Dichloro(dodeca-2,6,10-triene-1,12-diyl)ruthenium(IV): A highly efficient catalyst for the isomerization of allylic alcohols into carbonyl compounds in organic and aqueous media

Article abstract of DOI:10.1039/b313069j

The catalytic activity of the bis(allyl)-ruthenium(iv) complex [Ru(η³:η²:η³-C₁₂H ₁₈)Cl₂] in the transposition of allylic alcohols into carbonyl compounds, both in THF and H₂O as solvent, is reported.

Full text of DOI:10.1039/b313069j

Dichloro(dodeca-2,6,10-triene-1,12-diyl)ruthenium(IV): a highly efficient
catalyst for the isomerization of allylic alcohols into carbonyl compounds
in organic and aqueous media
Victorio Cadierno,* Sergio E. García-Garrido and José Gimeno*
Departamento de Química Orgánica e Inorgánica, Instituto Universitario de Química Organometálica
“Enrique Moles” (Unidad Asociada al CSIC), Facultad de Química, Universidad de Oviedo, 33071, Oviedo,
Spain. E-mail: jgh@sauron.quimica.uniovi.es (J. Gimeno); vcm@sauron.quimica.uniovi.es (V. Cadierno);
Fax: +34985103446; Tel: +34985103461
Received (in Cambridge, UK) 17th October 2003, Accepted 19th November 2003
First published as an Advance Article on the web 5th December 2003
The catalytic activity of the bis(allyl)-ruthenium(IV) complex
[Ru(h3:h2:h3-C12H18)Cl2] in the transposition of allylic alcohols
into carbonyl compounds, both in THF and H2O as solvent, is
reported.
rates than those observed in THF either in the presence or absence
of Cs2CO3 (Table 2; entry 1). Moreover, the effect of the co-catalyst
is in this case not so marked since in the absence of Cs2CO3 octan-
3-one was quantitatively obtained in only 50 min. These observa-
tions could be explained on the basis of the higher polarity of water
vs. THF which favors the dissociation of the chloride ligands in
complex 1 and therefore the coordination of the substrate to the
metal. In order to check whether Cs2CO3 acts exclusively as a
chloride abstractor, the isomerization of 1-octen-3-ol was studied in
THF using AgSbF6 as co-catalyst (substrate/Ru/AgSbF6 ratio: 500
: 1 : 2). In this case only 27% of conversion was attained after 24
h of reflux (6% without co-catalyst). This seems to indicate that
Cs2CO3 is acting not only as a chloride abstractor but also as a base.
Thus, the formation of the 1-octen-3-olate ruthenium complex,
after deprotonation of the substrate, could be envisaged as the first
step of the catalytic process.10
The catalytic activity of [Ru(h :h :h -C12H18)Cl2] (1) was tested
for a number of other allylic alcohols (results are summarized in
Table 2). As a general trend, the isomerization process was found
to take place faster in water (see columns 7 and 8 vs. 5 and 6,
respectively, in Table 2). As far as the allylic alcohols are
concerned, there is a strong dependence upon the substitution of the
carbon–carbon double bond as previously observed with other
catalytic systems.1 Thus, monosubstituted secondary alcohols (see
entries 1–4 in Table 2) are readily isomerized in aqueous medium
into the corresponding ketones using 0.2 mol% of 1 (TOF values
300–2000 h21 without Cs2CO3 or 1500–2000 h21 with Cs2CO3).11
The high catalytic activity of 1 at a lower loading (1024 mol%) is
also confirmed for the isomerization of 3-buten-2-ol (0.2 M in
water) into butan-2-one (without Cs2CO3; 100% yield in 20 h; TON
The conversion of allylic alcohols into the corresponding saturated
aldehydes or ketones is a useful synthetic process which conven-
tionally requires a two-step sequence of oxidation and reduction
reactions. An appealing alternative is the one-pot internal redox
process catalyzed by a variety of transition-metal complexes
(Scheme 1).1
Despite the great interest of this atom economical and catalytic
transformation in synthesis, efforts devoted to develop such a
reaction in water have been scarce.2 We have found that the readily
3
2
3
available
bis(allyl)-ruthenium(IV
)
complex
[Ru(h :h :h -
C12H18)Cl2] (C12H18 = dodeca-2,6,10-triene-1,12-diyl; see Fig.
