Catalytic isomerization of allylic alcohols by (η6-p-cymene) -ruthenium(II) complexes in organic and aqueous media: New recyclable and highly efficient catalysts in water containing ammonium-functionalized ligands

Article abstract of DOI:10.1002/adsc.200505279

The water-soluble complexes [RuCl₂(η⁶-p-cymene) {κ-(P)-PPh_3-n(OCH₂CH₂NMe ₃)_n}][SbF₆]_n [n = 1 (4a), 2 (4b) or 3 (4c)] have been prepared from the neutral precursors [RuCl₂(η ⁶-p-cymene){κ-(P)-PPh_3-n(OCH₂CH ₂NMe₂)_n}] [n = 1 (2a), 2 (2b) or 3 (2c)] and MeI via quaternization of the nitrogen atom of the terminal aminoalkyl groups, and subsequent counteranion exchange by the treatment with AgSbF₆. Complexes 2a-c and 4a-c have proven to be highly active catalysts for isomerization of allylic alcohols in THF and aqueous media, respectively. Moreover, the water-soluble catalysts 4a-c can be reused after a simple extraction process at the end of the reaction. In particular, 4c presents a remarkable capability to be recycled, being active during 10 successive runs.

Full text of DOI:10.1002/adsc.200505279

FULL PAPERS
DOI: 10.1002/adsc.200505279
Catalytic Isomerization of Allylic Alcohols by (h6-p-Cymene)-
Ruthenium(II) Complexes in Organic and Aqueous Media: New
Recyclable and Highly Efficient Catalysts in Water Containing
Ammonium-Functionalized Ligands
´
´
´
Pascale Crochet,* Josefina Díez, Mariano A. Fernandez-Zumel, Jose Gimeno*
´
´
´
Departamento de Química Organica e Inorganica, Instituto Universitario de Química Organometalica “Enrique Moles”
(Unidad Asociada al CSIC), Facultad de Química, Universidad de Oviedo, 33071 Oviedo, Spain
Fax: (þ34)-985 10 34 46, e-mail: pascale@fq.uniovi.es, jgh@uniovi.es
Received: July 15, 2005; Accepted; October 31, 2005
Dedicated to our friend Antonio Abad on the occasion of his retirement.
Supporting Information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The water-soluble complexes [RuCl2(h6-p- alcohols in THF and aqueous media, respectively.
cymene){k-(P)-PPh (OCH CH NMe ) }][SbF ]
Moreover, the water-soluble catalysts 4a–c can be
À
3
n
2
2
3
n
6 n
[n¼1 (4a), 2 (4b) or 3 (4c)] have been prepared from reused after a simple extraction process at the end
the neutral precursors [RuCl2(h6-p-cymene){k-(P)- of the reaction. In particular, 4c presents a remarka-
PPh3-n(OCH2CH2NMe2)n}] [n¼1 (2a), 2 (2b) or 3 ble capability to be recycled, being active during 10
(2c)] and MeI via quaternization of the nitrogen successive runs.
atom of the terminal aminoalkyl groups, and subse-
quent counteranion exchange by the treatment with
AgSbF6. Complexes 2a–c and 4a–c have proven to Keywords: allylic alcohol; ammonium ligands; isomer-
be highly active catalysts for isomerization of allylic ization, recycling; ruthenium; water-soluble
Introduction
have proven to be highly efficient with TOF values up
to ca. 62,000 hÀ1, they can be recycled only when volatile
Catalytic organic reactions in water are among the most products are formed.[3] In contrast, some complexes of
appealing challenges of modern organic chemistry.[1] type C have been reused upto seven times, albeit they
The use of water as an environmental friendly solvent present only moderate activity.[4] With these precedents
for organic reactions has been triggered by the interest in mind we believe that there is a need to developnew
both in academic laboratories and industries to accom- efficient and easily recyclable catalytic systems in water
plish the principles of green chemistry.[2] In particular, for this atom economy process.
catalytic transformations in water with atom economy
Transition metal complexes containing water-soluble
are specially attractive and significant achievements phosphines as ligands are among the most common
have recently been disclosed.[1,2]
In the context of our interest to developcatalytic syn-
and efficient catalysts in aqueous media.[5] In particular,
a series of metal catalysts of palladium,[6] rhodium,[7] and
thetic methodologies in water, we have recently report- ruthenium[7i,7k,8] containing cationic phosphine ligands
ed the isomerization of allylic alcohols into carbonyl bearing ammonium functions in the backbone have
compounds catalyzed by bis-allylruthenium(IV) com- been reported. Only some of them can be recycled while
plexes [RuCl2(h3:h2:h3-C12H18)] (A) (C12H18 ¼dodeca- retaining the catalytic activity throughout several cycles.
