properties as easily
modified ligands in metal complexes with catalytic
applications [1]. Whereas up to now only organic
substituents have been varied, either to optimize the
catalyst’s performance, or to introduce remote func-
tional groups to immobilize the catalyst on a solid
support, we are interested in the steric and electronic
influences exhibited by ferrocenyl substituents. Steri-
cally, the ferrocenyl moiety represents a quite bulky
group with unique spatial requirements due to its
cylindrical shape, and electronically, the powerful
donor capacity of ferrocene [2] might in principle be
of advantage for an additional stabilization of the
* Corresponding author. E-mail: benno.bildstein@uibk.ac.at.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00943-7

178
B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
Scheme 1. Synthesis of compounds 1–8 (Fc=ferrocenyl).
2. Results and discussion
tions of N-cuprio-N-acetyl ferrocenylamines with bro-
moferrocene [6,7]. N,N%-Diacetyl-orthophenylenedia-
mine has been chosen as starting material because its
two amino groups are already in a favorable position
for the formation of the five-membered ring in step (ii).
Interestingly, mono-N-substitution with one ferrocenyl
group is easily accomplished affording 1 in 62% yield,
but all our attempts to effect di-N,N%-substitution with
a second equivalent of ferrocenyl bromide did not
afford N,N%-diferrocenyl-N,N%-diacetyl-o-phenylenedi-
amine, probably due to steric hindrance. This steric
hindrance is corroborated by the NMR parameter of 1,
indicating two rotational isomers (compare Section 4).
Alkaline hydrolysis of 1 proved possible, but 1-ferro-
cenyl-2-methylbenzimidazole 2 was obtained—instead
of the desired N-ferrocenyl-o-phenylenediamine—by
an intramolecular condensation of mono-deprotected
N-ferrocenyl-N%-acetyl-orthophenylenediamine. Com-
pound 2 is of no further use in N-heterocyclic carbene
chemistry because its 2-methyl group prevents forma-
tion of benzimidazoline-2-ylidene carbenes. We also
note that an attempted analogous ferrocenyl substitu-
tion reaction with N,N%-diformyl-orthophenylenedi-
amine as starting material—with acyl groups which
cannot take part in such an undesired cyclization—
failed.
2.1. Synthesis of N-ferrocenyl azoles
The synthesis of N-ferrocenylated azoles is unexpect-
edly difficult and cannot be achieved by common
preparative methods. The only single report on these
compounds by Babin and coworkers [5] claimed that
ferrocenium salts react with sodium azolides (e.g. imi-
dazolide) in a free radical substitution to afford N-fer-
rocenyl azoles (e.g. N-ferrocenylimidazole) which were
‘characterized’ by observation of the corresponding
parent peaks in the mass spectra. However, in our
hands this reaction did not work at all under a variety
of experimental conditions employing a range of possi-
ble staring materials with no indications of trace
amounts of the desired ferrocenylimidazole. In addi-
tion, other likely methods of synthesis (including Meer-
wein reactions with N-diazonium azoles, substitution
reactions starting from N-iodo azoles, and others) were
investigated by us but met with failure.
Therefore we had to develop a new method of syn-
thesis which relies on (i) linking of the ferrocenyl moi-
ety to a non-cyclic precursor, (ii) subsequent ring
closure, and (iii) oxidation to the target azolium salt
(Scheme 1).
Step (i) in this synthetic sequence is analogous to the
synthesis of ferrocenylamines by cross-coupling reac-
Whereas attachment of a second (bulky) ferrocenyl
group to precursor 1 proved impossible, the corre-

B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
179
37.50(13)°), probably due to crystal packing. The bond
lengths and angles of the N(1)ꢀC(11)ꢀN(2) formami-
dinium subunit (compare Fig. 1) are similar to those of
other azolium salts without metallocenyl substituents
[1,3].
sponding N-ferrocenyl-N%-methyl derivative 3 could be
obtained without problems in 86% yield. Alkaline hy-
drolysis cleanly afforded mono-deprotected 4 and bis-
deprotected
N-ferrocenyl-N%-methyl-orthophenylene-
diamine 5, respectively, dependent on duration of the
reaction. Condensation with aqueous formaldehyde so-
lution resulted in 1-ferrocenyl-3-methyl-benzimidazo-
line 6 which was oxidized with trityl tetrafluoroborate
as a hydride abstracting reagent [8] in 67% yield to
benzimidazolium tetrafluoroborate 7. Ultrasonic pro-
moted anion exchange with sodium iodide in acetone
afforded the corresponding 1-ferrocenyl-3-methyl-benz-
imidazolium iodide 8, albeit in a relatively poor yield of
24%.
2.2. Carbene deri6ati6es of
N-ferrocenyl-N%-methyl-benzimidazoline-2-ylidene
Azolium salts in general are the most convenient
progenitors of N-heterocyclic carbenes, formed by ab-
straction of the proton at the formamidinium carbon
by interaction with a suitable base [1]. Such Wanzlick/
Arduengo carbenes can either be isolated or prepared
in situ and reacted with electrophilic reagents, giving
access to a wide range of derivatives. Therefore we were
interested in synthesizing a representative number of
carbene derivatives of the carbene derived from azolium
salts 7 or 8 to study the influence of the N-ferrocenyl
substituent in comparison to non-metallocenyl systems
as briefly outlined in the introduction. Whereas all our
attempts to generate and isolate the ‘free’ carbene N-
Both benzimidazolium salts 7 and 8 serve as the key
progenitors of all further benzimidazoline-2-ylidene
derivatives in this work. Spectroscopically, 7 and 8
show properties which are very similar for both salts
1
and, most important, with a typical H- and 13C-NMR
signal pattern of ‘regular’ mono-substituted ferrocenyl
groups, indicating no unusual interaction of the directly
attached ferrocene donor with the cationic amidinium
subunit, thereby ruling out any special metallocene
cation stabilization [2] which has been observed in
other ferrocenyl substituted cationic compounds. Struc-
turally (Fig. 1, Table 1), the ferrocenyl substituent of 7
is undistorted with bond distances and angles in line
with the expectations, but the steric bulk of the ferro-
cenyl group in comparison to the N%-methyl-benzimida-
zolium part of the molecule is quite evident. As will be
seen also in the following structures of carbene-deriva-
tives 11 and 12, the ferrocenyl substituent is tilted in
respect to the plane of the N-heterocycle (torsion angle
of Cp-plane C(6)–C(7)–C(8)–C(9)–C(10) versus N-
heterocyclic plane N(1)ꢀC(11)ꢀN(2)ꢀC(13)–C(18)=
ferrocenyl-N%-methyl-benzimidazoline-2-ylidene
met
with failure—under a variety of experimental condi-
tions with respect to choice of solvent and non-nucle-
ophilic base as summarized in reference [1]—the in situ
preparation and derivatization caused no problems.
Scheme 2 shows a reaction wheel starting from benzim-
idazolium salts 7 and 8.