1)3 (1) is an efficient catalyst for the isomerization of allylic
alcohols into carbonyl compounds, both in THF and in water as
solvent, representing the first example of a Ru(IV) catalyst for this
transformation.1
3
2
3
3
2
3
Firstly, we checked the activity of [Ru(h :h :h -C12H18)Cl2] (1)
in the isomerization of 1-octen-3-ol as a model reaction. Thus,
when a 0.2 M THF solution of 1-octen-3-ol was refluxed for 24 h
with a catalytic amount of 1 (0.2 mol%), octan-3-one was obtained
only in 6% yield. A dramatic rate-enhancement was observed upon
addition of 0.4 mol% of Cs2CO3 resulting in the quantitative
transformation of the alcohol into the saturated ketone in 70 min
(Table 1; entry 1).4 We note that, under these reaction conditions,
complex 1 is much more active than the classical ruthenium(II
)
6
catalysts
[{Ru(h -p-cymene)(m-Cl)Cl}2],4
[RuCl2(PPh3)3],4
5
5
[Ru(h -C9H7)Cl(PPh3)2]5 and [Ru(h -C5H5)Cl(PPh3)2]5 (entries
2–5 vs. entry 1 in Table 1).6 The exceptional high activity of 1 is
retained at lower catalyst loadings. As an example, using 1024
mol% of 1, 1-octen-3-ol (0.2 M in THF; substrate/Ru/Cs2CO3 ratio:
1000000 : 1 : 2) can be quantitatively isomerized within 18 hours
leading to the highest turnover number value (TON = 106; see
entry 6 in Table 1) reported to date for this catalytic transforma-
tion.1,7
= =
106; TOF 50000 h21). In contrast, when 1,1- and
1,2-disubstituted allylic alcohols are used longer reaction times and
higher catalyst loadings (5–10 mol%) are required to achieve total
conversions (see entries 6–9 in Table 2).
The catalyst recycling was also examined. Thus, we have found
that 1 can be recycled at least for three times after the conversion of
3-buten-2-ol in butan-2-one (0.2 M in water; 0.2 mol% of 1 and 0.4
mol% of Cs2CO3; separation of butan-2-one by distillation). No
Taking advantage of the known stability of complex 1 towards
water,8 the isomerization of 1-octen-3-ol was studied in aqueous
medium.9 Thus, we have found that the reaction proceeds at higher
Table 1 Ruthenium-catalyzed isomerization of 1-octen-3-ol into octan-
3-onea
Yield (%)b
(time)
Entry
Catalyst
TOF/h21c
3
2
3
1
2
3
4
5
6
[Ru(h :h :h -C12H18)Cl2]
100 (70 min)
100 (90 min)
92 (22 h)
38 (22 h)
1 (22 h)
429
333
21
6
[{Ru(h -p-cymene)(m-Cl)Cl}2]
Scheme 1 Isomerization of allylic alcohols into carbonyl compounds.
[RuCl2(PPh3)3]
5
[Ru(h -C9H7)Cl(PPh3)2]
9
5
[Ru(h -C5H5)Cl(PPh3)2]
< 1
55556
3
2
3
[Ru(h :h :h -C12H18)Cl2]d
100 (18 h)
a Reactions performed under N2 atmosphere at 75 °C using 4 mmol of
1-octen-3-ol (0.2 M in THF). Substrate/Ru/Cs2CO3 ratio: 500 : 1 : 2. b Yield
of octan-3-one determined by GC. c Turnover frequencies ((mol product/
mol Ru)/time) were calculated at the time indicated in each case. d Reaction
performed with a substrate/Ru/Cs2CO3 ratio: 1000000 : 1 : 2.