2,6,10-triene-1,12-diyl)
and
[{RuCl(m-Cl)(h3:h3-
Here we describe the synthesis of the novel water-solu-
C10H16)}2][3] (B) (C10H16 ¼2,7-dimethylocta-2,6-diene- ble arene-ruthenium(II) complexes [RuCl2(h6-p-cy-
1,8-diyl) and by arene-ruthenium(II) derivatives mene){k-(P)-PPh (OCH CH NMe ) }][SbF ] (n¼1, 2
À
3
n
2
2
3
n
6 n
[RuCl2(h6-arene){P(CH2OH)3}] (C) and [RuCl(h6-arene) or 3) and their neutral precursors [RuCl2(h6-p-cymene)
{P(CH2OH)3}2][Cl] (D).[4] Although catalysts A and B {k-(P)-PPh (OCH CH NMe ) }] as well as their catalytic
À
3
n
2
2
2 n
Adv. Synth. Catal. 2006, 348, 93 – 100
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93

Pascale Crochet et al.
FULL PAPERS
activity in the isomerization of allylic alcohols in water and (1c) ligands, the new phosphonite ligand PPh(OCH2-
THF, respectively. Both types of complexes are highly effi- CH2NMe2)2 (1b) was synthesized in good yield by con-
cient catalysts and the hydro-soluble derivatives show a re- densation of dichlorophenylphosphine with two equiva-
markable capability to be recycled (up to 10 cycles).
lents of dimethylaminoethanol in the presence of NEt3
(Scheme 1).
The reaction of the dimer [{RuCl(m-Cl)(h6-p-cym-
Results and Discussion
ene)}2][11] with a slight excess of ligand PPh (OCH -
À
3
n
2
CH2NMe2)n [n¼1 (1a); 2 (1b); 3 (1c)], in dichlorome-
In order to compare the catalytic activity in organic and thane at room temperature leads to the formation of
aqueous reaction media the arene-ruthenium(II) com- the corresponding complexes [RuCl2(h6-p-cymene)
plexes [RuCl (h6-p-cymene){k-(P)-PPh (OCH CH - {k-(P)-PPh (OCH CH NMe ) }] [n¼1 (2a); 2 (2b); 3
À
À
3 n
2
3
n
2
2
2
2
2 n
NMe2)n}] [n¼1 (2a), 2 (2b), 3 (2c)] and [RuCl2(h6-p-cym- (2c)] (Scheme 2). Spectroscopic and analytical data con-
ene){k-(P)-PPh (OCH CH NMe ) }][X] [X¼I, n¼1 firm the proposed formulation (see Supporting Infor-
À
3
n
2
2
3
n
n
(3a), 2 (3b), 3 (3c);X¼SbF6, n¼1(4a), 2 (4b), 3 (4c)], con- mation). In particular, the 31P{1H} NMR spectra show
taining neutral and cationic phosphorus-donor ligands, re- a unique signal at d¼113.1 (2a), 138.0 (2b) and 113.8
spectively, have been synthesized. The latter are formed (2c) ppm, in the expected range for phosphinite, phos-
by the quaternization of the nitrogen atom in the terminal phonite and phosphite complexes, respectively.[12] The
aminoalkyl groups of the neutral complexes.
iodide phosphonite derivative [RuI2(h6-p-cymene){k-
(P)-PPh(OCH2CH2NMe2)2}] (2’b) is similarly prepared
starting from the iodide dimer [{RuI(m-I)(h6-p-cym-
ene)}2][13] and ligand 1b.
