Direct synthesis of iron(0) N-heterocyclic carbene complexes by using Fe3(CO)12 and their application in reduction of carbonyl groups

Article abstract of DOI:10.1021/om3012085

Iron Fe(NHC)(CO)₄ complexes were formed by direct reaction of Fe₃(CO)₁₂ with equimolecular amounts of NHC imidazolium halide precursors; addition of base was not needed in this reaction. When excess (9:1 ratio) 1,3-dimesitylimidazolium chloride is reacted with the iron cluster Fe₃(CO)₁₂, a mixture of Fe(IMes)(CO)₄ and Fe(IMes)₂(CO)₃ is obtained. Single crystals of Fe(IMes)(CO)₄ and crystals resulting from the cocrystallization of Fe(IMes)(CO)₄ and Fe(IMes)₂(CO)₃ have been studied by X-ray diffraction. These iron(0) complexes were found to catalyze the reduction of benzaldehydes.

Full text of DOI:10.1021/om3012085

Article
pubs.acs.org/Organometallics
Direct Synthesis of Iron(0) N‑Heterocyclic Carbene Complexes by
Using Fe (CO) and Their Application in Reduction of Carbonyl
3
12
Groups
Svenja Warratz, Lorena Postigo, and Beatriz Royo*
́
́
Instituto de Tecnologia Química e Biologica, Universidade Nova de Lisboa, Avenida da Republica, EAN, 2780-157 Oeiras, Portugal
*
S Supporting Information
ABSTRACT: Iron Fe(NHC)(CO) complexes were formed by direct reaction of
4
Fe (CO) with equimolecular amounts of NHC imidazolium halide precursors;
3
12
addition of base was not needed in this reaction. When excess (9:1 ratio) 1,3-
dimesitylimidazolium chloride is reacted with the iron cluster Fe (CO) , a
3
12
mixture of Fe(IMes)(CO) and Fe(IMes) (CO) is obtained. Single crystals of
4
2
3
Fe(IMes)(CO) and crystals resulting from the cocrystallization of Fe(IMes)-
4
(
CO) and Fe(IMes) (CO) have been studied by X-ray diffraction. These iron(0) complexes were found to catalyze the
4 2 3
reduction of benzaldehydes.
N-Heterocyclic carbene (NHC) ligands have gained enormous
popularity in organometallic chemistry for their strong σ-
donating characteristics and ability to bind and stabilize a range
Encouraged by these results, we became interested in
exploring the reactivity of NHCs and their imidazolium
precursors with Fe (CO) . The reactivity of the related
3
12
1
,2
of transition-metal complexes. In recent years, the use of N-
heterocyclic carbenes in the chemistry of iron is attracting
considerable attention due to the potential applications of Fe-
ruthenium carbonyl cluster Ru (CO) with NHCs has been
3
12
15
recently investigated by the research groups of Cabeza,
16,17
18
19
Whittlesey,
Cole, and Wang. They described the
3
−8
NHC complexes in homogeneous catalysis
and biomimetic
successful C−H activation of NHCs at N-alkyl and heterocyclic
C−H positions when coordinated to triruthenium undecacar-
bonyl complexes Ru (NHC)(CO) , which are prepared by
9
chemistry. In general, iron-NHC complexes are prepared via
free carbenes generated from deprotonation of imidazolium
7
,10
3
11
salts by a strong base
or by metalation reactions where the
reaction of the corresponding NHCs with Ru (CO) in 1:1
3
12
imidazolium salt is deprotonated by the basic amide Fe[(N-
1
1
mol ratio. When the reaction of Ru
(CO)12 is carried out with
3
(
SiMe ) ] . Recently, we disclosed the unprecedented
3 2 2
an excess of NHC, the cluster cleavage products Ru-
synthesis of bidentate cyclopentadienyl-functionalized NHC
iron(II) complexes by direct reaction of the corresponding
imidazolium proligands with commercially available Fe (CO)
1
7
18
(
NHC) (CO)3 and Ru(NHC)(CO)4 are isolated. In
2
2
008, Cole and co-workers described the uncommon C−H
3
12
1
2
activation of 1,3-dimesitylimidazolium chloride (IMes·HCl) by
Ru (CO) . Equimolecular reaction of the NHC precursor
(
Scheme 1). This synthetic approach precludes the require-
18
3
12
IMes·HCl with Ru (CO) affords the dinuclear Ru (μ-
Scheme 1. Synthesis of Iron Complexes Containing
Cyclopentadienyl-Functionalized NHCs
3
12
2
Cl) (IMes) (CO) complex (Scheme 2), which represents an
2
2
4
unusual example of a ruthenium−ruthenium-bonded Ru(I)
dimer. Intrigued by the former reaction and taking into account
our findings on the C−H activation of imidazolium proligands
by Fe (CO) , we decided to investigate the reactivity of
3
12
Fe (CO) with simple monodentate imidazolium salts.
