Osmium impregnated on magnetite as a heterogeneous catalyst for the syn-dihydroxylation of alkenes

Article abstract of DOI:10.1016/j.apcata.2013.10.050

A new catalyst derived from osmium has been prepared, fully characterized and tested in the dihydroxylation of alkenes. The catalyst was prepared by wet impregnation methodology of OsCl₃·3H₂O on a commercial micro-magnetite surface. The catalyst allowed the reaction with one of the lowest osmium loadings for a heterogeneous catalyst and was selective for the monodihydroxylation of 1,5-dienes. Moreover, the catalyst was easily removed from the reaction medium by the simple use of a magnet. The selectivity of catalyst is very high with conversions up to 99%. Preliminary kinetics studies showed a first-order reaction rate with respect to the catalyst.

Full text of DOI:10.1016/j.apcata.2013.10.050

Applied Catalysis A: General 470 (2014) 177–182
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Osmium impregnated on magnetite as a heterogeneous catalyst for
the syn-dihydroxylation of alkenes
Rafael Cano, Juana M. Pérez, Diego J. Ramón∗
Instituto de Síntesis Orgánica (ISO), and Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Alicante, Apdo. 99, E-03080 Alicante,
Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 June 2013
Received in revised form 23 October 2013
Accepted 25 October 2013
Available online 5 November 2013
A new catalyst derived from osmium has been prepared, fully characterized and tested in the dihydrox-
ylation of alkenes. The catalyst was prepared by wet impregnation methodology of OsCl3·3H2O on a
commercial micro-magnetite surface. The catalyst allowed the reaction with one of the lowest osmium
loadings for a heterogeneous catalyst and was selective for the monodihydroxylation of 1,5-dienes. More-
over, the catalyst was easily removed from the reaction medium by the simple use of a magnet. The
selectivity of catalyst is very high with conversions up to 99%. Preliminary kinetics studies showed a
first-order reaction rate with respect to the catalyst.
Keywords:
Heterogeneous catalyst
Dihydroxylation process
Magnetite
© 2013 Elsevier B.V. All rights reserved.
Osmium oxide
1. Introduction
[37,38]. The majority of these catalyst preparation strategies suffer
the need of a large and complicated work in the corresponding cat-
The syn-dihydroxylation of alkenes for the preparation of diols
[1,2] is one of the most explored reactions in organic chemistry
due to the importance of these compounds for the fine chemical
industry and their use as intermediates for pharmaceuticals and
agrochemicals. The most employed catalyst for this transforma-
tion is OsO4, with the asymmetric version of this reaction being
performed using the appropriated chiral ligands [3–6]. The use of
the aforementioned oxide has important drawbacks such as the
high cost, its high volatility and its toxicity, which limits or makes
very difficult its application in industry, and in the laboratory.
In the last years a great effort has been made to prepare
heterogeneous catalysts [7–11] which overcome these problems.
Different supports having osmium salts in different load-
ings (osmium/support ratio), such as polymers (0.25–5 mol%)
[12–15], silica (0.25 mol%) [16], cinchona modified silica gel
(1 mol%) [17–19], hydrotalcites (8.5 mol%) [20,21], dendrimers
(0.25–1 mol%) [22,23], polysiloxane (1 mol%) [24], imigolite
(0.25 mol%) [25] fullerenes (3.8 mol%) [26], magnetically recov-
erable quaternary ammonium salts (2 mol%) [27], or zeolites
(0.6 mol%) [28] have been reported for this purpose, as well as
other strategies including microencapsulation (5 mol%) [29–31],
ion-exchange technique (0.5–2.5 mol%) [32–35], and the use of
poly(ethylene glycol) (0.5 mol%) [36] or ionic liquids (0.5–2 mol%)
alyst elaboration, so the initial interest has not been transformed
into general industrial applications.
We have recently developed a new, simple and robust method
to immobilize different metal oxides [39–48] on the surface of the
magnetite [49–51]. Here, we show the effective application of this
new osmium impregnated on magnetite catalyst in organic synthe-
sis for the syn-dihydroxylation of alkenes.
2. Experimental
2.1. General procedure for the preparation of catalyst
To a stirred solution of OsCl3·3H2O (349 mg, 1 mmol) in deion-
ized water (120 mL) was added Fe3O4 (4 g, 17 mmol, powder <5 ␮m,
BET area: 9.86 m2/g). After 10 min at room temperature, the mix-
ture was slowly basified with NaOH (1 M) until pH around 13. The
mixture was stirred during one day at room temperature. After that,
the catalyst was filtered under vacuum and washed several times
with deionized water (3 × 10 mL). The solid was dried at 100 ◦C
during 24 h in a standard glassware oven, obtaining the expected
catalyst.
2.2. Characterization of catalyst
XRD patterns were recorded on a Brucker D8 advance diffrac-
tometer with monochromatized Cu K␣ radiation (ꢀ = 0.15406 nm)
at a setting of 40 kV and 40 mA. TEM images were obtained on a JEOL
∗
Corresponding author. Tel.: +34 965903986; fax: +34 965903549.
E-mail address: djramon@ua.es (D.J. Ramón).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.10.050

