Synthesis of bis(N-heterocyclic carbene) complexes of iron(II) and their application in hydrosilylation and transfer hydrogenation

Article abstract of DOI:10.1021/om300298q

N-heterocyclic carbene (NHC) adducts of iron dichloride, (IMes) ₂FeCl₂ (1a; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol- 2-ylidene) and (IEtPh*)₂FeCl₂ (1b; IEtPh* = 1,3-bis((R)-1′-phenylethyl)imidazol-2-ylidene), were prepared in good yields from the reactions of Fe{N(SiMe₃)₂}₂ with imidazolium salts. While the iron atom of 1a has a tetrahedral geometry, replacement of the chlorides by methyl groups via treatment of 1a with MeLi led to the formation of the square-planar complex trans-(IMes)₂FeMe ₂ (2). The molecular structures of complexes 1a,b and 2 were identified by means of single-crystal X-ray diffraction analysis. Complexes 1a,b and 2 are good catalyst precursors in the transfer hydrogenation of 2′-acetonaphthone, and complex 2 also efficiently catalyzes the hydrosilylation of 2′-acetonaphthone.

Full text of DOI:10.1021/om300298q

Article
pubs.acs.org/Organometallics
Synthesis of Bis(N-heterocyclic carbene) Complexes of Iron(II) and
Their Application in Hydrosilylation and Transfer Hydrogenation
Takayoshi Hashimoto,†,‡ Slawomir Urban,† Ryoko Hoshino,‡ Yasuhiro Ohki,*,‡ Kazuyuki Tatsumi,*,‡
and Frank Glorius*,†
†Organisch-Chemisches Institut der Westfalischen Wilhelms-Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
̈
̈
̈
̈
‡Department of Chemistry, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8602, Japan
S
* Supporting Information
ABSTRACT: N-heterocyclic carbene (NHC) adducts of iron
dichloride, (IMes)2FeCl2 (1a; IMes = 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene) and (IEtPh*)2FeCl2 (1b;
IEtPh* = 1,3-bis((R)-1′-phenylethyl)imidazol-2-ylidene), were
prepared in good yields from the reactions of Fe{N(SiMe3)2}2
with imidazolium salts. While the iron atom of 1a has a
tetrahedral geometry, replacement of the chlorides by methyl
groups via treatment of 1a with MeLi led to the formation of the
square-planar complex trans-(IMes)2FeMe2 (2). The molecular
structures of complexes 1a,b and 2 were identified by means of single-crystal X-ray diffraction analysis. Complexes 1a,b and 2 are
good catalyst precursors in the transfer hydrogenation of 2′-acetonaphthone, and complex 2 also efficiently catalyzes the
hydrosilylation of 2′-acetonaphthone.
catalytic applications of NHC−iron complexes remain
scarce.5−7
In this work, we have synthesized some simple iron(II)
chloro and alkyl complexes having monodentate NHC ligands,
and we have explored their catalytic applications in hydrogen
transfer reactions and the hydrosilylation of 2′-acetonaphthone.
INTRODUCTION
■
N-heterocyclic carbenes (NHCs) constitute a growing class of
ligands in organometallic chemistry (Figure 1).1 While NHCs
RESULTS AND DISCUSSION
■
Synthesis of NHC−Iron(II) Dichlorides. Two typical
methods have been reported for the synthesis of NHC−iron
halide complexes. One is the ligation of free NHC ligands to
FeX2.5c,6a,8 Iron(II) dihalide complexes with monodentate
NHCs, (NHC)2FeX2, were synthesized by Grubbs et al.,6a
and this method was recently improved by Deng et al.,8 using
1,3-R2-3,4-dimethylimidazol-2-ylidene (R = Me, Et, Pri).
Another synthetic route is the metalation reaction, where the
imidazolium salt is deprotonated by basic ligands in iron
complexes;6d,i,9,10 the silylamide [N(SiMe3)2]− is the most
frequently employed basic ligand. Some bidentate or tridentate
NHC−iron dihalide complexes6i,9 have been synthesized from
Fe{N(SiMe3)2}2,11 and we have synthesized Cp*Fe(IMes)Cl6d
(IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)
from the reaction of Cp*Fe{N(SiMe3)2}12 with IMes·HCl.
