Highly water-soluble arene-ruthenium(ii) complexes: Application to catalytic isomerization of allylic alcohols in aqueous medium

Article abstract of DOI:10.1039/b914789f

Arene-ruthenium(ii) derivatives [RuCl₂(η⁶-C ₆H₅OCH₂CH₂OH)(L)] (L = P(OMe) ₃ (2a), P(OEt)₃ (2b), P(OⁱPr)₃ (2c), P(OPh)₃ (2d), PPh₃ (2e)) have been prepared from the dimer [{RuCl(μ-Cl)(η⁶-C₆H₅OCH ₂CH₂OH)}₂] and the appropriate P-donor ligand. The hydroxyethoxy substituent on the arene induces water-solubility of the resulting complexes (up to 755 g L^-1); in particular derivative 2a being one hundred times more soluble in water than its p-cymene congener [RuCl₂(η⁶-p-cymene){P(OMe)₃}]. Compounds 2a-e are active catalysts for isomerization of allylic alcohols into the corresponding ketones in aqueous medium. The best performances are obtained with derivatives 2a-c which have shown the highest activity reported to date for the isomerization of aromatic or disubstituted substrates in water. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b914789f

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www.rsc.org/greenchem | Green Chemistry
Highly water-soluble arene-ruthenium(II) complexes: application to
catalytic isomerization of allylic alcohols in aqueous medium†
Beatriz Lastra-Barreira, Josefina D´ıez and Pascale Crochet*
Received 28th April 2009, Accepted 20th July 2009
First published as an Advance Article on the web 17th August 2009
DOI: 10.1039/b914789f
6
Arene-ruthenium(II) derivatives [RuCl2(h -C6H5OCH2CH2OH)(L)] (L = P(OMe)3 (2a),
P(OEt)3 (2b), P(OiPr)3 (2c), P(OPh)3 (2d), PPh3 (2e)) have been prepared from the dimer
6
[{RuCl(m-Cl)(h -C6H5OCH2CH2OH)}2] and the appropriate P-donor ligand. The hydroxyethoxy
substituent on the arene induces water-solubility of the resulting complexes (up to 755 g L-1); in
particular derivative 2a being one hundred times more soluble in water than its p-cymene
6
congener [RuCl2(h -p-cymene){P(OMe)3}]. Compounds 2a–e are active catalysts for
isomerization of allylic alcohols into the corresponding ketones in aqueous medium. The best
performances are obtained with derivatives 2a–c which have shown the highest activity reported to
date for the isomerization of aromatic or disubstituted substrates in water.
functionalized-arene ruthenium(II) derivatives already known,5
Introduction
their behavior in water has been almost unexplored,6 most of
The main interest in using water as reaction solvent stems from
the reported studies being essentially focused on the formation
its low cost, and its non-toxic and non-hazardous nature. There-
of tethered derivatives.5,7
fore, during the last two decades, the increasing awareness of
environmental concerns has motivated the development of novel
metal-promoted processes in aqueous media, disclosing a wide
variety of highly efficient and selective synthetic approaches.1 In
this context, a large number of water-soluble organometallic
complexes were synthesized and applied as catalysts.1–3 The
A particularly attractive functionalized precursor is [{RuCl(m-
6
Cl)(h -C6H5OCH2CH2OH)}2] (1) which is readily prepared,
through a one-pot process, from commercial reagents. Its
synthesis, reported by White et al., is based on the reaction of
RuCl3·nH2O with 1-methoxy-1,4-cyclohexadiene and ethylene
glycol at 80 ◦C (Scheme 1).8 Despite the easy access to 1 in large
most common strategy to obtain such derivatives consists of
scale, its coordination chemistry and applications in catalysis
introducing hydrophilic ligands in the coordination sphere of
remain almost unexplored.8–10 Moreover, its behavior in water
the metal, P-donor ligands being usually employed.2–3 Thus,
a huge number of arene-ruthenium(II) complexes containing
has not been studied at all. Herein, we describe the synthesis
of novel complexes derived from 1 and their application in the
water-soluble phosphine ligands have been prepared, finding
catalytic redox-type isomerization of allylic alcohols in aqueous
applications associated to their biological properties,4 as well
media.
as their catalytic activity in aqueous media.3 Nevertheless, the
modulation of steric and electronic features of hydrophilic
P-donor ligands usually requires tedious synthetic work, there-
fore making difficult the optimization of the catalytic efficiency
of these systems.
An alternative to synthesize water-soluble arene-
ruthenium(II) complexes consists of using organometallic
6
precursors of the type [{RuCl(m-Cl)(h -arene)}2] bearing a
hydrophilic functionalized arene ligand. Then, their reactions
with conventional P-donor ligands, possessing different
Scheme 1 Synthetic pathway reported for precursor 1.
