Synthesis of new iron-NHC complexes as catalysts for hydrosilylation reactions

Article abstract of DOI:10.1002/aoc.3006

A series of new piano-stool iron(II) complexes comprising N-heterocyclic carbene ligands [Fe(Cp)(CO)₂(NHC)]I (NHC = 1,3-disubstituted imidazolidin-2-ylidene) have been synthesized and analyzed by ¹H NMR, ¹³C NMR, IR, elemental analysis and mass spectrometric techniques. These compounds were easily prepared from the reaction of disubstituted imidazolidin-2-ylidene with [FeI(Cp)(CO)₂] in toluene at room temperature. These complexes were tested in the catalytic hydrosilylation reaction of aldehydes and ketones with phenylsilane in solvent-free conditions. After a basic hydrolysis step, the corresponding alcohols were obtained in good yields. Copyright

Full text of DOI:10.1002/aoc.3006

Full Paper
Received: 23 February 2013
Revised: 1 April 2013
Accepted: 13 April 2013
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3006
Synthesis of new iron–NHC complexes as
catalysts for hydrosilylation reactions
a
a
a
b
Serpil Demir , Yasemin Gökçe , Nazan Kaloğlu , Jean-Baptiste Sortais ,
b
a
Christophe Darcel and İsmail Özdemir *
A series of new piano-stool iron(II) complexes comprising N-heterocyclic carbene ligands [Fe(Cp)(CO) (NHC)]I (NHC =
2
1
13
1
,3-disubstituted imidazolidin-2-ylidene) have been synthesized and analyzed by H NMR, C NMR, IR, elemental analysis and mass
spectrometric techniques. These compounds were easily prepared from the reaction of disubstituted imidazolidin-2-ylidene with
[
FeI(Cp)(CO) ] in toluene at room temperature. These complexes were tested in the catalytic hydrosilylation reaction of aldehydes
2
and ketones with phenylsilane in solvent-free conditions. After a basic hydrolysis step, the corresponding alcohols were obtained
in good yields. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords: iron; NHC ligands; hydrosilylation; aldehydes; ketones
[
23]
ligands.
(
Piano-stool Fe(II) complexes of the type [CpFe(CO)2
23,24]
Introduction
[
NHC)]X
and pincer Fe(II)/Fe(III) complexes of Fe(2,6-bis
[
20]
The development and application of efficient, convenient,
selective and environmentally friendly synthetic methods are
highly desirable in organic chemisrty. In light of this, transition-
metal-catalyzed processes have been developed in the synthesis
of organic compounds. In the last few decades, late transition
metal catalysts based on Pd, Ru, Rh, Ir, Au and Pt have exhibited
(NHC)pyridine)X
Guerchais and Gibson et al., respectively.
On the another hand, the catalytic reduction of carbonyl
compounds is most frequently performed using hydrogenation
with molecular hydrogen, or via transfer hydrogenation in
isopropanol or formic acid.
these methods for mild and selective reduction is the use of
the combined catalytic hydrosilylation/hydrolysis protocol.
Indeed, Brunner first reported the iron-catalyzed hydrosilylation
of carbonyl compounds in the early 1990s.
n
(n = 2 or 3)
were reported by Siebert,
[
25]
An interesting alternative to
[
1–6]
powerful catalytic ability.
However, the limited availability of
[
26]
these metals as well as their high price and significant toxicity
make it more desirable to search for more economical and envi-
ronmentally friendly alternatives. The application of inexpensive,
non-toxic, commercially available and environmentally friendly
iron complexes as catalysts in chemical synthesis has attracted
[
27]
After the renewal
[
28]
[29]
of this research area by Beller
hydrosilylation using iron as the catalyst is now well exemplified
for the hydrosilylation of aldehydes and ketones. Interestingly,
well-defined NHC–iron complexes such as tethered (Cp-NHC)
and Nishiyama
in 2007,
[7]
[30]
much attention. To date, the use of iron is becoming a highly
attractive and challenging area of research, with special
significance focused on homogeneous catalysis, and various
organic transformations catalysed by iron have been achieved,
[
31]
FeCl
activated aldehydes. Furthermore, cationic and neutral piano-
stool complexes [Cp(IMes)Fe(CO) ][I] and [Cp(IMes)Fe(CO)(I)],
respectively, are efficient catalysts not only for aldehydes and
are also efficient catalysts for hydrosilylation of
[
8]
[9]
including C-C cross-coupling reactions,
substitutions,
2
[10]
[11]
[12]
reductions,
cycloadditions
oxidations,
as well as polymerization.
C-H
functionalizations,
[13]
[14]
[32]
[33]
[34]
Ligands also play
ketones hydrosilylations, but also for imines and amides.
a pivotal role in the modulation of the metal center reactivity.
During the past decade, N-heterocyclic carbenes (NHCs) have
received increasing attention as alternative ligands for the
development of homogeneous catalyst based on last transition
When generated in situ from iron salts and NHC ligands, the
resulting catalysts are also able to promote the reduction of
[
35]
aldehydes, ketones and amides.
Based on these studies,
which demonstrate that iron complexes with NHC ligands play
a beneficial role in hydrosilylation catalysis, we report herein
the preparation of cationic piano-stool iron(II) complexes
containing saturated imidazolidin-2-ylidene NHC ligands and
[15]
metals.
A large number of well-defined NHC complexes of
Pd, Ru, Rh and Ir have been found to show outstanding catalytic
activity for cross-coupling reactions and related transformations.
As a result, iron complexes containing NHC ligands have been
[
16]
prepared and characterized ; however, they are seldom used
[17]
in catalysis. The first use of NHCs in homogeneous iron cataly-
sis was reported by Grubbs and co-workers in 2000 in atom trans-
fer radical polymerization of styrene and methyl methacrylate
*
Correspondence to: İsmail Özdemir, Department of Chemistry, Faculty of
Science and Art, Inönü University, 44280 Malatya, Turkey. Email: ismail.
ozdemir@inonu.edu.tr
[
18]
using well-defined [(NHC) FeX ] complexes as catalysts.
