Arene ruthenium complexes as versatile catalysts in water in both transfer hydrogenation of ketones and oxidation of alcohols. Selective deuterium labeling of rac-1-phenylethanol

Article abstract of DOI:10.1021/om3004702

The preparation of three series of arene Ru(II) half-sandwich compounds with the functional ligand 4,4′-dimethoxy-2,2′-bipyridine (dmobpy) is described. The new cationic derivatives have the general formula [(η⁶-arene)RuCl(κ²-N,N-dmobpy)]X (arene = benzene, X = Cl^- ([1]Cl), BF₄^- ([1][BF ₄]), TsO^- ([1]TsO), PF₆^- ([1][PF₆]); arene = p-cymene (p-cym), X = Cl^- ([2]Cl), BF₄^- ([2][BF₄]), TsO^- ([2]TsO), PF₆^- ([2][PF₆]); arene = 2-phenoxy-1-ethanol (phoxet), X = Cl^- ([3]Cl), BF₄^- ([3][BF ₄]), TsO^- ([3]TsO), PF₆^- ([3][PF₆])). The structures of [1]Cl, [1]TsO, [2]TsO, [2][BF ₄], and [2][PF₆] were determined by X-ray crystallography. All of the complexes except the PF₆^- salts were water-soluble, and they behaved as active catalysts in two different processes: the transfer hydrogenation of water-soluble and -insoluble ketones to the corresponding alcohols, using HCOONa as the hydrogen source at pH 4, and the oxidation of rac-1-phenylethanol to acetophenone with ^tBuOOH at pH 7, both in aqueous solution. For the transfer hydrogenation with p-cymene complexes the aqua, formato, and hydride species were detected by means of ¹H NMR experiments in D₂O. It was found that the cationic hydrido complex was [(η⁶-p-cymene)RuD(dmobpy)]⁺. The reversible and pH-dependent formation of the hydroxo derivative was also observed. When the catalytic transfer hydrogenation was performed in D ₂O, the 1-phenylethanol obtained was selectively deuterated at the benzylic carbon. Mechanistic proposals are also included.

Full text of DOI:10.1021/om3004702

Article
pubs.acs.org/Organometallics
Arene Ruthenium Complexes as Versatile Catalysts in Water in both
Transfer Hydrogenation of Ketones and Oxidation of Alcohols.
Selective Deuterium Labeling of rac-1-Phenylethanol
†
†
‡
,‡
‡
́
Cristina Aliende, Mercedes Perez-Manrique, Felix A. Jalon, Blanca R. Manzano,* Ana M. Rodrıguez,
́
́
́
and Gustavo Espino*,†
†
́
́
Departamento de Quımica, Facultad de Ciencias, Universidad de Burgos, Plaza Misael Banuelos s/n, 09001, Burgos, Spain
̃
‡
́
́
Departamento de Quımica Inorganica, Organica y Bioquımica, Facultad de Quımicas, Universidad de Castilla-La Mancha, Avda.
́
́
Camilo J. Cela 10, 13071 Ciudad Real, Spain
S
* Supporting Information
ABSTRACT: The preparation of three series of arene Ru(II) half-
sandwich compounds with the functional ligand 4,4′-dimethoxy-
2,2′-bipyridine (dmobpy) is described. The new cationic derivatives
have the general formula [(η6-arene)RuCl(κ2-N,N-dmobpy)]X
(arene = benzene, X = Cl− ([1]Cl), BF4 ([1][BF4]), TsO−
−
([1]TsO), PF6 ([1][PF6]); arene = p-cymene (p-cym), X = Cl−
−
([2]Cl), BF4 ([2][BF4]), TsO− ([2]TsO), PF6 ([2][PF6]);
−
−
arene = 2-phenoxy-1-ethanol (phoxet), X = Cl− ([3]Cl), BF4
−
−
([3][BF4]), TsO− ([3]TsO), PF6 ([3][PF6])). The structures of [1]Cl, [1]TsO, [2]TsO, [2][BF4], and [2][PF6] were
−
determined by X-ray crystallography. All of the complexes except the PF6 salts were water-soluble, and they behaved as active
catalysts in two different processes: the transfer hydrogenation of water-soluble and -insoluble ketones to the corresponding
alcohols, using HCOONa as the hydrogen source at pH 4, and the oxidation of rac-1-phenylethanol to acetophenone with
tBuOOH at pH 7, both in aqueous solution. For the transfer hydrogenation with p-cymene complexes the aqua, formato, and
1
hydride species were detected by means of H NMR experiments in D2O. It was found that the cationic hydrido complex was
[(η6-p-cymene)RuD(dmobpy)]+. The reversible and pH-dependent formation of the hydroxo derivative was also observed.
When the catalytic transfer hydrogenation was performed in D2O, the 1-phenylethanol obtained was selectively deuterated at the
benzylic carbon. Mechanistic proposals are also included.
cases, and Ru-, Rh-, or Ir-based complexes are the most popular
catalytic precursors.14 Moreover, the reaction can be carried out
in water using a mixture of HCOONa and HCOOH as the
hydrogen source and this approach has evident benefits from an
environmental point of view. Species of general formula [(η6-
arene)RuCl(N,N)]+ show good activities in this field, provided
that they are soluble in water. Several groups have exploited the
possibilities of chloro and aqua complexes, of general formula
[(η6-arene)Ru(NN)(X)]n+ (X = Cl, H2O; n = 1, 2), with
remarkable results.9,10,15
The oxidation of accessible primary and secondary alcohols
to prepare reactive aldehydes and ketones, respectively, is a
highly attractive synthetic strategy, and several protocols are
known. The classical Jones oxidation uses CrO3 in sulfuric
media to oxidize secondary alcohols to ketones and primary
alcohols to aldehydes under water-free conditions or carboxylic
acids in wet solvents.16 Nevertheless, Cr(VI) chemicals are
highly toxic, and their use is undesirable. Alternative protocols
avoid the use of toxic metals such as chromium, and these can
be carried out under very mild conditions. The Corey−Kim
INTRODUCTION
■
The number of organic reactions catalyzed by half-sandwich
Ru(II) arene complexes has increased considerably in the past
decade. Relevant examples of this proliferation include the
following: hydration of organonitriles,1 hydration of alkynes,2
Diels−Alder reactions,3 alkene metathesis,4 hydrogenation of
alkenes,5 asymmetric transfer hydrogenation of ketones6 and
imines, and oxidation of alcohols.7,8 In particular, we are
interested in the development of versatile catalysts in aqueous
media, for both the transfer hydrogenation of ketones9,10 and
the oxidation of alcohols.11 Obvious advantages result from the
use of water as a solvent, in that it avoids environmental issues
related to the use of organic solvents and it also makes the
separation of organics products easier.12,13
Several procedures are available to achieve the synthesis of
organic alcohols. Hydroboration−oxidation of alkenes, hydrol-
ysis of esters, nucleophilic substitution on haloalkanes, and
reduction of ketones are well-known procedures. In particular,
the reduction of ketones by catalytic transfer hydrogenation has
become established as one of the most useful protocols among
the latter group of reactions, mainly because it avoids the
drawbacks associated with the use of high-pressure molecular
hydrogen. 2-Propanol is the preferred hydrogen source in most
Received: May 29, 2012
Published: August 22, 2012
© 2012 American Chemical Society
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reaction and the Swern reaction are based on the “in situ”
generation of the dimethylchlorosulfonium ion, either from N-
chlorosuccinimide and dimethyl sulfide (Corey−Kim) or from
DMSO and oxalyl chloride (Swern), and both involve the use
of Et3N as a base.17 The Oppenauer oxidation is an aluminum-
catalyzed reaction based on hydride transfer from the α-carbon
of the corresponding alcohol to the carbonyl carbon of a ketone
such as benzophenone.18 The Dess−Martin oxidation makes
use of a hypervalent iodine compound to oxidize alcohols to
adehydes or ketones smoothly and selectively in dichloro-
methane or chloroform at room temperature.19 Many other
oxidants have been used in a variety of Ru-based catalytic
systems, namely chloramine-T,20 benzoquinone,21 iodosylben-
zene,22 NaIO4,8 N-methylmorpholine N-oxide (NMO),23 and
tBuOOH.24 The last peroxide is cheap and easy to use. In
addition, in some recent reports the efficiencies of different
oxidants have been compared.7,8,25
Most of these methodologies produce toxic byproducts and
employ organic solvents. Therefore, the use of cleaner oxidants,
such as hydrogen peroxide26 and molecular oxygen,21,27 in the
catalytic oxidation of alcohols has been developed to satisfy the
demands of greener technologies. Dehydrogenative oxidation
of alcohols accompanied by the release of H2 represents a
further step as far as atom efficiency is concerned, since it
avoids the use of any oxidant.28 The application of these
strategies in aqueous media is emerging as a safer, cleaner, and
cheaper alternative, and it also allows the separation of the
organic products and the reuse of the water-soluble catalysts by
simple liquid−liquid extraction. Consequently, significant
efforts have been dedicated to the design and preparation of
robust organometallic catalysts with hydrophilic functions to
enhance their water solubility.29
in the transfer hydrogenation of ketones.9,32 This pendant
group could also favor water solubility, according to previous
studies with phosphine ruthenium systems.33
The detection of intermediates in the transfer hydrogenation
process was also a goal of this work. In this context, we
observed selective deuteration at the benzylic carbon of the
phenylethanol obtained in the transfer hydrogenation of
acetophenone carried out in D2O. This finding indicates that
the hydride intermediate of the catalytic process undergoes a
fast and reversible interchange with D+ from the solvent.
RESULTS AND DISCUSSION
■
Synthesis and Structural Characterization of Com-
plexes. The commercial ligand 4,4′-dimethoxy-2,2′-bipyridine
(dmobpy) was used to prepare three series of new compounds
with the general formula [(η6-arene)RuCl(κ2-N,N-dmobpy)]X
(arene = benzene, X = Cl− ([1]Cl), BF4 ([1][BF4]), TsO−
−
−
([1]TsO), PF6 ([1][PF6]); arene = p-cymene (p-cym), X =
Cl− ([2]Cl), BF4 ([2][BF4]), TsO− ([2]TsO), PF6
−
−
([2][PF6]); arene = 2-phenoxy-1-ethanol (phoxet), X = Cl−
([3]Cl), BF4− ([3][BF4]), TsO− ([3]TsO), PF6− ([3][PF6]))
(see Scheme 1). The cationic derivatives were obtained in one-
Scheme 1. Structures and Numbering Scheme of the New
Ru(II) Arene Compounds of General Formula [(η6-
arene)RuCl(κ2-N,N-dmobpy)]X ([1]X, [2]X, and [3]X)
In the work described here, we targeted the synthesis and
characterization of new arene ruthenium complexes of formula
[(η6-arene)RuCl(NN)]X for their use as versatile catalysts in
the transfer hydrogenation of water-soluble and -insoluble
ketones, with HCOONa as the hydrogen source, and the
t
oxidation of alcohols with BuOOH as the oxidant, both in
aqueous solutions. The NN ligand 4,4′-dimethoxy-2,2′-
bipyridine (dmobpy) was chosen for this study. The
introduction of the methoxy groups was carried out with the
belief that they could enhance the solubility in water of the
corresponding Ru salts in comparison to similar complexes with
bpy. At the same time, we relied on the premise that dmobpy
could facilitate the activation of the catalytic precursors. It has
been reported that bipy, as a π-acceptor ligand, hinders the
dissociation of the chloride group in [(η6-arene)Ru(bipy)Cl]-
Cl.30 In contrast, we predicted that the presence of electron-
donating groups (−OMe) in dmobpy should moderate this π-
acceptor effect due to the diminished electron-withdrawing
ability. This in turn would decrease the positive charge on the
metallic center and would make the Cl− dissociation process
more favorable, which would increase the aquation rate.30
Another aim of the work was to analyze the effect of the
counteranion and/or the arene on the water solubility and the
pot processes by reacting the appropriate arene starting
material with the functional chelating ligand dmobpy and the
corresponding silver salt, when necessary, in polar solvents such
as methanol, ethanol, 2-propanol, acetonitrile, and water (see
the Experimental Section). The monomer [(η6-benzene)-
RuCl2(CH3CN)]34 was used to prepare [1]Cl, [1][BF4],
[1]TsO, and [1][PF6] (eqs 1 and 2 in Scheme 2), whereas
dimers of formula [(η6-arene)Ru(μ-Cl)Cl]2 (arene = p-cym,35
phoxet31) were employed to isolate compounds of series 2 and
[3]Cl (eqs 3 and 4 in Scheme 2). Finally, the complexes [3]X
(X = BF4 , TsO−, PF6 ) were prepared from [3]Cl according
to eq 5 in Scheme 2. The usual workup procedures afforded the
new complexes in moderate to good yields (47−88%) as air-
and moisture-stable yellow solids. Solubility tests proved that
most of the complexes are water-soluble (see Table 1), and this
is probably a consequence of both their cationic nature and the
presence of the −OMe groups, which can act as hydrogen bond
acceptors.36 However, relevant counterion and arene effects on
the solubility can be deduced from these tests. In general, the p-
cymene derivatives are more soluble. Concerning the anion
effect, the chloro salts are the most soluble in the case of
benzene or p-cymene complexes, while for the arene 2-
phenoxy-1-ethanol the solubility is higher for the derivative
−
−
−
catalytic behavior. Thus, different anions (X = Cl−, BF4 , TsO−,
−
PF6 ) and three distinct arenes were introduced. In addition to
the more commonly used benzene and p-cymene arenes, the
scarcely explored 2-phenoxy-1-ethanol (phoxet) was also used
in the synthesis of the catalytic precursors.6,31 It was thought
that the pendant group could have a positive effect on the
catalytic activity, bearing in mind that it has been established
that donor groups on the arene ring favor the catalytic behavior
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Scheme 2. Preparation of Compounds of the Series 1−3
(see the Experimental Section and Table S11 in the Supporting
Information). The H NMR spectra of compounds [2]X and
Table 1. Solubility Values in Water at Room Temperature
1
a
compd
solubility
[3]X in CD3OD at room temperature are consistent with Cs-
symmetric species (nonstereogenic and achirotopic Ru ion).
Thus, the p-cymene series shows the characteristic AA′BB′ spin
system for the aromatic protons of the arene and homotopic
methyl groups for the isopropyl moiety. Similarly, complexes of
series 3 exhibit an AA′BB′C spin system for the aromatic
protons of the phenoxyethanol ring and homotopic methylene
protons for the ethanol arm. Compounds of series 1 only
present a singlet for the six equivalent protons of the benzene at
around 6 ppm, and consequently, information about the
symmetry cannot be inferred in this case. On the other hand,
the dmobpy signals were shifted downfield in all the complexes
with respect to those of the free ligand, as a consequence of
coordination to the metallic center. As expected, δ(H6′) is
particularly sensitive to this effect, due to its proximity to the
metallic center. Complexes of series 2 and 3 show an equivalent
deshielding, Δδ(H6′) = 0.7 ppm, whereas complexes of series 1
exhibit a slightly higher displacement, Δδ(H6′) = 0.8 ppm.
Apparently, the lower π-donor ability of benzene, in
comparison to that of p-cymene and phenoxyethanol, is
compensated by a higher σ-donation from the N,N ligand to
the Ru ion. On the other hand, a counteranion effect was not
observed on the resonances in CD3OD. Additional peaks were
recorded for the TsO− anion in the spectra of 1[TsO], 2[TsO],
and 3[TsO]. The 13C{1H} NMR spectra of all the complexes
[1]Cl
11.1 (23.8)
0.5 (1.0)
0.7 (1.2)
11.3 (21.6)
2.9 (5.1)
5.0 (7.6)
2.9 (5.5)
2.0 (3.5)
6.4 (9.7)
[1][BF4]
[1]TsO
[2]Cl
[2][BF4]
[2]TsO
[3]Cl
[3][BF4]
[3]TsO
a
Values in mg mL−1 (values in parentheses in μmol mL−1).
containing the tosylate anion. The chloro salts [1]Cl and [2]Cl
have the highest solubilities. In contrast, the PF6 salts are
−
poorly soluble in water and they were therefore not used in the
catalytic studies.
The new products were fully characterized by H, 19F (for
1
BF4 salts), 31P (for PF6 salts), and 13C{1H} NMR
spectroscopy and also by IR spectroscopy, FAB mass
spectrometry, molar conductivity, and elemental analysis. The
structures of [1]Cl, [1]TsO, [2]TsO, [2][BF4], and [2][PF6]
were determined by single-crystal X-ray diffraction.
−
−
Full assignment of resonances in the H and 13C{1H} NMR
1
spectra of every complex was performed using 2D NMR
experiments such as gCOSY, NOESY, gHSQC, and gHMBC
Figure 1. ORTEP diagrams for complexes (a) [1]Cl and (b) [1]TsO. Hydrogens have been omitted for clarity.
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Figure 2. ORTEP diagrams for complexes (a) [2]TsO, (b) [2][BF4], and (c) [2][PF6]. Hydrogens have been omitted for clarity.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compounds [1]Cl, [1]TsO·H2O, [2]TsO, [2][BF4], and [2][PF6]
bond length/angle
[1]Cl
[1]TsO·H2O
[2]TsO
[2][BF4]
[2][PF6]
Ru(1)−Cl(1)
Ru(1)−N(1)
Ru(1)−N(2)
N(1)−Ru(1)−N(2)
N(1)−Ru(1)−Cl(1)
N(2)−Ru(1)−Cl(1)
2.3989(9)
2.085(2)
2.078(2)
76.19(8)
85.22(6)
84.80(6)
2.4192(7)
2.082(2)
2.075(2)
76.31(7)
84.15(5)
85.99(5)
2.409(2)
2.092(3)
2.082(3)
76.6(2)
2.410(1)
2.085(3)
2.084(3)
76.4(1)
2.392(1)
2.084(3)
2.091(3)
76.1(1)
84.23(9)
84.35(9)
85.25(9)
81.09(9)
83.99(8)
83.32(9)
Table 3. Selected Geometric Parameters for the Cations of [1]Cl, [1]TsO·H2O, [2]TsO, [2][BF4], and [2][PF6]
a
b
c
d
complex
[1]Cl
range of Ru−C dist (Å)
Ru−centroid (Å)
α(py−py) (deg)
β(dmobpy−“arene”) (deg)
γ(Cx−Cipso−Ru−Cl) (deg)
2.154(3)−2.186(3)
2.159(2)−2.199(2)
2.161(5)−2.237(5)
2.164(4)−2.210(4)
1.685
1.672
1.687
1.679
1.685
8.5
2.0
1.8
6.4
2.1
53.8
60.4
64.3
66.9
66.4
[1]TsO·H2O
[2]TsO
12.8
14.3
6.5
[2][BF4]
[2][PF6]
2.146(4)−2.225(4)
a
b
c
Calculated with Mercury, version 2.4.6. Dihedral angle between the two pyridyl rings. Dihedral angle between the arene and the dmobpy ligand.
d
Dihedral angle formed by the atoms Cx−Cipso−Ru−Cl; Cx represents the carbon atom of the methyl ([2]BF4 or [2]PF6) or isopropyl ([2]TsO)
groups of the p-cymene ring.
show characteristic signals for dmobpy and the corresponding
arenes with symmetry patterns fully consistent with those
established by H NMR (see the Experimental Section).
The FAB+ mass spectra for complexes of series 1−3 all
exhibit a characteristic set of peaks for the corresponding
cationic unit [M − X]+.
Figures 1 and 2. Selected bond lengths and angles are given in
Table 2, and relevant crystallographic parameters are given in
the Supporting Information. The molecular structures of the
five complexes present the classical three-legged piano-stool
arrangement with a pseudo-octahedral geometry and display
features similar to those of structurally related ruthenium
complexes with bpy-type ligands38,39 such as, for example,
1
FT-IR spectra were recorded for all complexes and are fully
consistent with the formulations described above. All
complexes show characteristic bands for the Ru−Cl stretching
39
[RuCl(p-cym)(bpy)]PF6 and [RuCl(bz)(bpy)]Cl.40
The ruthenium atom is coordinated to the corresponding η6-
arene ring, which occupies three facial coordination positions,
and also to the two nitrogen atoms of the dmobpy ligand and
the chloride group. The range of Ru−C distances is shown in
Table 3. This range is higher for [2]TsO and [2][BF4]. The
Ru−C distances trans to the chloro ligand are generally shorter
than those trans to the dmobpy ligand, thus reflecting a higher
trans influence of the nitrogenated ligand. The Ru−centroid
distances are also included in Table 3. It can be observed that
there are no clear differences in these values between the two
arenes benzene and p-cymene. The Ru−Cl and Ru−N bond
lengths and coordination angles are similar to those reported
for related arene Ru(II) complexes with bipyridine ligands
(Table 2). The two pyridyl rings of the dmobpy ligand are
practically coplanar (see dihedral angle in Table 3), and both
vibrations at around 280 cm−1. Furthermore, the BF4 salts
−
show strong diagnostic peaks at around 1058 cm−1 (νB−F),
whereas the TsO− salts show peaks at around 1212 (νas,SO
)
−
and 1188 cm−1 (νas,SO) and the PF6 salts at 841 (νP−F) and
558 cm−1 (δF−P−F).
The molar conductivity measurements (ΛM) for all the
monocationic complexes show that they behave as 1:1
electrolytes in acetonitrile solutions (10−3 M) (see the
Experimental Section and Table S12 in the Supporting
Information).37
X-ray Structure Determination. Single crystals of [1]Cl,
[1]TsO, [2]TsO, [2][BF4], and [2][PF6] were obtained, and
the corresponding structures were determined by single-crystal
X-ray diffraction analysis. The ORTEP diagrams are shown in
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rings and the chelate ring are also approximately coplanar, as
expected for complexes with this type of bidentate ligand. The
dihedral angle formed between the arene ring and the mean
plane of the dmobpy ligand is higher for the p-cymene
complexes, possibly for steric reasons (see Table 3). The
orientation of the p-cymene ring in the corresponding
complexes allows the formation of weak hydrogen bonds
between the chloride and the methyl ([2][BF4] or [2][PF6])
or isopropyl ([2]TsO) hydrogen atoms (distances: Cl1−C19 =
3.38 Å in [2][BF4] and 3.33 Å in [2][PF6] and Cl1−C20 =
3.44 Å in [2]TsO). To quantify the orientation of these groups,
we defined the dihedral angle formed by Cx−Cipso−Ru−Cl,
where Cx is the carbon atom of the methyl ([2][BF4] or
[2][PF6]) or isopropyl ([2]TsO) groups bonded to the arene
ring. It is noteworthy that, although the three derivatives
contain the same cation, a different orientation for the p-
cymene ring was found in [2]TsO with respect to the other
two derivatives.
the other derivatives are also involved in different hydrogen
bonds with other cations in the crystal structure.
In the case of [1]Cl there is a π−π stacking interaction
between the benzene rings of two cations that are related by an
inversion center. The parameters for this interaction are as
follows: distances, Ct−Ct = 3.49 Å and Ct−pl = 3.33 Å; angles,
α (angle between planes) = 0° and β (angle formed by the lines
Ct−Ct and Ct−pl) = 17° (Ct = centroid, pl = plane).
Catalytic Transfer Hydrogenation of Ketones in
Water. The activity of our complexes in the catalytic transfer
hydrogenation of cyclohexanone to cyclohexanol in water was
explored using a mixture of sodium formate/formic acid (pH 4)
as the hydrogen source at 80 °C under a nitrogen atmosphere,
according to the conditions established in the bibliography for
similar systems (eq 6).10 First, the corresponding blank and
The methoxy groups in all derivatives exhibit a coplanar
conformation with the bpy moiety, indicating a conjugation
effect, as usually found for methoxyphenyl groups bearing two
ortho H atoms.41 This situation has also been found in the
three reported ruthenium complexes containing the dmobpy
ligand.42 In complexes [1]TsO and [2][BF4] the two methoxy
groups exhibit a convergent orientation, while in the other
derivatives these two groups are in a divergent arrangement.
In the crystal structure the different counteranions participate
in the formation of hydrogen bonds with several cations (up to
5). In the case of [2]TsO, there are also hydrogen bonds
between the anions.
[1]TsO crystallizes with one water molecule per unit formula
that also participates in the formation of hydrogen bonds. The
crystal structure shows metal complex dimers with the two
cations in a head-to-tail disposition related by an inversion
center. The two cations interact with each other through
multiple hydrogen bonds. In particular, each chloride anion
behaves as the hydrogen acceptor in four different contacts with
the neighbor; thus, eight interactions are observed for each
dimer (see Figure 3). This situation may explain the convergent
orientation of the two methoxy groups. The methoxy groups of
control experiments were carried out for this reaction. The
formation of product was not detected without catalyst (Table
4, entry 1), in the presence of the free ligand dmobpy (Table 4,
entry 2), or in the presence of the starting material
[(bz)RuCl2(CH3CN)] (Table 4, entry 3). The reduction of
cyclohexanone to cyclohexanol was then evaluated in the
presence of [1][BF4] as the catalytic precursor under different
reaction conditions and also with the addition of different
additives, as either promoters or inhibitors (Table 4). The first
experiment was carried out with a catalyst/substrate ratio of 1/
200, with AgBF4 as a potential promoter, and with a reaction
time of 20 h (entry 4). A yield of 100% was achieved under
these conditions. The experiment was repeated without AgBF4
(entry 5) and the yield remained 100%, thus demonstrating
that activation by chloride abstraction is not necessary. When
the reaction time was reduced to 8 or 4 h (entries 6 and 7), the
yield was reduced to 84 and 26%, respectively, although in the
case of entry 6 the TOF was increased. When the catalyst/
substrate ratio was changed to 1/500 (20 h), an increase in the
TOF value was also achieved and a yield of 100% was obtained
(compare entries 5 and 8). In the next experiment NaCl (2.5
mol % with regard to catalyst) was added to hinder the chloride
dissociation and the formation of the labile aqua derivative,
which could be the putative active species. As expected, a
decrease in the yield was observed (compare entries 5 and 9),
indicating that activation of the catalyst probably requires
dissociation of the chloride. The use of H2O/MeOH (9/1) as
the solvent system diminished the conversion (entry 10). A
rough estimation of the pH effect was carried out by using
either HCOOH (pH 3) or HCOONa (pH 9) as the only
hydrogen source, with yields of 9 and 0% obtained (entries 11
and 12, respectively), thus confirming that a pH of 4 is the best
of those tested for our model system. Finally, the catalyst was
moderately active when the solvent was changed to H2O/
MeOH (9/1), using HCOONa as the only hydrogen source
(entry 13).
Catalyst Screening. In a second set of experiments,
−
ruthenium complexes [1]X−[3]X (X = Cl−, BF4 , TsO−)
were tested as precatalysts in the transfer hydrogenation of
cyclohexanone using the conditions shown in entry 5 in Table
4. In this way, the influence of the arene and the counteranion
could be evaluated. Derivatives with PF6− were not used in this
study because of their low solubility in water. Complexes
Figure 3. Dimers in the crystal structure of [1]TsO·H2O. Hydrogen
bonds are indicated with violet dashed lines.
−
[1]X−[3]X (X = Cl−, BF4 , TsO−) were totally soluble in the
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Table 4. Catalytic Transfer Hydrogenation of Cyclohexanone to Cyclohexanol Using [1][BF4] under Different Reaction
a
Conditions
entry
cat.