3
12
Scheme 2. Reaction of an NHC Precursor with Ru (CO)
Reported by Cole
3
12
18
ment for strong bases previously employed in the synthesis of
13
these half-sandwich iron carbonyl complexes. The formation
of (Cp-NHC)Fe(CO)I complexes implies the C−H activation
of the C−H bond of imidazolium to Fe(0) and constitutes a
rare example of Fe-NHC complexes prepared by direct reaction
Received: December 14, 2012
Published: January 29, 2013
14
of the corresponding imidazolium salts.
©
2013 American Chemical Society
893
dx.doi.org/10.1021/om3012085 | Organometallics 2013, 32, 893−897

Organometallics
Article
Figure 1. NHC Precursors Studied in this Work.
Scheme 3. Reaction of NHC Precursors with Fe (CO)12
3
Here we describe the reactivity of Fe (CO)12 with a variety
occurred. Signals ranging from 181 to 196 ppm, indicative of an
3
of NHC precursors, NHC·HX (X = Cl, I) (Figure 1), which led
to the formation of the mononuclear iron(0) carbonyl
complexes Fe(NHC)(CO) (1−5) and Fe(IMes) (CO) (6)
Fe−C
, are in the region of previously reported Fe-NHC
carbene
10,11
complexes.
The IR spectra of complexes 1−5 show the
characteristic strong carbonyl stretching absorptions (at 2035,
4
2
3
1949, and 1915 cm− for Fe(IMes)(CO)
1
; see Experimental
4
[
NHC = 1,3-dimesitylimidazol-2-ylidene (IMes), 1; 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene (IPr), 2; 1,3-dimethyli-
midazol-2-ylidene (IMe), 3; 1,3-diisopropylimidazol-2-ylidene
I Pr), 4; and 1-phenyl-3-methylimidazol-2-ylidene (IPhMe),
], and their catalytic application in the hydrosilylation of
carbonyl groups. Remarkably, addition of base is not needed to
generate the NHC ligands.