Deprotonation of 7 with potassium tertiary butoxide
in the presence of an excess of elemental sulfur afforded
thiourea 9 in 98% yield. Alternatively, thiocarbonyla-
tion of orthophenylenediamine 5 with one equivalent of
thiophosgene yielded 9 in 49% yield. Interestingly, the
13C chemical shift of the thione carbon (l (CꢁS)=
171.09 ppm) of 9 is detected at significantly higher field
in comparison to the methylene-spacered analogue 1-
(ferrocenylmethyl)-3-methyl-benzimidazoline-2-thione
(l (CꢁS)=198.00 ppm [3]), indicating some electron-
donation of the N-ferrocenyl substituent. This donor-
effect is also corroborated by electrochemical
measurements (see Section 2.3). Thiourea 9 is a possible
starting material for the synthesis of the ‘free’ carbene
N-ferrocenyl-N%-methyl-benzimidazoline-2-ylidene by
reduction with potassium in boiling THF according to
the procedure developed by Kuhn [9], however, in our
case this method failed and no reaction was observed
when 9 and stoichiometric amounts of potassium were
refluxed in THF for 2 days. The reason for this unob-
served reduction of 9 with alkali metal is probably
electronic in origin, because no steric hindrance can be
envisaged in this reaction.
Fig. 1. Molecular structure of the cation of 7, showing the atom
numbering scheme. Selected bond distances (pm) and angles (°):
N(1)–C(11)=133.2(5); N(2)ꢀC(11)=131.2(5); N(1)ꢀC(11)ꢀN(2)=
110.9(3); torsion angle plane C(6)ꢀC(7)ꢀC(8)ꢀC(9)ꢀC(10) vs plane
N(1)-C(11)ꢀN(2)ꢀC(13)ꢀC(18)=37.50(13).
Deprotonation of 7 with methyl lithium and reaction
with 9-diazofluorene gives yellow azine 10, in analogy
to such reactivity of Wanzlick carbenes [10,11].
Whereas azine 10 is readily obtained (albeit in a low

180
B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
Table 1
Crystal data and structure refinement for 7, 11 and 12
7
11
12
Molecular formula
Formula weight
Crystal system
Space group
a (pm)
C18H17BF4FeN2
404.00
Monoclinic
P21/c (No.14)
C
640.08
Monoclinic
P21/n (No.14)
23H16FeN2O5W
C40H32Fe2N4O4W·CH2Cl2
1013.17
Orthorhombic
P212121 (No.19)
1103.0(1)
1095.0(1)
1362.9(2)
b (pm)
1234.7(1)
1277.6(1)
1602.9(2)
c (pm)
1269.4(3)
1541.2(1)
1824.7(2)
h (°)
90
90
90
i (°)
99.85(1)
98.70(1)
90
k (°)
90
1.7033(5)
4
90
2.1313(3)
4
90
3.9862(9)
4
Volume (nm3)
Z
Temperature (K)
218
1.575
0.930
824
218
1.995
6.112
1232
213
1.688
3.777
2000
Dcalc. (mg m−3
)
Absorption coefficient (mm−1
F(000)
)
Color, habit
Crystal size (mm)
Theta range for data collection (°)
Index ranges
Yellow prism
0.70×0.30×0.20
2.80–20.49
05h512, −15k513,
−135l511
1838
1704 (Rint=0.0304)
1488
Orange prism
0.40×0.20×0.20
2.67–23.99
05h512, −15k514,
−175l517
3878
3319 (Rint=0.0373)
2990
C-scan
Yellow rectangular prism
0.37×0.37×0.25
2.54–22.49
−15h514, −15k517,
−15l519
Reflections collected
Independent reflections
Reflections with I\2|(I)
Absorption correction
Max/min transmission
Refinement method
3434
3270 (Rint=0.0319)
2992
None
–
C-scan
0.822 and 0.538
Full-matrix least-squares on
F2
1.000 and 0.689
Full-matrix least-squares on
Full-matrix least-squares on F2
F2
Data/restraints/parameters
Goodness-of-fit on F2
1634/0/255
1.047
3239/0/291
1.088
3205/2/474
1.050
Final R indices [I\2|(I)]
R indices (all data)
R1=0.0320, wR2=0.0815
R1=0.0416, wR2=0.1038
364 and −220
R1=0.0286, wR2=0.0729
R1=0.0341, wR2=0.0774
1717 and −692
R1=0.0397, wR2=0.0990
R1=0.0462, wR2=0.1035
1444 and −1128
Largest difference peak and hole (e
nm−3
)
quite poor y-acceptor ligand comparable to other imi-
dazoline-2-ylidenes [1]. This effect can be attributed to
electron-donation by the directly attached ferrocenyl
substituent in 11, because the otherwise analogous but
yield of 22%), the reaction with the extremely reactive
and electrophilic 4,5-dicyano-2-diazo-imidazole [12–14]
afforded a red solution, most likely an ylidic benzimida-
zolium-azo-dicyanoimidazolide
compound,
which
methylene-spacered
compound
[1,3-di(ferrocenyl-
proved in our hands too unstable to be isolated in
substance, although the positive and negative charge of
this azo-spacered zwitter-ion was expected to be highly
stabilized by the two heterocyclic termini.
methyl) - benzimidazoline - 2 - ylidene]pentacarbonyl -
tungsten(0) shows CꢁO stretching vibrations of 2060,
1971 and 1935 cm−1 [3], comparable to imidazolidine-
2-ylidenes [1]. X-ray quality single crystals could be
obtained for complex 11 (Fig. 2, Table 1), proving the
connectivity of the molecule and allowing comparisons
with solid state structures of related carbene–tungsten
complexes. The metal–carbene bond distance
W(1)ꢀC(11) is 227.0(5) pm, very close in value to the
methylene-spacered analogue (W–Ccarbene=226.4(14)
pm [3]) and the structural features of the coordinated
benzimidazoline (compare Fig. 1) are similar to other
non-ferrocenylated carbene ligands [1]. The ferrocenyl
group is tilted with respect to the benzimidazoline plane
(torsion angle of plane C(6)ꢀC(7)ꢀC(8)ꢀC(9)ꢀC(10) ver-
sus plane W(1)ꢀC(11)ꢀN(2)ꢀC(13)ꢀC(18)=49.47(22)°),
similar as in the progenitor 7.
