N-ferrocenyl-substituted planar-chiral N-heterocyclic carbenes and their PdII complexes

Article abstract of DOI:10.1002/ejic.200400691

The N-ferrocenyl-linked N-heterocyclic carbenes 1a and 1b were obtained by treatment of their imidazolium salts 12a and 12b with potassium tert-butoxide. The latter were shown to be accessible from (R)-1-amino-2-methylferrocene (9) and aminoferrocene, respectively, which were converted into the corresponding formamidines and then subjected to a novel cyclization procedure. Treating the ligand precursors 12a and 12b with [Pd(OAc)₂]₃ under different reaction conditions afforded the trans-pyridine-substituted Pd ^II complexes 14a and 14b as well as their trans-triphenylphosphane- substituted counterparts 16a and 16b and, in the case of the chiral ligand precursor, the dinuclear Pd^II complex 15a. Conformational analysis of the ligands based on the X-ray structures of 12a, 12b and 16a revealed the dependence of the two torsion angles between the central imidazolium core and the adjacent ferrocenyl substituents on the steric and electronic properties of the observed systems. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejic.200400691

FULL PAPER
N-Ferrocenyl-Substituted Planar-Chiral N-Heterocyclic Carbenes and Their
II
Pd Complexes
[a]
[a]
[a]
Andreas Bertogg, Francesco Camponovo, and Antonio Togni*
Keywords: Carbene ligands / Chirality / Ferrocenes / Nitrogen heterocycles / Palladium
The N-ferrocenyl-linked N-heterocyclic carbenes 1a and 1b
were obtained by treatment of their imidazolium salts 12a
and 12b with potassium tert-butoxide. The latter were shown
counterparts 16a and 16b and, in the case of the chiral ligand
precursor, the dinuclear Pd complex 15a. Conformational
analysis of the ligands based on the X-ray structures of 12a,
II
to be accessible from (R)-1-amino-2-methylferrocene (9) and 12b and 16a revealed the dependence of the two torsion
aminoferrocene, respectively, which were converted into the
corresponding formamidines and then subjected to a novel
angles between the central imidazolium core and the adja-
cent ferrocenyl substituents on the steric and electronic prop-
cyclization procedure. Treating the ligand precursors 12a and erties of the observed systems.
2b with [Pd(OAc) under different reaction conditions af-
forded the trans-pyridine-substituted Pd complexes 14a and (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
1
2 3
]
II
14b as well as their trans-triphenylphosphane-substituted
Germany, 2005)
Introduction
planar-chiral monodentate NHCs are as-yet unknown. We
reasoned that ligands showing the steric features of 1a and
II
1
b attached to Pd , in combination with two halides and
Phosphanes bearing planar-chiral ferrocenyl groups are
established ligands in coordination chemistry and have pro-
one potentially labile ligand, might lead to active systems
for the above-mentioned asymmetric catalytic applications.
We report here a new, high-yielding synthetic strategy lead-
ing to the isolation of both achiral and chiral imidazolium
iodides 12a and 12b that can be deprotonated to the carb-
enes 1a and 1b (Scheme 1). Complexes showing the desired
[
1]
ven to be very successful in asymmetric catalysis. Al-
though N-heterocyclic carbenes (NHCs) may often act as
phosphane substitutes, leading to considerably improved
performances of the resultant catalysts,[
2Ϫ5]
both achiral
[
6Ϫ16]
and chiral ferrocenyl-substituted NHCs are still rare.
These can be divided into two classes: either directly N-
constitution were synthesized from [Pd(OAc) ] and proved
2 3
[6,7]
to be active catalyst precursors in amide α-arylations.
ferrocenyl-substituted
or linked by a methylene, ethyl-
ene[
10,11,16]
or an ethenyl spacer.[12Ϫ15] The latter are of par-
[13,15]
ticular interest as bi- or tridentate ligands,
while for
monodentate ligands it seems appropriate to further restrict
the conformational freedom to the rotation around the two
nitrogenϪferrocenyl bonds, thus leading to directly N-ferro-
cenyl-substituted carbenes.[
17]
Achiral N,NЈ-diferrocenyl-
substituted imidazolium salts[ are known in the literature
18]
but the reported yields of their synthesis are moderate and
[6]
Scheme 1
the salts resisted controlled deprotonation.
II
Square-planar Pd complexes serve as catalyst precursors
in numerous cross-coupling and Heck-type reactions. Re-
cently, chiral monodentate NHCs have been shown to be
the ligands of choice in Pd-catalyzed asymmetric α-aryl-
ations of carbonyl compounds, of which cyclic amide α-aryl-
ations gave the best results.[ Pd complexes bearing chiral
Results and Discussion
Ligand Synthesis
19]
The chiral imidazolium iodide 12a was synthesized from
[
20]
monodentate NHCs are still rare and complexes bearing the known chiral acetal 2 in ten steps in an overall yield
of 30% (Scheme 2). Thus, stereoselective lithiation of 2 fol-
[
a]
Department of Chemistry and Applied Biosciences, Swiss lowed by electrophilic quenching with methyl iodide led to
Federal Institute of Technology, ETH,
the planar-chiral acetal 3, which was then converted into
the aldehyde 4. The carboxylic acid 6a, which served as
starting material in the following reaction sequence, was
Hönggerberg, 8093 Zürich, Switzerland
Fax: ϩ 41-1632-1310
E-mail: togni@inorg.chem.ethz.ch
DOI: 10.1002/ejic.200400691
Eur. J. Inorg. Chem. 2005, 347Ϫ356
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
347

A. Bertogg, F. Camponovo, A. Togni
FULL PAPER
produced by iodine-mediated oxidation of the aldehyde 4[21]
to the ester 5, followed by saponification. Its achiral
counterpart 6b is accessible by carboxylation of monolith-
[
22]
ioferrocene generated in situ from ferrocene (Scheme 3).
Scheme 3. Conditions: (a) tBuLi, THF, Ϫ78 °C to room temp. 67%;
(
b) i) preparation of activating reagent (in situ): DMF, thionyl chlo-
ride, benzene, room temp.; ii) reaction: activating reagent, NaN
py, Bu NBr, CH Cl , room temp., in situ; (c) benzylic alcohol, 90
C, 55% (two steps); (d) H , Pd/C, Me CHOH, room temp., 96%;
e) s-triazine, dioxane, 100 °C, 96%.; (f) 2-bromo-1,1-diethoxy-
3
,
4
2
2
°
2
2
(
3 2
ethane, NaH, DMF, 75 °C, 79%; (g) BF ·OEt , NaI, MeCN, room
8
temp., 75%; (h) KOtBu, pentane, room temp.; (i) S , benzene,
room temp.
Scheme 2. Conditions: (a) tBuLi, Et
MeI, Et O, Ϫ78 °C, 95%; (b) PTSA monohydrate, H
room temp., 98%; (c) I , KOH, MeOH, 0 °C to room temp. 77%;
d) NaOH, EtOH, H O, room temp., 93%; (e) i) preparation of
activating reagent (in situ): DMF, thionyl chloride, benzene, room upon heating to the corresponding isocyanates. Addition of
2
O, Ϫ78 °C to room temp. then
2
2
O, CH Cl
2
2
,
2
the ferrocenyl carbonyl azides 7a and 7b, which rearranged
(
2
temp.; ii) reaction: activating reagent, NaN
room temp., in situ; (f) benzylic alcohol, 90 °C, 81% (two steps);
g) H , Pd/C, Me CHOH, room temp., quant.; (h) s-triazine, diox-
3 4 2 2
, py, Bu NBr, CH Cl ,
benzylic alcohol followed by heating generated the car-
bamic acid esters 8a,b in a one-pot procedure from 6a,b
(
2
2
ane, 100 °C, quant.; (i) bromoacetaldehyde diethylacetal, NaH, (Scheme 2 and 3). Reductive deprotection of the Cbz-pro-
DMF, 75 °C, 82%; (j) BF ·OEt , NaI, MeCN, room temp., 71%;
k) KOtBu, pentane, room temp.; (l) S , benzene, room temp.
3
2
tected amines 8a,b led to the electron rich, strongly nucleo-
philic and air-sensitive amines 9a,b.
(
8
[
34]
The most frequently used reaction sequence from pri-
mary amines to imidazolium salts involves condensation of
Apart from the cyclization procedure discussed below, the amines with a 1,2-dialdehyde to yield the corresponding
another major challenge in the present ligand synthesis was diimine. Conversion of the latter with a one-carbon syn-
the generation of the nitrogen-ferrocene bond. Since amino- thetic equivalent in the formal oxidation state of formal-
ferrocenes serve as intermediates in the synthesis of various dehyde then leads to an imidazolium salt that is suitable for
ligands and optically active materials, this problem has at- deprotonation. In contrast to a recently published pro-
[
23Ϫ28]
[6]
tracted considerable interest.