electronic and steric properties, would offer an easy access
6
to a wide variety of water-soluble [RuCl2(h -arene)(PR3)]
compounds. Surprisingly, despite the great number of
Results and discussion
Synthesis of complexes [RuCl2(g6-C6H5OCH2CH2OH)(L)]
Departamento de Qu´ımica Orga´nica e Inorga´nica, Instituto de Qu´ımica
(L = P(OMe)3, P(OEt)3, P(OiPr)3, P(OPh)3, PPh3)
Organometa´lica “Enrique Moles”, Facultad de Qu´ımica, Universidad de
Oviedo, E-33071, Oviedo, Spain. E-mail: crochetpascale@uniovi.es;
Fax: +33-985 10 34 46; Tel: +33-985 10 50 76
† Electronic supplementary information (ESI) available: Experimental
details and X-ray diffraction data. CCDC reference numbers 728240 and
728241. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b914789f
6
Treatment of the dimeric precursor [{RuCl(m-Cl)(h -
C6H5OCH2CH2OH)}2] (1)8 with
a slight excess of the
appropriate phosphite or phosphine ligand in dichloromethane
at room temperature affords the new mononuclear ruthenium(II)
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Table 1 Water-solubility of different arene-ruthenium(II) complexesa
6
complexes [RuCl2(h -C6H5OCH2CH2OH)(L)] (L = P(OMe)3
(2a), P(OEt)3 (2b), P(OiPr)3 (2c), P(OPh)3 (2d), PPh3 (2e)),
which have been isolated as air-stable orange-red solids
(Scheme 2).
◦
Complexes
S20 (g L-1)
C
6
[{RuCl(m-Cl)(h -C6H5OCH2CH2OH)}2], 1
10.8
755
27.2
67.3
6
[RuCl2(h -C6H5OCH2CH2OH){P(OMe)3}], 2a
6
[RuCl2(h -C6H5OCH2CH2OH){P(OEt)3}], 2b
[RuCl2(h -C6H5OCH2CH2OH){P(OiPr)3}], 2c
6
6
[RuCl2(h -C6H5OCH2CH2OH){P(OPh)3}], 2d
insolubleb
insolubleb
7.3
6
[RuCl2(h -C6H5OCH2CH2OH)(PPh3)], 2e
6
[RuCl2(h -p-cymene){P(OMe)3}], 3a
6
[RuCl2(h -p-cymene){P(OEt)3}], 3b
insolubleb
insolubleb
insolubleb
insolubleb
[RuCl2(h -p-cymene){P(OiPr)3}], 3c
6
6
[RuCl2(h -p-cymene){P(OPh)3}], 3d
Scheme 2 Synthesis of complexes 2a–e.
6
[RuCl2(h -p-cymene)(PPh3)], 3e
a At 20 ◦C. b Water-solubility values inferior to 0.5 g L-1.
Spectroscopic data and elemental analyses for compounds
2a–e are in agreement with the proposed formulations. In
Behavior of complexes [RuCl2(g6-C6H5OCH2CH2OH)(L)]
(2a–e) in water
1
particular, the 31P{ H} NMR spectra recorded in CDCl3 show
a unique singlet signal at d = 110.1–121.0 (2a–d) and 31.1 (2e)
ppm, i.e. in the expected range for phosphite- and phosphine-
ruthenium complexes, respectively.11 The Cv-symmetry of 2a–e
Since the objective of this work is the use of compounds 2a–e as
catalysts in aqueous medium, their behavior in water has been
explored. Firstly, the water-solubility of 2a–e was measured at
20 ◦C (Table 1). Thus, we found that their solubility strongly
depends on the nature of the P-donor ligand coordinated
onto the metal. Complexes 2d and 2e, containing an aryl
phosphite or phosphine, respectively, are almost insoluble in
water, due to the repulsive interactions between the solvent and
the aromatic fragments. In contrast, derivatives 2a–c bearing
an aliphatic ligand readily dissolve in water. Among them, the
trimethylphosphite compound (2a) presents an extremely high
solubility, it being possible to dissolve 755 mg of this complex in
only 1 mL of water. As far as we known this is the highest water-
solubility reported up to now for arene-ruthenium(II) complexes,
1
is evidenced, in 1H as well as in 13C{ H} NMR spectra, by the
equivalency of the two meta- and the two ortho-positions of the
6
h -arene ligand.
In addition, the structure of 2b was unambiguously con-
firmed by a single crystal X-ray diffraction study. Complex
2b exhibits the expected pseudooctahedral three-legged piano-
stool geometry around the ruthenium atom (Fig. 1). The most
remarkable features are (i) the bond angle C(6)–O(1)–C(7) =
121.4(3)◦ and (ii) the torsion angle C(1)–C(6)–O(1)–C(7) =
2.1(5)◦, both consistent with a sp2-type hybridization for the
oxygen atom adjacent to the arene ring. This is indicative of the
participation of the oxygen nucleus to the delocalized p-system
of the arene. Similar structural data have been already reported
◦
the S20 values of such derivatives usually ranging from 0 to
C
6
70 g L-1.13,14
for other arene-ruthenium(II) complexes containing h -PhOR
units.8,9,12
In order to determine to what extend the hydroxyethoxy-
functionalized arene contributes to the water-solubility of com-
6
◦
plexes [RuCl2(h -C6H5OCH2CH2OH)(L)] (2a–e), S20 values
C
6
of the analogous p-cymene derivatives [RuCl2(h -p-cymene)(L)]
(L = P(OMe)3 (3a), P(OEt)3 (3b), P(OiPr)3 (3c), P(OPh)3 (3d),
PPh3 (3e))15,16 were also measured (Table 1). As we can observe,
replacement of C6H5OCH2CH2OH by p-cymene gives rise to a
dramatic decrease of the solubility in water. Thus, compound
6
[RuCl2(h -p-cymene){P(OMe)3}] (3a) is 100 time less soluble
6
than its congener [RuCl2(h -C6H5OCH2CH2OH){P(OMe)3}]
(2a), and 3b–3e are almost insoluble (Table 1).