Recently, Danopoulos et al.10 have synthesized (SIPr′)2FeCl2
(SIPr′ = 1,3-bis(2-isopropylphenyl)imidazolin-2-ylidene) from
the reaction of Fe{N(SiMe3)2}2 with SIPr′·HCl.
Figure 1. NHCs and their abbreviations.
are often used as alternatives to well-known phosphines, their
strong electron-donating ability leads to a more robust metal−
ligand interaction. The strong binding of NHCs to various
transition metals has been useful in homogeneous catalysis.1i,2
A recent example is the enantioselective hydrogenation of
substituted quinoxalines and benzofurans catalyzed by chiral
NHC−ruthenium complexes.3 It is notable that NHCs have
been mainly used as ligands for the second- and third-row
transition metals, particularly noble metals. In comparison to
generally toxic and costly noble metals typically used in
catalysis, iron offers some advantages; iron is cheap, nontoxic,
environmentally friendly, and abundant. Thus, there has been
increasing attention paid to the catalytic application of iron in
organic synthesis.4 However, details of the synthesis and
Received: April 12, 2012
Published: June 7, 2012
© 2012 American Chemical Society
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In this study, we chose a metalation reaction to synthesize
the iron dichloride complexes. The reaction of Fe{N(SiMe3)2}2
with 2 equiv of IMes·HCl13 in toluene afforded (IMes)2FeCl2
(1a)14 as a white crystalline powder in 89% yield (Scheme 1).
Scheme 1
An analogous complex with chiral NHC ligands,
(IEtPh*)2FeCl2 (1b; IEtPh* = 1,3-bis((R)-1′-phenylethyl)-
imidazol-2-ylidene)), was obtained in 86% yield from Fe{N-
(SiMe3)2}2 and IEtPh*·HCl.15 Further attempts to synthesize
(IPri)2FeCl2 (IPri = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-
ylidene) by the metalation method was not successful and gave
(IPri)FeCl{N(SiMe3)2}.10
Figure 3. Molecular structure of (IEtPh*)2FeCl2 (1b) with thermal
ellipsoids at the 50% probability level. Selected bond distances (Å) and
angles (deg): Fe−C1 = 2.148(4), Fe−C20 = 2.124(4), Fe−Cl1 =
2.2812(12), Fe−Cl2 = 2.3073(12); C1−Fe−C20 = 104.13(14), C1−
Fe−Cl1 = 116.56(11), C1−Fe−Cl2 = 105.14(11), C20−Fe−Cl1 =
108.39(11), C20−Fe−Cl2 = 116.58(11), Cl1−Fe−Cl2 = 106.46(5).
Complexes 1a,b are air and moisture sensitive both in
solution and in the solid state. These complexes are
paramagnetic, and their 1H NMR spectra exhibited broad
signals in the ranges of 27.8−2.2 ppm (1a) and 37−4.2 ppm
(1b). Their solution magnetic moments were determined by
the Evans method16 as 5.1 μB at 296 K (1a) and 5.2 μB at 297 K
(1b), respectively. These values are close to the spin-only value
for an S = 2 state (4.90 μB) and are consistent with a high-spin
electronic configuration for tetrahedral d6 complexes.17
The molecular structures of 1a,b were determined by X-ray
diffraction and are shown in Figures 2 and 3, respectively.
(102.05(6)°; IPr = 2,5-diisopropyl-3,4-dimethylimidazol-2-
ylidene).6a The large C(carbene)−Fe−C(carbene) angle of
1a is due to the steric congestion between the IMes ligands, and
this congestion may also lead to the narrow C22−Fe−Cl2
angle (94.97(10)°).
