Article pubs.acs.org/JACS
Electronic Effect of Ruthenium Nanoparticles on Efficient Reductive Amination of Carbonyl Compounds Tasuku Komanoya,† Takashi Kinemura,† Yusuke Kita,† Keigo Kamata,† and Michikazu Hara*,†,‡ †
Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503, Japan ‡ Advanced Low Carbon Technology Research and Development Program (ALCA), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi 332-0012, Japan S Supporting Information *
ABSTRACT: Highly selective synthesis of primary amines over heterogeneous catalysts is still a challenge for the chemical industry. Ruthenium nanoparticles supported on Nb2O5 act as a highly selective and reusable heterogeneous catalyst for the low-temperature reductive amination of various carbonyl compounds that contain reduction-sensitive functional groups such as heterocycles and halogens with NH3 and H2 and prevent the formation of secondary amines and undesired hydrogenated byproducts. The selective catalysis of these materials is likely attributable to the weak electron-donating capability of Ru particles on the Nb2O5 surface. The combination of this catalyst and homogeneous Ru systems was used to synthesize 2,5-bis(aminomethyl)furan, a monomer for aramid production, from 5-(hydroxymethyl)furfural without a complex mixture of imine byproducts.
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strongly depending on the size of the metal particles.11 However, even for metal particles of the same size, the support can have a strong effect on the catalytic performance for ammonia synthesis, the water−gas shift reaction, hydrogenation, and oxidation.12 In these cases, electronic metal− support interactions have been evidenced through a combination of experiments and theory. Therefore, control of the electronic effects between metal nanoparticles and support materials may lead to further efficient heterogeneous catalysts for the reductive amination of carbonyl compounds. In this paper, we report that weak electron-donating Ru on Nb2O5 surfaces catalyzes the highly selective reductive amination of various aromatic carbonyl compounds that contain reductionsensitive functional groups such as heterocycles and halogens.
INTRODUCTION Primary amines are important and versatile building blocks in organic synthesis because they are widely utilized as intermediates for the production of polymers, drugs, dyes, and detergents.1 Catalytic reductive amination of carbonyl compounds with ammonia (NH3) and dihydrogen (H2) as a nitrogen source and reductant, respectively, has received much attention as a selective synthetic route to primary amines which replaces synthetic processes with low atomic efficiency that use specific nitrogen sources and/or stoichiometric reductants.2−4 To date, several enzymes,5 homogeneous,6 and heterogeneous catalysts7 have been reported for the reductive amination of carbonyl compounds with NH3 and H2. From the many advantages of heterogeneous catalysts, such as ease of recovery, reusability, and stability,8 various systems based on zeolites,7f Ni,7a,l Cu,7e Pd,7b Ru,7c,d,i,k Rh,7d,j and Pt7g,h catalysts have been developed (Tables S1 and S2). However, the selective production of primary amines has been limited to the reductive amination of simple aryl and alkyl aldehydes (e.g., benzaldehyde) due to the formation of secondary and tertiary amines and/or undesired further hydrogenation of carbonyl groups and other substituents. In particular, the selective reductive amination of carbonyl compounds containing reductionsensitive functional groups such as heterocycles and halogens is commonly difficult.9,10 With this context, the development of effective heterogeneous catalysts to quantitatively produce various types of primary amines from carbonyl compounds with NH3 and H2 is an attractive, yet challenging goal. It has been well known that the catalytic performance of many metal-supported catalysts is influenced by the support materials and that the intrinsic activity and selectivity can vary © 2017 American Chemical Society
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RESULTS AND DISCUSSION Effect of Catalyst on Reductive Amination of Furfural. The supported metal catalysts (denoted as M/support; M = Ru, Rh, Pd, Ni, Cu, Ag, and Pt; support = Nb2O5, SiO2, TiO2, C, Al2O3, ZrO2, and MgO) were prepared by the following procedures: The aqueous solution containing metal source and support was evaporated to dryness and the resulting powder was dried and pretreated under H2/Ar flow at 673 K prior to use (see the Supporting Information). Morphological information, including electron microscopy, Ru particle size and dispersion are shown in Figures 1 and S1, and Table 1.13−16 The reductive amination of furfural (1a) to furfurylamine (2a) with a methanol solution of ammonia (8 mmol) over various Received: May 2, 2017 Published: July 31, 2017 11493
DOI: 10.1021/jacs.7b04481 J. Am. Chem. Soc. 2017, 139, 11493−11499
Article
Journal of the American Chemical Society
Table 2. Reductive Amination of 1a over Supported Metal Catalystsa yield (%)
Figure 1. SEM images of (a) Nb2O5 and (b) Ru/Nb2O5. (c) HAADF−STEM image of Ru/SiO2 and (d) particle size distribution.
catalyst
specific surface area (m2 g−1)
1 2 3 4 5 6
Ru/MgO Ru/Al2O3 Ru/SiO2 Ru/TiO2 Ru/ZrO2 Ru/Nb2O5
30 162 260 102 73 112
2a
othersd
1 2b 3 4 5 6 7 8 9 10 11 12 13 14 15c 16 17
Ru/Nb2O5 Ru/Nb2O5 Ru/SiO2 Ru/TiO2 Ru/C Ru/Al2O3 Ru/ZrO2 Ru/MgO Rh/Nb2O5 Pd/Nb2O5 Ni/Nb2O5 Cu/Nb2O5 Ag/Nb2O5 Pt/Nb2O5 Ru-PVP Nb2O5 −
89 99 84 72 31
