Mechanistic Studies of the Reduction of Nitroarenes by NaBH4 or Hydrosilanes Catalyzed by Supported Gold Nanoparticles

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• 作者：Stella Fountoulaki ; Vassiliki Daikopoulou ; Petros L. Gkizis ; Ioannis Tamiolakis ; Gerasimos S. Armatas ; Ioannis N. Lykakis
• 刊名：ACS Catalysis
• 出版年：2014
• 出版时间：October 3, 2014
• 年：2014
• 卷：4
• 期：10
• 页码：3504-3511
• 全文大小：393K
• ISSN：2155-5435

文摘

Herein, we show that mesoporous titania-supported gold nanoparticle assemblies (Au/MTA) catalyze the activation of NaBH₄ and 1,1,3,3-tetramethyl disiloxane (TMDS) compounds, which act as transfer hydrogenation agents for the reduction of nitroarenes to the corresponding anilines in moderate to high yields. On the other hand, nitroalkanes are reduced to the corresponding diazo and hydrazo compounds under the studied conditions. The substantial measured primary kinetic isotope effects found here suggested that B鈥揌 bond cleavage occurs in a rate-determining step and [Au]鈥揌 active hybrids are formed, which are responsible for the reduction of nitroarenes to the corresponding amines. Formal Hammett-type kinetic analysis of a range of para-X-substituted nitroarenes lends support to this hypothesis. Nitro compounds substituted with electron-withdrawing groups were reduced faster than the corresponding compounds with electron-donating groups. The presence of water enhanced the catalytic activity of Au/MTA in aprotic solvents. Nuclear magnetic resonance studies support the formation of the corresponding hydroxylamines as the only intermediate products. On the basis of the high observed chemoselectivities and the fast and clean reaction processes, these catalytic systems, i.e., Au/MTA-NaBH₄ and Au/MTA-TMDS, show promise for the efficient synthesis of aromatic amines at industrial levels.

Keywords:

gold nanoparticles; heterogeneous catalysis; nitro compounds; selective reduction; kinetic isotope effects; Hammett kinetics