Ru(O2CCF3)2(PPh3)2 and ruthenium phosphine complexes bearing fluoroacetate ligands: synthesis, characterization and catalytic activity

Article abstract of DOI:10.1039/c9dt00334g

The dinuclear ruthenium(ii) phosphine complexes Ru₂Cl(O₂CCH_xF_3?x)₃(PPh₃)₄(μ-H₂O) (x = 0, 1, 2), containing fluoroacetate ligands, were prepared from RuCl₂(P

Full text of DOI:10.1039/c9dt00334g

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Ru(O2CCF3)2(PPh3)2 and ruthenium phosphine
complexes bearing fluoroacetate ligands: syn-
thesis, characterization and catalytic activity†
a
Cite this: DOI: 10.1039/c9dt00334g
Daniela A. Hey,‡a Pauline J. Fischer,‡a Walter Baratta *b and Fritz E. Kühn
*
The dinuclear ruthenium(II) phosphine complexes Ru2Cl(O2CCHxF3−x)3(PPh3)4(µ-H2O) (x = 0, 1, 2), con-
t
taining fluoroacetate ligands, were prepared from RuCl2(PPh3)3 and NaO2CCHxF3−x in BuOH. The X-ray
characterization of these complexes reveals a bridging water molecule, stabilized by hydrogen bonds with
the fluoroacetate ligands. The isolation of the complex Ru(O2CCF3)2(PPh3)2 is described, starting from
RuCl2(PPh3)3 or Ru2Cl(O2CCF3)3(PPh3)4(µ-H2O) and TlO2CCF3, correcting the reported preparation in
which Ru2Cl(O2CCF3)3(PPh3)4(µ-H2O) was obtained. Ru(O2CCF3)2(PPh3)2 easily reacts with CO, affording
Ru(O2CCF3)2(CO)2(PPh3)2. The protonation of Ru(OAc)2(dppb) with trifluoroacetic acid in the presence of
bidentate O and N donor ligands affords the complexes Ru(O2CCF3)2(dppb)(LL) (LL = ethyleneglycol,
ethylenediamine), which are catalytically active in the transfer hydrogenation of ketones with 2-propanol.
In the reduction of cyclohexanone, the glycol derivative displays a higher catalytic activity than the
Received 24th January 2019,
Accepted 7th March 2019
DOI: 10.1039/c9dt00334g
rsc.li/dalton
diamine complex, reaching a TOF of 22 000 h−1
.
ation reactions (Fig. 1).1–5 The isolation of these complexes
Introduction
proved to be difficult in some cases.2 The active species were
Ruthenium(II) phosphine carboxylate complexes have been therefore often generated in situ, for instance from ruthenium
investigated in detail for the catalytic hydrogenation of olefins cyclooctadiene precursors, or the formed complexes were
and carbonyl compounds in the last few decades.6–12 Since the described as solvato- or water-adducts.4,5,25,26
1970s, ruthenium complexes containing trifluoroacetate
The difficult isolation of well-defined derivatives most prob-
ligands are known as active catalysts for the dehydrogenation ably led to ruthenium(II) diphosphine bis(trifluoroacetato) com-
of alcohols and the hydroformylation of alkenes.13–15 The plexes being scarcely examined nowadays, even though they offer
electron-withdrawing nature of trifluoroacetate in comparison promising catalyst precursors on account of their facile ligand dis-
with acetate and the resulting lability of the perfluorinated sociation.25,27 Based on this property, together with the enhanced
ligand set a detailed investigation of the reactivity of ruthe- performance of several catalysts by the addition of trifluoroacetic
nium(II) trifluoroacetato phosphine derivatives in motion.17–23 acid (TFA) to the reaction mixture,28–30 it was intended to syn-
Most literature-known trifluoroacetate complexes contain thesize trifluoroacetate complexes of the general formula Ru
ancillary ligands, such as carbonyl, hydride or carbene, (O2CCF3)2P2 (P = mono- or bidentate phosphine ligand) and to
while only
a
few examples of the general formula employ them in the catalytic hydrogenation of ketones.
Ru(O2CCF3)2P2 (P = PPh3, PCy3) can be found in literature.16,24
The synthesis of Ru(O2CCF3)2(PPh3)2 (1) has previously
In the 1990s, similar structures emerged, as chiral dipho- been described by Sanchez-Delgado and Wilkinson14 by reac-
sphines were explored in combination with the trifluoroacetate tion of RuCl2(PPh3)3 with TFA and NaHCO3 in boiling BuOH
t
ligand, affording active catalysts for enantioselective hydrogen- (Scheme 1, I), following the procedure reported for the prepa-
ration of Ru(O2CCH3)2(PPh3)2.
aMolecular Catalysis, Catalysis Research Center and Department of Chemistry,
Technische Universität München, Lichtenbergstr. 4, 85747 Garching bei München,
Germany. E-mail: fritz.kuehn@ch.tum.de
bDipartimento di Scienze AgroAlimentari, Ambientali e Animali (DI4A), Università di
Udine, Via Cotonificio 108, I-33100 Udine, Italy
†Electronic supplementary information (ESI) available: Crystallographic details,
NMR data, and catalytic kinetics. CCDC 1892668–1892675. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c9dt00334g
Fig. 1 Chiral Ru(O2CCF3)2P2 complexes employed as catalysts in
enantioselective hydrogenation reactions.1–5
‡These authors contributed equally to this work.
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Scheme 1 Reported synthetic routes to obtain Ru(O2CCF3)2(PPh3)2 (1)
from RuCl2(PPh3)3.14,16
Furthermore, a different procedure for the synthesis of 1
was reported by Yamamoto et al., by reacting RuCl2(PPh3)3 and
AgO2CCF3 in acetone (Scheme 1, II).16 However,
1 has
Fig. 2 ORTEP style drawing of the dinuclear complex 2. Phenyl rings
depicted in wireframe style. All hydrogen atoms but for H2O omitted for
clarity. RuII centers are bridged by TFA, Cl− and H2O. Hydrogen bond
distances between O7⋯H1 and O5⋯H7 are found to be 1.754 and
1.888 Å, respectively.
been poorly characterized only by IR spectroscopy and
elemental analysis.14 Other pathways to obtain Ru(O2CCF3)2P2
complexes via Ru(η3-methylallyl)2(COD) have also been pursued,
though only for phosphines different from PPh3.2,4,31
Since the reproduction of the literature data proved to be
difficult, these reactions were re-examined and a detailed study
of the formation and characterization of fluoroacetate ruthe-
nium phosphine complexes is described in this work. The
reactivity of the ruthenium precursors and preliminary studies
on their catalytic activity in the ketone transfer hydrogenation
are reported as well.
