10.1002/adsc.201701522
Advanced Synthesis & Catalysis
Experimental Section
During the deaminative homocoupling reaction of
the primary amine to a secondary amine, the
formation of ammonia was ascertained by FT-IR
analysis (Figure 1a). Interestingly, the liberation of
molecular hydrogen was also observed and confirmed
by gas chromatography (Figure 1b); this hydrogen
may participate in the other reactions. In the
dehydrogenation of benzylamine molecular hydrogen
was also liberated but ammonia formation was not
observed (Figure 1c).
Reactions were performed in a 30 mL stainless
steel autoclave equipped with a stirring bar and the
followings were place in the autoclave in the order:
amine (0.75 mmol), toluene (5 mL) and 5 mol%~7.5
mol% Co2Rh2 (45 mg ~ 67.5 mg of the immobilized
Co2Rh2/C). The reactor was purged with Ar gas, and
o
charged with 1 atm of Ar and heated at 180 C for 18
h. After the reactor was cooled to room temperature,
the solution was filtered and concentrated, and the
product was isolated by chromatography on a silica
gel column eluting with hexane and ethyl acetate.
Experimental evidence indicates that the proposed
Co2Rh2/C-catalyzed deaminative homocoupling of
primary amines to secondary and tertiary amines may
proceed through a number of sequential reactions
(Figure 2). In cycle 1, firstly, a primary amine
undergoes dehydrogenation to form an imine with the
concomitant and transitory formation of H2 or a
metal-hydride species. When R was a phenyl group,
the benzonitrile was formed due to the consecutive
dehydrogenation of the imine intermediate. The imine
readily reacts with the starting primary amine to
generate the corresponding N-alkylimine and NH3.
Finally, the hydrogenation of the N-alkylimine or
hydrogen transfer from the hydride to the N-
alkylimine proceeds to afford the desired secondary
amine. Under the optimal conditions for synthesis of
secondary amines, the catalytic cycle 1 ends with the
formation of the secondary amine. However, under
the optimal conditions for synthesis of tertiary amines,
cycles 1 and 2 operate. The secondary amine formed
in cycle 1 undergoes similar sequential processes to
generate a tertiary amines and the primary amine.
Acknowledgements
This work was supported by a National Research Foundation of
Korea (NRF) grant funded by the Korean government
(2014R1A5A1011165 and 2007-0093864). HHC is a recipient of
BK21 plus Fellowship.
References
[1] a) B. Li, J.-B. Sortais and C. Darcel, RSC Adv., 2016, 6,
57603; b) L. Huang, M. Arndt, K. Gooen, H. Heydt
and L. J. Gooen, Chem. Rev. 2015, 115, 2596; c) F.
Monnier and M. Taillefer, Angew. Chem., Int. Ed. 2009,
48, 6954; d) D. S. Surry and S. L. Buchwald, Angew.
Chem., Int. Ed. 2008, 47, 6338; e) G. Evano, N.
Blanchard and M. Toumi, Chem. Rev. 2008, 108, 3054;
f) T. E. Müller and M. Beller, Chem. Rev. 1998, 98,
675.
[2] a) W. Wen, Y. Zeng, L.-Y. Peng, L.-N. Fu and Q.-X.
Guo, Org. Lett. 2015, 17, 3922; b) O. S. Nayal, V.
Bhatt, S. Sharma and N. Kumar, J. Org. Chem. 2015,
80, 5912; c) I. Sorribes, K. Jung and M. Beller, J. Am.
Chem. Soc. 2014, 136, 14314; d) P. Ghorai, Chem.
Commun. 2012, 48, 8276; e) E. M. Dangerfield, C. H.
Plunkett, A. L. Win-Mason, B. L. Stocker and M. S. M.
Timmer, J. Org. Chem. 2010, 75, 5470.
[3] a) J. J. A. Celaje, X. Zhang, F. Zhang, L. Kam, J. R.
Herron, T. J. Williams, ACS Catal. 2017, 7, 1136; b) H.
Liu, D.-L. Wang, X. Chen, Y. Lu, X.-L. Zhao and Y.
Liu, Green Chem. 2017, 19, 1109; c) S. Elangovan, J.
Neumann, J.-B. Sortais, K. Junge, C. Darcel and M.
Beller, Nature Commun. 2016, 7, 12641; d) M.C. Fu, R.
Shang, W.-M. Cheng and Y. Fu, Angew. Chem., Int. Ed.
2015, 54, 9042; e) F. Monnier and M. Taillefer, Angew.
Chem. Int. Ed. 2009, 48, 6954; f) M. Carril, R.
SanMartin and E. Domínguez, Chem. Soc. Rev. 2008,
37, 639.
Figure 2. Proposed catalytic cycle
In conclusion, we have demonstrated that
Co2Rh2/C can be effectively and selectively applied to
the deaminative homo- and heterocoupling of primary
and secondary amines to secondary- and tertiary
amines and N-alkylanilines without any additive, base,
or ligand. The reaction can be extended to long chain
alkylamines without any difficulty. The reaction is
easy to perform and the Co2Rh2/C can be easily
separated from the reaction mixture by filtration and
reused.
[4] a) S. Tobisch, Chem. Sci. 2017, 8, 4410; b) S. Ibanez,
M. Poyatos and E. Peris, Chem. Commun. 2017, 53,
3733; c) A. J. Musacchio, B. C. Lainhart, X. Zhang, S.
G. Naguib, T. C. Sherwood and R. R. Knowles, Science
2017, 355, 727; d) L. Ackermann, Angew. Chem. Int.
Ed. 2005, 44, 5972; e) P. Roesky, Angew. Chem., Int.
Ed. 2005, 44, 7794.
[5]a) M. Yamashita, Y. Moroe, T. Yano and K. Nozaki,
Inorg. Chim. Acta 2011, 369, 15; b) W. He, L. D. Wang,
5
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