Section) consistent with trigonal bipyramidal Ru(NHC)-
1
8
(CO)
and Fe(SIMe)(CO) (SIMe = 1,3-dimethylimidazo-
4
20
4
i
(
5
linylidene) complexes. The structure of compound 1 was
determined by X-ray diffraction methods. The molecular
structure and selected bond lengths and angles are depicted
in Figure 2. The molecule can be described as a distorted
As shown in Scheme 3, the reaction of Fe (CO) with 3
3
12
equiv of 1,3-dimesitylimidazolium chloride in toluene under
reflux afforded the mononuclear tetracarbonyl complex Fe-
(
IMes)(CO) (1) in good yield (78%). Similar reaction of
4
Fe (CO) with 1,3-bis(2,6-diisopropylphenyl)imidazolium
3
12
chloride gave the corresponding complex Fe(IPr)(CO) (2)
4
in 91% yield. Iron tetracarbonyl complexes Fe(NHC)(CO)4
containing 1,3-dialkyl-substituted imidazol-2-ylidenes could
also be prepared by this route, although lower yields were
i
obtained, Fe(IMe)(CO) (3) in 30% and Fe(I Pr)(CO) (4) in
4
4
30%; the unsymmetrically substituted imidazolium salt 1-
phenyl-3-methylimidazolium iodide reacted with Fe (CO)
3
12
(
ratio 3:1) to give Fe(CO) (IMePh) (5) in 45% yield. Along
4
with the formation of Fe(NHC)(CO) complexes, unidentified
Figure 2. ORTEP of Fe(IMes)(CO)4 (1). Ellipsoids are at 50%
probability. All hydrogen atoms have been omitted for clarity. Selected
bond distances (Å) and angles (deg): Fe1−C1 1.992(2), Fe1−C22
4
species were formed in these reactions. In all cases, a black
residue insoluble in most common organic solvents (THF,
acetonitrile, toluene, dichloromethane) was formed. The IR
spectrum of the black residue did not display any carbonyl
stretching absorptions. Further characterization attempts of the
byproducts formed in the reaction were unsuccessful due to
their insolubility. The HX (X = halide) lost during Fe-NHC
formation might form some iron halide byproducts, although
the high yields isolated when NHC·HCl (NHC = IMes and
IPr) are reacted with Fe (CO) do not suggest formation of
1
1
.783(2), Fe1−C23 1.7971(19), Fe1−C24 1.797(2), Fe1−C25
.807(2), C22−O1 1.147(2), C23−O2 1.152(2), C24−O3 1.149(2),
C25−O4 1.149(2), N1−C1 1.373(2), N2−C1 1.366(2), C24−Fe1−
C23 119.01(9), C22−Fe−C25 86.34(9), C22−Fe1−C23 87.36(8),
C23−Fe1−C25 120.30(9), C22−Fe−C1 175.36(8), C24−Fe1−C1
8
4.41(8), C23−Fe1−C1 95.68(8), C25−Fe−C1 95.10(8), N2−C1−
N1 103.02(15).
3
12
trigonal bipyramid, with the NHC ligand occupying an axial
large amounts of any iron halides. Further reactivity studies are
carried out in our group in order to understand the mechanism
operating in these reactions.
position. The Fe−C
distance of 1.992(2) Å is comparable
carbene
to the value reported for the Fe−C
distance in
CO
carbene
21
Fe(IMe)(CO) , 2.007(5) Å. The C −Fe-C angle with
4
NHC
The iron complexes 1−5 were isolated as yellow crystalline
a value of 175.36(8)° presents a similar deviation to that
1
13
powders and were fully characterized by H and C NMR
spectroscopy, IR spectroscropy, and elemental analysis. The
observed in the molecular structure of Ru(IMes)(CO)
4
18
[176.5(2)°]. One of the O−C−Fe angles deviated from the
1
3
C NMR spectra confirm that coordination of NHC has
linear disposition with a value of 170.82(16)°.
8
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dx.doi.org/10.1021/om3012085 | Organometallics 2013, 32, 893−897

Organometallics
Article
The 1:6 stoichiometric reaction of Fe (CO) with IMes·HCl
Scheme 4. Reaction of 1,3-Dimesitylimidazol-2-ylidene and
Its Precursor with Fe (CO)
3
12
afforded a mixture of Fe(IMes)(CO)4 (1) and Fe-
3
12
(
IMes) (CO)3 (6) in ca. 1:1 ratio. Due to the similar
2
solubilities of complexes 1 and 6, their separation proved
difficult. A mixture of both complexes 1 and 6 was obtained
even when a considerably larger excess of NHC precursor was
reacted with Fe (CO) . From this mixture, a crystal that
3
12
resulted from the cocrystallization of complexes 1 and 6 was
isolated and studied by X-ray diffraction, confirming the
identity of this species. Figure 3 shows the independent
With these complexes in hand, we set out to examine their
potential in the reduction of carbonyl groups. Recent works on
iron chemistry have demonstrated the capability of this metal to
2
4
efficiently catalyze the reduction of carbonyl groups.