complex.35,36 Hydrogen bonding involving water and a tetra-
fluorosuccinate ligand has been reported for the related ruthe-
nium(II) complex [Ru(OCOC2F4OCO)(CO)(µ-H2O)(PPh3)2]2 by van
Buijtenen et al.37 Several water-bridged ruthenium(II) dinuclear
species with a corresponding dinuclear RuII–H2O–RuII structure
can be found in the literature, namely Ru2Cl4(µ-H2O)[P(3,5-
xylyl)3]4, Ru2Cl4(µ-H2O)(dppb)2, [Ru(C6H9PCy2)(CF3COO)]2(µ-
CF3COO)2(µ-H2O), [Ru2(C2H5)2(CO)4(µ-H2O)4](CF3SO3)2 and
[{η5:σ-Me2C(C5H4)(C2B10H10)}Ru(µ-H2O)]2.10,24,38,39
Results and discussion
Synthesis of fluoroacetate ruthenium(II) complexes
In CD2Cl2, 2 exhibits two pairs of doublets in the 31P NMR
2
Treatment of RuCl2(PPh3)3 with trifluoroacetic acid (TFA,
spectrum, at δ = 50.9 ppm (d, J(PP) = 42.1 Hz), 50.3 ppm (d,
t
5 equiv.) and NaHCO3 (4 equiv.) in refluxing BuOH14 for 3 h
2J(PP) = 42.1 Hz), 48.7 ppm (d, 2J(PP) = 38.9 Hz) and 47.7 ppm
(d, 2J(PP) = 38.8 Hz), evidencing two asymmetrically bound tri-
phenylphosphine ligands on each Ru center. The three sing-
lets at δ = −74.52, −74.60 and −76.70 ppm in the 19F NMR
spectrum account for one monodentate trifluoroacetate moiety
on each Ru center and a µ2-trifluoroacetate bridging the two
affords the dinuclear complex 2 as an orange precipitate,
which could be isolated in 85% yield (eqn (1)).
1
metal atoms. The H NMR spectrum of 2 at room temperature
ð1Þ
shows the two protons of the bridging H2O molecule as a broad
singlet downfield shifted to δ = 9.51 ppm due to the presence of
strong hydrogen bonds with the trifluoroacetate ligand. Upon
cooling to −80 °C, the proton signal splits into two singlets at
δ = 9.11 and 9.77 ppm, indicating that the two hydrogen atoms
are chemically non-equivalent as a consequence of the hydrogen
bonding to the TFA moieties (for NMR spectra see the ESI†). The
NMR studies therefore indicate that complex 2 exhibits the same
structure both in solution and in the solid state and that the sta-
bilizing water molecule undergoes a rapid exchange of the two
protons at room temperature, while this process can be inhibited
at low temperatures on the NMR time scale.
The X-ray crystal structure of 2 shows two ruthenium(II)
centers in a pseudo-octahedral geometry, bridged by a chlo-
ride, a trifluoroacetate and a water molecule (Fig. 2). As
expected, the Ru–O bond length of the bridging trifluoroace-
tate in trans position to PPh3 is longer (Ru2–O2 = 2.1520(17) Å)
than the Ru–O bond length in the trans position to the
η1-trifluoroacetate ligand (Ru1–O3 = 2.0947(17) Å) due to the
strong trans influence of the phosphine ligand.32–34
The Ru1–O1 and Ru2–O1 distances for the bridging water
molecule are relatively long (Ru1–O1 = 2.2537(19) Å and
Ru2–O1 = 2.2581(19) Å), indicating that H2O is weakly co-
ordinated. In addition, asymmetric O⋯H distances (1.754 Å
and 1.888 Å) between the protons of the bridging water mole-
cule and the oxygen atoms of the monodentate trifluoroacetate
ligands indicate the presence of hydrogen bonds stabilizing the
The results contradict the formation of 1 from RuCl2(PPh3)3
t
and TFA/NaHCO3 in BuOH as described by Sanchez-Delgado
and Wilkinson.14 The authors provide IR absorptions and elemen-
tal analysis data for the supposed complex 1, which stand in com-
plete agreement with those for the dinuclear species 2. Note that
the elemental analysis reported for 1 deviates significantly for
F,9,40 indicating that the authors had in fact isolated 2 but inter-
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preted it as 1. Furthermore, 1 has not been characterized by
Yamamoto et al., who reported the synthesis of 1 by the reaction
of RuCl2(PPh3)3 with AgO2CCF3.16 Therefore, while the reaction of
RuCl2(PPh3)3 with CH3CO2Na leads to the corresponding mono-
nuclear species Ru(O2CCH3)2(PPh3)2, employment of CF3CO2Na
affords the dinuclear complex Ru2Cl(O2CCF3)3(PPh3)4(µ-H2O),
containing chloride and water as bridging ligands, most likely
due to the lower coordination ability of the trifluoroacetate with
respect to the acetate anion.
To investigate the effect of the fluorine atoms on the coordi-
nation ability of the fluoroacetate ligands, RuCl2(PPh3)3 was
reacted with the salts CF3−xHxCO2Na (x = 1, 2). The reaction of
RuCl2(PPh3)3 with DFA and MFA (5 equiv.) and NaHCO3
t
(4 equiv.) in boiling BuOH (eqn (1)) for 3 h results in the for-
mation of the dinuclear complexes 3 (42% yield) and 4 (51%
yield) (Fig. 3 and 4).
Fig. 4 ORTEP style drawing of the dinuclear complex 4. Phenyl rings
depicted in wireframe style. All hydrogen atoms but for H2O omitted for
clarity. RuII centers are bridged by MFA, Cl− and H2O. Hydrogen bond
distances between O7⋯H1 and O5⋯H7 are found to be 1.705 and
1.888 Å, respectively.
The X-ray crystal structures of 3 and 4 are similar to that
of 2, showing two ruthenium(II) centers with pseudo-octa-
hedral coordination geometry, bridged by chloride, water and
the respective fluoroacetate. The formation of hydrogen bonds
from the bridging water molecule to the η1-fluoroacetate moi-
eties likewise explains the formation of dinuclear complexes as
most stable compounds under the applied conditions, analo-
gous to the observations for the trifluoroacetate species 2.