Synthesis of the Precursor Complexes [RuCl2(h6-p-
cymene){k-(P)-PPh3Àn(OCH2CH2NMe2)n}] [n¼1 (2a);
2 (2b); 3 (2c)]
Synthesis of the Cationic Complexes [RuCl2(h6-p-
Following a similar methodology to that previously used cymene){k-(P)-PPh3–n(OCH2CH2NMe3)n}][X]n [X¼I,
to prepare the related phosphinite PPh2(OCH2CH2- n¼1 (3a); 2 (3b); 3 (3c); X¼SbF6, n¼1 (4a); 2 (4b); 3
[10]
NMe2)[9] (1a) and phosphite P(OCH2CH2NMe2)3
(4c)]
The treatment of the amino-complexes 2a–c and 2’b
with an excess of methyl iodide affords the related qua-
ternary ammonium derivatives [RuCl2(h6-p-cymene)
{k-(P)-PPh (OCH CH NMe ) }][I] [n¼1 (3a);
2
À
3
n
2
2
3
n
n
(3b); 3 (3c)] and [RuI2(h6-p-cymene){k-(P)-PPh(OCH2-
Scheme 1. Synthesis of the phosphonite ligand 1b.
CH2NMe3)2}][I]2
(3’b),
respectively
(72–88%;
Scheme 2. Synthesis of arene-ruthenium(II) complexes.
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Catalytic Isomerization of Allylic Alcohols
FULL PAPERS
chloride complexes 3a–c in water evolve into a mixture
of compounds after a period of 2–24 hours. The spectro-
scopic data which are very similar to those of the related
starting complexes suggest the formation of mixtures
containing diiodide and chloride-iodide derivatives, as
the result of complete or partial metathesis between
chloride ligands and iodide counteranions, respectively
(Scheme 3). This is confirmed by the stability of the
all-iodide
complex
[RuI2(h6-p-cymene){k-(P)-
PPh(OCH2CH2NMe3)2}][I]2 (3’b) in water.
In order to avoid this metathical process, the iodide
counteranions in 3a–c were replaced by non-coordinat-
ing [SbF6]À anions. The reaction of complexes 3a, 3b and
3c with one, two and three equivalents of AgSbF6, re-
spectively, in dichloromethane or a mixture of dichloro-
methane and methanol, affords the hexafluoroantimo-
Scheme 3. Evolution of complexes 3a–c in water.
nate salts [RuCl (h6-p-cymene){k-(P)-PPh (OCH -
À
2
3
n
2
Scheme 2). As expected due to their ionic composition, CH2NMe3)n}][SbF6]n [n¼1 (4a);
2
(4b);
3
(4c)]
these compounds are water-soluble, the solubility in- (Scheme 2). The reactions proceed through the selective
creasing with the number of ammonium groups in the exchange of the iodide counteranions, keeping the
molecule. Nevertheless, the solutions of the cationic chloride ligands unchanged. The completion of this sub-
stitution process has been checked by ICP-MAS analy-
ses of iodine, which indicate in all cases a value lower
than 0.2%.
The structure of 4a has been unequivocally confirmed
by a single-crystal X-ray diffraction study. Although the
crystal contains two symmetrically independent mole-
cules, only one is described here since they show similar
features. An ORTEP view is shown in Figure 1; selected
bond distances and angles are listed in the caption. The
molecule shows a pseudooctahedral three-legged piano-
stool coordination around the ruthenium atom, which is
bonded to the p-cymene acting as a h6 ligand, the phos-
phorus atom of the phosphinite ligand and the two chlor-
ide ligands.
Catalytic Isomerization of Allylic Alcohols in Organic
Medium
In order to compare the efficiency of our catalysts in
both organic and aqueous media, we have explored first
the catalytic activity of the neutral complexes [RuCl2(h6-
p-cymene){PPh (OCH CH NMe ) }] (2a–c), in THF.
À
3
n
2
2
2 n
Since it is well known that the efficiency of the catalysts
in the isomerization of allylic alcohols strongly depends
Figure 1. ORTEP-type view of the structure of [RuCl2(h6-p-
cymene){PPh2(OCH2CH2NMe3)}][SbF6] (4a) showing the on the addition of base or chloride abstractor,[3,14,15] we
crystallographic labelling scheme. Hydrogen atoms are omit-
ted for clarity. Thermal ellipsoids are drawn at 50% probabil-
ity level. Selected bond lengths (Š) and angles (deg):
have checked the catalytic performances in the presence
of different co-catalysts. In a typical experiment, the
ruthenium precursor [RuCl2(h6-p-cymene){k-(P)-
PPh(OCH2CH2NMe2)2}] (2b) (1 mol % Ru) and the
À
À
À
Ru Cl(2)¼
Ru C*¼1.7246(2);
Ru Cl(1)¼2.4072(7);
À
À
O P¼1.612(2);
2.4123(7);
Ru P¼2.3149
C* Ru Cl(1)¼126.265(18);
(7);
À
À
À
À
C* Ru Cl(2)¼123.85(2);
À
À
À À
Cl(1) Ru Cl(2)¼88.86(2);
C* Ru P¼132.01(2);
À
À
À À
Cl(2) Ru P¼88.76(2);
Cl(1) Ru P¼83.30(2);
À À
À À
O P C(22)¼103.27(12);
O P C(16)¼95.09(12);
À À
C(16) P C(22)¼103.42(14). C*¼centroid of the p-cymene
ring [C(1), C(2), C(3), C(4), C(5), C(6)].