However, reports on Fe-NHC complexes are relatively scarce.
13
4,5,8
Recently, we and others
have described iron(II) NHC
complexes catalyzing the hydrogenation and hydrosilylation of
carbonyl compounds. To the best of our knowledge, iron(0)
NHC complexes have not been applied as catalysts in this
catalytic reaction. Notice that reduction of amides and
carboxamides has been successfully achieved using the iron
25
carbonyl Fe (CO) .
3
12
We examined the catalytic activity of complexes 1−4 in the
Figure 3. ORTEP of Fe(IMes) (CO) (6). Ellipsoids are at 50%
probability. All hydrogen atoms have been omitted for clarity. Selected
bond distances (Å) and angles (deg): Fe1−C1 1.982(4), Fe1−C22
2
3
reduction of benzaldehyde. The results are summarized in
Table 1. The reduction of benzaldehyde with PhSiH took
3
1
.976(4), Fe1−C43 1.758(5), Fe1−C44 1.775(5), Fe1−C45 1.781(5),
Table 1. Hydrosilylation of Benzaldehyde Catalyzed by
C43−O1 1.173(5), C44−O2 1.163(5), C45−O3 1.151(5), C1−Fe1−
C22 167.19(17), C45−Fe1−C44 116.1(2), C43−Fe1−C45 106.1(2),
C43−Fe1−C44 137.7(2), C43−Fe−C1 91.68(19), C44−Fe1−C1
a
Fe(NHC)(CO) Complexes
4
8
6.75(18), C45−Fe1−C1 95.07(18), N1−C1−Fe1 130.8(3), N2−
C1−Fe1 127.6(3), N3−C22−Fe1 130.5(3), N4−C22−Fe1 127.6(3).
b
t
conv, ycield
structure of 6, with salient bond lengths and angles provided in
the figure caption. The molecular structure consists of a
distorted trigonal bipyramid with the NHC ligands located in a
entry
cat(mol %)
silane
solv
(h)
(%)
1
2
3
4
5
6
7
8
Fe(IMes)(CO) (2)
PhSiH3
PhSiH3
THF
NCMe
THF
THF
THF
THF
THF
THF
4
24
24
4
>99 (94)
>99 (96)
80 (77)
>99 (94)
60 (57)
90 (87)
45 (43)
50 (48)
4
Fe(IMes)(CO) (2)
4
trans-axial arrangement [CNHC−Fe−C
angle of
Fe(IMes)(CO) (2)
Ph SiH2
2
NHC
4
1
67.9(17)°]. Similar trans-donor ligand disposition has been
Fe(IMes)(CO) (1)
PhSiH3
4
22
found in Fe(CO) (PPh ) . The bulk of the NHC ligands
Fe(IMes)(CO) (0.5) PhSiH3
4
3
3 2
4
leads to discrepancy in the equatorial angles, one of which is
Fe(IPr)(CO) (1)
PhSiH3
PhSiH3
PhSiH3
4
4
considerably larger than the other two CCO−Fe−C angles,
Fe(IMe)(CO) (1)
4
CO
4
i
with a value of 137.7(2)°. The Fe−C−O angles deviated from a
linear disposition, with angles ranging from 172.6(4)° to
Fe(I Pr)(CO) (1)
4
4
a
All reactions were carried out with 1.0 equiv of aldehyde, 1.2 equiv of
silane in the presence of the Fe-NHC catalysts at room temperature.
Yield determined by H NMR spectroscopy. Isolated yield after
1
76.5(4)°. The Fe−C
distances of 1.976(4) and 1.982(4) Å
NHC
b
1
c
are slightly shorter than the Fe−C
complex 1. As observed in the structures of Ru(NHC) (CO)
complexes, the structure of 6 showed an NHC tilting, which
distance found in
NHC
treatment with p-toluenesulfonic acid.