To
2
2
a Department of Chemistry, Faculty of Science and Art, Inönü University, 44280
Malatya, Turkey
date, only a few kinds of well-defined iron NHC complexes have
[
19]
[20]
been reported, which include hexacarbene,
tetracarbene,
[21]
[16,18,22]
tricarbene,
biscarbene
and piano-stool monocarbene
b Centre of Catalysis and Green Chemistry, Institut des Sciences Chimiques de
complexes that are co-ligated with cyclopentadienyl and CO
Rennes, Université de Rennes 1 (UMR 6226 CNRS), 35042 Rennes, Cedex, France
Appl. Organometal. Chem. 2013, 27, 459–464
Copyright © 2013 John Wiley & Sons, Ltd.

S. Demir et al.
their use in reduction of aldehydes and ketones by
hydrosilylation/hydrolysis reaction.
were then obtained in 51–67% isolated yields. All the new
complexes were characterized by spectral data (IR, NMR
spectroscopy, mass spectral data and elemental analysis). The
characterization data of the new compounds are consistent with
the assigned formula.
Results and Discussion
Notably, the mass spectra showed a peak which can be
+
2
Synthesis of NHC–Iron(II) Complexes
assigned to the cation [CpFe(NHC)(CO) ] , which confirmed the
proposed structures and the coordination of the NHC ligand to
the iron center. Moreover, the IR spectra clearly indicate that
the expected two CO ligands are coordinated to the metal centre
which can be observed as two peaks for CO stretching mode in
Iron–NHC complexes are generally prepared via free carbenes
(
generated from deprotonation of imidazolium salts by a strong
[18,20,36]
[22,37]
base)
or by using iron amides.
Recently, Chen and
colleages have have elucidated new approaches to Fe–NHC
the IR spectrum of all complexes (n
= 2026–2036 and nas(CO)
s(CO)
complexes: (i) the electrochemical synthesis using imidazolium
À1
=
1964–1987 cm ). These values are in good agreement with
[
38]
salts and metal plates and (ii) direct reaction of metal powders
previously reported values for piano-stool iron complexes
[
39]
with imidazolium salts or silver–NHC complexes.
Another
[23]
bearing an NHC ligand.
Interestingly, CO vibrations in such
synthetic route is also template-controlled formation of iron com-
monocarbene complexes are slightly lower than those described
[
40]
plex as described by Hahn.
for the similar SIMes imidazolin-2-ylidene iron complex [CpFe(CO)2
In this work, we have chosen the free carbene reaction
methodology to synthesize the iron complexes. According to
À1
(
SIMes)][I] (ns(CO) = 2043 and nas(CO) = 2005 cm ), illustrating that
the benzyl-substituted imidazolin-2-ylidene ligands 1a–f are
[
23]
the procedure described by Guerchais,
we have prepared
stronger donating carbenes than aryl-substituted ones such as
cationic NHC–Fe complexes with iodide as the counterion. The
13
SIMes. C NMR spectra indicated that the resonance characteris-
t
deprotonation of the imidazolidinium salts 1 with KOBu as a
tics of the carbene were located at d 199.3, 199.6, 199.7, 199.4,
base took place at room temperature for 5 h, leading to the
corresponding carbene, which was metalated in situ with [FeI
199.3 and 199.7 ppm for 2a–f, respectively. Carbonyl signals
were observed at d 211.5, 211.4, 211.4, 211.5, 211.9 and 211.6
pm for 2a–2f, respectively. During the time that the cationic
complexes were stirred in dichlorometane at room
temperature under visible light irradiation, no neutral complex
were obtained, which contrasts with the results obtained with
IMes or SIMes NHC iron complexes but showed the bulkier
(
Cp)(CO) ] as iron(II) precursor in toluene at room temperature
2
overnight in the dark (Scheme 1 and Fig. 1). Complexes 2a–f
Rm
Rm
[
32]
character of the present NHC.
N
+
N
1) KOBut, THF, rt, 5h
N
N
Cl-
I
Catalytic Hydrosilylation of Aldehydes and Ketones
The catalytic activities of the new [Fe(Cp)(CO) (NHC)]I cationic
Fe
2) [FeICp(CO)2]
Toluene, rt, overnight
CO
CO
2
complexes 2a–f have been studied for the hydrosilylation reaction
of aldehydes and ketones (Scheme 2).
Rn
Optimization of the hydrosilylation reaction was carried out
with benzadehyde and acetophenone as model carbonyl com-
pounds. Using complex 2a as the model catalyst (1 mol%), we
first surveyed different silanes as hydride sources (1.2 equiv.)
Rn
1
2
a-f
Scheme 1. Preparation of NHC–iron complexes (2a-f).
OMe
OMe
OMe
N
N
Fe
I
N
N
Fe
I
N
Fe
I
N
CO
CO CO
CO
CO CO
OMe
OMe
2
a(65%)
2b(62%)
2c(67%)
OMe
N
N
N
N
N
Fe
I
Fe
I
Fe
CO CO
I
N
CO
CO CO
CO
2
e(51%)
2d(59%)
2f (62%)
Figure 1. Cationic iron piano-stool cyclopentadienyl complexes bearing saturated NHC carbene ligands (in parentheses: isolated yields).
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2013, 27, 459–464

Synthesis and application of new piano-stool iron–NHC complexes
O
OH
H(R)
Using 1 mol% of complex 2a as the catalyst and 1.2 equiv.
phenylsilane under neat conditions, various methoxy-substituted
benzaldehyde derivatives were efficiently reduced under the
1
) Fe-NHC , silane
H(R)
R'
R'
H
2) NaOH, MeOH, rt
ꢀ
optimized conditions (conversion 85–98% at 100 C in 5 min to
Scheme 2. Fe–NHC-catalyzed hydrosilylation reaction.
