Aerobic oxidation of amines catalyzed by polymer-incarcerated au nanoclusters: Effect of cluster size and cooperative functional groups in the polymer

Article abstract of DOI:10.1246/bcsj.20100300

Aerobic oxidation reaction of amines to imines catalyzed by polymer-incarcerated Au nanoclusters (PI-Au) was developed. The effect of cluster size for this oxidation reaction was carefully examined using the same polymer support. We have succeeded in preparation of various PI-Au catalysts containing different size clusters by modification of standard preparation methods. The size of clusters and their distribution were analyzed by electron microscopy. Interestingly, catalysts containing relatively larger clusters (>5 nm) showed higher activity in aerobic oxidation of amines than catalysts containing smaller clusters (13 nm) that showed much better activity for aerobic oxidation of alcohols. In addition, novel Au nanocluster catalysts immobilized on newly prepared polymer with tertiary amine groups were developed and they showed excellent activity for aerobic oxidation of amines to imines. The relation between cluster size and catalytic activity and role of tertiary amine in polymer were discussed. These catalysts could be applied to aerobic oxidative deprotection of p-methoxybenzyl groups.

Full text of DOI:10.1246/bcsj.20100300

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Bull. Chem. Soc. Jpn. Vol. 84, No. 6, 588–599 (2011)
© 2011 The Chemical Society of Japan
BCSJ Award Article
Aerobic Oxidation of Amines Catalyzed by Polymer-Incarcerated
Au Nanoclusters: Effect of Cluster Size and Cooperative
Functional Groups in the Polymer
Hiroyuki Miyamura,1,3 Masataka Morita,2,3 Takeshi Inasaki,1,2,3 and Shū Kobayashi*1,2,3
1Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033
2Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033
3The HFRE Division, ERATO, Japan Science and Technology Agency (JST), Hongo, Bunkyo-ku, Tokyo 113-0033
Received October 25, 2010; E-mail: shu_kobayashi@chem.s.u-tokyo.ac.jp
Aerobic oxidation reaction of amines to imines catalyzed by polymer-incarcerated Au nanoclusters (PI-Au) was
developed. The effect of cluster size for this oxidation reaction was carefully examined using the same polymer support.
We have succeeded in preparation of various PI-Au catalysts containing different size clusters by modification of standard
preparation methods. The size of clusters and their distribution were analyzed by electron microscopy. Interestingly,
catalysts containing relatively larger clusters (>5 nm) showed higher activity in aerobic oxidation of amines than catalysts
containing smaller clusters (1-3 nm) that showed much better activity for aerobic oxidation of alcohols. In addition, novel
Au nanocluster catalysts immobilized on newly prepared polymer with tertiary amine groups were developed and they
showed excellent activity for aerobic oxidation of amines to imines. The relation between cluster size and catalytic
activity and role of tertiary amine in polymer were discussed. These catalysts could be applied to aerobic oxidative
deprotection of p-methoxybenzyl groups.
Since Haruta’s discovery, aerobic oxidation reactions cata-
compare systematically the activity of different sizes of Au
clusters using the same support.
lyzed by gold nanoclusters have been widely investigated.1,2
There are two important factors for the activity of gold
nanocluster catalysts, cluster size and a support.2-4 Cluster size
affects the activity of the catalysts by both surface area and
quantum size effect.4,5 Cluster size is also influenced by the
support, and some metal oxide supports can activate Au
clusters by electronic effects. In other cases, the support itself
sometimes works as a cocatalyst with Au clusters.4,6 In general,
smaller clusters show higher activity than larger clusters
because of their high surface area to volume ratio. Moreover,
the catalytic activity normalized by the number of surface
atoms of smaller Au cores is known to be higher than that of
larger clusters in the oxidation of CO, glucose, and alcohols.4,5
Recently, aerobic oxidation of amines to imines catalyzed by
various sizes of Au, such as bulk, microsize, nanosize, and
homogeneous Au, have been widely reported.7 Interestingly,
10-50 nm size Au clusters sometimes show very high activity
in these reports,7g-7i although over 10 nm Au clusters hardly
catalyze other aerobic oxidation reactions. In some cases in this
amine oxidation, it was concluded that smaller Au clusters have
higher activity;7d,7h however, there is no clear and direct
evidence that smaller clusters have higher activity for aerobic
oxidation of amines to imines because there are no reports that
We recently reported that gold nanocluster catalysts immo-
bilized on polystyrene-based polymers with crosslinking moie-
ties,8 polymer-incarcerated gold nanocluster catalysts (PI-Au),
were effective for aerobic oxidation of alcohols to ketones,
aldehydes, and esters and hydroquinones to quinones under
mild conditions.9,10 Moreover, PI-Au could be reused several
times by simple operations without loss of catalytic activity.
We now report aerobic oxidation of amines to imines
catalyzed by PI-Au. Comparison of catalytic activity using
different size Au clusters in the same polymer support with
different preparation methods is described. A novel Au
cluster catalyst immobilized on newly designed polymers
with cooperative functional groups for this reaction is also
described.
Results and Discussion
Preparation of Catalysts. PI-Au catalysts were prepared
following a previously reported method (Scheme 1).9a As the
loading level increased, the ratio of the loaded Au to the used
Au source decreased, probably because of saturation.
Oxidation of Dibenzylamine Catalyzed by PI-Au with
Different Au Loadings.
We have already shown the
Published on the web May 28, 2011; doi:10.1246/bcsj.20100300

H. Miyamura et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
589
x
y
z
coacervation
+ NaBH4
OH
AuClPPh3
Et2O
diglyme
O
O
O
4
crosslinking
no solvent 1) filtration
Polymer 1 (x:y:z = 1:1:1)
PI-Au 2
no solvent
2a: 0.06-0.08 mmolg−1
150 °C, 5 h
150 °C, 5 h
2) wash
(H2O, DCM, THF)
3) crush
2b: 0.22-28 mmolg−1
2c: 0.50-75 mmolg−1
4) dry
Scheme 1. Preparation of PI-Au catalysts.
Table 1. Aerobic Oxidation of Dibenzylamine Catalyzed by PI-Au Catalysts with Different Loadings
PI-Au (2 mol%)
N
H
N
conditions, O2
14
¹1
¹1
¹1
Loading: 0.078 mmol g
Loading: 0.25 mmol g
PI-Au 2b
Loading: 0.59 mmol g
PI-Au 2c
Conditions
Use
PI-Au 2a
yield/%a)
yield/%a)
yield/%a)
100 °C, 24 h, toluene
1st
10
30
27
92
77
94
28
36
39
98
100
98
46
54
47
97
100
98
2nd
3rd
1st
2nd
3rd
140 °C, 24 h, xylene
a) Determined by GC analysis.
Table 2. Evaluation of Catalytic Activity before and after Using for Amine Oxidation
PI-Au (2 mol%)
N
H
N
xylene, 140 °C, 6 h, O2
14
Yielda)/%
[PI-Au 2a]
Yielda)/%
[PI-Au 2c]
Fresh
18
74
73
89
After three sets of use
a) Determined by GC analysis.
relationship among loading level, cluster size, and activity of
PI-Au at room temperature in alcohol oxidation.9a When the
loading level of the catalyst was low (0.05-0.10 mmol g¹1 Au),
smaller clusters were observed and the catalyst showed higher
activity in aerobic oxidation of alcohols. On the other hand,
when the loading level was high (>0.20 mmol g¹1), larger
clusters were observed and the catalyst showed lower activity.
We investigated aerobic oxidation of benzylamine using
three catalysts with different loadings (PI-Au 2a 0.078, 2b
0.25, and 2c 0.59 mmol g¹1) under two different conditions
(Table 1: 100 °C, 24 h, in toluene; 140 °C, 24 h, in xylene).
Under the latter conditions, all catalysts gave the desired imine
in excellent yields, and no decrease of the catalytic activity was
observed during three sets of recovery and reuse. On the other
hand, under milder conditions at 100 °C, the results differed
greatly depending on the loadings of the catalysts. Interest-
ingly, the higher loading catalyst PI-Au 2c showed good
catalytic activity although the lower loading catalyst PI-Au 2a,
which showed excellent activity in aerobic oxidation of
alcohols, hardly catalyzed this reaction. Moreover, the recycled
catalyst surprisingly showed higher activity than the initial
catalyst in the cases of catalysts PI-Au 2a and 2b.
Effect of Recycling on Oxidation of Dibenzylamine
Catalyzed by PI-Au. To discover the reason, we evaluated
the catalytic activity of catalysts with high and low Au loading
1) before use and 2) after three sets of use under 140 °C, 24 h, in
xylene for the catalysts (Table 2). When the reaction time was
short under these conditions, 140 °C, 6 h, in xylene, only 18%
yield of the imine was obtained using fresh PI-Au 2a. In
contrast, the catalyst after being used three times for aerobic

