Tetrahedron Letters
Immobilization of Ru(III) complex on silica: a heterogenized catalyst
for selective oxidation of alcohols in water at room temperature
S. Ganesamoorthy a,b, M. Muthu Tamizh a,c, K. Shanmugasundaram , R. Karvembu
b
a,
⇑
a
Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu, India
Synthetic Chemistry, Syngene International Limited, Biocon Park, Bangalore 560099, Karnataka, India
b
c
Interdisciplinary School of Indian System of Medicine (ISISM), SRM University, Kattankulathur 603203, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
III
Article history:
2 2 2
We have developed a heterogenized catalyst (‘SiO ’–NH –Ru ) by the immobilization of [Ru(acac)
Received 9 August 2013
Revised 10 October 2013
Accepted 15 October 2013
Available online 22 October 2013
(
CH
3 2 6 2
CN) ]PF on SiO . The catalyst was characterized by SEM, solid state NMR, EPR, FT-IR, ICP, and BET
III
surface area analyses. ‘SiO
2
2
’–NH –Ru catalyzed the selective oxidation of alcohols with periodic acid
in water at room temperature. This protocol was applicable to the controlled oxidation of structurally
diverse primary and secondary alcohols. The catalyst could be quantitatively recovered and reused up
to six cycles without significant loss of catalytic activity.
Keywords:
Oxidation
Ó 2013 Elsevier Ltd. All rights reserved.
Alcohols
Ruthenium(III)
Water solvent
The aldehydes and ketones are being recognized as important
starting materials for multitude of carbon–carbon or carbon–het-
eroatom bond formation reactions. The scarce stability and com-
mercial availability of these compounds made the selective
oxidation of alcohols as an instant synthetic tool for laboratory
and industrial processes.1 The noncatalytic methods with stoichi-
ometric oxidants like dichromate and permanganate produce a tre-
mendous amount of metal salts as waste.6 Among several metal
based oxidation methods, selective oxidation of alcohols to the cor-
responding carbonyl compounds in the presence of catalytic
amount of a transition metal in water is very attractive in terms
of environmental and economic stand points.8 The reason is that
medium.19 This catalyst was immobilized onto silica by replacing
one of the weakly coordinated acetonitrile molecules with amine
III
functionalized silica to form ‘SiO
2
’–NH
2
–Ru . The newly developed
5 6
heterogenized Ru(III) catalyst in water with H IO as oxidant
showed the highest selectivity; it avoids carboxylic acid formation.
This is an inexpensive, mild protocol for the selective oxidation of
alcohols. Advantageously the catalyst has several benefits includ-
ing high stability, ease of use, leach proof, and reusability.
–5
,7
2
Fumed silica (1 g, surface area 225 m /g) was dispersed in dry
2
toluene under N atmosphere. To this 3-aminopropyl-1-triethox-
ysilane (12 mL) was added slowly and refluxed overnight under
stirring. The reaction mixture was cooled down to room tempera-
ture, 1.5 N HCl was added slowly and stirred for an hour. The mix-
ture was filtered and the resulting solid was washed with acetone
several times. The solid was dried at 100 °C under vacuum for 6 h
,9
aqueous H
2
O
2
or gaseous O
2
can be used as a stoichiometric oxi-
dant.1
0–14
However these oxidants are often employed under an
elevated temperature and high pressure, respectively, to influence
their reactivity. Moreover, it is difficult to control the consumption
to get ‘SiO
2
2
’–NH .
of gaseous O
2
added as an oxidant. In contrast, H
5
IO
6
as an oxidant
[Ru(acac)
ture method.
2
(CH
3
CN)
[Ru(acac)
2
]PF
6
was prepared according to the litera-
(CH CN) ]PF (0.2 g) and ‘SiO ’–NH
2
2
0
offers several advantages, including solubility in water, stability,
simple handling, controllable addition, safe operation, cost effec-
2
3
2
6
2
(1 g) were stirred at room temperature in dry toluene (20 mL) for
48 h. The reaction mixture was filtered and washed several times
tiveness, and nontoxic nature,15 even though H
and O
are envi-
metal
2
O
2
2
ronmentally
benign.
Recently,
heterogenized
with CH
2
Cl
2
. The obtained solid was subjected to the Soxhlet
Cl for two days to ensure leaching out of all
acetylacetonate complexes have been found more effective and
extraction using CH
unbound Ru(III). The filtration gives a solid which was dried at
100 °C under vacuum for 6 h to give a pale brown powder (1.1 g,
0.066 wt % of Ru, surface area 209 m /g) (Scheme 1). The Ru con-
2
2
selective than their homogeneous counterparts.1
course of our study, we proved [Ru(acac) (CH CN)
6–18
During the
as an effec-
2
3
2
]PF
6
2
tive catalyst for the controlled oxidation of alcohols in water
tent was estimated by ICP-OES analysis using a Perkin Elmer Opti-
ma 5300 DV instrument. The SEM image (Fig. S1 in Supplementary
data) of the catalyst was obtained using a JEOL JSM-6701F FE-SEM
⇑