Chemistry Reference
In-Depth Information
produce the desired carbonyl compound. Decoordination of aldehyde 5 and
water elimination afforded unstable intermediate V, which upon reaction
with molecular oxygen produced peroxide complex VI. Peroxo oxygen atom
transfer between complexes V and VI regenerated complex 19.
The cooperative activity of bimetallic nanoclusters has also been demon-
strated. For instance, a bimetallic Au-Pd/TiO
2
catalyst catalyzed the selective
oxidation of alcohols (primary alkyl alcohols) to aldehydes under mild solvent-
free reaction conditions.
21
Compared with monometallic Au or Pd nanocrystals,
bimetallic Au-Pd/TiO
2
showed impressive TOFs up to 269 000 h
1
.
Prati and co-workers reported that bimetallic Au-Pt nanoparticles sup-
ported on H-mordenite zeolite were highly ecient for the direct and se-
lective oxidation of glycerol to glyceric acid under practical acidic reaction
conditions.
22
Kobayashi's group synthesized Au-Pt bimetallic clusters sup-
ported on a cross-linked polystyrene for the aerobic oxidation of alcohols at
room temperature without a base in aqueous media.
23
Such a heterogeneous
catalyst can be reused several times without a decrease in activity. The same
group also reported carbon-stabilized polymer-incarcerated bimetallic
nanocluster catalysts (PI-CB catalysts) for the oxidation of alcohols
(Table 7.3).
24
Interestingly with these catalysts, the aldehyde versus carb-
oxylic acid (or ester) selectivity was strongly dependent on the content of Au
Table 7.3 Carbon-stabilized polymer-incarcerated bimetallic nanocluster-
catalyzed aerobic oxidation of alcohols.
O
O
O
PI-CB cata lyst
+
R
1
R
2
R
1
R
2
R
1
OR
3
conditions
O
2
(1 atm) , r.t.
Condition A : P I-CB/Au-P t (2 mol %), BTF/H
2
O (1/1), 0.25 M, 9 h
Condition B : P I-CB/Au-P t (2 mol %), BTF/H
2
O (1/1), 0.125 M, 2 4 h
Condition C : PI-CB /A u-Pd (1 mol %), MeOH/H
2
O (1/2), 0 .125 M, K
2
CO
3
(3 equiv), 24 h
Condition D : PI-CB /A u-Pd (1 mol %), MeOH/H
2
O (2/1), 0 .125 M, K
2
CO
3
(1 equiv), 24 h
Yield
a
(%)
Aldehyde
or ketone
Entry
Substrate
Conditions
Ester
Acid
Alcohol
---
8
90
1
1
A
Ph
OH
C
81
5
3
10
2
A
---
n.d.
>99
n.d.
3
Ph
OH
D
98
2
n.d.
n.d.
4
OH
5
B
---
-
94
n.d.
Ph
OH
6
B
---
-
96
n.d.
Ph
a
Yield determined by GC. n.d.: not detected.
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