The stability of complexes 2a–c in water has been studied.
1
31P{ H} NMR spectra of 2a–c recorded in D2O show, along with
6
the expected signals due to [RuCl2(h -C6H5OCH2CH2OH)(L)],
6
those corresponding to the aquo-species [RuCl(D2O)(h -
C6H5OCH2CH2OH)(L)][Cl], resulting from the dissociation of
one chloride ligand and the coordination of a D2O molecule
to the metal (Scheme 3).17 Spectroscopic data of these aquo-
derivatives are consistent with the loss of the CV-symmetry in
the molecule (details are given in the ESI†).18 Moreover, the
molar conductivities of 2a–c (KM = 47–79 S cm2 mol-1) measured
in water showed values in accordance with the presence of an
equilibrium between a neutral compound and a 1 : 1 electrolyte
species. As observed for other arene-ruthenium(II) complexes,
the formation of these aquo-derivatives is completely suppressed
6
Fig.
1
ORTEP-type view of the structure of [RuCl2(h -
C6H5OCH2CH2OH){P(OEt)3}] (2b). Hydrogen atoms, except the
OH one, are omitted for clarity. Thermal ellipsoids are drawn at
˚
20% probability level. Selected bond lengths (A) and angles (deg):
Ru–Cl(1) = 2.4128(8), Ru–Cl(2) = 2.4061(8), Ru–P = 2.2786(9),
C(6)–O(1) = 1.338(4), Cl(1)–Ru–Cl(2) = 87.34(3), Cl(1)–Ru–P =
87.79(3), Cl(2)–Ru–P = 90.44(3), C(6)–O(1)–C(7) = 121.4(3).
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Scheme 4 Catalytic redox isomerization of allylic alcohols.
much less studied in water.14,16,25,26 In particular, isomerizations
of aromatic and/or sterically hindered substrates are still
challenging in aqueous media.14,26
The catalytic activity of complexes 2a–e has been checked
in the isomerization of different allylic alcohols of the type
Scheme 3 Behavior of complexes 2a–c in water.
when a tenfold excess of NaCl is added to the aqueous solutions
(Scheme 3).17 The reversible Ru–Cl bond cleavage is the unique
process observed in water. In this sense, although free phosphites
are readily hydrolyzed in aqueous media, the coordinated
phosphites in 2a–c remain unaltered even after 24 h in water.19
=
CH2 CHCH(OH)R (Table 2), which contain a terminal
carbon–carbon double bond. In a typical experiment, 4 mmol
of substrate, 1 mol% of catalyst, 5 mol% of KOtBu and 20 mL
Electrochemical study of complexes
◦
[RuCl2(g6-C6H5OCH2CH2OH)(L)] (2a–e)
of water were heated at 75 C and the reaction was monitored
by GC analyses of aliquots. Under these conditions, excellent
performances have been achieved for all allylic alcohols tested, it
being possible to transform them quantitatively in 5–45 minutes
when catalysts 2a–c were employed. Aliphatic and aromatic
substrates give rise to similar results, and electron-withdrawing
(entries 11–13 and 16–18) or electron-donor substituents (entries
21–23 and 26–28) on the benzene ring do not particularly affect
the catalytic activity of 2a–c.
For all substrates, the poorly water-soluble derivatives
2d–e, and specially the triphenylphosphite one (2d), show lower
activities than the highly soluble catalysts 2a–c. Nevertheless,
this behavior does not seem to be directly related to the water-
solubility since the same tendency is observed in the catalytic
isomerizations performed in THF solutions (see ESI†), in which
all complexes are completely soluble. There is neither a clear
correlation between the catalytic performances of 2a–e and their
steric and electronic features.27 Thus, a possible explanation to
the low activity presented by 2d–e could be the easy deactivation
of the catalytic species through orthometalation of one of the
aromatic rings of PPh3 or P(OPh)3.28
The redox behavior of complexes 2a–e has been investi-
gated using cyclovoltammetry (CV). For comparative purposes,
the redox potentials of p-cymene and benzene analogues,
6
3a–e and [RuCl2(h -benzene)(L)] (L = P(OMe)3 (4a), P(OEt)3
(4b), P(OiPr)3 (4c), PPh3 (4e)),20 have been measured under
the same conditions.21 The CV of all the derivatives shows a
quasi-reversible oxidation wave corresponding to the Ru(II)-
Ru(III) redox system. Formal potentials (E◦¢) values versus
the ferrocinium–ferrocene redox couple are given in Fig. 2.22
Regardless of the nature of the arene, the formal potential of
6
complexes [RuCl2(h -arene)(L)] decreases in the sequence L =
P(OPh)3 (d) > P(OMe)3 (a) > P(OEt)3 (b) > PPh3 (e) > P(OiPr)3
(c), in accordance with the increasing donor capacity of the
ligand (Fig. 2). On the other hand, the C6H5OCH2CH2OH-
based compounds (2a–e) present higher potentials than their
p-cymene analogues (3a–e) but lower than the benzene ones
(4a–c, 4e). Therefore, we can conclude that the electronic donor
capacity of C6H5OCH2CH2OH is intermediate between that of
benzene and p-cymene.
