Incorporation of an n-butylsulfonate functionality to induce aqueous solubility on ruthenium(II) ν6-arene complexes

Article abstract of DOI:10.1021/om2005595

The reaction of the new building block sodium n-butyl sulfonate cyclohexadiene 3 with RuCl₃xH₂O leads to the formation of different dimeric halide-bridged ruthenium complexes, depending on the reaction conditions. Isolation of pure d

Full text of DOI:10.1021/om2005595

Article
pubs.acs.org/Organometallics
Incorporation of an n-Butylsulfonate Functionality To Induce
Aqueous Solubility on Ruthenium(II) η6-Arene Complexes
Morgane A. N. Virboul and Robertus J. M. Klein Gebbink*
Organic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG
Utrecht, The Netherlands
ABSTRACT: The reaction of the new building block sodium
n-butyl sulfonate cyclohexadiene 3 with RuCl3·xH2O leads to
the formation of different dimeric halide-bridged ruthenium
complexes, depending on the reaction conditions. Isolation of
pure dimeric complexes from these mixtures was not
successful. Changing the cyclohexadiene preligand in the
reaction to its neutral isobutyl-protected analogue 2 did allow
for the synthesis and isolation of neutral halide-bridged
dimeric complexes 5 (chloride bridged) and 6 (iodide
bridged) in good to excellent yields. Upon deprotection of the isobutyl sulfonate groups in 6 using sodium iodide, the
anionic, water-soluble dimeric complex 7 was obtained in near-quantitative yield. Complexes 6 and 7 are starting materials for the
synthesis of water-soluble heteroleptic Ru arene complexes, as was demonstrated by the reaction of 6 with (S,S)-TsDPEN,
followed by a reaction with NaI, to yield the mononuclear water-soluble Ru arene TsDPEN complex 8. In preliminary
experiments 8 was found to be an effective catalyst in the asymmetric transfer hydrogenation (ATH) of acetophenone to
quantitatively provide (S)-phenylethanol in 94% ee.
have otherwise required tedious synthetic work. Despite the
numerous examples of functionalized ruthenium arene
complexes, their hydrophilic counterparts have attracted little
attention. In 2009 Crochet et al. reported on the hydrophilic
properties of a ruthenium arene complex functionalized with a
hydroxyethoxy tail on its arene ligand (previously synthesized
by the group of White et al.) and its application in catalysis in
water.15,16 To the best of our knowledge, this is the only
example of this type of transition-metal complex demonstrating
INTRODUCTION
■
The development of greener approaches to known and effective
industrial processes is an important field of research in
homogeneous catalysis. From an economical point of view
and because of environmental considerations, the use of water
as a reaction medium is a very interesting strategy within this
field. As a result, a great number of important catalytic organic
transformations have already been studied in aqueous environ-
ments.1−3 Because of the poor solubility in water of most of the
well-known homogeneous catalysts, derivatization of the
transition-metal complex is often required to allow their use
as water-soluble catalysts. One way to induce water-solubility
properties to a metal complex is by coordination of a
hydrophilic ligand to the metal center.4,5
During the last 30 years the chemistry of ruthenium arene
complexes has been extensively studied.6−8 Because these
compounds are valuable precursors for a wide variety of
catalysts, the last few years have seen the development of
functionalized ruthenium η6-arene complexes.9 The increasing
interest in these molecules can be explained by the develop-
ment of straightforward methods for their preparation, making
them easily accessible precatalysts for a number of catalytic
applications: e.g., hydrogenation,10−12 polymerization,13 and
metathesis.14 Synthesis of a ruthenium arene precursor of the
type [{RuX2(η6-arene)}2] bearing a hydrophilic functionalized
arene ligand is of interest for the preparation of water-soluble
half-sandwich ruthenium(II) arene complexes. Functionaliza-
tion of the metal precursor at this stage would indeed allow for
the formation of many different catalyst precursors by simple
coordination of such “task specific” ligands, permitting an easy
access to water-soluble transition-metal complexes that would
water-soluble properties reported to date.
Introduction of ionic tags such as −SO3− and −NR3+ groups
is a very common approach to alter the solubility of a
ligand.17,18 We recently reported on a new methodology to
introduce an n-butylsulfonate functionality and on the use of
this sulfonate moiety as a versatile tool for catalyst
immobilization.19 Here, we wish to demonstrate the effective-
ness of such a functional group to fine-tune the solubility of the
molecular scaffold it is connected to. The approach developed
here allowed us to straightforwardly synthesize a chiral
sulfonate-functionalized ruthenium arene compound. The
activity of this precatalyst was tested in the asymmetric transfer
hydrogenation (ATH)20−24 of acetophenone in water, and the
preliminary results indicated a good catalytic activity under
nonoptimized conditions.
