Z-P. Han, Y. Li / Inorganic Chemistry Communications 22 (2012) 73–76
75
Table 1
Appendix A. Supplementary material
Conversion yields for the ketalization of 2-butanone.
a
CCDC 767584 contains the supplementary crystallographic data for
complex 1. The data can be obtained free of charge from The Cambridge
request/cif. Supplementary data associated with this article can
2012.05.023.
Time (h)
T (°C)
Conv.(%)
24
24
90
110
47
97
a
Conversion yields were detreminde by 1H NMR.
In order to confirm the valence-states of Cu atoms in 1, bond
valence sum (BVS) calculations [19] were performed for each Cu ion;
indeed, the BVS calculations for Cu1 (Cu1=1.82) agreed with the 2+
valence state, whereas those for Cu2, Cu2A, Cu3 and Cu3A (Cu2=
Cu2A=1.08; Cu3=Cu3A=1.00) confirmed the 1+ valence state.
The X-ray crystal structure analysis of 1 also reveals that two pla-
nar triangular copper units coupled via two Cu–Cu interactions (Cu2–
Cu3 and Cu2A–Cu3A). Compared to the metal–metal distances in the
open-shell metallic copper (2.556 Å) as well as to the estimated
sum of van der Waals radii (Cu–Cu) 2.80 Å, the presently documented
Cu–Cu distance is closer to the upper van der Waals limit. The ques-
tion of a cuprophilicity of CuI is still a matter of controversy [20].
However, there are scarce examples of ligand-unsupported CuI–CuI
interactions [21].
The hydrogen bonds between the coordinated water molecules
and deprotonated hydroxyl oxygen atoms have not affected the ge-
ometry of the mtpo− ligands. The chains are linked by the above-
mentioned hydrogen bonds to form a 2-D structure (Fig. 1b).
To estimate the stability of complex 1, its thermal behavior was
studied by TGA. The TGA curve of 1 (Fig. S4) shows a weight loss of
3.6% from 100 to 190 °C, which corresponds to the removal of the
two coordinated water molecules (theoretical value is 3.5%). The sec-
ond weight loss of 3.3% from 190 to 281 °C is observed, which is pos-
sibly due to the loss of one Cl− ion (calculated value is 3.4%). The
third weight loss occurs (57.5%) from 281 to 685.8 °C, which may be
ascribed to the removal of the four mtpo− ligands.
As the CuI ion of 1 is coordinatively unsaturated, it may exhibit
Lewis acid catalytic properties. We then found 1 is catalytically active
in heterogeneous ketal formation. Ketalization is an important meth-
od to protect carbonyl groups in organic synthesis and drug design
[22,23]. The reaction requires a Lewis acid catalyst to activate the ox-
ygen of the carbonyl group, allowing glycol to substitute the ketone
group. The experiment was performed with 2-butanone and ethylene
glycol in toluene and catalyst loading is 0.1% mmol (Scheme 2). Our
results are summarized in Table 1. As shown in Table 1, when the re-
action was performed at 90 °C, the product 2-ethyl-2-methyl-1,3-
dioxolane was obtained in 47% yield (Fig. S5). As the temperature is
increased to 110 °C, 97% yield (Fig. S6) of the product was resulted,
which indicates the ketone could be completely protected under the
relatively mild condition. Complex 1 is insoluble in common organic
solvent, indicating the heterogeneous nature of the catalysis.
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Acknowledgements
The authors appreciate the financial supports of Hundreds of Talents
Program (2005012) of CAS, Natural Science Foundation of China
(20872105), “Qinglan Project” of Jiangsu Province (Bu109805), A Pro-
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Higher Education Institution, and the Scientific Research Project of the
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