One of the oldest cedure, we decided not to construct the heterocyclic core
[
26]
routes is based on a Curtius degradation of ferrocenecar- of the target molecule by condensation of the ferrocenylam-
boxylic acid chloride; other methods have used ines with glyoxal, followed by cyclization with formal-
[
29Ϫ31]
[32]
bromoferrocene
or ferroceneboronic acid
as start- dehyde, due to low reported yields and demanding purifi-
ing material for copper-mediated amination reactions. cations. Instead, we chose to transform the ferrocenylam-
Based on its simplicity and on the easy accessibility of its ines 9a and 9b into N,NЈ-diferrocenyl-substituted amidines
starting materials, we chose to use the Curtius rearrange- and to use the latter as intermediates in the cyclization se-
ment sequence, which, in our case, proved to be attractive quence. The amidines 10a,b were easily obtained from the
both in terms of synthetic feasibility and the high isolated amines 9a,b by methinyl group transfer from s-triazine[35]
yields of the products. The chiral acid 6a as well as the and could be considered as being interesting potential li-
achiral acid 6b were activated[ and converted, in situ, into gands in their own right. The missing C fragment was in-
33]
2
348
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N-Ferrocenyl-Substituted Planar-Chiral N-Heterocyclic Carbenes
FULL PAPER
corporated into the structures by treating the amidinate strate. Pyridine seemed to be an advantageous hemilabile
anions of 10a,b with 2-bromo-1,1-diethoxyethane to give ligand as it can also be used in large excess as a solvent in
[
36]
the acetals 11a,b. Addition of an excess of BF ·OEt led the preparation of the catalyst precursor. Further advantage
3
2
to the desired cyclization and to the 4-ethoxy-4,5-dihydro- can be taken of its high dielectric constant, which allows
imidazolium cation, which, under prolonged heating, elim- complete dissolution of the imidazolium iodides, and of its
inated ethanol to form the aromatic target core. The imid- ability to act as a base, which might facilitate the in situ
azolium iodides 12a,b were obtained after anion exchange deprotonation of the imidazolium iodides. Thus, reaction of
and column chromatography. It is noteworthy that in the 12b and [Pd(OAc) ] in the presence of sodium iodide in
2
3
high yielding reaction sequence from the carbamic acid es- pyridine afforded the pyridine-substituted complex 14b re-
ters 8a,b to the imidazolium iodides 12a,b only one chroma- gardless of whether one or two equivalents of the imidazol-
tographic purification of the products and intermediates is ium iodide were used. Small amounts of the known com-
required. Both chiral and achiral carbenes 1a and 1b were plex PdI (pyridine) were separated from the main product
2
2
prepared by adding potassium tert-butoxide to a slurry of by column chromatography. Subjecting the chiral imidazol-
the imidazolium iodides 12a or 12b in pentane, followed by ium iodide 12a to the same reaction conditions resulted in
evaporation of the solvent and selective extraction of the an isolated equimolar mixture of both the pyridine-substi-
products with benzene. The carbenes proved to be stable in tuted complex 14a and the equivalent iodo-bridged di-
1
solution in C D over a period of 24 hours without any sign nuclear derivative 15a. Interestingly, the H NMR spectrum
6
6
1
of decomposition, as ascertained by H NMR spectroscopy. of the chromatographed mixture showed that the iodo-
In the C NMR spectra the diagnostic chemical shifts at bridged dimer 15a contains two non-equivalent ferrocenyl
δ ϭ 221.1 ppm (1a) and 216.1 ppm (1b) were detected. Ad- ligands, thereby indicating restricted rotation around the
1
3
ding S to either of the carbenes resulted in the formation PdϪC bond. This phenomenon has been observed before in
8
of the corresponding thiones 13a and 13b (Scheme 2 and 3). an analogous bridged complex bearing two ethenyl-linked,
diferrocenyl-substituted chiral NHCs that have been
characterized by NMR spectroscopy and X-ray diffraction
Synthesis of Palladium Complexes
[37]
studies.
In analogy to that case it seems very likely that
A series of NHC-substituted PdII complexes were ob- the observed anisotropy of the ferrocenyl substituents re-
tained from the reaction of the imidazolium iodides 12a,b sults from the typical butterfly conformation of the Pd I
2
2
[
38]
with [Pd(OAc)2]3 under different reaction conditions core.
Upon adding triphenylphosphane, the mixture of
(Scheme 4). We reasoned that Pd complexes substituted the two chiral complexes 14a and 15a was cleanly converted
with one NHC, two halides and one hemilabile ligand into the carbene phosphane complex 16a, whose trans con-
might be potent precatalysts for both Heck-type and cross- figuration was determined by X-ray analysis (vide infra).
coupling reactions since, in both cases, at least one ligand The achiral, pyridine-substituted complex 14b, under the
0
stabilizing the active Pd species as well as two free coordi- same reaction conditions, gave the analogous complex 16b.
nation sites cis to each other are required in the catalytic The trans configuration of both complexes 16a and 16b was
cycle. While the bulky and strongly bound carbene ligand further supported by the large coupling constants between
0
[39]
is supposed to stabilize the active Pd species and prevent the phosphorus nuclei and the carbene carbon nuclei.
precipitation of Pd black, the hemilabile ligand can be split Long-range coupling to the olefinic carbons of the NHC
off previous to oxidative addition of the aryl halide sub- over four bonds and long-range coupling to the olefinic hy-
Scheme 4
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
349

A. Bertogg, F. Camponovo, A. Togni
FULL PAPER
drogen atoms over five bonds were observed.[39] Selective
saturation of the phosphorus hydrogen transition resulted
1
in a decoupled H NMR spectrum, as performed in the case
of 16a.
Crystal Structures and Conformational Analysis
Single-crystal X-ray analysis of the imidazolium iodides
12a (Figure 1) and 12b (Figure 2) showed the expected
bond lengths and angles within the imidazolium cores, thus
indicating that the steric and electronic features of the ferro-
cenyl subunits do not significantly alter the properties of
the heterocycle. In both cations the ferrocenylϪ
imidazolium bond lengths lie in the range of a CϪN single
bond, thus excluding delocalisation of the π electrons be-
tween the cyclic moieties of the molecules. This conclusion
is in agreement with the observed non-planar arrangement
of the three connected cyclic subunits.[
40]
The
ferrocenylϪmethyl bond lengths in 12a do not show any
deviation from the expected value.
Figure 3. ORTEP view of the complex 16a, with 30% thermal ellip-
soids; hydrogen atoms are omitted for clarity; selected bond lengths
˚
[
A] and angles [°]: C(1)ϪPd 2.004(3), PdϪP 2.3298(9), PdϪI(1)
2
1
1
1
.6280(5), PdϪI(2) 2.5932(5), C(1)ϪN(1) 1.351(4), C(1)ϪN(2)
.359(4), C(2)ϪC(3) 1.323(5), N(1)ϪC(3) 1.385(4), N(2)ϪC(2)
.386(5), N(1)ϪC(4) 1.426(4), N(2)ϪC(15) 1.430(4), C(5)ϪC(6)
.489(6), C(16)ϪC(17) 1.502(6); N(1)ϪC(1)ϪN(2) 104.9(3),
C(1)ϪN(1)ϪC(4)ϪC(5)
45.4(4)
246.0(4),
C(1)ϪN(2)ϪC(15)ϪC(16)
2
Since the overall shape of the ligand and, as a conse-
quence, its ability to efficiently transfer chirality in asym-
Figure 1. ORTEP view of the cation of 12a, with 30% thermal
˚
ellipsoids; selected bond lengths [A] and angles [°]: C(1)ϪN(1)
1
1
1
.327(3), C(1)ϪN(2) 1.332(3), C(2)ϪC(3) 1.346(4), N(1)ϪC(3) metric catalytic reactions depends on its conformation, it is
.378(3), N(2)ϪC(2) 1.387(3), N(1)ϪC(4) 1.426(3), N(2)ϪC(15)
important to note that the latter is fully described by the
N(1)ϪC(1)ϪN(2) 108.6(2), C(1)ϪN(1)ϪC(4)ϪC(8) 310.5(4), two torsion angles between the central imidazolium core
.420(3),
C(8)ϪC(9)
1.498(4),
C(19)ϪC(20)
1.492(3);
C(1)ϪN(2)ϪC(15)ϪC(19) 143.8(3)
and the adjacent ferrocenyl substituents. Rotation around
the two ferrocenylϪnitrogen bonds in solution at room tem-
perature proved to be fast on the NMR timescale for 12b,
13b, 14b and 16b. No such conclusions can be drawn for
their chiral counterparts due to symmetry restrictions. In
the crystal structures, however, well-defined conformations
could be studied. In 12a torsion angles of 310.5(4)° and
143.8(3)°
around
C(1)ϪN(1)ϪC(4)ϪC(8)
and
C(1)ϪN(2)ϪC(15)ϪC(19), respectively, were detected. The
corresponding angles in 12b around C(1)ϪNϪC(3)ϪC(4)
and around C(1)ϪNЈϪC(3Ј)ϪC(7Ј) are 139.4(8)° and
3
20.9(11)°, respectively, whereas the C(1)ϪN(1)ϪC(4)
ϪC(5) and C(1)ϪN(2)ϪC(15)ϪC(16) angles in 16a are
.329(8), C(2)ϪC(2Ј) 1.331(14), NϪC(2) 1.380(8), NϪC(3) 246.0(4)° and 245.4(4)°, respectively. These at-first-sight ar-
Figure 2. ORTEP view of the cation of 12b, with 30% thermal
˚
ellipsoids; selected bond lengths [A] and angles [°]: C(1)ϪN(1)
1
1
.419(8); NϪC(1)ϪNЈ 108.4(8), C(1)ϪNϪC(3)ϪC(4) 139.4(8),
bitrary results can be rationalized by uncovering the forces
that determine the torsion angles.