1
h). Notably, with 2,5-dimethoxybenzaldehyde, a very short
reaction time (5 min) was necessary to reach full conversion.
and found that phenylsilane exhibited the best activity as full
conversion of benzaldehyde was observed after 1 h of reaction
at 100 C in neat conditions (Table 1, entry 4). Interestingly, a
low loading of 0.5 mol% 2a was also permitted to reached full
conversion under similar conditions (Table 1, entry 5). The reac-
tion was then performed with various silanes, including
polymethylhydrosiloxane and tetramethyldisiloxane, and only
phenylsilane was able to obtain good conversions. (Table 1,
entries 1–4). Notably, the catalytic activity of the cationic complex
In this case, complexes 2b, 2c and 2e also gave quite full
conversions (>96%) in only 5 min of reaction at 100 C. 4-tert-
ꢀ
ꢀ
Butylbenzaldehyde was converted into 4-tert-butylbenzyl alcohol
ꢀ
in only 30 min of reaction at 100 C, complexes 2a and 2b being
the most effective catalysts.
The reduction of ketones such as acetophenone and 4-
bromoacetophenone can also be achieved by hydrosilylation using
such complexes as catalysts, but a longer reaction time (4 h) was
ꢀ
necessary at 100 C to obtain the corresponding secondary
2a was examined in toluene, THF and without solvent, and only
alcohols. Notably, catalyst 2a once again showed the best activity.
solvent-free conditions were able to obtain good conversions.
Encouraged by the efficiency of the hydrosilylation of benzalde-
hyde with complex 2a (1 mol%) (1.2 equiv. phenylsilane, neat con-
Of notable interest, and incontrast to the previous results
[
32]
reported with simple IMes NHC ligands, using this type of ben-
zyl-substituted imidazolidin-2-ylidene NHC–iron complexes, no vis-
ible light activation was necessary to peform the reduction reaction.
ꢀ
dition, 100 C, 1 h), we then investigated the activities of different
NHC–iron catalysts 2b–f bearing different NHC ligands and the
scope of the reaction under these optimized conditions (Table 2).
Evaluation of the activity of complexes 2b–f was used as the
Experimental
ꢀ
catalyst (1 mol%) at 100 C under solvent-free conditions; using
General Procedures
1
.2 equiv. phenylsilane revealed that the best catalyst of the
series was complex 2a, which was able to obtain 94% conversion
in 1 h, whereas all the other complexes reached a maximum of
All synthesis were carried out under an inert atmosphere using
Schlenk line techniques. Chemicals and solvents were acquired
from Sigma Aldrich Co. (Poole, UK). Imidazolidinium salts were
9
0% (range 80–90% conversion).
a
Table 1. Optimization for the hydrosilylation of benzaldehyde and acetophenone with the catalyst 2a
ꢀ
b
Entry
2a (mol%)
Silane
Time (h)
Temp. ( C)
Conv. (%)
1
2
3
4
5
6
7
Benzaldehyde
Acetophenone
1
Ph
Ph
3
SiH
SiH
6
6
100
100
100
100
100
50
—
1
2
2
—
1
(MeO)
2
PhSiH
6
—
1
PhSiH
PhSiH
PhSiH
PhSiH
3
1
>97
>97
66
0.5
1
3
1
3
3
24
4
1
100
86
a
Reaction conditions: (i) benzaldehyde or acetophenone (1.0 mmol), silane (1.2 mmol), Fe–NHC complex (1.0 mol%) under neat conditions; (ii)
MeOH (1 ml), then NaOH (2M, 10 ml), room temperature, 1 h.
b
Conversion determined by GC after methanolysis.
a
Table 2. Hydrosilylation of carbonyl compounds by iron catalysts 2a–f
b
Carbonyl compound
Yield (%)
2
a
2b
2c
2d
2e
2f
C
6
H
5
-CHO
94 (1 h)
85 (1 h)
85 (1 h)
88 (1 h)
80 (1 h)
71 (1 h)
80 (1 h)
89 (1 h)
90 (1 h)
72 (1 h)
p-MeO-C
6
H
4
-CHO
-C -CHO
,4,5-(OMe) -C -CHO
-CHO
70 (1 h)
79 (1 h)
2
,5-(OMe)
2
6
H
3
> 8 (5 min)
>98 (30 min)
98 (30 min)
86 (4 h)
98 (5 min)
90 (30 min)
>98 (30 min)
75 (4 h)
97 (5 min)
75 (5 min)
81 (30 min)
96 (30 min)
81 (4 h)
96 (5 min)
98 (30 min)
95 (30 min)
71 (4 h)
78 (5 min)
>98 (30’)
93 (30’)
3
3
6
H
2
>98 (30 min)
86 (30 min)
65 (4 h)
p-(CH
3
)
3
C-C
6
H
4
C
6
H
5
-COCH
3
68 (4 h)
p-Br-C
6
H
4
-COCH
3
96 (2 h)
89 (2 h)
73 (2 h)
87 (2 h)
71 (2 h)
84 (2 h)
a
ꢀ
Reaction conditions: (i) aldehyde or ketone (1.0 mmol), phenylsilane (1.2 mmol), Fe–NHC complex (1.0 mol%) in neat conditions at 100 C; (ii)
MeOH (1 ml) then NaOH (2 M, 10 ml), room temperature, 1 h.
b
Yield determined by GC after methanolysis. In parentheses: time of reaction.
Appl. Organometal. Chem. 2013, 27, 459–464
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

S. Demir et al.
[
41]
13
1
synthesized in our laboratory according to the literature.
(m, 5H, CH
(CH -2,4,6); 49.6 and 49.3 (NCH
2,4,6); 56.2 (CH ); 87.8 (Cp); 127.2, 127.5, 128.2, 129.0,
129.7, 134.6, 137.9 and 138.7 (CH (CH -2,4,6 and
CH ); 199.6 (Fe-Ccarbene); 211.4 (CO). HR-MS: m/z 469.1579
[M+] calculated for C27 Fe 469.1578. Anal. Calcd for
FeI: C, 54.39; H, 4.90; N, 4.70, Found: C, 54.35; H, 4.92;
2
C
6
H
5
). C{ H} NMR (75 MHz, CDCl
3
): d 20.9 (CH
2 6 2
C H
) -
3 3
Solvents were dried with standard methods and freshly distilled
prior to use. Elemental analyses were performed by LECO
CHNS-932 elemental analyzer. Melting points were measured in
open capillary tubes with an Electrothermal-9200 melting point
apparatus. FT-IR spectra were recorded as KBr pellets in the range
3
)
3
2
CH N); 50.2 (CH
2
2
C
6
H
2
(CH
2 6 5
C H
2
C
6
H
2
3 3
)
2 6 5
C H
29 2 2
H N O
À1
1
13
4
00–4000 cm on a PerkinElmer Spectrum 100. H NMR and
C
27 29 2 2
C H N O
NMR spectra were recorded using a Varian As 400 Merkur
N, 4.66%.
