Activation-temperature dependence in enantioselective hydrogenation of unsaturated carboxylic acids over cinchonidine-modified Pd/C catalysts

Recent Advances of Pd/C-Catalyzed Reactions

The Pd/C-catalyzed reactions, including reduction reactions and cross-coupling reactions, play an irreplaceable role in modern organic synthesis. Compared to the homogeneous palladium catalyst system, the heterogeneous Pd/C catalyst system offers an alternative protocol that has particular advantages and applications. Herein, a review on Pd/C-catalyzed reactions is presented. Both the advances in Pd/C-catalyzed methodologies and the application of Pd/C-catalysis in total synthesis are covered in this review.

One-Pot Synthesis of d-Phenylalanine-Functionalized Multiwalled Carbon Nanotubes: A Metal-Free Chiral Material for the Asymmetric Electroreduction of Aromatic Ketones

A simple protocol to synthesize d-phenylalanine (d-PHE)-functionalized multiwalled carbon nanotubes (MWCNTs) via the one-pot method was established by grafting d-PHE onto MWCNTs to obtain d-PHE-MWCNTs under mild reaction conditions. The resulting d-PHE-MWCNTs were characterized in detail via spectroscopy and surface analysis. The electroreduction of 2,2,2-trifluoroacetophenone at the d-PHE-MWCNTs cathode afforded ( S)-α-(trifluoromethyl) benzyl alcohol whose yield was 65% and the enantiomeric excess was 40%. No extra catalysts were required in this electrochemical reaction solution compared with other reactions requiring homogeneous catalysis. The metal-free chiral material also showed acceptable asymmetric electroreduction performance, considerable stability, and favorable reusability.

Enantioselective hydrogenation of N-heteroaromatics catalyzed by chiral diphosphine modified binaphthyl palladium nanoparticles

The first application of binaphthyl-stabilized palladium nanoparticles (Bin-PdNPs) with chiral modifiers in asymmetric hydrogenation of N-heteroaromatics is revealed.

Time-Lapse STM Studies of Diastereomeric Cinchona Alkaloids on Platinum Metals

The adsorption of cinchonidine (CD) and cinchonine (CN) on Pt(111) and Pd(111) single crystals has been investigated by means of scanning tunneling microscopy (STM) in an ultrahigh vacuum system. In time-lapse series the mobilities of different adsorption species have been determined on a single molecule basis and with varying hydrogen background pressures in the system. The diastereomeric cinchona alkaloids, CD and CN, which are widely used as chiral modifiers of platinum group metals in catalytic enantioselective hydrogenation, showed similar adsorption modes and diffusion behavior on Pt(111), except that the flatly adsorbed CN molecules which were free (not in a dimer/cluster) were significantly more mobile than their CD analogues. CD adsorbed on Pd(111) showed similar adsorption modes as observed on Pt(111) but at considerably higher mobility of the flatly absorbed species already in the low-pressure region. The observed adsorption behaviors are discussed in the context of independent ATR-IR measurements and theoretical calculations. Special emphasis is put on the nonlinear effect observed in hydrogenation reactions with CD/CN mixtures. Our observations corroborate that this effect is mainly a consequence of the different adsorption strengths of CD and CN on Pt.