C(1)ϪNЈϪC(3Ј)ϪC(7Ј) 320.9(11)
X-ray analysis of the chiral Pd complex 16a (Figure 3)
Conformational analysis of the solid-state structures of
reveals that the main structural features of 12a, apart from compounds 12a, 12b, 16a and of two analogous achiral de-
[
6]
the torsion angles, are preserved in the ligand. While the rivatives reported by Bildstein et al. reveals that their con-
extent of delocalization in the heterocyclic fragment is formations are mainly governed by two opposing forces: i)
slightly decreased and the NϪCϪN angle is reduced from pseudo allylic repulsion[41] between the ortho substituents
1
08.6(2)° to 104.9(3)°, the ferrocenylϪimidazolium bond of the ferrocenyl fragments and the ortho substituents of the
lengths stay constant. The palladiumϪcarbon bond of heterocycle, and ii) steric interactions between the substitu-
˚
[40]
2.004(3) A lies in the typical range.
ents on the imidazolium core and the unsubstituted Cp
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350
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N-Ferrocenyl-Substituted Planar-Chiral N-Heterocyclic Carbenes
ring. The orientation of the two ferrocenyl planes with re-
FULL PAPER
First attempts to perform the catalytic asymmetric amide
[
42]
[19]
spect to each other appears to be of minor importance, as cyclizations previously studied by Lee et al.
using the
can be seen by comparing the orientations in the crystal newly synthesized chiral ligand gave the expected cycliza-
structures of, for example, 12a and 12b. Therefore, the two tion product in 70% yield and 9% ee. Although this result
torsion angles in a molecule can be analyzed separately, does not compare favorably with that reported in the study
thus simplifying the analysis: only the tilt angles (0° Յ tilt mentioned above, where ee values of up to 70% were ob-
angle Յ 90°) between the ferrocenyl planes and the hetero- tained, it shows the high activity of the observed system
cyclic plane need to be considered as relevant. As shown in and marks a starting point for systematic variations in the
Figure 4, all known tilt angles of the discussed imidazolium chiral ligand. Efforts to shorten the ligand synthesis while
salts lie in a specific range between 36.2(3)° and 49.5(4)°, introducing sterically more demanding groups attached to
whereas the sulfur adduct 13b[ shows slightly larger angles the ferrocenyl moieties are currently being undertaken.
of 53.7(3)°. This shows that even small atoms or substitu-
6]
ents such as hydrogen, methyl or thiooxo attached to the
Experimental Section
position adjacent to the bond connecting the Cp and the
heterocycle on either of the cyclic moieties exclude tilt
angles near to 0° or 90°. The rotational potential energy
changes around the energy minima seem to be small. Only
in 16a, where two substituents ortho to the flexible bond
are present, is it not surprising to find considerably in-
creased torsion angles of 65.4(4)° and 66.0(4)° (Figure 4).
General Remarks: All experiments were conducted under argon or
dinitrogen using standard Schlenk-type glassware or a glovebox.
Unless otherwise stated, the reactions were carried out at room
temperature. All solvents were stored over activated molecular si-
˚
eves (4 A) unless otherwise indicated. In the case of freshly distilled
solvents, the following drying agents were used: CaH
MeCN, MeOH and pyridine; Na/benzophenone for pentane; Na
for benzene and C . Chromatography was carried out with
Merck silica gel 60. The NMR spectra were recorded with Bruker
2 2 2
for CH Cl ,
6
D
6
1
13
31
Avance 250 (250.1 MHz, H; 62.5 MHz, C; 101 MHz, P), 300
1
13
31
(
(
300.1 MHz, H; 75.0 MHz,
C; 122 MHz,
P) and 500
1
13
15
31
500.2 MHz, H; 125 MHz, C; 50.7 MHz, N; 203 MHz, P)
1
13
1
spectrometers. H and C{ H} NMR chemical shifts (δ) were ref-
erenced internally by the residual solvent signal relative to tetra-
3
1
15
methylsilane. P NMR and N NMR chemical shifts were refer-
enced with respect to H PO and MeNO , respectively. All spectra
3
4
2
were recorded at room temperature. Optical rotations were meas-
ured in 1-dm cells with a PerkinϪElmer model 341 polarimeter at
22 °C. High-resolution MALDI mass spectra were measured by the
analytical service of the Laboratorium für Organische Chemie of
the ETH Zürich with an IonSpec ultima FT MALDI mass spec-
trometer. Elemental analyses were obtained with a Leco CHN-900
analyzer. All chemicals were purchased from Fluka, Aldrich,
Acros, Lancaster or ABCR and were used without further purifi-
[
20]
cation.
(2S,4S)-2-Ferrocenyl-4-(hydroxymethyl)-1,3-dioxane,
[20]
Figure 4. Tilt angles between planes of the Cp substituent and the
heterocyclic core in imidazolium cations, in a thione and in a Pd-
bound carbene ligand
(2S,4S)-2-ferrocenyl-4-(methoxymethyl)-1,3-dioxane, (2S,4S,RFc)-
[43]
4
2
-(methoxymethyl)-2-(2-methylferrocenyl)-1,3-dioxane (3),
-methylferrocenecarboxaldehyde (4),
(R)-
[43]
and ferrocenecarboxylic
[22]
acid (6b) were prepared as reported.
Benzyl N-Ferrocenylcarbamate (8b): Ferrocenecarboxylic acid
Conclusion
(
1.25 g, 5.43 mmol, 1.0 equiv.), Bu NBr (349 mg, 1.10 µmol, 0.2
equiv.) and NaN (723 mg, 11.0 mmol, 2.0 equiv.) were placed in a
00-mL Schlenk flask. Addition of 35 mL of distilled CH Cl and
pyridine (1.34 mL, 1.30 g, 16.5 mmol, 3.0 equiv.) caused the forma-
protonation of their imidazolium iodide precursors 12a and tion of an orange slurry. In a separate 10-mL Schlenk flask N,N-
4
3
The bulky, planar-chiral, N-ferrocenyl-substituted NHC
1
2
2
1a as well as its achiral analog 1b were synthesized by de-
1
2b. The latter were prepared by a synthetic strategy based dimethylchlorosulfitomethaniminium chloride was prepared in situ
on a Curtius degradation to form the ferrocenylϪnitrogen by adding thionyl chloride (0.8 mL, 11.0 mmol) to a mixture of
DMF (1.0 mL, 10.2 mmol) and 5 mL of benzene. After approxi-
mately 1 min, two phases separated, with the lower one containing
bond and a novel cyclization procedure to build up the het-
erocyclic cores of the target molecules. The reaction of 12b
with [Pd(OAc) ] in the presence of pyridine led to the
trans-pyridine-substituted complex 14b, but when 12a was
subjected to the same reaction conditions a mixture of the
mononuclear complex 14a and the dinuclear complex 15a
was isolated. Both 16a and 16b were obtained by addition
the desired reagent. Addition of 730 µL of the fresh, clear and
colorless N,N-dimethylchlorosulfitomethaniminium chloride to the
2
3
vigorously stirred orange slurry during 3 min led to a clear wine-
red solution and a white precipitate (presumably Bu
h, water was added. Extraction of the organic layer with CH
followed by drying with Na SO and evaporation of the solvents
4
NBr). After 1
2
Cl
2
,
2
4
of triphenylphosphane to 14b and to a mixture of 14a and led to an intensely red-colored oil. Benzylic alcohol (6 mL) was
5b, respectively. then added and the remaining pyridine was evaporated under vac-
1
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351

A. Bertogg, F. Camponovo, A. Togni
FULL PAPER
uum. The resulting solution of ferrocenecarboxylic azide (7b) in
benzylic alcohol was stored in a 100-mL round-bottomed flask at CH
room temperature under argon overnight. Upon heating to 90 °C
during 30 min, the red color disappeared. The resulting brown yel-
lowish mixture was concentrated to dryness under reduced pressure
515 mg (79%). 1H NMR (C
6
D
6
): δ ϭ 1.16 (t, J ϭ 7.1 Hz, 3 H,
), 1.16 (t, J ϭ 7.1 Hz, 3 H, CH ), 3.44Ϫ3.54 (m, 2 H,
CH ), 3.68Ϫ3.78 (m, 2 H, CH CH ), 3.81 (t, J ϭ 1.8 Hz, 1 H,
3
3
CH
2
3
2
3
CpsubstϪCH), 3.81 (t, J ϭ 1.8 Hz, 1 H, CpsubstϪCH), 3.98 (t, J ϭ
1.8 Hz, 1 H, CpsubstϪCH), 3.98 (t, J ϭ 1.8 Hz, 1 H, CpsubstϪCH),
by using a distillation apparatus. A pure, orange, solid product was 4.02 (s, 5 H, Cp), 4.12 (d, J ϭ 5.3 Hz, 2 H, NCH
obtained by column chromatography (CC; CH Cl ϩ 1% Et N) on H, Cp), 4.31Ϫ4.35 (m, 4 H, 4 CpsubstϪCH), 5.13 (t, J ϭ 5.2 Hz, 1
silica gel. Yield: 994 mg (55%). H NMR (CDCl ): δ ϭ 3.99 (s, 2 H, NCH
H, 2 CpsubstϪCH), 4.15 (s, 5 H, Cp), 4.48 (br. s, 2 H, 2 (CDCl ): δ ϭ 15.6 (CH
CpsubstϪCH), 5.17 (s, 2 H, CH ), 5.86 (br. s, 1 H, NH), 7.34Ϫ7.40 61.7 (CpsubstϪCH), 64.0 (CH
m, 5 H, phenyl) ppm. MS (HR MALDI): m/z ϭ 335.0609 (calcd. (CpsubstϪCH), 69.0 (Cp), 100.5 (NCH
108.4 (CpsubstϪCquat), 150.6 (NϭCHϪN) ppm. MS (HR MALDI):
2
CH), 4.19 (s, 5
2
2
3
1
CH), 8.28 (s, 1 H, NϭCHϪN) ppm. 13C{ H} NMR
CH ), 52.5 (NCH CH), 60.3 (CpsubstϪCH),
CH ), 65.0 (CpsubstϪCH), 65.2
CH), 105.5 (CpsubstϪCquat),
1
3
2
3
2
3
2
2
2
3
(
2
ϩ
2 2
for C18H17FeNO ); found 335.0606 [M ]. C18H17FeNO (335.18):
calcd. C 64.50, H 5.11, N 4.18; found C 64.42, H 5.30, N 4.03.
