Synthesis of an ionic paramagnetic ruthenium(III) complex and its application as an efficient and recyclable catalyst for the transfer hydrogenation of ketones

Article abstract of DOI:10.1002/ejic.201200280

A novel ionic complex, bis[1-butyl-2-(diphenylphosphanyl)-3- methylimidazolium]tetrachloridoruthenium(III) hexafluorophosphate (2), has been synthesized and fully characterized. The single-crystal X-ray diffraction analysis showed that 2 is composed of an Ru complex cation and PF ₆^- anion. The cation has a highly symmetrical Ru-centered octahedron geometry with four Cl atoms in the equatorial plane and two imidazolium-substituted phosphane ligands in the axial positions. It exhibits paramagnetism due to the presence of one unpaired electron in the phosphane-ligated low-spin Ru^III complex. Complex 2 exhibited good catalytic performance in the transfer hydrogenation of a wide range of ketones by using alcohols as hydrogen donors. Owing to its high polarity, good thermal stability, and insensitivity to moisture and oxygen, complex 2 could be used in six catalytic cycles in the transfer hydrogenation of acetophenone without any obvious loss of activity. A novel ionic complex 2 containing an Ru^III cation and PF₆^- anion has been synthesized. The Ru ^III cation possesses ideal octahedral geometry and exhibits paramagnetism due to the presence of one unpaired electron in the phosphane-ligated low-spin Ru^III complex. Complex 2 proves to be an efficient and recyclable catalyst for the transfer hydrogenation of ketones with alcohols as hydrogen donors. Copyright

Full text of DOI:10.1002/ejic.201200280

FULL PAPER
DOI: 10.1002/ejic.201200280
Synthesis of an Ionic Paramagnetic Ruthenium(III) Complex and Its
Application as an Efficient and Recyclable Catalyst for the Transfer
Hydrogenation of Ketones
Chengliang Zhou,[a] Jing Zhang,[a] Marijana Aakovic´,[b] Zora Popovic´,[b] Xiaoli Zhao,[a] and
Ye Liu*[a]
Keywords: Ruthenium / Paramagnetism / Hydrogenation / Ketones / Homogeneous catalysis
A novel ionic complex, bis[1-butyl-2-(diphenylphosphanyl)-
3-methylimidazolium]tetrachloridoruthenium(III) hexafluoro-
phosphate (2), has been synthesized and fully characterized.
The single-crystal X-ray diffraction analysis showed that 2 is
paired electron in the phosphane-ligated low-spin RuIII com-
plex. Complex 2 exhibited good catalytic performance in the
transfer hydrogenation of a wide range of ketones by using
alcohols as hydrogen donors. Owing to its high polarity, good
thermal stability, and insensitivity to moisture and oxygen,
–
composed of an Ru complex cation and PF6 anion. The cat-
ion has a highly symmetrical Ru-centered octahedron geom- complex 2 could be used in six catalytic cycles in the transfer
etry with four Cl atoms in the equatorial plane and two imid-
azolium-substituted phosphane ligands in the axial positions.
It exhibits paramagnetism due to the presence of one un-
hydrogenation of acetophenone without any obvious loss of
activity.
amine–bis(phenolate)s, chiral ligands, and heterocyclic li-
gands[5–16] are the most prominent catalysts and exhibit
high activities in the transfer hydrogenation of ketones. In
contrast to electron-rich ligands as strong σ-donors,[17] elec-
tron-deficient ligands are less explored.[18] Few catalytic
processes have been shown to benefit from the use of elec-
tron-deficient ligands,[19] particularly when the Lewis acid-
ity of the metal center is crucial.[20] Cationic phosphanes
bearing quaternary ammonium moieties possessing elec-
tron-deficient character,[21] such as the amidiniophosphane
ligands with a positive charge vicinal to the PIII atom,[22]
are, however, of great interest in organometallic chemistry
and catalysis.[23]
Compared with RuII analogues, there exist relatively few
reported examples of paramagnetic RuIII complexes con-
taining tertiary phosphanes[24] and their application to
transfer hydrogenation. On the other hand, the recycling of
homogeneous ruthenium complex catalysts is still a chal-
lenging problem due to difficult separation workup and ra-
pid deactivation.
Introduction
The reduction of carbonyl compounds to alcohols is an
industrially important reaction for the preparation of fine
chemicals, perfumes, agrochemicals, and pharmaceuticals.[1]
Methods for the metal-catalyzed transformation of carb-
onyl compounds into alcohols include hydrogenation by
H2, transfer hydrogenation, and hydrosilylation.[2–4] Trans-
fer hydrogenation is a particularly useful protocol in which
unsaturated compounds can be hydrogenated without the
use of molecular H2. In comparison with hydrogenation by
H2 or with a hydride reagent, transfer hydrogenation is at-
tractive due to its operational simplicity and the reduction
of risk associated with the use of high pressure, which are
beneficial for large-scale production from environmental
and economic points of view.[5] Transition-metal complexes
have been extensively investigated as catalysts for the trans-
fer hydrogenation of ketones to secondary alcohols.[6–8]
Ruthenium(II) complexes bearing N-heterocyclic carbenes
(NHCs), phosphanes, diamines, aminodiphosphanes,
In this work, a novel ionic paramagnetic ruthenium(III)
complex, bis[1-butyl-2-(diphenylphosphanyl)-3-methylimid-
azolium]tetrachloridoruthenium(III) hexafluorophosphate
(2), was synthesized by the complexation of the ionic imid-
azolium-substituted phosphane ligand 1 and hydrated ru-
thenium(III) chloride. Detailed crystallographic data for 2
are reported. The catalytic performance and recyclability of
2 for the reduction of ketones to the corresponding alcohols
by transfer hydrogenation have been fully investigated
(Scheme 1).
[a] Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, Chemistry Department of East China Normal
University,
Shanghai 200062, P. R. China
Fax: +86-21-62233424
E-mail: yliu@chem.ecnu.edu.cn
[b] General and Inorganic Laboratory, Chemistry Department,
University of Zagreb,
10000 Zagreb, Croatia
Fax: +385-1-4606341
E-mail: zpopovic@chem.pmf.hr
Eur. J. Inorg. Chem. 2012, 3435–3440
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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C. Zhou, J. Zhang, M. aakovic´, Z. Popovic´, X. Zhao, Y. Liu
FULL PAPER
Scheme 1. Synthesis of 2 as a catalyst precursor for the transfer
hydrogenation of ketones.
Results and Discussion
Synthesis and Characterization of 2
Complex 2 was prepared by applying procedures similar
to those used for the preparation of [RuIICl2(PPh3)3].[25] It
was assumed that a structurally similar complex would be
Figure 1. Molecular structure of 2 (anion PF6– and the solvent mo-
obtained by replacing the PPh3 ligand with 1[26] and al- lecule, acetone, have been omitted for clarity).
lowing 1 to coordinate to RuCl3·3H2O. However, surpris-
ingly, a novel complex in which the Ru ion is in a valence
Table 1. Selected bond lengths [Å] and bond angles [°] for 2.
state of +3 was obtained. Complex 2, which was isolated as
Ru1–Cl1
Ru1–Cl2
Ru1–P1
2.363(1)
2.344(1)
2.408(1)
89.63(4)
90.37(4)
90.59(4)
90.28(4)
89.41(4)
89.72(4)
180.00(5)
180.0
Ru1–Cl1a
Ru1–Cl2a
Ru1–P1a
Cl2a–Ru1–Cl1
Cl2a–Ru1–Cl1a
Cl2a–Ru1–P1
Cl1a–Ru1–P1
Cl2a–Ru1–P1a
Cl1a–Ru1–P1a
Cl1–Ru1–Cl1a
2.363(1)
2.344(1)
2.408(1)
90.37(4)
89.63(4)
89.41(4)
89.72(4)
90.59(4)
90.28(4)
180.0
an orange solid in good yield (75 wt.-%), is air- and moist-
ure-stable both in the solid state and in organic solvents at
room temperature. But dmso could not be used as a solvent
for 2 due to the displacement of the ligand L by dmso.
Single crystals for X-ray diffraction analysis were obtained
by recrystallization from acetone/hexane.
Cl2–Ru1–Cl1
Cl2–Ru1–Cl1a
Cl2–Ru1–P1
Cl1–Ru1–P1
Cl2–Ru1–P1a
Cl1–Ru1–P1a
Cl2–Ru1–Cl2a
P1–Ru1–P1a
The molecular structure of 2 is depicted in Figure 1. It is
–
composed of the Ru complex cation and PF6 anion. The
Ru complex cation exhibits an ideal octahedral geometry
with the RuIII (d5) ion situated exactly in the center of the
octahedron and hexacoordinated by four chlorine atoms in
the equatorial plane and two imidazolium-substituted phos- tron donor and a good reducing reagent. In contrast, L is
phane ligands in the axial positions. The bond angles of a relatively weak electron donor with weakened reduction
P1–Ru1–P1a, Cl1–Ru1–Cl1a, and Cl2–Ru1–Cl2a are 180° ability. Consequently, the redox reaction between 1 and
(Table 1). The two Ru–P bond lengths are the same at RuCl3·3H2O during the complexation was avoided, leading
2.408(1) Å, much longer than the classical values (2.2– to an unchanged valance state for Ru3+
.
2.3 Å) in typical phosphane-ligated RuII complexes.[25,27,28]
The cation [RuCl4L2]+ in 2 is formally a 17-electron com-
As L is an electron-deficient ligand relative to PPh3, the plex, which is supposed to be unstable, whereas in the reso-
length of the Ru–P bond can be attributed to an enhanced nance structure of [LRuCl4]L+, the RuIII center is formally
partial ionic character of the Ru–P bond of the type a 15-electron complex. The contribution to both forms in
[LRuCl4]L+. This particular feature could be dictated by the the resonating description corresponds to a stabilized
+3 oxidation state of the Ru center: Indeed, imidazolio- average of a 16-electron cationic complex. On the other
phosphanes bearing a positively charged imidazolium moi- hand, the highly symmetrical octahedral configuration fur-
ety similar to L have been reported to afford typical coval- ther facilitates the stability of [RuCl4L2]+ in 2. In addition,
ent complexes with much less electronegative metal centers 1 is characterized by strong oxidation tolerance due to its
(M = PdII, RhI) in which the M–P bond lengths are in the electron-deficient nature; the corresponding complex of 2
classical range.[22,29,30]
with partial ionic character is also moisture- and air-insen-
The Ru center in 2 may have a +3 valance state for sitive at room temperature. TG/DTA analysis indicated that
HSAB (hard-soft acid-base theory) reasons. The cationic 2 thermally decomposed in air at 205 °C, revealing its good
phosphane of L is harder than that of PPh3, which is com- thermal stability.