Synthesis of an NHC−Iron(II) Dimethyl Complex. Four-
coordinate, tetrahedral NHC−iron(II) alkyl complexes,
(IEt)2FeR2 (IEt = 1,3-diethyl-3,4-dimethylimidazol-2-ylidene,
R = Me, CH2TMS), were synthesized by Deng et al.8 from the
reactions of (IEt)2FeCl2 with 2 equiv of MeLi or
TMSCH2MgCl. From an analogous reaction of (IMes)2FeCl2
(1a) with 2 equiv of MeLi in THF, the square-planar complex
trans-(IMes)2FeMe2 (2) was isolated in 86% yield as an air- and
moisture-sensitive reddish orange powder (Scheme 2). We also
Scheme 2
Figure 2. Molecular structure of (IMes)2FeCl2 (1a) with thermal
ellipsoids at the 50% probability level. Selected bond distances (Å) and
angles (deg): Fe−C1 = 2.140(4), Fe−C22 = 2.144(3), Fe−Cl1 =
2.2796(17), Fe−Cl2 = 2.2998(16); C1−Fe−C22 = 126.09(14), C1−
Fe−Cl1 = 99.74(9), C1−Fe−Cl2 = 115.77(10), C22−Fe−Cl1 =
112.46(11), C22−Fe−Cl2 = 94.97(10), Cl1−Fe−Cl2 = 107.28(7).
attempted to synthesize (IEtPh*)2FeMe2 from 1b and MeLi.
1
The H NMR measurement of the reaction mixture revealed
the disappearance of 1b and the formation of a new iron
complex, but its isolation was unsuccessful. Complex 2 is
paramagnetic, as evidenced by the solution magnetic moment
of 3.5 μB at 296 K. The temperature-dependent magnetic
susceptibility in the solid state (Figure 4) also exhibited μeff
values ranging from 2.74 to 3.24 μB at 30−300 K, which are
comparable to the spin-only value for an S = 1 state (2.83 μB).
When the magnetic moment and the square-planar structure
are taken into account, complex 2 can be assigned as an
There are two independent molecules in the asymmetric unit of
1b. As they are very similar to each other, the following
discussion is based on one of the molecules. In complexes 1a,b,
the iron atom has a distorted-tetrahedral geometry with two
NHC ligands and two chlorides. The Fe−C(carbene) distacnes
are 2.140(4) and 2.144(3) Å in 1a and 2.148(4) and 2.124(4)
Å in 1b, which are comparable to those in other tetrahedral
Fe(II) bis-carbene chloride complexes (2.1298(16)−
2.1363(15) Å).6a,10 The C(carbene)−Fe−C(carbene) angle of
1a (126.09(14)°) is notably larger than those for (SIPr′)2FeCl2
(103.33(13)°),10 1b (104.13(14)°), and (IPr)2FeCl2
2
2
intermediate-spin S = 1 state with an unoccupied dx −y
orbital.17
Complex 2 was structurally identified by an X-ray diffraction
study. There are two independent molecules in the asymmetric
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distance in 2 is possibly due to the strong trans influence of
CH3 groups.
Catalytic Reduction of 2′-Acetonaphthone via Trans-
fer Hydrogenation and Hydrosilylation. Recently, several
groups have reported iron(II) NHC complexes which catalyze
the hydrogenation/hydrosilylation of carbonyl compounds.7
For example, Royo et al. reported cyclopentadienyl-function-
alized NHC−Fe complexes for the transfer hydrogenation of
ketones,7a and Darcel et al. reported cyclopentadienyl NHC−
Fe complexes for the hydrosilylation of aldehydes and ketones
under visible light irradiation.7b With new NHC−FeII
complexes in hand, we also examined the catalytic reduction
of 2′-acetonaphthone (3) via transfer hydrogenation and
hydrosilylation.20 The progress of the reactions was monitored
by GC-MS or 1H NMR signals of the corresponding alcohol or
silyl ether. In the transfer hydrogenation reactions, 2-propanol
was used as the hydrogen source, and the results are
summarized in Table 1. In the presence of t-BuOK as a base
Figure 4. Temperature-dependent magnetic susceptibility of 2 in the
solid state.
unit of 2, and one of these is shown in Figure 5. The iron atom
is coordinated by two IMes ligands in trans positions and two
a
Table 1. Transfer Hydrogenation of 2′-Acetonaphthone (3)
b
entry
cat. (amt (mol %))
T (°C)/t (h)
yield (%)
ee (%)
c
1
1a (1.0)
2 (1.0)
1a (1.0)
2 (1.0)
1a (1.0)
none
80/6
80/6
80/3
80/3
80/3
80/3
70/3
70/3
50/5
25/12
70/3
70/3
48
55
98
97
10
9
c
2
3
4
d
5
e
6
7
1a (1.0)
2 (1.0)
1a (1.0)
1a (1.0)
1a (0.1)
1b (0.1)
97
97
52
0
8
9
Figure 5. Molecular structure of (IMes)2FeMe2 (2) with thermal
ellipsoids at the 30% probability level. Selected bond distances (Å) and
angles (deg): Fe−C1 = 2.125(5), Fe−C2 = 1.959(5); C1−Fe−C2 =
90.69(19), C1−Fe−C2* = 89.30(19).