CAS 98639-14-6.
ϩ
m/z ϭ 528.116 (calcd. for C27
32Fe (528.25): calcd. C 61.39, H 6.11, N 5.30; found C
1.54, H 6.18, N 5.32.
2 2 2
H32Fe N O ); found 528.116 [M ].
C
6
27
H
2 2 2
N O
Aminoferrocene (9b): Compound 8b (962 mg, 2.87 mmol, 1.0
equiv.) was suspended in 35 mL of isopropyl alcohol in a dry 100-
mL Schlenk flask. After degassing the suspension in an ultrasonic
bath by passing argon over it, the reaction vessel was heated to 60
C until the substrate had dissolved completely, resulting in a clear
orange solution. Pd on charcoal (10% Pd, 301 mg, 261 µmol, 0.09
equiv.) was added at room temperature and H was placed over
the reaction mixture. After 90 min, the solvent was removed under
reduced pressure, and the residue was taken up in distilled CH Cl
N,NЈ-Diferrocenylimidazolium Iodide (12b): Compound 11b (2.38 g,
.51 mmol, 1.0 equiv.) was dissolved in 50 mL of distilled MeCN
in a dry 100-mL Schlenk flask. After addition of BF ·OEt (3.4
4
3
2
°
mL, 3.8 g, 27 mmol, 6.0 equiv.), which caused an immediate dark-
ening of the clear, red solution, the reaction temperature was raised
·OEt (1.7 mL, 1.9 g, 14 mmol,
3 2
.0 equiv.) was added and the reaction mixture was stirred for 15 h.
Evaporation of the solvent under reduced pressure gave a brown
yellowish solid. NaI (3.38 g, 22.6 mmol, 5.0 equiv.) and 50 mL of
distilled MeOH were added and the resulting mixture was stirred
at 70 °C for 30 min. After evaporation of the solvent, the crude
2 2
Cl ϩ 5% MeOH)
to give the pure product as a light-yellow foam. Yield: 1.92 g (75%).
2
to 70 °C. After 3 h, additional BF
3
2
2
and filtered. The resulting yellow solution was concentrated to dry-
ness. The pure product was isolated as an orange solid and stored
in a glovebox. Yield: 553 mg (96%). H NMR (CDCl
1
3
): δ ϭ 2.59
(
br. s, 2 H, NH
J ϭ 1.8 Hz, 2 H, 2 CpsubstϪCH), 4.10 (s, 5 H, Cp) ppm. CAS 1273-
2-1.
2
), 3.84 (t, J ϭ 1.8 Hz, 2 H, 2 CpsubstϪCH), 3.99 (t,
product was chromatographed on silica gel (CH
8
1
H NMR (CDCl
H, 2 CpsubstCH), 5.33 (t, J ϭ 2.0 Hz, 2 H, CpsubstϪCH), 7.64 (d,
J ϭ 1.5 Hz, 2 H, NCHCHN), 10.74 (t, J ϭ 1.5 Hz, 1 H, Nϭ
3
): δ ϭ 4.34 (s, 10 H, 2 Cp), 4.36 (t, J ϭ 2.0 Hz,
4
N,NЈ-Diferrocenylformamidine (10b): In a glovebox, compound 9b
2.42 g, 12.0 mmol, 1.0 equiv.) and 1,3,5-triazine (2.92 g,
6.0 mmol, 3.0 equiv.) were placed in a dry, 500-mL round-bot-
(
3
1
3
1
CHϪN) ppm. C{ H} NMR (CD
7.8 (CpsubstϪCH), 70.8 (Cp), 92.0 (CpsubstϪCquat), 122.2
NCHCHN), 135.1 (NϭCHϪN) ppm. MS (HR MALDI): m/z ϭ
2 2
Cl ): δ ϭ 63.2 (CpsubstϪCH),
6
(
4
tomed Schlenk flask. After taking the flask out of the glovebox, 42
mL of dioxane was added, the resulting suspension was degassed
in an ultrasonic bath by passing argon over it, and the reaction
vessel was heated to 100 °C for 4.5 h, which led to a wine-red solu-
tion and an orange precipitate. The strong smell of ammonia upon
careful opening of the reaction vessel (preventing the entry of air)
indicated product formation. The reaction solvents were evapo-
rated to dryness under reduced pressure using a distillation appa-
ratus. At the same time, excess 1,3,5-triazine was completely sub-
ϩ
ϩ
37.0404 (calcd. for C23
2 2
H21Fe N ); found 437.0406 [M Ϫ I].
21Fe IN (564.02): calcd. C 48.98, H 3.75, I 22.50, N 4.97;
C
23
H
2
2
found C 49.12, H 4.03, I 22.55, N 4.87.
N,NЈ-Diferrocenylimidazol-2-ylidene (1b): A 20-mL Schlenk vessel
was charged with compound 12b (30 mg, 53 µmol, 1.0 equiv.) and
KOtBu (12 mg, 106 µmol, 2.0 equiv.) in a glovebox. Addition of
.5 mL of distilled pentane caused the formation of an orange
slurry. After stirring for 14 h, all volatiles were evaporated under
reduced pressure, the residue was taken up in 1 mL of distilled
deuterated benzene and filtered through a 4 A frit. A light orange,
clear solution of the product was obtained; the yield was not deter-
): δ ϭ 3.86 (t, J ϭ 2.0 Hz, 4 H, 2
CpsubstCH), 4.02 (s, 10 H, 2 Cp), 4.82 (t, J ϭ 2.0 Hz, 4 H, 2
1
limed, leading to an analytically pure amorphous orange solid that
1
was stored in a glovebox. Yield: 2.37 g (96%). H NMR (CDCl
3
):
δ ϭ 4.04 (t, J ϭ 1.8 Hz, 4 H, 4 CpsubstϪCH), 4.20 (s, 10 H, 2 Cp),
.26 (t, J ϭ 1.8 Hz, 4 H, 4 CpsubstϪCH), 8.03 (s, 1 H, NϭCHϪN)
˚
4
13
1
ppm. C{ H} NMR (CDCl
CpsubstϪCH), 67.2 (CpsubstϪCquat), 69.2 (Cp), 150.2 (NϭCHϪN)
ppm. MS (HR MALDI): m/z ϭ 412.033 (calcd. for C21 20Fe );
(412.09): calcd. C 61.21, H 4.89,
3
): δ ϭ 60.5 (CpsubstϪCH), 65.1
1
mined. H NMR (C
6
D
6
(
H
2 2
N
1
3
1
ϩ
CpsubstCH), 6.86 (s, 2 H, NCHCHN) ppm. C{ H} NMR (C
6 6
D ):
2 2
found 412.032 [M ]. C21H20Fe N
N 6.80; found C 61.15, H 4.97, N 6.68.
δ ϭ 62.2 (CpsubstϪCH), 65.8 (CpsubstϪCH), 69.2 (Cp), 100.4
1
5
(
CpsubstϪCN), 118.9 (NCHCHN), 216.1 (NCN) ppm. N NMR
N-(2,2-Diethoxyethyl)-N,NЈ-diferrocenylformamidine (11b): Com-
pound 10b (500 mg, 1.23 mmol, 1.0 equiv.) was suspended in 10
mL of DMF in a 50-mL Schlenk flask and cooled to 0 °C. After
addition of NaH (55Ϫ65% in mineral oil, 100 mg, 2.25 mmol, 1.8
equiv.), the mixture was kept at 0 °C for 5 min and then slowly
(C D ): δ ϭ Ϫ186.3 ppm.