patible with a hard RuIII center. It is also believed that the
Because 2 is in a low-spin state with an indication of the
reduction of RuIII to RuII in the formation of [RhII- presence of one unpaired electron in the RuIII center,[12] it
Cl2(PPh3)3] could be accomplished by PPh3 as a strong elec- has a paramagnetic nature. Consequently, the H and 31P
1
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 3435–3440

Synthesis of an Ionic Paramagnetic Ruthenium(III) Complex
NMR signals attributed to L in the cationic complex are preventing metal catalysts from leaching.[31] Because 2 is
broadened to flatness. However, the 31P NMR spectrum thermally stable (thermal decomposition temperature
–
still shows the signal of the PF6 counteranion at δ = 205 °C) and insensitive to moisture and oxygen, 2 could be
–143.1 ppm, consistent with its solid-state structure, due to recovered in water and open air, which facilitated the sepa-
the negligible influence of RuIII magnetic moments on the ration workup greatly. In contrast, the recovery and recycl-
counteranion.
ing of the [RuIICl2(PPh3)3] catalyst were unsuccessful.
Table 3. Recycling of 2 as catalyst in the transfer hydrogenation of
acetophenone.[a]
Catalytic Performance of 2 in Transfer Hydrogenation
Run[b]
Conv. [%][c]
Sel. [%][c]
TOF [h–1]
1
2
3
4
5
6
87
84
85
81
86
77
100
100
100
100
100
100
29
28
28
27
29
26
Transfer hydrogenation catalyzed by 2 was investigated
by using acetophenone as a model substrate with 2-propa-
nol as the hydrogen donor under solvent-free conditions
(Table 2). 2-Propanol is inexpensive and easy to handle (b.p.
82 °C) and the volatile acetone that is formed can also be
easily removed in the separation process. Because the cata-
lytic performance of the ruthenium complexes could be im-
proved dramatically under alkaline conditions,[3] tBuOK
was chosen as the optimal promoter after screening the
bases K2CO3, KOH, and tBuOK. In the absence of base,
transfer hydrogenation of acetophenone did not occur. For
comparison, [RuIICl2(PPh3)3] and RuCl3·3H2O were also
used as catalysts. As shown in Table 2, used fresh, 2 and
[RuIICl2(PPh3)3] exhibit competitive activities irrespective
of whether the Ru ion is in a valence state of +3 or +2
(Entries 2 and 4). However, transfer hydrogenation did not
occur with RuCl3·3H2O, that is, in the absence of phos-
phane ligation (Entry 3).
[a] Complex 2 (1.5 mol-%), acetophenone (5 mmol), 2-propanol
(3 mL), tBuOK (10 mol-%), reaction temperature 100 °C, reaction
time 2 h. [b] tBuOK (10 mol-%) was added to each run. [c] Deter-
mined by GC.
In fact, 2 is only a catalyst precursor. During the catalytic
reaction, derivation of 2 to the catalytic species must occur.
This derivation of 2 was monitored during the recycling by
31P NMR spectroscopy (Figure 2). Upon completion of
each run, the reaction mixture was extracted with the ionic
liquid (IL) of [Bpy]BF4 (N-n-butylpyridinium tetrafluoro-
borate, 2 mL) for 31P NMR analysis. Because [Bmim]BF4
(1-n-butyl-3-methylimidazolium tetrafluoroborate) can act
as a potential NHC ligand, [Bpy]BF4 with noncoordinating
ability was selected as the extracting reagent for the polar
Ru-based catalyst to rule out any possible coordination in-
fluence. The IL extract obtained was analyzed by 31P NMR
spectroscopy directly at ambient temperature. An unidenti-
fied signal (δ = 16 ppm; Figure 2) that did not belong to 2
(no signal) or L (δ = –28.5 ppm) was observed throughout
the recycling experiments. It was proven that the species
with the chemical shift at δ = 16 ppm was responsible for
Table 2. Transfer hydrogenation of acetophenone catalyzed by dif-
ferent Ru catalysts.[a]
Entry
Catalyst
Time [h] Conv. [%][b] Sel. [%][b] TOF [h–1 [c]
]
1
2
3
4
2
2
1
2
2
2
47
87
–
100
100
–
31
29
–
RuCl3·3H2O
[RuIICl2(PPh3)3]
86
100
29
[a] Catalyst (1.5 mol-%), acetophenone (5 mmol), 2-propanol
(3 mL), , tBuOK (10 mol-%), reaction temperature 100 °C. [b] De-
termined by GC. [c] TOF = turnover frequency.