10
f
g
11
(92)
f
g
12
(91)
<5
a
The reactions were carried out using 3 (0.20 mmol), Fe catalyst, i-
b
PrOLi (0.24 mmol), and i-PrOH (2.0 mL) under Ar. Yield
c
1
determined by H NMR spectroscopy. t-BuOK was used as a base.
methyl groups, and the four carbon atoms bound to iron are
crystallographically coplanar with iron. From Figures 2 and 5,
one can see that the replacement of chlorides in 1a by methyl
groups induces a geometric change. This change is probably
caused by both steric and electronic factors. The square-planar
geometry with trans IMes ligands is suitable for reducing the
steric congestion between the mesityl groups of the IMes
ligands, and the two IMes ligands are twisted against each other
with a torsion angle of 57.3(2)° between the N-containing five-
membered rings. The strong σ-donating properties of IMes and
methyl ligands lead to a strong ligand field, enabling the square-
planar configuration for four-coordinate complex 2 with an
d
e
The reaction was carried out with i-PrOLi (0.015 mmol). The
f
reaction was carried out without Fe catalyst. The reaction was
conducted on a 5-fold scale (1.0 mmol of 3). The yield of the isolated
g
product is given in parentheses.
(1.2 equiv to 3), complexes 1a and 2 (1.0 mol %) catalyzed the
hydrogenation of 3 at 80 °C to give the desired alcohol 4 in
moderate yields (entries 1 and 2). The product yields became
excellent upon changing the base to i-PrOLi (entries 3 and 4).
However, a catalytic amount of i-PrOLi (7.5 mol %) was
insufficient, and only a 10% yield of 4 was obtained (entry 5).
Adolfsson et al.21 reported that i-PrOLi works as an efficient
catalyst for the transfer hydrogenation of ketones at high
temperature (i.e. i-PrOLi (6 mol %), 180 °C, 20 min for
acetophenone, 94% yield); however, the Fe catalyst appeared to
be necessary for the quantitative conversion of the substrate in
our reaction (entry 6). The reaction proceeds smoothly at 70
°C (entries 7 and 8), whereas a lower reaction temperature (50
or 25 °C) results in a drop of the yield (entries 9 and 10).
Interestingly, a 5-fold increase of the reaction scale (1.0 mmol
of 3) with 0.1 mol % of 1a afforded the desired alcohol 4 in
2
2
efficiently destabilized antibonding dx −y orbital. The Fe−
C(carbene) bond length is 1.959(5) Å, which is shorter than
those of tetrahedral Fe(II) bis-carbene complexes (2.075(4)−
2.1363(15) Å)6a,c,i,8,9c,10 and is comparable to those of reported
square planar Fe(II) bis-carbene complexes (1.801(9)−
2.010(9) Å).9c,18 The Fe−CH3 bond length of 2.125(5) Å is
longer than those reported for the square-planar Fe complexes
{Li(THF)4}[(PDI)FeMe]19a (2.013(9) Å, PDI = {2,6-[2,6-(i-
Pr)2PhN=C(CH3)]2}(C5H3N)), (PDI)FeMe19b (2.001(6) Å),
and [(PDI)FeMe](BPh4) (2.006(4) Å).19c The long Fe−CH3
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92% isolated yield (entry 11). Complex 1b, having chiral NHC
ligands, was also highly active in catalyzing the transfer
hydrogenation of 3 (entry 12), while the enantioselectivity of
4 was almost negligible. The catalytic performances of 1a,b are
significant, as a product yield of >90% at 70 °C with a catalyst
loading as low as 0.1 mol % (entries 11 and 12) is comparable
to the results for the best iron catalysts thus far reported.7a,22,23
The results of the catalytic hydrosilylation of 3 are
summarized in Table 2. In the presence of 1a (5 mol %), the
loading appeared to be sufficient for the transfer hydrogenation
catalyzed by 1a,b and the hydrosilylation catalyzed by 2.