Scheme 4. Isomerization of 1-octen-3-ol into octan-3-one.
Adv. Synth. Catal. 2006, 348, 93 – 100
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95

Pascale Crochet et al.
Table 1. Isomerization of 1-octen-3-ol into octan-3-one in THF catalyzed by 2b in presence of different co-catalysts.[a]
FULL PAPERS
[b]
Entry
Co-catalyst
Time [min]
Yield [%]
TOF [hÀ1
]
1
2
3
4
5
6
7
8
9
10
11
12
13
–
–
240
165
290
290
215
195
295
135
60
0
6
0
0
2
0
AgSbF6
Li2CO3
Na2CO3
K2CO3
Cs2CO3
LiOH[c]
CsOH[c]
KO-t-Bu
KO-t-Bu
KO-t-Bu
KO-t-Bu[d]
KO-t-Bu[e]
(2 mol %)
(2 mol %)
(2 mol %)
(2 mol %)
(2 mol %)
(2 mol %)
(2 mol %)
(2 mol %)
(1 mol %)
(5 mol %)
(5 mol %)
(5 mol %)
8
2
98
98
22
98
99
98
99
99
0
27
30
5
44
99
38
1188
4950
0
155
5
60
60
[a]
Reactions carried out at 758C using 4 mmol of 1-octen-3-ol and 1 mol % of 2b in 20 mL of THF.
Turnover frequency [(mol product/mol Ru)/time].
Monohydrated.
With 0.02 mol % of 2b.
In the absence of ruthenium catalyst.
[b]
[c]
[d]
[e]
co-catalyst (2 mol %) were added to a 0.2 M solution of m(II) complexes, namely [{RuCl(m-Cl)(h6-p-cym-
1-octen-3-ol (4 mmol) in THF and heated at 758C ene)}2], [RuCl2(h6-p-cymene)(PPh3)] and [RuCl2(h6-p-
(Scheme 4), the reaction being monitored by gas chro- cymene){P(OEt)3}] (5), have been also checked (entries
matography. Results are summarized in Table 1.
7–9 in Table 2). In contrast to the dimer [{RuCl(m-
The key role of the co-catalyst is clearly evidenced Cl)(h6-p-cymene)}2] for which the transformation re-
when the reaction is carried out in the presence of only quires a significantly longer reaction time, the mononu-
the precursor 2b since no conversion is observed after clear derivatives present similar activity to that of com-
4 hours (entry 1). Although the catalyst 2b becomes ac- plexes 2a–c. Noteworthy, the novel compound [RuCl2
tive in the presence of 2 mol % of alkaline carbonate (h6-p-cymene){P(OEt)3}] (5) (see preparation in Sup-
and hydroxide (entries 4–8) and AgSbF6 (entry 2), the porting Information) leads to quantitative yield in only
best result is obtained in the presence of KO-t-Bu (entry 10 min (entry 9).
9). Performing experiments with different Ru/KO-t-Bu
Complex 2a, the most active amino-derivative cata-
molar ratios it is found that a considerable improvement lyst, is also highly efficient in the isomerization of other
of the catalytic activity is observed by increasing the mo- allylic alcohols such as 1-hepten-3-ol, 1-hexen-3-ol, 1-
lar ratio from 1 to 5 (entries 9–11), the isomerization be- penten-3-ol, 3-penten-2-ol and 1-phenyl-prop-2-en-1-
ing completed within only 5 minutes for the latter molar ol which are quantitatively transformed within 15 mi-
ratio (entry 11). In a blank experiment, we have also nutes (entries 1–5, Table 3). Furthermore, homoallylic
checked that co-catalyst KO-t-Bu is not able to promote substrates, such as 4-penten-2-ol, can be also isomerized
the transformation in the absence of the ruthenium com- into the corresponding carbonyl compound although a
plex (entry 13). Remarkably, the activity of 2b is re- longer reaction time is required (entry 6).