Metal carbene derivatives of the carbene derived
from 7 or 8 can be prepared by established methods
[1,3] (Scheme 2). Deprotonation with lithium diiso-
propylamide (LDA) and subsequent reaction with
W(CO)5THF afforded mono-substituted complex 11 in
17.5% yield and (although an excess of W(CO)5THF
was employed) bis-substituted complex 12 as the main
product in a yield of 31%. In general, the CꢁO stretch-
ing frequencies in the IR spectrum are a sensitive probe
of the electronic properties of ligands in substituted
carbonyl metal complexes. The observed values of
2060, 1966 and 1898 cm−1 for complex 11 indicate that
N-ferrocenyl-N%-methyl-benzimidazoline-2-ylidene is a

B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
181
Scheme 2. Synthesis of compounds 9–14 (Fc=ferrocenyl).
to start from the corresponding azolium iodide as the
carbene progenitor [1,3]. Due to a very poor solubility
of both compounds 13 and 14 only IR and mass, but
no NMR spectroscopic data are available and, unfortu-
nately, no suitable single crystals could be obtained (in
contrast to methylene-spacered analogues [3]). There-
fore the true structure of palladium complex 14 with
regard to possible different diastereoisomers (cis-trans,
trans-syn, trans-anti) cannot be assigned with the lim-
ited data available and no comparisons with other
N-heterocyclic carbene Pd complexes are possible at
this point.
For the bis-substituted complex 12, which is formed
as the main product in the interaction of in situ gener-
ated carbene with W(CO)5THF, cis and trans isomers
are in principle possible. Experimentally only the cis
isomer is observed according to carbonyl IR stretching
vibrations (1991, 1873, 1854 and 1837 cm−1) and as
can be seen in the crystal structure of 12 (Fig. 3, Table
1). The two ferrocenyl carbene ligands of 12 show
structural parameters analogous to those of mono-sub-
stituted complex 11 (12: W(1)ꢀC(11)=226.5(13) pm;
W(1)ꢀC(31)=227.6(13) pm; tilt angles 49.97(61) and
45.53(60)° for ferrocenes Fe(1) and Fe(2), respectively),
as anticipated. In addition, for both tungsten complexes
11 and 12 staggered conformations with regard to the
benzimidazoline/pentacarbonyltungsten stereochemistry
is observed in the crystalline state, obviously a result of
intramolecular steric hindrance by the bulky ferrocenyl
groups; similar structural features have been reported
for other non-metallocenyl carbene pentacarbonyltung-
sten complexes [1,15].
2.3. Electrochemistry
One objective of this work has been to evaluate the
influence of the directly attached ferrocenyl substituent
in these carbene derivatives in comparison to other
systems with spacered [3] or without [1] metallocenyl
groups. Most conveniently this can be addressed with
cyclic voltammetry by comparing relative shifts in the
half wave potentials of the ferrocene/ferrocenium (Fc/
Fc+) couple. There are, however, some restrictions:
because the presence of iodine ligands or counter-ions
results in overlapping signals (with respect to the Fc/
Fc+signal) [3], cyclic voltammetry of benzimidazolium
Reaction of benzimidazolium salt 8 with metal ac-
etates (M(OAc)2; M=Pd2+, Hg2+) yields the expected
metal carbene products 13 and 14 by in situ deprotona-
tion with acetate as base and subsequent complex for-
mation. In the case of palladium complex 14, iodine is
necessary as a co-ligand; therefore it is most convenient

182
B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
salt 7 (but not 8) was performed and, for similar
reasons and more important because of the poor solu-
bility of metal complexes 13 and 14 no data are avail-
able for these systems. Table 2 summarizes the
electrochemical results obtained for compounds 7, 9,
10, 11 and 12. As can be seen from inspection of Table
2, the half-wave potentials differ significantly, indicat-
ing substantial electronic communication between the
ferrocenyl moiety and the carbene subunit.
In comparison to structurally analogous methylene-
spacered compounds [3], the observed values of the
Fc/Fc+ couple are shifted to higher potentials (7: E1/
2= +0.74 V; CH2-spacered analogue [3]: E1/2= +0.57
V; 9: E1/2= +0.51 V; CH2-spacered analogue [3]: E1/
2= +0.47 V) in consonance with increased electron-
donation by the directly attached ferrocenyl substituent
to the formamidinium or thiourea acceptor moiety.
In the case of azine 10, five distinct redox processes
are observed (Fig. 4). The more cathodic signals at
negative potentials are due to three consecutive reduc-
tions of the N2-fluorene part of the molecule in good
agreement with results obtained on fluorenone azine
(E1/2= −1.37, −0.96 V [16]) and benzophenone azine
(E1/2= −1.40, −0.98 V [17]). The Fc/Fc+ couple
correlates most likely to the signal at +0.48 V, close in
value to ferrocene itself (FcH/FcH+: E1/2= +0.42 V
vs saturated calomel electrode (SCE) [18]), and the
irreversible signal at +1.04 V can be assigned to an
N-centered oxidation of the ferrocenyl-N-heterocycle,
Fig. 3. Molecular structure of 12, showing the atom numbering
scheme. Dichloromethane (solvent molecule) has been omitted for
clarity. Ferrocene carbons are numbered for ferrocene Fe(1) from
C(1) to C(10), and for ferrocene Fe(2) from C(21) to C(30), respec-
tively. Selected bond distances (pm) and angles (°): C(11)ꢀW(1)=
226.5(13); C(11)ꢀN(1)=141(2); C(11)ꢀN(2)=136(2); N(1)ꢀC(18)
=140(2); N(2)ꢀC(13)=139(2); C(13)ꢀC(18)=134(2); N(1)ꢀC(11)
ꢀN(2)=103.7(11); C(11)ꢀN(1)ꢀC(18)=108.7(11); C(11)–N(2)ꢀC(13)
=112.6(12); torsion angle of plane C(6)ꢀC(7)ꢀC(8)ꢀC(9)ꢀC(10) vs
plane W(1)-C(11)ꢀN(2)ꢀC(13)ꢀC(18)=49.97(61); C(31)ꢀW(1)=227.6
(13); C(31)ꢀN(3)=136(2); C(31)ꢀN(4)=139(2); N(3)ꢀC(38)=140(2);
N(4)ꢀC(33)=138.1(14); C(33)ꢀC(38)=137(2); N(3)ꢀC(31)ꢀN(4)=
103.2(10);
C(31)ꢀN(3)ꢀC(38)=113.1(10);
C(31)ꢀN(4)ꢀC(33)=
111.0(9); torsion angle of plane C(26)ꢀC(27)ꢀC(28)ꢀC(29)ꢀC(30) vs
plane W(1)ꢀC(31)ꢀN(4)ꢀC(33)-C(38)=45.53(60).
observed at lower potential in comparison to such
irreversible N-oxidations in non-aromatic ferrocenyl
amines (FcNH2: +1.35; Fc2NH: +1.69; Fc3N: +1.82
V vs SCE [19,20]).