3
2
3
Fig. 1 Structure of complex [Ru(h :h :h -C12H18)Cl2] (1).
232
C h e m . C o m m u n . , 2 0 0 4 , 2 3 2 – 2 3 3
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

3
2
3
Table 2 Isomerization of various allylic alcohols catalyzed by complex [Ru(h :h :h -C12H18)Cl2] (1) in THF and H2Oa
THF THF/Cs2CO3 H2O
H2O/Cs2CO3
Catalyst
concentration TOF/h21c
Yield (%)b (time) Yield (%)b (time) Yield (%)b (time) Yield (%)b (time)
Entry Substrate
1
Product
TOF/h21c
TOF/h21c
TOF/h21c
0.2 mol%
0.2 mol%
0.2 mol%
0.2 mol%
6 (24 h)
1
100 (70 min)
429
100 (50 min)
600
100 (15 min)
2000
2
3
4
97 (24 h)
20
100 (65 min)
462
100 (15 min)
2000
100 (20 min)
1500
100 (22 h)
23
100 (20 min)
1500
100 (15 min)
2000
100 (15 min)
2000
100 (18 h)
28
100 (45 min)
667
100 (100 min)
300
100 (20 min)
1500
5
6
5 mol%
5 mol%
3 (24 h)
< 1
100 (6 h)
3
100 (75 min)
16
100 (10 min)
120
65 (24 h)
< 1
100 (15 h)
1
100 (10 h)
2
100 (3 h)
7
7
8
9
5 mol%
10 mol%
10 mol%
2 (24 h)
< 1
100 (9 h)
2
92 (24 h)
< 1
100 (3 h)
7
69 (24 h)
< 1
100 (13 h)
< 1
100 (7 h)
1
100 (3 h)
3
63 (24 h)
< 1
100 (16 h)
< 1
100 (9 h)
1
100 (4.5 h)
2
a Reactions performed under N2 atmosphere at 75 °C using 4 mmol of the corresponding allylic alcohol (0.2 M). When Cs2CO3 was used as co-catalyst it
was added in a 2 : 1 molar ratio with respect to complex 1. b Yield of the aldehyde or ketone determined by GC. c Turnover frequencies ((mol product/mol
Ru)/time) were calculated at the time indicated in each case.
4 Addition of 0.4 mol% of Na2CO3 or K2CO3 results also in quantitative
formation of octan-3-one in 4 or 2.5 h, respectively. The use of co-
catalysts is well documented. See for example: (a) J.-E. Bäckvall and U.
Andreasson, Tetrahedron Lett., 1993, 34, 5459; (b) R. Uma, M. K.
Davies, C. Crévisy and R. Grée, Eur. J. Org. Chem., 2001, 3141.
5 B. M. Trost and R. J. Kulawiec, J. Am. Chem. Soc., 1993, 115, 2027.
6 The highest TOF values reported for the isomerization of 1-octen-3-ol,
appreciable loss of activity was observed in the first and second
runs (100% yield in 20 min). However, deactivation of the catalyst
takes place in the third and fourth runs (100% and 43% yields in 24
h, respectively).
We have also found that [Ru(h :h :h -C12H18)Cl2] (1) remains
active in the presence of isoprene.12 It should be mentioned that
almost all known catalysts able to perform allylic alcohol
isomerization fail in the presence of conjugated dienes.1 Since
allylic alcohols can be obtained by hydration of dienes, complex 1
can be envisaged as a catalyst for the direct one-pot transformation
of dienes into saturated ketones.13
In summary, these promising preliminary results open the
possibility to develop a biphasic catalytic system based on complex
1. Efforts in this direction, as well as studies concerning the
mechanism of this catalytic process, are now in progress.
This work was supported by the Ministerio de Ciencia y
Tecnología (MCyT) of Spain (Project BQU2000-0227). S.E.G.-G.
and V.C. thank the MCyT for the award of a Ph.D. grant and a
Ramón y Cajal contract, respectively.
3
2
3
6
by using K2CO3 as co-catalyst, are the following: 33 h21 [{Ru(h -p-
5
cymene)(m-Cl)Cl}2], 285 h21 [RuCl2(PPh3)3] and 8 h21 [Ru(h -
C5H5)Cl(PPh3)2] (see ref. 4a).
7 (a) TON values up to 3000 (TOF up to 36000 h21) have been reported
for the isomerization of 2-propen-1-ol into propionaldehyde using
5
complexes [Ru(h -C5H5)(PR3)(NCMe)2][PF6] (PR3 = PPh3, PCy3) as
catalysts: C. Slugovc, E. Rüba, R. Schmid and K. Kirchner, Organome-
tallics, 1999, 18, 4230; (b) TON values up to 6000 have been also
reported for the isomerization of 3-buten-2-ol into butan-2-one using
5
complex [RuCl(h -C5H5)(PPh3)2] as catalyst and AgOTs (silver p-
toluenesulfonate) as co-catalyst (a TOF value > 200000 h21 has been
claimed): R. C. van der Drift, M. Vailati, E. Bouwman and E. Drent, J.
Mol. Catal. A, 2000, 159, 163.
8 J. W. Steed and D. A. Tocher, J. Chem. Soc., Chem. Commun., 1991,
1609.
9 Although complex 1 itself is insoluble in water, it readily becomes
soluble in the presence of the allylic alcohol.
Notes and references
1 For reviews see: R. C. van der Drift, E. Bouwman and E. Drent, J.
Organomet. Chem., 2002, 650, 1; R. Uma, C. Crévisy and R. Grée,
Chem. Rev., 2003, 103, 27.
10 The chelate coordination of the allylic alkoxide has been proposed as the
initial step in the catalytic isomerization of allylic alcohols by the
5
5
complexes [Ru(h -C9H7)Cl(PPh3)2] and [Ru(h -C5H5)Cl(PPh3)2] (see
ref. 5).
2 H. Alper and K. Hachem, J. Org. Chem., 1980, 45, 2269; D. V.
McGrath, R. H. Grubbs and J. W. Ziller, J. Am. Chem. Soc., 1991, 113,
3611; D. V. McGrath and R. H. Grubbs, Organometallics, 1994, 13,
224; C. de Bellefon, S. Caravieilhes and E. G. Kuntz, C. R. Acad. Sci.,
Ser. IIc: Chim., 2000, 3, 607; C. Bianchini, A. Meli and W. Oberhauser,
New J. Chem., 2001, 25, 11; D. A. Knight and T. L. Schull, Synth.
Commun., 2003, 33, 827.
11 In contrast, due probably to steric reasons, the isomerization of
1-phenyl-2-propen-1-ol requires 5 mol% of the catalyst to achieve 100%
of conversion in reasonable reaction times (entry 5 in Table 2).
12 As an example, in the presence of 15 mmol of isoprene, 4 mmol of
1-octen-3-ol (0.2 M in H2O) can be quantitatively isomerized within 65
min using 0.2 mol% of 1 (without Cs2CO3; TOF = 461 h21 to be
compared with entry 1 in Table 2).
3 J. E. Lydon, J. K. Nicholson, B. L. Shaw and M. R. Truter, Proc. Chem.
Soc., 1964, 421; J. K. Nicholson and B. L. Shaw, J. Chem. Soc. A, 1966,
807.
13 R. C. van der Drift, J. W. Sprengers, E. Bouwman, W. P. Mul, H.
Kooijman, A. L. Spek and E. Drent, Eur. J. Inorg. Chem., 2002,
2147.
C h e m . C o m m u n . , 2 0 0 4 , 2 3 2 – 2 3 3
233