The recovery and recycling of homogeneous Ru catalysts
in transfer hydrogenation are important from an economic
point of view due to the high cost of ruthenium compounds
as well as for preventing the contamination of the final
products by toxic metals. Thus, recycling experiments were
conducted by using complex 2 in the transfer hydrogenation
of acetophenone. The results in Table 3 show that 2 could
be used five times without any obvious activity loss. How-
ever, in the sixth run, the conversion of acetophenone de-
creased to 77%, mainly due to the manipulative loss of the
catalyst. In each run, upon completion, the organic com-
pounds, including acetophenone, 1-phenylethanol, 2-propa-
nol, and acetone, were extracted with petroleum ether for
GC analysis. The leaching of Ru into the extracted organic
phase was below the detection limit of ICP (Ͻ0.1 μg/g) due
to the high polarity of 2 as a result of the imidazolium
Figure 2. Evolution of 2 in the recycling experiments reported in
Table 3 recorded by proton-decoupled 31P NMR spectroscopy (a:
IL extract after 1st run; b: IL extract after 2nd run; c: IL extract
after 3rd run; d: IL extract after 4th run; e: IL extract after 5th
ring, which has been recognized as a useful technique for run).
Eur. J. Inorg. Chem. 2012, 3435–3440
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3437

C. Zhou, J. Zhang, M. aakovic´, Z. Popovic´, X. Zhao, Y. Liu
FULL PAPER
Table 4. Transfer hydrogenation of different ketones catalyzed by 2.[a]
Entry
Ketone
Alcohol
Conv. [%][b]
Sel. [%][b]
TOF [h–1]
1
2
3
4
5
6
7
8
9
acetophenone
benzophenone
cyclohexanone
2-propanol
2-propanol
2-propanol
2-propanol
2-propanol
2-propanol
2-propanol
2-propanol
2-propanol
2-propanol
2-hexanol
87
91
99
98
–
99
49
90
91
70
70
80
100
100
100
100
–
29
31
33
33
–
31
12
26
31
23
16
11
2-adamantanone
1-methylpyrrolidin-2-one
chalcone
93[c]
74[d]
85[e]
100
100
100
100
3,5,5-trimethylcyclohex-2-enone
6-methylhept-5-en-2-one
octan-2-one
10
11[f]
12[g]
heptan-4-one
acetophenone
cyclohexanone
2-phenylethanol
[a] Complex 2 (1.5 mol-%), ketone (5 mmol), alcohol (3 mL), tBuOK (10 mol-%), temperature 100 °C, time 2 h. [b] Determined by GC
and GC–MS. [c] Major product was 1,3-diphenylpropan-1-one. The byproduct was 3,5-diphenylcyclohex-2-enone. [d] Major product was
3,3,5-trimethylcyclohexanone. The byproduct was 3,3,5-trimethylcyclohexanol. [e] Major product was 6-methylheptan-2-one. The byprod-
uct was 6-methylheptan-2-ol. [f] Time 3 h. [g] Time 5 h.
the catalytic transformation of acetophenone into 1-phen- both the C=C and C=O bonds (Entries 7 and 8), revealing
ylethanol. Without the formation of this species in the ab- the poor chemoselective reduction of the C=O bond with 2
sence of tBuOK in the reaction, the reduction of acetophe- as catalyst for unsaturated ketone substrates. The aliphatic
none by 2-propanol did not occur. Thus, the species with ketones octan-2-one and heptan-4-one were converted into
the signal observed at δ = 16 ppm can be attributed to the the secondary alcohols in good conversions and with excel-
RuII–P-based catalytic species derived from 2, but not to a lent selectivities (Entries 9 and 10). It was also found that
free phosphane derivative such as HP(O)Ph2. The latter when 2-hexanol and 2-phenylethanol were used as the hy-
could be formed upon cleavage of the N2C+–P bond in 2. drogen donors in place of 2-propanol, the transfer hydro-
The good stability of the real catalytic RuII–P species in genation occurred efficiently (Entries 11 and 12). However,
the transfer hydrogenation, which is not silent in 31P NMR the reduction of aldehydes to primary alcohols with con-
spectroscopy due to its diamagnetism, could account for trolled chemoselectivity by transfer hydrogenation is con-
the recyclability of 2. However, at this stage, without any sidered rather difficult due to the side-reaction that occurs
further analytic evidence, it is difficult to determine whether under basic conditions.
the signal at δ = 16 ppm in Figure 2 can be ascribed to the
formation of an NHC–Ru complex with the P ligand or
others.
To examine the generality of 2 as a catalyst for transfer
Conclusions
The paramagnetic ionic ruthenium complex of 2, in
which the Ru ion is in the valence state of +3, has been
synthesized for the first time. The single-crystal X-ray struc-
ture of 2 shows a highly symmetrical RuIII-centered octa-
hydrogenation, the scope of ketones with different elec-
tronic and steric effects was investigated under similar con-
ditions (Table 4). Benzophenone with a large steric hin-
drance was converted into diphenylmethanol even faster
than acetophenone, implying facial access of the substrate
to catalyst 2 (Entry 2 vs. 1). With cyclohexanone and 2-
adamantanone, efficient transfer hydrogenations were
achieved with excellent conversion and 100% selectivity to
the corresponding alcohols, because the C=O group is di-
rected out of the six-membered ring (Entries 3 and 4). How-
ever, the hydrogenation of 1-methylpyrrolidin-2-one was not
observed, probably due to its potential coordination to the
Ru center as an N-containing ligand (Entry 5). With the
unsaturated ketones, chalcone was converted into 1,3-di-
phenylpropan-1-one in high yield due to the reduction of
only the C=C bond. The Michael addition of chalcone with
2-propanol and subsequent aldol condensation led to the
formation of 3,5-diphenylcyclohex-2-enone as a byproduct.
