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Notes and references
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Overall, the Pd1Ag1.70 catalyst has excellent functional group
compatibility and the reaction provides rapid access to an array
of secondary amines.
Importantly, leaching of soluble Pd or Ag from the Pd1Ag1.70
catalyst into the reaction filtrate was not detected by ICP-AES.
TEM studies showed that the spent catalyst had no observable
structural change relative to the fresh catalysts. The catalyst
could be recovered by centrifugation and reused at least 6 times
without decay in activity and selectivity, consistent with its
stability mentioned above (ESI†).
Evidence from control experiments (ESI†) led us to postulate
the reaction mechanism as shown in Scheme 1. The selective
formation of the secondary amine could be understood by
invoking a dynamic selection, where the favored hydrogenation
of nitrobenzene and rapid imine formation helped catalyst
turnover and minimized benzyl alcohol formation. Studies to
uncover the underlying reason for favored nitrobezene hydro-
genation are being actively carried out in our laboratories.
In conclusion, we successfully identified a general, selective
and recyclable bimetallic Pd1Ag1.70 nanocatalyst for the reduc-
tive amination between aldehydes and nitroarenes. The clear
composition–activity/selectivity relationship observed in this
study helped us to design and identify the optimal catalyst,
underscoring the possibility of ‘‘rational’’ heterogeneous
catalyst design. We envision that such an approach could be
extended to the development of novel heterogeneous catalysts
for other important transformations given increasing under-
standing and control of nanoparticle catalysis.37,38
This work was supported by the state key project of Funda-
mental Research for Nanoscience and Nanotechnology
(2011CB93240 and 2011CBA00500), the National Natural
Science Foundation of China (grant no. 20921001 and
21131004), and W.H. gratefully acknowledges financial support
from the Tsinghua–Peking University Joint Centers for Life
Sciences and the National Key Basic Research Program of China
(2012CB224802).
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c
This journal is The Royal Society of Chemistry 2013
Chem. Commun.