1
13
spectrometer operating at 400 MHz ( H), 100 MHz ( C) in CDCl
3
Dicarbonyl-[1,3-bis(3,4,5-trimethoxybenzyl)imidazolin-2-ylidene]cyclopentadienyl
iron(II) iodide, 2c
with tetramethylsilane as an internal reference. The NMR studies
were carried out in high-quality 5 mm NMR tubes. Signals are
quoted in parts per million as d downfield from tetramethylsilane
ꢀ
0.49 g; yield 67%; m.p.: decomposition temperature 230 C. IR
À1
1
(d 0.00) as an internal standard. Coupling constants (J values)
(KBr, cm ): n(CN) = 1590, n(CO) = 2026 and 1977. H NMR
(300 MHz, CDCl ): d 3.86 (s, 18H, CH C H (OCH ) -3,4,5); 3.91
are given in hertz. NMR multiplicities are abbreviated as follows:
s = singlet, d = doublet, t = triplet, m = multiplet signal. HR mass
spectra and elemental analysis were recorded on a Bruker MicrO-
Tof-Q 2 spectrometer at the CRMPO (Centre Régional de Mesure
Physiques de l’Ouest), University of Rennes 1. All catalytic reac-
tions were monitored on a Agilent 6890N GC system by GC-FID
with a HP-5 column of 30 m length, 0.32 mm diameter and 0.25
mm film thickness. Column chromatography was performed
using silica gel 60 (70-230 mesh). Solvent ratios are given as v/v.
3
2
6
2
3 2
(s, 4H, NCH CH N); 4.97 (s, 4H, CH C H (OCH ) -3,4,5); 5.64
(s, 5H, Cp); 6.58 (s, 4H, CH C H (OCH ) -3,4,5). C{ H} NMR
(75 MHz, CDCl ): d 50.2 (NCH CH N); 56.8 (CH C H (OCH ) -3,4,5);
2
2
2
6
2
3 2
13
1
2
6
2
3 2
3
2
2
2
6
2
3 2
60.9 (CH C H (OCH ) -3,4,5); 87.9 (Cp); 104.9, 129.8, 138.1 and
2
6
2
3 2
153.8 (CH C H (OCH ) -3,4,5); 199.7 (Fe-Ccarbene); 211.4 (CO). HR-
MS: m/z 607.1718 [M+] calculated for C H N O Fe 607.1719. Anal.
Calcd for C H N O FeI: C, 49.07; H, 4.80; N, 3.81, Found: C, 49.05; H,
4.78; N, 3.87%.
2
6
2
3 2
3
0 35 2 8
3
0 35 2 8
Dicarbonyl-[1-(2,4,6-trimethylbenzyl)-3-(4-methylbenzyl)imidazolin-2-ylidene]
General Experimental Procedure for the Preparation of the
cyclopentadienyliron(II) iodide, 2d
Iron–NHC Complexes
ꢀ
0
.36 g; yield 59%; m.p.: decomposition temperature 170 C, IR
t
À1
1
A mixture of freshly sublimed KO Bu and the NHC precursor in
THF was stirred at room temperature for 5 h. After evaporation
of the solvent, toluene was added in the Schlenk tube and the
(KBr, cm ): n(CN) = 1493, n(CO) = 2034 and 1982. H NMR
(300 MHz, CDCl ): d 2.28 (s, 3H, CH C H (CH ) -2,4,6); 2.35
(s, 3H, CH C H (CH )-4); 2.43 (s, 6H, CH C H (CH ) -2,4,6); 3.66-
3
2
6
2
3 3
2
6
4
3
2
6
2
3 3
solution was subsequently filtered. [CpFe(CO) I] complex was
2 2 2 6 4 3
3.33 (m, 4H, NCH CH N); 4.83 (s, 2H, CH C H (CH )-4); 5.05
2
then added to the bright light-yellow solution at room tempera-
ture. The Schlenk tube was wrapped with aluminium foil and the
solution was stirred overnight at room temperature. The solvent
was removed under vacuum and the crude product washed
several times diethyl ether to remove starting iron complex.
2 6 2 3 3 2 6 2
(s, 2H, CH C H (CH ) -2,4,6); 5.67 (s, 5H, Cp); 6.90 (s, 2H, CH C H
13
1
(CH ) -2,4,6); 7.19 (s, 4H, CH C H (CH )-4). C{ H} NMR (75 MHz,
3
3
2
6
4
3
CDCl ): d 20.9 (CH C H (CH ) -2,4,6); 21.1 (CH C H (CH )-4); 49.5
3
2
6
2
3 3
2
6
4
3
2
2
2
6
2
3 3
2 6 4
and 49.2 (NCH CH N); 50.2 (CH C H (CH ) -2,4,6); 55.9 (CH C H
(CH )-4); 87.8 (Cp); 127.2, 127.5, 129.6, 129.7, 129.8, 131.4,
3
1
1
37.9 and 138.6 (CH
99.4 (Fe-Ccabene); 211.5 (CO). HR-MS: m/z 483.1734 [M+] calculated
Fe 483.1735. Anal. Calcd for C28 FeI: C, 55.10;
H, 5.12; N, 4.59, Found: C, 55.13; H, 5.17; N, 4.56%.