The reduction of the C=O bond in chalcone was not ob-
served (Entry 6). For both 3,5,5-trimethylcyclohex-2-enone
and 6-methylhept-5-en-2-one, the major products were ob-
tained by the reduction of only the C=C bond, whereas the
–
hedron cation with PF6 as the counteranion. As a result
of its high polarity, good thermal stability, and insensitivity
to moisture and oxygen, complex 2 proved to be an efficient
and recyclable precatalyst for the transfer hydrogenation of
a wide range of ketones when using alcohols as hydrogen
donors.
Experimental Section
Reagents and Analysis: All syntheses were carried out under nitro-
gen by using standard Schlenk techniques. All reagents were pur-
chased from Aladin Reagent Co., Shanghai, China and used as
received. The FTIR spectra were recorded with a Nicolet NEXUS
670 spectrometer. The 1H and 31P NMR spectra were recorded with
a Bruker Avance 500 spectrometer. The 31P NMR spectra were
referenced to 85% H3PO4 sealed in a capillary tube as an internal
standard. Elemental analyses for CHN were obtained by using an
Elementar Vario EL III instrument, whereas the amount of Ru in
the sample was quantified by using an inductive coupled plasma
minor products obtained were a result of the reduction of atomic emission spectrometer (ICP-AES) equipped with an IRIS
3438 Eur. J. Inorg. Chem. 2012, 3435–3440
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis of an Ionic Paramagnetic Ruthenium(III) Complex
Intrepid II XSP instrument (Thermo Electron Corporation). TG/
DTA was performed with a Mettler TGA/SDTA 851e instrument
and STARe thermal analysis data processing system. TG/DTA
analysis was performed in a flow of air with a temperature ramp
of 10 °Cmin–1 between 50 and 800 °C. GC analysis was performed
with a Shimadzu-2014 instrument equipped with a Rtx-Wax capil-
lary column (30 mϫ0.25 mmϫ0.25 μm). GC–MS was performed
with an Agilent 6890 instrument equipped with an Agilent 5973
mass-selective detector.
Table 5. Crystal data and structure refinement for 2.
2·2(CH3)2(CO)
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C46H60Cl4F6N4O2P3Ru
1150.76
monoclinic
C2/c
25.2640(9)
9.7111(3)
22.9382(8)
90
α [°]
Synthesis
β [°]
104.148
90
5457.0(3)
4
1.401
0.630
γ [°]
1-Butyl-2-(diphenylphosphanyl)-3-methylimidazolium Hexafluoro-
phosphate (1): Salt 1 was prepared according to published meth-
ods[19] but with some modifications. Under nitrogen, a solution of
V [Å3]
Z
Dcalcd. [gcm–3]
μ(Mo-Kα) [mm–1]
T [K]
1-butyl-3-methylimidazolium
hexafluorophosphate
(15.0 g,
296(2)
53.0 mmol) in dry CH2Cl2 (50 mL; previously heated at reflux with
calcium hydride and freshly distilled) was cooled to –78 °C, and
nBuLi (27 mL, 2.2 m in hexane, 59.4 mmol) was added dropwise.
After stirring the solution for 1 h, chlorodiphenylphosphane
(PPh2Cl; 11.7 g, 53.0 mmol) was added dropwise. The resultant
mixture was stirred overnight and the reaction temperature was
increased to ambient. After quenching excess nBuLi with deionized
water, the solvent was removed in vacuo. The residue was recrys-
tallized from EtOH to yield 1 as a white solid (yield: 18.5 g, 75 wt.-
λ
0.71073
30584
4777 (0.0219)
0.0449
0.1354
2364
Total reflections
Unique reflections (Rint
R1 [IϾ2σ(I)]
wR2 (all data)
F(000)
)
General Procedure for the Transfer Hydrogenation Catalyzed by 2:
In a typical experiment, the isolated crystalline 2 (0.075 mmol) was
mixed sequentially with acetophenone (5 mmol), 2-propanol
(3 mL, excess), and a base. The homogeneous mixture obtained
was purged with N2 and then stirred vigorously in a sealed Teflon-
lined stainless-steel autoclave. Upon completion, distilled water
(5 mL) was added, and the mixture was stirred vigorously. Then
the solution was extracted with petroleum ether (5 mL ϫ3). The
combined petroleum ether extracts were analyzed by GC to deter-
mine the conversions (n-dodecane as internal standard) and selec-
tivities (normalization method). The products were further iden-
tified by GC–MS. The remaining aqueous solution was dried under
vacuum to afford the residue for further use.