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R. Cano et al. / Applied Catalysis A: General 470 (2014) 177–182
Fig. 1. X-Ray photoelectron spectroscopy and TEM image of the fresh osmium impregnated magnetite catalyst.
JEM-2010 electron microscope equipped with an X-ray detector for
microanalysis (EDS). XRF analyses were obtained on a X-ray spec-
trometer PHILIPS MAGIX PRO equipped with a rhodium X-ray tube
and a beryllium window. Surfaces areas were determined by the
application of the BET equation to N2 adsorption isotherm at 77 K.
Adsorption data were obtained from a QUANTACROME AUTOSORB-
6 equipment.
increasing of the pH of the solution up to nearly 13 by addition of
2 M aqueous solution of NaOH, filtering, washing with water and
evaporation of water at 100 ◦C during 24 h rendered the catalyst
(non osmium species were detected in the aqueous mixture,
coming from the evaporated phase, which was collected in a liquid
nitrogen trap). The XRD analysis of freshly prepared catalyst did
not provide any concluding information due to the low metal
osmiun loading and its high dispersion, with exception of the
support diffraction peaks (Fe3O4, see Appendices A and B). The
total incorporation of osmium was around 1.6%, according to the
XRF and the BET area surface was 8.6 m2/g, almost the same as
in the starting magnetite (9.8 m2/g). The distribution of osmium
particles seems to be homogenous on the surface of magnetite,
according to the TEM images (Fig. 1), and the size distribution was
1.7 0.6 nm. The XPS spectra showed the presence of two osmium
species in a nearly 1:1 mixture, and these species seemed to be
OsO2 and OsO2(OH)2 according to the binding energies (Fig. 1)[52].
2.3. General procedure for the dihydroxylation of alkenes
To a stirred solution of alkene (1, 1 mmol) in a mixture of
acetone:H2O 2:1 (3 mL) in a pressure tube, OsO2–Fe3O4 (10 mg,
0.08% of osmium) and NMO (234 mg, 2 mmol) were added. The
resulting mixture was stirred at 100 ◦C during 3 h. The catalyst was
removed by a magnet and the resulting solution was extracted with
ether. The organic phases were dried over MgSO4, and the solvents
were removed under reduced pressure. The product was usually
purified by chromatography on silica gel (hexane/ethyl acetate)
to give the corresponding products 2 or 4. Physical and spectro-
scopic data as well as literature for all compounds are included
as Appendices A and B. FT-IR spectra were obtained on a Nicolet
impact 400D spectrophotometer. NMR spectra were recorded on
a Bruker AC-300 apparatus (300 MHz for 1H and 75 MHz for 13C)
using CDCl3 as a solvent and TMS as internal standard for 1H and
13C; chemical shifts are given in ı (parts per million) and coupling
constants (J) in Hertz. Mass spectra (EI) were obtained at 70 eV
on a spectrometer Agilent GC/MS-5973N, giving fragment ions in
m/z with relative intensities (%) in parentheses. Thin layer chro-
matography (TLC) was carried out on DC-Fertigfolien ALUGRAM
plates coated with a 0.2 mm layer of silica gel; detection by UV254
light, staining with phosphomolybdic acid [25 g phosphomolybdic
acid, 10 g Ce(SO4)2·4H2O, 60 mL of concentrated H2SO4 and 940 mL
H2O]. Column chromatography was performed using silica gel 60
of 35–70 mesh.
3.2. Dihydroxylation reactions
Once the catalyst was prepared and fully characterized, we faced
the problem of their activity in dihydroxylation processes. Initial
studies were performed upon the reaction of (E)-1-phenylprop-1-
ene (1a) with 4-methylmorpholine N-oxide (NMO), as the oxidant,
in a mixture of solvents (acetone/H2O: 2/1) at 70 ◦C and the effects
of different parameters were evaluated (Table 1). First, the effect of
the temperature of the reaction was studied (entries 1–4). When
the temperature was reduced to 50 ◦C the reaction took place,
although it needed a longer reaction time to achieve similar yield.
The increase of the temperature to 100 ◦C allowed to obtain the
corresponding diol 2a in 72% yield in only 3 h (entry 3). However, a
further increase on the temperature gave similar results (entry 4).
Then, other solvents were tested in the reaction (entries 5–7), but
the initial mixture of acetone:H2O gave the best results. Only in the
case of using toluene, it was possible to obtain the diol 2a in mod-
est yield (entry 7). The reaction failed when other oxidants, such
as t-BuOOH, H2O2, or isoquinoline N-oxide, were used. Only using
trimethylamine N-oxide similar result was obtained (entry 10). The
importance of the amount of oxidant was also evaluated (entries
12 and 13). When the amount of the oxidant was increased to
200 mol% the corresponding diol was obtained in 97% yield in only
1 h. However, increasing the amount of the oxidant to 300 mol%
3. Results and discussion
3.1. Synthesis of catalyst
The catalyst was easily prepared by the typical wet impreg-
nation methodology. The addition of commercial micro-particles
of magnetite to an aqueous solution of OsCl3, followed by the