Received: June 28, 2011
Published: December 21, 2011
© 2011 American Chemical Society
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Scheme 1. Synthesis of the Cyclohexadiene Derivatives
Scheme 2. Synthesis of Arene Ruthenium Dimer in EtOH/Water (Conditions 1) and MeOH/Water (Conditions 2)
refluxing acetone to give the alkyl sulfonate tethered cyclo-
hexadiene 3 as the sodium salt in excellent yields.
RESULTS AND DISCUSSION
■
Synthesis. The most common preparation method to
The coordination of 3 to ruthenium was first attempted in
refluxing aqueous ethanol in the presence of RuCl3·xH2O for 6
h. After cooling and concentration of the reaction mixture, an
orange solid was obtained. The 1H NMR spectrum of the crude
product clearly indicated the presence of at least two different
species (Scheme 2, conditions 1). The products present were
found to have chemical shifts different from those of the
starting material 3, but attempts to separate the different
species were unsuccessful. A possible reaction product was
thought to be the isomerized ligand 3, as isomerization is a
preliminary step involved in the coordination of the Ru metal
center.26 In order to improve the synthesis of the ruthenium
dimer, the reaction was performed in a MeOH/water mixture
(conditions 2) instead of aqueous EtOH. Under these
conditions another side product formed which is believed to
be the oxidized form of the ligand 3, as evidenced by the
access ruthenium arene complexes is by reaction of
RuCl3·xH2O with a cyclohexadiene derivative in an EtOH/
water mixture.25,26 During the course of such a reaction, the
cyclohexadiene is dehydrogenated to yield the arene ligand with
concomitant reduction of RuIIICl3 to yield a dimeric chloro-
bridged ruthenium(II) arene compound. The first step toward
the synthesis of a functionalized ruthenium arene complex is
therefore the synthesis of the desired cyclohexadiene derivative.
Starting from 3-(cyclohexa-1,4-dien-1-yl)propan-1-ol, which
is readily available from 3-phenylpropan-1-ol via a Birch
reduction,27 the alkyl bromide 1 was obtained in 60% yield
by bromination using PBr3 in diethyl ether (Scheme 1).
Reaction of isobutyl methylsulfonate with nBuLi generated the
corresponding lithiated species,28 which was subsequently
reacted with 1 to afford the isobutyl-protected sulfonate 2 in
reasonable yields. Compound 2 was deprotected with NaI in
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Figure 1. ESI-MS spectrum of 4 (conditions 2) measured in negative ion mode in MeOH. The top spectrum represents the theoretical isotopic
pattern of [Ru2(arene)2(OH)2(MeO)]−.
Scheme 3. Synthesis of a Water-Soluble Ruthenium Arene Dimer
presence of signals in the aromatic region (see Scheme 2,
conditions 2).
Despite the successful formation of sulfonate-functionalized
ruthenium arene dimers, the synthetic methods used did not
allow for the isolation of one of the dimeric products in a pure
form. Due to these difficulties, another approach was envisaged
for the synthesis of a water-soluble ruthenium arene complex.
The alternative synthetic route that was investigated involves
the deprotection of the sulfonate moiety at a later stage
(Scheme 3). Ruthenium dimer 5 was synthesized very
straightforwardly by refluxing the sulfonate-functionalized
cyclohexadiene 2 with RuCl3·xH2O in aqueous ethanol for 6
h. The resulting chloro-bridged dimer 5 was then suspended
with KI in refluxing aqueous ethanol for 2 h to yield the neutral
iodo-bridged dimer 6. This halide exchange was necessary to
The crude product mixture obtained under both sets of
conditions was further analyzed by ESI-MS measurements,
confirming the presence of ruthenium arene dimers. These
compounds do not bear chloride bridging ligands but rather
hydroxy and methoxy ligands, as evidenced by ESI-MS (see
Figure 1). The dimers observed in ESI-MS correspond to the
s p e c i e s w i t h t h e g e n e r a l f o r m u l a
[Ru2(arene)2(OH)n(MeO)3−n]−, where arene stands for the
negatively charged η6-coordinated ligand 4-phenylbutanesulfo-
nate.
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Scheme 4. Synthesis of Chiral Half-Sandwich Ru(II) Complex 8
avoid any possible halide scrambling that could occur during
the deprotection of the sulfonate, as this step requires the use of
NaI.
sodium salt), as an excess of the ligand is necessary for the
reaction to go to completion (see Scheme 2). Remarkably, the
formation of the 4-phenylbutane sulfonate was only observed
when an aqueous solution of methanol was used, suggesting
that the oxidation of the solvent is less favorable under these
conditions than the oxidation of the ligand. In general, the
formation of the side products is not an issue as the ruthenium
complex precipitates, leaving the side products in the reaction
medium and enabling an easy purification. Due to the polar
nature of the ligand used here for the reaction, the alkoxy-
bridged ruthenium dimers could not be separated from the side
products formed during the course of the reaction, in spite of all
the efforts to selectively crystallize or precipitate it.
