Organometallics
NOTE
Table 2. Isomerization of 1-Octen-3-ol Catalyzed by Com-
involve the presence of phosphines and no base as cocatalyst is
required, this synthetic methodology can be considered as a
genuine example of a catalytic application of an organometallic
compound in a green chemical process. Mechanistic studies and
further efforts to develop new catalytic systems active and re-
coverable in ionic liquids are presently underway.
plex 3 in Water and [BMIM][BF ]: Catalyst Recycling
4
H
2
O
4
[BMIM][BF ]
’
EXPERIMENTAL SECTION
b
c
b
c
cycle
time
yield, % (TON)
time
yield, % (TON)
Typical Procedure for the Catalytic Reactions. The corre-
1
2
3
4
5
5 min
10 min
10 min
20 min
1.5 h
99 (99)
99 (198)
99 (297)
96 (396)
99 (495)
5 min
20 min
30 min
1 h
99 (99)
99 (198)
95 (293)
97 (390)
96 (487)
sponding allylic alcohol (1À4 mmol) and the appropriate solvent (water
5
À20 mL; 1À2 g of [BMIM][BF
4
]) were introduced into a sealed tube
under a nitrogen atmosphere. Complex 3 (0.2À10 mol % of Ru) was
then introduced at room temperature, and the resulting solution was
heated at 75 °C for the indicated time (the course of the reaction was
monitored by regular sampling and analysis by GC). After completion of
the reaction, the organic product was extracted with hexane (3 Â 5 mL).
2 h
a
General conditions: reactions performed at 75 °C under N atmo-
sphere using 4 mmol of 1-octen-3-ol in 20 mL of H O or 2 mmol of
-octen-3-ol in 2 g of [BMIM][BF ]. Determined by GC. Cumulative
4
2
2
b
c
1
TON values (turnover number = (mol of product)/(mol of Ru)).
’ AUTHOR INFORMATION
Corresponding Author
E-mail: jgh@uniovi.es.
*
Complex 3 also shows a high catalytic efficiency using ionic
liquids as alternative environmentally friendly solvents. Thus, in a
model reaction, to our satisfaction, the isomerization of 1-octen-
15
’
ACKNOWLEDGMENT
3
-ol was catalyzed by 3 (1 mol %) at 75 °C in [BMIM][BF ]
4
(
[BMIM][BF ] = 1-butyl-3-methylimidazolium tetrafluorobo-
We are indebted to the Ministerio de Ciencia e Innovaci ꢀo n
4
rate), affording quantitatively and chemoselectively 3-octanone
(MICINN) of Spain (Projects CTQ2006-08485/BQU, Consol-
ider Ingenio 2010 (CSD2007-00006), and CTQ2008-00506) for
financial support. J.G.-A. thanks the MICINN and the European
Social Fund for the award of a “Juan de la Cierva” contract.
16
in only 5 min (entry 1, Table 1). As for the isomerization in water,
the catalytic reaction in the ionic liquid also tolerates a diverse
array of allylic alcohols. Thus, the monosubstituted alcohols are
À1
readily isomerized (entries 1À7, TOF values 100À1200 h ),
while disubstituted allylic alcohols (entries 8À11) required longer
reaction times and higher Ru loadings (5À10 mol %), as pre-
’
REFERENCES
17
(1) See, for example: (a) Trost, B. M. Science 1991, 254, 1471. (b)
viously observed in water. Nevertheless, complex 3 is totally
Trost, B. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 259. (c) Sheldon, R. A.
Pure Appl. Chem. 2000, 72, 1233. (d) Trost, B. M. Acc. Chem. Res. 2002,
inactive in the isomerization of trisubstituted allylic alcohols such
as 3-methyl-2-buten-1-ol in [BMIM][BF ] (entry 12).
4
3
5, 695. (e) Trost, B. M.; Frederiksen, M. U.; Rudd, M. T. Angew. Chem.,
Int. Ed. 2005, 44, 6630. (f) Sheldon, R. A. Green Chem. 2007, 9, 1273.