Interestingly, complexes 2a–c are also highly active in the
isomerization of 3-penten-2-ol (Scheme 5 and Table 3), an
=
allylic alcohol disubstituted on the C C bond. It is well known
that the transformation of such a substrate is problematic,24,29
particularly in aqueous medium.26a–c Indeed, allylic alcohols of
1
2
=
the type R HC CHCH(OH)R are difficult to isomerize, giving
rise to low turnover frequencies (TOF values ranging from 0 to
10 h-1).26a–c
6
Scheme 5 Isomerization of 3-penten-2-ol.
Fig. 2 Formal potential (in V) of complexes [RuCl2(h -arene)(L)]
(arene = C6H5OCH2CH2OH (2), p-cymene (3), benzene (4); L =
P(OMe)3 (a), P(OEt)3 (b), P(OiPr)3 (c), P(OPh)3 (d), PPh3 (e)). Numeric
values indicated in ref. 23.
It is worthy of mention that catalyst 2a is able to convert
quantitatively 3-pent-2-ol into 2-pentanone within only 30 min
(Table 3, entry 1). This result, which corresponds to a TOF
value of 200 h-1, is by far the best reported up to now for the
isomerization of a disubstituted allylic alcohol in an aqueous
medium.26a–c As observed in Table 3, compounds 2b–c are also
able to promoted the transformation of 3-penten-2-ol, although
their catalytic activity is lower than that of 2a (Table 3). For
this substrate, it seems that the increasing steric hindrance when
Catalytic isomerization of allylic alcohols into carbonyl
compounds
The redox isomerization of allylic alcohols promoted by tran-
sition metal complexes represents a straightforward synthetic
route to the corresponding saturated ketones (Scheme 4).24 This
process, extensively developed in organic medium, has been
=
moving from 2a to 2c makes the coordination of the C C bond
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6
a
=
Table 2 Isomerization of allylic alcohols CH2 CHCH(OH)R catalyzed by complexes [RuCl2(h -C6H5OCH2CH2OH)(L)] (2a–e)
Entry
R
Catalyst [L]
Time/min
Yield (%)b
TOF/h-1c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
nPent
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
2d [P(OPh)3]
2e [PPh3]
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
2d [P(OPh)3]
2e [PPh3]
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
2d [P(OPh)3]
2e [PPh3]
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
2d [P(OPh)3]
2e [PPh3]
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
2d [P(OPh)3]
2e [PPh3]
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
2d [P(OPh)3]
2e [PPh3]
15
15
5
40
30
10
15
10
60
60
20
30
30
22 h
45
15
25
99
99
99
99
96
99
99
99
96
99
98
97
98
78
90
97
96
99
84
93
99
99
99
99
99
97
99
99
79
82
400
400
1200
150
192
600
400
600
96
100
294
194
196
4
Ph
4-ClC6H4
4-BrC6H4
4-Me2NC6H4
4-MeOC6H4
120
388
230
132
3
45
25 h
17 h
15
15
30
6 h
60
10
15
15
5
400
400
200
17
100
582
400
400
3
24 h
24 h
3
a Reactions carried out at 75 ◦C using 4 mmol of appropriate allylic alcohols, 1 mol% of Ru, 5 mol% of KOtBu and 20 mL of water. b GC determined.
c Turnover frequency ((mol product/mol Ru)/time).
Table 3 Isomerization of 3-penten-2-ol catalyzed by complexes
of allylic alcohols in aqueous medium. They are particu-
larly effective to transform challenging substrates, such as
aromatic or disubstituted ones (i.e. allylic alcohols of the
6
[RuCl2(h -C6H5OCH2CH2OH)(L)] (2a–c)a
Entry
Catalyst [L]
Time/min
Yield (%)b
TOF/h-1c
1
2
=
type CH2=CHCH(OH)R or R HC CHCH(OH)R ). For these
particular substrates, the catalytic performances reached are, by
far, the highest reported to date for isomerization in an aqueous
medium.
1
2
3
2a [P(OMe)3]
2b [P(OEt)3]
2c [P(OiPr)3]
30
30
240
99
92
86
200
184
22
a Reactions carried out at 75 ◦C using 4 mmol of 3-penten-2-ol, 1 mol% of
Ru, 5 mol% of KOtBu and 20 mL of water. b GC determined. c Turnover
frequency ((mol product/mol Ru)/time).
Experimental
The manipulations were performed under an atmosphere of dry
nitrogen using vacuum-line and standard Schlenk techniques.
Solvents were dried by standard methods and distilled under
nitrogen before use. All reagents were obtained from commercial
on the metal center more difficult,30 resulting in a lower catalytic
efficiency (TOF values from 200 to 22 h-1).