R. Cano et al. / Applied Catalysis A: General 470 (2014) 177–182
179
Table 1
Optimization of reaction conditionsa.
Entry
T (◦C)
Solvent
Oxidant (mol%)
Conversion (%)b
t (h)
Yield (%)c
1
2
3
4
5
6
7
8
70
50
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
H2O
NMO (130)
NMO (130)
NMO (130)
NMO (130)
NMO (130)
NMO (130)
NMO (130)
t-BuOOH (130)
H2O2 (130)
(CH3)3N–O (130)
Isoquinoline N-oxide (130)
NMO (200)
NMO (300)
NMO (200)
NMO (200)
NMO (200)
NMO (200)
65
43
72
71
10
10
45
15
5
55
2
99
90
90
84
24
48
3
63
43
72
71
0
0
40
0
0
52
0
97
89
87
77
100
130
100
100
100
100
100
100
100
100
100
100
100
100
100
3
24
24
24
24
24
3
24
1
1
1
1
1
1
PhMe:H2O (2:1)
PhMe
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
Acetone:H2O (2:1)
9
10
11
12
13
14d
5e
16f
17h
55(99)g
20(33)i
55(96)g
12(27)i
a
Reactions performed using 1a (1 mmol) in 3 mL of solvent.
Calculated from GC analysis of crude mixture.
Isolated yield.
Reaction performed with 0.8 mol% of catalyst.
Reaction performed with 0.2 mol% of catalyst.
Reaction performed with 0.08 mol% of catalyst.
The result after 3 h of reaction appear in parenthesis.
Reaction performed with 0.04 mol% of catalyst.
The result after 48 h of reaction appear in parenthesis.
b
c
d
e
f
g
h
i
did not improve the previous result. Finally, the amount of cata-
lyst was optimized (entries 14–16), finding that a good result was
obtained when 0.4 mol% of osmium was added (entry 12). How-
ever, similar yield was obtained when a lower amount of osmium
(0.08 mol%) was added (entry 16), but the reaction time had to
be increased up to 3 h in order to achieve the same yield (96%).
In order to test the formation of toxic volatile osmium species,
after performing the reaction at 100 ◦C and removing carefully the
catalyst and the solution, the walls and the cap of pressure tube
were washed with methanol and water. This washing solution was
analyzed by ICP–MS, with the amount of osmium in this wash-
ing solution being lower than 0.01% of the initial charged osmium.
When the reaction was repeated with only 0.04 mol% of catalyst,
the yield decreased drastically (entry 17), and in this case, when
the reaction was repeated increasing the reaction time to 3 h the
yield kept modest (27%). In almost all cases, the only compound
detected by GC–MS analysis of the crude mixture was the product
2a, and variable amounts of starting alkene 1a. To the best of our
knowledge, the optimal conditions found for this reaction involved
the use of the lowest catalyst loading ever reported, without taking
in account the possible recyclability.The evolution of yield of com-
pound 2a with the time at different catalyst loadings is depicted
in Fig. 2. Assuming that the equation rate is simple and that the
reaction conditions permit a pseudo-first order approximation for
all reagents, the equation rate could be expressed as Ln r0i = ˛ Ln
[catalyst]i + constant.
Fig. 2. Plot-time yield for the standard preparation of compound 2a using different
amounts of catalyst [NMO (200 mol%), Me2CO:H2O (2:1), 100 ◦C, 3 h].
The estimation of the initial reaction rate for each trial and their
representation permitted us to calculate the value of the reaction
order for the catalyst (Fig. 3), with the obtained value (1.1) being
very close to a first order.
The magnetite support was tested in order to confirm that it was
inert, and after 24 h the starting alkene was recovered unmodified.
Other transition metal oxides impregnated on magnetite such as
Fig. 3. Correlation between initial rates and catalyst amount for the standard prepa-
ration of compound 2a [NMO (200 mol%), Me2CO:H2O (2:1), 100 ◦C, 3 h].