Hydrogen bond lengths between the hydrogen atoms of the
Table 1 Characteristic bond lengths of complexes 2, 3 and 4
Complex
2
3
4
O7⋯H1, O5⋯H7 [Å]
Ru1–O4 [Å] (µ1)
Ru2–O6 [Å] (µ1)
1.754, 1.888
2.106(2)
2.099(2)
1.735, 1.887
2.097(3)
2.101(3)
1.705, 1.888
2.101(3)
2.106(3)
bridging water and the oxygen atoms of the terminal fluoroace- Ru1–O3 [Å] (µ2)
tate ligands in 3 (1.735 Å and 1.887 Å) and 4 (1.705 Å and
2.0947(17)
2.1520(17)
2.089(3)
2.134(3)
2.091(3)
2.136(3)
Ru2–O2 [Å] (µ2)
1.888 Å) lie in the range of those found for 2 (Table 1). The
slight decrease of the hydrogen bond lengths from 2 over 3 to
4 points towards a higher donor strength of the less fluori- integrating for two F atoms, whereas the MFA ligands of 4
nated ligands, even though the difference is relatively small.
afford three singlets at δ = −216.38, −218.43 and −218.89 ppm
In solution, 3 and 4 exhibit two pairs of doublets in the 31P for one η1- and two η2-MFA moieties. At room temperature, the
NMR spectrum for four non-equivalent phosphine ligands, bridging H2O molecule causes signals at δ = 10.34 and
analogous to 2. In the 19F{1H} NMR spectrum, the DFA ligands 10.19 ppm in the 1H NMR spectra of 3 and 4, respectively.
in 3 cause five singlets at δ = −124.08, −124.32, −124.33, Upon cooling to −40 °C, the water signal of 4 splits into two
−124.88 and −125.25 ppm, with the signal at δ = −124.88 ppm singlets at δ = 10.27 and 11.54 ppm for the non-equivalent
hydrogen-bonding protons, in accordance with 2. Therefore,
the NMR studies in solution are consistent with the
measured solid-state crystal structures, indicating that 3
and
4 are formed as dinuclear species in contrast to
Ru(O2CCH3)2(PPh3)2. A summary of selected characteristics of
2, 3 and 4 is given in Table 1.
Based on the dinuclear complex 2, the mononuclear
species 1 is synthesized. Complex 1 is obtained in 45% yield
by reacting 2 with TlO2CCF3 (1 equiv.) in acetone at room
temperature for 2 d (Scheme 2, I).
Alternatively, 1 can be prepared from RuCl2(PPh3)3, with
TlO2CCF3 (3 equiv.) in acetone at room temperature for 1 h
(Scheme 2, II) in 57% yield. Following the latter pathway, the
high solubility of 1 in various organic solvents complicates the
isolation of 1 as a pure product. Purification of 1 from PPh3 is
finally achieved by concentrating the filtered solution to a
minimum amount of acetone and subsequent precipitation by
addition of n-heptane. The formation of 1 is evidenced by sing-
Fig. 3 ORTEP style drawing of the dinuclear complex 3. Phenyl rings
depicted in wireframe style. All hydrogen atoms but for H2O omitted for
clarity. RuII centers are bridged by DFA, Cl− and H2O. Hydrogen bond
distances between O7⋯H1 and O5⋯H7 are found to be 1.735 and
1.887 Å, respectively.
lets at
δ =
54.4 ppm in the 31P NMR spectrum and
δ = −75.38 ppm in the 19F NMR spectrum. The liquid injection
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2.171 Å), as expected from the strong trans influence exerted
by PPh3. The structure of 1a resembles the one reported by
Airliguie et al. for [Ru(C6H9PCy2)(CF3COO)]2(µ-CF3COO)2(µ-
H2O).24 Crystallization of 1 in anhydrous CH2Cl2/n-heptane
and in the presence of TlO2CCF3 yields a mixed complex
containing two ruthenium and two thallium atoms
[Ru(O2CCF3)2(PPh3)2(TlO2CCF3)]2 (1b) (see the ESI†).
Scheme 2 Synthesis of
RuCl2(PPh3)3 (II) in acetone.
1 from dinuclear complex 2 (I) or from
Complex 1 shows a high reactivity towards the formation of
adducts, especially with water, which strongly interacts with
ruthenium and the trifluoroacetate moiety. However, even
though structures 1a and 1b are obtained in the solid state,
NMR measurements clearly confirm that 1 is formed as a
mononuclear species without an additional H2O molecule in
solution. Furthermore, only the mass for the monoculear
complex and no higher mass signals are detected in the
LIFDI-MS, corroborating that the formation of the dinuclear
complexes 1a and 1b only occurs upon crystallization.
field desorption ionization mass spectrum (LIFDI-MS) further
confirms the formation of 1 as a mononuclear complex,
showing m/z = 851.49, in agreement with the theoretical value
of m/z = 852.06. The LIFDI-MS analytical technique was chosen
due to its mild ionization in comparison with the electrospray
ionization (ESI) technique. Furthermore, the possibility to
work under argon atmosphere makes this technique especially
useful for sensitive complexes. Upon diffusion of n-heptane
To circumvent the relatively toxic thallium reagent for the
synthesis of 1, AgO2CCF3 was examined as an alternative
into
a
solution of
1
in CH2Cl2, crystals of
Ru2(O2CCF3)4(PPh3)4(µ-H2O) (1a) are obtained. The X-ray struc-
ture of 1a shows a dinuclear complex with two pseudo-octa-
hedrally coordinated ruthenium(II) centers, bridged by two tri-
fluoroacetate ligands and one H2O molecule (Fig. 5).
reagent. However, attempts to prepare
1
by reacting
RuCl2(PPh3)3 with AgO2CCF3 in acetone at room temperature,
following the procedure of Yamamoto et al.,16 failed. The
appearance of two sharp singlets at δ = 56.5 and 17.0 ppm in
the 31P NMR spectrum was observed. A color change of the
reaction solution from orange to deep purple hints towards
side reactions (e.g. redox processes) involving silver.
With 1 in hand, the reactivity of this labile complex was
examined towards carbon monoxide and free phosphines.
Thus, 1 undergoes facile carbonylation under CO (8 bar) in
toluene-d8 at room temperature overnight (eqn (2)). NMR
Analogous to complexes 2, 3 and 4, the dinuclear complex
1a is stabilized in the solid state by the inclusion of a water
molecule. The bridging H2O is probably incorporated due to
the high affinity of the ruthenium trifluoroacetate complexes
to water, which originates from moisture remnants in the
CH2Cl2 used for crystallization. Additional stabilization in the
solid state takes place through hydrogen bond formation
between the bridging water molecule and the η1-trifluoroace-
tate ligands, with both O⋯H distances measuring 1.761 Å. The
Ru–O bond of the trifluoroacetate ligand in trans position
to PPh3 is considerably longer than the one in the trans posi-
tion to the η1-trifluoroacetate (Ru1–O2 = 2.088 Å vs. Ru1–O3 =
measurements of the resulting carbonyl derivative
5 in
toluene-d8 show a sharp singlet at δ = 30.8 ppm in the 31P
NMR spectrum, evidencing the formation of a symmetric
species with two trans P–P ligands.41 The 13C spectrum reveals
a triplet at δ = 196.6 ppm (2J(CP) = 10.9 Hz), in accordance
with the carbonyl in cis position to the phosphorus moieties.