H source
solvent
additive
cat./S
yield (%)
t (h)
TON
TOF (h−1
)
1
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
HCOOH/HCOONa
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
0
0
20
20
20
20
20
8
0
0
0
0
2
dmobpy
1/200
1/200
1/200
1/200
1/200
1/200
1/500
1/200
1/200
1/200
1/200
1/200
3
[bzRuCl2(CH3CN)]
[1][BF4]
0
0
0
b
4
AgBF4
100
100
84
26
100
83
79
9
200
200
168
52
10
10
21
13
25
8.3
7.9
0.9
0
5
[1][BF4]
6
[1][BF4]
7
[1][BF4]
4
8
[1][BF4]
20
20
20
20
20
20
500
166
158
18
c
9
[1][BF4]
NaCl
10
11
12
13
[1][BF4]
H2O/MeOH (9/1)
H2O
d
[1][BF4]
HCOOH
[1][BF4]
HCOONa
HCOONa
H2O
0
0
[1][BF4]
H2O/MeOH (9/1)
44
88
4.4
a
Control experiments are also included. Conditions: T = 80 °C, cat./S/HCOONa = 1/200/6000, 1.6 μmol of cat., 5 mL of H2O (except for entry 8,
b
cat./S/HCOONa = 1/500/6000), pH 4 (adjusted with HCOOH). AgBF4 was added to an aqueous solution of the catalyst, which contained
c
d
HCOOH/HCOONa, before the substrate. NaCl (2.5% with regard to catalyst). cat./S/HCOOH = 1/200/200. TON: turnover number = (mol of
ketone converted to alcohol)/(mol of catalyst). TOF: turnover frequency = (mol of product)/((mol of precatalyst) h) (calculated at the end of the
reaction).
reaction conditions. It was verified that the dimers [(p-
cym)RuCl2]2 and [(phoxet)RuCl2]2 were completely inactive
in this transformation. The activity of [(bz)RuCl2]2 was not
assessed, due to its insolubility in aqueous media. All of the
Table 6. Transfer Hydrogenation of Cyclohexanone to
Cyclohexanol Using Different Precatalysts
a
entry
complex
yield (%) (t (h))
TON
TOF (h−1
)
complexes [1]X−[3]X (X = Cl−, BF4 , TsO−) gave full
−
1
[RuCl2(p-cym)]2
[RuCl2(phoxet)]2
[1]Cl
0 (8)
0
0
0
0
2
0 (8)
conversion to the expected product after 20 h of reaction (see
Table 5). The activity of the complex [(p-cym)RuCl(bpy)]Cl,
3
49 (8)
84 (8)
53 (8)
100 (8)
87 (8)
100 (8)
76 (8)
48 (8)
62 (8)
70 (4)
69 (4)
90 (4)
98
12
21
13
25
22
25
19
12
16
35
35
45
4
[1][BF4]
[1]TsO
168
106
200
174
200
152
96
5
Table 5. Transfer Hydrogenation of Cyclohexanone to
a
6
[2]Cl
Cyclohexanol Using Different Precatalysts
7
[2][BF4]
[2]TsO
entry
complex
yield (%) (t (h)) TON TOF (h−1
)
8
9
[3]Cl
1
[(p-cym)RuCl2]2
[(phoxet)RuCl2]2
[(p-cym)RuCl(bpy)]Cl
[1]Cl
0 (20)
0
0
0
10
11
12
13
14
[3][BF4]
[3]TsO
2
0 (20)
0
124
140
138
180
3
78 (20)
100 (20)
100 (20)
100 (20)
100 (20)
100 (20)
100 (20)
100 (20)
100 (20)
100 (20)
156
200
200
200
200
200
200
200
200
200
7.8
[2]Cl
4
10
[2][BF4]
[2]TsO
5
[1][BF4]
10
10
10
10
10
10
10
10
6
[1]TsO
a
7
[2]Cl
Conditions: T = 80 °C, cat./S/HCOONa = 1/200/6000, 1.6 μmol of
8
[2][BF4]
cat., 5 mL of H2O, pH 4 (adjusted with HCOOH). TOF: (mol of
product)/((mol of precatalyst) h) (calculated at the end of the
reaction). No additive was used in any of these experiments.
9
[2]TsO
10
11
12
[3]Cl
[3][BF4]
[3]TsO
and an 87% yield for [2][BF4] (Table 6, entries 6−8). The
benzene and phenoxyethanol derivatives gave lower yields
(entries 3−5 and 9−11), thus confirming an arene effect on the
catalytic activity. Two different arguments must be considered
to explain these results. As previously stated, it has been
reported10 that electron-donating substituents have a beneficial
effect on the transformation rate, a situation that supports the
hypothesis of η4 transition states postulated by Ogo.10 This may
explain the different performances of p-cymene and benzene
derivatives. On the other hand, the pendant −OCH2CH2OH
group on the phenoxyethanol ring could, a priori, compete with
the hydrogen donor (formate) or the substrate for a position in
the coordination sphere, thus neutralizing the electron-donating
effect of this substituent and accounting for the reduced activity
of the phenoxyethanol catalysts with respect to the p-cymene
derivatives.
a
Conditions: T = 80 °C, pH 4, cat./S/HCOONa =1/200/6000, 1.6
μmol of cat., 5 mL of H2O. TON: turnover number = (mol of ketone
converted to alcohol)/(mol of catalyst) (calculated after 20 h). TOF:
(mol of product)/((mol of precatalyst) h) (calculated after 20 h).
similar to [1]Cl but with a bpy ligand, was also analyzed. The
yield was lower (78%) than that obtained with [1]Cl (entries 3
and 4), and this shows the beneficial effect of the methoxy
groups on the nitrogenated ligand. Several attempts to recycle
the catalyst were made, but the catalytic efficiency was much
lower in the second cycle.
In order to obtain a yield of less than 100% so that we could
carry out a comparative analysis of the different precatalysts, the
activities of all the complexes were determined again after 8 h
of reaction (Table 6). In this block of trials the p-cymene
complexes gave the highest yields of cyclohexanol, with full
conversions for reactions in the presence of [2]Cl and [2]TsO
Finally, the reaction time was shortened once again, from 8
to 4 h, for reactions performed in the presence of the p-cymene
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a
Table 7. Transfer Hydrogenation of Different Substrates Using [1][BF4]
a
b
Conditions: T = 80 °C, cat./S/HCOONa =1/200/6000, 1.6 μmol of cat., 5 mL of H2O, pH 4 (adjusted with HCOOH). Addition of HCOOH
was avoided (the pH was not adjusted to 4), and a H2O/MeOH (9/1) mixture was used as solvent. TOF: (mol of product)/((mol of precatalyst) h)
(calculated at the end of the reaction).
derivatives ([2]X) in order to improve the comparison of the
three precatalysts and to obtain higher TOF values (Table 6,
entries 12−14). Thus, we can conclude that [2]TsO is the
most active precatalyst of this family, with a TOF value of 45
h−1, after 4 h.
Comparison of the three different groups of experiments
(entries 3−5, 6−8, and 12−14) allows us to establish the effect
of the counteranion. This effect is not uniform for the three
series. The derivatives that perform best are those with
tetrafluoroborate, chloride, and tosylate for the benzene,
phenoxyethanol, and p-cymene series, respectively. The results
obtained for the catalyst [2]OTs are similar to those of other
similar previously reported systems10,11 if the TOF at the end
of the reaction is used for the comparison.
Substrate Scope. The scope of the transformation was
investigated with three other substrates: cyclohexenone
(soluble in water), 3-pentanone (moderately soluble in
water), and acetophenone (sparingly soluble in water) using
the [1][BF4] precatalyst. Cyclohexenone was chosen to
compare the activity of the catalysts in the hydrogenation of
ketone or olefin double bonds. The results are shown in Table
7. It was concluded that the ruthenium complexes tested are
rather tolerant with regard to the substrate, and the three
compounds were reduced under the conditions used. Control
experiments for the three substrates were run in order to prove
that reaction did not take place in the absence of catalysts
(entries 3, 6, and 10).
Total conversion to the alcohol was obtained with
acetophenone (entry 8), and a yield of 94% was achieved in
the case of 3-pentanone (entry 12) after 20 h of reaction. The
tests with a reaction time of 8 h (entries 1, 7, and 11) showed
the following order of reactivity: cyclohexanone ≅ acetophe-
none > 3-pentanone. The straight-chain ketone is converted to
the corresponding alcohol less efficiently than the cyclic ketone,
possibly due to steric reasons. The data shown in entry 9
demonstrate that, as previously observed, the yield is lower
when the pH is not adjusted to 4.
The reduction of cyclohexenone was effectively achieved by
[1][BF4], and two products, cyclohexanone and cyclohexanol,
were detected, meaning that both the alkene and carbonyl
functions are reduced under these conditions (entries 4 and 5,
Table 7). The presence of cyclohexanone and not cyclohexenol
indicates that the alkene functionality is reduced more easily.
Stability of Complex 2·BF4 in Aqueous Solution:
Aquation−Anation Equilibrium, Basic Hydrolysis, and
Reactivity in the Presence of HCOONa. In order to obtain
information about the mechanism of the transfer hydrogenation
process and to detect possible intermediates or active species,
1
we studied by means of H NMR the stability of different
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Figure 4. Reaction of [2][BF4] with HCOONa in D2O at 25 °C: (a) downfield area of the 1H NMR spectrum of [2][BF4] in D2O; (b−f) Evolution
with time of the same sample after adding an excess of HCOONa (and HCOOH to adjust to pH 4.35). Labeling of signals: [(p-
+
+
cym)Ru(Cl)(dmobpy)]+ (2); [(p-cym)Ru(D2O)(dmobpy)]2+ (4); [(p-cym)Ru(HCOO)(dmobpy)] (6); [(p-cym)Ru(D)(dmobpy)] (7); (
▲
)
−
HCOO ; ( ) 13C satellites.
●
1
Figure 5. Evolution of the formate complex 6 in D2O with time and temperature at pH 7: (a) downfield area of the H NMR spectrum of 6 with
traces of 2 and 4 in D2O; (b) evolution of the same sample after 4 h and 10 min of heating; (c) after 3 h more at 80 °C. Labeling of signals: [(p-
+
+
cym)Ru(Cl)(dmobpy)]+ (2); [(p-cym)Ru(D2O)(dmobpy)]2+ (4); [(p-cym)Ru(HCOO)(dmobpy)] (6); [(p-cym)Ru(D)(dmobpy)] (7); (
▲
)
−
HCOO ; ( ) 13C satellites.
●
complexes in aqueous solution and also the effect of the
addition of HCOONa to acidic or basic solutions of [2][BF4].
First, the 1H NMR spectrum of [2][BF4] in D2O was
recorded at 25 °C to study the corresponding aquation/anation
equilibrium. Two sets of peaks were observed immediately after
preparation of the sample (<5 min) and these are assigned to
[2][BF4] and a new species 4, with an integration ratio of 52:48
(Figure 4a). The sample was allowed to stabilize for 20 min, but
further changes were not detected, suggesting that equilibrium
concentrations are reached quickly. An excess of NaCl was then
added to the sample and a new spectrum was recorded, which
contained one set of peaks. Consequently, the surviving signals
can be assigned to the parent chloro complex [2][BF4] and the
resonances that were no longer observed to the corresponding
aqua cation [(p-cym)Ru(OD2)(dmobpy)]2+ (4). This assign-
ment is consistent with that reported for similar systems, where
aqua complexes show resonances that are displaced to higher
frequencies in comparison to those of the parent chloro
complexes.43,44 In conclusion, dissociation of the chloride
group in complex 2 is highly favored in water and the
corresponding aquation/anation equilibrium is reversible.
Indeed, it is well-known that protic solvents facilitate the
dissociation of chloro ligands by providing strong hydrogen-
bond donors.45 Similar reversible equilibria were observed in
D2O for [1][BF4], [2]TsO, and [3]TsO. The respective Ru−
Cl/Ru−OD2 species coexist with molar ratios of 27/73, 56/44,
and 44/56, according to NMR integration.
These studies confirm that for the catalytic activity of the
species of the type [(arene)RuCl(NN)]X, the isolation of the
corresponding aqua derivatives is not necessary because
activation of the chloro precursors takes place easily in water.
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Figure 6. (a) Downfield area of the 1H NMR spectrum of [2][BF4] in D2O at 25 °C, (b−g) evolution with time of the same sample after adding an
excess of KOH (pH >13), and (h, i) the same sample after adding HCOONa, showing no reaction with anion HCOO−. Labels: [(p-
cym)Ru(Cl)(dmobpy)]+ (2); [(p-cym)Ru(OD2)(dmobpy)]2+ (4); [(p-cym)Ru(OD)(dmobpy)]+ (5).
In an additional experiment, we added an equimolar amount
of HCOOH to an equilibrated solution of [2][BF4] in D2O at
room temperature (containing a 56/44 mixture of 2 and 4) in
an NMR tube. In this case, however, reaction evidence was not
detected. In a separate experiment an excess of HCOONa was
added to an equilibrated solution of [2][BF4] in D2O. The pH
value was adjusted to 4.35 with HCOOH, and the subsequent
evolution was monitored (see Figure 4). Two sets of new
signals (6 and 7) of increasing intensity were observed together
with those of 2 and 4, which decreased correspondingly. The
formation of species 6 is very fast and initially took place at the
expense of the aqua cation 4, the resonances of which also
decreased rapidly at the beginning (the species distribution
after 5 min was determined by integration, with 59/5/36 ratios
for 2/4/6). The simultaneous appearance of a singlet at 7.85
ppm, assigned to a coordinated formate anion, allowed us to
formulate 6 as the formato cation [(p-cym)Ru(OOCH)-
(dmobpy)]+. After 10 min, a clear decrease in the chloro
complex 2 was also observed, compound 6 continued to be
formed, and the first evidence of 7 was detected. Finally, the
system seemed to reach an equilibrium after 4 h, with 6 and 7
as the main species in an 86/13 ratio along with trace amounts
of 2 and 4. Signals for 7 appeared shifted upfield relative to the
other species, an observation consistent with the formation of a
hydride complex according to the literature examples for similar
systems.43 However, a Ru−H resonance was not detected at
low frequencies. As explained below, compound 7 is the species
[(p-cym)Ru(D)(dmobpy)]+. In conclusion, this sequence of
reactions can explain the formation of the active species and the
different intermediates in the possible mechanism for the
hydrogen transfer reaction of ketones. An excess of
acetophenone was subsequently added in order to prove that
either species 6 or 7 were catalytically active in the transfer
hydrogenation of the carbonyl substrate. Signals of 7
disappeared immediately, and rac-1-phenylethanol was formed
slowly at room temperature with a yield of 77%, after 6 days
(estimated by integration).
the addition of an excess of HCOONa to an equilibrated
solution of [2][BF4] in D2O, but at pH 7.5 at either 25 °C or
80 °C. At 25 °C, the species 6 and 7 were also detected, but in
this case the proportion of the hydride 7 was higher (6/7 = 69/
31). Furthermore, at 80 °C species 7 was the major component
of the reaction mixture (see Figure 5). Once more, the Ru−H
resonance of this compound was not visible at high field.
In order to obtain information about the dependence of the
behavior of the catalysts on pH, an excess of solid KOH (pH
>13) was added to an NMR sample of [2][BF4] in D2O at 25
°C and the evolution of the system was monitored by 1H NMR
for 40 min (see Figure 6). Signals attributed to the aqua species
Ru−OD2 were almost completely suppressed after 5 min of
reaction, and a new set of resonances, assigned to the new
species 5, was observed along with those of decreasing amounts
of 2. In fact, peaks due to the Ru−Cl derivative 2 also
disappeared during the next 30 min to produce a spectrum in
which the only visible signals corresponded to 5. Protons of 5
were more shielded than those of 2 and 4, and 5 was
formulated as the hydroxo complex [(p-cym)Ru(OD)-
(dmobpy)]+. Next, an excess of HCOONa was added to this
sample but no further changes took place, even after 3 days.
This finding demonstrates that the Ru−OD derivative was very
inert with regard to substitution processes, and this situation is
consistent with the results of previous studies.46 The
reversibility of the basic hydrolysis equilibrium was probed by
performing two additional experiments. First, an excess of solid
KOH (pH >13) was added to an NMR sample of [2][BF4] in
D2O at 25 °C and, when the reaction was complete (after 40
min), an excess of HClO4 (pH <1) was also added to confirm
that the hydroxo derivative 5 is able to regenerate 4 as the only
species. In a parallel NMR test, KOH (pH >13) and HCl (pH
<1) were successively added to show that the hydroxo species 5
can also regenerate the chloride derivative 2 under acidic
conditions (Figure S1, Supporting Information).
Taking into account the preceding results, we postulate the
catalytic cycle reflected in Scheme 3 for the transfer
hydrogenation of ketones in the presence of complexes of the
type [(arene)Ru(Cl)(dmobpy)]+. Initially, the chloro complex
2 (the catalytic precursor) undergoes aquation to give 4, which
is the active species in the catalytic cycle. Then, in the presence
of the formate anion complex 6 is formed as the result of a
In order to increase the amount of 7 and taking into account
the results by Ogo et al.,10 who demonstrated that the
formation of the corresponding hydride from [(η6-C6Me6)Ru-
(bpy)(H2O)]SO4 is favored at pH 7−8 and at high
temperatures, we performed two similar experiments involving
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Scheme 3. Proposed Mechanism for the Transfer Hydrogenation of Carbonyl Substrates, Using HCOONa as the Hydrogen
Donor and Complex [2]X as the Catalyst
substitution reaction. In the next step β-hydrogen elimination
gives rise to the hydrido derivative 7, via transition state A,
where the arene undergoes partial slippage to generate a vacant
site in the coordination sphere and the formate proton interacts
with the metallic center. This key step would involve evolution
of CO2, and this has also been assumed by other groups for
similar processes.39,43 Finally, the coordination of the ketone is
followed by hydride transfer in the transition state B, and then
the alcohol is formed after protonation (in acidic media) and
the aqua complex is regenerated. A possible alternative to B is
an outer-sphere transition state similar to that proposed by
Ogo.10
Furthermore, we have shown that the system is pH
dependent, since the reversible formation of unreactive 5 at
high pH leads to a dead end (see the interior part of the cycle
in Scheme 3).
Deuterium Labeling and H/D Exchange. As anticipated
previously, the Ru−H resonance of species 7 was not visible in
1
the H NMR spectrum (D2O), likely as a consequence of
deuteration. In an effort to demonstrate the hydride nature of 7,
we repeated the experiment described in Figure 5, using a
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Figure 7. High-field region of the 13C{1H} NMR spectrum for acetophenone-d, acetophenone-d2, and 1-rac-phenylethanol-d2. The asterisk indicates
impurities.
1
D2O/H2O mixture (1/1). Thus, the corresponding H NMR
spectrum for the reaction of [2][BF4] with HCOONa (80 °C,
4 h, D2O/H2O) showed a broad signal at −6.2 ppm, which we
ascribed to the Ru−H. The integration of this resonance is
significantly lower than that corresponding to 1H, indicating
that this group is partially deuterated in this media.
transfer process. The reason this process occurs is apparent if
we consider the appearance of the Me signal for the residual
acetophenone (56% by integration) in both the H and the
1
13C{1H} NMR spectra (Figure 7 and Figure S2 (Supporting
Information)). Resonances for the respective isotopomers with
CH3, CDH2, and CD2H groups are visible. It is well-known that
this group can be readily deuterated in an acidic medium
through keto−enol tautomerism. Once the Me groups of the
substrate have been partially deuterated, the observation of
deuterium in the Me group of the phenylethanol is easily
understood. Conditions for a full conversion experiment are
described in the Experimental Section.
Moreover, we indirectly proved the involvement of the Ru−
D group of 7 in the transfer hydrogenation process through the
hydrogenation of acetophenone in D2O, which led to
deuterium incorporation in the resulting rac-1-phenylethanol
(an excess of acetophenone was added to the NMR tube under
the conditions of the spectrum in Figure 4f at 25 °C).
1
Interestingly, in the corresponding H NMR (D2O, 25 °C)
It is noteworthy that the selective labeling of the hydro-
genated substrate supports two impressive facts: (i) the putative
intermediate of the hydrogenation, monohydride 7, must be
deuterated in the hydride position by D2O, and (ii) more
importantly, this deuteration must be very fastat least as fast
as the hydride transfer to the benzophenone. Ready H/D
exchange in the hydride position of metal hydride derivatives is
a known process that is postulated to occur through dihydrogen
species.47 This means that the monohydride 7 is quickly
deuterated in D2O in a reversible way, forming a transient
dihydrogen Ru(HD) intermediate. Very few examples of the
protonation of hydride species with this reversible behavior
have been described. Stabilization of the dihydrogen species
and their evolution to give the homolytic cleavage of H2 to give
classical dihydrides, or the release of this molecule, are more
common ways of evolution. In the absence of other
information, we postulate that the formic acid added to the
reaction is the protonating agent that transfers deuterons from
D2O. In contrast to a hypothetical direct deuteration from
water, our proposal is based on the acidity of this agent as
compared with that of water. As stated, it is very interesting that
the H/D interchange process in 7 is faster than the proton/
deuterium incorporation in the reaction product, 1-phenyl-
ethanol. This situation allows practically total deuterium
incorporation in the benzylic position of this alcohol. Given
this possibility, it is necessary to consider a lateral equilibrium
in the mechanism proposed in Scheme 3, starting from 7 and
concerning the H/D exchange of this species (see Scheme 4).
spectrum of this alcohol the resonances for the CH(OH) group
were not detected (possibly obscured by the residual H2O) and
a singlet was observed for the methyl signal (the expected 3JHD
was smaller than the width of the signal at medium height),
suggesting deuteration of the benzylic carbon. In order to fully
characterize this product, a transfer hydrogenation experiment
was carried out in D2O at 80 °C and pH 4. The water-insoluble
organic products were removed and dissolved in CDCl3, and
the H and 13C{1H} NMR spectra were recorded. The H
NMR spectrum showed signals for a mixture of acetophenone
and rac-1-phenylethanol (molar ratio 56/44), particularly a
quartet with an anomalously low integration (0.21H instead of
the expected 1H) for the CH group of the alcohol. The
13C{1H} NMR spectrum validated the selective deuteration of
1-rac-phenylethanol, as three lines of equal intensity were
observed at 69.9 ppm for the −CD group (see Figure 7).
Although the relative integration in 13C spectra cannot be
considered as a valuable measure for the molar ratio of the
species, the difference in intensity for the CD and residual CH
resonances at around 70 ppm implies that deuteration is
dominant over this position of the alcohol. As far as the
aromatic resonances are concerned, evidence for the existence
of CD groups in these positions was not obtained. The signal of
the CH3 group appears at around 25 ppm as a singlet, but at
higher field a resonance consisting of three lines of equal
intensity can be assigned to a CDH2 group (see Figure 7).
Deuteration in this position is unexpected for a hydrogen
1
1
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Scheme 4. Mechanism Proposed for the Deuteration of
Species 7
Table 8. Catalytic Oxidation of rac-1-Phenylethanol to
Benzophenone Using the Oxidants BuOOH and H2O2 and
t
the Catalysts [RuCl2(p-cym)]2, [RuCl2(phoxet)]2, [1][BF4],
a
[2][BF4], and [3][BF4]
S/
yield (%) (t
TOF
(h−1
entry
cat.
none
oxidant
cat.
(h))
TON
)
1
2
tBuOOH
tBuOOH
0 (3)
The selective deuterium or tritium labeling of organic substrates
is currently a very active research field with applications in
spectroscopy, mechanistic studies, and medicine.48,49 The
processes described in this work allow the incorporation of
deuterium from a cheap and green source (water), and this is a
very attractive characteristic. Very few examples of such a
process have been reported to date, and many that have been
described occur only under very stringent reaction con-
ditions.49,50
The results discussed above open the possibility of new
experimental routes focused on the selective deuterium labeling
of new substrates bearing not only CO functionalities but
also CC groups. This latter aspect is supported by the results
obtained in this work concerning the hydrogenation of
cyclohexenone. Work aimed at addressing these questions is
planned in our research group in the near future.
[(p-cym)
RuCl2]2
103 100 (3)
103 100 (1)
103 100 (0.5)
104 100 (1)
1000
1000
1000
10000
8900
1000
1000
10000
8800
333
1000
3
[(p-cym)
RuCl2]2
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
4
[(p-cym)
RuCl2]2
2000
5
[(p-cym)
RuCl2]2
10000
53400
1000
6
[(p-cym)
RuCl2]2
104 89
(10 min)
103 100 (1)
103 100 (0.5)
104 100 (1)
7
[(phoxet)
RuCl2]2
8
[(phoxet)
RuCl2]2
2000
9
[(phoxet)
RuCl2]2
10000
52800
10
[(phoxet)
RuCl2]2
104 88
(10 min)
Catalytic Oxidation of Alcohols in Water. Inspired by the
search for versatile catalysts that could be active in different
catalytic transformations, and based on the studies reported by
11
12
13
14
15
16
17
18
19
20
21
22
23
24
[1][BF4]
[1][BF4]
[1][BF4]
[1][BF4]
[1][BF4]
[2][BF4]
[2][BF4]
[2][BF4]
[2][BF4]
[3][BF4]
[3][BF4]
[3][BF4]
[3][BF4]
[3][BF4]
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
tBuOOH
H2O2
103 98 (3)
103 85 (1)
103 62 (0.5)
104 69 (1)
103 100 (3)
103 84 (1)
103 67 (0.5)
104 100 (3)
104 90 (1)
103 100 (3)
103 100 (1)
103 65 (0.5)
104 84 (1)
103 0 (3)
980
850
327
850
Suss-Fink11 and Singh,7,8 we tested the activity of a selection of
620
1240
6900
333
̈
6900
1000
840
our complexes in the catalytic oxidation of rac-1-phenylethanol
t
with BuOOH in aqueous media (see eq 7 and Table 8). A
840
670
104
1340
3333
9000
333
9000
1000
1000
650
blank experiment was initially run in the absence of metallic
species to rule out any possible activity attributable to a
noncatalytic reaction (Table 8, entry 1). A number of
experiments were then carried out to evaluate the performance
of several catalytic precursors, namely [1][BF4], [2][BF4], and
[3][BF4] and the precursors [(p-cym)RuCl2]2 and [(phoxet)-
RuCl2]2 (entries 2, 6, 9, 13, and 18). To our surprise, the
conversion of rac-1-phenylethanol to acetophenone (%) after 3
h was complete in all cases and [1][BF4] (entry 9) exhibited a
conversion close to this value (98%). To the best of our
knowledge, this is the first time that water-soluble Ru
complexes have been described as versatile catalytic precursors
for both the transfer hydrogenation of ketones and the
oxidation of alcohols in aqueous media, despite the fact that
specific precursors are known for each of these catalytic
processes.
Reactions with shorter times (1 h, 0.5 h) and higher
substrate/catalyst ratios (104) were also performed. The tests
enabled better comparisons to be made. It was concluded that
[2][BF4] and [3][BF4] were more active than [1][BF4] and
gave TOF values of 9000 and 8400 h−1 (measured at the end of
the reaction). The results for the dimeric species [(p-
cym)RuCl2]2 and [(phoxet)RuCl2]2 were even more satisfac-
tory, giving 100% yields for reaction times of either 1 or 0.5 h
and TOF values as high as 53 000 h−1 for shorter reaction times
on using a substrate/catalyst ratio of 104 (entries 6 and 10). It is
noteworthy that yields of about 90% were achieved in times as
short as 10 min. One relevant result obtained in this work is
that these easily made dimeric species are very active without
the need for a specific additional ligand.