2 6 2 3 3 2 6 4 3
C H (CH ) -2,4,6 and CH C H (CH )-4);
Dicarbonyl-[1-(2,4,6-trimethylbenzyl)-3-(3,5-dimethylbenzyl)imidazolin-2-
ylidene] cyclopentadienyliron(II) iodide, 2a
for C28
H N O
31 2 2
31 2 2
H N O
ꢀ
0
(
.40 g; yield 65%; m.p.: decomposition temperature 190 C. IR
À1
1
KBr, cm ): n(CN) = 1498, n(CO) = 2036 and 1985. H NMR
Dicarbonyl-[1,3-bis(2,3,5,6-tetramethylbenzyl)imidazolin-2-ylidene]
cyclopentadienyl iron(II) iodide, 2e
(
300 MHz, CDCl ): d 2.28 (s, 3H, CH C H (CH ) -2,4,6); 2.32
3
2
6
2
3 3
(
s, 6H, CH C H (CH ) -3,5); 2.44 (s, 6H, CH C H (CH ) -2,4,6);
2 6 3 3 2 2 6 2 3 3
ꢀ
0.34 g; yield: 51%; m.p.: decomposition temperature 200 C. IR
(KBr, cm ): n(CN) = 1426, n(CO) = 2036 and 1968. H NMR
(300 MHz, CDCl ): d 2.25, (s, 12H, CH C H(CH ) -2,3,5,6); 2.33
3
.68–3.35 (m, 4H, NCH CH N); 4.84 (s, 2H, CH C H (CH ) -3,5);
2
2
2
6
3
3 2
À1
1
5
.00 (s, 2H, CH C H (CH ) -2,4,6); 5.67 (s, 5H, Cp); 6.90 (s, 4H,
2
6
2
3 3
CH C H (CH ) -2,4,6 and CH C H (CH ) -3,5); 6.95 (s, 1H, CH C H
2
6
2
3 3
2
6
3
3 2
2
6
3
3
2
6
3 4
1
3
1
(
CH ) -3,5). C{ H} NMR (75 MHz, CDCl ): d 20.9 (CH C H (CH ) -
(s, 12H, CH C H(CH ) -2,3,5,6); 3.28 (s, 4H, NCH CH N); 4.91
3
2
3
2
6
2
3 3
2 6 3 4 2 2
2
,4,6); 21.3 (CH C H (CH ) -3,5); 49.5 and 49.2 (NCH CH N); 50.1
(s, 4H, CH C H(CH ) -2,3,5,6); 5.76 (s, 5H, Cp); 6.99 (s, 2H, CH C H
2 6 3 4 2 6
2
6
3
3 2
2
2
13
1
(
1
2
CH
C H
2 6 2
(CH
27.2, 129.7, 129.8, 134.4, 137.9 and 138.6 (CH
,4,6 and CH (CH -3,5); 199.3 (Fe-Ccarbene); 211.5 (CO).
Fe 497.1892.
FeI: C, 55.79; H, 5.33; N, 4.49; Found: C,
3 3
)
-2,4,6); 56.1 (CH
2
C
6
H
3
(CH
3
)
2
-3,5); 87.7 (Cp); 125.3,
(CH ) -2,3,5,6). C{ H} NMR (75 MHz, CDCl ): d 16.7(CH C H(CH ) -
3 4 3 2 6 3 4
2 6 2 3 3
C H (CH ) -
2,3,5,6), 20.5 (CH C H(CH ) -2,3,5,6); 48.7 (NCH CH N); 50.9
2 6 3 4 2 2
(CH C H(CH ) -2,3,5,6); 87.7 (Cp); 130.2, 132.4, 134.1, and 134.4
2 6 3 4
(CH C H(CH ) -2,3,5,6); 199.3 (Fe-Ccabene); 211.9 (CO). HR-MS: m/z
2 6 3 4
539.2357 [M+] calculated for C H N O Fe 539.2361. Anal. Calcd
32 39 2 2
C H
2 6 3
)
3 2
HR-MS: m/z 497.1893 [M+] calculated for C29
Anal. Calcd for C29
5.73; H, 5.38; N, 4.45%.
H N O
33 2 2
H N O
33 2 2
5
for C H N O FeI: C, 57.67; H,5.90; N, 4.20, Found: C, 57.65; H,
32 39 2 2
5.92; N, 4.17%.
Dicarbonyl-[1-(2,4,6-trimethylbenzyl)-3-(benzyl)imidazolin-2-ylidene]
cyclopentadienyl iron(II) iodide, 2b
Dicarbonyl-[1-(2,4,6-trimethylbenzyl)-3-(benzhydryl)imidazolin-2-ylidene]
cyclopenta dienyliron(II) iodide, 2f
ꢀ
.37 g; yield 62%. m.p.: decomposition temperature 120 C. IR
0
À1
1
ꢀ
(
(
(
4
(
KBr, cm ): n(CN) = 1593, n(CO) = 2034 and 1987. H NMR
300 MHz, CDCl ): d 2.23 (s, 3H, CH (CH -2,4,6); 2.43
s, 6H, CH -2,4,6); 3.66–3.34 (m, 4H, NCH CH N);
.84 (s, 2H, CH -2,4,6); 5.68
-2,4,6); 7.33–7.37
0.42 g; yield: 62%; m.p.: decomposition temperature 220 C. IR
À1
1
3
2
C
6
H
2
3
)
3
(KBr, cm ): n(CN) = 1417, n(CO) = 2036 and 1964. H NMR
(300 MHz, CDCl ): d 2.28, (s, 6H, CH (CH -2,4,6); 2.45
(s, 3H, CH (CH -2,4,6); 3.51–3.37 (m, 4H, NCH CH N); 5.05
(s, 2H, CH (CH -2,4,6); 5.44 (s, 5H, Cp); 6.89 (s, 2H, CH
2
C
6
H
2
(CH
3
)
3
2
2
3
C H
2 6 2
3 3
)
2
C
6
H
5
); 5.10 (s, 2H, CH
2
C
6
H
2
(CH
3
)
3
C H
2 6 2
)
3 3
2
2
s, 5H, Cp); 6.90 (s, 2H, CH
2
C
6
H
2
(CH
3
)
3
C H
2 6 2
)
3 3
2 6 2
C H
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2013, 27, 459–464

Synthesis and application of new piano-stool iron–NHC complexes
pp. 177–196; b) B. Plietker, Angew. Chem. Int. Ed. 2006, 45, 1469; c)
B. Plietker, in Iron Catalysis in Organic Chemistry (Ed.: B. Plietker),
Wiley-VCH, Weinheim, 2008, pp. 197–215.