For the two tungsten complexes 11 and 12, the
number of detected redox processes (Fig. 5) does not
parallel—at first sight—the number of ferrocenyl
Table 2
Cyclic voltammetrya of compounds 7, 9, 10, 11 and 12
Compound
number
Formulab
E1/2 (V vs SCE)
7
9
[HL]+BF−4
SL
+0.74
+0.51
10
C13H8N2L
−1.85, −1.42, −1.06, +0.48,
+1.04c
Fig. 2. Molecular structure of 11, showing the atom numbering
scheme. Ferrocene carbons are numbered from C(1) to C(10). Se-
lected bond distances (pm) and angles (°): C(11)ꢀW(1)=227.0(5);
C(11)ꢀN(1)=138.4(7); C(11)ꢀN(2)=136.6(6); N(1)ꢀC(18)=140.9(7);
N(2)ꢀC(13)=138.6(7); C(13)ꢀC(18)=138.5(7); N(1)ꢀC(11)ꢀN(2)=
104.0(4); C(11)ꢀN(1)ꢀC(18)=110.8(4); C(11)ꢀN(2)ꢀC(13)=112.6(4);
torsion angle of plane C(6)–C(7)ꢀC(8)ꢀC(9)ꢀC(10) vs plane
W(1)ꢀC(11)ꢀN(2)ꢀC(13)ꢀC(18)=49.47(22).
11
12
[W(CO)5L]
[W(CO)4L2]
+0.59, +1.05c
+0.37d, +0.75
a In CH3CN solution with 0.1 M [(n-Bu)4N]PF6 electrolyte with a
scan rate of 100 mV s−1 at 20°C.
b L=N-ferrocenyl-N%-methyl-benzimidazoline-2-ylidene.
c Peak potential EPox of irreversible redox process.
d Reversible at a scan rate of 20 mV s−1
.

B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
183
3. Summary and conclusions
The preparation of N-ferrocenylated benzimida-
zolium salts has been achieved by a synthetic sequence of
cross-coupling of bromoferrocene with N-cuprio-N,N%-
diacetyl-phenylenediamine, N%-alkylation, hydrolysis of
the acetyl groups, ring closure with formaldehyde, and
oxidation with trityl tetrafluoroborate. These are the first
azolium compounds with directly attached N-ferrocenyl
substituents. In situ deprotonation afforded 1-ferro-
cenyl-3-methyl-benzimidazoline-2-ylidene carbene which
was reacted with various selected reagents, yielding the
respective thiourea, fluorene azine, and metal complexes
of W(0), Hg(II) and Pd(II). Spectroscopic, structural and
electrochemical parameters of these N-ferrocenyl-N-het-
erocyclic carbene derivatives have been compared with
those of non-ferrocenylated and alkyl-spacered ana-
logues, respectively, showing that directly linked ferro-
cenyl substituents exhibit mainly an electronic inductive
donor effect, indicated by the cyclic voltammetry results.
Fig. 4. Cyclic voltammetry of 10.
groups in these two compounds; in both cases two
signals were obtained. Mono-carbene complex 11 ex-
hibits, as expected, a reversible first oxidation at +0.59
V which is assigned to the Fc/Fc+ couple and an
irreversible second N-centered oxidation at a potential
similar to that of azine 10. In contrast, bis-carbene
complex 12 shows two reversible waves at +0.37 and
+0.75 V which might be either assigned to two consec-
utive Fc/Fc+ couples or to one Fc/Fc+ couple fol-
4. Experimental part
4.1. General techniques and instrumentation
lowed by
a
reversible N-centered oxidation.
Interestingly, the second redox couple in the bis-substi-
tuted complex 12 is at a potential similar to that of
benzimidazolium tetrafluoroborate 7 (but much lower
than all other measured N-centered oxidations) indicat-
ing quite efficient electronic coupling between the two
ferrocenyl groups under the assumption that two con-
secutive ferrocene oxidations and no N-centered oxida-
tion occur in this complex. The pentacarbonyltungsten
fragment seems to be a superior acceptor to sulfur
(compare E1/2 of 9 and 11) in contrast to a tetracar-
bonyltungsten(monocarbene) moiety which shifts the
first Fc/Fc+ redox process to a potential more negative
than those in 9 or in ferrocene, respectively.
Reactions of air-sensitive materials were carried out
using standard Schlenk techniques and vacuum-line
manipulations. Solvents were deoxygenated, purified,
and dried prior to use. Standard instrumentation was as
recently published [3]. Cyclic voltammetric measure-
ments were performed at room temperature with a POS
88 Potentiostat (Bank Elektronik), using a standard
three electrode apparatus, an atmosphere of purified
argon, acetonitrile as solvent, a scan rate of 100 mV
s
−1, and 0.1 M tetrabutylammonium hexafluorophos-
phate ([TBA]PF6) as the conducting salt. The signals
were referenced to the SCE by calculating the corre-
sponding half wave potentials from cobaltocenium/
cobaltocene as an internal standard versus SCE
(cobaltocene: E1/2= −0.93 V vs SCE).
4.2. X-ray structure determinations of 7, 11 and 12
X-ray crystallographic data (Table 1) were collected
by
a
Siemens P4 diffractometer with graphite-
monochromatized Mo–Kh radiation (u=71.073 pm).
The unit cell parameters were determined from 25
randomly selected reflections, obtained by P4 automatic
routines. Data were measured via ꢀ-scan and corrected
for Lorentz and polarisation effects, an empirical ab-
sorption correction, based on C-scans, was applied.
The structures were solved by direct methods
(SHELXS-86) [21] and refined by a full matrix least-
squares procedure using F2 (SHELXL-93) [22]. The
Fig. 5. Cyclic voltammetry of 11 and 12.

184
B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
function minimized was S[w(F20−Fc2)2] with the weight
defined as w−1=[|2(F02)+(xP)2+yP] and P=(F20+
2F2c)/3. All non-hydrogen atoms were refined with an-
isotropic displacement parameters. Hydrogen atoms
were located by difference Fourier methods, but in the
refinement they were included in calculated positions
and refined with isotropic displacement parameters 1.2
and 1.5 (for methyl hydrogen atoms) times higher than
Ueq of the attached atoms. Further details of the crystal
structure investigations of 7, 11 and 12 are available
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge, CB2 1EZ, UK, on quoting
the full journal citation.
w, 1285 w, 1261 w, 1103 m, 1070 m, 1059 m, 1028 s,
1001 s, 825 s, 800 s, 750 s, 503 s, 486 s, 441 m. MS(EI,
70 eV): m/z(%) 316(100) (M+), 251(43) (M+ –Cp),
195(25) (M+ –FeCp), 121(39) (FeCp). 1H-NMR
(CDCl3): l 2.61 (s, 3H, CH3), 4.24 (s, 5H, Cpunsubst),
4.26 (m, 2H, Cpsubst), 4.56 (m, 2H, Cpsubst), 7.16–7.30
(m, 2H, phenylene), 7.62–7.67 (m, 1H, phenylene),
7.97–8.01 (m, 1H, phenylene). 13C-NMR (CDCl3): l
15.76 (CH3); 63.40, 65.62, 69.59, 93.72 (Fc); 111.90,
119.01, 122.01, 122.14, 135.52, 142.67, 152.60
(phenylene).