tained at lower catalyst loadings. As an example, using
0.02 mol % of ruthenium, 1-octen-3-ol (0.2 M in THF,
substrate/Ru/KO-t-Bu¼5000/1/250)[16] is quantitatively Catalytic Isomerization of Allylic Alcohols in Water
transformed within 1 hour (entry 12; TOF¼4950 hÀ1).
Under the optimal catalytic conditions found for the The catalytic isomerization of 1-octen-3-ol and 1-pent-
model reaction (substrate/Ru/KO-t-Bu ratio¼100/1/ en-3-ol in water using the hydro-soluble catalysts 4a–c
5), the catalytic activities of complexes 2a and 2c have has been studied. The reactions were performed using
also been investigated (Table 2) and we found that the 1 mol % of ruthenium pre-catalyst, 5 mol % of KO-t-
transformation is likewise completed in only 5 min (en- Bu, and 4 mmol of the corresponding allylic alcohol in
tries 1–3). When the reaction temperature is lowered 20 mL of water at 758C. The results are summarized in
(358C) the efficiency of catalysts 2a–c still remains Table 4. Although all of them are active, catalysts 4a
very high affording quantitative conversion into 3-octa- and 4b are able to convert quantitatively both substrates
none within 15–30 min (entries 4–6). For comparative very rapidly within 15 min (entries 1, 3, 4 and 6). The fol-
purposes the catalytic activity of other arene-rutheniu- lowing features deserve to be mentioned: a) Complexes
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Catalytic Isomerization of Allylic Alcohols
Table 2. Comparison of different catalysts in the isomerization of 1-octen-3-ol into octan-3-one in THF.[a]
FULL PAPERS
[c]
Entry
Catalyst
T [8C]
Time [min]
Yield [%][b]
TOF [hÀ1
]
1
2
3
4
5
6
7
8
9
2a
2b
2c
2a
2b
2c
75
75
75
35
35
35
35
35
35
5
5
5
15
15
30
105
30
10
99
99
99
99 [30]
99 [20]
99 [3]
97
99
98
1188
1188
1188
396
396
198
55
[{Ru(h6-p-cymene)(m-Cl)Cl}2]
[Ru(h6-p-cymene)Cl2(PPh3)]
[Ru(h6-p-cymene)Cl2{P(OEt)3}] (5)
198
588
[a]
Reactions carried out using 4 mmol of 1-octen-3-ol, 1 mol % of catalyst and 5 mol % of KO-t-Bu, in 20 mL of THF.
Yields after 5 min in brackets.
Turnover frequency [(mol product/mol Ru)/time].
[b]
[c]
Table 3. Isomerization of various unsaturated alcohols catalyzed by complex 2aa
[b]
Entry
Substrate
Product
T [8C]
35
Time
Yield [%]
TOF [hÀ1
]
1
2
3
15 min
15 min
15 min
99
99
99
396
35
396
35
396
4
75
15 min
99
396
5[c]
75
75
5 min
5h25
95[d]
85[e]
228
16
6
[a]
Reactions carried out using 4 mmol of substrate, 1 mol % of 2a and 5 mol % of KO-t-Bu in 20 mL of THF.
Turnover frequency [(mol product/mol Ru)/time].
[b]
[c]
[d]
[e]
Substrate/Ru/KO-t-Bu¼100/5/25.
Along with 5% of penten-2-ol and 3-penten-2-one.
Along with 14% of penten-2-ol and 3-penten-2-one.