2
3
1
7
23
is reflected in the N−C
−Fe angles [N1−C1−Fe1,
place in the presence of a catalytic amount (2 mol %) of
complex 1 at room temperature in THF (entry 1). The reaction
also proceeded in NCMe, although longer reaction times (24 h,
entry 2) were needed to achieve quantitative yields.
Diphenylsilane can also be used as reducing agent in this
catalytic reaction (entry 3), but (EtO) MeSiH and (EtO) SiH
are not applicable. The amount of catalyst could be decreased
to 1 mol % without decreasing the yield (entry 4); if decreased
to 0.5 mol %, the yield of the isolated alcohol drops to 57%
(entry 5). In order to explore the effect of the NHC in the
performance of the catalyst, complexes 1−4 were applied in the
reduction of benzaldehyde. As shown in Table 1, entries 4 and
6−8, the best catalysts are complexes 1 and 2, containing the
bulkier IMes and IPr ligands. To further investigate the scope
carbene
1
1
30.8(3)°; N2−C1−Fe1, 127.6(3)°; N3−C22−Fe1,
30.5(3)°; N4−C22−Fe1, 127.6(3)°].
We have also attempted the synthesis of an iron trinuclear
NHC derivative analogous to [Ru (NHC)(CO) ] with the
idea of exploring the capability of iron in promoting C−H
activation of NHCs at N-alkyl or aryl positions and resembling
the reactivity of the ruthenium undecacarbonyl. In contrast to
the reactivity described for the ruthenium cluster Ru (CO) ,
3
11
2
3
3
12
the reaction of 1 equiv of 1,3-dimethylimidazol-2-ylidene with
Fe (CO) in THF afforded Fe(IMes)(CO) (1) as the only
3
12
4
isolable product. A similar result is obtained when the reaction
is carried out with 1 equiv of the imidazolium salt IMes·HCl
(
Scheme 4).
8
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Organometallics
Article
6.8 Hz, Me), 1.00 (d, 12H, J = 6.8 Hz, Me). 13C NMR (C
D ): 215.8
6 6
of the reaction, benzaldehyde substrates containing halo, cyano,
nitro, and acyl functionalities were reduced, giving the
corresponding alcohols in high yields (isolated yields 83−
(
Fe-CO), 191.7 (Fe-CCarbene), 146.6 (CiPh), 137.0 (CiPh), 130.9 (CHPh),
1
25.7 (CH ), 124.6 (CH ), 28.9 (CH ), 25.8 (Me), 22.7 (Me).
Ph Imid iPr
Anal. Calc for C H N FeO (556.47): C, 66.91; H, 6.52; N, 5.04.
9
7%, Scheme 5). The ketone 3-(trifluoromethyl)acetophenone
31 36
2
4
Found: C, 67.29; H, 6.68; N, 5.43. IR (KBr): ν(CO) 2035, 1947, 1928,
−
1
1
919 cm .
Scheme 5. Scope of the Reduction of Benzaldehyde
Derivatives Catalyzed by Fe(IMes)(CO)4
Synthesis of Fe(IMe)(CO) (3). A procedure similar to that used
4
for the preparation of 1 was applied by using 3 equiv of 1,3-
bis(methylimidazolium) iodide (0.40 g, 1.78 mmol) and 1 equiv of
1
Fe (CO) (0.30 g, 0.59 mmol). Yield: 0.14 g (30%). H NMR
(
3
12
C D ): 5.74 (s, 2H, CH ), 3.05 (s, 6H, Me). 13C NMR (C D ):
6 6 Imid 6 6
2
16.9 (Fe-CO), 181.2 (Fe-CCarbene), 123.2 CHImid), 39.2 (Me). IR
−1
(
(
KBr): ν(CO) 2036, 1938, 1924 cm . Anal. Calc for C H N FeO
264.02): C, 40.94; H, 3.05; N, 10.61. Found: C, 40.70; H, 2.92; N,
9 8 2 4
+
1
1
0.52. MS (ESI-TOF, MeOH): m/z [M − 4CO] calcd for C H N Fe
5
8
2
+
52, found 152 [Fe(IMe)] .