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R. Cano et al. / Applied Catalysis A: General 470 (2014) 177–182
Fig. 4. X-Ray photoelectron spectroscopy and TEM image of the recycled osmium impregnated magnetite catalyst [NMO (200 mol%), Me2CO:H2O (2:1), 100 ◦C, 3 h].
cobalt, nickel, copper, ruthenium, palladium, iridium, or platinum
were also tested in the reaction, but none of them showed activity.
Finally, the reaction was performed in absence of catalyst, and the
starting material was recovered after 24 h.
with only 21% yield (compare with entry 10 in Table 2). Therefore,
we could not exclude that the final leached osmium was partially
responsible for the reaction results.
With the best conditions in hand, the scope of the reaction
was evaluated (Table 2). The reaction gave excellent yields inde-
pendently of the substitution of the alkene (entries 1–5). A slight
decrease in the yields was observed when 1,1-disubstituted alkenes
were used (entries 4 and 5). Then, the influence of the configura-
tion of the alkene was evaluated performing the reaction with (Z)-
and (E)-stilbene (entries 6 and 7), and better result was obtained
in the case of the E-isomer. The reaction with the Z-isomer ren-
dered the expected diol in lower yield (compare entries 6 and 7),
and 16% of the diol arising from the isomerization of the starting
Z-alkene to the E-isomer, followed by a dihydroxylation process.
However, the related aliphatic alkenes did not show this isomer-
ization process (entries 8 and 9), and only the syn-dihydroxylation
products were detected for the reaction of (Z)- and (E)-hex-3-
ene. Excellent results were achieved when aliphatic alkenes were
tested, with independence of the nature of the alkene, such as ter-
minal or internal (entries 8–15). The tolerance of other functional
groups was also tested using allylic ether or ester moieties, obtain-
ing the corresponding diol with similar results (entries 16 and 17).
Unfortunately, when the reaction was performed with a conjugated
alkene, the yield decreased somewhat (entry 18), and the reaction
failed when a (Z/E)-mixture of ␤-bromostyrene was used, recov-
ering unchanged the starting material (entry 19). Finally, it should
be pointed out that the selectivity of the reaction was nearly 100%
since the only product detected by GC–MS from the crude mixture
was the expected diol 2 and the corresponding unchanged alkene 1,
with the exception of the (Z)-stilbene case (entry 7).The same reac-
tion conditions were applied to afford the hydroxylation of dienes
(Scheme 1). However, the only isolated product from the reaction
media was the diol arising from a monodihydroxylation process
in low yields using 400 mol% of oxidant, with the starting reagent
being the other product detected by CG–MS from the crude reaction
Once the activity of the catalyst was demonstrated, the prob-
lem of the recyclability was faced. After the reaction, the catalyst
was kept inside the vessel using a magnet, decanting the liquid
reaction media. Then, the catalyst was washed with diethyl ether,
and re-used under the same reaction conditions described in the
entry 16 of Table 1. Unfortunately, the yield obtained in the second
cycle was only 40% after 24 h of reaction. The ICP–MS analysis of
the reaction solution, after the first trial, showed the presence of
osmium (5.1% of the initial amount) and iron (0.01% of the initial
amount). Meanwhile, the XRF data of used catalyst showed 1.4% of
osmium amount, in good agreement with the ICP–MS analysis of
reaction solution. The XPS studies showed that the iron species in
the initial and in the recovered catalyst were the same. In the case
of oxygen, the expected decrease of the relative intensity between
oxygen bonded to osmium and to iron was also detected, being in
both cases the same species (see Appendices A and B). However,
just one species of osmium (OsO2) on the surface of catalyst was
detected (Fig. 4). However, it should be pointed out that the initial
catalyst data had showed the presence of OsO2 and OsO2(OH)2 in a
1:1 ratio. So, the decrease on the catalyst activity would be due to
the partial leaching of the OsO2(OH)2 species as well as its trans-
formation to OsO2 in the reaction media. Finally, it should notice
that the simple removal of catalyst by a magnet is quite efficient
since more than 97% of initial mass was recovered according to its
weight.
The analysis of the TEM images of the used catalyst showed a
slight process of sinterization of the particles. Initially the particles
of osmium had a distribution of size of 1.7 0.6 nm, and after the
reaction the distribution was 2.2 0.7 nm, but this change is not
sufficient to explain the lost of its activity (Fig. 5). The BET area of
the recycled catalyst was 11.9 m2/g, which is in the range of starting
values.
To know if the reaction took place by the leached osmium to
the organic medium, we performed the standard dihydroxylation
of alkene 1a (Table 1, entry 16). After that, the catalyst was removed
carefully by a magnet at high temperature. The solvents of the above
solution, without catalyst, were removed under low pressure and
dodec-1-ene, NMO, acetone and water were added to the above
residue. The resulting mixture was heated again at 100 ◦C for 3 h.
The analysis of crude mixture, after hydrolysis, revealed the forma-
tion of compound 2a in 93% (catalyzed process) and product (2j)
Scheme 1. Selective dihydroxylation of 1,5-dienes.