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out using standard
Schlenk techniques and a glovebox under a nitrogen or an argon
atmosphere. Toluene, diethyl ether, THF, and hexane were purified by
the method of Grubbs,26 where the solvents were passed over columns
of activated alumina and a supported copper catalyst supplied by
Hansen & Co. Ltd. Other solvents were degassed and distilled from
sodium benzophenone ketyl. Deuterated solvents, C61D6 and d8-THF,
were dried by sodium and distilled prior to use. The H and 13C{1H}
NMR spectra were recorded on a JEOL ECA-600 spectrometer. The
signals were referenced to the residual peak of the deuterated solvent.
Solid magnetic susceptibility was measured using a Quantum Design
MPMS-XL SQUID-type magnetometer, and the crystalline samples
were sealed in quartz tubes. Solution magnetic susceptibilities were
determined by the Evans method, using C6D6/hexamethylbenzene or
d8-THF/hexamethylbenzene solutions.16 GC-MS spectra were re-
corded on an Agilent Technologies 7890A GC system with Agilent
5975C VL MSD or 5975 inert mass selective detector (EI) on a HP-
5MS column (0.25 mm × 30 m, film 0.25 μm). Elemental analyses
were performed on a LECO CHNS-932 microanalyzer, where the
samples were sealed into silver capsules in a glovebox. X-ray diffraction
data were collected on a Rigaku AFC8 or a Rigaku RA-Micro7
equipped with a CCD area detector by using graphite-monochromated
Mo Kα radiation. Fe{N(SiMe3)2}2,11 IMes·HCl (IMes = 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene),13 and IEtPh*·HCl (IEtPh* =
1,3-bis((R)-1′-phenylethyl)imidazol-2-ylidene)15 were prepared ac-
cording to literature procedures.
a
Table 2. Hydrosilylation of 2′-Acetonaphthone (3)
b
entry cat (amt (mol %)) silane (amt (equiv)) T (°C)/t (h) yield (%)
1
2
3
4
5
6
7
8
1a (5.0)
1a (2.0)
2 (5.0)
2 (1.2)
2 (1.2)
2 (1.2)
2 (0.1)
2 (0.1)
(EtO)3SiH (2.0)
(EtO)3SiH (1.5)
(EtO)3SiH (2.0)
(EtO)3SiH (1.1)
Ph2SiH2 (1.1)
80/5
50/10
80/5
25/5
40/5
40/10
25/5
40/5
0
c
0
99
99
99
0
Et3SiH (1.1)
d
d
e
e
(EtO)3SiH (1.1)
Ph2SiH2 (1.1)
(91)
(96)
a
The reactions were carried out using 3 (0.20 mmol), Fe catalyst,
b
silane, and THF (2.0 mL) under Ar. Yield determined by GC-MS.
c
d
Na(acac) (5.0 mol %) was added. The reaction was conducted on a
Synthesis of (IMes)2FeCl2 (1a). Fe{N(SiMe3)2}2 (1.00 g, 2.67
mmol) and IMes·HCl (1.82 g, 5.33 mmol) were charged into a 100
mL flask, and toluene (60 mL) was added at room temperature. The
mixture was stirred overnight. The resulting brown solution was
concentrated under reduced pressure, during which time a white
crystalline powder of 1a appeared. The crystalline powder was
collected, washed with hexane, and dried under vacuum (1.75 g, 89%).
Single crystals suitable for crystallography were obtained from a
toluene solution at −30 °C. 1H NMR (600 MHz, C6D6): δ 27.8 (4H),
5.66 (8H), 3.75 (24H), 2.22 (12H). Magnetic susceptibility (C6D6,
296 K): μeff = 5.1 μB. Anal. Calcd for C42H48N4FeCl2: C, 68.58; H,
6.58; N, 7.62. Found: C, 68.14; H, 6.76; N, 7.36.
e
5-fold scale (1.0 mmol of 3). The yield of the isolated product is given
in parentheses.
hydrosilylation of 3 did not proceed at all (entry 1). Nishiyama
et al.24l reported the positive effect of Na(acac) in iron-
catalyzed hydrosilylation; however, the addition of Na(acac)
(5.0 mol %) did not change the outcome (entry 2). In contrast
to the unsuccessful reactions with 1a, complex 2 (5.0 mol %)
was found to efficiently catalyze the hydrosilylation of 3 in THF
at 80 °C, in the presence of 2 equiv of (EtO)3SiH (entry 3).