Compound 6 was deprotected in the presence of NaI in
refluxing acetone, affording the Ru(II) dimer 7 as a purple solid
in excellent 95% yield. Compound 7 was alternatively
synthesized by refluxing 5 in acetone with NaI for 48 h,
1
yielding the expected product. 7 was analyzed by H and 13C
NMR in D2O, with both spectra confirming the absence of the
peaks corresponding to the isobutyl protecting group, thus
confirming the successful deprotection of 5 or 6. High-
resolution mass spectrometry of 7 displayed a typical isotopic
pattern at m/z 1160.6030 corresponding to the monoanion [7
− Na]−.
The formation of a monomeric precatalyst with a task-
specific ligand was evaluated by coordination of the chiral
diamino ligand (1S,2S)-N-p-toluenesulfonyl-1,2-diphenylethy-
lenediamine ((S,S)-TsDPEN), well-known for its ability in
chiral induction. Because of the low solubility of dimer 7 in
organic solvents, the coordination was attempted in water.
Unfortunately, the poor solubility of the (S,S)-TsDPEN ligand
in water did not allow for the coordination to take place. The
coordination was then performed using neutral compound 6 in
2-propanol in the presence of NEt3 to allow for deprotonation
of the amine group (Scheme 4). Deprotection of the sulfonate
group was then carried out in a separate step by treating the
reaction product with NaI in refluxing acetone to yield
sulfonato complex 8 as a purple solid in 52% yield starting
from 6. The solubility profile of 8 was dramatically changed by
the deprotection of the sulfonate moiety: the ruthenium
complex thus formed is highly soluble in water, insoluble in
organic solvent, and poorly soluble in ethanol and methanol.
Compound 8 was characterized by 1H and 13C NMR
spectroscopy and ESI-MS spectroscopy, showing the successful
coordination of the chiral ligand (S,S)-TsDPEN to the
ruthenium metal center. The high-resolution mass spectrum
of 8 displayed a characteristic isotopic pattern at m/z 806.9997
coinciding with the calculated isotopic pattern of the
monoanion [8 − Na]−. The coordination of the chiral diamine
ligand to the ruthenium metal center was also demonstrated by
the presence in 1H and 13C NMR of the typical peaks
corresponding to the TsDPEN ligand.
Ruthenium(II) η6-arene complexes are commonly synthe-
sized by reduction of RuCl3·xH2O in the presence of an excess
of 1,4-cyclohexadiene in refluxing aqueous ethanol. Under these
conditions, the [RuCl2(η6-arene)]2 dimer precipitates from the
reaction medium and can be easily isolated by simple filtration.
Our attempts to synthesize a [RuCl2(η6-arene)]2 complex using
this method in the presence of the sulfonate-modified 1,4-
cyclohexadiene compound 3 were unsuccessful. Instead of the
expected chloro-bridged ruthenium arene dimer, methoxy-
and/or hydroxy-bridged ligand ruthenium dimers were formed,
as evidenced by ESI-MS analysis. This result is noteworthy,
considering that these types of alkoxy-bridged dimers are
usually prepared by ligand exchange from the halide-bridged
counterpart, usually in the presence of a strong base.29 The
formation of [RuX2(η6-arene)]2 (X = OH−, OMe−, OEt−) can
be explained by the high solubility of both reagents and
products in the reaction medium; when the reaction is
performed with a less polar ligand, the product precipitates
immediately from the reaction mixture and cannot be engaged
in further reactions such as, for example, ligand exchange. We
postulate that the reaction medium is basic enough to promote
this ligand exchange from Cl− to OH−, EtO−, or MeO−, leading
to the formation of the unexpected dimers. In the case of the
ruthenium dimer formed in aqueous ethanol, it is thought that
another ligand exchange occurs during the ESI-MS measure-
ment which is performed in methanol, yielding the formation of
methoxy-bridged ruthenium dimer and not ethoxy-bridged
dimers.