i
Synthesis of Fe(I Pr)(CO) (4). A procedure similar to that used
4
for the preparation of 1 was applied by using 3 equiv of 1,3-
bis(isopropylimidazolium) chloride (0.20 g, 1.05 mmol) and 1 equiv of
1
Fe (CO) (0.18 g, 0.35 mmol). Yield: 0.10 g (30%). H NMR
3
12
can also be reduced using 1 (2 mol %) as catalyst and PhSiH3
as reducing agent, but heating to 70 °C is needed to achieve
good conversion of the corresponding alcohol (78% yield in 4
h). The catalytic performance of 1 in the reduction of carbonyl
groups compares well with those of reported Fe(II)-NHC
(C
6
D
6
): 6.46 (s, 2H, CHImid), 5.24 (q, 2H, CHiPr), 0.99 (d, 12H, J =
13
6
1
1
5
.8 Hz, Me). C NMR (C D ): 218.5 (Fe-CO), 177.6 (Fe-CCarbene),
19.3 (CHImid), 52.4 (CH ), 22.7 (Me). IR (KBr): ν(CO) 2023,
998, 1942 cm . Anal. Calc for C H N FeO (320.19): C, 48.77; H,
.04; N, 8.75. Found: C, 48.40; H, 5.32: N, 9.12.
6 6
iPr
−
1
13 16
2
4
4
,5,8,13
Synthesis of Fe(IPhMe)(CO) (5). A procedure similar to that
used for the preparation of 1 was applied by using 3 equiv of 1-phenyl-
4
catalysts.
In conclusion, we have described here the reactivity of
Fe (CO) with NHCs and their precursors. We have proved
3
-methylimidazolium iodide (0.50 g, 1.78 mmol) and 1 equiv of
3
12
1
Fe (CO) (0.29 g, 0.59 mmol). Yield: 0.09 g (45%). H NMR (400
3
12
that Fe(0) carbonyl complexes are capable of promoting C−H
activation of simple monodentate imidazolium salts. We believe
that the direct reaction of iron(0) with imidazolium salts can be
a useful reaction for the preparation of Fe-NHC complexes,
MHz, C D ): 7.00 (m, 5H, CH ), 6.13 (d, 1H, J = 3.1 Hz, CHImid),
6
6
Ph
13
1
5
.89 (d, 1H, J = 3.1 Hz, CHImid), 3.23 (s, 3 H, Me). C{ H} NMR
(100 MHz, C D ): 216.1 (Fe-CO), 184.2 (Fe-CCarbene), 141.5 (CiPh),
6
6
1
29.5 (CH ), 124.1 (CH ), 123.4 (CHImid), 39.1 (Me). IR (KBr):
Ph Imid
t
−1
avoiding the use of strong bases such as KO Bu or BuLi
ν(CO) 2034, 1950, 1925, 1896 cm . Anal. Calc for C H N FeO
1
4
10
2
4
generally required for the in situ generation of free NHCs. The
iron(0) NHC carbonyl complexes prepared in this work
catalyzed the reduction of benzaldehyde and acetophenone,
giving high yields of the corresponding alcohols.
(326.00): C, 51.57; H, 3.09; N, 8.59. Found: C, 51.28; H, 3.37; N,
8.21.
Reaction of Fe
(0.20 g, 0.58 mmol) was added to a THF solution of Fe
(CO)12 with One Equivalent of IMes. IMes
(CO)12 (0.09
3
3
g, 0.19 mmol), and the mixture was stirred at room temperature for 16
h. Volatiles were removed under vacuum, and the resulting crude was
extracted with toluene (10 mL). Removal of the toluene afforded an
orange solid, which was recrystallized from THF−hexane to yield
EXPERIMENTAL SECTION
■
General Procedures. All reactions and manipulations were carried
out under dry, oxygen-free nitrogen standard Schlenk techniques, and
solvents were purified from appropriate drying agents and distilled
prior to use. The imidazolium salts NHC·HX (Figure 1) were
prepared according to the published procedures. All other reagents
were purchased from commercial suppliers and used without further
purification.
