Xu et al. Sci China Chem April (2016) Vol.59 No.4
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that phenylacetylene and ammonium can produce oxidation
reactions with the use of metal complexes of manganese as
catalysts and hydrogen peroxide as an oxidant, with amide
yields of up to 80%. One great step for amide synthesis is
that Gunanathan et al. [10] achieved pretty high yields using
equal amounts of alcohol and amine catalyzed by ruthenium
complexes with two dehydrogenation steps (Scheme 1(b)).
Other metals, Au [11], Cu [12], and Fe [13], all played an
important role in the field of amide synthesis.
Although the above improved methods overcame aspects
of drawbacks, such as cost, pollution, toxicity and atom
efficiency, the amidation step restricts the starting materials
as benzylamines and secondary cyclic amines, which ob-
sessed lower or even no yields when it referred to phenyl-
amines. Despite the relatively high temperature and narrow
substrate extension, Shang et al. [14] and Deng et al. [15]
(Scheme 1(c)) developed two different nonmetallic pro-
cesses with phenylamines occasionally. Likewise, we also
hope to find an efficient approach for different amide prep-
aration. Herein, we report a new amide synthesis method
directly from various aldehydes and amines in a one-pot
reaction with platinum nanowires (Pt NWs, Figure S1,
Supporting Information online, no Fe exists according to the
ICP analysis) as catalysts. In this method, pyridine and alu-
minium chloride were used as co-catalysts and the oxidant,
tert-butylhydroperoxide (TBHP), was the only source of
oxygen (Scheme 1(d)). The method not only extended the
scope for substrates of amines and aldehydes but also re-
sulted in yields up to 90%.
at this temperature for half an hour without stirring. The
black solution was then cooled to room temperature and
centrifuged in excess ethanol. The precipitate was redis-
persed in methanol and washed by ethanol for three times.
FePt NWs (100 mg, in 20 mL methanol) were firstly
treated by oxygen bubbling at 100 °C, and HCl/methanol
(1:1, 10 mL) solution was added into the above suspension.
The solution was heated and stirred at 60 °C for 1 h, and the
resultant precipitates were obtained following 10 minutes of
centrifugation (3000 r/min). The dark solid was washed
with methanol for at least two times and stored in methanol.
2.3 General procedure for the Pt nanowires catalyzed
amides formation of aldehydes with amines
To a 25 mL screw-capped vial, Pt nanowires dispersed in
methanol (500 μL, 0.01 mol/L) were added. The solvent
was removed under reduced pressure. Then, a spinvane
Teflon stirbar, aldehyde (1.1 mmol), amine (1.0 mmol),
pyridine (1.0 mmol) and AlCl3 (0.25 mmol) were added in
toluene (2.0 mL) stepwise. The mixture was sealed with a
Teflon-lined cap and stirred at 100 °C for 18 h (monitored
by GC). The mixture was purified by flash silica gel column
chromatography to give amide. The characterizations of
amides are listed in the Supporting Information online.
3 Results and discussion
Initially, we selected the model reaction between aniline
and benzaldehyde with TBHP as the oxidant under the
co-catalysts pyridine and aluminium chloride to examine
platinum-based catalysts. Pt NWs showed excellent catalyt-
ic efficiency, but platinum nanoparticles (Pt NPs) and plat-
inum nanorods (Pt NRs) possessed lower catalytic activity
in the synthesis of amides (Table S1, Supporting Infor-
mation online). Pyridine and aluminium chloride, as
co-catalysts, played an important role in the amidation reac-
tion (Table S2). Without the pyridine or aluminium chlo-
ride, less than 20% of the target product was obtained.
After the catalyst and co-catalysts were determined, we
tested five commonly used solvents to optimize the reaction
conditions (Table 1, entries 1–5). In toluene, the phenyl-
benzamide had the greatest yield at 92%. Using the strongly
polar solvents CH3OH and CHCl3, no target product was
detected and most of the substrate was converted to
N-benzylidene-benzeneamine. In 1,4-dioxane and dimethyl
sulfoxide (DMSO), only 17% and 26% yields, respectively,
were obtained for the target product. The reaction tempera-
ture was also investigated with toluene as solvent and
Pt NWs as catalysts with the presence of pyridine and alu-
minium chloride. The results showed good yields at 100 °C,
along with a sharp decrease as the temperature dropped (en-
tries 5–7). Other oxidants, such as O2 and H2O2, were also
evaluated. But no target product was detected. Consequently,
2 Experimental
2.1 General experimental section
All reagents were used as received from commercial
sources, unless otherwise specified or prepared as described
in the literature. All reagents were weighed and handled in
air. Flash column chromatography was performed over
silica-gel powder 200–300 mesh (75–48 m).
1H and 13C NMR spectra were respectively recorded at
400 and 100 MHz. Chemical shifts () were expressed in
parts per million.
2.2 General procedure for preparation of Pt nanowires
catalyst
Pt NWs were achieved by acidic etching of FePt NWs,
which was synthesized according to the procedure described
by Sun et al. [16] and Gu et al. [17]. Pt(acac)2 (200 mg) and
oleylamine (20 mL) were mixed at room temperature under
nitrogen atmosphere and heated to 120 °C under stirring,
which was then maintained at 120 °C for 20 min. Fe(CO)5
(150 µL) was injected into the hot solution and the temper-
ature was raised to 160 °C gradually. The reaction was kept
Xu, Dawei