Catalysis. To show the application of the sulfonated
Ru(arene) moiety in aqueous catalysis, its corresponding
(S,S)-TsDPEN complex 8 was tested in the catalytic
asymmetric transfer hydrogenation of acetophenone in
water.30−34 The benchmark substrate acetophenone was used
as the substrate in this study to enable a comparison with
previous studies, and the reaction was performed in neat water
using sodium formate as the hydrogen source (Scheme 5). The
choice of the hydrogen source, i.e. sodium formate, seems
During the formation of the ruthenium dimer, several
reactions occur at the same time: the reduction of the metal
precursor from Ru(III) to Ru(II), the isomerization and
dehydrogenation of the ligand, and the oxidation of the
solvent.26 These processes consequently lead to the formation
of the desired compound but also to side products such as the
dehydrogenated ligand (the 4-phenylbutane sulfonate) or the
isomerized ligand (1-(4-sulfonatobutyl)-1,3-cyclohexadiene
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maintaining stereoselectivity after recycling under nonopti-
mized conditions. We expect that the applicability of sulfonated
ruthenium precursors 6 and 7 is not limited to ATH and that
these compounds are of interest in constructing other water-
soluble complexes and catalysts.
Scheme 5. Asymmetric Reduction of Acetophenone
crucial for the achievement of good enantioselectivity and
conversion, as the use of this reductant avoids the possibility of
the reverse reaction (oxidation of phenylethanol) to occur.20
The other advantages of using HCO2Na are the easy handling
of this reagent and its high solubility in water. From this
preliminary catalytic study, it was found that complex 8 is able
to fully convert acetophenone to (S)-phenylethanol within 4 h
with a very good enantioselectivity of 94%. This showed that 8
is able to perform the reaction with comparable enantiose-
lectivities but with an activity somewhat lower than for
comparable systems reported up to now.34
In order to test the recyclability of 8, it was used in three
consecutive runs. To this end, the reaction mixture at the end
of a catalytic run was extracted three times with a 2 mL portion
of degassed diethyl ether to remove all organic products formed
and the next catalytic run started after addition of sodium
formate and acetophenone. As can be seen in Table 1, complex
EXPERIMENTAL SECTION
■
General Information. All reactions (unless otherwise mentioned)
were performed under a N2 atmosphere using standard Schlenk
techniques. Toluene, Et2O, and THF were dried through a solvent
purification system (SPS), and CH2Cl2 was dried over CaH2, distilled,
and degassed before use. Extra-dry NMP was purchased from Aldrich
and distilled before use. All reagents were purchased from Aldrich or
Acros and were used as received. 3-(Cyclohexa-1,4-dien-1-yl)propan-
1-ol was prepared as reported in the literature.27 1H and 13C{1H}
NMR spectroscopic measurements were conducted at 25 °C on a
Varian Inova 300, a Varian Oxford AS400, or a Bruker Avance III 600
MHz spectrometer. Chemical shifts (δ) are given in ppm referenced to
the residual solvent peak, and coupling constants are given in hertz
(Hz). Time-of-flight electrospray ionization mass spectra (ESI-MS)
were measured by the Biomolecular Mass Spectrometry and
Proteomics Group, Utrecht University, on a Micromass LC-T mass
spectrometer (Waters, Manchester, U.K.), operating in negative ion
mode. The nanospray needle potential was typically set to 1300 V and
the cone voltage to 60 V. The source block temperature was set to 80
°C. Elemental analyses were performed by Dornis and Kolbe,
Table 1. Catalytic Activity of 8 in the ATH of Acetophenone
Mikroanalytische Laboratorium, Mulheim a/d Ruhr, Germany. GC
̈
samples were analyzed using a Perkin-Elmer Clarus 500 GC equipped
with a Chromapack Chirasil-Dex CB (25 m × 0.25 mm) column.
1-(3-Bromopropyl)-1,4-cyclohexadiene (1). To a solution of 3-
(cyclohexa-1,4-dien-1-yl)propan-1-ol (2.77 g, 20 mmol) in dry Et2O
(30 mL) was added PBr3 (0.7 mL, 7.33 mmol) at 0 °C. The mixture
was then stirred for 4 h at room temperature. The reaction was
quenched with water (15 mL) and the product extracted with Et2O (3
× 20 mL). The volatiles were evaporated and the crude product
purified by silica gel column chromatography using hexane/Et2O (95/
5, v/v) as the eluent, yielding a colorless oil (2.65 g, 66%).
a
b
run
cat.
loading (mol %)
time (h)
yield (%)
ee (%)
1
2
3
8
8
8
2
2
2
4
20
13
>99
97
94
93
93
21
a
b
Yields were determined by chiral GC analysis. ee values were
determined by chiral GC analysis, and the S configuration of the
product was confirmed by comparison with an authentic enantiopure
sample.
1H NMR (400 MHz, CDCl3): δ 5.74−5.73 (br, 2H; CHCH diene),
5.47 (br 1H; CH diene), 3.40 (t, 2H, JHH = 6.9 Hz; (CH2)2CH2Br),
8 was able to reduce acetophenone to phenylethanol with high
yields and high enantioselectivities in the second run. A second
recycling run (run 3) showed a decrease in activity, without loss
of enantioselectivity, however.