4a–c remain efficient even in the absence of base (en- which acts both as base and as halide abstractor (entries
tries 2, 5 and 8), although the reaction proceeds at a low- 10 and 12, Table 4), affording the transformation of 1-
er rate. This behavior contrasts with that of catalysts 2a– octen-3-ol and 1-penten-3-ol in 10 and 5 min, respective-
c in THF, which are totally inactive without base. Prob- ly.
ably, the higher polarity of water vs. THF favors the dis-
Since KO-t-Bu readily undergoes hydrolysis in water
sociation of the chloride ligands in the catalysts[17] and leading to the formation of KOH and tert-butanol, we
the deprotonation of the allylic alcohol. b) In contrast also performed the isomerization of 1-octen-3-ol using
to the catalyst 4c containing hexafluoroantimonate as KOH as co-catalyst. In all the cases, the catalytic activi-
counteranion, the related iodide compound [RuCl2(h6- ties are identical or slightly lower than that obtained
p-cymene){k-(P)-P(OCH2CH2NMe3)3}][I]3 (3c) only with KO-t-Bu,[18] and they still remain inferior when a
leads to very low conversion (entry 11) indicating that mixture of KOH and tert-butanol is used. These small
the presence of a non-coordinative counteranion is cru- differences in activity can be ascribed to the higher pro-
cial. As we have commented before, the complex 3c un- pensity of KOH to be carbonated and hydrated.
dergoes a chloride-iodide exchange process in water,
Since the great solubility of complexes 4a–c in water
giving rise to a mixture containing iodide complexes allows the easy separation of the organic product from
which are less prone to dissociate the halide ligands, as the catalyst by simple liquid-liquid extraction at the
required to create a vacancy at the metal center. This end of the reaction (see details in the Experimental Sec-
problem can be circumvented by addition of KO-t-Bu, tion), we have examined the catalyst recycling. Remark-
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Pascale Crochet et al.
FULL PAPERS
Table 4. Isomerization of allylic alcohols in water catalyzed by complexes 3c, 4a–c.[a]
[b]
Entry
Substrate
Catalyst
Time [min]
Yield [%]
TOF [hÀ1
]
1
2
3
4
5
6
7
8
9
1-octen-3-ol
1-octen-3-ol
1-penten-3-ol
1-octen-3-ol
1-octen-3-ol
1-penten-3-ol
1-octen-3-ol
1-octen-3-ol
1-penten-3-ol
1-octen-3-ol
1-octen-3-ol
1-penten-3-ol
4a
10
150
15
15
45
99
88
97
99
99
99
99
99
99
97
15
99
594
35
4a[c]
4a
388
396
132
1188
170
52
15
582
6
4b
4b[c]
4b
5
35
4c
4c[c]
4c
115
400
10
160
5
10
11
12
3c
3c[c]
3c
1188
[a]
Reactions carried out at 758C using 4 mmol of substrate, 1 mol % of catalyst and 5 mol % of KO-t-Bu, in 20 mL of water.
Turnover frequency [(mol product/mol Ru)/time].
Without KO-t-Bu.
[b]
[c]
ably, catalysts 4a, 4b and 4c can be recycled 3, 7 and 9 ents the higher capacity to be recycled (at least 10
times, respectively, after the isomerization of 1-octen- runs). In contrast, 4a can be only recycled 3 times, prob-
3-ol into octan-3-one (Table 5). It seems that the higher ably due to the leaching of the catalyst during the extrac-
the water-solubility of the catalyst precursor is, the bet- tion process with the organic solvents in which it is some-
ter is the recycling process. Indeed, the tricationic com- what soluble.
plex 4c, which is the most water-soluble catalyst, pres-
As far as we know, the performance of the pre-catalyst
4c in terms of recycling capacity is at present the best re-
ported.[3,4,19] Previous attempts to reuse the catalysts are
limited to the ruthenium(IV) complexes [RuCl2-
(h3:h2:h3-C12H18)] (C12H18 ¼dodeca-2,6,10-triene-1,12-
diyl) and [{RuCl(m-Cl)(h3:h3-C10H16)}2] (C10H16 ¼2,7-di-
methylocta-2,6-dien-1,8-diyl),[3] the arene-ruthenium
Table 5. Recycling of catalysts 4a–c in the isomerization of
1-octen-3-ol into octan-3-one.[a]
Entry Catalyst Cycle Time [min] Yield [%] TON[b]
derivatives
[RuCl2(h6-arene){P(CH2OH)3}]
and
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
4a
4b
1
2
3
4
5
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9
10
10
25
40
120
200
15
99
99
99
99
0
99
198
297
396
[RuCl(h6-arene){P(CH2OH)3}2][Cl][4] and some rhodi-
um complexes containing aryl-phosphonated and -sul-
fonated phosphines.[19] Itis worthy ofmention that 1-oct-
en-3-ol represents one of the most challenging sub-
strates for isomerization of allylic alcohols in water
due to its steric requirement and its low water-solubility.
