Electrochimica Acta, Vol.260, 606-613, 2018
Amino acid-functionalized multi-walled carbon nanotubes: A metal-free chiral catalyst for the asymmetric electroreduction of aromatic ketones
We report new metal-free chiral electrodes for catalyzing the asymmetric reduction of aromatic ketones. Multi-walled carbon nanotubes (MWCNTs) were functionalized by chiral amino acids. The resulting amino acid-functionalized MWCNTs were fully characterized by surface analysis and spectroscopic tools and were used as a cathode for the electroreduction of 2,2,2-trifluoroacetophenone in MeCN/n-amyl alcohol (1: 1)-TEAI (0.1 M). Electroreduction at L-arginine-MWCNTs and D-arginine-MWCNTs cathodes afforded, respectively, (R)- and (S)-a-(trifluoromethyl) benzyl alcohol in 60-61% yield with 43-44% enantiomeric excess (ee). The L-lysine-MWCNTs cathode gave a lower ee value of the R enantiomer (30%). The yields and ee values were a little bit lower for the electroreduction of acetophenone and other arylalkyl ketones. These amino acid-functionalized MWCNTs electrodes, in addition to showing good catalytic performance, are very stable and can be reused without loss of activity and selectivity. (C) 2017 Elsevier Ltd. All rights reserved.
Keywords:Functionalization;Multi-walled carbon nanotubes;Metal-free;Chiral electrode;Asymmetric electroreduction