Fe(IMes)(CO) . Yield: 0.08 g (30%).
4
Reaction of Fe (CO) with Excess IMes·HCl. A mixture of 6
3
12
26
equiv of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (0.39 g,
1.14 mmol) and 1 equiv of Fe (CO)12 (0.09 g, 0.19 mmol) in toluene
3
(15 mL) was heated under reflux for 14 h. The suspension was filtered
through Celite, and the filtrate was evaporated to dryness, yielding a
mixture of complexes 1 and 6 in ca. 1:1 ratio. Crystallization from
THF−hexane solutions led to yellow crystals suitable for X-ray
Synthesis of Fe(IMes)(CO)4 (1). A mixture of 1,3-bis(2,4,6-
trimethylphenyl)imidazolium chloride (0.20 g, 0.58 mmol) and
Fe (CO) (0.09 g, 0.19 mmol) in toluene (15 mL) was heated
3
12
1
under reflux for 14 h. The suspension was filtered through Celite, and
the filtrate was evaporated to dryness, yielding complex 1 as a
crystalline yellow solid. Yield: 0.21 g (78%). Crystallization from
THF−hexane leads to yellow crystals suitable for X-ray diffraction
diffraction studies. NMR data for 6: H NMR (400 MHz, C D ): 6.77
6
6
(
s, 4H, CH ), 6.11 (s, 2H, CHImid), 2.19 (s, 6H, Me), 2.10 (s, 12H,
Ph
13
1
Me). C{ H} NMR (100 MHz, C D ): 222.3 (Fe-CO), 196.9 (Fe-
6
6
CCarbene), 138.4 (C ), 137.4 (C ), 135.0 (C ), 125.7 (CHImid), 21.2
1
iPh
iPh
Ph
studies. H NMR (400 MHz, C D ): 6.78 (s, 4H, CH ), 6.16 (s, 2H,
6
6
Ph
(
Me), 18.8 (Me).
Typical Procedure for the Reduction of Carbonyls. A dried J.
13
1
CHImid), 2.11 (s, 6H, Me), 2.05 (s, 12H, Me). C{ H} NMR (100
MHz, C D ): 217.0 (Fe-CO), 187.7 (Fe-CCarbene), 139.4 (CiPh), 137.2
6
6
Young tube equipped with a Teflon screw cap was flushed with
nitrogen and charged with the appropriate amount of catalyst in 0.5
mL of the corresponding solvent. Then, neat silane (1.20 mmol) and
the corresponding substrate (1.0 mmol) were added. The samples
(
CiPh), 135.9 (CH ), 124.6 (CHImid), 21.1 (Me), 18.1 (Me). Anal. Calc
Ph
for C H N FeO (472.31): C, 63.51; H, 5.08; N, 5.93. Found: C,
2
5
24
2
4
−1
6
(
3.70; H, 5.30; N, 6.29. IR (KBr): ν(CO) 2035, 1949, 1915 cm . MS
+
ESI-TOF, toluene): m/z [M − 4CO + toluene] calcd for
1
+
were monitored periodically by H NMR. When the reaction was
C H N Fe 452, found 452 [Fe(IMes)(toluene)] .
28
32
2
completed, the mixture was treated with 1 mL of a 1% solution of p-
toluenesulfonic acid in MeOH for 2 h. The solvent was removed under
vacuum, and the alcohol was extracted in diethyl ether (5 mL). This
solution was filtered through silica, and the filtrate was concentrated
under vacuum to yield the corresponding alcohol. Reaction times and
temperatures are indicated in Table 1.