%). 1H NMR (CDCl3):
δ = 0.78 (t, J = 8.0 Hz, 3 H,
CH2CH2CH2CH3), 1.15 (m, 2 H, CH2CH2CH2CH3), 1.56 (m, 2 H,
CH2CH2CH2CH3), 3.48 (s, 3 H, NCH3), 4.26 (t, J = 7.8 Hz, 2 H,
CH2CH2CH2CH3), 7.30 [m, 4 H, CH3NCP(Ph2)N+], 7.49 [m, 6 H,
CH3NCP(Ph2)N+], 7.59 [s, 1 H, NC(H)C(H)N+], 7.62 [s, 1 H,
NC(H)C(H)N+] ppm. 31P NMR (CDCl3): δ = –28.5 (s, PPh2),
–143.5 (sept, PF6) ppm.
Bis[1-butyl-2-(diphenylphosphanyl)-3-methylimidazolium]tetrachlor-
idoruthenium(III) Hexafluorophosphate (2): Under N2, a solution of
RuCl3·3H2O (0.5 g, 1.8 mmol) in methanol (20 mL) was heated at
reflux for 10 min and then cooled to room temperature. Salt 1
(3.4 g, 7.2 mmol) was then added. The resulting mixture was stirred
under reflux for 8 h. The solid obtained was washed with alcohol
and diethyl ether, and dried in vacuo to give 2 as an orange powder
(yield: 1.5 g, 75 wt.-%), which was recrystallized from acetone/hex-
ane. TG/DTA (in air flow): The thermal decomposition tempera-
Acknowledgments
This work was financially supported by the Science and Technology
Commission of the Shanghai Municipality (No. 09JC1404800), the
National Natural Science Foundation of China (Nos. 20973063 and
21076083), the 973 Program of the Ministry of Science and Tech-
nology of China (2011CB201403), the Ministry of Science and
Technology of China for Croatian-Chinese Scientific and Techno-
logical Cooperation, the Fundamental Research Funds for the
Central Universities, and the Shanghai Leading Academic Disci-
pline Project (B409).
ture of 2 was 205 °C. FTIR (KBr pellet): ν = 3737 (w), 3447 (w),
˜
2960 (s), 1620 (w), 1395 (m), 1260 (m), 841 (P–F, s) cm–1. As a
result of the paramagnetic nature of the RuIII complex, the 1H and
31P NMR signals of 2 (in [D6]acetone) attributed to the phosphane
ligand were broadened to flatness, but the 31P NMR ([D6]acetone)
–
signal attributed to the PF6 counteranion was observed clearly at
δ = –143.5 ppm (sept). C40H48Cl4F6N4P3Ru (1035): calcd. C 46.4,
H 4.68, N 5.42; found C 45.6, H 4.58, N 5.20.
X-ray Crystallography: Intensity data for 2 were collected at room
[1] a) S. E. Clapham, A. Hadzovic, R. H. Morris, Coord. Chem.
Rev. 2004, 248, 2201–2237; b) H. U. Blaser, B. Pugin, F. Spin-
dler, “Special Products” in Applied Homogeneous Catalysis with
Organometallic Compounds, 2nd ed. (Eds.: B. Cornils, W. A.
Hermann), Wiley-VCH, Weinheim, 2002. pp. 1131–1149.
temperature (296 K) with
a Bruker SMARTAPEX II dif-
fractometer by using graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å). Data reduction included absorption corrections by
the multiscan method. The structure was solved by direct methods
and refined by full-matrix least squares using SHELXS-97[32] with
all non-hydrogen atoms refined anisotropically. Hydrogen atoms
were included in their geometrically ideal positions and refined iso-
tropically. Crystal data and refinement details are given in Table 5.
CCDC-805636 contains the supplementary crystallographic data
forthispaper.ThesedatacanbeobtainedfreeofchargefromTheCam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[2] a) C. Romain, S. Gaillard, M. K. Elmkaddem, L. Toupet, C.
Fischmeister, C. M. Thomas, J. Renaud, Organometallics 2010,
˙
29, 1992–1995; b) N. Gürbüz, S. Yasar, E. Ö. Özcan, I. Özde-
¸
mir, B. Çetinkaya, Eur. J. Inorg. Chem. 2010, 3051–3056.
[3] D. Addis, S. Zhou, S. Das, K. Junge, H. Kosslick, J. Harloff,
H. Lund, A. Schulz, M. Beller, Chem. Asian J. 2010, 5, 2341–
2345.
[4] N. A. Marinos, S. Enthaler, M. Driess, ChemCatChem 2010, 2,
846–853.
Eur. J. Inorg. Chem. 2012, 3435–3440
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3439

C. Zhou, J. Zhang, M. aakovic´, Z. Popovic´, X. Zhao, Y. Liu
FULL PAPER
[5]
[18] a) C. L. Pollock, G. C. Saunders, E. C. M. S. Smyth, V. I. Soro-
kin, J. Fluorine Chem. 2008, 129, 142–166; b) M. L. Clarke, D.
Ellis, K. L. Mason, A. G. Orpen, P. G. Pringle, R. L. Wingad,
D. A. Zaher, R. T. Baker, Dalton Trans. 2005, 1294–1300; c) S.
Jeulin, S. D. De Paule, V. Ratovelomanana-Vidal, J. P. Genêt,
N. Champion, P. Dellis, Angew. Chem. 2004, 116, 324; Angew.
Chem. Int. Ed. 2004, 43, 320–325.
