DOI: 10.1002/cctc.201500300
Communications
Facet-Dependent Catalytic Activity of Palladium
Nanocrystals in Tsuji–Trost Allylic Amination Reactions
with Product Selectivity
Kaushik Chanda, Sourav Rej, Shu-Ya Liu, and Michael H. Huang*[a]
Pd nanocubes, cuboctahedra, and octahedra with good size
control were used to catalyze CÀN bond formation in the
Tsuji–Trost allylic amination reaction of aniline. Nanocubes
gave either monoallylaniline or diallylaniline depending on the
amount of allyl bromide used, but the octahedra and cubocta-
hedra only gave mixtures of monoallylaniline and diallylaniline
under the same reaction conditions. The Pd nanocubes were
stable over multiple cycles of the reaction. The cubes and octa-
hedra were demonstrated to catalyze the amination reaction
by using a wide variety of substituted anilines, but the cubes
were the best catalyst with consistently the highest efficiency,
product yield, and product selectivity. This work demonstrates
that the use of metal nanocrystals with proper facet control is
important for catalyzing coupling reactions with product selec-
tivity.
tuted amines or alcohols with allyl groups and has broad appli-
cations in the synthesis of natural products and biologically
active molecules.[22–24] Essentially, only Pd complexes have
been used to catalyze these reactions. In two reports, Pd nano-
particles were found to catalyze the allylic amination and ally-
lation of active methylene compounds, but the nanoparticles
were not well characterized.[25,26] It would be interesting to ex-
amine facet-dependent catalytic activity of polyhedral Pd
nanocrystals for Tsuji–Trost allylic amination reactions.[27] Previ-
ously, strongly facet-dependent catalytic activities were ob-
served in polyhedral Au and Cu2O nanocrystals.[28–31] In this
study, uniform Pd nanocubes, cuboctahedra, and octahedra
synthesized in aqueous solution were employed to catalyze
the Tsuji–Trost allylic amination reaction between allyl bromide
and aniline. Strongly facet-dependent catalytic activity was ob-
served. Remarkably, the particle facet can affect product selec-
tivity. A possible explanation for this product selectivity is
given. Diverse products were synthesized from various aromat-
ic amines by using these Pd nanocrystal catalysts.
Palladium nanostructures have been shown to efficiently cata-
lyze organic coupling reactions such as the Suzuki and Sono-
gashira reactions.[1–3] They are also active in catalyzing hydro-
genation and formic acid oxidation reactions.[4–14] Facet-depen-
dent catalytic activity is a highly interesting but rarely explored
direction of Pd nanocrystal research. To investigate facet-de-
pendent catalytic activity, Pd nanoparticles with specific sur-
face facets exposed, such as cubes and octahedra, are
needed.[15–19] Pd nanocrystals synthesized by using similar reac-
tion conditions are most suitable for facet-dependent property
studies.[20,21] Beyond reactions involving CÀC bond formation, it
would be interesting to examine the facet-dependent catalytic
activities of Pd nanocrystals toward new coupling reactions
such as the formation of CÀN bonds.[15]
We developed a method to directly grow Pd nanocrystals
with cubic, cuboctahedral, and octahedral shapes by mixing an
aqueous solution of H2PdCl4, cetyltrimethylammonium chloride
(CTAC), KBr, KI, and ascorbic acid at 358C for 30 min. Table S1
(Supporting Information) provides the exact reagent amounts
used to make the Pd nanocrystals. The particles were thor-
oughly washed to remove the CTAC surfactant. Figure 1 shows
representative SEM images of the synthesized Pd cubes, cu-
boctahedra, and octahedra with average edge lengths of 49,
62, and 50 nm, respectively. Good particle shape control was
achieved. The size-distribution histograms of the particles are
provided in Figure S1.
The Tsuji–Trost reaction is a Pd-catalyzed substitution reac-
tion of a nucleophile with a substrate containing a leaving
group in an allylic position under basic conditions. It has been
proven to be a powerful method for the generation of substi-
We considered the use of these Pd nanocrystals to catalyze
Tsuji–Trost allylic amination reactions, because such CÀN bond-
forming reactions are quite useful but are rarely explored with
the use of Pd particles. Initially, an aqueous Pd nanocube solu-
tion (527 mL) was added to a mixture of allyl bromide
(1.25 mmol, 3 equiv.) and aniline (0.42 mmol, 1 equiv.) in the
presence of K2CO3 (0.83 mmol) as the base to synthesize N-al-
lylbenzenamine (3a) in water at 658C (Table 1, entry 1). After
1.5 h, the crude mixture was purified, and it indicated the for-
mation of only N,N-diallylbenzenamine (4a) with a product
yield of 100% and the absence of any other byproducts, as
shown by TLC. The diagnostic resonance for the N-CH2-CH
proton in the 1H NMR spectrum of product 4a appears as
a multiplet at d=5.84 ppm. Similarly, the resonance for the N-
CH2-CH carbon atom in the 13C NMR spectrum of 4a appears
at d=52.7 ppm. Upon repeating the same reaction with
[a] Prof. K. Chanda,+ S. Rej, S.-Y. Liu, Prof. M. H. Huang
Department of Chemistry and Frontier Research Center
on Fundamental and Applied Science of Matter
National Tsing Hua University
Hsinchu 30013 (Taiwan)
[+] Present address:
Organic Chemistry Division
School of Advanced Science
VIT University
Vellore-632014 (India)
Supporting Information for this article is available on the WWW under
ChemCatChem 2015, 7, 1813 – 1817
1813
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim