Subscriber access provided by UNIV OF MISSOURI ST LOUIS
Article
Highly Selective Semihydrogenation of Alkynes to Alkenes by Using an Unsupported Nanoporous Palladium Catalyst: No Leaching of Palladium into Reaction Mixture Ye Lu, Xiujuan Feng, Balaram S. Takale, Yoshinori Yamamoto, Wei Zhang, and Ming Bao ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b02915 • Publication Date (Web): 25 Oct 2017 Downloaded from http://pubs.acs.org on October 26, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Highly Selective Semihydrogenation of Alkynes to Alkenes by Using an Unsupported Nanoporous Palladium Catalyst: No Leaching of Palladium into Reaction Mixture Ye Lu,†,ǁ Xiujuan Feng,†,ǁ Balaram S. Takale,†,# Yoshinori Yamamoto,†,§ Wei Zhang,┴ and Ming Bao*,†,‡ †
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116023,
China. ‡
School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin
124221, China. §
WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
and Research Organization of Science and Technology, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan. ┴
School of Materials Science and Engineering, Dalian University of Technology, Dalian 116023,
China.
ACS Paragon Plus Environment
1
ACS Catalysis
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 25
ABSTRACT: We report the highly chemoselective and stereoselective semihydrogenation of alkynes to Z-internal and terminal alkenes by using unsupported nanoporous palladium (PdNPore) as a heterogeneous catalyst under mild reaction conditions (room temperature and 1 atm H2). The semihydrogenation of various terminal/internal and aromatic/aliphatic alkynes afforded the corresponding alkenes in good chemical yields with high selectivities. PdNPore further showed high chemoselectivity toward terminal-alkynes in the presence of internal alkynes, which has not yet been achieved using supported palladium nanoparticle catalysts. H–H heterolysis of H2 on the surface of PdNPore was strongly suggested by deuterium labeling experiments. No Pd leached from PdNPore during the reaction, and the catalyst was easily recovered and reused without activity loss.
KEYWORDS: alkyne, semihydrogenation, heterogeneous catalysis, nanoporous palladium, no leaching INTRODUCTION The selective hydrogenation of alkynes to (Z)-alkenes is highly important for the construction of numerous valuable compounds, such as bioactive molecules, natural products, flavors, and industrial materials.1 Various catalysts are available for the conversion of alkynes into (Z)alkenes. In previous catalytic approaches, this transformation is accomplished in the presence of either a homogeneous2 (e.g., Pd, Ni, Ru, Rh, and Co complexes) or a heterogeneous3 (e.g., Pd catalysts, Ni catalysts, and Au nanoparticles) catalyst. Among the known catalytic methods, hydrogenation using Lindlar catalyst (Pd/CaCO3 treated by Pb salts) is the most popular and widely used.4 Unfortunately, Lindlar catalyst has the following serious drawbacks: the requirement of a toxic lead salt, partial isomerization of Z-alkene to E-alkene, double-bond
ACS Paragon Plus Environment
2
Page 3 of 25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
shifting, and lack of highly reproducible results.1a Furthermore, Lindlar catalyst has a limited substrate scope, i.e., only internal alkynes are selectively hydrogenated into desired alkenes, whereas terminal alkynes often suffer from the rapid overhydrogenation of resulting alkenes to alkanes. From the perspective of green chemistry and other practical concerns, the development of more environmentally benign and efficient catalyst systems for the semihydrogenation of alkynes is highly desirable. Catalysis using unsupported nanoporous metal materials is attracting increased interest given their potentially green and sustainable catalytic properties.5 The interesting features of nanoporous metals such as nontoxicity, robustness, high recyclability, and simple recovery render them attractive as heterogeneous catalysts. Over the past few years, we have demonstrated that nanoporous metals are promising green heterogeneous catalysts for liquid-phase organic synthesis.6 We have recently reported that nanoporous gold (AuNPore) is effective for the transfer semihydrogenation of alkynes (Scheme 1, Eq. 1).6d,6o However, this method requires excess amounts of formic acid/triethylamine or costly organosilanes as a hydrogen source. Therefore, the formation of stoichiometric amounts of byproduct is inevitable. The use of hydrogen gas has well-accepted advantages over H-transfer reagents because no waste is generated after the reaction using hydrogen.7 We have further demonstrated that AuNPore can serve as a robust catalyst for the semihydrogenation of alkynes to alkenes with very high Zselectivity by using H2 as hydrogen source (Scheme 1, Eq. 2).6p Although we have achieved high yields and selectivities, a slightly high hydrogen pressure (8 atm) and temperature (90 °C) required for the reaction hinders industrial application. Hence, we became curious if alkynes can be reduced using other metal nanoporous materials such as PdNPore under mild conditions.
ACS Paragon Plus Environment
3
ACS Catalysis
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 25
Another important and long-standing concern for both heterogeneous and homogeneous palladium catalysis is the leaching problem.8 The topic of palladium leaching from nanoparticle form is debatable. The degree of leaching depends on palladium nanoparticle size, support material, and reaction media and conditions. Palladium leaching in liquid-phase reactions using PdNPore such as cross-coupling reactions has been investigated, and data clearly show much less palladium leaching from PdNPore than palladium black and Pd/C (i.e., 1.14 ppm for Heck reaction and 0.69 ppm for Suzuki coupling).9 To the best of our knowledge, reports on Pd noleaching in reactions using heterogeneous palladium catalysts are very few.10 In this paper, we report the highly stereoselective and chemoselective semihydrogenation of alkynes to Z-alkenes achieved by using unsupported nanoporous palladium under 1 atm H2 at room temperature (Scheme 1, Eq. 3). In this hydrogenation, no palladium leaching from PdNPore was observed. Scheme 1. Semihydrogenation of Alkynes Catalyzed by AuNPore or PdNPore
RESULTS AND DISCUSSION
ACS Paragon Plus Environment
4
Page 5 of 25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Preparation and Characterization of PdNPore Catalyst. Pd nanoporous catalyst was prepared according to previous literature.11 First, pure palladium (99.99%) and aluminum (99.99%) were melted in a quartz crucible using a high-frequency induction furnace to form Pd20Al80 ingots. Then, a single-roller melt spinning apparatus was used to remelt the prealloyed ingots (about 2–4 g) by high-frequency induction heating in a quartz tube and then meltspun onto a 0.35 mdiameter copper roller at 1000 or 1500 rpm in controlled argon atmosphere. The ribbons obtained were typically 20–50 µm thick, 2–4 mm wide, and several centimeters long. Finally, the Pd20Al80 alloy ribbons were dealloyed in 20 wt% NaOH aqueous solution under corrosion-free conditions. Using 20 wt% NaOH solution, Pd20Al80 was dealloyed at room temperature until no obvious bubbles emerged. Dealloying was continuously performed in alkaline solution at 90 °C to further leach out residual Al in the samples. Dealloying was generally complete within