6
6
N,NЈ-Diferrocenylimidazole-2-thione (13b): A 20-mL Schlenk vessel
was charged with compound 1b (45 mg, 103 µmol, 1 equiv.) and S
(6.2 mg, 192 µmol, 2 equiv.) in a glovebox. Addition of 1 mL of
distilled THF led to a brown solution and a small amount of pre-
cipitate. After 16 h, the reaction vessel was taken out of the glove-
8
warmed to room temperature, leading to gas evolution (H
2
). After
100 min stirring at room temperature 2-bromo-1,1-diethoxyethane
(380 µL, 477 mg, 2.45 mmol, 2.0 equiv.) was added and the clear box and water was added, leading to a color change to bright yel-
red solution was quickly heated to 76 °C. After 90 min, the dark-
ened, hot mixture was concentrated to dryness under vacuum. The
crude product was dissolved in MeCN followed by filtration under
argon. The pure product was isolated as a clear, red oil. Yield:
low. The mixture was extracted with CH
2 4 3
and dried with Na SO . H NMR (CDCl ): δ ϭ 4.24 (t, J ϭ 2.0 Hz,
4 H, 2 CpsubstCH), 4.28 (s, 10 H, 2 Cp), 4.90 (t, J ϭ 2.0 Hz, 4 H,
2 CpsubstCH), 7.13 (s, 2 H, NCHCHN). CAS 249644-45-9.
2
Cl
2
, washed with water
1
352
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 347Ϫ356

N-Ferrocenyl-Substituted Planar-Chiral N-Heterocyclic Carbenes
FULL PAPER
Methyl (R)-2-Methylferrocenecarboxylate (5): (R)-2-Methylferro-
sion in an ultrasonic bath by passing argon over it, the reaction
cenecarboxaldehyde (4) (6.74 g, 29.6 mmol, 1.0 equiv.) and 120 mL vessel was heated to 70 °C until the substrate had dissolved com-
of MeOH were added to a 1-L flask and cooled to 0 °C. Addition
of KOH (16.6 g, 296 mmol, 10 equiv.) was followed by addition
pletely, resulting in a clear orange solution. Pd on charcoal (10%
Pd, 656 mg, 573 µmol, 0.1 equiv.) was added at room temperature
of I
2
(37.5 g, 148 mmol, 5.0 equiv.). After 4 h, the solvents were
and H
solvent was removed under reduced pressure, the residue was taken
up in distilled CH Cl and filtered. The resulting yellow solution
was concentrated to dryness. The pure product was isolated as a
): δ ϭ 2.28 (s, 3 H, bright-orange solid and stored in a glovebox. Yield: 1.23 g (quant).
2
was placed over the reaction mixture. After 110 min, the
evaporated under reduced pressure at 0 °C (to prevent overoxid-
ation to the corresponding ferrocenium cation) and the remaining
2
2
residue was chromatographed on silica gel (CH
oil. Yield: 5.87 mg (77%). 1H NMR (CDCl
CpϪCH ), 3.81 [s, 3 H, C(O)OCH ], 4.12 (s, 5 H, Cp), 4.23 (t, J ϭ
.6 Hz, 1 H, CpsubstϪCH), 4.31 (t, J ϭ 1.6 Hz, 1 H, CpsubstϪCH), 3.66 (t, J ϭ 2.1 Hz, 1 H, CpsubstϪCH), 3.70Ϫ3.77 (m, 2 H,
.71 (dd, J ϭ 2.6, J ϭ 1.6 Hz, 1 H, CpsubstϪCH) ppm. CAS CpsubstϪCH), 3.91 (s, 5 H, Cp) ppm. CAS 31760-79-9.
2242-23-8.
2 2
Cl ) to give a red
3
1
3
3
6 6 3 2
H NMR (C D ): δ ϭ 1.72 (s, 3 H, CH ), 2.03 (br. s, 2 H, NH ),
2
4
1
1
2
N,NЈ-Bis[(R)-2-methylferrocen-1-yl]formamidine (10a): Compound
(
2
R)-2-Methylferrocenecarboxylic Acid (6a): Compound 5 (7.33 g,
8.4 mmol) was dissolved in 140 mL of EtOH in a 500-mL round-
9a (1.17 g, 5.44 mmol, 1.0 equiv.) and 1,3,5-triazine (1.32 g,
16.3 mmol, 3.0 equiv.) were placed in a dried 100-mL, round-bot-
bottomed flask. An aqueous solution of NaOH (70 mL, 1.1 m)
was added, then the reaction mixture was stirred for 4 h at room
temperature and for a further 12 h at 60 °C. Water was then added
and the organic impurities were extracted with tert-butyl methyl
ether. The aqueous phases were acidified with 0.7 m aqueous HCl
tomed Schlenk flask in a glovebox. After taking the flask out of
the glovebox, 18 mL of dioxane was added and the resulting sus-
pension was degassed in an ultrasonic bath by passing argon over
it. The reaction vessel was then heated to 100 °C for 2.25 h, which
led to a clear red solution. The strong smell of ammonia upon
careful opening of the reaction vessel (preventing the entry of air)
indicated product formation. The reaction solvents were evapo-
rated to dryness under reduced pressure using a distillation appa-
ratus. At the same time, excess 1,3,5-triazine was completely sub-
and extracted with CH
NaSO , the solvent was evaporated and the product was isolated
in the form of red crystals. Yield: 6.45 g (93%). H NMR (CDCl
δ ϭ 2.31 (s, 3 H, CH ), 4.20 (s, 5 H, Cp), 4.31 (t, J ϭ 2.5 Hz, 1 H,
CpsubstϪCH), 4.39 (t, J ϭ 1.9 Hz, 1 H, CpsubstϪCH), 4.80 (dd,
2 2
Cl . The organic layers were dried with
4
1
3
):
3
limed, leading to an analytically pure amorphous orange solid that
J
(
(
1
ϭ 2.5, J
CD Cl ):
CpsubstϪCH), 70.8 (Cp), 71.0 (CpsubstϪCH), 74.4 (CpsubstϪCH),
7.7 (CpsubstϪCquat), 178.9 (COOH) ppm. CAS 12241-80-4.
2
ϭ 1.8 Hz, 1 H, CpsubstϪCH) ppm. 13C{ H} NMR
1
1
was stored in a glovebox. Yield: 1.48 g (quant). H NMR (C
6
D
6
):
2
2
δ
ϭ
14.8 (CH ), 68.1 (CpsubstϪCquat), 69.7
3
3
δ ϭ 1.95 (s, 6 H, 2 CH ), 3.81 (t, J ϭ 2.6 Hz, 2 H, 2 CpsubstϪCH),
3
.89 (t, J ϭ 1.7 Hz, 2 H, 2 CpsubstϪCH), 4.04 (s, 10 H, 2 Cp), 4.22
8
13
1
(
br. s, 2 H, 2 CpsubstϪCH), 7.99 (s, 1 H, NϭCHϪN) ppm. C{ H}
NMR (CDCl ): 12.2 (CH ), 58.8 (CpsubstϪCH), 62.3
CpsubstϪCH), 66.6 (CpsubstϪCH), 69.1 (CpsubstϪCquat), 69.4 (Cp),
3
δ
ϭ
3
Benzyl N-[(R)-2-Methylferrocenyl]carbamate (8a): Compound 6a
4.10 g, 16.82 mmol, 1.0 equiv.), Bu NBr (1.09 g, 3.44 mol, 0.2
equiv.) and NaN (2.26 g, 34.4 mmol, 2.0 equiv.) were placed in a
00-mL Schlenk flask. Addition of 114 mL of distilled CH Cl and
(
(
4
7
6.5 (CpsubstϪCquat), 150.6 (NϭCHϪN) ppm. MS (HR MALDI):
3
ϩ
m/z ϭ 440.0638 (calcd. for C23
24Fe (440.14): calcd. C 62.76, H 5.50, N 6.36; found C
2.59, H 5.38, N 6.55. [α]22 ϭ ϩ1229 (c ϭ 1, CHCl ).
2 2
H24Fe N ); found 440.0630 [M ].