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Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011) BCSJ AWARD ARTICLE
PI-Au 2a before use
PI-Au 2b before use
PI-Au 2c before use
PI-Au 2c after 3 uses
PI-Au 2a after 3 uses
PI-Au 2b after 3 uses
Figure 1. Typical TEM images of PI-Au before and after use for amine oxidation.
60
50
Befor use
After use
40
30
20
10
0
Before use
40
After use
20
0
0~1
1~2
2~3
3~4
4~5
5~6
6~7 7~8
8~9 9~10 10~11 11~12
Cluster size/nm
Cluster size/nm
Figure 3. Size distribution of PI-Au 2b before and after use
for amine oxidation.
Figure 2. Size distribution of PI-Au 2a before and after use
for amine oxidation.
60
oxidation of dibenzylamine under 140 °C, 24 h, in xylene,
showed rather good activity. In the case of PI-Au 2c, the activity
of the catalyst increased after recycling, however the difference
was less dramatic than in the case of the low-loading catalyst.
Transmission electron microscopy (TEM) analysis revealed
that the cluster size of the recycled catalyst was increased by
aggregation of the clusters (Figure 1). In the case of PI-Au 2a,
the range of cluster size changed from 1 to 10 nm (average:
3.0 nm) to 4-12 nm (average: 6.9 nm) with a comparatively
narrow distribution (Figure 2). On the other hand, in the cases
of PI-Au 2b and 2c, the range of cluster sizes in the initial
catalyst was 1-10 (average: 3.2 nm) and 1-16 nm (average:
3.8 nm), respectively, which changed to 3-41 (average: 14.3
nm) and 3-50 nm (average: 16.0 nm), respectively, after three
sets of use in amine oxidation reactions (Figures 3 and 4).
Based on these results, we formed a working hypothesis that
clusters with a size over 5 nm possess higher reactivity for
aerobic oxidation of amines than those with a size around 1-3
Befor use
After use
40
20
0
Cluster size/nm
Figure 4. Size distribution of PI-Au 2c before and after use
for amine oxidation.
nm, which are generally highly active for aerobic oxidation of
alcohols.
Effect of Preheating on Reactivity and Cluster Size. PI-
Au 2a with 0.078 mmol g¹1 Au loading was heated in xylene at

H. Miyamura et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
591
140 °C for different periods under Ar, and we studied the
relationship among heating time, cluster size and activity for
the dibenzylamine oxidation reaction (Scheme 2 and Table 3).
The average cluster size was correlated with heating time, and
larger cluster size was obtained by longer heating time. It is
noted that reactivity also increased as the size of the clusters
increased.
Another approach to obtain PI-Au catalysts with larger
clusters was to heat polymer microcapsules in an appropriate
solvent in the process of crosslinking. We prepared PI-Au 4
and 5 by crosslinking in mesitylene and decane at 150 °C,
respectively, and tested them in amine oxidation reactions
(Scheme 3). As a result, PI-Au 4 crosslinked in mesitylene had
an average cluster size of 6.6 nm and showed high activity even
with low loading of Au (Figures 5 and 6). PI-Au 5 crosslinked
in decane had an average cluster size of 8.5 nm and showed
high activity. When these catalysts were applied to the aerobic
oxidation of an alcohol, the activity was in inverse proportion
to the activity of amine oxidation (Table 4). Therefore, it was
clarified that an important factor for oxidation of amines is not
Au loading but cluster size.
Based on these results, when polymer 1 was used as a
support, apparently the optimum cluster size for aerobic
oxidation of amines was larger than that for oxidation of
alcohols.
Effect of a Functional Group in the Polymer on
Reactivity and Cluster Size. Next, we changed the polymer
structure from polymer 1 to 6, which contains an amine moiety
(Figure 7). The preparation method follows that of PI-Au 4,
crosslinking being conducted in mesitylene to afford PI-Au 7
(Scheme 4). The distribution of cluster sizes was measured by
scanning transmission electron microscopy (STEM) analysis,
and it was found that the average cluster size was 5.0 nm and
the median cluster size was 5 to 6 nm. This size distribution
was quite similar to that of PI-Au 4 (Figures 8 and 9).
Catalytic activities of PI-Au 2a, 2c, 4, and 7 were compared
in the aerobic oxidation of an amine at various temperatures
(Table 5). PI-Au 2a and 2c showed good activity at 140 °C,
however the reaction was sluggish at 100 °C. On the other
hand, PI-Au 4 and 7 smoothly worked at 100 °C. This is
xylene
PI-Au 2a
ΔPI-Au 3
(0.078 mmolg−1)
140 °C, time, Ar
Scheme 2. Activation of PI-Au 2a by heating.
Table 3. Relationship among Reactivity, Heating Time, and Cluster Size
ΔPI-Au 3 (1 mol%)
N
N
H
xylene, 140 °C, O2, 6 h
14
Preheating time/h
Yield/%a)
0
0.5
38
1
3
8
24
72
150
61
40
40
41
45
52
57
Average cluster size/nm
3.0
3.0
3.5
4.1
a) Determined by GC analysis.
PI-Au 4
crosslinking
coacervation
Polymer 1 + NaBH4
(solvent = mesitylene)
in solvent
150 °C, 5 h
1) filtration
2) wash
(H2O, DCM, THF)
3) crush
150 °C, 5 h
AuClPPh3
Et2O
diglyme
no solvent
PI-Au 5
(solvent = decane)
4) dry
Scheme 3. Preparation of PI-Au 4 and 5.
30
20
10
0
Cluster size/nm
Figure 5. Size distribution of PI-Au 4.
Figure 6. Typical STEM image of PI-Au 4.