(
CH
3
)
3
-2,4,6); 6.82 (s 1H, CH(C
6
H
5
)
2
); 7.29-7.43 (m, 10H, CH(C
): d 20.9 (CH (CH -2,4,6), 20.3
-2,4,6); 49.1 (NCH CH N); 51.1 (CH (CH
,4,6); 67.1 (CH(C ); 87.6 (Cp); 127.3, 128.5, 128.6, 129.1, 129.4,
29.8, 137.8 and 138.5 (CH (CH -2,4,6 and CH(C ); 199.7
6 5 2
H ) ).
13
1
C{ H} NMR (75 MHz, CDCl
CH (CH
3
C H
2 6 2
3 3
)
(
2
1
2
C
H
6 2
)
3 3
2
2
2
C
6
H
2
3 3
) -
[
[
10] a) K. Junge, K. Schröder, M. Beller, Chem. Commun. 2011, 4849; b)
B. A. F. Le Bailly, S. P. Thomas, RSC Advances 2011, 1, 1435; c)
R. H. Morris, Chem. Soc. Rev. 2009, 38, 2282; d) S. Gaillard,
J.-L. Renaud, ChemSusChem 2008, 1, 505.
11] A. C. Mayer, C. Bolm, in Iron Catalysis in Organic Chemistry (Ed.:
B. Plietker), Wiley-VCH, Weinheim, 2008, pp. 73–124.
12] C. L. Sun, B. J. Li, Z. J. Shi, Chem. Rev. 2011, 111, 1293.
13] a) A. Fürstner, K. Majima, R. Martin, H. Krause, E. Kattnig, R. Goddard,
C. W. Lehmann, J. Am. Chem. Soc. 2008, 130, 1992; b) N. Saino,
D. Kogure, S. Okamoto, Org. Lett. 2005, 7, 3065; c) B. R. D’Souza,
T. K. Lane, J. Louie, Org. Lett. 2011, 13, 2936.
6 5 2
H )
C
2 6
H
2
)
3 3
6 5 2
H )
(
Fe-Ccabene); 211.6 (CO). HR-MS: m/z 545.1928 [M+] calculated for
Fe 545.1931. Anal. Calcd for C33 FeI: C, 58.95;
H, 4.95; N, 4.17, Found: C, 58.91; H, 4.97; N, 4.21%.
C
33
H
33
N O
2 2
33 2 2
H N O
[
[
General Procedure for the Hydrosilylation of Carbonyl
Compound-Catalyzed Fe-NHC
[
14] V. C. Gibson, G. A. Solan, in Catalysis without Precious Metals (Ed.:
M. Bullock), Wiley-VCH, Weinheim, 2010, pp. 111–141.
Under a nitrogen atmosphere, carbonyl compound (1.0 mmol),
silane (1.2 mmol) and Fe-NHC complex (1.0 mol%) were added
[15] a) D. Bourissou, O. Guerret, F. P. Gabbai, G. Bertrand, Chem. Rev.
2000, 100, 39; b) W. A. Herrmann, Angew. Chem. Int. Ed. 2002, 41,
1290; c) E. Peris, R. H. Crabtree, Coord. Chem. Rev. 2004, 248, 2239;
d) C. M. Crudden, D. P. Allen, Coord. Chem. Rev. 2004, 248, 2247; e)
D. Pugh, A. A. Danopoulos, Coord. Chem. Rev. 2007, 251, 610; f)
J. A. Mata, M. Poyatos, E. Peris, Coord. Chem. Rev. 2007, 251, 841; g)
S. Würtz, F. Glorious, Acc. Chem. Res. 2008, 41, 1523; h) S. Diez-
Gonzalez, N. Marion, S. P. Nolan, Chem. Rev. 2009, 109, 3612; i)
O. Kühl, Coord. Chem. Rev. 2009, 253, 2481; j) R. Corberán, E. Mas-Marzá,
E. Peris, Eur. J. Inorg. Chem. 2009, 1700; k) O. Schuster, L. Yang,
H. G. Raubenheimer, M. Albrecht, Chem. Rev. 2009, 109, 3445.
in an oven-dried Schlenk tube. The reaction was stirred at
ꢀ
1
00 C for 5 min to 4 h. The reaction mixture was then cooled
to room temperature and MeOH (1 ml) was added, followed
by aqueous NaOH (2 M, 10 ml). The resulting mixture was stirred
for 1 h and subsequently extracted with diethyl ether (2 Â 10 ml).
The combined organic layer was dried with MgSO , filtered, and
4
the solvent was removed under reduced pressure. The conversion
was determined by GC and NMR spectroscopy and compared to
the corresponding known substances. The NMR result of the prod-
[
16] a) A. A. Danopoulos, J. A. Wright, W. B. Motherwell, Chem. Commun.
2005, 784; b) D. Pugh, N. J. Wells, D. J. Evans, A. A. Danopoulos,
Dalton Trans. 2009, 7189; c) Y. S. Wang, H. M. Sun, X. P. Tao, Q. Shen,
Y. Zhang, Chin. Sci. Bull. 2007, 52, 3193; d) L. Mercs, G. Labat, A. Neels,
A. Ehlers, M. Albrecht, Organometallics 2006, 25, 5648; e) L. Mercs,
H. Stoeckli-Evans, M. Albrecht, Dalton Trans. 2009, 7168; f)
S. A. Llewellyn, M. L. H. Green, J. C. Green, A. R. Cowley, Dalton Trans.
[42]
ucts was identical to data published literature.
Conclusions
A novel series of cationic piano-stool iron complexes bearing benzyl-
substituted imidazolidin-2-ylidene NHC ligand was synthesized from
in situ generated carbene ligand and [CpFe(CO) I] iron precursor,
2
2
006, 2535; g) V. César, N. Lugan, G. Lavigne, J. Am. Chem. Soc. 2008,
130, 11286; h) M. J. Ingleson, R. A. Layfield, Chem. Commun. 2012,
48, 3579.
[
[
[
17] D. Bézier, J.-B. Sortais, C. Darcel, Adv. Synth. Catal. 2013, 355, 19.
18] J. Louie, R. H. Grubbs, Chem. Commun. 2000, 1479.
19] R. Fränkel, U. Kernbach, M. Bakola-Christianopoulou, U. Plaia, M. Suter,
W. Ponikwar, H. Nöth, C. Moinet, W. P. Fehlhammer, J. Organomet.
Chem. 2001, 617–618, 530.
and characterized by NMR, IR, high-resolution mass spectrometry
and elemental analysis. The catalytic activity of the new complexes
was evaluated in the hydrosilylation of aldehydes and ketones,
ꢀ
which proceeded in a short reaction time (up to 5 min at 100 C).
[
20] D. S. McGuinness, V. C. Gibson, J. W. Steed, Organometallics 2004, 23,
Further investigation into the activity of in situ NHC/iron
salt catalytic system is currently underway in our laboratory.
6
288.
[
21] C. Vogel, F. W. Heinemann, J. Sutter, C. Anthon, K. Meyer, Angew.
Chem. Int. Ed. 2008, 47, 2681.
Acknowledgements
[22] a) A. A. Danopoulos, N. Tsoureas, J. A. Wright, M. E. Light, Organome-
tallics 2004, 23, 166; b) B. Liu, Q. Q. Xia, W. Z. Chen, Angew. Chem. Int.
Ed. 2009, 48, 5513; c) A. Raba, M. Cokoja, S. Ewald, K. Riener,
E. Herdweck, A. Pöthig, W. A. Herrmann, F. E. Kühn, Organometallics
This work was financially supported by the Technological and
Scientific Research Council of Turkey TUBİTAK, and the CNRS
2
012, 31, 2793.
23] a) P. Buchgraber, L. Toupet, V. Guerchais, Organometallics 2003, 22,
144; b) see ref. 16f; c) L. Mercs, G. Labat, A. Neels, A. Ehlers,
M. Albrecht, Organometallics 2006, 25, 5648.
(France) [project 210T051] and İnönü University Research Fund.
[
CD and JBS are grateful to the Université de Rennes 1, Rennes
Métropole and Ministère de l’Enseignement Supérieur et de la
Recherche for support.
5
[24] A. Wacker, C. G. Yan, G. Kaltenpoth, A. Ginsberg, A. M. Arif, R. D. Ernst,
H. Pritzkow, W. Siebert, J. Organomet. Chem. 2002, 641, 195.
[
25] a) C. Hedberg, in Modern Reduction Methods (Eds.: P. G. Anderson,
I. J. Munslow), Wiley-VCH, Weinheim, 2008, pp. 109–134; b) J. G. de
Vries, C. J. Elsevier (Eds), Handbook of Homogeneous Hydrogenation,
Wiley-VCH, Weinheim, 2007.
26] a) S. Rendler, M. Oestreich, in Modern Reduction Methods (Eds.:
P. G. Anderson, I. J. Munslow), Wiley-VCH, Weinheim, 2008,
pp. 183–208; b) H. Nishiyama, in Transition Metals for Organic
Synthesis, 2nd edn (Eds.: M. Beller, C. Bolm), Wiley-VCH, Weinheim,
References
[1] E. M. Beccalli, G. Broggini, M. Martinelli, S. Sottocornola, Chem. Rev.
2
007, 107, 5318.
[
[2] B. M. Trost, F. D. Toste, A. B. Pinkerton, Chem. Rev. 2001, 101, 2067.
[3] M. P. Doyle, R. Duffy, M. Ratkinov, L. Zhou, Chem. Rev. 2010, 110, 704.
[4] S. Conejero, M. Paneque, M. L. Poveda, L. L. Santos, E. Carmona, Acc.
Chem. Res. 2010, 43, 572.
2
004, pp. 182–194.
[5] Z. Li, C. Brouwer, C. He, Chem. Rev. 2008, 108, 3239.
[6] A. Fürstner, P. W. Davies, Angew. Chem. Int. Ed. 2007, 46, 3410.
[7] a) C. Bolm, J. Legros, J. Le Paih, L. Zani, Chem. Rev. 2004, 104, 6217; b)
B. Plietker, in Iron Catalysis in Organic Chemistry (Ed.: B. Plietker),
Wiley-VCH, Weinheim, 2008; c) A. Correa, O. Garcia Mancheño,
C. Bolm, Chem. Soc. Rev. 2008, 37, 1108.
[
27] a) H. Brunner, R. Eder, B. Hammer, U. Klement, J. Organomet. Chem.
1990, 394, 555; b) H. Brunner, K. Fisch, Angew. Chem. Int. Ed Engl.
1990, 29, 1131; c) H. Brunner, K. Fisch, J. Organomet. Chem. 1991,
412, C11; d) H. Brunner, M. Rötzer, J. Organomet. Chem. 1992, 425,
119.
[
8] a) W. M. Czaplik, M. Mayer, J. Cvengros, A. Jacobi von Wangelin,
ChemSusChem. 2009, 2, 396; b) B. D. Sherry, A. Fürstner, Acc. Chem.
Res. 2008, 41, 1500.
9] a) J. Kischel, K. Mertins, I. Jovel, A. Zapf, M. Beller, in Iron Catalysis in
Organic Chemistry (Ed.: B. Plietker), Wiley-VCH, Weinheim, 2008,
[28] N. Shaikh, K. Junge, M. Beller, Org. Lett. 2007, 9, 5429.
[29] H. Nishiyama, A. Furuta, Chem. Commun. 2007, 760.
[30] a) H. Nishiyama, A. Furuta, Tetrahedron Lett. 2008, 49, 110; b)
N. S. Shaikh, S. Enthaler, K. Junge, M. Beller, Angew. Chem. Int. Ed.
2008, 47, 2497; c) A. M. Tondreau, E. Lobkovsky, P. J. Chirik, Org. Lett.
[
Appl. Organometal. Chem. 2013, 27, 459–464
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

S. Demir et al.
2
008, 10, 2789; d) B. K. Langlotz, H. Wadepohl, L. H. Gade, Angew.