3
2.72−2.65 (m, 2H; CH2 diene), 2.61−2.55 (m, 2H; CH2 diene), 2.11
3
(t, 2H, JHH = 6.9 Hz; CH2(CH2)2Br), 2.02−1.92 (m, 2H;
CH2CH2CH2Br) 13C{1H} NMR (100 MHz, CDCl3): δ 133.2,
124.4, 124.2, 119.7, 35.8, 33.6, 30.5, 28.9, 26.8. Anal. Calcd for
C9H13Br: C, 53.75; H, 6.52. Found: C, 54.19; H, 6.41.
The conditions used for the recycling experiments were
exactly identical with those of the first run, implying the use of
HCO2Na as the reductant. These conditions seem not to be
ideal, as the activity of the catalyst rapidly decreased after the
first run. This finding can be attributed to the fact that ATH in
water is dependent on the pH and that repeated addition of
HCO2Na can induce a dramatic pH change,35,36 resulting in
lower activity of the catalyst. It is also likely that a high
concentration of salt can have consequences on the diffusion of
the reactants in the medium, thus contributing to the observed
lower activity.
Isobutyl 4-(Cyclohexa-1,4-dien-1-yl)butane-1-sulfonate (2).
In a Schlenk flask was introduced isobutylmethanesulfonate (3.66 g, 24
mmol) with THF (25 mL). The reaction mixture was cooled to −78
°C, followed by dropwise addition of a 1.6 M solution of nBuLi in
hexane (11 mL, 17.6 mmol), and the mixture was stirred at this
temperature for 2 h. The mixture was then added via cannula to a
solution of 1 (2.78 g, 13.8 mmol) in a mixture of THF (35 mL) and
NMP (15 mL). The reaction mixture was warmed to room
temperature and was stirred for another 20 h. The resulting mixture
was quenched with water (20 mL) and extracted with diethyl ether (3
× 30 mL). The crude product was concentrated in vacuo and purified
by silica gel column chromatography using hexane/diethyl ether (8/2,
v/v) as the eluent, yielding the pure compound as a colorless liquid
(2.10 g, 56%).
CONCLUSION
■
In summary, we have shown that the introduction of an alkyl
sulfonate chain to the arene ligand of the prototypical
[Ru(arene)Cl2]2 complex renders it hydrophilic. To this end
several (protected) alkyl sulfonate Ru(II) arene complexes were
synthesized, which are precursors for the synthesis of
heteroleptic water-soluble Ru arene complexes. As an example,
these hydrophilic precursors enabled the synthesis of a versatile
water-soluble chiral ruthenium arene TsDPEN complex of
interest for asymmetric transfer hydrogenations in water.
Indeed, the new sulfonate-appended ruthenium(II) η6-arene
complex 8 was proven to be efficient for this reaction,
1H NMR (400 MHz, CDCl3): δ 5.68 (br, 2H; CHCH diene), 5.41
(br, 1H; CH diene), 3.95 (d, 2H, 3JHH = 6.4 Hz; CH2 iBu), 3.08 (t, 2H,
3JHH = 7.6 Hz; (CH2)3CH2SO3), 2.68−2.63 (m, 2H; CH2 diene),
2.57−2.53 (m, 2H; CH2 diene), 2.06−1.96 (m, 1H + 2H; overlap CH
iBu and CH2(CH2)3SO3), 1.87−1.79 (m, 2H; (CH2)2CH2CH2SO3),
1.59−1.52 (m, 2H; CH2CH2(CH2)2SO3), 0.96 (d, 6H, 3JHH = 6.8 Hz;
(CH3)2 iBu). 13C{1H} NMR (100 MHz, CDCl3): δ 133.8, 124.3,
124.1, 119.3, 75.3, 50.1, 36.7, 28.7, 28.3, 26.7, 25.7, 23.1, 18.7. Anal.
Calcd for C14H24O3S: C, 61.73; H, 8.88. Found: C, 61.10; H, 8.75.
1-(4-Sulfonatobutyl)-1,4-cyclohexadiene Sodium Salt (3).
Compound 2 (0.560 g, 2.06 mmol) and NaI (0.616 g, 4.11 mmol)
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were stirred at reflux temperature for 48 h in acetone (25 mL). The
resulting mixture was cooled, and the solids were filtered and washed
with acetone and Et2O, yielding the desired compound as a white solid
(0.436 g, 89%).