Even under more challenging conditions, with 1.1 equiv of
(EtO)3SiH and a reduced amount of 2 (1.2 mol %), the
hydrosilylation of 3 proceeded quantitatively at 25 °C (entry
4). The hydrosilylation of 3 also took place with Ph2SiH2 (entry
5), whereas Et3SiH was not applicable in this system (entry 6).
Only 0.1 mol % of 2 was enough for the reactions on a 5-fold
scale (1.0 mmol of 3) in the presence of 1.1 equiv of
hydrosilanes ((EtO)3SiH or Ph2SiH2) at room temperature,
and the isolated yields of 4 were 91−96% (entries 7 and 8).
The catalytic performance of 2 in hydrosilylation can be
compared with those of the good iron catalysts thus far
reported.22,24,25
Synthesis of (IEtPh*)2FeCl2 (1b). Fe{N(SiMe3)2}2 (350 mg,
0.929 mmol) and IEtPh*·HCl (585 mg, 1.87 mmol) were charged into
a 100 mL flask, and toluene (30 mL) was added at room temperature.
The mixture was stirred overnight. The resulting white suspension was
evaporated until dryness, and the white residue was washed with
hexane. After extraction with THF (40 mL), the extract was
centrifuged to remove a small amount of insoluble solid, and the
THF solution was evaporated under reduced pressure. The white solid
was washed with hexane to afford a white powder of 1b (544 mg,
86%). Single crystals suitable for crystallography were obtained from a
1
toluene/THF solution at room temperature. H NMR (600 MHz, d8-
THF): δ 37.0 (4H), 7.54 (8H), 6.89 (4H), 6.23 (8H), 4.22 (12H).
Magnetic susceptibility (d8-THF, 297 K): μeff = 5.2 μB. Anal. Calcd for
C38H40N4FeCl2: C, 67.17; H, 5.93; N, 8.25. Found: C, 67.17; H, 6.21;
N, 7,92.
CONCLUDING REMARKS
Synthesis of (IMes)2FeMe2 (2). An Et2O solution of MeLi (1.06
M, 1.40 mL, 1.48 mmol) was added to a THF (12 mL) solution of 1a
(501 mg, 0.68 mmol) at −78 °C. The mixture was gradually warmed
to room temperature and was stirred overnight. The resulting orange
solution was evaporated until dryness. After it was washed with
hexane, the residue was extracted with toluene (20 mL) and the extract
was centrifuged to remove LiCl. The solution was evaporated under
reduced pressure to afford 2 as a reddish orange powder (405 mg,
86%). Single crystals suitable for crystallography were obtained from a
■
In this study, the two NHC−FeII chloride complexes
(IMes)2FeCl2 (1a) and (IEtPh*)2FeCl2 (1b) were synthesized
from the reactions of Fe{N(SiMe3)2}2 with imidazolium salts.
Treatment of (IMes)2FeCl2 with MeLi resulted in the
formation of the square-planar complex (IMes)2FeMe2 (2).
Complexes 1a,b and 2 revealed high catalytic activities in the
hydrogen transfer reaction of 2′-acetonaphthone. Complex 2
was also found to serve as a good catalyst for the hydrosilylation
of 2′-acetonaphthone. Remarkably, only 0.1 mol % catalyst
1
toluene solution at −30 °C. H NMR (600 MHz, C6D6): δ 2.09,
−2,20, −2,61, −3.59, −32.0. Magnetic susceptibility (C6D6, 296 K):
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μeff = 3.5 μB. Anal. Calcd for C44H54N4Fe: C, 76.06; H, 7.83; N, 8.06.
Found: C, 76.15; H, 7.99; N, 7.57.
frame data were integrated using the CrystalClear program package,
and the data sets were corrected for absorption using a REQAB
program. The calculations were performed with the CrystalStructure
program package. All structures were solved by direct methods and
refined by full-matrix least squares. Anisotropic refinement was applied
to all non-hydrogen atoms except for disordered atoms (refined
isotropically), and all hydrogen atoms were placed at calculated
positions. In the asymmetric unit of 1b, there are two crystallo-
graphically independent molecules. Three phenyl groups of the IEtPh*
ligand of 1b are disordered over two positions in 2/3, 1/1, and 2/3
ratios, respectively. In the asymmetric unit of 2, there are two
crystallographically independent molecules. The hydrogen atoms of
one of the Fe−CH3 groups are disordered over two positions in a 1/1
ratio. Additional data are available as Supporting Information.