4.5. N-Ferrocenyl-N%-methyl-N,N%-diacetyl-o-
phenylenediamine 3
4.3. N-ferrocenyl-N,N%-diacetyl-o-phenylenediamine 1
A solution of 1.673 g (4.4 mmol) 1 in 100 ml THF
was cooled to −80°C and metalated with 3.0 ml (4.5
mmol) of a 1.5 molar t-butyl lithium solution in pen-
tane. The mixture was allowed to warm to room tem-
perature and 0.28 ml (4.5 mmol) methyl iodide was
added. Aqueous work-up yielded 1.5 g (3.8 mmol, 86%)
3. Yellow crystals, m.p. 193°C. Anal. Found: C, 64.50;
H, 5.67 C21H22FeN2O2. Calc.: C, 64.63; H, 5.68%.
IR(KBr): cm−1 2932 w, 1647 s (CO), 1595 s, 1497 s,
1460 s, 1379 s, 1331 m, 1261 w, 1207 w, 1150 m, 1107
w, 1086 w, 1032 w, 1003 m, 937 w, 823 m, 771 m, 727
w, 648 w, 613 w, 571 w, 499 w. MS(EI, 75 eV): m/z(%)
390(11) (M+), 332(100) (M+ –COCH3–CH3), 325(6)
(M+ –Cp), 267(90) (M+ –CH3CO–CH3–Cp), 121(14)
(FeCp). 1H-NMR (CDCl3): l 1.89 (s, 3H, CH3), 3.01 (s,
3H, CH3), 3.12 (s, 3H, CH3), 3.79 (m, 1H, Cpsubst), 3.84
(m, 1H, Cpsubst), 3.91 (m, 2H, Cpsubst), 4.21 (s, 5H,
Cpunsubst), 7.08–7.38 (m, 4H, phenylene). 13C-NMR
(CDCl3): l 21.86, 36.26, 40.45 (CH3); 57.64, 57.84,
63.58, 63.71, 68.06 (Fc); 124.58, 125.72, 128.36, 128.84
(phenylene), 159.63 (CO).
A mixture of 2.18 g (11.3 mmol) N,N%-diacetyl-o-
phenylenediamine and 0.49 g (12.5 mmol) sodium
amide in 100 ml toluene was refluxed for 1 h. Solvent
and volatile materials were removed in vacuo, the re-
sulting crude white residue was dissolved in 100 ml
toluene, and 1.63 g (11.3 mmol) Cu(I)Br, 4 ml pyridine,
and 3 g (11.3 mmol) bromoferrocene were added. After
refluxing the mixture for 3 days a tan suspension was
obtained. Work-up: solvents were removed in vacuo in
a rotary evaporator and the crude product was chro-
matographed on Al2O3, first eluting unreacted bromo-
ferrocene and biferrocene with dichloromethane as
eluent, and second eluting the product with ethyl ac-
etate as eluent, yielding 2.65 g (7 mmol, 62.1%) 1.
Yellow crystals, m.p. 210°C. Anal. Found: C, 63.59; H,
5.63 C20H21FeN2O2. Calc.: C, 63.68; H, 5.61%.
IR(KBr): cm−1 3314 w (N–H), 2965 w, 1696 s (CO),
1655 s (CO), 1593 s, 1524 s, 1452 s, 1375 m, 1331 s,
1298 m, 1246 w, 1103 m, 1043 w, 829 m, 820 m, 769 s,
486 m, 478 m. MS(EI, 70 eV): m/z(%) 376(100) (M+),
334(52) (M+ –COCH3), 312(26) (M+ –Cp), 227(36)
(FcNCO), 199(47) (FcN), 121(26) (FeCp). 1H-NMR
(CDCl3): l 1.82 (s, 3H, CH3), 2.08 (s, 3H, CH3), 3.39 (s,
5H, Cpunsubst), 4.06 (br s, 2H, Cpsubst), 4.09 (br s, 2H,
Cpsubst), 4.76 (s, 0.5H, NH), 7.16–7.43 (m, 4H,
phenylene), 8.32 (s, 0.5H, NH). 13C-NMR (DMSO-d6):
l 22.67, 23.46, 24.54 (CH3); 62.25, 63.32, 64.79, 65.73,
68.70 (Fc); 122.96, 123.89, 125.01, 127.25, 128.65,
129.46, 129.99, 134.27, 135.25 (phenylene); 168.68,
169.34 (CO).
4.6. N-Ferrocenyl-N%-methyl-N%-acetyl-o-
phenylenediamine 4
A mixture of 0.25 g (0.6 mmol) 3 and 2.0 g (36
mmol) KOH in 15 ml Ar-saturated ethanol was
refluxed for 5 h. Aqueous work-up yielded 0.199 g (0.5
mmol, 98%) 4. Yellow crystals, m.p. 100° dec. Anal.
Found: C, 65.42; H, 5.77 C19H20FeN2O. Calc.: C,
65.53; H, 5.79%. IR(KBr): cm−1 3299 w (NH), 2961 w,
2927 w, 1655 s (CO), 1605 s, 1589 s, 1530 s, 1483 w,
1470 m, 1458 m, 1385 w, 1314 m, 1142 w, 1105 w, 1070
m, 1047 m, 1036 m, 1020 m, 812 s, 503 w. MS(EI, 75
eV): m/z(%) 348(100) (M+), 305(21) (M+ –COCH3),
283(20) (M+ –Cp), 239(35) (M+ –CH3CO–Cp),
149(85) (M+ –Fc–CH3), 121(53) (FeCp). 1H-NMR
(CDCl3): l 1.88 (s, 3H, CH3), 3.21 (s, 3H, CH3), 4.06
(m, 2H, Cpsubst), 4.16 (s, 5H, Cpunsubst), 4.21 (m, 1H,
Cpsubst), 4.29 (m, 1H, Cpsubst), 5.08 (s, 1H, NH), 7.15–
4.4. 1-Ferrocenyl-2-methylbenzimidazole 2
A mixture of 0.145 g (0.4 mmol) 1 and 0.60 g (11
mmol) KOH in Ar-saturated ethanol was refluxed for 3
h. Aqueous work-up yielded 109 mg (0.3 mmol, 89%) 2.
Yellow crystals, m.p. 165–168°C. Anal. Found: C,
68.32; H, 5.12 C18H16FeN2. Calc.: C, 68.38; H, 5.10%.
IR(KBr): cm−1 2963 w, 2927 w, 1524 m, 1497 s, 1387

B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
185
7.23 (m, 4H, phenylene). 13C-NMR (CDCl3): l 21.94,
35.41 (CH3); 62.26, 63.07, 64.74, 64.81, 69.02, 98.54
(Fc); 114.14, 118.50, 127.81, 129.12 (phenylene), 172.18
(CO).