(150 MHz, DMSO-d6): δ 143.8, 139.9, 139.2, 137.9, 128.9, 128.0,
127.6, 127.5, 127.0, 126.4, 126.3, 125.8, 99.9, 84.8, 83.1, 82.2, 81.9,
81.0, 71.4, 68.2, 51.2, 32.6, 29.1, 24.8, 20.7. HRMS (ES−): calcd for
C31H34IN2S2O5Ru m/z = 806.9997, found 807.0016 [M − Na]−.
General Procedure for the Asymmetric Transfer Hydro-
genation of Acetophenone. The ruthenium dimer 7 (11.8 mg, 0.01
mmol) and (S,S)-TsDPEN (8.8 mg, 0.024 mmol) were suspended in
degassed water (2 mL). After it was stirred at 40 °C for 1 h, the
suspension was used for the reduction reactions. In the case of the
preformed precatalyst, 8 (8.3 mg, 0.02 mmol) was dissolved in
degassed water (2 mL) and the solution was heated at 40 °C. After the
precatalysts were prepared, HCO2Na (340 mg, 5 mmol) and
acetophenone (120 mg, 1.0 mmol) were added to the solution and
allowed to react for a certain period of time. After it was cooled to
room temperature, the organic phase was extracted with Et2O (3 × 2
mL) and passed through a short silica gel column before being
subjected to chiral GC analysis.
For the recycling tests, the reaction mixture was extracted in the
same manner with degassed Et2O (3 × 2 mL) and the resulting water
phase was heated at 40 °C and flushed with N2 to ensure evaporation
of residual Et2O. HCO2Na (340 mg, 5 mmol) and acetophenone (120
mg, 1.0 mmol) were subsequently added to the solution and allowed
to react for a certain period of time.
The yields and enantiomeric excesses were determined with a chiral
GC (carrier gas helium, 80 psi; injection temperature 250 °C; column
temperature 120 °C; retention time 7.20 min (R) and 7.47 (S)). The
absolute configuration of the product was confirmed by injection of an
authentic enantiopure sample on the chiral GC.
1H NMR (400 MHz, MeOH-d4): δ 5.67 (br, 2H; CHCH diene),
3
5.44 (br, 1H; CH diene), 2.80 (t, 2H, JHH = 8 Hz; (CH2)3CH2SO3),
2.65−2.63 (m, 2H; CH2 diene), 2.60−2.55 (m, 2H; CH2 diene), 2.01
3
(t, 2H, JHH = 8 Hz; CH2(CH2)3SO3), 1.82−1.74 (m, 2H;
(CH2)2CH2CH2SO3), 1.58−1.51 (m, 2H; CH2CH2(CH2)2SO3).
13C{1H} NMR (100 MHz, MeOH-d4): δ 135.8, 125.3, 125.2, 119.8,
67.0, 38.3, 29.7, 27.7, 27.6, 25.8. Anal. Calcd for C10H15NaO3S: C,
50.41; H, 6.35. Found: C, 50.17; H, 6.32.
[{RuCl2(η6-C6H5(CH2)4SO3iBu)}2] (5). RuCl3·xH2O (0.321 g, 1.27
mmol) and 2 (1.39 g, 5.09 mmol) were dissolved in ethanol (25 mL)
and heated at reflux temperature for 5 h. After cooling of the reaction
mixture, the precipitate was filtered, washed with cold ethanol, and
dried in vacuo, yielding the product (0.449 g, 80%) as an orange solid.
1H NMR (400 MHz, CD2Cl2): δ 5.62−5.58 (m, 4H + 2H; m-ArH
overlap with p-ArH), 5.35 (d, 4H, 3JHH = 5.6 Hz ; o-ArH), 3.97 (d, 4H,
3JHH = 6.4 Hz; CH2 iBu), 3.15 (t, 4H, 3JHH = 7.6 Hz; (CH2)3CH2SO3),
3
2.55 (t, 4H, JHH = 8 Hz; CH2(CH2)3SO3), 2.07−1.97 (m, 2H; CH
iBu), 1.95−1.87 (m, 4H; (CH2)2CH2CH2SO3), 1.82−1.74 (m, 4H;
3
CH2CH2(CH2)2SO3), 0.98 (d, 12H, JHH = 6.8 Hz; (CH3)2 iBu).
13C{1H} NMR (100 MHz, CD2Cl2): δ 100.4, 84.3, 80.7, 80.6, 76.2,
50.0, 33.1, 28.8, 28.0, 23.7, 18.9. Anal. Calcd for C28H44Cl4O6Ru2S2: C,
38.01; H, 5.01. Found: C, 38.41; H, 4.95.