IR measurements show two strong carbonyl stretching bands
at ν(CO) = 1997 and 2059 cm−1, indicating a cis configuration
of these two CO ligands. The ν(OCO)asym = 1684 cm−1 evi-
dences a κ1-binding mode of the trifluoroacetate ligands and
thus the substitution of the product with two
carbonyl moieties.42 The data are in accordance with the
formation of the thermodynamic dicarbonyl product
Ru(O2CCF3)2(CO)2(PPh3)2 (5), in line with literature data.43–45
ð2Þ
In order to stabilize 1, the bidentate 1,4-bis(diphenylpho-
sphino)butane (dppb) was added. The reaction of 1 with dppb
(2 equiv.) in CD2Cl2 for 1 h at room temperature results in the
complete transformation of 1 and the liberation of PPh3, as
Fig. 5 ORTEP style drawing of the symmetric complex 1a. Phenyl rings
depicted in wireframe style. All hydrogen atoms but for H2O omitted for
clarity. RuII centers are bridged by two trifluoroacetate ligands and one
H2O molecule. The distance between O5⋯H1 is found to be 1.761 Å.
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monitored by 31P NMR measurements. Instead of the expected 19F NMR spectrum is consistent with the coordination of the
singlet for Ru(O2CCF3)2(dppb), which would result from the trifluoroacetate in 1. The work-up and isolation of the product
phosphine exchange of the two PPh3 ligands of 1 to the biden- failed on account of the high sensitivity of 1 towards H2O,
tate dppb, two broad multiplets at δ = 25.1 and 42.1 ppm are acids and coordinating solvents (alcohols, ethers), resulting in
observed in the 31P NMR spectrum. The resulting species the formation of several species in the examined solvents, as
could not be isolated, and a structure determination was observed by 19F and 31P NMR measurements.
carried out by SC-XRD. Upon slow diffusion of n-pentane to
Protonation of Ru(OAc)2(PPh3)2 with the less acidic DFA
the CD2Cl2-solution, single crystals of 6 were formed (Fig. 6). and MFA gave similar results to those obtained with TFA
The X-ray structure of 6 shows two ruthenium(II) centers in a (eqn (3)), affording the elimination of acetic acid. In the 31P
pseudo-octahedral coordination geometry, bridged by a dppb NMR spectra, singlets at δ = 56.8 ppm (DFA) and δ = 55.5 ppm
ligand, with one dppb and two trifluoroacetate moieties on (MFA) evidence the formation of mononuclear species similar
each ruthenium center. The composition of complex 6 indi- to 1 in CDCl3 at room temperature. In the 1H NMR spectra,
cates that additional stabilization of the examined trifluoroace- singlets at δ = 2.15 ppm (DFA) and δ = 2.07 ppm (MFA) are
tate complexes occurs through the formation of dinuclear attributed to the release of acetic acid. The isolation of these
species. Furthermore, 6 shows different behavior of the tri- ruthenium complexes failed, affording a mixture of products.
fluoroacetate- compared to the analogous acetate-complex, the
latter yielding Ru(O2CCH3)2(dppb) upon reaction with the prompted to attempt the stabilization of this complex by
bidentate phosphine.46
addition of appropriate coordinating ligands. To force the TFA
The high lability of the trifluoroacetate ligands of 1
Due to the toxicity of thallium reagents and the failure of ligands in 1 into a η1 binding mode, which has been shown to
the silver route, another thallium-free pathway was envisioned be beneficial for the stabilization of (fluoro-)acetate com-
for the synthesis of complex 1. Based on the higher acidity of plexes,46,47 a chelating ligand was added. Additives like ethyle-
the fluorinated acetic acids in comparison with acetic acid, the neglycol and ethylenediamine were chosen due to their ability
protonation of Ru(OAc)2(PPh3)2 with TFA, DFA and MFA to to coordinate as bidentate ligands. The functional groups,
exchange the anion was anticipated (eqn (3)).
especially the amino group, are further known to enhance the
catalytic activity of the respective complexes in hydrogenation
reactions of carbonyl compounds,48–53 beneficial for the cata-
lytic performance of those precursors. In addition, bidentate
phosphine ligands, such as dppb, can stabilize ruthenium
complexes in comparison with the monodentate PPh3 ana-
logues. Thus, the stabilized complex 7 is obtained in 78%
yield by addition of ethyleneglycol (1 equiv.) to a solution of
Ru(OAc)2(dppb) and TFA (3 equiv.) in THF at room tempera-
ture for 3 h (eqn (4)).
ð3Þ
Addition of trifluoroacetic acid (3–6 equiv.) to
Ru(OAc)2(PPh3)2 in CDCl3 results in an immediate reaction at
room temperature, as inferred by NMR spectroscopy. In the
31P NMR spectrum, the resonance of the starting material at
δ = 63.8 ppm disappears and a sharp singlet at δ = 52.6 ppm,
attributable to 1, is observed. In the 1H NMR spectrum, a shift
of the acetate CH3 resonance from δ = 1.51 ppm to 2.12 ppm
indicates the elimination of acetic acid, whereas the shift of
the CF3 signal from δ = −76.55 ppm to −75.98 ppm in the
ð4Þ
Single crystals of 7 were obtained by slow diffusion of
n-pentane to a concentrated solution of 7 in Et2O. The X-ray
crystal structure confirms the formation of 7 in the solid state
(Fig. 7), showing the pseudo-octahedral coordination of dppb,
ethyleneglycol and two TFA ligands to the ruthenium(II)
center. Complex 7 is stabilized by hydrogen bonds between the
hydrogen atoms of the ethylene glycol OH-group to the oxygen
atoms of the monodentate TFA ligands, with O⋯H distances
of 1.770 Å and 1.796 Å, similar to the water adducts 2–4.
In the 31P NMR spectrum, 7 exhibits a sharp singlet at
δ = 53.0 ppm for the dppb ligand in trans position to the
glycol ligand, and a singlet at δ = −75.99 ppm in the 19F NMR
spectrum. The 1H NMR spectrum of 7 shows a singlet at
δ = 9.85 ppm for the two OH protons interacting with the
trifluoroacetate ligand by hydrogen bonding. LIFDI-MS
Fig. 6 ORTEP style drawing of the symmetric dinuclear complex 6
formed by the reaction of 1 with 2 equiv. dppb in CD2Cl2. Phenyl rings
depicted in wireframe style. All hydrogen atoms are omitted for clarity.
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NMR and MS studies are consistent with the X-ray measure-
ments, indicating that 8 exhibits the same structure in solu-
tion and in the solid state.
The results indicate that ruthenium fluoroacetate com-
plexes are reactive species displaying a flexible fluoroacetate
ligand that can act as a bidentate or monodentate ligand by
the addition of O and N donating ligands. OH and NH func-
tionalities are of particular interest for the stabilization of the
complexes via hydrogen bond formation.
To summarize, the synthesis of ruthenium(II) fluoroacetate
phosphine complexes can be accomplished starting from
RuCl2(PPh3)3 and NaO2CHxCF3−x (x = 0, 1, 2) via different path-
ways to achieve the dinuclear species 2, 3 and 4 (Scheme 3).
The reaction of TlO2CCF3 with RuCl2(PPh3)3 or with the dinuc-
lear species 2 leads to the highly dynamic complex 1 with
labile trifluoroacetate ligands. Complex 1 can easily react
with water, CO and the diphosphine dppb (Scheme 3).
Trifluoroacetate complexes are also obtained from
Ru(OAc)2(dppb) as precursor and TFA in the presence of
ethyleneglycol and ethylenediamine, affording complexes 7
and 8. With the successfully synthesized ruthenium(II)
trifluoroacetates 1, 7 and 8 in hand, examinations of these
catalyst precursors in the transfer hydrogenation of ketones
were carried out. Furthermore, comparison of the dinuclear
complexes 2, 3 and 4 in the catalytic transfer hydrogenation
was attempted.
Fig. 7 ORTEP style drawing of complex 7. Phenyl rings depicted in wire-
frame style. All hydrogen atoms but for OH omitted for clarity. Hydrogen
bond distances between O2⋯H6 and O4⋯H5 are found to be 1.770 and
1.796 Å, respectively.
measurements confirm the formation of 7, with m/z = 815.59.
The NMR and MS studies in solution are in accordance with
the crystal structure obtained for 7.
Complex
8
can be isolated by the reaction of
Ru(OAc)2(dppb) and TFA (3 equiv.) with ethylenediamine
(1 equiv.) in THF at room temperature in 98% yield (eqn (4)).
The crystal structure of 8 shows a pseudo-octahedral coordi-
nation of two TFA ligands, ethylenediamine and dppb to the
ruthenium(II) center. Complex 8 is additionally stabilized by
hydrogen bonds between the oxygen atoms of the TFA ligands
and the NH hydrogen atoms of ethylenediamine, with O⋯H
distances of 2.103 Å and 2.145 Å (Fig. 8).
Catalytic transfer hydrogenation of ketones
The catalytic activities of complexes 1–4 and 7, 8 were exam-
ined in the transfer hydrogenation (TH)54–58 of aromatic and
In the 31P NMR spectrum, 8 exhibits a sharp singlet at
δ = 43.7 ppm for the dppb ligand in trans position to the N
ligand, and a singlet at δ = −75.96 ppm in the 19F NMR spec-
trum. The 1H NMR spectrum of 8 shows a singlet at
δ = 4.22 ppm for the four NH protons. LIFDI-MS measure-
ments confirm the formation of 8, with m/z = 814.17. The
i
aliphatic ketones in PrOH as hydrogen donor with NaOiPr as
base (eqn (5)).
ð5Þ
Complex 1 (0.1 mol%) displays poor catalytic activity in the
TH of acetophenone with 21% conversion to 2-phenylethanol
in 48 h in the presence of NaiOPr (2 mol%). The dinuclear
complexes 2–4 (0.05 mol%) show up to 50% conversion of acet-
ophenone to 2-phenylethanol in 7 h in the presence of NaiOPr
(2 mol%), with TOFs of up to 75 h−1 (calculated at 50% conver-
sion of acetophenone). The low catalytic activity of 1–4 can be
attributed to catalyst instability. When 1 and 2–4 are dissolved
i
in PrOH and kept at room temperature overnight or at 60 °C
for 1 h, respectively, a color change from orange to pink and
turquoise was observed, suggesting catalyst decomposition.
Complexes 7 and 8, bearing a bidentate phosphine dppb
and bidentate O and N ligands, display a higher catalytic
activity in the ketone TH. Acetophenone can easily be reduced
with 7 and 8 (78% and 97% conversion) with TOFs of 5000 h−1
and 4200 h−1, respectively (Table 2, entries 1 and 2).
Despite its higher TOF, the glycol-containing complex 7
only reaches a maximum of 78% conversion, indicating a
facile formation of the active species, but a lower stability than
its amine analogue 8. These results prompted further examin-
Fig. 8 ORTEP style drawing of complex 8. Phenyl rings depicted in wire-
frame style. All hydrogen atoms but for NH2 omitted for clarity. Hydrogen
bond distances measured between O2⋯H2 and O4⋯H1 are 2.103 and
2.145 Å, respectively.
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Scheme 3 Ruthenium(II) trifluoroacetate complexes synthesized in this work.
Table 2 Transfer hydrogenation of ketones in iPrOH at 90 °C with NaOiPr as basea
Entry
Substrate
Catalyst
Catalyst loading [mol%]
Time [min]
Conversion [%]
TOFb [h−1
]
1
2
7
8
0.1
0.1
480
30
78
97
5000
4200
3
4
7
8
0.1
0.1
480
480
45
78
60
1900
5
6
7
8
7
8
7
8
0.1
0.1
0.03
0.03
5
40
240
1500
100
100
82
15 000
4100
22 000
1700
69
a S : B = 1000 : 20. b Calculated at 50% conversion.
ations of the influence of the NH2 group of the ethylenedi- ketones. While derivatives 1–4 show a low catalytic activity, pre-
amine ligand in comparison with the OH of ethyleneglycol on sumably due to their instability under the applied conditions,
the catalytic activity of the complexes.50,52 In the TH of benzo- compounds 7 and 8 exhibit good catalytic properties. For the
phenone (Table 2, entries 3 and 4), the amine catalyst 8 shows aliphatic substrate cyclohexanone, the glycol derivative 7 dis-
a higher activity with respect to the glycol derivative 7 (TOF = plays a higher activity compared to the diamine complex 8,
1900 h−1 vs. 60 h−1, respectively). Conversely, cyclohexanone with TOFs up to 22 000 h−1
was reduced quantitatively to cyclohexanol in 5 min with 7
.
(0.1 mol%), whereas 8 required 40 min, affording TOFs of
15 000 h−1 and 4100 h−1, respectively (Table 2, entries 5 and
6). At a lower catalyst loading of 7 and 8 (0.03 mol%), up to
Conclusions
82% and 69% conversion were obtained, with TOFs of Ruthenium(II) phosphine complexes bearing mono-, di- and
22 000 h−1 and 1700 h−1 (Table 2, entries 7 and 8). The results trifluoroacetato ligands have been isolated and characterized
indicate that ethyleneglycol can be used as a suitable ligand in solution and in the solid state. The complexes have been
for ruthenium diphosphine catalysts, affording a superior synthesized starting from RuCl2(PPh3)3 via substitution reac-
accelerating effect with respect to the well-known ethylenedi- tions or from Ru(OAc)2(dppb) by protonation with fluoroacetic
amine ligand in the reduction of the aliphatic cyclohexanone.