1000
1300
8400
8400
a
Conditions: reactions carried out at room temperature, pH 7,
oxidant/S/cat = 4000/1000/1 or 40 000/10 000/1, 1 μmol of cat., 5
mL of H2O. The yield was determined by 1H NMR and GC for every
experiment. Caution: gas formation and high pressures were observed
for those experiments with oxidant/S/cat. = 40 000/10 000/1, which
were carried out using 5 mL of H2O.
Finally, the reaction was tested using H2O2 as the oxidant
and [2][BF4] as the catalytic precursor, but in this case the
conversion was zero, showing that H2O2 is not an appropriate
oxidant with our systems (see entry 24, Table 8). Additional
experiments are ongoing in our laboratory to extend the
reaction scope to other alcohols.
CONCLUSIONS
■
A new family of organometallic Ru(II) arene (benzene, p-
cymene, 2-phenoxy-1-ethanol) complexes with the commercial
ligand 4,4′-dimethoxy-2,2′-bipyridine (dmobpy) were synthe-
sized. Most of these compounds are water-soluble, due to a
combination of their cationic nature and the presence of −OMe
groups in the ligand. It was found that the arene and the
counteranion have an influence on the solubility values. The
complexes were active as catalysts in aqueous media, in both
the transfer hydrogenation of water-soluble and -insoluble
ketones to the corresponding alcohols (with HCOONa as the
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Organometallics
Article
spectra were recorded on a Nicolet Impact 410 spectrophotometer
(4000−400 cm−1 range) as KBr pellets and on a Jasco FT/IR-6300
spectrophotometer (630−150 cm−1 range) as Nujol mulls deposited
on a polyethylene film. FAB mass spectra (position of the peaks in Da)
were recorded with an Autospec spectrometer. The isotopic
distribution of the heaviest set of peaks matched very closely that
calculated for the formulation of the complex cation in every case.
NMR samples were prepared under a nitrogen atmosphere by
dissolving the suitable amount of compound in 0.5 mL of the
respective oxygen-free deuterated solvent, and the spectra were
recorded at 298 K (unless otherwise stated) on a Varian Unity Inova-
hydrogen source) and the oxidation of alcohols to the
corresponding ketones (using BuOOH as the oxidant). Yields
of 100% were obtained in these reactions. To our knowledge,
this constitutes the first example in which Ru complexes have
shown this versatility in aqueous solution.
t
In the alcohol oxidation process it was demonstrated that the
dimeric species [(p-cym)RuCl2]2 and [(phoxet)RuCl2]2 exhibit
a very high activity (TOF = 53 000 h−1). This is a very
important finding, considering that these compounds are easily
made and the presence of an additional ligand is not necessary.
The most active precatalysts in the transfer hydrogenation
process were the p-cymene derivatives, and among these, the
ones that contained the tosylate anion gave rise to the highest
TOF values. The activity of the catalysts was very dependent on
the pH. A pH value of 4 was found to be the most favorable. In
any case, from the results described here and those from
previous studies, it seems clear that the presence of the
nitrogenated ligand in the Ru precursors is essential for their
catalytic performance in the transfer hydrogenation of ketones.
The activity of a similar precursor containing a bpy ligand
without the methoxy groups was lower, thus showing the
beneficial effect of these groups. Moreover, the Ru−Cl
complexes with dmobpy undergo easy activation (aquation)
in water, meaning that it is not necessary to isolate the
corresponding aqua derivatives to achieve good catalytic
activities.
1
400 (400 MHz for H; 161.9 MHz for 31P; 100.6 MHz for 13C).
Typically, 1D 1H NMR spectra were acquired with 32 scans into 32 k
data points over a spectral width of 16 ppm. 1H and 13C{1H} chemical
shifts were internally referenced to TMS via 1,4-dioxane in D2O (δ
1
3.75 ppm and δ 67.19 ppm, respectively) or via the residual H and
13C signals of the corresponding solvents, CD3OD (δ 3.31 ppm and δ
49.00 ppm) and (CD3)2CO (δ 2.05 ppm and δ 29.84 ppm), according
to the values reported by Fulmer et al.51 Chemical shift values are
reported in ppm and coupling constants (J) in Hertz. The splitting of
1
proton resonances in the reported H NMR data is defined as s =
singlet, d = doublet, t = triplet, st = pseudotriplet, q = quartet, sept =
septet, m = multiplet, and bs = broad singlet. All 31P resonances were
referenced to 85% H3PO4 at 0 ppm. 2D spectra were recorded using
standard pulse−pulse sequences. For COSY spectra, a standard pulse
sequence, an acquisition time of 0.214 s, a pulse width of 10 μs, a
relaxation delay of 1 s, 16 scans, and 512 increments were used. The
NOE difference spectra were recorded with 5000 Hz, an acquisition
time of 3.27 s, a pulse width of 90°, a relaxation delay of 4 s, and an
irradiation power of 5−10 dB. The probe temperature ( 1 K) was
controlled by a standard unit calibrated with a methanol reference. All
NMR data processing was carried out using MestReNova version
6.1.1.
pH Measurement. The pH values of NMR samples in D2O were
measured at room temperature before and after recording the NMR
spectra, using a Metrohm 16 DMS Titrino pH meter fitted out with a
combined glass electrode and a 3 M KCl solution as a liquid junction,
which was calibrated with Radiometer Analytical SAS buffer solutions
at pH 1.679, 2.000, 4.005, 6.865, 7.000, and 7.413. No correction was
applied for the effect of deuterium on the glass electrode.
A number of 1H NMR experiments allowed the detection of
several intermediates in the transfer hydrogenation process,
including formate and hydride species. Furthermore, the
reversible formation of hydroxo derivatives in alkaline media
and their inertness to substitution reactions was also observed.
On the basis of all these results, a catalytic mechanism was
formulated.
It has been demonstrated that the hydride species is quickly
deuterated in a reversible way in the presence of D2O and
formic acid, forming a transient dihydrogen Ru(X2) (X = H, D)
intermediate. This deuteration is faster than the hydrogenation
process on benzophenone and allows the selective deuteration
of phenylethanol at the benzylic carbon. This process opens up
new possibilities for the selective deuteration of different
unsaturated organic substrates.
X-ray Crystallography. A summary of crystal data collection and
refinement parameters for all compounds is given in the Supporting
Information.
Single crystals of [1]Cl, [1]TsO, [2]TsO, [2][BF4], and [2][PF6]
were obtained by liquid−liquid diffusion or evaporation experiments
from the following solvent systems: methanol/diethyl ether ([1]Cl),
H2O ([1]TsO·H2O), methanol/diethyl ether ([2]TsO), methanol
([2][BF4]), and acetone ([2][PF6]) respectively. The single crystals
were mounted on a glass fiber and transferred to a Bruker X8 APEX II
CCD-based diffractometer equipped with a graphite-monochromated
Mo Kα radiation source (λ = 0.710 73 Å). The highly redundant data
sets were integrated using SAINT52 and corrected for Lorentz and
polarization effects. The absorption correction was based on fitting a
function to the empirical transmission surface as sampled by multiple
equivalent measurements with the program SADABS.53
EXPERIMENTAL SECTION
■
General Methods and Starting Materials. Starting Materials.
RuCl3·xH2O was purchased from Apollo Scientific Ltd. and used as
received. [(η6-C6H6)RuCl2(CH3CN)]34 or [(η6-arene)Ru(μ-Cl)Cl]2
(arene = benzene, p-cymene,35 phenoxyethanol31), were prepared
according to literature procedures. AgBF4, AgTsO, AgPF6, and the
ligand 4,4′-dimethoxy-2,2′-bipyridine (dmobpy) were purchased from
Aldrich and used without further purification. Ketones and alcohols
were purchased from Aldrich. Deuterated solvents were obtained from
SDS and Euriso-top. The aqueous solutions were prepared with
doubly deionized water from a Millipore Q apparatus (APS; Los
Angeles, CA).
The software package SHELXTL version 6.1054 was used for space
group determination, structure solution, and refinement by full-matrix
least-squares methods based on F2. A successful solution by direct
methods provided most non-hydrogen atoms from the E map. The
remaining non-hydrogen atoms were located in an alternating series of
least-squares cycles and difference Fourier maps. All non-hydrogen
atoms were refined with anisotropic displacement coefficients unless
specified otherwise. Hydrogen atoms were placed using a “riding
model” and included in the refinement at calculated positions. For the
molar conductimetry measurements, the ΛM values are given in S cm2
mol−1 and were obtained at room temperature for 10−3 M solutions of
the corresponding complexes in CH3CN, using a CRISON 522
conductimeter equipped with a CRISON 5292 platinum conductivity
cell.
General Methods. All synthetic manipulations were carried out
under an atmosphere of dry, oxygen-free nitrogen using standard
Schlenk techniques. Solvents were distilled from the appropriate
drying agents and degassed before use. Elemental analyses were
performed with a Perkin-Elmer 2400 CHN microanalyzer. The
analytical data for the new complexes were obtained from crystalline
samples when possible. In some cases the data were totally accurate,
but in others the agreement of calculated and found values for carbon
was >0.4%, so that solvent molecules were introduced in the molecular
formulas to improve agreement. In any case, all the complexes were
obtained in enough analytic purity to be used as starting materials. IR
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Article
Synthesis of Complexes. [(η6-benzene)RuCl(dmobpy)]Cl ([1]Cl).
In a 100 mL Schlenk flask, dmobpy (74.2 mg, 0.343 mmol) was added
under a nitrogen atmosphere to a suspension of [(η6-bz)-
RuCl2(CH3CN)] (100 mg, 0.343 mmol) in degassed methanol (20
mL). The mixture was stirred at room temperature for 40 h. The
solvent was then removed under vacuum, and the residue was washed
with n-hexane and dried under vacuum to produce a yellow solid.
Yield: 0.136 g (0.29 mmol, 85%). Mr (C18H18N2O2Cl2Ru) = 466.3278
g/mol. Anal. Calcd for C18H18N2O2Cl2Ru·2.5H21O: C, 42.28; H, 5.53;
N, 5.48. Found: C, 42.51; H, 4.125; N, 5.833. H NMR (400 MHz,
CD3OD): δ 9.27 (d, J = 6.6 Hz, 2H, H6′), 8.05 (d, J = 2.8 Hz, 2H,
H3′), 7.29 (dd, J = 6.6, 2.8 Hz, 2H, H5′), 6.07 (s, 6H, H-bz), 4.09 (s,
6H, HOMe) ppm. 13C{1H} NMR (101 MHz, CD3OD): δ 170.09 (s,
2C, C4′), 158.04 (s, 2C, C2′), 157.40 (s, 2C, C6′-dmobpy), 114.77 (s,
2C, C5′), 111.28 (s, 2C, C3′), 87.77 (s, 6C, C-bz), 57.53 (s, 2C, -OMe)
OTs), 7.28 (dd, J = 6.6, 2.8 Hz, 2H, H5′), 7.22 (m, 2H, Hc-OTs), 6.06
(s, 6H, H-bz) 4.08 (s, 6H, HOMe), 2.36 (s, 3H, He-OTs) ppm. 13C{1H}
NMR (101 MHz, CD3OD) 170.06 (s, 2C, C4′), 158.02 (s, 2C, C2′),
157.41 (s, 2C, C6′), 143.65 (s, 1C, Ca-TsO−), 141.61 (s, 1C, Cd-
TsO−), 129.79 (s, 2C, Cc-TsO−), 126.97 (s, 2C, Cb-TsO−), 114.77 (s,
2C, C5′), 111.27 (s, 2C, C3′), 87.77 (s, 6C, C-bz), 57.53 (s, 2C,
−OMe), 21.30 (s, 1C, Ce-TsO−) ppm. FT-IR (KBr, cm−1; selected
bands): 3078 (m, νCH,sp ), 2991 (w, νCH,sp ), 1620 (s, νCC+CN), 1615
(s, νCC+CN), 1559 (m), 1495 (s, νCC+CN), 1440 (s, νCC+CN),
1343 (m), 1268 (m), 1253 (s), 1232 (s, νas,OMe), 1216 (vs, νas,SO),
1195 (vs, νas,SO), 1121 (m), 1049 (s, νs,OMe), 1032 (s, TsO−), 1011
(s, TsO−), 856 (m), 840 (m), 819 (m, TsO−), 682 (s, TsO−), 569 (s,
TsO−). FT-FIR (Nujol, cm−1; selected bands): 376 (w), 305 (w), 281
(m), 249 (w). MS (FAB+, CH3OH): m/z (%) 431 (47) ([M −
TsO]+). Molar conductivity (CH3CN): 107 S cm2 mol−1. Solubility:
soluble in water, methanol, and acetonitrile and poorly soluble in
acetone, ethanol, and dichloromethane.
2
3
ppm. FT-IR (KBr, cm−1; selected bands): 3065 (m, νCH,sp ), 3031 (m),
2
1620 (s, νCC+CN), 1615 (s, νCC+CN), 1558 (m), 1497 (s,
νCC+CN), 1435 (s, νCC+CN), 1339 (m), 1316 (m), 1270 (s), 1255
(s), 1232 (s, νas,OMe), 1047 (s, νs,OMe), 1029 (s), 1004 (m), 886 (w),
842 (m), 629 (w), 587 (w). FT-FIR (Nujol, cm−1; selected bands):
379 (w), 303 (w), 278 (w), 254 (w). MS (FAB+, CH3OH): m/z (%)
431 (17) ([M − Cl]+). Molar conductivity (CH3CN): 120 S cm2
mol−1. Solubility: soluble in water, methanol, ethanol, and acetonitrile
and slightly soluble in acetone and dichloromethane.