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Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011) BCSJ AWARD ARTICLE
Table 4. Evaluation of Catalytic Activity of PI-Au 4 and 5 and Their Loadings and Cluster Sizes
PI-Au (2 mol%)
N
H
N
xylene, 140 °C, O2, 6 h
14
OH
O
PI-Au (1 mol%)
K2CO3 (3 equiv), BTF/H2O, rt, 3 h, O2
ketone
Cluster size
Loading
/mmol g
Yield of 14
Yield of ketone
Entry
PI-Au
¹1
/nmb)
/%a)
/%a)
1
2
3
4
2a
2c
4
3.0
3.8
6.6
8.5
0.078
0.59
0.072
0.069
40
84
94
90
>90
56
5
5
8
a) Determined by GC analysis. b) Average value.
because Au clusters in PI-Au 2a and 2c could aggregate and be
activated at 140 °C, but not at 100 °C. It should be noted that
PI-Au 7 gave a satisfactory result even at 80 °C.
x
y
z
w
Relationship among Reactivity, Cluster Size, and Func-
tional Groups in the Polymer. Judging from the results in
Table 2 and Figures 2-5, the recycled catalyst that contained
larger Au clusters (over 5 nm) showed higher activity for amine
oxidation than the initial catalysts with 2-4 nm clusters on
average. However, the size distributions of the recycled
catalysts in Table 2 were too scattered to determine the best
range of cluster size. On the other hand, PI-Au 4 and 7, which
were crosslinked in mesitylene, showed relatively narrow size
distributions of Au clusters between 4 and 7 nm on average and
O
OH
O
O
N
4
Polymer 6 (x:y:z:w = 6:6:6:1)
Figure 7. Polymer containing a tertiary amine group.
crosslinking
coacervation
Polymer 6 + NaBH4
PI-Au 7
in mesitylene 1) filtration
150 °C, 5 h
150 °C, 5 h
no solvent
AuClPPh3
Et2O
diglyme
2) wash
(H2O, DCM, THF)
3) crush
4) dry
Scheme 4. Preparation of PI-Au 7.
40
30
20
10
0
1~2
2~3
3~4
4~5
5~6
6~7
7~8
8~9 9~10 10~11 11~12 12~13
Cluster size/nm
Figure 8. Size distribution of PI-Au 7.
Figure 9. Typical STEM image of PI-Au 7.

H. Miyamura et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
593
Table 5. Comparison of Catalytic Activities of PI-Au 2a, 2c, 4, and 7 under Various Conditions
PI-Au (2 mol%)
N
H
N
conditions, O2
14
Yield/%
PI-Au conditions
2a
2c
4
7
Toluene, 80 °C, 20 ha)
Toluene, 100 °C, 12 ha)
Toluene, 100 °C, 24 ha)
Xylene, 140 °C, 6 ha)
Xylene, 140 °C, 24 ha)
®
®
10
®
92
®
®
46
84
97
40
73
®
94
®
54c) (83)b),c)
88c)
®
®
®
a) Yield was determined by GC analysis. b) With 5 mol % of PI-Au for 42 h. c) No Au leaching
was confirmed by ICP analysis (<0.04%).
We thought that the relationship between the cluster size and
the reactivity could be explained by a balance of adsorption of
substrates and products because relative adsorption strength of
imines against amines on small clusters, K1/K2 (small cluster),
might be larger than that on large clusters, K1/K2 (big cluster)
(Figure 10).
Another factor to improve the catalytic activity was the
introduction of a tertiary amine group in the polymer
(Figure 7). Although the size distribution and average
cluster size of PI-Au 4 and 7 were similar (Figure 8), PI-Au
7, which was immobilized on polymer with a tertiary amine,
showed higher activity, especially at lower temperature than
PI-Au 4.
One of the effects of a tertiary amine in the polymer may be
explained by its role as a base. Aerobic oxidation of alcohols
catalyzed by PI-Au was strongly influenced by addition of a
base. Although oxidation of amines was seldom affected by
external addition of a base, a substrate itself that was a
secondary amine might work as a base in the amine oxidation. It
is possible that the tertiary amine in the polymer, which is more
basic than the substrate, can play a role as a base and enhance the
reactivity more effectively, cooperating with gold nanoclusters
inside the same reaction environment of the polymer.
Another effect of the tertiary amine can be explained by
controlling the balance of adsorption and desorption. The
product, an imine, can be adsorbed strongly on gold nano-
clusters; thus, a higher temperature is required to replace it on a
substrate for amine oxidation than for alcohol oxidation. The
tertiary amine in the polymer can eliminate an adsorbed imine
and make the catalytic cycle faster because of its nucleophi-
licity and bulkiness (Figure 10).
Figure 10. Assumed mechanism of aerobic oxidation of
amines on a gold nanocluster.
their reactivity for the amine oxidation was higher than that of
PI-Au 2a and 2c both before and after recycling.
While average cluster size and distribution are not so
different among PI-Au with 0.078 mmol g¹1 2a, 0.25 mmol g
¹1
2b, and 0.59 mmol g¹1 2c, the activity of the amine oxidation at
100 °C for 24 h was very different from the reaction at 140 °C
for 6 h. We already confirmed that aggregation of Au clusters
hardly occurred without solvent even at 170 °C.9a In contrast,
Au clusters aggregated easily at 140 °C for all loading levels of
catalysts in the presence of a solvent that swelled the polymer,
because crosslinked polymer fixed small Au clusters less
tightly and Au clusters could move to aggregate in swelled
polymer with solvents. Au clusters easily aggregated to form
larger clusters in the catalyst with higher loading, because the
concentration of clusters was higher and clusters could
encounter each other with shorter moving distances. On the
other hand, when a catalyst was heated in an appropriate
solvent just after microencapsulation in the crosslinking step
(PI-Au 4 and 5), larger clusters that showed higher reactivity
could be obtained even for low-loading catalysts, probably
because Au clusters could move more freely inside the polymer
before extensive crosslinking (Scheme 3 and Table 4, Entries 3
and 4).
Substrate Scope.
The scope of the substrates was
examined using PI-Au catalysts. First, benzylaniline deriva-
tives were chosen as substrates (Table 6). The reactions
proceeded smoothly at 100 °C with electron-donating groups
on the benzene ring of the benzyl group both by PI-Au 2c and
7, however a higher temperature was required when electron-
withdrawing groups existed on the benzene ring of the benzyl
group. On the other hand, electron-withdrawing groups on the
benzene ring connected to nitrogen did not affect the reactivity.
These results suggest that hydride transfer at the benzylic
position may be a rate-determining step similar to oxidation of
alcohols to carbonyl compounds.11