acids. The presence of weakly coordinating fluoroacetate
In summary, complexes 1–4 and 7 and 8 are active catalysts ligands affords reactive ruthenium complexes, which are
in the transfer hydrogenation of aromatic and aliphatic stabilized by water, glycol and amine ligands, and are
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soluble in
a
variety of organic solvents. Isolation of reduced pressure. The sample solution is transmitted to a
Ru(O2CCF3)2(PPh3)2 (1) is reported for the first time, correcting tungsten wire coated with thousands of micro-graphite den-
the former preparation, where the dinuclear complex drites. The sample is distributed over the emitter and the
Ru2Cl(O2CCF3)3(PPh3)4(µ-H2O) (2) had been obtained instead. employed solvent is evaporated in the prevacuum of the mass
Complex 2 is stabilized by hydrogen bonds between the brid- spectrometer. A potential of 5 kV is applied between the
ging water and the trifluoroacetate ligands. Preliminary studies emitter and the counter electrode in order to ionize and accel-
show that the ruthenium triphenylphosphine fluoroacetate erate the sample molecules to the counter electrode and then
derivatives exhibit rather poor activity in ketone transfer hydro- to the argon-flushed detector. In order to increase the mobility
genation reactions with 2-propanol, whereas the dppb com- of the molecules on the emitter, an electrical current ramp of
plexes 7 and 8, which are additionally stabilized by ethylenegly- 30 mA min−1 is applied through the tungsten wire.
col and ethylenediamine, display much better catalytic activi-
Synthesis of Ru(O2CCF3)2(PPh3)2 (1)
ties. The best performance is achieved with the glycol deriva-
tive
7
in the reduction of cyclohexanone (TOFs up to
From complex 2. A suspension of 100 mg 2 (1 equiv.,
22 000 h−1). Studies to extend the use of these reactive precur- 0.061 mmol) and 23.2 mg TlO2CCF3 (1.2 equiv., 0.073 mmol)
sors and their application in catalysis are currently in progress. in 1 mL acetone is stirred at room temperature for 2 d and
then filtered under argon. The filtrate is stripped to a
minimum amount of acetone and the product is precipitated
in n-heptane. Drying under vacuum affords 46.6 mg of the
product (45% yield). El. Anal. Calcd for C40H30F6O4P2Ru: C,
Experimental
General
56.41; H, 3.55. Found: C, 56.19; H, 4.14. MS (LIFDI, m/z): calc.
1
All reactions were carried out under argon atmosphere for C40H30F6O4P2Ru: 852.0579; found: 851.4905 [M]−. H-NMR
using standard Schlenk techniques. Solvents were used after (500 MHz, CD2Cl2, 293 K): δ (ppm) = 6.14–7.88 (m, 30H, aro-
distillation or taken from a solvent purification system (SPS) matic protons). 13C{1H}-NMR (126 MHz, CD2Cl2, 293 K):
2
from MBraun (THF), degassed and stored over molar sieves δ (ppm) = 168.2 (q, J(CF) = 38.3 Hz, O2CCF3), 133.9–135.0 (m,
(3 and 4 Å). Ruthenium precursors were obtained from aromatic carbon atoms), 130.2 (s, aromatic carbon atoms),
Johnson Matthey Ltd and all other chemicals were purchased 127.8–128.4 (m, aromatic carbon atoms), 104.5–120.4 (m,
from Sigma Aldrich, Merck and abcr. Ru(OAc)2(dppb) was pre- O2CCF3). 19F{1H}-NMR (471 MHz, CD2Cl2, 293 K): δ (ppm) =
pared following a literature procedure.46 TlO2CCF3 was syn- −75.38 (s). 31P{1H}-NMR (203 MHz, CD2Cl2, 293 K): δ (ppm) =
thesized by reacting Tl2(CO3) with an excess of TFA and sub- 54.4 (s).
sequent drying under vacuum. NMR measurements were per-
From RuCl2(PPh3)3. A suspension of 100 mg RuCl2(PPh3)3
formed on Bruker AV-500 cr and AC-200 instruments. (1 equiv., 0.104 mmol) and 99.3 mg TlO2CCF3 (3 equiv.,
Chemical shifts in ppm are reported relative to the stated 0.313 mmol) in 1 mL acetone is stirred at room temperature
solvent for 1H and 13C{1H} spectra, relative to H3PO4 for 31P for 1 h and then filtered under argon. The filtrate is stripped
{1H} spectra, and relative to CF3COOH for 19F and 19F{1H} to a minimum amount of acetone and the product is precipi-
experiments. Elemental analyses (C, H, N) were carried out on tated and washed with n-heptane (4 × 0.5 mL). Drying under
a Varian SpectrAA-400 instrument and on a Flash EA1112 vacuum affords 50.5 mg of the product (57% yield).
elemental analyzer from Carlo Erba. GC analyses were per-
General procedure for the synthesis of dinuclear fluoroacetate
complexes 2–4
formed on Varian CP-3380/Agilent 7890B gas chromatographs
equipped with a MEGADEX-ETTBDMS-β chiral column of 25 m
length/an HP-5 column with 30 m length, column pressure To
a suspension of RuCl2(PPh3)3 (1 equiv., 100 mg,
5 psi, H2/Ar as carrier gases, and a flame ionization detector 0.104 mmol) and NaHCO3 (4 equiv., 35 mg, 0.417 mmol) in
(FID). The injector and detector temperatures were 6 mL tBuOH, the respective fluoroacetic acid (5 equiv.,
250 °C/300 °C, with initial T = 95 °C/80 °C ramped to 140 °C at 0.521 mmol) is added. The mixture is heated to 90 °C for 3 h
3 °C min−1/138 °C at 8 °C min−1 and then to 210 °C at 20 °C and then cooled to room temperature. The orange precipitate
min−1/300 °C at 30 °C min−1. Infrared (IR) spectra were col- is filtered under argon, washed with H2O (4 × 1 mL), MeOH
lected on
a
Mettler-Toledo react-IR 45
m
spectrometer (2 × 1 mL) and Et2O (1 × 0.5 mL) and dried under vacuum.
Crystals for SC-XRD measurements were obtained by
equipped with a Sentinel/Si-Comp probe and a Mercury
Cadmium Telluride (MCT) detector. Samples for mass spectra diffusion of n-pentane to a solution of the ruthenium complex
(MS) measurements were dissolved in CH2Cl2, filtered through in dichloromethane.
a syringe filter and sealed with a Teflon cap under argon
Ru2Cl(O2CCF3)3(PPh3)4(µ-H2O) (2). The orange product 2
atmosphere. The spectra were recorded on a Waters LCT was obtained in 85% yield (72.9 mg). El. Anal. Calcd for
device equipped with a liquid injection field desorption ioniza- C78H62ClF9O7P4Ru2: C, 56.99; H, 3.80. Found: C, 57.05; H,
tion (LIFDI) source under an air free atmosphere to enable 3.25. 1H-NMR (200 MHz, CD2Cl2, 293 K): δ (ppm) = 9.51 (s, 2H,
measurements of air-sensitive compounds. Sample introduc- H2O), 8.25–6.29 (m, 60H, aromatic protons). 13C{1H}-NMR
tion was carried out by withdrawing the solution from the (50 MHz, CD2Cl2, 293 K): δ (ppm) = 166.0–167.5 (m, O2CCF3),
closed vessel through the septum with a glass capillary under 122.5–138.8 (m, aromatic carbon atoms), 99.9–116.4 (m,
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O2CCF3). 19F{1H}-NMR (188 MHz, CD2Cl2, 293 K): δ (ppm) = 293 K): δ (ppm) = 30.8 (s). IR (tol-d8): ν (cm−1) = 2059
−74.52 (s, 3F), −74.60 (s, 3F), −76.70 (s, 3F). 31P{1H}-NMR (COstretch), 1997 (COstretch), 1684 (OCOasym).