53.41; H, 4.22 C18H17BF4FeN2. Calc.: C, 53.51; H,
4.24%. IR(KBr): cm−1 3073 w, 1634 m, 1568 s, 1503 w,
1489 w, 1456 w, 1410 w, 1263 w, 1246 w, 1178 w, 1124
s, 1107 s, 1084 s, 1038 s, 1003 s, 866 w, 835 w, 777 w,
758 m, 534 m, 497 m. MS(FAB): m/z(%) 317(100)
(M+of cation). 1H-NMR (CDCl3): l 4.21 (s, 3H, CH3),
4.33 (s, 5H, Cpunsubst), 4.36 (m, 2H, Cpsubst), 4.85 (m,
2H, Cpsubst), 7.60–7.86 (m, 4H, phenylene), 9.60 (s, 1H,
NꢁCH–N). 13C-NMR (CDCl3): l 33.68 (CH3); 64.15,
67.68, 70.49, 91.04 (Fc); 113.37, 113.86, 127.39, 127.50,
132.00, 132.26 (phenylene); 142.11 (NꢁCH–N). CV
(CH2Cl2, 20°C) [V]: +0.74. Single crystals were ob-
tained from layering a CH2Cl2 solution with n-hexane
(Fig. 1, Table 1).
4.7. N-ferrocenyl-N%-methyl-o-phenylenediamine 5
A mixture of 0.25 g (0.6 mmol) 3 and 2.0 g (36
mmol) KOH in 30 ml Ar-saturated ethanol was
refluxed for 20 h. Aqueous work-up yielded 0.167 g
(0.55 mmol, 85%) 5. Yellow crystals, m.p. dec. Anal.
Found: C, 66.73; H, 5.95 C17H18FeN2. Calc.: C, 66.69;
H, 5.93%. IR(KBr): cm−1 3357 w (NH), 2963 w, 1603
s, 1516 s, 1495 s, 1452 w, 1435 w, 1283 m, 1263 s, 1165
w, 1105 s, 1040 m, 1022 m, 1001 w, 814 s, 742 s, 488 m.
MS(EI, 70 eV): m/z(%) 306(100) (M+), 290(37) (M+
4.10. 1-Ferrocenyl-3-methylbenzimidazolium iodide 8
1
–CH3), 236(45) (M+ –Cp), 121(54) (FeCp). H-NMR
(CDCl3): l 2.85 (s, 3H, CH3), 3.64 (s, 1H, NH), 3.99
(m, 2H, Cpsubst), 4.07 (m, 2H, Cpsubst), 4.19 (s, 5H,
Cpunsubst), 4.35 (s, 1H, NH), 6.69–7.24 (m, 4H,
phenylene). 13C-NMR (CDCl3): l 30.85 (CH3); 59.58,
63.84, 68.65, 103.78 (Fc); 110.85, 117.87, 118.31,
122.60, 132.94, 141.09 (phenylene).
To a solution of 1.824 g (4.5 mmol) 7 in 50 ml
acetone was added an excess of sodium iodide and the
mixture was sonicated in an ultrasonic cleaning bath
for 10 min. Acetone was removed on a rotary evapora-
tor and the residue was washed with portions of H2O
until TLC showed no remaining traces of 7. In this
manner, 0.477 g (1.1 mmol, 24%) 8 was obtained.
Yellow crystals, m.p. 198–200°C. Anal. Found: C,
48.59; H, 3.87 C18H17FeIN2. Calc.: C, 48.68; H, 3.86%.
IR(KBr): cm−1 3066 m, 2965 m, 1611 m, 1570 s, 1503
w, 1487 w, 1456 m, 1412 w, 1315 w, 1263 m, 1250 m,
1180 w, 1136 w, 1105 m, 1030 w, 1003 w, 866 m, 821 m,
777 m, 756 s, 609 w, 499 s. MS(FAB): m/z(%) 317(100)
4.8. 1-Ferrocenyl-3-methyl-benzimidazoline 6
A solution of 0.937 g (3.1 mmol) 5 in 20 ml acetone
was mixed with 3.0 g of a 35% aqueous solution of
formaldehyde (35 mmol) and with 10 ml H2O. After
stirring the mixture at room temperature for 12 h, 100
ml H2O was added to precipitate the product, yielding
0.543 g (1.7 mmol, 56%) 6. Yellow crystals, m.p. dec.
Anal. Found: C, 67.80; H, 5.72 C18H18FeN2. Calc.: C,
67.94; H, 5.70%. IR(KBr): cm−1 2923 w, 2861 w, 2797
w, 1601 w, 1518 s, 1474 s, 1452 w, 1310 m, 1296 s, 1271
m, 1130 m, 1103 s, 1090 m, 1049 w, 1032 w, 1014 w,
999 w, 833 m, 818 m, 806 m, 740 s, 731 s, 495 s, 486 s.
MS(EI, 75 eV): m/z(%) 318(100) (M+), 253(5) (M+
–Cp), 197(22) (M+ –FeCp), 186(68) (Fc), 121(18)
1
(M+ of cation). H-NMR (DMSO-d6): l 3.33 (s, 3H,
CH3), 4.40 (s, 5H, Cpunsubst), 4.52 (m, 2H, Cpsubst), 5.06
(m, 2H, Cpsubst), 7.72–8.16 (m, 4H, phenylene), 10.04
(s, 1H, NꢁCH–N). 13C-NMR (DMSO-d6): l 33.45
(CH3); 63.59, 67.27, 70.15, 91.16 (Fc); 113.87, 114.17,
126.77, 127.05, 131.00, 132.03 (phenylene); 142.99
(NꢁCH–N).
1
4.11. 1-Ferrocenyl-3-methyl-benzimidazoline-2-thione 9
(FeCp). H-NMR (CDCl3): l 2.81 (s, 3H, CH3), 4.02
(m, 2H, Cpsubst), 4.17 (s, 5H, Cpunsubst), 4.22 (m, 2H,
Cpsubst), 4.78 (s, 2H, CH2), 6.45–7.61 (m, 4H,
phenylene). 13C-NMR (CDCl3): l 34.28 (CH3); 57.53,
63.79, 68.09 (Fc); 76.32 (CH2); 105.79, 107.43, 118.76,
119.27 (phenylene).
Method (a) is thionation of the in situ generated
benzimidazoline-2-ylidene.
A
Schlenk vessel was
charged with 0.137 g (0.34 mmol) 7 in 20 ml THF, 0.2
g (1.8 mmol) KOtBu, and 0.3 g (1.2 mmol) sulfur at
room temperature. After stirring for 3 h, the mixture
was filtered through a short plug of Al2O3 and worked-
up in the usual manner, yielding 115 mg (0.33 mmol,
98%) 9.
4.9. 1-Ferrocenyl-3-methylbenzimidazolium
tetrafluoroborate 7
Method (b) is thiocarbonylation of ortho-phenylene-
diamine 5. A Schlenk vessel was charged with 2.33 g
(7.6 mmol) 5 in 100 ml toluene, 2.2 ml (30 mmol)
triethylamine, and 0.58 ml (7.6 mmol) thiophosgene.
The mixture was stirred at ambient temperature for 2
days and worked-up in the usual manner, yielding 1.3 g
(0.37 mmol, 49%) 9.
