Q.-x. Kang et al. / Journal of Organometallic Chemistry 690 (2005) 6309–6313
6311
Table 4
We can find that the reaction using 4 mg of catalyst
gives 100% conversion as well as 100% selectivity within
6 h. The same data were obtained by using 5 mg of catalyst,
it means that the optimum amount of catalyst consumption
is 4 mg in this oxidation system.
Catalytic oxidation of benzyl alcohol with PS–Phen–Ru in different
solvents
Entry
Solvent
Conversion (%)
Selectivity (%)
1
2
3
4
5
DCM
THF
Toluene
DCE
64
37
25
72
100
100
100
100
100
100
3.2.1.4. The amount of the iodosylbenzene. According to
the literatures, when alcohol was oxidized by iodosylben-
zene, the suitable amount of oxidant used ranged from
1.4 to 2.5 equiv. As for our novel catalytic system, we also
investigated the amount of iodosylbenzene consumption in
the oxidation. We changed the amount of oxidant from 0.5
to 2.5 equiv., the corresponding results were listed in the
table (Table 3).
It showed in Table 3 that the utilization of 2.5 equiv. of
iodosylbenzene afforded 100% benzyl alcohol conversion
and 100% selectivity in the same condition. This suggested
the suitable amount of oxidant in the oxidation was
2.5 equiv.
CH3CN
Condition: benzyl alcohol 0.1 mmol, cat. 4 mg, PhIO 2.5 equiv., solvent
2 mL, 60 °C, 2 h.
products. Because of the different molecular structures of
the alcohols, which, however, result in the different space
hindrance between the substrates and the catalyst, the
reaction time for each of the oxidation are not the same
as that for the oxidation of benzyl alcohol. The results of
the oxidations were concluded in the table (Table 5), and
the corresponding reaction time needed to obtain the listed
results was also listed in the table.
It shows in the Table 5 that: (i) the catalyst show prom-
ising catalytic activity for the oxidation of benzyl alcohol
and its derivatives, benzhydrol and its derivatives, long-
chained primary alcohols as well as some ordinary ali-
phatic alcohols with the oxidant of iodosylbenzne under
mild reaction conditions. With the catalysis of the complex,
all of the selected alcohols can be oxidized to the corre-
sponding aldehydes or ketones with the selectivity of
100%. There is no by-product observed in these oxidations.
(ii) Because of the different group of these alcohols, the
reaction time of each oxidation reaction is not the same.
We monitored each of the reaction, and decided the prom-
ising time for them. (iii) We can find that the catalytic activ-
ity of PS–Phen–Ru complex to each group of alcohols, e.g,
benzyl alcohol and its derivatives, benzhydrol and its deriv-
atives, long-chained primary alcohols and ordinary ali-
phatic alcohols, is differed due to different structures of
these alcohols. The activity to benzyl alcohol and its deriv-
atives is the best, whereas the activity to benzhydrol and its
derivatives is not very good. This may come from the
strong stereohindrance of the two benzene rings near the
hydroxyl group in benzhydrol molecule, which hindered
the electrophilic attack of the Ru atom of the catalyst to
the oxygen atom of the substrate. (iv) This complex can
catalyze the oxidation of aliphatic alcohols, which differed
itself from other system. As we know, most of these sub-
strates can not be easily oxidized unless a rigorous reaction
condition was provided. It means that the catalytic system
is a novel and more active one for the oxidation of
alcohols.
3.2.1.5. The solvent. The oxidation can be occurred in sev-
eral solvents, such as dichloromethane (DCM), 1,2-dichlo-
roethane (DCE), tetrahydrofuran (THF), toluene and
acetonitrile. Among these solvents, acetonitrile serves as
the most significant one under same reaction conditions.
The conclusion can be verified with the results shown in
the table (Table 4).
We can find from Table 4 that DCM and DCE can also
give promising results, but we cannot carry on the oxida-
tion at 60 °C. Meanwhile, CH3CN gives the highest conver-
sion under identical reaction condition.
From all of the investigation of the oxidation condi-
tions, it can be concluded that the optimum condition for
the oxidation is: catalyst 4 mg, iodosylbenzene 2.5 equiv.,
temperature 60 °C, solvent CH3CN 2 mL.
3.2.2. Catalytic oxidation property for other alcohols
Many of other alcohols, including benzyl alcohol and its
derivatives, benzhydrol and its derivatives, long-chained
aliphatic alcohols as well as some general aliphatic
alcohols, were well oxidized to the corresponding alde-
hydes or ketones with the PS–Phen–Ru complex under
the optimum reaction conditions mentioned above. All of
the oxidations bear the selectivities of 100% to the carbonyl
Table 3
Catalytic oxidation of benzyl alcohol by PS–Ru–Phen with different
amount of PhIO
Entry
PhIO (g)
Conversion (%)
Selectivity (%)
3.3. The recycling property of PS–Phen–Ru
1
2
3
4
5
0.011 (0.5 equiv.)
0.022 (1.0 equiv.)
0.033 (1.5 equiv.)
0.044 (2.0 equiv.)
0.055 (2.5 equiv.)
57
75
79
86
100
100
100
100
100
100
The supported catalysis is mostly aimed at the recycling
of the catalyst. As for those rear metal-containing catalysts,
this is something more significant than other consider-
ations. Merrifield resin (chloromethyl polystyrene resin) is
Condition: benzyl alcohol 0.1 mmol, cat. 4 mg, CH3CN 2 mL, 60 °C, 2 h.