2
(81 MHz, CD2Cl2, 293 K): δ (ppm) = 50.9 (d, J(PP) = 42.1 Hz),
Synthesis of Ru(O2CCF3)2(dppb)(HOCH2CH2OH) (7)
50.3 (d, 2J(PP) = 42.1 Hz), 48.7 (d, 2J(PP) = 38.9 Hz), 47.7 (d,
2J(PP) = 38.8 Hz).
To a suspension of Ru(OAc)2(dppb) (1 equiv., 100 mg,
Ru2Cl(O2CCHF2)3(PPh3)4(µ-H2O) (3). The orange product 3 0.155 mmol) in THF, 3 equiv. TFA (36 µL, 0.465 mmol) are
was obtained in 42% yield (34.2 mg). El. Anal. Calcd for added. After stirring at 30 °C for 5 min, a spatula of CaCO3 is
C81H71ClF6O7P4Ru2: C, 58.93; H, 4.12. Found: C, 58.64; H, 4.09. added to the resulting solution to precipitate Ca(OAc)2, and
1H-NMR (500 MHz, CDCl3, 293 K): δ (ppm) = 10.34 (br s, 2H, the mixture is stirred for another 2 h at 30 °C. Ethyleneglycol
H2O), 6.25–7.89 (m, 60H, aromatic protons), 5.13 (t, 2J(HF) = is added (1 equiv., 8.7 µL, 0.310 mmol) and the suspension is
55.0 Hz, 1H, CHF2), 5.10 (t, 2J(HF) = 55.0 Hz, 1H, CHF2), 4.75 (t, stirred for another 3 h. After filtration from Ca(OAc)2 under
2J(HF) = 55.0 Hz, 1H, CHF2). 13C{1H}-NMR (126 MHz, CDCl3, argon, the solution is dried under vacuum to afford 98.8 mg of
293 K): δ (ppm) = 172.7–174.7 (m, O2CCHF2), 123.4–138.2 (m, the orange product (78% yield). El. Anal. Calcd for
1
aromatic carbon atoms), 107.3 (t, J(CF) = 250.2 Hz, O2CCHF2), C34H34F6O6P2Ru: C, 50.07; H, 4.20. Found: C, 50.45; H, 3.85.
1
106.7 (t, J(CF) = 250.2 Hz, O2CCHF2). 19F{1H}-NMR (471 MHz, MS (LIFDI, m/z): calc. for C34H34F6O6P2Ru: 816.0778; found:
1
CDCl3, 293 K): δ (ppm) = −124.08 (s, 1F), −124.32 (s, 1F), 815.5901 [M]−. H-NMR (200 MHz, CD2Cl2, 293 K): δ (ppm) =
−124.33 (s, 1F), −124.88 (s, 2F), −125.25 (s, 1F). 19F-NMR 9.85 (s, 2H, OH), 6.46–8.14 (m, 20H, aromatic protons), 3.63 (s,
(471 MHz, CDCl3, 293 K): δ (ppm) = −124.08 (d, 2J(HF) = 4H, HOCH2CH2OH), 2.12–2.89 (m, 4H, CH2CH2P), 1.37–1.87
55.0 Hz), −124.27 (d, 2J(HF) = 55.0 Hz), −124.38 (d, 2J(HF) = (m, 4H, CH2CH2P). 13C{1H}-NMR (101 MHz, CDCl3, 293 K):
55.0 Hz), −124.88 (d, 2J(HF) = 55.0 Hz), −125.25 (d, 2J(HF) = δ (ppm) = 168.7 (q, 2J(CF) = 37.6 Hz, O2CCF3), 132.9 (t, 1J(CP) =
55.0 Hz). 31P{1H}-NMR (203 MHz, CDCl3, 293 K): δ (ppm) = 51.8 4.5 Hz, aromatic carbon atoms), 129.9 (s, aromatic carbon
2
2
2
(d, J(PP) = 40.6 Hz), 49.7 (d, J(PP) = 40.6 Hz), 49.2 (d, J(PP) = atoms), 128.1 (t, 2J(CP) = 4.7 Hz, aromatic carbon atoms),
40.6 Hz), 48.3 (d, 2J(PP) = 40.6 Hz). 113.4 (dd, 1J(CF) = 578.2 Hz, 289.3 Hz, O2CCF3), 64.9 (s,
Ru2Cl(O2CCH2F)3(PPh3)4(µ-H2O) (4). The orange product 4 HOCH2CH2OH), 26.5–28.28 (m, CH2CH2P), 22.7 (s, CH2CH2P).
was obtained in 51% yield (49.5 mg). El. Anal. Calcd for 19F{1H}-NMR (471 MHz, CDCl3, 293 K): δ (ppm) = −75.99 (s,
C78H68ClF3O7P4Ru2: C, 61.00; H, 4.46. Found: C, 60.60; H, 6F). 31P{1H}-NMR (162 MHz, CDCl3, 293 K): δ (ppm) = 53.0 (s).
3.85. 1H-NMR (200 MHz, CD2Cl2, 293 K): δ (ppm) = 10.19 (br s,
Synthesis of Ru(O2CCF3)2(dppb)(H2NCH2CH2NH2) (8)
2H, H2O), 6.35–7.95 (m, 60H, aromatic protons), 4.17 (d,
2J(HF) = 48.8 Hz, 2H, CH2F), 4.06 (d, 2J(HF) = 48.8 Hz, 2H, To
a
suspension of Ru(OAc)2(dppb) (1 equiv., 200 mg,
CH2F), 3.44–4.40 (m, 2H, CH2F). 13C{1H}-NMR (50 MHz, 0.310 mmol) in THF, 3 equiv. TFA (72 µL, 0.929 mmol) are
CD2Cl2, 293 K): (ppm) 171.6–181.9 (m, O2CCH2F), added. After stirring at 30 °C for 5 min, a spatula of CaCO3 is
δ
=
120.2–142.7 (m, aromatic carbon atoms), 79.9 (d, 1J(CF) = added to the resulting solution to precipitate Ca(OAc)2, and
184.4 Hz, O2CCH2F), 79.8 (d, 1J(CF) = 184.9 Hz, O2CCH2F), the mixture is stirred for another
2
h
at 30 °C.