[{RuI2(η6-C6H5(CH2)4SO3iBu)}2] (6). Compound 5 (0.192 g, 0.217
mmol) was suspended in a mixture of aqueous ethanol (50% v/v, 10
mL) with KI (0.360 g, 2.17 mmol). After 2 h at reflux temperature, the
precipitate was collected by filtration, washed with ethanol, and dried
in vacuo to yield the product as a purple solid (0.264 g, 97%).
AUTHOR INFORMATION
■
Corresponding Author
3
1H NMR (400 MHz, CD2Cl2): δ 5.71 (t, 2H, JHH = 5.6 Hz; p-
ArH), 5.63 (t, 4H, 3JHH = 5.6 Hz; m-ArH), 5.49 (d, 4H, 3JHH = 6 Hz; o-
*Fax: (+31) 30-252-3615. E-mail: r.j.m.kleingebbink@uu.nl.
3
3
ArH), 3.97 (d, 4H, JHH = 6.4 Hz; CH2 iBu), 3.17 (t, 4H, JHH = 7.6
3
Hz; (CH2)3CH2SO3), 2.70 (t, 4H, JHH = 7.6 Hz; CH2(CH2)3SO3),
ACKNOWLEDGMENTS
■
2.07−1.97 (m, 2H; CH iBu), 1.96−1.88 (m, 4H;
This work was financially supported by the Council for the
Chemical Sciences of The Netherlands Organization for
Scientific Research (CWNWO) through a VIDI scholarship
to R.J.M.K.G.
(CH2)2CH2CH2SO3), 1.83−175 (m, 4H; CH2CH2(CH2)2SO3), 0.98
3
(d, 12H, JHH = 6.8 Hz; (CH3)2 iBu). 13C{1H} NMR (100 MHz,
CD2Cl2): δ 101.1, 84.5, 83.5, 83.4, 76.2, 50.1, 34.2, 28.5, 28.4, 23.3,
18.5.
[{RuI2(η6-C6H5(CH2)4SO3)}2][Na]2 (7). Compound 6 (0.134 g,
0.107 mmol) was suspended in acetone (20 mL) with NaI (0.272 g,
1.82 mmol). After 20 h of stirring at reflux temperature, the precipitate
was collected by filtration, washed with ethanol, and dried in vacuo to
yield the product as a purple solid (0.126 g, 100%).
REFERENCES
■
(1) Li, C. J. Chem. Rev. 2005, 105, 3095−3165.
(2) Li, C. J.; Chen, L. Chem. Soc. Rev. 2006, 35, 68−82.
(3) Lindstrom, U. M. Chem. Rev. 2002, 102, 2751−2771.
(4) Joo, F. Aqueous Organometallic Catalysis; Kluwer Academic:
Dordrecht, The Netherlands, 2001.
Compound 7 was alternatively synthesized by refluxing compound
5 with NaI in acetone for 48 h, yielding a compound with the same
spectroscopic features as described below.
1H NMR (400 MHz, D2O): δ 5.93−5.84 (m, 10H; ArH), 3.01−
2.92 (m, 4H; (CH2)3CH2SO3), 2.73−2.59 (m, 4H; CH2(CH2)3SO3),
1.90−1.73 (m, 4H; CH2(CH2)2CH2SO3). 13C{1H} NMR (100 MHz,
D2O with MeOH-d4 as internal standard): δ 101.8, 82.4, 81.3, 81.2,
51.3, 34.3, 29.4, 24.4. HRMS (ES−): calcd for C20H26I4NaO6Ru2S2 m/z
1160.5334, found 1160.6030 [M − Na]−.
(5) Cornils, B., Herrmann, W. A. Aqueous-Phase Organometallic
Catalysis; Wiley-VCH: Weinheim, Germany, 2004.
(6) Murahashi, S.-I. Ruthenium in Organic Synthesis; Wiley-VCH:
Weinheim, Germany, 2004.
(7) Bennett, M. A. Coord. Chem. Rev. 1997, 166, 225−254.
(8) Rigby, J. H.; Kondratenko, M. A. Top. Organomet. Chem. 2004, 7,
181−204.
[RuI(η6-C6H5(CH2)4SO3){(S,S)-TsDPEN}][Na] (8). Compound 6
(73 mg, 0.0584 mmol), (S,S)-TsDPEN (41 mg, 0.112 mmol), and
NEt3 (23 mg, 0.224 mmol) were mixed in 2-propanol (10 mL) and
heated at 80 °C for 1 h. The orange solution was concentrated and the
resulting solid filtered. The solids were washed with a small amount of
water and dried in vacuo. The resulting material was mixed with NaI
(18 mg, 0.12 mmol) in acetone (15 mL) and refluxed for 24 h. The
mixture was then cooled to ambient temperature, and the solids were
filtered and washed with acetone (10 mL) and Et2O (10 mL), yielding
the desired compound as a purple solid (50 mg, 52%).