Typical Procedure for Transfer Hydrogenation of 2′-
Acetonaphthone (3). (IMes)2FeCl2 (1a; 1.0 mg, 1.4 × 10−3 mol),
2′-acetonaphthone (3; 170 mg, 1.0 mmol), and i-PrOLi (79.2 mg, 1.2
mmol) were charged into a 10 mL J. Young tube. Under an argon
atmosphere, i-PrOH (3.0 mL) was added, and the mixture was stirred
for 3 h at 70 °C. The consumption of 3 was monitored by GC-MS.
The reaction mixture was filtered through a plug of silica. The filtrate
was evaporated until dryness. The residue was purified by silica gel
column chromatography (with ethyl acetate/pentane 1/1 as eluent) to
give the desired alcohol 4 (159 mg, 0.92 mmol) in 92% yield. The
1
product was analyzed by H and 13C NMR.
Typical Procedure for Hydrosilylation of 2′-Acetonaph-
thone (3). (IMes)2FeMe2 (2; 1.0 mg, 1.4 × 10−3 mol), 2′-
acetonaphthone (3; 170 mg, 1.0 mmol), and THF (3.0 mL) were
charged into a 10 mL J. Young tube. Under an argon atmosphere,
(EtO)3SiH (0.21 mL, 1.1 mmol) was added, and the mixture was
stirred for 5 h at room temperature. The consumption of 3 was
monitored by GC-MS. A THF solution of tetrabutylammonium
fluoride (TBAF, 1.0 M, 2.0 mL), KF (116 mg), MeOH (1.0 mL), and
H2O (1.0 mL) was added at 0 °C. The mixture was extracted with
ethyl acetate (30.0 mL) and was washed with water (5.0 mL) and
brine (5.0 mL). The combined organic layer was dried over anhydrous
MgSO4 and was evaporated until dryness, and then the residue was
purified by silica gel column chromatography (with ethyl acetate/
pentane 1/1 as eluent) to give the desired alcohol 4 (156 mg, 0.91
mmol) in 91% yield.
ASSOCIATED CONTENT
* Supporting Information
CIF files giving X-ray crystallographic data for the structures of
1a,b and 2. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: glorius@uni-muenster.de (F.G.); i45100a@nucc.cc.
nagoya-u.ac.jp (K.T.); ohki@chem.nagoya-u.ac.jp (Y.O.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was performed within the framework of the
International Research Training Group (IRTG) Munster/
Nagoya and financially supported by the Deutsche For-
schungsgemeinschaft (DFG) and Grant-in-Aids for Scientific
Research (No. 23000007 and 23685015) from the Ministry of
Education, Culture, Sports, Science and Technology of Japan.
■
Table 3. Crystal Data for (IMes)2FeCl2 (1a), (IEtPh*)2FeCl2
(1b), and (IMes)2FeMe2 (2)
̈
1a
1b·1/2 C4H8O
2
formula
fw
C42H48Cl2FeN4
735.62
C40H44Cl2FeN4O0.5
715.56
C44H54FeN4
694.78
temp (°C)
cryst syst
space group
a (Å)
−100
−100
−160
We thank Christoph Grohmann (WWU Munster) for careful
̈
triclinic
P-1 (#2)
9.797(6)
10.669(7)
20.094(13)
79.27(3)
79.53(3)
69.92(3)
1922(2)
2
orthorhombic
P212121 (#19)
9.117(2)
monoclinic
C2/c (#15)
20.835(7)
20.799(6)
18.861(6)
reading of the manuscript and Professors Hirofumi Yoshikawa,
Michio Matsushita, and Kunio Awaga (Nagoya University) for
aiding us with the SQUID-type magnetometer.
b (Å)
25.346(4)
c (Å)
32.221(6)
REFERENCES
α (deg)
β (deg)
γ (deg)
V (Å3)
■
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