6
suppliers with the exception of compounds [{RuCl(m-Cl)(h -
6
C6H5OCH2CH2OH)}2] (1),8 [RuCl2(h -p-cymene)(L)] (L =
Conclusions
P(OMe)3 (3a), P(OEt)3 (3b), P(OiPr)3 (3c), P(OPh)3 (3d), PPh3
6
In this work, an easy route to functionalized-arene ruthenium(II)
(3e))15 and [RuCl2(h -C6H6)(L)] (L = P(OMe)3 (4a), P(OEt)3
6
complexes [RuCl2(h -C6H5OCH2CH2OH)(L)] (L = P(OMe)3
(4b), P(OiPr)3 (4c), PPh3 (4e))20 which were prepared following
the methods reported in the literature. NMR spectra were
recorded on a Bruker DPX300 instrument at 300 MHz (1H),
121.5 MHz (31P) or 75.4 MHz (13C) using SiMe4 or 85% H3PO4
as standards. DEPT experiments have been carried out for all
the compounds reported in this paper. The conductivities were
measured at room temperature, in ca. 10-3 mol dm-3 water solu-
tions, with a Jenway PCM3 conductimeter. Cyclovoltammetric
measurements were performed at 20 ◦C with a “mAutolab type
III” apparatus equipped with a three-electrode system. Platinum
(2a), P(OEt)3 (2b), P(OiPr)3 (2c), P(OPh)3 (3d), PPh3 (3e))
has been described in a two-step process from commercially
available precursors. We have evidenced that the presence of the
hydroxyethoxy substituent on the arene could confer high water-
solubility to the resulting organometallic derivatives. In par-
6
ticular, [RuCl2(h -C6H5OCH2CH2OH){P(OMe)3}] is 100 times
more soluble in water than its p-cymene parent.
Complexes 2a–c, containing aliphatic P-donor ligands, have
proven to be highly efficient catalysts for redox isomerization
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disk electrode, spiral shaped platinum wire and silver wire were
used as working-, counter- and reference-electrodes, respectively.
CV experiments were carried out with CH2Cl2 solutions of the
appropriate complex (0.5 ¥ 10-3 M) and [NnBu4][PF6] (0.1 M)
as electrolyte. Formal CV potentials (E◦¢) are referenced relative
to potential of the [Cp2Fe]–[Cp2Fe]+ couple (E◦ = 0.184 V)
run under identical conditions (E◦¢ = E◦(complex+/complex) -
E◦([Cp2Fe]+/[Cp2Fe])).21 Infrared spectra were recorded on a
Perkin-Elmer 1720-XFT spectrometer. The C and H analyses
were carried out with a Perkin-Elmer microanalyzer. GC and
GC/MSD measurements were made on a Hewlett-Packard
HP6890 equipment (Supelco Beta-DexTM 120 column; 30 m;
250 mm) and an Agilent 6890 N equipment coupled to a 5973
mass detector (HP-1MS column; 30 m; 250 mm), respectively.
d: 143.8 (d, 2JPC = 4.8, Cipso), 93.0 (s, Cmeta), 73.1 (s, Cpara), 72.1 (s,
CH2O), 71.5 (d, 2JPC = 7.2, Cortho), 71.3 (d, 2JPC = 10.4, CHMe2),
60.5 (s, CH2OH), 24.0 (d, 3JPC = 4.0, CHMe2). Anal. calcd for
C17H31Cl2O5PRu: C, 39.39; H, 6.03. Found: C, 39.51; H, 5.89.
IR (KBr), n(OH): 3492 cm-1. KM = 47 S cm2 mol-1 (in water).
S20 C(H2O) = 67.3 mg.mL-1.
◦
Preparation of [RuCl2(g6-C6H5OCH2CH2OH){P(OPh)3}], 2d
Following the same procedure, 2d was prepared as a red solid,
using 0.300 g (0.484 mmol) of 1 and 304 mL (1.161 mmol) of
P(OPh)3. Chromatographic purification was carried out with a
1 : 1 mixture of CH2Cl2 and acetone. Yield: 0.304 g (51 %).
1
31P{ H} NMR, CDCl3, d: 113.8 (s). 1H NMR, CDCl3, d: 7.45–
7.19 (m, 15 H, OPh), 5.48 (m, 2 H, Hmeta), 4.84 (d, 2 H, 3JHH
=
6.3, Hortho), 4.24 (m, 2 H, OCH2), 3.98 (m, 2 H, OCH2), 3.58 (t,
Preparation of [RuCl2(g6-C6H5OCH2CH2OH){P(OMe)3}], 2a
1
1 H, 3JHH = 5.3, Hpara), 3.41 (broad s, 1 H, OH). 13C{ H} NMR,
2
2
6
CDCl3, d: 151.1 (d, JPC = 8.8, Cipso OPh), 145 (d, JPC = 4.0,
A slurry of 0.300 g of [{Ru(m-Cl)Cl(h -C6H5OCH2CH2OH)}2]
Cipso), 129.7, 125.3 and 121.8 (all s, Caromatic OPh), 93.2 (s, Cmeta),
(1) (0.484 mmol) and 137 mL of P(OMe)3 (1.161 mmol) in
150 mL of dichloromethane was stirred for 9 h at room
temperature. The resulting solution was then filtered through
Kieselguhr and evaporated to dryness. The purification by
column chromatography over silica gel, using a mixture of
CH2Cl2–acetone (1 : 2), afforded 2a as a red solid. Yield: 0.207 g
2
72.3 (d, JPC = 5.6, Cortho), 71.7 (s, Cpara), 71.6 (s, CH2O), 60.7
(s, CH2OH). Anal. calcd for C26H25Cl2O5PRu: C, 50.33; H, 4.06.
Found: C, 50.20; H, 4.29. IR (KBr), n(OH): 3420 cm-1. S20 C(H2O)
◦
inferior to 0.5 mg mL-1.