It has been reported that its transformation is slow com-
pared with other allylic alcohols[4,19a] and dramatic deac-
tivation of the catalytic system is observed in the second
cycle, requiring at least 24 h to complete the reaction.[4]
In this context, both the high activities of 4a–c and the
excellent capability of recycling of 4c represent a great
advancement.
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
198
297
396
495
594
693
792
99
198
297
396
495
594
693
792
891
990
40
150
105
120
115
200
310
35
65
65
70
70
70
80
115
80
215
4c
Conclusions
The isomerization of allylic alcohols into the corre-
sponding saturated carbonyl compounds catalyzed by
transition metal complexes represents a straightforward
synthetic process which otherwise requires a two-steps
sequence of oxidation and reduction reactions.[20,21] Fur-
thermore, the total atom economy of this transforma-
tion makes it particularly attractive from an environ-
mental point of view.[2] Despite these facts, the number
[a]
Reactions carried out at 758C using 4 mmol of 1-octen-3-
ol, 1 mol % of catalyst, 5 mol % of KO-t-Bu, in 20 mL of
water.
[b]
TON¼Turnover number (mol product/mol Ru). Cumula-
tive TON values.
98
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 93 – 100

Catalytic Isomerization of Allylic Alcohols
FULL PAPERS
ether. Then traces of organic solvent were eliminated at re-
duced pressure. Substrate (4 mmol) was added and the mixture
was heated again at the indicated temperature.
of catalysts which are able to promote efficiently the iso-
merization of allylic alcohols in water remains very lim-
ited.[22,23]
In this work, a synthetic methodology to prepare new
water-soluble complexes of the type [RuCl2(h6-p-cyme-
Crystal Structure Determination
ne){k-(P)-PPh (OCH CH NMe ) }][SbF ] (n¼1, 2 or
À
3
n
2
2
3
n
6 n
3) has been developed from the neutral derivatives
Crystallographic data for 4a have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication CCDC278297. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cam-
bridge CB21EZ, UK [Fax: (internat.) þ44–1223/336–033; E-
mail: deposit@ccdc.cam.ac.uk].
[RuCl (h6-p-cymene){k-(P)-PPh (OCH CH NMe ) }]
À
2
3
n
2
2
2 n
via quaternization of the nitrogen atom of the terminal
aminoalkyl groups and subsequent anion exchange.
Both the water-soluble ionic complexes and their neu-
tral precursors have proven to be highly active catalysts
for the isomerization of allylic alcohols in aqueous and
organic media, respectively. They are among the more
efficient catalysts already reported. Moreover, the hy-
dro-soluble complexes present a remarkable capacity
to be recycled (upto 10 runs) which has no precedent
in the literature.
Supporting Information Available
Preparation and characterization of 1b, 2a–c, 2’b, 3a–c, 3’b,
4a–c and 5. Details of X-ray diffraction analysis.
We have also found that complexes 4a–c remain ac-
tive in the presence of isoprene.[24] It should be men-
tioned that almost all known catalysts able to perform
allylic alcohol isomerization fail in presence of conjugat-
ed dienes.[22] Since allylic alcohols can be obtained by hy-
dration of dienes, these complexes can be envisaged as
potential catalysts for direct one-pot transformation of
dienes into saturated ketones.[23c]
Acknowledgements
We are indebted to the Ministerio de Ciencia y Tecnología
(MCyT)of Spain (Project BQU2003–00255)and the Gobierno
del Principado de Asturias (Project PR-01-GE-6)for financial
support. M. A. F.-Z. thanks the MEC for the award of a Ph.D.
´
grant. P. C. thanks the MCyT for “Ramon y Cajal” contract.
References and Notes
Experimental Section
[1] See, for example: a) C. J. Li, Chem. Rev. 1993, 93, 2023;
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General Remarks
The manipulations were performed under an atmosphere of
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GC measurements were made on a Hewlett-Packard HP6890
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column.
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Under an inert atmosphere, the ruthenium catalyst precursor
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´
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[16] If both the ruthenium complex and base loadings are
lowered the reaction proceeds significantly slower. As
an example, only 13% of 1-octen-3-ol (0.2 M THF, sub-
100
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 93 – 100