[(η6-benzene)RuCl(dmobpy)]PF6 ([1][PF6]). In a 100 mL Schlenk
flask protected from light, [(η6-bz)RuCl2(CH3CN)] (100 mg, 0.343
mmol) was dissolved in a degassed methanol/acetonitrile mixture (10
mL/10 mL), under a nitrogen atmosphere. Then, AgPF6 (86.7 mg,
0.343 mmol) was added, and the suspension was stirred for 2 h in the
dark, at room temperature. The precipitate of AgCl was removed by
filtration, and the resulting solution was treated with dmobpy (74.2
mg, 0.343 mmol) and stirred overnight at room temperature. Then,
the solvents were removed under vacuum. The solid residue was
washed with diethyl ether (10 mL) and dried under vacuum to
produce a yellow solid. Yield: 0.160 g (0.28 mmol, 81%). Mr
(C18H18N2O2ClRuPF6) = 575.843 g/mol. Anal. Calcd for
C18H18N2O2ClRuPF6: C, 37.55; H, 3.15; N, 4.86. Found: C, 37.50;
H, 3.28; N, 5.04. 1H NMR (400 MHz, CD3OD): δ 9.27 (d, J = 6.6 Hz,
2H, H6′), 8.05 (d, J = 2.7 Hz, 2H, H3′), 7.29 (dd, J = 6.6, 2.7 Hz, 2H,
H5′), 6.07 (s, 6H, bz), 4.08 (s, 6H, HOMe) ppm. 1H NMR (400 MHz,
CD3COCD3): δ 9.42 (d, J = 6.6 Hz, 2H, H6′-dmobpy), 8.16 (d, J = 2.8
Hz, 2H, H3′-dmobpy), 7.32 (dd, J = 6.6, 2.8 Hz, 2H, H5′-dmobpy),
6.20 (s, 6H, bz), 4.12 (s, 6H, HOMe-dmobpy) ppm. 13C{1H} NMR
(101 MHz, CD3COCD3) 169.26 (s, 2C, C4′), 157.41 (s, 2C, C2′),
157.31 (s, 2C, C6′), 114.35 (s, 2C, C5′), 110.94 (s, 2C, C3′), 87.47 (s,
6C, C-bz), 57.51 (s, 2C, −OMe) ppm. 31P{1H} NMR (162 MHz,
[(η6-benzene)RuCl(dmobpy)]BF4 ([1][BF4]). In a 100 mL Schlenk
flask protected from light, [(η6-bz)RuCl2(CH3CN)] (100 mg, 0.343
mmol) was dissolved in a degassed methanol/acetonitrile mixture (9
mL/9 mL), under a nitrogen atmosphere. Then, AgBF4 (66.8 mg,
0.343 mmol) was added, and the suspension was stirred overnight in
the dark at room temperature. Solid AgCl was removed by filtration,
and the resulting solution was treated with dmobpy (74.2 mg, 0.343
mmol) and stirred overnight at room temperature. Then, the volume
of the solution was reduced under vacuum to just 2 mL to precipitate a
yellow solid that was collected by filtration and dried under vacuum.
Yield: 0.125 g (0.24 mmol, 70.4%). Mr (C18H18N2O2ClRuBF4) =
517.6698 g/mol. Anal. Calcd for C18H18N2O2ClRuBF4·0.5H2O: C,
41.05; H, 3.64; N, 5.32. Found: C, 40.89; H, 3.664; N, 5.724. 1H NMR
(400 MHz, CD3OD): δ 9.27 (d, J = 6.6 Hz, 2H, H6′), 8.05 (d, J = 2.8
Hz, 2H, H3′), 7.28 (dd, J = 6.6, 2.8 Hz, 2H, H5′), 6.07 (s, 6H, H-bz),
4.09 (s, 6H, HOMe) ppm. 13C{1H} NMR (101 MHz, CD3OD): δ
169.75 (s, 2C, C4′), 157.84 (s, 2C, C2′), 157.61 (s, 2C, C6′), 114.77 (s,
2C, C5′), 111.43 (s, 2C, C3′), 87.71 (s, 6C, C-bz), 57.84 (s, 2C,
−OMe) ppm. 19F NMR (376 MHz, CD3OD): δ −155.35 (s, 10B−F,
−
CD3COCD3): δ −143.17 (sept, J = 708 Hz, 1P, PF6 ) ppm. 19F NMR
−
(376 MHz, CD3COCD3): δ −72.99 (d, J = 708 Hz, 6F, PF6 ) ppm.
FT-IR (KBr, cm−1; selected bands): 3096 (m, νCH,sp ), 3041 (m), 2948
2
3
(m, νCH,sp ), 1619 (s, νCC+CN), 1561 (m), 1495 (s, νCC+CN),
−
−
BF4 ), −155.40 (s, 11B−F, BF4 ) ppm. Integration ratio (1/4) in
1471 (m), 1441 (s, νCC+CN), 1342 (m), 1315 (m), 1289 (m), 1270
(s), 1254 (s), 1234 (s, νas,OMe), 1048 (s, νs,OMe), 1031 (s), 1006 (w),
841 (vs, νP−F), 741 (w), 558 (s, δF−B−F). FT-FIR (Nujol, cm−1;
selected bands): 374 (w), 307 (w), 280 (m), 248 (w). MS (FAB+,
CH3OH): m/z (%) 431 (32) ([M − PF6]+). Molar conductivity
(CH3CN): 140 S cm2 mol−1. Solubility: soluble in acetone and
acetonitrile and partially soluble in methanol, ethanol, and dichloro-
methane.
agreement with the isotopic distribution for 10B/11B (20/80). FT-IR
(KBr, cm−1; selected bands): 3089 (w, νCH,sp ), 3032 (w), 1620 (s,
2
νCC+CN), 1616 (s, νCC+CN), 1559 (m), 1495 (s, νCC+CN),
1440 (s, νCC+CN), 1343 (m), 1314 (m), 1268 (s), 1253 (s), 1235 (s,
νas,OMe), 1062 (s, νd,BF), 1048 (s, νs,OMe), 1032 (s), 1006 (m), 894 (w),
841 (m), 629 (w), 588 (w), 522 (m, δBF). FT-FIR (Nujol, cm−1;
selected bands): 374 (w), 308 (w), 280 (m), 250 (w). MS (FAB+,
CH3OH): m/z (%) 431 (10) ([M − BF4]+). Molar conductivity
(CH3CN): 126 S cm2 mol−1. Solubility: soluble in water, ethanol,
acetonitrile, and dichloromethane and slightly soluble in acetone and
methanol.
[(η6-p-cymene)RuCl(dmobpy)]Cl ([2]Cl). In a 100 mL Schlenk flask,
dmobpy (70.5 mg, 0.326 mmol) was added under a nitrogen
atmosphere to a solution of [(η6-p-cymene)RuCl2]2 (100 mg, 0.163
mmol) in degassed ethanol (30 mL). The mixture was stirred
overnight at room temperature. The solvent was removed under
vacuum, and the solid residue was washed with n-hexane (2 × 5 mL)
and dried under vacuum, to produce a yellow solid. Yield: 152.5 mg
(0.3 mmol, 89.4%). Mr (C22H26N2O2 Cl2Ru) = 522.435 g/mol. Anal.
Calcd for C22H26N2O2Cl2Ru·2H2O: C, 47.32; H, 5.41; N, 5.02. Found:
C, 47.37; H, 4.91; N, 5.04. 1H NMR (400 MHz, CD3OD): δ 9.19 (d, J
= 6.6 Hz, 2H, H6′), 8.06 (d, J = 2.8 Hz, 2H, H3′), 7.30 (dd, J = 6.6, 2.8
Hz, 2H, H5′), 6.02 (d, J = 6.4 Hz, 2H, H2,6-cym), 5.76 (d, J = 6.4 Hz,
2H, H3,5-cym), 4.09 (s, 6H, HOMe), 2.62 (sept, J = 6.9 Hz, 1H, H7-
cym), 2.26 (s, 3H, H10-cym), 1.06 (d, J = 6.9 Hz, 6H, H8,9-cym) ppm.
13C{1H} NMR (101 MHz, CD3OD): δ 170.03 (s, 2C, C4′), 157.82 (s,
2C, C2′), 157.30 (s, 2C, C6′), 114.97 (s, 2C, C5′), 111.28 (s, 2C, C3′),
105.05 (s, 1C, C1-cym), 104.81 (s, 1C, C4-cym), 87.53 (s, 2C, C2,6-
cym), 84.64 (s, 2C, C3,5-cym), 57.54 (s, 2C, COMe), 32.33 (s, 1C, C7-
cym), 22.31 (s, 2C, C8,9-cym), 18.98 (s, 1C, C10-cym) ppm. FT-IR
[(η6-benzene)RuCl(dmobpy)]OTs ([1]OTs). In a 100 mL Schlenk
flask protected from light, [(η6-bz)RuCl2(CH3CN)] (100 mg, 0.343
mmol) was dissolved in a degassed methanol/acetonitrile mixture (9
mL/9 mL), under a nitrogen atmosphere. Then, AgOTs (95.7 mg,
0.343 mmol) was added, and the suspension was stirred for 2 h in the
dark, at room temperature. The precipitate of AgCl was removed by
filtration, and the resulting solution was treated with dmobpy (74.2
mg, 0.343 mmol) and stirred overnight at room temperature. Then,
the solvents were removed under vacuum. The solid residue was
washed with diethyl ether (10 mL) and dried under vacuum to
produce a yellow solid. Yield: 0.160 g (0.27 mmol, 77.5%). Mr
(C25H25N2O5ClSRu) = 602.0706 g/mol. Anal. Calcd for
C25H25N2O5ClSRu·1.5H2O: C, 47.73; H, 4.49; N, 4.45. Found: C,
47.85; H, 4.349; N, 5.021. 1H NMR (400 MHz, CD3OD): δ 9.27 (d, J
= 6.6 Hz, 2H, H6′), 8.04 (d, J = 2.8 Hz, 2H, H3′), 7.70 (m, 2H, Hb-
6119
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Organometallics
Article
(KBr, cm−1; selected bands): 3027 (w, νCH,sp ), 2971 (w, νCH,sp ), 1614
(vs, νCC+CN), 1558 (m), 1496 (s, νCC+CN), 1422 (s), 1346 (m),
1317 (w), 1281 (s), 1255 (w), 1231 (s, νas,OMe), 1046 (s, νs,OMe), 1031
(m), 1017 (m), 864 (w), 840 (m). FT-FIR (Nujol, cm−1; selected
bands): 381 (w), 303 (w), 279 (m), 250 (w). MS (FAB+, CH3OH):
m/z (%) 487 (100) ([M − Cl]+); 353 (25) ([M − Cl − cym]+).
Molar conductivity (CH3CN): 109 S cm2 mol−1. Solubility: soluble in
water, methanol, ethanol, dichloromethane, and acetonitrile and
poorly soluble in acetone.
1421 (m), 1343 (m), 1283 (s), 1255 (w), 1231 (s, νas,OMe), 1214 (vs,
νas,SO), 1196 (vs, νas,SO), 1121 (m), 1048 (s, νs,OMe), 1033 (s,
TsO−), 1011 (s, TsO−), 864 (w), 841 (m), 819 (m, TsO−), 682 (s,
TsO−), 568 (s, TsO−). FT-FIR (Nujol, cm−1; selected bands): 368
(w), 303 (w), 289 (m), 253 (w). MS (FAB+, CH3OH): m/z (%) 487
(100) ([M − TsO]+); 353 (19) ([M − TsO − cym]+). Molar
conductivity (CH3CN): 121 S cm2 mol−1. Solubility: soluble in
methanol and acetonitrile and poorly soluble in water, acetone,
ethanol, and dichloromethane.
2
3
Synthesis of [(η6-p-cymene)RuCl(dmobpy)]BF4 ([2][BF4]). In a 100
mL Schlenk flask protected from light, AgBF4 (63.5 mg, 0.326 mmol)
was added under a nitrogen atmosphere to a solution of [(η6-p-
cymene)RuCl2]2 (100 mg, 0.163 mmol) in degassed ethanol (30 mL).
The mixture was stirred for 2 h in the dark, at room temperature. The
precipitate of AgCl was removed by filtration. Then, the ligand
dmobpy (70.5 mg, 0.326 mmol) was added and the mixture was
stirred overnight at room temperature. The volume of the resulting
solution was reduced under vacuum to 10 mL, and n-hexane (40 mL)
was added to fully precipitate a yellow solid, which was collected by
filtration and dried under vacuum. Yield: 140 mg (0.24 mmol, 76%).
