Dalton Transactions
Paper
As described above, the catalytic reactions were carried out in an
aqueous media. Since both Cu complexes contain bulky hydro-
Notes and references
II
phobic organic peripheral groups, it is unlikely that they are
soluble in the solution, Therefore, it is possible that the catalytic
reactions by (R)-1 and (S,R)-2 took place under heterogeneous
conditions and this precludes a detailed mechanistic study. The
design of new copper cluster complexes that can homogeneously
catalyse aerobic alcohol oxidations will be necessary to reveal
1 I. W. C. A. Arends and R. A. Sheldon, in Modern Oxidation
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II
mechanistic details, and further catalytic studies on related Cu
cluster compounds are highly desirable in order to reveal the
structure-catalytic activity relationship between the metal cata-
lysts with various nuclearities.
4 R. A. Sheldon, I. W. C. E. Arends, G.-J. T. Brink and
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Conclusions
In conclusion, we have synthesized two chiral copper(II)-based
Schiff base complexes, (R)-1 and (S,R)-2, respectively, through
one-pot self-assembly reactions. Upon reacting the optically
pure (R)-2-aminoglycinol, 3,5-di-tert-butyl-2-hydroxybenzalde-
hyde with copper(II) acetate in the presence of triethylamine,
complex (R)-1 has been isolated as single crystals. The crystal
structure confirms that (R)-1 is a chiral tetranuclear tetra-
ligand complex containing a Cu (μ-O) (μ -O) N O core that is
surrounded by the Schiff base ligands formed in situ. In con-
trast, (S)-1 was also prepared by the same procedure using an
S-configuration amino alcohol starting material and the CD
spectra revealed the opposite chirality of the resulting copper(II)
complexes. (S,R)-2 was subsequently synthesized by using a
more bulky amino alcohol, (1S,2R)-2-amino-1,2-diphenyletha-
nol under the same reaction conditions, and the structural
analysis shows (S,R)-2 is a dinuclear bis-ligand complex with
8
9
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two μ-O bridging Cu centres. Both complexes have been
2
applied to the catalytic aerobic oxidation of benzylic alcohols
mediated by TEMPO. The results indicated that (R)-1 efficiently
catalysed the oxidation of benzyl alcohol in the air and in an
3
8 Z. Ma, L. Wei, E. C. B. A. Alegria, L. M. D. R. S. Martins,
2 3
aqueous K CO solution with TON up to 770, while relatively
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under the same conditions. Other substrates were also tested
in order to compare their different catalytic abilities. Although
it was insufficient to draw a conclusion on what made the
different reactivity of both Cu complexes for catalysis, based
on the present data obtained in this research, we have tenta-
tively attributed this to the nuclearities of both structures
2014, 43, 4048.
1
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focused on elucidating the structure-catalytic activity relation-
ship and the catalytic mechanism involving multiple metal
centres, and the possible applications of the chiral metal com-
plexes in asymmetric catalysis, in particular the kinetic resolu-
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Acknowledgements
We thank the Office for the Advancement of Research at CUNY
John Jay College for a Seed grant, and the Novartis Foundation, 26 N. E. Shepherd, H. Tanabe, Y. Xu, S. Matsunaga and
formerly Ciba-Geigy Jubilee Foundation for support.
M. Shibasaki, J. Am. Chem. Soc., 2010, 132, 3666.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12313–12320 | 12319