2) For reviews on transition-metal-catalyzed isomerization of allylic
The lifetime of a catalytic system and its level of reusability are
18
very important factors. In this regard, the good solubility
(
of complex 3 in both water (4.7 mg/mL) and [BMIM][BF4]
alcohols into carbonyl compounds, see: (a) van der Drift, R. C.; Bouwman,
E.; Drent, E. J. Organomet. Chem. 2002, 650, 1. (b) Uma, R.; Cr ꢀe svisy, C.;
Gre ꢀe , R. Chem. Rev. 2003, 103, 27. (c) Cadierno, V.; Crochet, P.; Gimeno, J.
Synlett 2008, 1105.
(4.8 mg/mL) allows it to be recycled easily after simple extrac-
tion of the final product with immiscible hexane (3 Â 5 mL).
Comparative results in water and [BMIM][BF ] using the isomer-
4
ization of 1-octen-3-ol into 3-octanone as a model reaction are
shown in Table 2. Thus, we have found that while no appreciable
loss of activity occurs in water during the first four consecutive
runs (5À20 min, 99% GC yields), the efficiency of the ionic
liquid solution decreases considerably after the first four recy-
cling cycles, 1 h of heating being required in the fourth cycle to
obtain a quantitative conversion. It is important to note that both
catalytic systems could be recycled in five consecutive times in
(3) (a) Jo ꢀo , F. Aqueous Organometallic Catalysts; Kluwer: Dordrecht,
The Netherlands, 2001. (b) Li, C. H.; Chan, T.-H. Comprehensive
Organic Reactions in Aqueous Media;2nd ed.; Wiley: New York, 2007.
(c) Organic Reactions in Water: Principles, Strategies and Applications;
Lindstr €o m, V. M., Ed.; Wiley-Blockwell: New York, 2007. (d) Li, C.-J.;
Chen, L. Chem. Soc. Rev. 2006, 35, 68.
(4) For recent metal-catalyzed isomerization of allylic alcohols in
water, see: (a) Fekete, M.; Jo ꢀo , F. Catal. Commun. 2006, 7, 783. (b)
Leung, D. H.; Bergman, R. G.; Raymond, K. N. J. Am. Chem. Soc. 2007,
129, 2746. (c) Campos-Malpartida, T.; Fekete, M.; Jo ꢀo , F.; Kath ꢀo , Aꢀ .;
1
.5 or 2 h (entry 5), leading to cumulative TON values of 495 and
4
87. The aqueous solution could be recycled for one more
Romerosa, A.; Saoud, M.; Wojtk ꢀo w, W. J. Organomet. Chem. 2008, 693,
468. (d) Servin, P.; Laurent, R.; Gonsalvi, L.; Tristany, M.; Peruzzini,
M.; Majoral, J.-P.; Caminade, A.-M. Dalton Trans. 2009, 4432. (e) Azua,
A.; Sanz, S.; Peris, E. Organometallics 2010, 29, 3661. (f) Ahlsten,
N.; Lundberg, H.; Martín-Matute, B. Green Chem. 2010, 12, 1628.
consecutive cycle, needing for this case 18 h of heating to achieve
a quantitative conversion.
3
3
In summary, we have demonstrated that the complex [Ru(η :η -
2
C H )Cl(κ O,O-CH CO )] (3), which is soluble in both water
10
16
3
2
(
g) Lastra-Barreira, B.; Díez, J.; Crochet, P. Green Chem. 2009, 11, 1681
and references therein.
5) (a) Li, C.-J. Green Chem. 1998, 239. (b) Wang, M.; Li, C.-J.
and ionic liquids, is a highly efficient and recoverable catalyst for
the isomerization of allylic alcohols into their corresponding
saturated carbonyl derivatives. It is important to note that this
catalyst not only is among the most efficient ones reported in the
literature in water but also is active under very mild reaction
conditions (35 °C). Since, in addition, this catalyst does not
(
Top. Organomet. Chem. 2004, 11, 321. (c) Cadierno, V.; Crochet, P.;
García-Garrido, S. E.; Gimeno, J. Curr. Org. Chem. 2006, 10, 165.
(d) Herrerias, C. I.; Yao, X.; Li, Z.; Li, C.-J. Chem. Rev. 2007,
106, 2546.
2
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dx.doi.org/10.1021/om200184v |Organometallics 2011, 30, 2893–2896