[19] a) V. Farina, B. Krishman, J. Am. Chem. Soc. 1991, 113, 9585–
9595; b) N. G. Andersen, R. McDonald, B. A. Keay, Tetrahe-
dron: Asymmetry 2001, 12, 263–269; c) M. P. Magee, W. Luo,
W. H. Hersh, Organometallics 2002, 21, 362–372; d) R. A.
Baber, M. L. Clarke, K. M. Heslop, A. C. Marr, A. G. Orpen,
P. G. Pringle, A. Ward, D. E. Zambrano-Williams, Dalton
Trans. 2005, 1079–1085.
[20] a) G. Celentano, T. Benincori, S. Radaelli, M. Sada, F. San-
nicolò, J. Organomet. Chem. 2002, 643, 424–430; b) J. J. Becker,
L. J. Van Orden, P. S. White, M. R. Gagné, Org. Lett. 2002, 4,
727–730; c) E. Pizzo, P. Sgarbossa, A. Scarso, R. A. Michelin,
G. Strukul, Organometallics 2006, 25, 3056–3062; d) N. Sakai,
S. Mano, K. Nozaki, H. Takaya, J. Am. Chem. Soc. 1993, 115,
7033–7034; e) Y. Yan, Y. Chi, X. Zhang, Tetrahedron: Asym-
metry 2004, 15, 2173–2175.
a) T. Ikariya, A. J. Blacker, Acc. Chem. Res. 2007, 40, 1300–
1308; b) W. Wang, Z. Li, W. Mu, L. Su, Q. Wang, Catal. Com-
mun. 2010, 11, 480–483; c) S. Sanz, A. Azua, E. Peris, Dalton
Trans. 2010, 39, 6339–6343; d) Y. Cheng, X.-Y. Lu, H.-J. Xu,
Y.-Z. Li, X.-T. Chen, Z.-L. Xue, Inorg. Chim. Acta 2010, 363,
430–437; e) M. Aydemir, F. Durap, A. Baysal, N. Meric, A.
Buldag˘, B. Gümgüm, S. Özkar, L. T. Yildirim, J. Mol. Catal.
A 2010, 326, 75–81; f) M. J. Page, J. Wagler, B. A. Messerle,
Organometallics 2010, 29, 3790–3798; g) M. Aydemir, A. Bay-
sal, Polyhedron 2010, 29, 1219–1224.
C. A. Sandoval, T. Ohkuma, K. Muniz, R. Noyori, J. Am.
Chem. Soc. 2003, 125, 13490–13503.
R. Noyori, M. Yamakawa, S. Hashiguchi, J. Org. Chem. 2001,
66, 7931–7944.
B. J. Sarmah, D. K. Dutta, J. Organomet. Chem. 2010, 695,
781–785.
a) M. Poyatos, J. A. Mata, E. Falomir, R. H. Crabtree, E. Peris,
Organometallics 2003, 22, 1110–1114; b) A. A. Danopoulos, S.
Winston, W. B. Motherwell, Chem. Commun. 2002, 1376–1378;
c) J. Louie, C. W. Bielawski, R. H. Grubbs, J. Am. Chem. Soc.
2001, 123, 11312–11313.
[6]
[7]
[8]
[9]
[21] a) J. Andrieu, M. Azouri, Inorg. Chim. Acta 2007, 360, 131–
135; b) J. Andrieu, L. Harmand, M. Picquet, Polyhedron 2012,
29, 601–605; c) J. J. Brunet, R. Chauvin, G. Commenges, B.
Donnadieu, P. Leglaye, Organometallics 1996, 15, 1752–1754;
d) V. Cadierno, J. Francos, J. Gimeno, Chem. Eur. J. 2008, 22,
6601–6605.
[22] a) M. Azouri, J. Andrieu, M. Picquet, P. Richard, B. Hanquet,
I. Tkatchenko, Eur. J. Inorg. Chem. 2007, 4877–4883; b) N.
Debono, Y. Canac, C. Duhayon, R. Chauvin, Eur. J. Inorg.
Chem. 2008, 2991–2999; c) M. Azouri, J. Andrieu, M. Picquet,
H. Cattey, Inorg. Chem. 2009, 48, 1236–1242; d) Y. Canac, N.
Debono, C. Lepetit, C. Duhayon, R. Chauvin, Inorg. Chem.
2011, 50, 10810–10819; e) J. Andrieu, M. Azouri, P. Richard,
Inorg. Chem. Commun. 2008, 11, 1401–1404; f) N. Kuhn, J.
Fahl, Z. Anorg. Allg. Chem. 1999, 625, 729–734; g) N. Kuhn,
M. Göhner, Z. Anorg. Allg. Chem. 1999, 625, 1415–1416; h) N.
Kuhn, M. Göhner, M. Steimann, Z. Anorg. Allg. Chem. 2002,
628, 896–900.
[23] a) R. Chauvin, Eur. J. Inorg. Chem. 2000, 577–591; b) K. H.
Shaughnessy, Eur. J. Inorg. Chem. 2006, 1827–1835; c) C. Li,
Chem. Rev. 2005, 105, 3095–3165.
[24] J. R. Polam, L. C. Porter, J. Coord. Chem. 1993, 28, 297–304.