Preparation of [RuCl2(g6-C6H5OCH2CH2OH)(PPh3)], 2e
1
(49 %). 31P{ H} NMR, CDCl3, d: 121.0 (s). 1H NMR, CDCl3,
3
d: 5.89 (m, 2 H, Hmeta), 5.37 (d, 2 H, JHH = 5.1, Hortho), 4.94
Following the same procedure, 2e was prepared as an orange
solid, using 0.300 g (0.484 mmol) of 1 and 0.304 g (1.161 mmol)
of PPh3. Chromatographic purification was carried out with a
2 : 1 mixture of CH2Cl2 and acetone. Yield: 0.301 g (54 %).
3
(t, 1 H, JHH = 4.9, Hpara), 4.40 (m, 2 H, OCH2), 4.03 (m, 2 H,
OCH2), 3.81 (d, 9 H, 3JPH = 11.1, OMe), 3.5 (broad s, 1 H, OH).
1
2
13C{ H} NMR, CDCl3, d: 144.3 (d, JPC = 5.6, Cipso), 92.9 (s,
Cmeta), 72.6 (s, Cpara), 72.3 (s, CH2O), 72.0 (d, 2JPC = 10.4, Cortho),
1
1
31P{ H} NMR, CDCl3, d: 31.1 (s). H NMR, CDCl3, d: 7.76–
2
60.6 (s, CH2OH), 54.2 (d, JPC = 5.6, OMe). Anal. calcd for
7.35 (m, 15 H, PPh3), 5.41 (m, 2 H, Hmeta), 5.26 (d, 2 H, 3JHH
=
C11H19Cl2O5PRu: C, 30.43; H, 4.41. Found: C, 30.21; H, 4.14.
5.4, Hortho), 4.39 (m, 2 H, OCH2), 4.05 (m, 2 H, OCH2), 4.00 (t,
IR (KBr), n(OH): 3446 cm-1. KM = 79 S cm2 mol-1 (in water).
1 H, 3JHH = 5.1, Hpara), 3.66 (broad s, 1 H, OH). 13C{ H} NMR,
1
S20 C(H2O) = 755 mg.mL-1.
◦
CDCl3, d: 142.2 (s, Cipso), 128.2–134.2 (m, Caromatic), 91.8 (s, Cmeta),
2
75.7 (s, Cpara), 72.3 (s, CH2O), 70.3 (d, JPC = 7.2, Cortho), 60.7
Preparation of [RuCl2(g6-C6H5OCH2CH2OH){P(OEt)3}], 2b
(s, CH2OH). Anal. calcd for C26H25Cl2O2PRu: C, 54.55; H, 4.40.
Found: C, 54.34; H, 4.21. IR (KBr), n(OH): 3420 cm-1. S20 C(H2O)
◦
Following the same procedure, 2b was prepared as an orange
solid, using 0.300 g (0.484 mmol) of 1 and 0.2 mL (1.161 mmol)
inferior to 0.5 mg mL-1.
1
of P(OEt)3. Yield: 0.181 g (39 %). 31P{ H} NMR, CDCl3, d:
Typical procedure for catalytic isomerization of allylic alcohols
into ketones
116.9 (s). 1H NMR, CDCl3, d: 5.81 (m, 2 H, Hmeta), 5.33 (d, 2 H,
3JHH = 5.1, Hortho), 4.88 (t, 1 H, 3JHH = 5.1, Hpara), 4.37 (m, 2 H,
3
3
OCH2), 4.18 (dq, 6 H, JHH = JPH = 7.0, CH2Me), 4.02 (m, 2
Under an nitrogen atmosphere, the ruthenium catalyst precursor
(0.04 mmol, 1 mol%), 20 mL of deoxygenated water, potassium
tert-butoxide (0.2 mmol, 5 mol%), and allylic alcohol (4 mmol)
were introduced into a Schlenk tube fitted with a condenser.
Then, the mixture was heated at 75 ◦C. The reaction was
monitored by GC and GC/MSD analyses of aliquots, taken
every 5 min during the first hour and then the interval time
was increased progressively. Saturated ketones were the only
products generated. The identity of the products was assessed
H, CH2OH), 3.58 (broad s, 1 H, OH), 1.29 (t, 9 H, 3JHH = 7.0,
1
CH2Me). 13C{ H} NMR, CDCl3, d: 144.0 (d, 2JPC = 5.6, Cipso),
92.8 (s, Cmeta), 72.7 (s, Cpara), 72.2 (s, CH2O), 71.8 (d, 2JPC = 10.4,
2
Cortho), 63.1 (d, JPC = 5.6, CH2Me), 60.5 (s, CH2OH), 16.2 (d,
3JPC = 6.4, CH2Me). Anal. calcd for C14H25Cl2O5PRu: C, 35.30;
H, 5.29. Found: C, 35.44; H, 5.38. IR (KBr), n(OH): 3441 cm-1.
KM = 74 S cm2 mol-1 (in water). S20 C(H2O) = 27.2 mg.mL-1.
◦
Preparation of [RuCl2(g6-C6H5OCH2CH2OH){P(OiPr)3}], 2c
1
by comparison of the 1H and 13C{ H} NMR spectra with
the spectroscopic data already reported for the corresponding
ketones and the fragmentation observed in GC/MSD analyses.