5
2
2
C
6
23
H
2 2
N
pyridine (4.18 mL, 4.07 g, 515 mmol, 3.0 equiv.) gave an orange-
red solution. In a separate 10-mL Schlenk flask, N,N-dimethylchlo-
rosulfitomethaniminium chloride was prepared in situ by adding
thionyl chloride (4.6 mL, 62.9 mmol) to a mixture of DMF (5.7
mL, 58.4 mmol) and 28 mL of benzene. After approximately 1 min,
two phases separated, with the lower one containing the desired
reagent. Addition of 2.29 mL of the fresh, clear and colorless N,N-
dimethylchlorosulfitomethaniminium chloride to the vigorously
stirred orange slurry during 3 min led to a clear wine-red solution
3
N-(2,2-Diethoxyethyl)-N,NЈ-bis[(R)-2-methylferrocen-1-yl]formamidine
11a): Compound 10a (1.14 mg, 2.58 mmol, 1.0 equiv.) was dis-
(
solved in 20 mL of DMF in a 100-mL Schlenk flask. The mixture
was degassed in an ultrasonic bath by passing argon over it and
cooled to 0 °C. After addition of NaH (55Ϫ65% in mineral oil,
2
1
03 mg, 4.64 mmol, 1.8 equiv.), the mixture was kept at 0 °C for
5 min and then slowly warmed to room temperature, leading to
4
and a white precipitate (presumably Bu NBr). After 1 h 25 min, 23
2
gas evolution (H ). After 2 h 40 min of stirring at room tempera-
ture, 2-bromo-1,1-diethoxyethane (802 µL, 1.02 g, 5.17 mmol, 2.0
equiv.) was added and the clear red solution was quickly heated to
mL of benzylic alcohol was added and the remaining dichlorometh-
ane and pyridine were evaporated under high vacuum. The re-
sulting solution of (R)-2-methylferrocenecarboxylic azide (7a) in
benzylic alcohol was stirred at 90 °C during 10 min, which caused
darkening of the reaction mixture. The resulting brownish-yellow
solvents were evaporated to dryness under reduced pressure during
80 °C. After 3 h 20 min, another portion of bromoacetaldehyde
diethylacetal (802 µL, 254 mg, 1.29 mmol, 0.5 equiv.) was added
and stirring was continued for 90 min. The reaction solvents were
evaporated to dryness under vacuum. The crude product was dis-
solved in distilled MeCN and filtered under argon. The pure prod-
4
5 min at 90 °C by using a distillation apparatus. A pure, orange,
solid product was obtained by CC (CH Cl ϩ 1% NEt ) on silica
gel. Yield: 4.72 g (81%). H NMR (CDCl ): δ ϭ 1.95 (s, CH ), 3.90
t, 2.5 Hz, H, CpsubstϪCH), 3.95Ϫ3.97 (m, H,
CpsubstϪCH), 4.06 (s, 5 H, Cp), 4.62 (br. s, 1 H, CpsubstϪCH), 5.18
s, 2 H, CH ), 5.89 (br. s, 1 H, NH), 7.34Ϫ7.38 (m, 5 H, phenyl)
ppm. MS (HR MALDI): m/z 349.0765 (calcd. for
); found 349.0757 [M ]. C19 19FeNO (349.20):
2
2
3
1
1
uct was isolated as a clear, red oil. Yield: 1.17 g (82%). H NMR
3
3
(
C
6
D
6
): δ ϭ 1.13 (t, J ϭ 6.8 Hz, 3 H, CH
H, CH CH ), 1.86 (s, 3 H, CpϪCH ), 2.24 (s, 3 H, CpϪCH
.45Ϫ3.74 (m, 4 H, 2 CH CH ), 3.74Ϫ3.77 (m, 1 H, CpsubstϪCH),
.77Ϫ3.80 (m, H, CpsubstϪCH), 3.89Ϫ3.92 (m, H,
2
CH
3
), 1.18 (t, J ϭ 7.0 Hz,
(
J
ϭ
1
1
3
3
3
2
3
3
3
),
2
3
(
2
1
1
ϭ
ϩ
CpsubstϪCH), 4.04 (s, 5 H, Cp), 4.09 (d, J ϭ 5.5 Hz, 2 H,
NCH CH), 4.13 (s, 5 H, Cp), 4.18Ϫ4.22 (m, 1 H, CpsubstϪCH),
.25Ϫ4.29 (m, 1 H, CpsubstϪCH), 5.30 (t, J ϭ 5.2 Hz, 1 H,
C
19
H19FeNO
2
H
2
2
calcd. C 65.35, H 5.48, N 4.01; found C 65.46, H 5.44, N 3.92.
CAS 32196Ϫ69Ϫ3.
4
1
3
1
NCH
2
CH), 8.57 (s, 1 H, NϭCHϪN) ppm. C{ H} NMR
): δ ϭ 12.9 (cpϪCH ), 13.3 (cpϪCH ), 15.6 (CH CH ), 15.6
CH ), 53.4 (NCH CH), 57.7 (CpsubstϪCH), 62.6
cohol in a dry 100-mL Schlenk flask. After degassing the suspen- (CpsubstϪCH), 62.7 (2 CpsubstϪCH), 63.7 (CH
(R)-1-Amino-2-methylferrocene (9a): Compound 8a (2.00 g,
(CDCl
(CH
3
3
3
2
3
5.73 mmol, 1.0 equiv.) was suspended in 35 mL of isopropyl al-
2
3
2
2
CH
3
), 64.0
Eur. J. Inorg. Chem. 2005, 347Ϫ356
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
353

A. Bertogg, F. Camponovo, A. Togni
FULL PAPER
(
(
(
CH
Cp), 78.8 (CpsubstϪCCH
NCH CH), 104.7 (CpsubstϪCN), 107.2 (CpsubstϪCN), 153.3 (Nϭ
2
CH
3
), 67.0 (CpsubstϪCH), 67.2 (CpsubstϪCH), 69.8 (Cp), 70.0 Palladium Complex 14b: Compound 12b (200 mg, 354 µmol, 1.0
), 79.3 (CpsubstϪCCH ), 99.9 equiv.) and [Pd(OAc) (79.6 mg, 351 µmol, 1.0 equiv.) were dis-
solved in 7 mL of distilled pyridine in a dry 20-mL Schlenk flask.
3
3
2 3
]
2
CHϪN) ppm. MS (HR MALDI): m/z ϭ 556.1476 (calcd. for The resulting yellow solution was stirred for 3 h, then NaI (270 mg,
ϩ
C
29
H
36Fe
2
N
2
O
2
); found 556.1475 [M ]. C29
calcd. C 62.61, H 6.52, N 5.04; found C 62.46, H 6.68, N 5.33.
α]22 ϭ ϩ675 (c ϭ 1, CHCl ).
H
36Fe
2
N
2
O
2
(556.30):
1.80 mmol, 5.1 equiv.) was added, leading to a color change to
brown and the formation of a precipitate (other than NaI). After
18 h of stirring, all volatiles were evaporated under reduced press-
[
3
ure. The pure orange product was obtained by CC (CH
silica gel. Yield: 160 mg (59%). H NMR (C D
6 6
2
Cl
): δ ϭ 3.99 (t, J ϭ
.9 Hz, 4 H, 2 Cpsubst-CH), 4.10 (s, 10 H, 2 Cp), 5.50 (t, J ϭ 1.8 Hz,
H, 2 CpsubstϪCH), 6.22Ϫ6.26 (m, 2 H, py), 6.53 (tt, J ϭ 1.8,
ϭ 7.8 Hz, 1 H, py), 7.03 (s, 2 H, NCHCHN), 8.98Ϫ9.00 (m, 2
2
) on
N,NЈ-Bis[(R)-2-methylferrocen-1-yl]imidazolium Iodide (12a): Com-
pound 11a (1.36 g, 2.45 mmol, 1.0 equiv.) was dissolved in 28 mL
of distilled MeCN in a dry 100-mL Schlenk flask. After addition
of BF ·OEt (1.88 mL, 2.09 g, 14.7 mmol, 6.0 equiv.) at room tem-
3 2
perature, which caused an immediate darkening of the reaction
1
1
4
J
1
2
13
1
H, py) ppm. C{ H} NMR (C
6
D
6
): δ ϭ 66.3 (CpsubstϪCH), 66.6
mixture, the reaction temperature was raised to 70 °C. After 3 h,
additional BF ·OEt (0.9 mL, 1.0 g, 7.0 mmol, 2.9 equiv.) was ad-
3 2
(CpsubstϪCH), 70.1 (Cp), 97.7 (CpsubstϪCquat), 123.5 (NCHCHN),
1
23.9 (py), 136.8 (py), 151.1 (NϪCPdϪN), 154.4 (py) ppm. MS
Pd);
found 795.7470 [M Ϫ py] with the expected isotopic pattern.
Pd (769.02): calcd. C 38.37, H 2.99, N 4.79, I 28.96;
ded and the reaction mixture was stirred for 15 h. Evaporation of
the solvent under reduced pressure gave a brown yellowish solid.
NaI (1.83 g, 12.3 mmol, 5.0 equiv.) and 28 mL of distilled MeOH
were added and the resulting mixture was stirred at 70 °C for 2 h.
After evaporation of the solvent, the crude product was first filtered
2 2 2
(HR MALDI): m/z ϭ 795.7450 (calcd. for C23H20Fe N I
ϩ
28 2 2 3
C H25Fe I N
found C 38.57, H 3.08, N 4.59, I 29.08.
Palldium Complexes 14a and 15a: Compound 12a (100 mg, 169
µmol, 1.0 equiv.) and [Pd(OAc) ] (38.0 mg, 169 µmol, 1.0 equiv.)
2 3
through a silica-gel pad (CH
NaI and borate waste, and then chromatographed on silica gel
CH Cl ϩ 5% MeOH) to give the product as a light-yellow foam.