[36] a) J. F. Capo, S. E. Hassoui, P. Schollhammer, Organometallics 2005,
24, 2020; b) C.-H. Hsieh, M. Y. Darensbourg, J. Am. Chem. Soc. 2010,
132, 14118; c) V. Lavallo, R. H. Grubbs, Science, 2009, 326, 559; e)
L. Xiang, J. Xiao, L. Deng, Organometallics 2011, 30, 2018; f) H. Gao,
C. Yan, X. Tao, Y. Xia, H. Sun, Q. Shen, Y. Zhang, Organometallics
2010, 29, 4189.
[37] a) A. A. Danopoulos, P. Braunstein, N. Stylianides, M. Wesolek,
Organometallics 2011, 30, 6514; b) R. A. Layfield, J. J. W. McDouall,
M. Scheer, C. Schwarzmaier, F. Tuna, Chem. Commun. 2011, 47,
10623; c) A. A. Danopoulos, D. Pugh, H. Smith, J. Sabmannshausen,
Chem. Eur. J. 2009, 15, 5491; d) S. Zlatogorsky, C. A. Muryn,
F. Tuna, D. J. Evans, M. J. Ingleson, Organometallics 2011, 30,
4974.
Chem. Int. Ed. 2008, 47, 4670; e) D. V. Gutsulyak, L. G. Kuzmina,
J. A. K. Howard, S. F. Vyboishichikov, G. I. Nikonov, J. Am. Chem.
Soc. 2008, 130, 3732; f) T. Inagaki, L. T. Phong, A. Furuta, J.-I. Ito,
H. Nishiyama, Chem. Eur. J. 2010, 16, 3090; g) T. Inagaki, A. Ito, J.-i.
Ito, H. Nishiyama, Angew. Chem. Int. Ed. 2010, 49, 9384; h) J. Yang,
D. Tilley, Angew. Chem. Int. Ed. 2010, 49, 10186; i) D. Addis, N. Shaikh,
S. Zhou, S. Das, K. Junge, M. Beller, Chem. Asian J. 2010, 5, 1687; j)
L. C. Misal Castro, D. Bézier, J.-B. Sortais, C. Darcel, Adv. Synth. Catal.
2
011, 353, 1279; k) A. P. Dieskau, J.-M. Begouin, B. Plietker, Eur. J.
Org. Chem. 2011, 5291; l) P. Bhattacharya, J. A. Krause, H. Guan,
Organometallics 2011, 30, 4720; m) M. Flückiger, A. Togni, Eur.
J. Org. Chem. 2011, 4353; n) T. Hashimoto, S. Urban, R. Hoshino,
Y. Ohki, K. Tatsumi, F. Glorius, Organometallics 2012, 31, 4474; o)
J. Zheng, L. C. Misal Castro, T. Roisnel, C. Darcel, J.-B. Sortais, Inorg.
Chim. Acta 2012, 380, 301; p) S. Warratz, L. Postigo, B. Royo, Organo-
metallics, 2013, 32, 893.
[38] B. Liu, Q. Xia, W. Chen, Angew. Chem. Int. Ed. 2009, 121, 5621.
[39] B. Liu, Y. Zhang, D. Xu, W. Chen, Chem. Commun. 2011, 47, 2883.
[40] A. F. Figueroa, T. Pape, J. J. Weigand, F. E. Hahn, Eur. J. Inorg. Chem.
2010, 2907.
[
31] a) V. V. K. M. Kandepi, J. M. S. Cardoso, E. Peris, B. Royo, Organometal-
[41] a) İ. Özdemir, S. Demir, S. Yaşar, B. Çetinkaya, Appl. Organometal.
Chem. 2005,19, 55; b) N. Gürbüz, İ. Özdemir, S. Demir, B. Çetinkaya,
J. Mol. Catal. A: Chem. 2004, 209, 23; c) S. Demir, İ. Özdemir,
B. Çetinkaya, J. Organomet. Chem. 2009, 694, 4025; d) Ö. Dogan,
N. Gürbüz, İ. Özdemir, B. Çetinkaya, J. Heterocycle Chem. 2009, 46,
186; e) S. Yasar, İ. Özdemir, B. Çetinkaya, J.-L. Renaud, C. Bruneau,
Eur. J. Org. Chem. 2008, 2142.
[42] a) H.-J. Zhu, C. U. Pittman, Synth. Commun. 2003, 33, 1733; b) L. Shi,
Y. Liu, Q. Liu, B. Wei, G. Zhang, Green Chem. 2012, 14, 1372; c) J. Mack,
D. Fulmer, S. Stofel, N. Santos, Green Chem. 2007, 9, 1041; d) S. V. Ley,
A. J. P. Stewart-Liddon, D. Pears, R. H. Perni, K. Treacher, Beilstein
J. Org. Chem. 2006, 2, 1; e) S. Kawai, T. Umezawa, T. Higuchi, Wood
Res. 1986, 73, 18.
lics 2010, 29, 2777; b) J. M. S. Cardoso, B. Royo, Chem. Commun.
2
012, 48, 4944.
32] a) F. Jiang, D. Bézier, J.-B. Sortais, C. Darcel, Adv. Synth. Catal. 2011,
53, 239; b) D. Bézier, F. Jiang, T. Roisnel, J.-B. Sortais, C. Darcel, Eur.
[
3
J. Inorg. Chem. 2012, 1333.
[
[
33] L. C. Misal Castro, J.-B. Sortais, C. Darcel, Chem. Commun. 2012, 48, 151.
34] D. Bézier, G. T. Venkanna, L. C. Misal Castro, J. Zheng, T. Roisnel,
J.-B. Sortais, C. Darcel, Adv. Synth. Catal. 2012, 354, 1879.
35] a) E. Buitrago, L. Zani, H. Adolfsson, Appl. Organomet. Chem. 2011,
[
25, 748; b) E. Buitrago, F. Tinnis, H. Adolfsson, Adv. Synth.Catal.
2
2
012, 354, 217; c) A. Volkov, E. Buitrago, H. Adolfsson, Eur. J. Org.
013, 2066.
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