Organometallics
Article
A couple of observations remain without rationalization. One
is the negative effect of acidity on the quinaldine formation in
the presence of 1 equiv of PPh3. Since acidity has no negative
effect on the hydroamination cycle40 and should have a positive
effect on the catalyst regeneration step (G to A in Scheme 7) in
the heterocyclization cycle, it is conceivable that it will
negatively affect the follow up process leading from the
enamine and imine intermediates 5 and 6 to quinaldine
(Scheme 3). Note that the formation of the quinaldine
byproduct during the hydroamination catalytic run in the
presence of TfOH and absence of PPh3 (run 7 in Table 1) was
not reported, hinting to a negative effect of acidity
independently on the PPh3 presence. It is also not clear at
this point whether the heterocyclization process from 5 and 6 is
metal catalyzed or not. Another obscure feature is the pathway
to catalyst deactivation when PPh3 is present, which does not
involve reduction to Pt0. The isolation and characterization of
the spent catalyst, to be attempted in future investigations, will
hopefully clarify this point.
AUTHOR INFORMATION
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Corresponding Author
*Tel: +33-561333173. Fax: +33-561553003. E-mail: rinaldo.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We are grateful to the Centre National de la Recherche
Scientifique (CNRS), the Institut Universitaire de France
(IUF), and the Agence Nationale de la Recherche (ANR, Grant
“HYDROAM” No. NT09_442499) for financial support.
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CONCLUSION
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We have reported here the peculiar effect of the addition of
PPh3 (1 P/Pt) to the Brunet catalyst in terms of the selectivity
for the reaction between aniline and ethylene, in favor of the
formation of quinaldine. Optimization of the reaction has
shown that, contrary to the hydroamination process, the
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have a positive effect on the catalytic activity. The optimum
amount and type of the phosphine ligand is 1 equiv of PPh3, the
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ASSOCIATED CONTENT
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(28) Arisawa, M.; Theeraladanon, C.; Nishida, A.; Nakagawa, M.
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S
* Supporting Information
Supporting figures. This material is available free of charge via
(29) Theeraladanon, C.; Arisawa, M.; Nishida, A.; Nakagawa, M.
Tetrahedron 2004, 60, 3017−3035.
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dx.doi.org/10.1021/om400020k | Organometallics 2013, 32, 1882−1891