2 3
Yield: 1.03 g (71%). H NMR (CD ): δ ϭ 1.99 (s, 6 H, 2 CH ),
2 2
Cl ϩ 5% MeOH) to remove excess
were dissolved in 5 mL of distilled pyridine in a dry 20-mL Schlenk
flask. The resulting clear, brown solution was stirred for 3.5 h, then
NaI (132 mg, 879 µmol, 5.2 equiv.) was added to the darkened mix-
ture, which caused a slight lightening of the color and the forma-
tion of a precipitate (other than NaI). After 15 h of stirring, all
volatiles were evaporated under reduced pressure. An orange mix-
(
2
2
1
2
Cl
.28 (t, J ϭ 2.7 Hz, 2 H, 2 CpsubstϪCH), 4.33 (s, 10 H, 2 Cp),
.39Ϫ4.42 (m, 2 H, 2 CpsubstϪCH), 4.85 (dd, J ϭ 2.7, J ϭ 1.2 Hz,
H, 2 CpsubstϪCH), 7.85 (d, J ϭ 1.5 Hz, 2 H, NCHCHN), 9.03
4
4
2
1
2
13
1
(
t, J ϭ 1.5 Hz, 1 H, NϭCHϪN) ppm. C{ H} NMR (CD
δ ϭ 13.0 (CpsubstϪCH ), 65.6 (CpsubstϪCH), 65.8 (CpsubstϪCH),
9.5 (CpsubstϪCH), 71.2 (Cp), 79.2 (CpsubstϪCquat), 92.6
CpsubstϪCquat), 125.4 (NCHCHN), 137.3 (NϭCHϪN) ppm. MS
2 2
Cl ):
2 2
ture of the two products was obtained by CC (CH Cl ) on silica
gel. Yield: 106 mg (54%). The mixture consists of 53.5 mg (59.2
3
6
µmol) of the mononuclear and 52.3 mg (31.7 µmol) of the dinuclear
(
(
1
1
ϩ
2
6 6
species, as determined by H NMR spectroscopy. H NMR (C D ;
HR MALDI): m/z ϭ 465.0717 (calcd. for C25
H
25Fe
2
N
); found
(592.07): calcd. C 50.71, H 4.26,
N 4.73; found C 50.93, H 4.49, N 4.68. [α]22 ϭ ϩ104 (c ϭ 1,
CHCl ).
ϩ
resonances that belong to 14a are designated with M, those belong-
ing to 15a with D): δ ϭ 1.69 (s, 6 H, 2 CH , D), 2.01 (s, 6 H, 2
CH ; D), 2.11 (s, 6 H, 2 CH , M), 3.86 (s, 10 H, 2 Cp, D), 3.92 (s,
2 2
465.0715 [M Ϫ I]. C25H25Fe IN
3
3
3
3
1
2
5
0 H, 2 Cp, D), 3.97 (s, 10 H, 2 Cp, M), 4.02 (t, J ϭ 2.6 Hz, 2 H,
CpsubstϪCH, M), 4.27 (t, J ϭ 2.5 Hz, 2 H, 2 CpsubstϪCH, D),
.64Ϫ5.68 (m, 2 H, 2 CpsubstϪCH, D), 5.71Ϫ5.75 (m, 2 H, 2
N,NЈ-Bis[(R)-2-methylferrocen-1-yl]imidazol-2-ylidene (1a): A 20-
mL Schlenk vessel was charged with compound 12a (20 mg, 34
µmol, 1.0 equiv.) and KOtBu (8 mg, 71 µmol, 2.1 equiv.) in a glove-
box. Addition of 2 mL of distilled pentane caused the formation
of an orange slurry. After stirring for 3.5 h, all volatiles were evapo-
rated under reduced pressure, the residue was taken up in 1 mL of
CpsubstϪCH, D), 6.00 (dd, J
1 2
ϭ 2.5, J ϭ 1.0 Hz, 2 H, 2
CpsubstϪCH, M), 6.10Ϫ6.17 (m, 2 H, py, M), 6.39Ϫ6.48 (m, 1 H,
py, M), 7.19Ϫ7.22 (m, 2 H, NCHCHN, D), 7.34 (s, 2 H,
NCHCHN, M), 8.76Ϫ8.81 (m, 2 H, py, M) ppm.
˚
distilled deuterated benzene and filtered through a 4 A frit, which
1
Palladium Complex 16a: Addition of 1.5 mL of CH
2
Cl
2
to a dry
led to a clear light-yellow solution. H NMR (C
6
D
6
): δ ϭ 2.26 (s,
20-mL Schlenk flask containing a mixture of 14a and 15a (97 mg,
1
6
3
H, 2 CH ), 3.81 (t, J ϭ 2.5 Hz, 2 H, 2 CpsubstCH), 3.90 (t, J ϭ
II
23 µmol Pd , 1.0 equiv.) and triphenylphosphane (60.2 mg, 230
2
.0 Hz, 2 H, 2 CpsubstCH), 4.07 (s, 10 H, 2 Cp), 4.38Ϫ4.40 (m, 2
H, 2 CpsubstCH), 7.01 (s, 2 H, NCHCHN) ppm. 1 C{ H} NMR
3
1
µmol, 2.8 equiv.) caused the formation of a clear red to orange
solution. After 1 h of stirring, all volatiles were removed under
reduced pressure and the residue was rinsed five times with pen-
tane. Drying under reduced pressure yielded a pale-yellow solid.
Yield: 115 mg (86%). H NMR (CD
(
(
(
(
C
6
D
6
):
δ
ϭ
14.5 (CpsubstϪCH
68.0 (CpsubstϪCH),
), 99.8 (CpsubstϪCN), 120.8 (NCHCHN), 221.2
3
), 63.6 (CpsubstϪCH), 64.2
CpsubstϪCH),
CpsubstϪCCH
70.0 (Cp), 79.6
3
5
1
NCN) ppm. 1 N NMR (C
2
Cl
2
): δ ϭ 2.08 (s, 6 H, 2 CH
3
),
6 6
D ): δ ϭ Ϫ188.2 ppm.
4
.27Ϫ4.30 (m, 14 H, 2 cp and 4 CpsubstϪCH), 5.34 (t, 2 H, 2
CpsubstϪCH, J ϭ 2.0 Hz), 7.29Ϫ7.33 (m, 6 H, PPh ), 7.34Ϫ7.40
(m, 3 H, PPh ), 7.43Ϫ7.49 (m, 6 H, PPh ), 7.72 (d, 2 H, J ϭ 1.0 Hz,
NCHCHN) ppm. C NMR (CD ): δ ϭ 13.1 (CpsubstϪCH ),
0 min, 1H NMR analysis of the solution showed complete and 64.0 (CpsubstϪCH), 68.1 (CpsubstϪCH), 68.7 (CpsubstϪCH), 70.0
N,NЈ-Bis[(R)-2-methylferrocen-1-yl]imidazole-2-thione (13a):
4.1 mg, 128 µmol, 3.5 equiv.) was added to the solution of com-
pound 1a in benzene prepared above. After a reaction time of
S
8
3
(
3
3
1
3
2
Cl
2
3
3
1
clean conversion. H NMR (C
t, J ϭ 2.5 Hz, 2 H, 2 CpsubstCH), 3.86 (t, J ϭ 2.1 Hz, 2 H, 2 5.6 Hz, (NCHCHN), 127.5 (d, J ϭ 10.1 Hz, PPh
CpsubstCH), 3.98 (s, 10 H, 2 Cp), 4.49Ϫ4.51 (m, 2 H, 2 CpsubstCH), 2.3 Hz, PPh ), 133.0 (d, J ϭ 44.3 Hz, PPh ), 135.4 (d, J ϭ 11.0 Hz,
), 165.2 (d, J ϭ 193.7 Hz, NϪCPdϪN) ppm. P NMR
Cl ): δ ϭ 17.7 ppm. MS (HR MALDI): m/z ϭ 958.9629
), 96.5 (calcd. for C43
CpsubstϪCN), 119.6 (NCHCHN), 170.3 (NCN) ppm. MS (HR expected isotopic pattern. C43
24Fe S); found 47.53, H 3.62, I 23.36, N 2.58, P 2.85; found C 47.60, H 3.73, I
23.11, N 2.51, P 3.02. [α]22 ϭ ϩ79 (c ϭ 1, CHCl ).
6
D
6
): δ ϭ 1.94 (s, 6 H, 2 CH
3
), 3.79
(Cp), 79.3 (CpsubstϪCN), 97.9 (CpsubstϪCCH
3
), 124.6 (d, J ϭ
(
3
), 129.9 (d, J ϭ
3
3
1
31
7
.01 (s, 2 H, NCHCHN) ppm. 13C{ H} NMR (C
), 64.6 (CpsubstϪCH), 67.6 (CpsubstϪCH), 68.0
CpsubstϪCH), 70.1 (Cp), 81.7 (CpsubstϪCCH
6
D
6
): δ ϭ 13.5 PPh
(CD
3
(
(
(
CpsubstϪCH
3
2
2
ϩ
3
H39Fe
2
IN
2
PPd); found 958.9654 [M Ϫ I ] with the
PPd (1086.68): calcd. C
H
2 2 2
39Fe I N
MALDI): m/z ϭ 496.0359 (calcd. for C25
H
2 2
N
ϩ
496.0359 [M ].
