Communication
product for the dehalogenation of chlorobenzene.
The good solubility of the alkoxide base may have
led to the conversion of the substrate, and a much
higher yield was achieved with DMSO as solvent
(Table 1, entry10), compared with other solvents
(Table 1, entries 7–13). The conversion increased with
elevated temperature (Table 1, entry 10 and en-
tries 14–16) and an improved selectivity was ob-
tained at 1008C (89%, Table 1, entry 15). Only little
coupling product, diphenylaniline was obtained
when monometallic Pd was used as the catalyst
(entry 17) and no product was found when monome-
tallic Au was used as the catalyst (entry 18). Further-
more, a slightly increased conversion was obtained
when a mixture of monometallic Pd and Au was
used. Triphenylamine was obtained because of the
further reaction of chlorobenzene with diphenyla-
mine.
Table 2. Scope of the Buchwald–Hartwig reaction catalyzed by nano PdAu catalyst
under optimized conditions.[a]
Entry[a] R1X
R2R3NH
Conv. [%] of 1[b] Sel. [%] of 3[b]
1
2
3
4
5
Morpholine (2b)
N,N-Dibutylaniline (2c) >99
Piperidine (2d)
N-Methylaniline (2e)
N-Ethylaniline (2 f)
>99
96
95
93
94
91
98
93
91
6[c]
Diphenylaniline (2g)
83
96
7
8
Morpholine (2b)
N,N-Dibutylaniline (2c) 94
96
95
94
9[c]
Diphenylaniline (2g)
81
83
As the product of the primary amine can further
react with chlorobenzene in a coupling reaction, we
assumed that a higher yield could be obtained when
a secondary amine and chlorobenzene are used as
substrates. Thus, we further investigated the scope of
halogenated aromatics that could be tolerated in the
Buchwald–Hartwig reaction with a secondary amine
(morpholine, Table 2) under the optimized reaction
conditions. The coupling of chlorobenzene (1a) pro-
ceeded smoothly to yield N-phenylmorpholine (3ab)
in 97% yield (entry 1). Chloroarenes containing elec-
tron-donating groups also reacted under the current
reaction conditions. 4-Chloroanisole (1b) and 4-chlor-
otoluene (1c) were each coupled with morpholine
(2b) under the current conditions to give 3bb and
3cb in yields of 96% and 95%, respectively (Table 2,
entries 1 and 7). Chloroarenes with an electron-with-
drawing group in the para-position (1d) also under-
went coupling well to afford the desired products
(Table 2, entry 13). The PdAu nano-alloy catalyst was
also tolerant to bromobenzene (1e) and iodoben-
zene (1 f), and the reaction could proceed smoothly
to afford the desired products (Table 2, entries 16
10
11
12[c]
Morpholine (2b)
N,N-Dibutylaniline (2c) 99
98
91
93
Diphenylaniline (2g)
80
89
13
14
15[c]
Morpholine (2b)
N,N-Dibutylaniline (2c) 90
98
94
92
Diphenylaniline (2c)
82
82
16
17
Bromobenzene Morpholine (2b)
Iodobenzene Morpholine (2b)
>99
>99
92
94
[a] Table 2 condition: 1a, 0.5 mmol; 2a, 1 mmol; 3 mol% catalyst (based on metal);
KOtBu, 1.5 mmol; solvent, 4 mL; time, 12 h. [b] determined by GC with n-decane as an
internal standard. [c] 24 h is needed.
and 17). Next, we checked the catalytic activity of the above
chlorobenzenes bearing different substituents with other
amines. To our satisfaction, high catalytic activities were ob-
served for both aliphatic amines (Table 2, entries 2, 3, 8 and 14)
and aromatic amines (Table 2, entries 4 and 5), affording the
corresponding CÀN coupling compounds in excellent yields
under the optimized reaction conditions. For example, 94%
conversion and 94% selectivity towards N,N-dibutylaniline
(3bc) could be obtained when 4-chloroanisole (1b) was react-
ed with di-n-butylamine (2c); N-phenylpiperidine (3ad) with
93% selectivity could be obtained when chlorobenzene (1a)
was reacted with piperidine (2d). Also N-methylaniline (2e)
and N-ethylaniline (2 f) can give 94% and 91% selectivity, re-
spectively, upon coupling with chlorobenzene (1a). The ob-
served slightly decreased yield of triphenylanilines may be be-
cause of sterical hindrance, and a longer reaction time (24 h) is
needed to obtain higher conversion (Table 2, entries 6, 9, 12,
and 15).
To understand the chemical state of PdAu in the activation
of CÀCl bonds, we referred to X-ray photoelectron spectrosco-
py (XPS) to inspect the interaction between the two metals. As
shown in Figure 3, the XPS spectra show that the binding en-
ergies of Pd 3d5/2 and Pd 3d3/2 peaks are located at 336 eV and
341.2 eV, respectively, which are slightly shifted to the higher
side in binding energy. By comparison, the Au 4f7/2 and Au 4f5/
2 peaks of PdAu are shifted obviously to the lower side in bind-
ing energy. This tendency indicates that the Au atoms gained
electrons from Pd atoms by alloying interaction. Based on the
charge compensation concept, Pd atoms in PdAu may have
electronic poor states which may play a crucial role in the acti-
vation of CÀCl bonds or the enhancement of reaction pathway
of cross-coupling, leading to the high activity.
Chem. Asian J. 2016, 11, 351 – 355
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