(9) Therrien, B. Coord. Chem. Rev. 2009, 253, 493−519.
(10) Canivet, J.; Karmazin-Brelot, L.; Suss-Fink, G. J. Organomet.
Chem. 2005, 690, 3202−3211.
(11) Geldbach, T. J.; Dyson, P. J. J. Am. Chem. Soc. 2004, 126, 8114−
8115.
(12) Chaplin, A. B.; Dyson, P. J. Organometallics 2007, 26, 4357−
4360.
(13) Simal, F.; Demonceau, A.; Noels, A. F. Angew. Chem., Int. Ed.
1999, 38, 538−540.
(14) Dias, E. L.; Grubbs, R. H. Organometallics 1998, 17, 2758−2767.
(15) Soleimannejad, J.; White, C. Organometallics 2005, 24, 2538−
2541.
(16) Lastra-Barreira, B.; Diez, J.; Crochet, P. Green Chem. 2009, 11,
1681−1686.
(17) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643−710.
1H NMR (600 MHz, DMSO-d6): δ 7.10−6.55 (m, 14H; ArH p-Ts
and SO2NCH(C6H5)CH(C6H5)NH2), 6.03 (m, 1H; NHH), 5.83−
5.53 (m, 5H; ArH arene), 3.77−3.69 (m, 1H + 1H; overlap of
PhCHNH2 and PhCHNTs), 3.17 (m, 1H; NHH), 2.57 (m, 2H;
CH2(CH2)3SO3−), 2.47 (t, 3JHH = 7.8 Hz, 2H; (CH2)3CH2SO3−), 2.21
(s, 3H, CH3 p-Ts), 1.67 (m, 4H; CH2(CH2)2CH2SO3). 13C{1H} NMR
90
dx.doi.org/10.1021/om2005595 | Organometallics 2012, 31, 85−91

Organometallics
Article
(18) Snelders, D. J. M.; van Koten, G.; Klein Gebbink, R. J. M. Chem.
Eur. J. 2011, 17, 42−57.
(19) Virboul, M. A. N.; Lutz, M.; Siegler, M. A.; Spek, A. L.; van
Koten, G.; Klein Gebbink, R. J. M. Chem. Eur. J. 2009, 15, 9981−9986.
(20) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97−102.
(21) Ikariya, T.; Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300−1308.
(22) Samec, J. S. M.; Backvall, J. E.; Andersson, P. G.; Brandt, P.
Chem. Soc. Rev. 2006, 35, 237−248.
(23) Everaere, K.; Mortreux, A.; Carpentier, J. F. Adv. Synth. Catal.
2003, 345, 67−77.
(24) Gladiali, S.; Alberico, E. Chem. Soc. Rev. 2006, 35, 226−236.
(25) Zelonka, R. A.; Baird, M. C. Can. J. Chem. 1972, 50, 3063−3072.
(26) Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974,
233−241.
(27) Ohnishi, T.; Miyaki, Y.; Asano, H.; Kurosawa, H. Chem. Lett.
1999, 809−810.
(28) Xie, M. Q.; Widlanski, T. S. Tetrahedron Lett. 1996, 37, 4443−
4446.
(29) Arthur, T.; Robertson, D. R.; Tocher, D. A.; Stephenson, T. A. J.
Organomet. Chem. 1981, 208, 389−400.
(30) Bubert, C.; Blacker, J.; Brown, S. M.; Crosby, J.; Fitzjohn, S.;
Muxworthy, J. P.; Thorpe, T.; Williams, J. M. J. Tetrahedron Lett. 2001,
42, 4037−4039.
(31) Rhyoo, H. Y.; Park, H. J.; Chung, Y. K. Chem. Commun. 2001,
2064−2065.
(32) Ma, Y. P.; Liu, H.; Chen, L.; Cui, X.; Zhu, J.; Deng, J. E. Org.
Lett. 2003, 5, 2103−2106.
(33) Wu, X. F.; Li, X. G.; Hems, W.; King, F.; Xiao, J. L. Org. Biomol.
Chem. 2004, 2, 1818−1821.
(34) Wu, X. F.; Xiao, J. L. Chem. Commun. 2007, 2449−2466.
(35) Wu, X. F.; Liu, J. K.; Di Tommaso, D.; Iggo, J. A.; Catlow, C. R.
A.; Bacsa, J.; Xiao, J. L. Chem. Eur. J. 2008, 14, 7699−7715.
(36) Wang, C.; Li, C. Q.; Wu, X. F.; Pettman, A.; Xiao, J. L. Angew.
Chem., Int. Ed. 2009, 48, 6524−6528.
91
dx.doi.org/10.1021/om2005595 | Organometallics 2012, 31, 85−91