79.5 (d, J(CF) = 182.6 Hz, O2CCH2F). 19F{1H}-NMR (188 MHz, Ethylenediamine is added (1 equiv., 21 µL, 0.310 mmol) and
CD2Cl2, 293 K): δ (ppm) = −216.38 (s, 1F), −218.43 (s, 1F), the suspension is stirred for another 3 h. After filtration from
−218.89 (s, 1F). 19F-NMR (188 MHz, CD2Cl2, 293 K): δ (ppm) = Ca(OAc)2 under argon, the solution is dried under vacuum to
−216.38 (t, 2J(HF) = 48.8 Hz), −218.43 (t, 2J(HF) = 48.8 Hz), afford 247.0 mg of the orange product (98% yield). El. Anal.
1
−218.89 (t, J(HF) = 48.8 Hz). 31P{1H}-NMR (81 MHz, CD2Cl2, Calcd for C34H36F6N2O4P2Ru: C, 50.19; H, 4.46; N, 3.44. Found:
2
2
2
293 K): δ (ppm) = 53.5 (d, J(PP) = 38.9 Hz), 50.5 (d, J(PP) = C, 51.49; H, 4.53; N, 2.44. MS (LIFDI, m/z): calc. for
42.8 Hz), 50.5 (d, 2J(PP) = 36.5 Hz), 49.7 (d, 2J(PP) = 40.1 Hz).
C34H36F6N2O4P2Ru: 814.1098; found: 814.1747 [M]−. 1H-NMR
(500 MHz, CD2Cl2, 293 K): δ (ppm) = 6.46–7.86 (m, 20H, aro-
matic protons), 4.22 (s, 4H, NH2), 2.65 (s, 4H, H2NCH2CH2NH2),
Spectral evidence for Ru(O2CCF3)2(CO)2(PPh3)2 (5)
A solution of 10 mg 1 (1 equiv., 0.012 mmol) in 0.45 mL 2.44–2.56 (m, 4H, CH2CH2P), 1.52–1.72 (m, 4H, CH2CH2P). 13C
toluene-d8 is subjected to 8 bar CO in a high-pressure NMR {1H}-NMR (126 MHz, CD2Cl2, 293 K): δ (ppm) = 166.2 (q, J(CF)
2
tube and the mixture is reacted overnight. The colorless solu- = 35.8 Hz, O2CCF3), 132.9 (t, 1J(CP) = 4.6 Hz, s, aromatic carbon
tion is then analyzed by NMR and IR spectroscopy. 1H-NMR atoms), 129.7 (s, aromatic carbon atoms), 128.4 (t, 2J(CP) = 4.3 Hz,
(200 MHz, tol-d8, 293 K): δ (ppm) = 7.91–7.71 (m, 12H, aro- s, aromatic carbon atoms), 113.8 (q, 1J(CF) = 291.5 Hz,
matic protons), 7.61 (ddd, 3J(HH) = 12.01 Hz, 4J(HH) = 7.97 Hz, O2CCF3), 44.6 (s, H2NCH2CH2NH2), 23.8–25.3 (m, CH2CH2P),
5J(HH) = 1.68 Hz, 2H, aromatic protons), 7.39–7.23 (m, 4H, 22.3 (s, CH2CH2P). 19F{1H}-NMR (471 MHz, CD2Cl2, 293 K):
aromatic protons), 7.13–7.04 (m, 12H, aromatic protons). 13C δ (ppm) = −75.96 (s, 6F). 31P{1H}-NMR (203 MHz, CD2Cl2,
{1H}-NMR (101 MHz, tol-d8, 293 K): δ (ppm) = 196.6 (t, 2J(CP) = 293 K): δ (ppm) = 43.8 (s).
10.9 Hz, CO), 162.0 (q, 2J(CF) = 37.2 Hz, O2CCF3), 116.0 (q,
Procedure for the catalytic transfer hydrogenation of ketones
1J(CF) = 290.1 Hz, O2CCF3), 138.2–135.8 (m, aromatic carbon
atoms), 134.6–133.6 (m, aromatic carbon atoms), 129.6–128.7 Ruthenium mononuclear (1.0 μmol) or dinuclear complexes
i
(m, aromatic carbon atoms). 19F{1H}-NMR (471 MHz, tol-d8, (0.5 μmol) are dissolved in 10 mL dry and degassed PrOH.
293 K): δ (ppm) = −73.71. 31P{1H}-NMR (162 MHz, tol-d8, The ketone substrate (1 mmol) is dissolved in dry and
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i
degassed PrOH, and the solution is heated to 90 °C under 14 R. A. Sanchez-Delgado, J. S. Bradley and G. Wilkinson,
argon. After addition of 1.0 mL of the catalyst solution and J. Chem. Soc., Dalton Trans., 1976, 399–404.
200 μL NaOiPr in dry and degassed PrOH (0.1 M; 0.02 mmol), 15 A. Dobson and S. D. Robinson, Inorg. Chem., 1977, 16, 137–
the reduction of the ketone starts immediately (final volume 142.
of the solution 10 mL). The reaction is sampled by removing 16 K. Yamamoto, M. Takagi and J. Tsuji, Bull. Chem. Soc. Jpn.,
an aliquot of the reaction mixture to which diethyl ether is 1988, 61, 319–321.
added (1/1, v/v). The solution is filtered over a short silica pad 17 E. B. Boyar, A. Dobson, S. D. Robinson, B. L. Haymore and
i
and subsequently the conversion is determined by GC analysis
(Ru 0.1 mol%, NaOiPr 2 mol%, and acetophenone 0.1 M).
J. C. Huffman, J. Chem. Soc., Dalton Trans., 1985, 4, 621–
627.
18 J. Gotzig, R. Werner and H. Werner, J. Organomet. Chem.,
1985, 290, 99–114.
19 R. A. Sanchez-Delgado, N. Valencia, R. Marquez-Silva,
A. Andriollo and M. Medina, Inorg. Chem., 1986, 25, 1106–
1111.
Conflicts of interest
There are no conflicts to declare.
20 M. O. Albers, D. C. Liles and E. Singleton, Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun., 1987, 43, 860–863.
21 T. Arliguie and B. Chaudret, Chem. Commun., 1989, 3, 155–
157.
Acknowledgements
The authors thank Prof. Janos Mink for discussions on the IR 22 P. Sarkhel, S. C. Sarker, A. K. Gupta and R. K. Poddar,
spectra and Dr Paolo Martinuzzi, Benjamin Hofmann and Transition Met. Chem., 1996, 21, 250–253.
Sebastian Hölzl for NMR, IR and MS measurements. The TUM 23 P. González-Herrero, B. Weberndörfer, K. Ilg, J. Wolf and
Graduate Schools of Chemistry and MSE are gratefully
acknowledged for financial support for D. A. H. and P. J. F.
H. Werner, Angew. Chem., Int. Ed., 2000, 39,
3266–3269.
24 T. Arliguie, B. Chaudret, G. Chung and F. Dahan,
Organometallics, 1991, 10, 2973–2977.
25 L. Bonomo, P. Dupau and S. Bonnaudet, Switzerland Pat.,
WO2011/145032A2, 2011.
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