[25] A. R. Cowley, J. R. Dilworth, C. A. Maresca, W. vonBeckh,
Acta Crystallogr., Sect. E 2005, 61, m1237–1239.
[26] D. J. Brauer, K. W. Kottsieper, C. Liek, O. Stelzer, H. Waf-
fenschmidt, P. Wasserscheid, J. Organomet. Chem. 2001, 630,
177–184.
[27] I. Abdellah, C. Lepetit, Y. Canac, C. Duhayon, R. Chauvin,
Chem. Eur. J. 2010, 16, 13095–13108.
[10]
a) R. Noyori, T. Ohkuma, Angew. Chem. 2001, 113, 40; Angew.
Chem. Int. Ed. 2001, 40, 40–73; b) T. Ohkuma, H. Ooka, S.
Harshiguchi, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 1995,
117, 2675–2676; c) T. Okhuma, H. Takeno, R. Noyori, Adv.
Synth. Catal. 2001, 343, 369–375.
[11] a) Z. R. Dong, Y. Y. Li, J. S. Chen, B. Z. Li, Y. Xing, J. X. Gao,
Org. Lett. 2005, 7, 1043–1045; b) C. Bianchini, E. Farnetti, L.
Glendenning, M. Graziani, G. Nardin, M. Peruzzini, E. Rocch-
ini, F. Zanobini, Organometallics 1995, 14, 1489–1502; c) C.
Bianchini, L. Glendenning, F. Zanobini, E. Farnetti, M. Grazi-
ani, E. Nagy, J. Mol. Catal. A 1998, 132, 13–19.
[12] S. Kannan, K. N. Kumar, R. Ramesh, Polyhedron 2008, 27,
701–708.
[13] M. L. Clarke, M. B. Diaz-Valenzuela, A. M. Z. Slawin, Orga-
nometallics 2007, 26, 16–19.
[14] F. Fache, E. Schulz, M. L. Tommasino, M. Lemaire, Chem.
Rev. 2000, 100, 2159–2231.
[15] N. Gürbüz, S. Yas¸ar, E. Ö. Özcan, I. Özdemir, B. Çetinkaya,
˙
Eur. J. Inorg. Chem. 2010, 3051–3056.
[16] a) M. Zhao, Z. Yu, S. Yan, Y. Li, J. Organomet. Chem. 2009,
694, 3068–3075; b) A. Schlattera, W.-D. Woggon, Adv. Synth.
Catal. 2008, 350, 995–1000; c) F. K. Cheung, C. X. Lin, F. Min-
issi, A. L. Criville, M. A. Graham, D. J. Fox, M. Wills, Org.
Lett. 2007, 9, 4659–4662; d) W. Baratta, M. Ballico, S. Baldino,
G. Chelucci, E. Herdtweck, K. Siega, S. Magnolia, P. Rigo,
Chem. Eur. J. 2008, 14, 9148–9160; e) R. J. Lundgren, M. A.
Rankin, R. McDonald, G. Schatte, M. Stradiotto, Angew.
Chem. 2007, 119, 4816; Angew. Chem. Int. Ed. 2007, 46, 4732–
4735; f) W. Baratta, P. Rigo, Eur. J. Inorg. Chem. 2008, 4041–
4053.
[17] a) S. Wurtz, F. Glorius, Acc. Chem. Res. 2008, 41, 1523–1533;
b) N. Marion, S. Díez-Gonzalez, S. P. Nolan, Angew. Chem.
2007, 119, 3046; Angew. Chem. Int. Ed. 2007, 46, 2988–3000;
c) D. Pugh, A. A. Danopoulos, Coord. Chem. Rev. 2007, 251,
610–641; d) N. Kuhn, A. Al-Sheikh, Coord. Chem. Rev. 2005,
249, 829–859; e) E. Peris, R. H. Crabtree, Coord. Chem. Rev.
2004, 248, 2239–2246; f) C. M. Crudden, D. P. Allen, Coord.
Chem. Rev. 2004, 248, 2247–2273; g) V. César, S. Bellemin-La-
ponnaz, L. H. Gade, Chem. Soc. Rev. 2004, 33, 619–636; h) D.
Bourissou, O. Guerret, F. P. Gabbaï, G. Bertrand, Chem. Rev.
2000, 100, 39–92.
[28] Y. Canac, N. Debono, L. Vendier, R. Chauvin, Inorg. Chem.
2009, 48, 5562–5568.
[29] R. H. Wang, Z. Zeng, B. Twamley, M. M. Piekarski, J. M.
Shreeve, Eur. J. Org. Chem. 2007, 4, 655–661.
[30] I. J. B. Lin, C. S. Vasam, J. Organomet. Chem. 2005, 690, 3498–
3512.
[31] a) R. Wang, M. M. Piekarski, J. M. Shreeve, Org. Biomol.
Chem. 2006, 4, 1878–1886; b) J. C. Xiao, B. Twamley, J. M.
Shreeve, Org. Lett. 2004, 6, 3845–3847.
[32] G. M. Sheldrick, SHELXTL 5.1 for Windows NT, Structure
Determination Software Programs, Bruker Analytical X-ray
Systems Inc., Madison, WI, 1997.
Received: March 20, 2012
Published Online: June 6, 2012
3440
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