10.1002/anie.201903841
Angewandte Chemie International Edition
COMMUNICATION
[10] Some patents have reported the synthesis of anilines from NH3 and
cyclohexanones, which is limited by the high reaction temperature,
limited substrate scope, and/or the low selectivity to products, for
examples, see: a) J. M. Solomon, B. R. Bluestein, U. S. Patent 3,553,268,
1971; b) N. Goetz, L. Hupfer, W. Hoffmann, M. Baumann, U. S. Patent
4,255,180, 1982; c) G. R. Wilder, J. E. Van Verth, U. S. Patent 3,219,704,
1965; d) F. Haese, J. Wulff-Doring, U. Kohler, P. Gaa, F.-F. Pape, J.-P.
Melder, M. Julius, U. S. Patent 2009/0076306 A1, 2009.
the best result in the transformation of 1a to 2a (Table S2). Needless to
say, the use of acidic supports is not suitable as NH3 is used in this
reaction. Previously, we have reported that Pd nanoparticle catalysts
prepared using basic supports effectively promoted the dehydrogenation
of cyclohexanones to phenols.[12e] Thus, the use of basic supports is also
not suitable for the present reaction. Therefore, we concluded that HAP,
which has very weak acid-base property, was the best support for the
present reaction.
[11] Previously, our group has reported that the reaction of NH3 (or its
surrogates, e.g., urea) and cyclohexanones using supported Pd catalysts
under relatively harsh conditions (≥150°C) affords symmetrically
substituted diarylamines with the release of H2. Thus, such harsh
conditions should be avoided for the selective synthesis of primary
anilines. For this report, see: Y. Koizumi, K. Taniguchi, X. Jin, K.
Yamaguchi, K. Nozaki, N. Mizuno, Chem. Commun. 2017, 53, 10827–
10830.
[16] The effect of Pd contents in Pd/HAP is discussed in the Supporting
Information.
[17] T. A. Nijhuis, F. M. Dautzenberg, J. A. Moulijin, Chem. Eng. Sci. 2003,
58, 1113–1124.
[18] The adsorption energies of styrene and an imine formed via the
condensation of 1a and 2a (6a) on Pd clusters were estimated by DFT
calculations using a Pd13 cluster model (Figure S5). In the Pd13 cluster
model, the adsorption energies for the (100) and (111) facets can be
estimated. The adsorption energies of styrene and imine 6a on the (100)
facet were calculated to be −46.8 and −43.6 kcal mol–1, respectively
(Figure S6). The adsorption energies of styrene and imine 6a on the
(111) facet were calculated to be −62.2 and −58.7 kcal mol–1, respectively
(Figure S6). By considering the adsorption to either facet, styrene
exhibited larger adsorption energies. These results were consistent with
those obtained by the competitive hydrogenation of styrene and 6ab. The
details of the computational study are described in the Supporting
Information.
[12] In addition to references
8 and 11, our group has reported the
heterogeneous Au–Pd- or Pd-catalyzed synthesis of phenols and aniline
derivatives via dehydrogenative aromatization. Please see: a) K.
Taniguchi, X. Jin, K. Yamaguchi, N. Mizuno, Chem. Commun. 2015, 51,
14969–14972; b) K. Taniguchi, X. Jin, K. Yamaguchi, N. Mizuno, Catal.
Sci. Technol. 2016, 6, 3929–3937; c) X. Jin, K. Taniguchi, K. Yamaguchi,
N. Mizuno, Chem. Sci. 2016, 7, 5371–5383; d) K. Taniguchi, X. Jin, K.
Yamaguchi, K. Nozaki, N. Mizuno, Chem. Sci. 2017, 8, 2131–2142; e) X.
Jin, K. Taniguchi, K. Yamaguchi, K. Nozaki, N. Mizuno, Chem. Commun.
2017, 53, 5267–5270.
[19] R. A. Sheldon, M. Wallau, I. W. C. E. Arends, U. Schuchardt, Acc. Chem.
Res. 1998, 31, 485–493.
[13] Li et al. have reported the synthesis of N-cyclohexylanilines from NH3
and diaryl ethers by the in situ hydrogenolysis of diaryl ether to
cyclohexanones. In this article, N-cyclohexylidene-aniline intermediates
are considered to be hydrogenated to the corresponding N-
cyclohexylanilines, see: D. Cao, H. Zeng, C.-J. Li, ACS Catal. 2018, 8,
8873–8878.
[20] From several pieces of experimental evidence, we concluded that the
observed catalysis is determined to be heterogeneous. However, one of
the reviewers pointed out that the possibility of fine Pd clusters leached
out of Pd/HAP being truly active species can not be completely denied.
In response to this point, we plan to conduct some additional experiments
(e.g., three-phase test) and draw a firm conclusion.
[14] I. Chorkendorff, J. W. Niemantsverdriet, Concepts of Modern Catalysis
and Kinetics, Wiley-VCH, Weinheim, 2003, pp. 23–78.
[21] a) J. Choi, H. Park, H. J. Yoo, S. Kim, E. J. Sorensen, C. Lee, J. Am.
Chem. Soc. 2014, 136, 9918–9921; b) S. Wang, Y. Otani, X. Liu, M.
Kawahata, K. Yamaguchi, T. Ohwada, J. Org. Chem. 2014, 79, 5287–
5300.
[15] In this study, we prepared four kinds of supported Pd nanoparticle
catalysts, such as Pd/HAP, Pd/Al2O3, Pd/TiO2, and Pd/LDH. As can be
seen from Figure S2, their average Pd nanoparticle sizes and
dispersions were almost the same. Among these catalysts, Pd/HAP gave
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