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Dalton Transactions
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9
solution. One reason is that the strong coordinating ability of
THF disturbs or displaces agostic interactions to occupy an
active site of the catalyst. Another reason may be competition
between THF and substrate to interact with Cu, decelerating the
rate of formation of the copper carbene intermediate.
Considering that THF has been shown to displace an agostic
interaction in a Ti complex,14 it is believed that the first reason
may be the more important but both factors cannot be ruled out
as potential influences on the reaction process.
A set of analogous reactions was performed using Ph2NH in
place of PhNH2, and similar results were obtained (see entries
11 to 18 in Table 1), implying that the substitution of hydrogen
by the bulkier phenyl group has no significant influence on the
reaction.
10 T. Ziegler, Can. J. Chem., 1995, 73, 743.
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22 M. K. Yadav, G. Rajput, L. B. Prasad, M. G. B. Drew and
N. Singh, New. J. Chem., 2015, 39, 5493.
Conclusions
In conclusion, we report the design and syntheses of novel Cu(I)
complexes with interesting catalytic properties due to the
inherent structural feature of an intramolecular C–H∙∙∙Cu
interaction. These compounds are synthesized by reaction of a
Cu(I) precursor with the [BBN(pz*)2]– ligand. All the Cu(I)
complexes have been structurally characterized and possess
agostic or anagostic C–H∙∙∙Cu interactions. Their catalytic
behaviors toward carbenoid insertion into N‒H bonds are
examined, demonstrating that the C–H∙∙∙Cu interaction acts as a
“switch”, with the “off” state featuring an agostic interaction
and the “on” state featuring the binding of the substrate to the
Cu(I) center. It is found that steric effects and the coordinating
ability of the chosen solvent both influence the catalytic ability
of the Cu(I) complexes: higher yields are observed for less
sterically crowded catalysts in non-coordinating benzene while
relatively low yields are observed for more sterically crowded
catalysts in coordinating THF.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21371051, 21501048 and 21571052). We
are also grateful for the financial support from Henan Province
(14B150032).
36 C. J. Moody, Angew. Chem. Int. Ed., 2007, 46, 9148.
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