Synthesis of Fe(IPr)(CO) (2). A procedure similar to that used for
the preparation of 1 was applied by using 3 equiv of 1,3-bis(2,6-
4
diisopropylphenyl)imidazolium chloride (0.25 g, 0.58 mmol) and 1
1
equiv of Fe (CO) (0.09 g, 0.19 mmol) Yield: 0.30 g (91%). H NMR
3
12
(
6
C D ): 7.28 (t, 2H, J = 7.7 Hz, CH ), 7.13 (d, 4H, J = 7.7 Hz, CH )
6 6 Ph Ph
.59 (s, 2H, CHImid), 2.72 (q, 4H, J = 6.8 Hz, CH ), 1.43 (d, 12H, J =
iPr
8
96
dx.doi.org/10.1021/om3012085 | Organometallics 2013, 32, 893−897

Organometallics
Article
Chem.Eur. J. 2009, 15, 5491. (e) Zlatogorsky, S.; Muryn, C. A.;
Tuna, F.; Evans, D. J.; Ingleson, M. J. Organometallics 2011, 30, 4974.
ASSOCIATED CONTENT
■
*
S
Supporting Information
CIF files giving X-ray crystallographic data for complexes 1 and
. This material is available free of charge via the Internet at
(12) Cardoso, J. M. S.; Royo, B. Chem. Commun. 2012, 48, 4944.
(13) Kandepi, V. V. K. M.; Cardoso, J. M. S.; Peris, E.; Royo, B.
6
Organometallics 2010, 29, 2777.
http://pubs.acs.org.
(14) (a) Liu, B.; Xia, Q.; Chen, W. Angew. Chem., Int. Ed. 2009, 48,
5
4
513. (b) Liu, B.; Zhang, Y.; Xu, D.; Chen, W. Chem. Commun. 2011,
7, 2883.
AUTHOR INFORMATION
■
(
15) (a) A recent review on NHC chemistry of transition metal
carbonyl clusters: Cabeza, J. A.; García-Alvarez, P. Chem. Soc. Rev.
2011, 40, 5389. (b) Cabeza, J. A.; del Río, I.; Miguel, D.; Sanchez-
Vega, M. G. Chem. Commun. 2005, 3956. (c) Cabeza, J. A.; del Río, I.;
Miguel, D.; Perez-Carreno, E.; Sanchez-Vega, M. G. Dalton Trans.
008, 1937. (d) Cabeza, J. A.; Perez-Carreno, E. Organometallics 2008,
7, 4697. (e) Cabeza, J. A.; del Río, I.; Miguel, D.; Perez-Carreno, E.;
chez-Vega, M. G. Organometallics 2008, 27, 211.
16) (a) Ellul, C. E.; Mahon, M. F.; Saker, O.; Whittlesey, M. K.
Corresponding Author
E-mail: broyo@itqb.unl.pt.
*
́
Notes
́
̃
́
The authors declare no competing financial interest.
2
2
́
̃
́
̃
ACKNOWLEDGMENTS
San
́
(
■
Financial support by FCT (Fundaca
̧
o
̃
para a Cien
̂
cia e a
Angew. Chem., Int. Ed. 2007, 46, 6343. (b) Critall, M. R.; Ellul, C. E.;
Mahon, M. F.; Saker, O.; Whittlesey, M. K. Dalton Trans. 2008, 4209.
Tecnologia) through projects PTDC/QUI-QUI/110349/2009,
REDE/1517/RMN/2005, and REDE/1504/REM/2005 is
gratefully acknowledged. S.W. is grateful to the Leonardo da
Vinci Programme.
(17) Ellul, C. E.; Saker, O.; Mahon, M. F.; Apperley, D. C.;
Whittlesey, M. K. Organometallics 2008, 27, 100.
(18) Bruce, M. I.; Cole, M. L.; Fung, R. S. C.; Forsyth, C. M.; Hilder,
M.; Junk, P. C.; Konstas, K. Dalton Trans. 2008, 4118.
(
2
19) (a) Zhang, C.; Li, B.; Song, H.; Xu, S.; Wang, B. Dalton Trans.
009, 7230. (b) Zhang, C.; Li, B.; Song, H.; Xu, S.; Wang, B.
Organometallics 2011, 30, 3029.
20) (a) Cetinkaya, B.; Dixneuf, P.; Lappert, M. F. J. Chem. Soc.,
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