Magnetic Nanoparticles-Supported Platinum Nanoparticles

Key words

platinum - magnetic nanoparticles - ionic liquids - hydrogenation

Significance

Platinum nanoparticles supported by magnetic nanoparticles that were modified with ionic liquid were prepared and applied to the selective hydrogenation. Thus, imidazole 1 reacted with octyl chloride 2 at 120 °C to give the imidazolium chloride 3 in 97% yield (eq. 1). Treatment of 3 with the magnetic nanoparticles, Fe₃O₄, in the presence of ammonia afforded ionic liquid modified Fe₃O₄ 4. Anion exchange reaction of 4 with K₂PtCl₄ followed by reduction with hydrazine provided the supported platinum nanoparticles 5. The hydrogenation of diphenylacetylene was carried out in the presence of 2.5 mol% of catalyst 5 under 200 psi of hydrogen at 90 °C for 16 h to give cis-stilbene as a major product in 95% yield (eq. 2). Cinnam­aldehyde was chemoselectively hydrogenated under similar reaction conditions to afford 3-phenylprop-2-en-1-ol in 99% yield (eq. 3).

Comment

The modification of Fe₃O₄ with ionic liquid is important for successful formation of the platinum nanoparticles on the surface of the magnetic nanoparticles. Without the modification with ionic liquid, the formation of platinum nanoparticles took place outside the surface of the magnetic support. In the selective hydrogenation of diphenyl­acetylene, the catalyst can be separated from the reaction mixture by an external magnet and reused four times without significant loss of catalytic activity (1^st use: 100% conv., cis/trans = 95:5; 2^nd use: 97% conv., cis/trans = 92:5; 3^rd use: 99% conv., cis/trans = 93:6; 4^th use: 97% conv., cis/trans = 93:4).