3
354
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 347Ϫ356

N-Ferrocenyl-Substituted Planar-Chiral N-Heterocyclic Carbenes
FULL PAPER
Table 1. X-ray crystallographic data of 12a, 12b and 16a
12a
12b
16a
Empirical formula
Formula mass
C
25
H
25Fe
2
IN
2
C
23
H
21Fe
2
IN
2
43 2 2 2
C H39Fe I N PPd
1086.63
293(2)
592.07
200(2)
0.71073
triclinic
P1
a ϭ 9.0692(7) A
b ϭ 25.0236(19) A
564.02
298(2)
0.71073
orthorhombic
Pnma
a ϭ 7.1601(4) A
b ϭ 7.5642(4) A
c ϭ 10.9701(6) A
α ϭ 84.6960(10)°
β ϭ 85.4760(10)°
γ ϭ 73.4130(10)°
2071.3(3)
Temperature [K]
˚
Wavelength [A]
0.71073
Crystal system
Space group
Unit cell dimensions
monoclinic
P2
a ϭ 10.299(3) A
b ϭ 11.827(3) A
c ϭ 16.900(4) A
1
˚
˚
˚
˚
˚
˚
˚
˚
˚
c ϭ 9.1270(7) A
α ϭ 90°
β ϭ 90°
γ ϭ 90°
566.13(5)
1
1.737
2.659
0.39 ϫ 0.23 ϫ 0.14
5840, 5118
0.0114
α ϭ 90°
β ϭ 99.772(5)°
γ ϭ 90°
˚
3
Volume [A ]
2028.7(9)
2
1.779
Z
4
3
Calcd. density [g/cm ]
1.809
2.902
0.21 ϫ 0.08 ϫ 0.05
12775, 2172
0.0346
Absorption coefficient [mmϪ1]
Crystal size [mm]
2.738
0.60 ϫ 0.28 ϫ 0.23
20853, 9926
0.0253
Reflections collected, unique
R
int
2
Refinement method
Data, restraints, parameters
GOF
full-matrix least squares on F
2172, 0, 130
1.322
5118, 3, 273
1.057
9926, 1, 462
1.048
R, R
w
0.0214, 0.0531
0.695/Ϫ0.287
0.0822, 0.1525
1.706/Ϫ1.334
0.0290, 0.0635
0.994/Ϫ0.505
Min./max. residual [e·AϪ3]
˚
Palladium Complex 16b: A 100-mL Schlenk vessel was charged with
compound 14b (157 mg, 204 µmol, 1.0 equiv.) and triphenylphos-
phane (107 mg, 408 µmol, 2.0 equiv.). After addition of 3.0 mL of
Road, Cambridge CB2 1EZ, UK; Fax: ϩ44 1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk].
CH
tion within 5 min. After 2 h, the solvent was evaporated under
reduced pressure, and the product was separated from excess PPh
as a yellow powder, by repeated washing with pentane. Yield:
2 2
Cl , the cloudy orange mixture turned into a clear yellow solu-
Acknowledgments
Support from the Swiss National Science Foundation is gratefully
acknowledged. We thank Sebastian Gischig for performing the X-
3
,
1
195 mg (94%). H NMR (CD
2 2
Cl
): δ ϭ 4.26Ϫ431 (m, 14 H, 2 cp ray crystallographic studies of compounds 12a, 12b and 16a.
and 2 CpsubstϪCH), 5.18 (t, J ϭ 2.0 Hz, 2 CpsubstϪCH), 7.24Ϫ7.61
1
3
(
m, 15 H, PPh
NMR (CD Cl
Cp), 97.3 (d, J ϭ 0.8 Hz, CpsubstϪCN), 123.6, (d, J ϭ 5.6 Hz,
NCHCHN), 127.6 (d, J ϭ 10.2 Hz, PPh ), 130.0 (d, J ϭ 2.3 Hz,
), 132.7 (d, J ϭ 44.4 Hz, PPh ), 135.2 (d, J ϭ 10.9 Hz, PPh
59.8 (d, J ϭ 189.9 Hz, NϪCPdϪN) ppm. 31P NMR (CD
Cl
3
), 7.58 (d, J ϭ 1.2 Hz, 2 H, NCHCHN) ppm.
C
[1]
[2]
Ferrocenes (Eds.: A. Togni, T. Hayashi), Wiley-VCH,
Weinheim, 1995.
2
2
): δ ϭ 65.6 (CpsubstϪCH), 66.1 (CpsubstϪCH), 69.7
(
(
C. W. K. Gstoettmayr, V. P. W. Bohm, E. Herdtweck, M. Gros-
che, W. A. Herrmann, Angew. Chem. Int. Ed. 2002, 41, 1363.
C. L. Yang, H. M. Lee, S. P. Nolan, Org. Lett. 2001, 3, 1511.
T. M. Trnka, R. H. Grubbs, Acc. Chem. Res. 2001, 34, 18.
S. R. Stauffer, S. W. Lee, J. P. Stambuli, S. I. Hauck, J. F. Hart-
wig, Org. Lett. 2000, 2, 1423.
3
[3]
PPh
1
3
3
3
),
):
[4]
2
2
[
[
5]
6]
δ ϭ 16.7 ppm. MS (HRes MALDI): m/z ϭ 930.9316 (calcd. for
ϩ
C
41
H
35Fe
isotopic pattern. C41
.33, N 2.65; found C 47.30, H 3.44, N 2.63.
2
IN
2
PPd); found 930.9334 [M Ϫ I ] with the expected
B. Bildstein, M. Malaun, H. Kopacka, K. Wurst, M. Mitter-
bock, K. H. Ongania, G. Opromolla, P. Zanello, Organometall-
ics 1999, 18, 4325.
B. Bildstein, M. Malaun, H. Kopacka, K. H. Ongania, K.
Wurst, J. Organomet. Chem. 1999, 572, 177.
B. Bildstein, J. Organomet. Chem. 2001, 617, 28.
R. Jackstell, A. Frisch, M. Beller, D. Rottger, M. Malaun, B.
Bildstein, J. Mol. Catal. A 2002, 18, 105.
B. Bildstein, M. Malaun, H. Kopacka, K. H. Ongania, K.
Wurst, J. Organomet. Chem. 1998, 552, 45.
C. Bolm, M. Kesselgruber, G. Raabe, Organometallics 2002,
21, 707.
D. Broggini, A. Togni, Helv. Chim. Acta 2002, 85, 2518.
H. Seo, H. Park, B. Y. Kim, J. H. Lee, S. U. Son, Y. K. Chung,
Organometallics 2003, 22, 618.
H. Seo, B. Y. Kim, J. H. Lee, H. J. Park, S. U. Son, Y. K.
Chung, Organometallics 2003, 22, 4783.
2 2 2
H35Fe I N
PPd (1058.64): calcd. C 46.52, H
3
[
[
7]
8]
X-ray Crystallographic Study: X-ray structural measurements were
carried out with a Bruker CCD diffractometer (Bruker SMART
PLATFORM, with CCD detector, graphite monochromator, Mo-
[9]
α
K radiation). The program SMART was used for data collection.
Integration was performed with SAINT. The structure solution and
refinement on F2 were accomplished with SHELXTL 97. Model
plots were made with ORTEP32. All structures were solved by di-
rect methods. All non-hydrogen atoms were refined freely with an-
isotropic displacement parameters. Hydrogen atoms were refined
at calculated positions riding on their carrier atoms. Weights were
optimized in the final refinement cycles. A summary of the most
important crystallographic data is given in Table 1. CCDC-239875
[10]
[11]
[
[
12]
13]
[14]
(12b), -239876 (16a) and -239877 (12a) contain the supplementary
[15]
[16]
S. Gischig, A. Togni, Organometallics 2004, 23, 2479.
F. Demirhan, O. Yildirim, B. Cetinkaya, Trans. Met. Chem.
2003, 28, 558.
crystallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre, 12 Union
[17]
An N,NЈ-dicyclophane-substituted carbene analogous to 1a
Eur. J. Inorg. Chem. 2005, 347Ϫ356
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
355

A. Bertogg, F. Camponovo, A. Togni
FULL PAPER
[
[
[
27]
28]
29]
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[
[
[
18]
19]
20]
Ϫ
Ϫ
[31]
4
Anions: BPh , TfO .
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[
[
[
21]
22]
23]
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[35]
[36]
C. Grundmann, A. Kreutzberger, J. Am. Chem. Soc. 1955,
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year Arimoto and Haven synthesized aminoferrocene (ref.[
)
26]
The acetal was synthesized instead of the aldehyde in order to
prevent oxazole formation in the following cyclization step.
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2
Pd(dba) , 15% of 12a and 1.5 equiv. of NaOtBu in 1,4-dioxane
at 50 °C for 26 h gave (ϩ)-1,3-dimethyl-3-(1-naphthyl)oxindole
in the mentioned yield and ee. When 16a was used, the ee val-
ues and activity were slightly lower.
G. G. A. Balavoine, J.-C. Daran, G. Iftime, P. G. Lacroix, E.
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Received August 11, 2004
from ferrocenecarboxylic acid by using the Curtius synthetic
strategy, but the overall yield was lower than 20%. Other ap-
proaches including Beckmann rearrangement from the oxime
proved fruitless. Lehner and Schlögl, in 1970 (ref.[ ), reported
the synthesis of planar-chiral (R)-1-amino-2-methylferrocene in
[37]
[38]
27]
[39]
[40]
1
1
26% yield from (R)-2-methylferrocenecarboxylic acid by a
modified procedure and determined its absolute configuration.
The approach presented here differs from Schlögl’s approach
in various reaction conditions such as temperatures, solvents,
the activation of the carboxylic acid and the fact that the se-
quence was performed in two steps in 82% yield. A recent ex-
ample of a high yielding (80%) Curtius degradation sequence
leading to achiral aminoferrocene can be found in ref.[
M. Herberhold, ‘‘Ferrocene Compounds Containing Heteroe-
lements’’, in Ferrocenes (Eds.: A. Togni, T. Hayashi), Wiley-
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Early View Article
Published Online December 2, 2004
F. S. Arimoto, A. C. Haven, J. Am. Chem. Soc. 1955, 77, 6295.
356
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 347Ϫ356