A solution of 543 mg (1.7 mmol) 6 in 20 ml
dichloromethane was cooled to −80°C and 564 mg
(1.7 mmol) tritylium tetrafluoroborate was added. The
mixture was stirred for 2 h and the product was precip-
itated by addition of 40 ml ether. Chromatography
(Al2O3; CH2Cl2/CH3CN 1/1) yielded 0.469 g (1.1 mmol,
67%) 7. Yellow crystals, m.p. 65°C. Anal. Found: C,

186
B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
tion of W(CO)5 ·THF was added to the benzimidazo-
line-2-ylidene derived from 7. After stirring at room
temperature for 30 min the mixture was worked-up and
chromatographed, yielding 224 mg (0.35 mmol, 17.5%)
11 and 291 mg (0.31 mmol, 31.0%) 12.
Data for 9: yellow crystals, m.p. 65°C. Anal. Found:
C, 62.13; H, 4.61 C18H16FeN2S. Calc.: C, 62.08; H,
4.63%. IR(KBr): cm−1 2925 w, 1723 m, 1634 s, 1497 s,
1474 m, 1410 m, 1383 m, 1371 m, 1339 s, 1302 m, 1232
m, 1200 s, 1122 w, 1107 w, 1028 w, 1003 w, 874 w, 821
m, 740 s, 632 w, 559 w, 499 s, 424 w. MS(EI, 70 eV):
Data for 11: yellow crystals, m.p. 210°C. Anal.
Found: C, 43.08; H, 2.51. C23H16FeN2O5W. Calcd.: C,
43.16; H, 2.52%. IR(KBr): cm−1 2060 s (wCꢁO), 1966 s
(wCꢁO), 1898 s (wCꢁO), 1638 s, 1491 w, 1470 w, 1431 w,
1369 w, 1342 w, 1180 m, 1107 w, 1086 w, 1057 w, 1024
w, 818 m, 754 m, 748 w, 609 w, 590 w, 580 w, 495 w,
478 w. MS(EI, 70 eV): m/z(%) 640(25) (M+), 612(23)
(M+ –CO), 556(27) (M+ –3CO), 528(12) (M+
1
m/z(%) 348(62) (M+), 283(100) (M+ –Cp). H-NMR
(CDCl3): l 3.88 (s, 3H, CH3), 4.29 (s, 5H, Cpunsubst),
4.34 (m, 2H, Cpsubst), 5.08 (m, 2H, Cpsubst), 7.18–8.14
(m, 4H, phenylene). 13C-NMR (CDCl3): l 31.58 (CH3);
65.37, 65.58, 69.89, 93.44 (Fc); 108.95, 112.04, 122.64,
123.38, 132.33, 132.88 (phenylene); 171.09 (CꢁS). CV
(CH2Cl2, 20°C) [V]: +0.51.
1
–4CO), 500(100) (M+ –5CO). H-NMR (CD2Cl2): l
4.12. [1-Ferrocenyl-3-methyl-benzimidazoline-
2-ylidene]-[ fluorene-9-ylidene]-hydrazine 10
4.12 (s, 3H, CH3), 4.29 (s, 5H, Cpunsubst), 4.46 (m, 2H,
Cpsubst), 4.86 (m, 2H, Cpsubst), 7.37–8.65 (m, 4H,
phenylene). 13C-NMR (CD2Cl2): l 37.95 (CH3), 66.44,
67.71, 70.24 (Fc); 110.38, 114.29, 122.77, 124.00
(phenylene); 198.50, 201.68 (only two out of three low
field signals were detected: CO and/or carbene–C). CV
(CH2Cl2, 20°C) [V]: +0.59, +1.05. Single crystals
were obtained from N-hexane/CH2Cl2 (Fig. 2, Table 1).
Data for 12: yellow crystals, m.p. 140°C. Anal.
Found: C, 51.70; H, 3.45. C40H32Fe2N4O4W. Calc.: C,
51.76; H, 3.47%. IR(KBr): cm−1 1991 s (wCꢁO), 1873 s
(wCꢁO), 1854 s (wCꢁO), 1837 s (wCꢁO), 1638 w, 1495 m,
1472 m, 1427 w, 1362 w, 1337 m, 1317 w, 1290 m, 1263
m, 1173 w, 1153 m, 1128 w, 1105 w, 1074 w, 1061 w,
1022 w, 1003 w, 827 m, 746 m, 615 w, 497 m. MS(EI,
70 eV): m/z(%) 928(9) (M+), 900(9) (M+ –CO),
872(11) (M+ –2CO), 844(9) (M+ –3CO), 816(20)
(M+ –4CO), 317(100) (ferrocenylmethylbenzimidazo-
line–2-ylidene). 1H-NMR (CD2Cl2): l 3.88 (s, 6H,
CH3), 4.01 (m, 4H, Cpsubst), 4.13 (s, 10H, Cpunsubst),
4.46 (m, 4H, Cpsubst), 7.24–8.46 (m, 8H, phenylene).
13C-NMR (CD2Cl2): l 37.06 (CH3), 64.88, 66.28, 69.59,
97.32 (Fc); 109.69, 113.44, 121.75, 123.09, 128.22,
135.42 (phenylene); 209.99 (only one out of three ex-
pected low field signals were detected: carbene–C or
C=O). CV (CH2Cl2, 20°C) [V]: +0.37, +0.75. Single
crystals were obtained from n-hexane/CH2Cl2 (Fig. 3,
Table 1).
A solution of 0.14 g (0.3 mmol) 7 in 20 ml THF was
metalated with 0.23 ml of a 1.5 molar methyl lithium
solution (0.3 mmol) in ether at −80°C, the mixture
was allowed to warm to room temperature, a solution
of 66 mg (0.3 mmol) 9-diazofluorene in 15 ml THF was
added dropwise, and stirring was continued for 30 min.
Aqueous work-up and chromatography (Al2O3; hex-
ane/ether 4/1) yielded 71 mg (0.1 mmol, 22.2%) 10.
Yellow crystals, m.p. 163°C. Anal. Found: C, 73.15; H,
4.75 C31H24FeN4. Calc.: C, 73.24; H, 4.76%. IR(KBr):
cm−1 2959 w, 2923 m, 2851 s, 1728 m, 1597 m, 1526 m,
1495 m, 1474 s, 1449 m, 1429 m, 1393 s, 1377 w, 1352
w, 1321 w, 1261 w, 1155 w, 1099 m, 1074 s, 1020 w, 804
w, 733 s. MS(EI, 70 eV): m/z(%) 508(100) (M+),
1
443(98) (M+ –Cp). H-NMR (CDCl3): l 4.13 (s, 3H,
CH3), 4.23 (s, 5H, Cpunsubst), 4.31 (m, 2H, Cpsubst), 4.94
(m, 2H, Cpsubst), 6.90-8.90 (m, 12H, phenylene+
fluorene). 13C-NMR (CDCl3): l 29.69 (CH3); 64.99,
65.09, 69.35 (Fc); 107.25, 110.96, 119.38, 119.50,
120.02, 120.12, 120.67, 121.42, 121.92, 122.89, 127.08,
127.47, 127.78, 127.93, 128.02, 128.20, 128.23, 128.62,
129.82, 130.96, 131.38 (phenylene+fluorene+CꢁN–
NꢁC). CV (CH2Cl2, 20°C) [V]: −1.85, −1.42, −1.06,
+0.48, +1.04.