Mr (C22H26N2O2ClBF4Ru) = 573.777 g/mol. Anal. Calcd for
C22H26N2O2ClBF4Ru: C, 46.05; H, 4.57; N, 4.88. Found: C, 46.34;
H, 4.51; N, 4.48. 1H NMR (400 MHz, CD3OD): δ 9.18 (d, J = 6.6 Hz,
2H, H6′), 8.06 (d, J = 2.8 Hz, 2H, H3′), 7.29 (dd, J = 6.6, 2.8 Hz, 2H,
H5′), 6.02 (d, J = 6.4 Hz, 2H, H2,6), 5.75 (d, J = 6.4 Hz, 2H, H3,5), 4.09
(s, 6H, HOMe), 2.62 (sept, J = 6.9 Hz, 1H, H7), 2.26 (s, 3H, H10), 1.06
(d, J = 6.9 Hz, 6H, H8,9) ppm. 13C{1H} NMR (101 MHz, CD3OD): δ
170.02 (s, 2C, C4′), 157.81 (s, 2C, C2′), 157.29 (s, 2C, C6′), 115.00 (s,
2C, C5′), 111.25 (s, 2C, C3′), 105.03 (s, 1C, C1-cym), 104.82 (s, 1C,
C4-cym), 87.53 (s, 2C, C2,6-cym), 84.64 (s, 2C, C3,5-cym), 57.53 (s,
2C, COMe), 32.33 (s, 1C, C7-cym), 22.31 (s, 2C, C8,9-cym), 18.98 (s,
1C, C10-cym) ppm. 19F NMR (376 MHz, CD3OD): δ −155.35 (s,
[(η6-p-cymene)RuCl(dmobpy)]PF6 ([2][PF6]). In a 100 mL Schlenk
flask protected from light, AgPF6 (82.6 mg, 0.326 mmol) was added
under a nitrogen atmosphere to a solution of [(η6-p-cymene)RuCl2]2
(100 mg, 0.163 mmol) in degassed methanol (20 mL). The mixture
was stirred for 2 h in the dark at room temperature. The precipitate of
AgCl was removed by filtration. Then, the ligand dmobpy (70.5 mg,
0.326 mmol) was added and the mixture was stirred overnight at room
temperature. The resulting solution was concentrated under vacuum
to a final volume of 10 mL, and diethyl ether was added (30 mL) to
precipitate a yellow solid, which was collected by filtration and dried
under vacuum. Yield: 113.5 mg (0.18 mmol, 55.0%). Mr
(C22H26N2O2ClPF6Ru) = 631.9366 g/mol. Anal. Calcd for
C22H26N2O2ClPF6Ru: C, 41.81; H, 4.15; N, 4.43. Found: C, 41.92;
H, 4.28; N, 4.45. 1H NMR (400 MHz, CD3OD): δ 9.18 (d, J = 6.6 Hz,
2H, H6′), 8.06 (d, J = 2.8 Hz, 2H, H3′), 7.30 (dd, J = 6.6 Hz, 2.8 Hz,
2H, H5′), 6.02 (d, J = 6.4 Hz, 2H, H2,6), 5.75 (d, J = 6.4 Hz, 2H, H3,5),
4.09 (s, 6H, -OMe), 2.60 (sept, J = 6.9 Hz, 1H, H7), 2.26 (s, 3H, H10),
1.06 (d, J = 6.9 Hz, 6H, H8,9) ppm. 1H NMR (400 MHz,
CD3COCD3): δ 9.32 (d, J = 6.6 Hz, 2H, H6′), 8.14 (d, J = 2.8 Hz,
2H, H3′), 7.32 (dd, J = 6.6 Hz, 2.8 Hz, 2H, H5′), 6.14 (d, J = 6.4 Hz,
2H, H2,6), 5.88 (d, J = 6.3 Hz, 2H, H3,5), 4.12 (s, 6H, -OMe), 2.75
(sept, J = 6.9 Hz, 1H, H7), 2.28 (s, 3H, H10), 1.10 (d, J = 6.9 Hz, 6H,
H8,9) ppm. 13C NMR (101 MHz, CD3COCD3): δ 169.21 (s, 2C, C4′),
157.25 (s, 2C, C2′), 157.14 (s, 2C, C6′), 114.58 (s, 2C, C5′), 110.92 (s,
2C, C3′), 104.81 (s, 1C, C1), 104.06 (s, 1C, C4), 86.95 (s, 2C, C2,6),
84.39 (s, 2C, C3,5), 57.46 (s, 2C, −OMe), 31.82 (s, 1C, C7), 22.30 (s,
2C, C8,9), 18.89 (s, 1C, C10) ppm. 31P{1H} NMR (162 MHz,
−
−
10B−F, BF4 ), −155.40 (s, 11B−F, BF4 ) ppm. Integration ratio (1/4)
in agreement with the isotopic distribution for 10B/11B (20/80). FT-IR
(KBr, cm−1; selected bands): 3076 (w, νCH,sp ), 2963 (w, νCH,sp ), 1615
(vs, νCC+CN), 1558 (m), 1497 (s, νCC+CN), 1479 (m), 1423 (m),
1346 (m), 1281 (s), 1255 (w), 1229 (s, νas,OMe), 1083 (s), 1065 (s,
νd, BF), 1046 (s, νs,OMe), 1032 (m), 1017 (m), 864 (w), 839 (m), 522
(w, δBF). FT-FIR (Nujol, cm−1; selected bands): 303 (w), 282 (m),
252 (w). MS (FAB+, CH3OH): m/z (%) 487 (100) ([M − BF4]+);
353 (31) ([M − BF4 − cym]+). Molar conductivity (CH3CN): 143 S
cm2 mol−1. Solubility: soluble in methanol and acetonitrile and poorly
soluble in water, acetone, ethanol, and dichloromethane.
2
3
−
CD3COCD3): δ −143.15 (sept, J = 708 Hz, 1P, PF6 ) ppm. 19F NMR
−
(376 MHz, CD3COCD3): δ −72.99 (d, J = 708 Hz, 6F, PF6 ) ppm.
FT-IR (KBr, cm−1; selected bands): 3087 (w, νCH,sp ), 2971 (w,
2
3
νCH,sp ), 2932 (w), 1620 (vs, νCC+CN), 1614 (vs, νCC+CN), 1561
(m), 1495 (s, νCC+CN), 1475 (s), 1421 (s), 1340 (m), 1314 (w),
1281 (s), 1254 (w), 1230 (s, νas,OMe), 1047 (s, νs,OMe), 1031 (m), 879
(m), 841 (vs, νP−F), 558 (s, δF−B−F). FT-FIR (Nujol, cm−1; selected
bands): 375 (w), 290 (m), 248 (w). MS (FAB+, CH3OH): m/z (%)
487 (43) ([M − PF6]+). Molar conductivity (CH3CN): 127 S cm2
mol−1. Solubility: soluble in acetone, partially soluble in methanol,
ethanol, and dichloromethane, and poorly soluble in water.
[(η6-p-cymene)RuCl(dmobpy)]OTs ([2]OTs). In a 100 mL Schlenk
flask protected from light, AgOTs (91.0 mg, 0.326 mmol) was added
under a nitrogen atmosphere to a solution of [(η6-p-cymene)RuCl2]2
(100 mg, 0.163 mmol) in degassed ethanol (30 mL). The mixture was
stirred for 2 h in the dark at room temperature. The precipitate of
AgCl was removed by filtration. Then, the ligand dmobpy (70.5 mg,
0.326 mmol) was added and the mixture was stirred overnight at room
temperature. The solvent of the resulting solution was removed under
vacuum, and the solid residue was washed with n-hexane (20 mL) and
dried under vacuum to produce a yellow solid. Yield: 140.5 mg (0.21
mmol, 66.6%). Mr (C29H33N2O5ClSRu) = 658.1778 g/mol. Anal.
Calcd for C29H33N2O5ClSRu·H2O: C, 51.51; H, 5.22; N, 4.14. Found:
C, 51.51; H, 5.63; N, 4.01. 1H NMR (400 MHz, CD3OD): δ 9.18 (d, J
= 6.6 Hz, 2H, H6′), 8.05 (d, J = 2.8 Hz, 2H, H3′), 7.71 (m, 2H, Hb-
OTs), 7.29 (dd, J = 6.6, 2.8 Hz, 2H, H5′), 7.23 (m, 2H, Hc-OTs), 6.02
(d, J = 6.4 Hz, 2H, H2,6-cym), 5.75 (d, J = 6.4 Hz, 2H, H3,5-cym), 4.08
(s, 6H, HOMe), 2.61 (sept, J = 6.9 Hz, 1H, H7-cym), 2.37 (s, 3H, He-
OTs), 2.25 (s, 3H, H10-cym), 1.05 (d, J = 6.9 Hz, 6H, H8,9-cym) ppm.
13C{1H} NMR (101 MHz, CD3OD): δ 169.99 (s, 2C, C4′), 157.79 (s,
2C, C2′), 157.33 (s, 2C, C6′), 143.67 (s, 1C, Ca-OTs), 141.62 (s, 1C,
Cd-OTs), 129.81 (s, 2C, Cc-OTs), 126.98 (s, 2C, Cb-OTs), 114.99 (s,
2C, C5′), 111.26 (s, 2C, C3′), 105.02 (s, 1C, C4-cym), 104.79 (s, 1C,
C1-cym), 87.53 (s, 2C, C2,6-cym), 84.63 (s, 2C, C3,5-cym), 57.55 (s,
2C, COMe), 49.00, 32.32 (s, 1C, C7-cym), 22.32 (s, 2C, C8,9-cym),
21.30 (s, 1C, Ce-OTs), 18.99(s, 1C, C10-cym) ppm. FT-IR (KBr,
[(η6-phoxet)RuCl(dmobpy)]Cl ([3]Cl). In a 100 mL Schlenk flask
under a nitrogen atmosphere, [(η6-phoxet)RuCl2]2 (90 mg, 0.145
mmol) was dissolved in degassed isopropyl alcohol (6 mL). The ligand
dmobpy (62.7 mg, 0.29 mmol) was added, and the mixture was
refluxed at 80 °C for 1 h. The resulting solution was concentrated to 2
mL under vacuum; the solid was collected by filtration and dried under
vacuum to produce a dark yellow solid. Yield: 0.1242 g (0.24 mmol,
81.4%). Mr (C20H22N2O4Cl2Ru) = 526.3802 g/mol. Anal. Calcd for
C20H22N2O4Cl2Ru·0.5H2O: C, 44.87; H, 4.33; N, 5.23. Found: C,
44.76; H, 4.373; N, 5.117. 1H NMR (400 MHz, CD3OD): δ 9.19 (d, J
= 6.6 Hz, 2H, H6′), 8.04(d, J = 2.8 Hz, 2H, H3′), 7.29 (dd, J = 6.6, 2.8
Hz, 2H, H5′), 6.27 (dd, J = 6.7, 5.5 Hz, 2H, H3-phoxet), 5.64 (d, J =
6.7 Hz, 2H, H2-phoxet), 5.50 (t, J = 5.5 Hz, 1H, H4-phoxet), 4.13(m,
2H, H5-phoxet), 4.08 (s, 6H, HOMe), 3.86 (m, 2H, H6-phoxet) ppm.
13C{1H} NMR (101 MHz, CD3OD): δ 169.96 (s, 2C, C4′), 158.04 (s,
2C, C2′), 156.93 (s, 2C, C6′), 139.56 (s, 1C, C1-phoxet), 114.71 (s,
2C, C5′), 111.12 (s, 2C, C3′), 95.48 (s, 2C, C2-phoxet), 73.92 (s, 1C,
C4-phoxet), 72.92 (s, 1C, C5-phoxet), 65.78 (s, 2C, C3-phoxet), 60.89
(s, 1C, C6-phoxet), 57.49 (s, 2C, −OMe) ppm. FT-IR (KBr, cm−1;
2
3
selected bands): 3182 (w), 3064 (w, νCH,sp ), 2924 (w, νCH,sp ), 1614
(vs, νCC+CN), 1558 (m), 1530 (s, phoxet), 1496 (s, νCC+CN),
1469 (m), 1425 (m), 1351 (m), 1281 (vs), 1235 (s, νas,OMe), 1048 (s,
νs,OMe), 1030 (m), 1019 (m), 864 (m), 839 (m), 665 (m, phoxet). FT-
cm−1; selected bands): 3068 (w, νCH,sp ), 2967 (w, νCH,sp ), 1615 (vs,
νCC+CN), 1558 (m), 1496 (s, νCC+CN), 1472 (m), 1441 (m),
2
3
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FIR (Nujol, cm−1; selected bands): 374 (w), 303 (w), 274 (m), 247
(w). MS (FAB+, CH3OH): m/z (%) 491 (12) ([M − Cl]+). Molar
conductivity (H2O): 158 S cm2 mol−1. Solubility: soluble in water and
methanol and poorly soluble in acetone, ethanol, dichloromethane,
and acetonitrile.
[(η6-phoxet)RuCl(dmobpy)]PF6 ([3][PF6]). In a 100 mL Schlenk
flask protected from light, AgPF6 (38.4 mg, 0.152 mmol) was added
under a nitrogen atmosphere to a solution of [(η6-phoxet)RuCl-
(dmobpy)]Cl (80 mg, 0.152 mmol) in distilled and degassed water (5
mL). The mixture was stirred overnight in the dark, at room
temperature. The precipitate of AgCl was removed by filtration. The
solid residue was extracted with acetone, and both the organic and
aqueous solutions were combined and evaporated to dryness under
vacuum. The resulting solid was washed with n-hexane (2 × 5 mL)
and dried under vacuum to produce a yellow solid. Yield: 0.0421 g
(0.066 mmol, 43.6%). Yield: 0.0421 g (0.066 mmol, 44.5%). Mr
(C20H22N2O4ClPF6Ru) = 635.896 g/mol. Anal. Calcd for
C20H22N2O4ClPF6Ru: C, 37.78; H, 3.49; N, 4.41. Found: C, 37.45;
H, 3.19; N, 4.93. 1H NMR (400 MHz, CD3COCD3): δ 9.32 (d, J = 6.6
Hz, 2H, H6′), 8.12 (d, J = 2.6 Hz, 2H, H3′), 7.33 (dd, J = 6.6, 2.6 Hz,
2H, H5′), 6.41 (dd, J = 6.7, 5.5 Hz, 2H, H3-phoxet), 5.73 (d, J = 6.7
Hz, 2H, H2-phoxet), 5.62 (t, J = 5.5 Hz, 1H, H4-phoxet), 4.27 (m, 2H,
H5-phoxet), 4.11 (s, 6H, HOMe-dmobpy), 3.88 (m, 2H, H6-phoxet)
ppm. 13C{1H} NMR (101 MHz, CD3COCD3): δ 169.15 (s, 2C, C4′),
157.43 (s, 2C, C2′), 156.78 (s, 2C, C6′), 139.43 (s, 1C, C1-phoxet),
114.29 (s, 2C, C5′), 110.77 (s, 2C, C3′), 95.01 (s, 1C, C2-phoxet),
73.71 (s, 1C, C4-phoxet), 72.81 (s, 1C, C5-phoxet), 65.45 (s, 1C, C3-
phoxet), 60.75 (s, 1C, C6-phoxet), 57.43 (s, 2C, −OMe) ppm.
31P{1H} NMR (162 MHz, acetone): δ −143.17 (sept, J = 708 Hz, 1P,
General Procedure for the Synthesis of [3][BF4] and [3]TsO.
In a 100 mL Schlenk flask protected from light, the corresponding
silver salt AgX (0.190 mmol) was added under a nitrogen atmosphere
to a solution of [(η6-phoxet)RuCl(dmobpy)]Cl (100 mg, 0.190
mmol) in distilled/degassed water (5 mL). The mixture was stirred
overnight in the dark, at room temperature. The precipitate of AgCl
was removed by filtration, and the resulting solution was evaporated to
dryness under vacuum. The solid residue was washed with diethyl
ether (2 × 5 mL) and dried under vacuum to produce a yellow solid.
[(η6-phoxet)RuCl(dmobpy)]BF4 ([3][BF4]). AgBF4 (37 mg, 0.190
mmol) and [(η6-phoxet)RuCl(dmobpy)]Cl (100 mg, 0.190 mmol).
Yield: 0.0485 g (0.084 mmol, 44.2%). Mr (C20H22N2O4ClBF4Ru) =
577.7222 g/mol. Anal. Calcd for C20H22N2O4ClBF4Ru: C, 41.58; H,
3.84; N, 4.85. Found: C, 41.57; H, 4.37; N, 4.89. 1H NMR (400 MHz,
CD3OD): δ 9.19 (d, J = 6.6 Hz, 2H, H6′), 8.04 (d, J = 2.7 Hz, 2H,
H3′), 7.28 (dd, J = 6.6, 2.7 Hz, 2H, H5′), 6.27 (dd, J = 6.7, 5.5 Hz, 2H,
H3-phoxet), 5.64 (d, J = 6.7 Hz, 2H, H2-phoxet), 5.49 (t, J = 5.5 Hz,
1H, H4-phoxet), 4.13 (m, 2H, H5-phoxet), 4.08 (s, 6H, HOMe), 3.86
(m, 2H, H6-phoxet) ppm. 13C{1H} NMR (101 MHz, CD3OD): δ
169.95 (s, 2C, C4′), 158.04 (s, 2C, C2′), 156.92 (s, 2C, C6′), 139.55 (s,
1C, C1-phoxet), 114.70 (s, 2C, C5′), 111.12 (s, 2C, C3′), 95.48 (s, 2C,
C2-phoxet), 73.92 (s, 1C, C4-phoxet), 72.91 (s, 1C, C5-phoxet), 65.77
(s, 2C, C3-phoxet), 60.89 (s, 1C, C6-phoxet), 57.49 (s, 2C, −OMe)
−
PF6 ) ppm. 19F NMR (376 MHz, acetone): δ −72.99 (d, J = 708 Hz,
−
6F, PF6 ) ppm. FT-IR (KBr, cm−1; selected bands): 3083 (w, νCH,sp ),
2
3
2948 (w, νCH,sp ), 1621 (vs, νCC+CN), 1561 (m), 1533 (s, phoxet),
1496 (s, νCC+CN), 1471 (m), 1453 (m), 1422 (m), 1343 (m), 1280
(s), 1269 (s), 1255 (s), 1233 (s, νas,OMe), 1050 (s, νs,OMe), 1032 (m),
841 (vs, νP−F), 667 (m, phoxet), 559 (s, δF−B−F). FT-FIR (Nujol,
cm−1; selected bands): 377 (w), 300 (w), 280 (m), 276 (m), 251 (w).
MS (FAB+, CH3COCH3): m/z (%) 491 (18) ([M − PF6]+). Molar
conductivity (CH3CN): 141 S cm2 mol−1. Solubility: soluble in
acetone and partially soluble in water and dichloromethane.
−
ppm. 19F NMR (376 MHz, CD3OD): δ −155.20 (s, 10B−F, BF4 ),
−
−155.25 (s, 11B−F, BF4 ), ppm. Integration ratio (1/4) in agreement
with the isotopic distribution for 10B/11B (20/80). FT-IR (KBr, cm−1;
2
3
selected bands): 3083 (w, νCH,sp ), 2925 (w, νCH,sp ), 1620 (vs,
νCC+CN), 1560 (m), 1524 (s, phoxet), 1496 (s, νCC+CN), 1470
(m), 1425 (m), 1345 (m), 1267 (s), 1256 (s), 1234 (s, νas,OMe), 1069
(s, νd,B−F), 1050 (s, νs,OMe), 1031 (s), 922 (m), 864 (m), 853 (m), 838
(m), 668 (m, phoxet), 521 (w, δF−B−F). FT-FIR (Nujol, cm−1; selected
bands): 376 (w), 301 (w), 281 (m), 253 (w), 248 (w). MS (FAB+,
CH3OH): m/z (%) 491 (13) ([M − BF4]+). Molar conductivity
(H2O): 158 S cm2 mol−1. Solubility: soluble in water, methanol, and
ethanol and slightly soluble in acetone, dichloromethane, and
acetonitrile.
Catalytic Transfer Hydrogenation of Ketones. A Radley
Carousel 12 Reaction Station was used to run sets of experiments
simultaneously under similar conditions. In a typical experiment for
the catalytic transfer hydrogenation of ketones to the corresponding
secondary alcohols, the procedure was as follows: the ketone (0.32
mmol) was dissolved in degassed/distilled water (5 mL). Then, the
hydrogen source HCOONa (9.6 mmol), and complexes of series 1, 2,
or 3 (1.6 μmol), as the catalysts, were added under a nitrogen
atmosphere. The pH was adjusted to a value of 4 with HCOOH (1
M), or KOH (1 M). The solutions were stirred at 80 °C for the given
time. Then, the reaction mixtures were cooled in the refrigerator to
quench the reaction, and a fraction of the crude product was analyzed
[(η6-phoxet)RuCl(dmobpy)]OTs ([3]OTs). AgTsO (52 mg, 0.190
mmol) and [(η6-phoxet)RuCl(dmobpy)]Cl (100 mg, 0.190 mmol).
Yield: 0.0875 g (0.132 mmol, 69.6%). Mr (C27H29N2O7ClSRu) =
662.123 g/mol. Anal. Calcd for C27H29N2O7ClSRu: C, 48.98; H, 4.41;
1
N, 4.23. Found: C, 48.71; H, 4.45; N, 4.33. H NMR (400 MHz,
CD3OD): δ 9.19 (d, J = 6.6 Hz, 2H, H6′), 8.04 (d, J = 2.8 Hz, 2H,
H3′), 7.71 (m, 2H, Hb-OTs−), 7.28 (dd, J = 6.6, 2.8 Hz, 2H, H5′), 7.23
(m, 2H, Hc-OTs−), 6.27 (dd, J = 6.4, 5.5 Hz, 2H, H3-phoxet), 5.64 (d,
J = 6.4 Hz, 2H, H2-phoxet), 5.49 (t, J = 5.5 Hz, 1H, H4-phoxet), 4.12
(m, 2H, H5-phoxet), 4.08 (s, 6H, HOMe), 3.85 (m, 2H, H6-phoxet),
2.37 (s, 3H, He-OTs−) ppm. 13C{1H} NMR (101 MHz, CD3OD): δ
169.95 (s, 2C, C4′), 158.04 (s, 2C, C2′), 156.92 (s, 2C, C6′), 139.55 (s,
1C, C1-phoxet), 129.81 (s, 2C, Cc-OTs), 126.98 (s, 2C, Cb-OTs),
114.70 (s, 2C, C5′), 111.12 (s, 2C, C3′), 95.48 (s, 2C, C2-phoxet),
73.92 (s, 1C, C4-phoxet), 72.91 (s, 1C, C5-phoxet), 65.77 (s, 2C, C3-
phoxet), 60.89 (s, 1C, C6-phoxet), 57.49 (s, 2C, −OMe) ppm. Some
peaks are missing due to low-quality spectrum. FT-IR (KBr, cm−1;
1
by H NMR (D2O/1,4-dioxane). In addition, the organic products of
the main fraction were extracted with diethyl ether and identified by
GC, on a Hewlett-Packard 5890 Series II equipment, using an HP-
FFAP (12 m × 0.2 mm × 0.33 mm) capillary column. The yield of
1
alcoholic products (%) was determined by integration of H NMR
signals and GC peaks. All the experiments were carried out twice.
Catalytic Transfer Hydrogenation of acetophenone in D2O.
Selective Deuteration Experiments. In an NMR tube, acetophe-
none (50 μL, 51.5 mg, 0.43 mmol) was dissolved in degassed D2O
(0.5 mL) under a nitrogen atmosphere. Then, HCOONa (0.8865 g,
13 mmol) and [2][BF4] (2.5 mg, 4.4 μmol) were added. The pH was
adjusted to a value of 4 with HCOOH (1 M). The solutions were
stirred at 80 °C for the given time (24−72 h). The reaction mixture
was cooled in the refrigerator to quench the reaction, and the
supernatant organic phase was taken with a Pasteur pipet and
2
3
selected bands): 3083 (w, νCH,sp ), 2966 (w, νCH,sp ), 1620 (vs,
νCC+CN), 1614 (vs, νCC+CN), 1559 (m), 1527 (s, phoxet), 1497
(s, νCC+CN), 1470 (m), 1444 (m), 1422 (m), 1344 (m), 1263 (vs),
1219 (vs, νas,SO), 1187 (vs, νas,SO), 1122 (m), 1101 (s), 1049 (s,
νs,OMe), 1034 (s, TsO−), 1011 (s, TsO−), 913 (w), 853 (m), 802 (m,
TsO−), 683 (s, TsO−), 668 (w, phoxet), 568 (s, TsO−). FT-FIR
(Nujol, cm−1; selected bands): 376 (w), 301 (w), 281 (m), 247 (w).
MS (FAB+, CH3OH): m/z (%) 491 (11) ([M − TsO]+). Molar
conductivity (H2O): 58 S cm2 mol−1. Solubility: soluble in water and
methanol, poorly soluble in ethanol and dichloromethane, and
insoluble in acetone.
1
dissolved in CDCl3. The sample was analyzed by H NMR and 13C
NMR (CDCl3, 25 °C). The yield of alcoholic products (%) was
1
determined by integration of H NMR signals.
rac-1-Phenylethanol-d2. 1H NMR (400 MHz, CDCl3): δ 7.32 (m,
5H, Ph), 4.88 (m, 0.4H, CHOD), 2.59 (s, 0.08H, OH), 1.49 (s, CH3)
ppm. 13C NMR (101 MHz, CDCl3): δ 145.89 (s, 1C, Ci-Ph), 128.61
(s, 2C, Ph), 127.58 (s, 1C, Ph), 125.51 (s, 2C, Ph), 70.43 (s, CHOD);
1
70.01 (m, JCD = 21.97 Hz, CDOD), 25.21 (s, 1C, CH3) ppm.
6121
dx.doi.org/10.1021/om3004702 | Organometallics 2012, 31, 6106−6123

Organometallics
Article
t
Catalytic Oxidation of 1-rac-Phenylethanol with BuOOH or
H2O2. Caution! Gas formation and high pressures were observed for
those experiments with oxidant/S/cat. = 40 000/10 000/1 that were
carried out using 5 mL of H2O.
3.95 (s, 3H, MeO), 2.63 (sept, J = 6.9 Hz, 1H), 2.22 (s, 3H, Me), 1.11
(d, J = 6.9 Hz, 6H) ppm.
ASSOCIATED CONTENT
* Supporting Information
■
A Radley Carousel 12 Reaction Station was used to run sets of
experiments simultaneously under similar conditions. In a typical
experiment for the catalytic oxidation of 1-rac-phenylethanol to
acetophenone using the molar ratio oxidant/S/cat. = 4000/1000/1,
the procedure was as follows: the alcohol (1 mmol) was dissolved in
S
Tables and CIF files giving relevant crystallographic parameters
for all the X-ray structures together with figures giving NMR
figures and tables giving characterization data. This material is
available free of charge via the Internet at http://pubs.acs.org.
t
degassed/distilled water (5 mL). Then the oxidant, BuOOH (4
mmol) or H2O2 (5 mmol), and the catalyst, [1]X, [2]X, or [3]X (1
μmol), were added under a nitrogen atmosphere. The pH was adjusted
to a value of 7 with HCl (1 M) or KOH (1 M). The solutions were
stirred at room temperature for 3 h. Finally, the reaction mixtures were
cooled in the refrigerator to quench the reaction, and a fraction of the
crude product was analyzed by 1H NMR (D2O/1,4-dioxane).
Furthermore, the organic products of the main fraction were extracted
with diethyl ether and identified by GC, on a Hewlett-Packard 5890
Series II equipment using an HP-FFAP (12 m × 0.2 mm × 0.33 mm)
capillary column. The yield of ketonic products (%) was determined
AUTHOR INFORMATION
Corresponding Author
*E-mail: Blanca.Manzano@uclm.es (B.R.M.); gespino@ubu.es
(G.E.).
■
Notes
The authors declare no competing financial interest.
1
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the
MINECO of Spain (project CTQ2011-24434, FEDER Funds).
by integration of H NMR signals and GC peaks. All the experiments
■
were carried out twice, and the yield data were expressed as averaged
values. For those experiments with the molar ratio oxidant/S/cat. = 40
000/10 000/1 two phases were obtained; therefore, the reaction
mixtures were cooled in the refrigerator to quench the reaction, the
organic phase was separated, and the aqueous phase was extracted with
n-hexane. Both organic phases were mixed, and a fraction was diluted
with diethyl ether and analyzed by GC.
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