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Iterative Preparation of Platinum Nanoparticles in an Amphiphilic Polymer Matrix: Regulation of Catalytic Activity in HydrogenationThis work was supported by the JST-ACCEL program (JPMJAC401). We are also grateful for funding from the JSPS KAKENHI [Grants-in-Aid for Challenging Exploratory Research (No. 26620090) and for Scientific Research (C) (No. 16K05876)].
Received: 23 March 2019
Accepted after revision: 09 April 2019
25 April 2019 (online)
Published as part of the Cluster Iterative Synthesis
We demonstrate that iteration of the seeded preparation of platinum nanoparticles dispersed in an amphiphilic polystyrene–poly(ethylene glycol) resin (ARP–Pt) regulates their catalytic activity in the hydrogenation of aromatic compounds in water. The catalytic activity of the fifth generation of ARP–Pt [G5] prepared through four iterations of the seeded preparation was far superior to that of the initial ARP–Pt [G1] in the hydrogenation of aromatic compounds in water.
Key wordsiterative preparation - platinum catalysis - nanoparticles - hydrogenation - aromatic compounds
References and Notes
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- 7 Flow hydrogenations of C=C and C=O double bonds have been performed with ARP-Pt(G1) for up to 7852 min at 30–100 °C in aqueous medium, during which no leaching from the catalyst was observed (ICP-AES analysis). These observations showed that hydrogenation catalyzed by ARP-Pt takes place heterogeneously [see refs 6 (c) and (d)].
- 8 1 g of TentaGel S NH2 (particle size: 90 μm) contains about 2.86 × 106 beads. We estimated the densities of platinum based on the platinum loading and the volume of a polymer bead. For details, see: http://www.rapp-polymere.com/index.php?id=98.
- 9 The trans/cis ratio of 3 was about 6:4 to 7:3, suggesting that iteration of the seeded preparation did not affect the trans/cis selectivity of the fully hydrogenated product.
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- 11 Iterative preparation of ARP–Pt For the initial preparation of ARP–Pt, a mixture of PS–PEG–NH2 (TentaGel S-NH2: 0.27 mmol/g NH2; 3.0 g, 0.81 mmol) and K[PtCl3(C2H4)]·H2O (0.35 g, 0.89 mmol, 1.1 equiv) in H2O (20 mL) was shaken at r.t. for 1 h under N2. The resulting supported platinum complex was collected by filtration and washed with H2O (3 × 20 mL). The supported platinum complex and BnOH (5 mL, 48 mmol) were added to H2O (20 mL), and the mixture was shaken at 80 °C for 18 h. The resulting supported platinum nanoparticles were collected by filtration, washed sequentially with H2O (3 × 20 mL) and acetone (3 × 20 mL) then dried under vacuum overnight to give black beads of the first generation of ARP–Pt (G1). For iteration of the seeded preparation, G1 was treated with K[PtCl3(C2H4)]· H2O (1.1 equiv) in H2O (20 mL) and then reduced with BnO (5 mL) under similar conditions to the initial preparation to afford a second generation of ARP–Pt (G2). Further iterations were conducted similarly to provide G3 through G5. Hydrogenation of p-Methylstyrene (1a) in Water; Typical Procedure A Schlenk tube was charged with ARP–Pt (1 mol% Pt, 0.003 mmol) and p-methylstyrene (1a) (35.4 mg, 0.3 mmol). H2O (3 mL) was added, and the mixture was degassed by three freeze–pump–thaw cycles. The tube was then filled with H2 gas by using a balloon and the mixture was heated at 80 °C for 8 h. The resulting mixture was extracted with MTBE (3 × 2 mL), and the combined organic layer was analyzed by FID-GC with mesitylene as the internal standard to determine the yields of products 2a and 3a. Data for all compounds agreed well (match factor >998; structural probability >98%) with authentic GC–MS data from the NIST Reference Library; see: Stein S. E.; J. Am. Soc. Mass Spectrom. 1995, 6, 644.
For typical examples with platinum nanoparticles, see: