Communication
Green Chemistry
recovered palladium catalyst in different types of downstream
reactions (Fig. 1). This has been the first systematic investi-
gation focused on the multi-task and comprehensive utiliz-
ation of limited and recovered transition metal catalyst, which
provide a novel and environmental benign strategy for the
reuse of deactivated catalyst. Especially, it was shown that all
the model transformations with palladium as the catalyst,
from simple PdCl2 to the recovered palladium residue, were
carried out successfully under exceptionally mild conditions.
On top of the advantages of multi-task and maximum reutili-
zation of expensive palladium catalysts, the corresponding new
palladium catalyst systems in related reactions provide the fol-
lowing merits: (i) a simple and high-yield method for the deoxy-
genated reduction of aromatic ketones or benzylic alcohols
with the solid, reactive, and functional hydrosilane (Si–H)-con-
taining material; (ii) a ligand-free and simple Suzuki process
for the synthesis of diaryls; (iii) a copper-free and ligand-free
Sonogashira coupling of aryl halides and terminal alkynes;
(iv) the first example of chlorobenzene serving as an activating
additive in Pd-mediated cross-coupling reactions; and (v) an
efficient Knoevenagel condensation and Knoevenagel-like or
trans-condensation were demonstrated with the reused palla-
dium residue. In addition, all these reactions could be carried
out in environmentally friendly ethanol. More importantly, we
have developed various procedures for the preparation of
alkanes, diaryls, aryl alkynes, and α,β-unsaturated carbonyl
compounds respectively under mild conditions with a single
palladium catalyst. In view of the established utility of the
recovered palladium in various downstream reactions, we
anticipate that this concept of multi-task and maximum reuse
catalysis (MTMRC) of expensive metal catalyst as well as
related catalysts and reactions will find wide application and
offer the possibility for the development of synthetic appli-
cations of waste or deactivated transition metal catalysts for
organic transformations.
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The authors gratefully thank the financial support of the
National Natural Science Foundation of China (NSFC, no.
51203037 and 21173064), Zhejiang Provincial Natural Science
Foundation of China (Q12B020037), and Program for Excellent
Young Teachers in Hangzhou Normal University (HNUEYT,
JTAS 2011-01-014).
7 The
PMHS-based
semi-interpenetrating
network
(PMHSIPN) is a novel organosilicon material and the
research work about the synthesis of PMHSIPN will be
reported elsewhere in the future.
8 (a) R. J. Rahaim and R. E. Maleczka, Org. Lett., 2011, 13,
584–587; (b) H. Wang, L. Li, X. F. Bai, J. Y. Shang,
K. F. Yang and L. W. Xu, Adv. Synth. Catal., 2013, 355,
341–347.
9 (a) The isolated yields given in this scheme are the average
value of three runs, and the yields of the reduction reaction
with ketones provided in Scheme 1 are the same as those
of alcohols. There is no difference between the two types
of substrates (b) The amount of palladium in the silicone-
based IPN material before and after the reaction was
determined by graphite furnace atomic absorption spec-
trometry. It was found that there are no obvious differences
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Green Chem.
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