Following the same procedure, 2c was prepared as a red solid,
using 0.300 g (0.484 mmol) of 1 and 287 mL (1.164 mmol) of
1
P(OiPr)3. Yield: 0.223 g (44 %). 31P{ H} NMR, CDCl3, d: 110.1
Crystal structure determination
(s). 1H NMR, CDCl3, d: 5.77 (m, 2 H, Hmeta), 5.24 (d, 2 H, 3JHH
=
6.3, Hortho), 4.89 (m, 3 H, CHMe2), 4.82 (t, 1 H, 3JHH = 5.1, Hpara),
Crystallographic data for 2a and 2b have been deposited with
the Cambridge Crystallographic Data Center as supplementary
publications Nos. CCDC 728240 (2a) and 728241 (2b). Copies
4.37 (m, 2 H, OCH2), 4.02 (m, 2 H, OCH2), 3.65 (broad s, 1 H,
1
OH), 1.29 (d, 18 H, 3JHH = 6.3, CHMe2). 13C{ H} NMR, CDCl3,
This journal is
The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 1681–1686 | 1685
©

View Article Online
of the data can be obtained free of charge in the ESI† or via
www.ccdc.cam.ac.uk/data_request/cif.
following the procedures previously reported in ref. 11 and in:
(a) M. A. Bennett and A. K. Smith, J. Chem. Soc., Dalton Trans.,
1974, 233; (b) S. A. Serron and S. P. Nolan, Organometallics, 1995,
14, 4611.
16 P. Crochet, J. D´ıez, M. A. Ferna´ndez-Zu´mel and J. Gimeno, Adv.
Synth. Catal., 2006, 348, 93.
Acknowledgements
17 (a) For similar hydrolysis processes see for example: P. Csabai and F.
Joo´, Organometallics, 2004, 23, 5640; (b) R. Ferna´ndez, M. Melchart,
A. Habtemariam, S. Parsons and P. J. Sadler, Chem.–Eur. J., 2004,
10, 5173; (c) C. Scolaro, A. Bergamo, L. Brescacin, R. Delfino, M.
Cocchietto, G. Laurenczy, T. J. Geldbach, G. Sava and P. J. Dyson,
J. Med. Chem., 2005, 48, 4161.
This work was supported by Spanish “Ministerio de Educacio´n
y Ciencia” (Projects CTQ2006-084885/BQU and CSD2007-
00006 (Consolider Ingenio 2010 program)) and FICYT of
Asturias (Project IB08-036). B.L.-B. thanks FICYT of Asturias
for the award of a Ph.D grant (PCTI-Severo Ochoa program).
6
18 Attempts to crystallize the aquo-derivative [RuCl2(H2O)(h -
C6H5OCH2CH2OH){P(OMe3)}][Cl] from water-solutions led only
6
to the neutral derivative [RuCl2(h -C6H5OCH2CH2OH){P(OMe)3}]
Notes and references
(details of X-ray diffraction study given in the ESI†).
19 S. K. McIntyre and T. M. Alam, Magn. Reson. Chem., 2007, 45,
1022.
1 (a) F. Joo´, in Aqueous Organometallic Catalysis, Kluwer, Dordrecht,
2001; (b) Aqueous-Phase Organometallic Catalysis, ed. B. Cornils and
W. A. Herrmann, Wiley-VCH, Weinheim, 2004; (c) M. Wang and
C.-J. Li, Top. Organomet. Chem., 2004, 11, 321; (d) Multiphase Ho-
mogeneous Catalysis, ed. B. Cornils, W. A. Herrmann, I. T. Horva´th,
W. Leitner, S. Mecking, H. Olivier-Bourbigou and D. Vogt, Wiley-
VCH, Weinheim, 2005; (e) C.-J. Li, Chem. Rev., 2005, 105, 3095; (f) L.
Chen and C.-J. Li, Adv. Synth. Catal., 2006, 348, 1459; (g) Organic
Reactions in Water, ed. U. M. Lindstro¨m, Blackwell Publishing,
Oxford, 2007.
20 (a) R. A. Zelonka and M. C. Baird, J. Organomet. Chem., 1972, 35,
C43; (b) H. Werner, H. Kletzin and K. Roder, J. Organomet. Chem.,
1988, 355, 401.
21 (a) Redox potentials of some p-cymene and benzene ruthenium(II)
complexes have been already reported but under different experimen-
tal conditions: D. Devanne and P. H. Dixneuf, J. Organomet. Chem.,
1990, 390, 371; (b) R. Bhalla, C. J. Boxwell, S. B. Duckett, P. J. Dyson,
D. G. Humphrey, J. W. Steed and P. Suman, Organometallics, 2002,
21, 924.
22 (a) G. Gritzner and J. Kuta, Pure Appl. Chem., 1984, 56, 461; (b) N. G.
Connelly and W. E. Geiger, Chem. Rev., 1996, 96, 877.
23 Formal oxidation potentials (in V): 2a, 0.82; 2b, 0.77; 2c, 0.70; 2d,
0.86; 2e, 0.71; 3a, 0.71; 3b, 0.66; 3c, 0.61; 3d, 0.76; 3e, 0.60; 4a, 0.85;
4b, 0.83; 4c, 0.74; 4e, 0.81.
24 (a) R. C. van der Drift, E. Bouwman and E. Drent, J. Organomet.
Chem., 2002, 650, 1; (b) R. Uma, C. Cre´visy and R. Gre´e, Chem. Rev.,
2003, 103, 27; (c) V. Cadierno, P. Crochet and J. Gimeno, Synlett,
2008, 1105.
2 (a) N. Pinault and D. W. Bruce, Coord. Chem. Rev., 2003, 241, 1;
(b) K. H. Shaughnessy, Chem. Rev., 2009, 109, 643.
3 V. Cadierno and P. Crochet, in Advances in Organometallic Chemistry
Research, ed. K. Yamamoto, Nova Science Publishers, New York,
2007, pp. 37–65.
4 W. E. Ang and P. J. Dyson, Eur. J. Inorg. Chem., 2006, 4003.
5 (a) J. Gimeno, V. Cadierno and P. Crochet, in Comprehensive
Organometallic Chemistry III, ed. R. H. Crabtree and D. M. P. Min-
gos, Elsevier, Oxford, 2006, vol. 6, pp. 465; (b) B. Therrien, Coord.
Chem. Rev., 2009, 253, 493.
25 (a) D. V. McGrath, R. H. Grubbs and J. W. Ziller, J. Am. Chem. Soc.,
1991, 113, 3611; (b) T. Karlen and A. Ludi, Helv. Chim. Acta, 1992,
75, 1604; (c) D. V. McGrath and R. H. Grubbs, Organometallics,
1994, 13, 224; (d) H. Schumann, V. Ravindar, L. Meltser, W. Baidossi,
Y. Sasson and J. Blum, J. Mol. Catal. A: Chem., 1997, 118, 55; (e) V.
Cadierno, P. Crochet, S. E. Garc´ıa-Garrido and J. Gimeno, Dalton
Trans., 2004, 3635; (f) V. Cadierno, P. Crochet, S. E. Garc´ıa-Garrido
and J. Gimeno, Curr. Org. Chem., 2006, 10, 165; (g) M. Fekete and
F. Joo´, Catal. Commun., 2006, 7, 783; (h) T. Campos-Malpartida, M.
6 T. J. Geldbach, G. Laurenczy, R. Scopelliti and P. J. Dyson,
Organometallics, 2006, 25, 733.
7 J. R. Adams and M. A. Bennett, Adv. Organomet. Chem., 2006, 54,
293.
8 J. Soleimannejad and C. White, Organometallics, 2005, 24, 2538.
9 (a) J. Soleimannejad, A. Sisson and C. White, Inorg. Chim. Acta,
2003, 352, 121; (b) J. Soleimannejad, H. Adams and C. White, Anal.
Sci.: X-Ray Struct. Anal. Online, 2005, 21, x151.
10 S. Dougan, A. Habtemariam, M. Melchart and P. Sadler, PCT Int.
Appl., WO 2007101997A1, 2007.
11 See for example E. Hodson and S. J. Simpson, Polyhedron, 2004, 23,
2695.
12 (a) T. Hayashida and H. Nagashima, Organometallics, 2002, 21, 3884;
(b) J. Soleimannejad, H. Adams and C. White, Acta Crystallogr., Sect.
C: Cryst. Struct. Commun., 2005, 61, m125.
´
Fekete, F. Joo´, A. Katho´, A. Romerosa, M. Saoud and W. Wojtko´w,
J. Organomet. Chem., 2008, 693, 468.
26 (a) V. Cadierno, S. E. Garc´ıa-Garrido and J. Gimeno, Chem.
Commun., 2004, 232; (b) V. Cadierno, S. E. Garc´ıa-Garrido, J.
´
Gimeno, A. Varela-Alvarez and J. A. Sordo, J. Am. Chem. Soc., 2006,
128, 1360; (c) D. H. Leung, R. G. Bergman and K. N. Raymond,
J. Am. Chem. Soc., 2007, 129, 2746; (d) V. Cadierno, J. Francos, J.
Gimeno and N. Nebra, Chem. Commun., 2007, 2536.
13 (a) W. H. Ang, E. Daldini, C. Scolaro, R. Scopelliti, L. Juillerat-
Jeannerat and P. J. Dyson, Inorg. Chem., 2006, 45, 9006; (b) V.
Cadierno, J. Francos and J. Gimeno, Chem.–Eur. J., 2008, 14, 6601;
(c) G. W. Wong, W.-C. Lee and B. J. Frost, Inorg. Chem., 2008, 47,
612; (d) R. Schuecker, R. O. John, M. A. Jakupec, V. B. Arion and
B. K. Keppler, Organometallics, 2008, 27, 6587.
27 Tolman angles (q) for P(OMe)3, P(OEt)3, P(OPh)3, P(OiPr)3, PPh3:
107, 123, 128, 130 and 145◦, respectively.
28 For such a process see for example: F. L. Joslin, J. T. Mague and
D. M. Roundhill, Organometallics, 1991, 10, 521.
´
29 P. Crochet, M. A. Ferna´ndez-Zu´mel, J. Gimeno and M. Scheele,
Organometallics, 2006, 25, 4846.
14 A. E. D´ıaz-Alvarez, P. Crochet, M. Zablocka, C. Duhayon, V.
Cadierno, J. Gimeno and J. P. Majoral, Adv. Synth. Catal., 2006,
348, 1671.
15 Preparation and characterization of the new compound 3c are
described in the ESI.† Complexes 3a–b and 3d–e were synthesized
=
30 Coordination of the C C bond on the metal during the catalytic
cycle is usually proposed for these processes. See, for example, ref. 24
and 26b.
1686 | Green Chem., 2009, 11, 1681–1686
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The Royal Society of Chemistry 2009
©