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Electronic Effect of Ruthenium Nanoparticles on Efficient Reduc-tive Amination of Carbonyl Compounds Tasuku Komanoya, Takashi Kinemura, Yusuke Kita, Keigo Kamata, and Michikazu Hara J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b04481 • Publication Date (Web): 31 Jul 2017 Downloaded from http://pubs.acs.org on July 31, 2017
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Journal of the American Chemical Society
Electronic Effect of Ruthenium Nanoparticles on Efficient Reductive Amination of Carbonyl Compounds Tasuku Komanoya,a Takashi Kinemura,a Yusuke Kita,a Keigo Kamata,a and Michikazu Hara*ab a
Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, Na‐ gatsuta‐cho 4259, Midori‐ku, Yokohama 226‐8503, Japan
b
Advanced Low Carbon Technology Research and Development Program (ALCA), Japan Science and Technology Agency (JST), 4‐1‐8 Honcho, Kawaguchi 332‐0012, Japan
ABSTRACT: Highly selective synthesis of primary amines over heterogeneous catalysts is still a challenge for the chemical industry. Ruthenium nanoparticles supported on Nb2O5 acts 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 prevents 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 com‐ plex mixture of imine byproducts.
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 car‐ bonyl 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 en‐ zymes,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, reus‐ ability, and stability,8 various systems based on zeolites,7f Ni‐,7a,7l Cu,7e Pd‐,7b Ru‐,7c,7d,7i,7k Rh‐,7d,7j and Pt‐7g,7h catalysts have been developed (Tables S1 and S2). However, the se‐ lective 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 con‐ taining reduction‐sensitive functional groups such as het‐ erocycles and halogens is commonly difficult.[9,10] With this context, the development of effective heterogeneous cata‐ lysts 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 sup‐ port materials and that the intrinsic activity and selectivity can vary strongly depending on the size of the metal parti‐ cles.11 However, even for metal particles of the same size, the support can have a strong effect on the catalytic per‐ formance for ammonia synthesis, the water‐gas shift reac‐ tion, hydrogenation, and oxidation.12 In these cases, elec‐ tronic metal–support interactions have been evidenced through a combination of experiments and theory. There‐ fore, control of the electronic effects between metal nano‐ particles and support materials may lead to further effi‐ cient 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 reduction‐sensitive functional groups such as heterocycles and halogens. 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 fol‐ lowing procedures: The aqueous solution containing metal source and support was evaporated to dryness and the re‐ sulting 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
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(8 mmol) over various supported metal catalysts was ex‐ amined under a H2 (4 MPa) atmosphere (Tables 2 and S3). This is a promising reaction for the production of versatile chemicals from sugars through furan aldehydes.17 Figure 2 shows possible pathways for the reaction of 1a in the pres‐ ence of NH3 and H2. According to the free energy diagram for these reactions calculated using density functional the‐ ory (DFT) (Table S4), formation of the primary amine 2a was determined to be more thermodynamically unfavora‐ ble than formation of the secondary amine and the unde‐ sired hydrogenated product, which indicates the difficulty in the highly selective synthesis of the primary amine. N‐ furfurylidenefurfurylamine (3a), 2,4,5‐tris(2‐furyl)imidaz‐ oline (4a), hydrogenated products (tetrahydrofurfuryla‐ mine (5a), furfuryl alcohol (6a) and difurfurylamine (7a)) are the main byproducts.
Figure 1. SEM images of (a) Nb2O5 and (b) Ru/Nb2O5. (c) HAADF–STEM image of Ru/SiO2 and (d) particle size distribution.
Table 1. Specific surface area and CO‐pulse titration re‐ sults of supported Ru catalysts on metal oxides Specific surface Ru dispersion (%)a area (m2 g–1) 1 Ru/MgO 30 22 (6.0) 2 Ru/Al2O3 162 18 (7.5) 260 41 (3.3) 3 Ru/SiO2 102 56 (2.4) 4 Ru/TiO2 73 69 (1.9) 5 Ru/ZrO2 24 (5.5) 6 Ru/Nb2O5 112 a Ru dispersion determined with CO‐pulse titration tech‐ nique. The stoichiometry of CO/Ru = 0.6 was assumed.13 Values in parentheses are the Ru particle sizes (nm) esti‐ mated from the dispersion. Entry
(a)
O
NH 8a 31
+NH3 H 2O O
+H2 O
O 1a
NH2 2a
0
+1a H2 O
4
O
O
N 3a 21
+H 2
O
O
N H 7a
+2H 2
43 O
NH2 5a
76
(b)
NH 3 O
1
1a (0 kJ mol )
H2
H2O O
O NH3
1
H2O 8a (+31 kJ mol )
2a (4 kJ mol ) 1a
O OH
O
H2O N
O
3a (21 kJ mol 1)
6a (2 kJ mol 1 ) N
NH2
5a (76 kJ mol 1 )
1a
H2O
NH3
O
NH 2 1
2x8a
H2
O
2H 2 O
NH
NH
H2 O
O 4a (+1 kJ mol 1 )
O
N H
Catalyst
O
7a (43 kJ mol 1)
Figure 2. (a) Computational free energy diagrams of the reductive amination of 1a and related side‐reactions. Ener‐ gies are shown in kJ mol–1. (b) Proposed reaction pathways for the reductive amination of 1a over a Ru/Nb2O5 catalyst. Values in parentheses are computational free energies based on 1a. S1, and Table 1.13–16 The reductive amination of furfural (1a) to furfurylamine (2a) with a methanol solution of ammonia
First, the effect of the supports in the supported ruthe‐ nium catalysts was examined (Tables 2 and S3). Among the catalysts tested, Ru/Nb2O5 provided the highest yield of 2a at 89% without significant formation of other byproducts (Table 2, entry 1).18 The reaction almost quantitatively pro‐ ceeded to give 2a in 99% yield when gaseous NH3 was used instead of a methanol solution (Table 2, entry 2). The con‐ version of 1a (>99%) and yield of 2a (95%) of Ru/Nb2O5 without passivation were almost the same as those of Ru/Nb2O5 with passivation under the reaction conditions of entry 2 in Table 2. Thus, it is not necessarily to perform this passivation pre‐treatment to attain the high yield of 2a. Ru/SiO2, Ru/TiO2 and Ru/C also gave 2a in good to mod‐ erate yields (31–84%), although complex mixtures of sev‐ eral byproducts 3a–7a were formed with total yields of 4– 14% (Table 2, entries 3–5). In the case of amphoteric and basic oxide supports (Al2O3, ZrO2, and MgO), 4a was mainly formed without the production of 2a (Table 2, en‐ tries 6–8), and these product distributions are comparable to that without a catalyst (Table 2, entry 17).19 Next, the ef‐ fect of metal species supported on Nb2O5 was investigated. The Rh/Nb2O5 catalyst gave 2a in 75% yield, but subse‐ quent hydrogenation of the dimeric imine 6a to the sec‐ ondary amine 7a was inevitable (Table 2, entry 9). Group 10 metal (Pd, Ni, and Pt) catalysts gave a complex mixture of 2a–7a (Table 2, entries 10, 11 and 14). On the other hand,
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Entry Catalyst Yield (%) 2a Othersd 1 Ru/Nb2O5 89 4 2 b Ru/Nb2O5 99 1 3 Ru/SiO2 84 8 4 Ru/TiO2 72 14 5 Ru/C 31 4 6 Ru/Al2O3