R. Cano et al. / Applied Catalysis A: General 470 (2014) 177–182
181
Fig. 5. Particle size of fresh and recycled [NMO (200 mol%), Me2CO:H2O (2:1), 100 ◦C, 3 h] osmium oxide derivatives on the surface of magnetite.
Table 2
Dihydroxylation of alkenesa.
Entry
Alkene
Compound
Conversion (%)b
Yield (%)c
1
2
3
4
5
6
7
8
(E)-1-phenylprop-1-ene
Styrene
1-Phenylprop-1-ene
Methylenecyclopentane
1,1-Diphenylethene
(E)-stilbene
(Z)-stilbene
(E)-hex-3-ene
(Z)-hex-3-ene
Dodec-1-ene
4-Phenylbut-1-ene
Cyclohexene
Cyclooctene
1-Methylcyclohex-1-ene
1H-indene
Allyloxybenzene
Allyl benzoate
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
2q
2r
99
90
99
72
75
90
75
83
80
99
95
80
95
85
70
85
90
65
0
96
87
98
71
73
87
54d
81
77
99
93
79
92
84
66
80
75
49
0e
9
10
11
12
13
14
15
16
17
18
19
Methyl cinnamate
(Z/E)-␤-bromostyrene
2s
a
Reactions performed using 1 (1 mmol), NMO (2 mmol) in acetone (2 mL) and water (1 mL) at 100 ◦C during 3 h.
Calculated from GC analysis of crude mixture.
Isolated yield.
Compound 2f was isolated in 16% yield.
Starting material recovered unchanged.
b
c
d
e
media. The catalyst was selective for this process, because the dou-
achieved in the case of 1,5-diines, with only the monodihydrox-
ylation process being performed. Moreover, the catalyst is easily
removed from the reaction medium just by the use of a simple
magnet.
ble dihydroxylation product was not detected even when a large
excess of oxidant was added (800 mol%). It should be pointed that
the reaction gave the monohydroxylation products in similar yields
(4a: 49%, 4b: 42%), with only 200 mol% of oxidant.
Acknowledgements
4. Conclusion
This work was supported by the Spanish Ministerio de
Economía y Competitividad (CTQ2011-24151). J. M. P. thanks
the M.E.C. for a fellowship through the FPI program. We grate-
fully acknowledge the polishing of our English by Mrs. Oriana C.
Townley.
In conclusion, we have demonstrated that the impregnated
osmium on magnetite system is a good catalyst for the dihydroxy-
lation of alkenes, with one of the lowest osmium loadings described
for heterogeneous catalyst so far. An interesting selectivity was

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R. Cano et al. / Applied Catalysis A: General 470 (2014) 177–182
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