4.13. [1-Ferrocenyl-3-methyl-benzimidazoline-2-ylidene]
pentacarbonyl tungsten(0) 11 and bis[1-ferrocenyl-3-
methyl-benzimidazoline-2-ylidene]tetracarbonyl
tungsten(0) 12
4.14. Bis[1-ferrocenyl-3-methyl-benzimidazoline-2-
ylidene]mercury(II) diiodide 13
A mixture of 121 mg (0.27 mmol) 8 and 87 mg (0.27
mmol) mercury(II) acetate was refluxed in THF for 30
min. During this reflux period a color change yellow–
brown–tan took place. THF was removed on a rotary
evaporator, the residue was washed with three portions
of ether, and the crude product was dissolved in
dichloromethane and crystallized by addition of a small
layer of hexane, yielding 84 mg (0.08 mmol, 28.4%) 13.
A Schlenk vessel was charged with 0.8 g (2.0 mmol)
7 and 200 ml THF. The mixture was cooled to −80°C
and lithiated with lithium diisopropylamide (1.0 ml of a
2.0 molar hexane solution, 2.0 mmol). While this solu-
tion was allowed to warm to room temperature, a
second Schlenk vessel was charged with 1.3 g (3.7
mmol) W(CO)6 and 50 ml THF, and photolyzed with a
150 W high pressure mercury lamp. The resulting solu-

B. Bildstein et al. / Journal of Organometallic Chemistry 572 (1999) 177–187
187
Yellow crystals, m.p. 180°C. Anal. Found: C, 39.68; H,
References
2.96. C36H32Fe2N4HgI2. Calc.: C, 39.79; H, 2.97%.
IR(KBr): cm−1 3081 w, 1549 s, 1497 s, 1478 s, 1449 m,
1402 s, 1385 s, 1339 m, 1258 m, 1136 w, 1107 s, 1030 m,
1005 m, 962 w, 872 w, 829 s, 810 s, 752 s, 659 w, 553
w, 497 s. MS(FAB): m/z(%) 961(15) (M+ –I+H),
831(15) (M+ –2I–H), 645(100) (M+ –HgI). NMR
analysis was precluded by insufficient solubility.
[1] W.A. Herrmann, C. Ko¨cher, Angew. Chem. 109 (1997) 2257;
Angew. Chem. Int. Ed. Engl. 36 (1997) 2162; and references
cited therein.
[2] J. Lukasser, H. Angleitner, H. Schottenberger, H. Kopacka, M.
Schweiger, B. Bildstein, K.-H. Ongania, K. Wurst, Organometal-
lics 14 (1995) 5566.
[3] B. Bildstein, M. Malaun, H. Kopacka, K.-H. Ongania, K.
Wurst, J. Organomet. Chem. 552 (1998) 45.
[4] B. Bildstein, M. Malaun, K. Wurst, submitted for publication.
[5] V.N. Babin, Yu.A. Belousov, V.V. Gumenyuk, R.B. Ma-
terikova, R.M. Salimov, N.S. Kochetkova, J. Organomet. Chem.
214 (1981) 13.
4.15. Bis[1-ferrocenyl-3-methyl-benzimidazoline-2-
ylidene]diiodopalladium(II) 14
[6] M. Herberhold, M. Ellinger, L. Haumaier, Organomet. Synth. 3
(1986) 81.
[7] M. Herberhold, M. Ellinger, U. Thewalt, F. Stollmaier, Angew.
Chem. 94 (1982) 70; Angew. Chem. Int. Ed. Engl. 21 (1982) 74;
Angew. Chem. Suppl. (1982) 98.
A mixture of 0.2 g (0.45 mmol) 8 and 51 mg (0.23
mmol) Pd(II) acetate was refluxed in 25 ml THF for 30
min. During this reflux period a color change yellow–
brown–tan took place. THF was removed on a rotary
evaporator, the residue was washed with three portions
of ether, and the crude product was dissolved in
dichloromethane and crystallized by addition of a small
layer of hexane, yielding 185 mg (0.2 mmol, 83%) 14.
Yellow crystals, m.p. not observed up to 350°C. Anal.
Found: C, 43.47; H, 3.24. C36H32Fe2N4PdI2. Calc.: C,
43.56; H, 3.25%. IR(KBr): cm−1 2963 w, 2927 w, 1634
w, 1501 m, 1474 s, 1439 m, 1410 m, 1389 w, 1341 w,
1302 w, 1261 s, 1242 m, 1209 w, 1105 s, 1026 s, 872 w,
804 s, 744 s, 704 w, 497 m, 443 w. MS(FAB): m/z(%)
991.92(100) (M+). NMR analysis was precluded by
insufficient solubility.
[8] D.A. Straus, C. Zhang, T.D. Tilley, J. Organomet. Chem. 369
(1989) 13.
[9] N. Kuhn, T. Kratz, Synthesis (1993) 561.
[10] H.W. Wanzlick, B. Ko¨nig, Chem. Ber. 97 (1964) 3513.
[11] H. Reimlinger, Chem. Ber. 97 (1964) 3503.
[12] W.A. Sheppard, O.W. Webster, J. Am. Chem. Soc. 95 (1973)
2695.
[13] P. Gronski, K. Hartke, Chem. Ber. 111 (1978) 272.
[14] G. Tappeiner, B. Bildstein, F. Sladky, Chem. Ber. 124 (1991)
699.
[15] W.A. Herrmann, L.J. Goossen, G.R.J. Artus, C. Ko¨cher,
Organometallics 16 (1997) 2472.
[16] K.L. Handoo, Indian J. Chem. 16a (1978) 63.
[17] F.M. Triebbe, M.D. Hawley, J. Electroanal. Chem. 125 (1981)
421.
[18] B. Bildstein, A. Hradsky, H. Kopacka, R. Malleier, K.-H.
Ongania, J. Organomet. Chem. 540 (1997) 127.
[19] W.E. Britton, R. Kashyap, M. El-Hashash, M. El-Kady, M.
Herberhold, Organometallics 5 (1986) 1029.
Acknowledgements
[20] A. Houlton, P.T. Bishop, R.M.G. Roberts, J. Silver, M. Herber-
hold, J. Organomet. Chem. 364 (1989) 381.
[21] G.M. Sheldrick, SHELXS-86, Program for Crystal Structure
Solutions, Go¨ttingen, Germany, 1986.
[22] G.M. Sheldrick, SHELXl-93, Program for the Refinement of
Crystal Structures, Go¨ttingen, Germany, 1993.
We thank the European HCM-project ‘Electron and
Energy Transfer in Model Systems and Their Implica-
tions for Molecular Electronics’ (Grant No. CHRX-
CT94-0538) for partial funding of this work.
.