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Table 6. Substrate Scope of Oxidation of Benzylaniline Derivatives
PI-Au (2 mol%)
N
N
R2
R2
conditions, O2
H
R1
R1
Entry
PI-Au
R1, R2
Conditions
Product
Yield/%a)
1
2
3
4
5
6
7
8
9
7
7
7
7
7
7
7
7
4-MeO, 4-Cl
4-MeO, 4-Br
4-Cl, H
4-Cl, H
4-Br, H
Toluene, 100 °C, 12 h
15
16
17
17
18
18
19
20
21
21
22
23
89
69
6
91
15
>99
>99
92
82b)
94b)
60b)
90b)
Toluene, 100 °C, 12 h
Toluene, 100 °C, 12 h
Xylene, 140 °C, 20 h
Toluene, 100 °C, 12 h
Xylene, 140 °C, 20 h
Toluene, 100 °C, 20 h
Toluene, 100 °C, 20 h
Toluene, 100 °C, 24 h
Xylene, 140 °C, 24 h
Toluene, 100 °C, 20 h
Xylene, 140 °C, 24 h
4-Br, H
4-MeO, H
3,4-diMeO, H
2,4-diMeO, H
2,4-diMeO, H
3,4,5-triMeO, H
H, H
2c
2c
7
10
11
12
2c
a) Isolated yield. b) Determined by GC analysis.
Table 7. Substrate Scope of Oxidation of Primary Benzylamines
PI-Au (x mol)
NH2
N
xylene, 140 °C, O2, T h
R
R
R
R
PI-Au
x/mol %
T/h
Product
Yield/%a)
H
H
2a
7
2a
2b
2c
7
2a
2a
2a
4
2.5
1
1
1
1
1
1
4
24
30
24
24
24
24
24
24
24
14
14
24
24
24
24
25
26
27
70b)
90b)
72b)
70b)
88b)
99b)
61
p-MeO
p-MeO
p-MeO
p-MeO
o-MeO
m-MeO
p-CF3
52
45
a) Isolated yield. b) Determined by GC analysis.
Next, oxidation of primary benzylamines was examined
(Table 7). A high temperature was required to obtain the
desired imine in high yields, and electron-donating groups on
the benzene ring facilitated the reaction, similar to the case of
benzylaniline substrates, probably for the same reasons.
Oxidative aromatization reactions also proceeded well in the
presence of PI-Au catalysts (Table 8). Indoline and tetra-
hydroquinoline were oxidized to indole and quinoline respec-
tively however dihydroquinoline was not observed. On the
other hand, tetrahydroisoquinoline was oxidized to dihydro-
isoquinoline as a major product, isoquinoline being a minor
product. The best result was obtained at 100 °C in the presence
of PI-Au 7, and total yield decreased at higher temperatures,
probably because of decomposition of the products.
methoxybenzylaniline as model substrate for recovery and
reuse because analytically pure product could be obtained after
filtration of catalyst and concentration. PI-Au 7 was added to a
solution of p-methoxybenzylaniline in toluene. The mixture
was stirred at 100 °C under oxygen atmosphere (with oxygen
balloon) for 20 h. After filtration of the catalyst, solvent was
removed to afford analytically pure 19. Filtered PI-Au was
dried in vacuo and collected. A small amount of catalyst could
not be recovered because it was trapped by filtration paper.
Recovered PI-Au was used for the second reaction and reaction
scale was adjusted depending on the amount of recovered
catalyst.
Substrate Scope of One-Pot Deprotection of the
p-Methoxybenzyl Group Catalyzed by PI-Au.
One-pot
N-Phenyltetrahydroisoquinoline was oxidized to a mixture
of amide 8 and further oxidized amide 9 in the presence of PI-
Au 7 (Table 9). While the ratio of amide 9 was increased at
higher temperature, the total yield was decreased.
oxidative deprotection of the p-methoxybenzyl group of a
secondary amine was examined (Table 11), and both aryl and
alkyl amines could be obtained in high yields. Substrates 11a
and 12a had two ¡-hydrogens of amine, which could be
oxidized, however, only benzylideneamines formed and gave
aliphatic amines after hydrolysis. On the other hand, a tertiary
amine substrate did not react in xylene at 140 °C (Scheme 5).
Recovery and Reuse of PI-Au.
PI-Au 7 could be
recovered and reused without loss of activity at least seven
times by simple filtration and drying (Table 10). We chose p-

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Table 8. Substrate Scope of the Aromatization Reaction
PI-Au (2 mol%)
amine
imine
conditions, O2
PI-Au
(2 mol %)
Amine
Product
Conditions
Yielda)/%
7
7
Xylene, 140 °C, 24 h
Toluene, 120 °C, 24 h
79 (11)b)
82 (12)b)
NH
N
N
7
Toluene, 100 °C, 24 h
87 (13)b)
2a
2b
2c
Xylene, 140 °C, 24 h
Xylene, 140 °C, 24 h
Xylene, 140 °C, 24 h
64
75
57
N
N
H
H
7
Xylene, 140 °C, 24 h
76
N
N
H
1
a) Determined by GC analysis. b) Isolated as a mixture and ratio was determined by H NMR.
Table 9. Oxidation of Tetrahydroisoquinoline Derivative
PI-Au 7 (2 mol%)
N
+
N
N
toluene, temp, O2
O
O
8
9
Entry
Temperature/°C
Time/h
8/9 yield/%a)
1
2
120
100
20
20
29/48
46/35
1
a) Isolated as a mixture and ratio was determined by H NMR.
Therefore, the tertiary amine group in the polymer might be
intact under these oxidative conditions.
Further investigations to reveal the reaction mechanism and
relationship between reactivity and cluster size would provide
valuable information about Au cluster catalysis.
Conclusion
Experimental
Polymer-incarcerated gold (PI-Au) catalysts were applied
to aerobic oxidation of amines to imines. Investigation of
recovery and reuse of PI-Au in the amine oxidation, careful
TEM and STEM analysis to examine distribution and average
size of clusters and modified preparation methods of the
catalysts to control cluster size revealed interesting relationship
among Au loading, cluster size, and reactivity. Relatively large
Au clusters (5 to 10 nm) seem to be more effective for amine
oxidation than small Au clusters (2 to 3 nm), which, in contrast,
showed excellent reactivity for aerobic oxidation of alcohols.
Catalysts prepared from a polymer with a tertiary amine group
showed excellent catalytic activity, probably because of the
cooperative effect of such functional groups with Au clusters.
Various primary and secondary benzylamines could be
successfully oxidized to the corresponding imines using this
oxidation system. Aromatization reactions and one-pot depro-
tection of p-methoxybenzyl groups could be achieved. More-
over, the catalyst could be reused several times by simple
operations without significant loss of activity.
General. 1H and 13C NMR spectra were recorded on a
JEOL JNM-LA300, JNM-LA400, or JNM-LA600 spectrome-
ter. Tetramethylsilane (¤ = 0) was used as an internal standard
for 1H NMR and CDCl3 (¤ = 77.0) for 13C NMR. The structures
of the known compounds were confirmed by comparison with
commercially available compounds or data shown in the
literature. GC analysis was performed on a Shimadzu GC-
2010 apparatus (column: J & W SCIENTIFIC DB-1; gas
pressure: 157.5 kPa, total flow: 41.3 mL min¹1, column flow:
0.93 mL min¹1, linear velocity: 21.1 cm s¹1, split ratio: 40:1,
injection temperature: 300 °C, detector temperature: 300 °C).
Inductively coupled plasma (ICP) analysis was performed
on Shimadzu ICPS-7510 equipment. High-resolution electro-
spray ionization mass spectra (HR-MS) were measured with
JEOL JMS-T100TD AccuTOF TLC. Water was treated by
MILLIPORE Elix-UV before use. Column chromatography was
performed on silica gel 60 (Merck), and preparative TLC was
carried out using Wakogel B-5F (Wako Pure Chemical

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Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011) BCSJ AWARD ARTICLE
Table 10. Recovery and Reuse of PI-Au 7
PI-Au 7 (2 mol%)
N
N
H
toluene, 100 °C, 20 h, O2
MeO
MeO
19
Run
Yield/%a)
1st
2nd
3rd
4th
5th
>99
6th
7th
>99
>99
>99
>99
>99
>99
a) Isolated yield.
Table 11. Substrate Scope of Oxidative Deprotection of PMB Groups
Yield
/%a)
Entry
Substrate
Product
Conditions
OMe
NH2
H
N
1
Xylene, 140 °C
Toluene, 100 °C
Toluene, 100 °C
91
92
88
10b
11b
10a
OMe
H
N
NH2
NH2
2
11a
OMe
H
N
3
Me
Me
12b
12a
a) Isolated yield.
OMe
No reaction
(Starting material
was recovered)
PI-Au 2b (1 mol%)
N
xylene, 140 °C, 24 h, O2
13
Scheme 5. Oxidative deprotection of PMB at a tertiary amine.
Industry). STEM and TEM images were obtained using a JEOL
JEM-2100F instrument operated at 200 kVand JEOL JEM-1010
instrument operated at 80 kV. All TEM specimens were
prepared by placing a drop of solution on carbon-coated Cu
grids and allowing to dry in air (without staining).
(m, 4H). 13C NMR (CDCl3): ¤ 24.4, 26.0, 54.5, 63.6, 113.3,
125.9, 129.4, 136.2, 136.7, 138.3.
Preparation of Copolymer 6. Styrene (1.07 g), glycidyl 4-
vinylbenzyl ether (1.90 g), 2-(2-{2-[2-(4-vinylbenzyloxy)eth-
oxy]ethoxy}ethoxy)ethanol (3.15 g), 1-(4-vinylbenzyl)piperi-
dine (342 mg), and 2,2¤-azobis(4-methoxy-2,4-dimethylvalero-
nitrile) (102.5 mg) were combined in chloroform (11.0 mL).
The mixture was stirred for 72 h at room temperature. The
resulting polymer solution was diluted with THF (15 mL) and
slowly poured into diethyl ether (800 mL). The solvent was
removed by decantation and the residue was dissolved again in
THF (15 mL). The polymer solution was slowly poured into
diethyl ether (800 mL) again. The same procedure was repeated
a total of three times. The precipitated polymer was filtered and
washed with ether several times and dried in vacuo within
10 min to afford the desired copolymer (6, 3.75 g). If the
polymer was dried in vacuo for too long time, crosslinking
sometimes occurred, therefore, polymer was dissolved in THF
(37.5 mL) and stored in refrigerator. The mole ratio of the
Preparation of ¦PI-Au 3. PI-Au 2 (55 mg), prepared by a
previously reported method,9a was heated in xylene (2 mL) at
140 °C under Ar atmosphere for 0.5, 1, 3, 8, and 24 h. The
mixture was cooled to room temperature and the catalyst was
collected by filtration and washed with EtOAc (5 mL). The
catalyst was dried in vacuo to afford ¦PI-Au 3.
Preparation of 1-(4-Vinylbenzyl)piperidine.12
K2CO3
(16.14 g) was added to a solution of 4-vinylbenzyl chloride
(9.26 g) and piperidine (5.13 g) in acetonitrile (50 mL). The
mixture was refluxed for 2 h and cooled to room temperature.
Solvent was removed and the residue was purified by column
chromatography to afford 1-(4-vinylbenzyl)piperidine (10.7 g,
1
87%). H NMR (CDCl3): ¤ 1.38-1.40 (m, 2H), 1.49-1.56 (m,
4H), 3.42 (s, 2H), 5.17 (d, 1H, J = 10.6 Hz), 5.68 (d, 1H,
J = 17.4 Hz), 6.66 (dd, 1H, J = 10.9 Hz, 17.4 Hz), 7.21-7.32
1
components was determined by H NMR analysis.

H. Miyamura et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
597
Preparation of PI-Au 4. Copolymer 1 (420.6 mg)9a and
NaBH4 (27.0 mg) were dissolved in diglyme (25 mL) at room
temperature. Chlorotriphenylphosphine gold(I) (150.0 mg) with
3 mL of THF was slowly added to this solution, whereupon the
solution turned wine red. The mixture was stirred for 3 h at
room temperature and diethyl ether (80 mL) was slowly added
to the mixture at room temperature. Brown coacervates
enveloped the metal dispersed in the medium. The catalyst
capsules were then washed with diethyl ether several times and
dried at room temperature. Next, the catalyst capsules were
heated at 150 °C in mesitylene (20 mL) for 5 h. The prepared
catalyst was washed with water, dichloromethane (DCM), and
THF, crushed and dried to afford a wine-red powder. This
powder was heated at 150 °C for 5 h without solvent to afford
PI-Au 4 (283.5 mg). 10-20 mg of PI-Au 4 was heated in a
mixture of sulfuric acid and nitric acid at 200 °C for 3 h, the
mixture was cooled to room temperature and aqua regia was
added. The amount of gold in the resulting solution was
measured by ICP analysis to determine the loading of gold
stirred at 100 °C under oxygen atmosphere (with oxygen
balloon) for 20 h. After filtration of the catalyst, solvent was
removed to afford analytically pure 19 (244.0 mg, >99%
yield). Filtered PI-Au was dried in vacuo and collected
(50.4 mg). A small amount of catalyst could not be recovered
because it was trapped by filtration paper. Recovered PI-Au
was used for the second reaction and reaction scale was
adjusted depending on the amount of recovered catalyst.
Oxidation of 1,2,3,4-Tetrahydro-2-phenylisoquinoline
Catalyzed by PI-Au (Isolation by pTLC).
PI-Au 7
(2 mol % Au, 10.6 mg) was added to a solution of 1,2,3,4-
tetrahydro-2-phenylisoquinoline (43.8 mg, 0.210 mmol) in tol-
uene. (1 mL) The mixture was stirred at 120 °C under oxygen
atmosphere (with oxygen balloon) for 20 h. After filtration of
the catalyst, solvent was removed. The mixture was separated
by preparative TLC (ethyl acetate:hexane = 3:1). Yellow oil
was obtained in 35.7 mg and was analyzed by 1H NMR to
determine the ratio of 3,4-dihydro-2-phenylisoquinolin-1(2H)-
one (29% yield) and 2-phenylisoquinolin-1(2H)-one (48%
yield).
¹1
(0.805 mmol g Au).
Preparation of PI-Au 7. Copolymer 6 (344.2 mg) and
NaBH4 (27.0 mg) were dissolved in diglyme (25 mL) at room
temperature. Chlorotriphenylphosphine gold(I) (150.0 mg) with
3 mL of THF was slowly added to this solution, whereupon the
solution turned wine red. The mixture was stirred for 3 h at
room temperature and diethyl ether (80 mL) was slowly added
to the mixture at room temperature. Brown coacervates
enveloped the metal dispersed in the medium. The catalyst
capsules were then washed with diethyl ether several times and
dried at room temperature. Next, the catalyst capsules were
heated at 150 °C in mesitylene (20 mL) for 5 h. The prepared
catalyst was washed with water, DCM, and THF, crushed and
dried to afford a wine-red powder. This powder was heated at
150 °C for 5 h without solvent to afford PI-Au 7 (279.6 mg).
10-20 mg of PI-Au 7 was heated in a mixture of sulfuric acid
and nitric acid at 200 °C for 3 h, the mixture was cooled to
room temperature and aqua regia was added. The amount of
gold in the resulting solution was measured by ICP analysis to
Oxidation of 1,2,3,4-Tetrahydroisoquinoline Catalyzed
by PI-Au (Isolation by pTLC). PI-Au 7 (2 mol % Au, 10.6
mg) was added to a solution of 1,2,3,4-tetrahydroisoquinoline
(35.4 mg, 0.266 mmol) in xylene (1 mL). The mixture was
stirred at 140 °C under oxygen atmosphere (with oxygen
balloon) for 24 h. After filtration of the catalyst, solvent was
removed. The mixture was separated by preparative TLC (ethyl
acetate:hexane = 3:1). Yellow oil was obtained in 31.4 mg and
was analyzed by 1H NMR to determine the ratio of 3,4-
dihydroisoquinoline (79% yield) and isoquinoline (11% yield).
N-(Benzylidene)benzylamine (14):13 1H NMR (CDCl3): ¤
4.82 (s, 2H), 7.24-7.28 (m, 1H), 7.33-7.43 (m, 4H), 7.41-7.43
(m, 3H), 7.77-7.80 (m, 2H), 8.40 (s, 1H). 13C NMR (CDCl3): ¤
65.0, 127.0, 127.9, 128.2, 128.5, 128.6, 130.7, 136.1, 139.3,
161.9.
N-(4-Methoxybenzylidene)-4-chloroaniline (15):14 1H NMR
(CDCl3): ¤ 3.79 (s, 3H), 6.90 (d, 2H, J = 8.2 Hz), 7.03-7.05
(m, 2H), 7.24-7.26 (m, 2H), 7.75 (d, 2H, J = 7.6 Hz), 8.26
(s, 1H). 13C NMR (CDCl3): ¤ 55.4, 114.2, 122.2, 129.0, 129.2,
130.6, 131.0, 150.9, 160.0, 162.4.
N-(4-Methoxybenzylidene)-4-bromoaniline (16):14 1H NMR
(CDCl3): ¤ 3.86 (s, 3H), 6.96 (d, 2H, J = 8.9 Hz), 7.05 (d, 2H,
J = 8.9 Hz), 7.47 (d, 2H, J = 8.3 Hz), 7.81 (d, 2H, J = 8.3 Hz),
8.43 (s, 1H). 13C NMR (CDCl3): ¤ 55.4, 114.3, 118.8, 122.6,
129.0, 130.6, 132.1, 151.3, 160.0, 162.5.
¹1
determine the loading of gold (0.887 mmol g Au).
A Typical Procedure for Oxidation of Dibenzylamine
Catalyzed by PI-Au (Determination of Yield by GC Analy-
sis, Table 5, PI-Au 7, 100 °C, 12 h). PI-Au 7 (2 mol % Au,
10.3 mg) was added to a solution of dibenzylamine (50.3 mg,
0.255 mmol) in toluene (1 mL). The mixture was stirred at
100 °C under oxygen atmosphere (with oxygen balloon) for
12 h. After filtration of the catalyst, anisole was added as an
internal standard. The mixture was analyzed by GC and yield
was calculated as N-(benzylidene)benzylamine: 44.0 mg, 88%;
dibenzylamine: 3.6 mg, 7%; benzaldehyde: 1.3 mg, 5%. After
determining the yield, the solvents of the mixture were removed
in vacuo. To each residue were added sulfuric acid and aqua
regia then the volume of the residue was adjusted to 50 mL using
water to give a sample for ICP analyses for the measurement of
the leaching of gold (Au was not detected; <0.04%).
N-(4-Chlorobenzylidene)aniline (17):13 1H NMR (CDCl3):
¤ 7.22-7.28 (m, 3H), 7.40-7.48 (m, 4H), 7.84-7.87 (m, 2H),
8.43 (s, 1H). 13C NMR (CDCl3): ¤ 120.8, 126.2, 129.0, 129.2,
129.9, 134.7, 137.3, 151.6, 158.8.
N-(4-Bromobenzylidene)aniline (18):15 1H NMR (CDCl3):
¤ 7.22-7.28 (m, 3H), 7.40-7.44 (m, 2H), 7.63 (d, 2H, J =
8.2 Hz), 7.8 (d, 2H, J = 8.2 Hz), 8.43 (s, 1H). 13C NMR
(CDCl3): ¤ 120.8, 125.9, 126.2, 129.2, 130.1, 132.0, 135.6,
151.7, 158.9.
A Typical Procedure for Oxidation of Amine Catalyzed
by PI-Au (Isolation by Filtration) and the Following
Recovery and Reuse of PI-Au. PI-Au 7 (2 mol % Au, 53.8
mg) was added to a solution of N-(p-methoxybenzyl)aniline
(245.0 mg, 0.364 mmol) in toluene (1 mL). The mixture was
N-(4-Methoxybenzylidene)aniline (19):13 1H NMR (CDCl3):
¤ 3.87 (s, 3H), 7.01 (d, 2H, J = 8.2 Hz), 7.22-7.27 (m, 3H),
7.40-7.53 (m, 2H), 7.88 (d, 2H, J = 8.9 Hz), 8.43 (s, 1H).
13C NMR (CDCl3): ¤ 55.2, 114.1, 114.9, 120.8, 125.4, 129.0,
130.4, 152.2, 159.5, 162.1.

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Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011) BCSJ AWARD ARTICLE
1H NMR
N-(3,4-Dimethoxybenzylidene)aniline (20):16
acetate. The combined organic layer was dried over Na2SO4
and solvent was removed in vacuo. The residue was purified by
column chromatography (hexane:ethyl acetate = 15:1) as an
eluant to give N-(4-methoxybenzyl)aniline (0.9547 g, 96%).
N-(4-Methoxybenzyl)aniline (Table 6, Entry 7): 1H NMR
(CDCl3): ¤ 3.80 (s, 3H), 4.08 (br, 1H), 4.24 (s, 2H), 6.64 (d,
2H, J = 7.56 Hz), 6.72 (t, 1H, J = 6.90 Hz), 6.88 (t, 2H,
J = 2.10 Hz), 7.15-7.19 (m, 2H), 7.29 (d, 2H, J = 8.88 Hz).
N-(4-Chlorobenzyl)aniline (Table 6, Entries 3 and 4):
1H NMR (CDCl3): ¤ 4.26 (br, 1H), 4.43 (s, 2H), 6.61 (d, 2H,
J = 7.56 Hz), 6.71 (t, 1H, J = 7.56 Hz), 7.15-7.21 (m, 4H),
7.24-7.42 (m, 2H).
N-(3,4,5-Trimethoxybenzyl)aniline (Table 6, Entry 11):
1H NMR (CDCl3): ¤ 3.84 (s, 9H), 4.26 (s, 2H), 6.61 (s, 2H),
6.67 (d, 2H, J = 7.56 Hz), 6.75 (t, 2H, J = 6.84 Hz), 7.19
(t, 2H, J = 8.22).
N-(2,4-Dimethoxybenzyl)aniline (Table 6, Entries 9 and
10): 1H NMR (CDCl3): ¤ 3.79 (s, 3H), 3.82 (s, 3H), 4.24 (s,
2H), 6.42 (dd, 1H, J = 2.70, 8.22 Hz), 6.47 (d, 1H, J = 2.4 Hz),
6.65-6.70 (m, 3H), 7.14-7.25 (m, 3H).
A Typical Procedure for Preparation of an N-(4-Meth-
oxybenzyl)amine. 4-Methoxybenzylamine (1.6 g, 11.3 mmol)
was added to a cooled solution of 3-phenyl-1-bromopropane
(1.5 g, 7.53 mmol) in CH2Cl2 (25 mL). Et3N (2.1 mL, 15.1
mmol) was added to the mixture under ice cooling. This was
stirred at room temperature for 3 h. Water was added to work up
the reaction and the mixture was extracted with CH2Cl2. The
combined organic layer was dried over MgSO4 and the solvent
was removed in vacuo. The residue was dissolved in CH2Cl2.
Et3N (2.0 equiv) and Boc2O (1.5 equiv) were added to the
mixture. This was stirred at room temperature for 12 h. Water
was added to the mixture to work up the reaction and the
mixture was extracted with CH2Cl2. The combined organic
layers were washed with brine and concentrated in vacuo. The
residue was purified by silica gel column chromatography to
give a pale red-orange oil (0.9447 g, 35%). This oil was then
dissolved in dioxane. 4 M HCl/dioxane was added to the
solution. The solution was stirred at room temperature for 12 h.
The solvent was removed in vacuo. The resulting solid was
triturated with isopropyl ether/isopropyl alcohol to give
colorless crystals. These were suspended in ethyl acetate and
washed with 1 M NaOH. The organic layer was dried over
Na2SO4 and concentrated to give N-(4-methoxybenzyl)-
3-phenylpropan-1-amine (11a) (0.62 g, 32% three steps).
(CDCl3): ¤ 3.94 (s, 3H), 3.99 (s, 3H), 6.93 (d, 1H, J = 8.2 Hz),
7.22-7.26 (m, 3H), 7.30-7.34 (m, 1H), 7.39-7.43 (m, 2H), 7.65
(d, 1H, J = 1.8 Hz), 8.37 (s, 1H). 13C NMR (CDCl3): ¤ 55.8,
56.0, 108.9, 110.4, 120.7, 124.3, 125.4, 129.0, 129.4, 149.3,
151.9, 152.1, 159.7.
N-(4-Methoxybenzylidene)-4-methoxybenzylamine (24):13
1H NMR (CDCl3): ¤ 3.80 (s, 3H), 3.84 (s, 3H), 4.73 (s, 2H)
6.87-6.93 (m, 4H), 7.25-7.26 (m, 2H), 7.71-7.73 (m, 2H), 8.29
(s, 1H). 13C NMR (CDCl3): ¤ 55.2, 55.3, 64.3, 113.8, 113.9,
129.1, 129.7, 131.6, 158.6, 160.8, 161.6.
N-(2-Methoxybenzylidene)-2-methoxybenzylamine (25):13
1H NMR (CDCl3): ¤ 3.83 (s, 3H), 3.86 (s, 3H), 4.82 (s, 2H),
6.85-6.96 (m, 4H), 7.20-7.39 (m, 3H), 8.00-8.03 (m, 1H), 8.83
(s, 1H). 13C NMR (CDCl3): ¤ 55.3, 55.5, 59.6, 110.2, 110.9,
120.5, 120.7, 124.9, 127.5, 127.9, 128.2, 129.1, 131.7, 157.1,
158.3, 158.8.
N-(3-Methoxybenzylidene)-3-methoxybenzylamine (26):13
1H NMR (CDCl3): ¤ 3.78 (s, 3H), 3.82 (s, 3H), 4.78 (s, 2H),
6.78-6.97 (m, 4H), 7.22-7.37 (m, 4H), 8.33 (s, 1H). 13C NMR
(CDCl3): ¤ 55.2, 55.4, 64.9, 111.7, 112.4, 113.6, 117.6, 120.3,
121.6, 129.46, 129.54, 137.6, 140.8, 159.8, 159.9, 162.0.
N-(4-Trifluoromethylbenzylidene)-4-trifluoromethylben-
zylamine (27):13 1H NMR (CDCl3): ¤ 4.88 (s, 2H), 7.44-7.47
(m, 2H), 7.58-7.69 (m, 4H), 7.87-7.90 (m, 2H), 8.45 (s, 1H).
13C NMR (CDCl3): ¤ 64.3, 120.0 (d, J = 34.3 Hz), 122.7 (d,
J = 34.3 Hz), 125.4 (q, J = 3.8 Hz), 125.6 (q, J = 3.8 Hz),
128.1, 128.5, 129.4 (q, J = 32.4 Hz), 132.5 (q, J = 32.4 Hz),
139.0 (d, J = 1.9 Hz), 143.1, 161.1.
A Typical Procedure for Preparation of N-(4-Methoxy-
benzylidene)aniline (19) (GC Standard). Aniline (1.0 g) and
anisaldehyde (1.5 g) were dissolved together in ethanol and left
to stand overnight at room temperature. The solvent was
evaporated off, and the product was recrystallized from EtOH
to give N-(4-methoxybenzylidene)aniline (19) (1.92 g, 85%).
Preparation of 24 (GC Standard). p-Methoxybenzalde-
hyde was added to a solution of p-methoxybenzylamine in
CH2Cl2. The mixture was stirred at room temperature for 20 h
with molecular sieves 3A. The mixture was filtered through
a celite pad and concentrated. The resulting crude oil was
purified by distillation under reduced pressure (178 °C,
<1 mmHg) to give 24 as a colorless oil.
N-(2,4-Dimethoxybenzylidene)aniline (21):16
1H NMR
(CDCl3): ¤ 3.86 (s, 6H), 6.46 (d, 1H, J = 2.76 Hz), 6.59 (t, 1H,
J = 2.10 Hz), 7.17-7.21 (m, 3H), 7.34-7.37 (m, 2H), 8.12 (br,
1H), 8.80 (s, 1H). 13C NMR (CDCl3): ¤ 55.2, 55.3, 97.8, 105.6,
118.0, 120.9, 125.1, 128.7, 128.8, 152.9, 155.7, 160.8, 163.6.
N-(3,4,5-Trimethoxybenzylidene)aniline (22):17 1H NMR
(CDCl3): ¤ 3.92-3.96 (m, 9H), 7.13-7.26 (m, 5H), 7.40 (t, 2H,
J = 7.56 Hz), 8.36 (s, 1H).
N-(4-Methoxybenzyl)-3-phenylpropan-1-amine
(11a):
1H NMR (CDCl3): ¤ 1.65 (br, 1H), 1.83 (quintet, 2H, J =
7.50 Hz), 2.64-2.67 (m, 4H), 3.71 (s, 2H), 3.80 (s, 3H), 6.86
(dd, 2H, J = 2.10, 4.08 Hz), 7.16-7.28 (m, 7H). 13C NMR
(CDCl3): ¤ 31.7, 33.6, 48.8, 53.4, 55.3, 113.8, 125.7, 128.3,
128.4, 129.3, 132.5, 142.2, 158.6.
N-(Benzylidene)aniline (23):13 1H NMR (CDCl3): ¤ 7.22-
7.25 (m, 3H), 7.37-7.41 (m, 2H), 7.43-7.46 (m, 3H), 7.90-7.92
(m, 2H), 8.43 (s, 1H). 13C NMR (CDCl3): ¤ 120.7, 125.8,
128.6, 128.7, 129.0, 131.2, 136.1, 151.9, 160.1.
A Typical Procedure for Preparation of N-Benzylaniline.
NaBH4 was added to a solution of N-(4-methoxybenzyli-
dene)aniline (1.0 g, 4.73 mmol) in MeOH at room temperature.
The mixture was stirred at the same temperature for 12 h. The
reaction was worked up with water and extracted with ethyl
N-(4-Methoxybenzyl)-4-phenylbutan-2-amine
(12a):
1H NMR (CDCl3): ¤ 1.13 (d, 3H, J = 6.18 Hz), 1.23 (br, 1H),
1.63-1.68 (m, 1H), 1.78-1.81 (m, 1H), 2.62-2.67 (m, 2H),
2.70-2.74 (m, 1H), 3.67 (d, 2H, J = 12.36 Hz), 3.76 (d, 2H,
J = 12.36 Hz), 3.80 (s, 3H), 6.85 (dd, 2H, J = 2.04, 6.18 Hz),
7.17-7.28 (m, 7H). 13C NMR (CDCl3): ¤ 31.7, 33.6, 48.8, 53.4,
55.3, 113.8, 125.7, 128.3, 128.4, 129.3, 132.5, 142.2, 158.6.
A Typical Procedure for Oxidative Deprotection of
4-Methoxybenzylamine. PI-Au 2b (15.6 mg, 0.25 mmol g
¹1
)

H. Miyamura et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
599
6
a) M. Okumura, S. Nakamura, S. Tsubota, T. Nakamura, M.
was added to a solution of N-(4-methoxybenzyl)-3-phenyl-
propan-1-amine (11a) (99.3 mg, 0.389 mmol) in toluene
(2 mL). The mixture was stirred at 100 °C for 24 h under
oxygen atmosphere. The catalyst was removed by filtration and
washed with ethyl acetate. A mixture of MeOH (2 mL) and 1 M
HCl(aq) (1 mL) was added to the filtrate and stirred for 12 h.
The aqueous phase was washed with ethyl acetate and
NaOH(aq) was added to basify the solution (pH 12-13). The
mixture was extracted with ethyl acetate and the combined
organic layer was dried over Na2SO4. Solvent was removed in
vacuo and the residue was purified by column chromatography
to give 3-phenylpropan-1-amine (11b) (48.3 mg, 92%).
3-Phenylpropan-1-amine (11b): 1H NMR (CDCl3): ¤ 1.25
(br, 2H), 1.77 (quintet, 2H, J = 6.90 Hz), 2.65 (t, 2H, J =
7.56 Hz), 2.73 (t, 2H, J = 6.90 Hz), 7.17-7.20 (m, 3H), 7.25-
7.29 (m, 2H). 13C NMR (CDCl3): ¤ 33.3, 35.4, 41.8, 125.8,
128.3, 128.4, 142.1.
Azuma, M. Haruta, Catal. Lett. 1998, 51, 53. b) A. Abad, P.
Concepción, A. Corma, H. García, Angew. Chem., Int. Ed. 2005,
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a) B. Zhu, R. J. Angelici, Chem. Commun. 2007, 2157. b)
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260, 1. c) R. J. Angelici, J. Organomet. Chem. 2008, 693, 847. d)
L. Aschwanden, B. Panella, P. Rossbach, B. Keller, A. Baiker,
ChemCatChem 2009, 1, 111. e) L. Aschwanden, T. Mallat, F.
Krumeich, A. Baiker, J. Mol. Catal. A: Chem. 2009, 309, 57. f) L.
Aschwanden, T. Mallat, J.-D. Grunwaldt, F. Krumeich, A. Baiker,
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Ho, C.-M. Che, Chem. Asian J. 2009, 4, 1551. h) A. Grirrane, A.
Corma, H. Garcia, J. Catal. 2009, 264, 138. i) L. Aschwanden, T.
Mallat, M. Maciejewski, F. Krumeich, A. Baiker, ChemCatChem
2010, 2, 666.
8
Review: a) R. Akiyama, S. Kobayashi, Chem. Rev. 2009,
4-Phenylbutan-2-amine (12b): 1H NMR (CDCl3): ¤ 1.11
(d, 3H, J = 6.18 Hz), 1.65-1.68 (m, 2H), 2.09 (br, 2H), 2.62-
2.93 (m, 2H), 2.92 (q, 1H, J = 6.90 Hz), 7.15-7.29 (m, 3H),
7.25-7.28 (m, 2H). 13C NMR (CDCl3): ¤ 23.7, 32.8, 41.5, 46.6,
125.5, 128.3, 128.3, 142.2.
109, 594. b) S. Kobayashi, H. Miyamura, Chem. Rec. 2010, 10,
271.
9
a) H. Miyamura, R. Matsubara, Y. Miyazaki, S. Kobayashi,
Angew. Chem., Int. Ed. 2007, 46, 4151. b) H. Miyamura, M.
Shiramizu, R. Matsubara, S. Kobayashi, Chem. Lett. 2008, 37,
360. c) H. Miyamura, T. Yasukawa, S. Kobayashi, Green Chem.
2010, 12, 776. d) T. Yasukawa, H. Miyamura, S. Kobayashi,
Chem. Asian J. 2011, 6, 621.
10 For related polymer-immobilized nanocluster catalysts for
aerobic oxidation reactions: a) H. Miyamura, R. Matsubara, S.
Kobayashi, Chem. Commun. 2008, 2031. b) H. Miyamura, M.
Shiramizu, R. Matsubara, S. Kobayashi, Angew. Chem., Int. Ed.
2008, 47, 8093. c) C. Lucchesi, T. Inasaki, H. Miyamura, R.
Matsubara, S. Kobayashi, Adv. Synth. Catal. 2008, 350, 1996. d)
N. Wang, T. Matsumoto, M. Ueno, H. Miyamura, S. Kobayashi,
Angew. Chem., Int. Ed. 2009, 48, 4744. e) H. Miyamura, K.
Maehata, S. Kobayashi, Chem. Commun. 2010, 46, 8052. f) K.
Kaizuka, H. Miyamura, S. Kobayashi, J. Am. Chem. Soc. 2010,
132, 15096. g) W.-J. Yoo, H. Miyamura, S. Kobayashi, J. Am.
Chem. Soc. 2011, 133, 3095.
This work was partially supported by a Grant-in-Aid for
Science Research from the Japan Society for the Promotion of
Science (JSPS), Global COE Program, The University of
Tokyo, MEXT, Japan, and NEDO. H. M. thanks the JSPS
fellowship for Japanese Junior Scientist. Special thanks to Mr.
Noriaki Kuramitsu (The University of Tokyo) for electronic
microscopy analysis.
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