Phosphine-Enhanced Semi-Hydrogenation of Phenylacetylene by Cobalt Phosphide Nano-Urchins

Transition metal phosphides are promising, selective, and air-stable nanocatalysts for hydrogenation reactions. However, they often require fairly high temperatures and H2 pressures to provide quantitative conversions. This work reports the positive effect of phosphine additives on the activity of cobalt phosphide nano-urchins for the semi-hydrogenation of phenylacetylene. While the nanocatalyst's activity was low under mild conditions (7 bar of H2 , 100 °C), the addition of a catalytic amount of phosphine remarkably increased the conversion, e. g., from 13 % to 98 % in the case of Pn Bu3 . The heterogeneous nature of the catalyst was confirmed by negative supernatant activity tests. The catalyst integrity was carefully verified by post-mortem analyses (TEM, XPS, and liquid 31 P NMR). A stereo-electronic map was proposed to rationalize the activity enhancement provided over a selection of nine phosphines: the strongest effect was observed for low to moderately hindered phosphines, associated with strong electron donor abilities. A threshold in phosphine stoichiometry was revealed for the enhancement of activity to occur, which was related to the ratio of phosphine to surface cobalt atoms.

An Efficient Continuous Flow Synthesis for the Preparation of N-Arylhydroxylamines: Via a DMAP-Mediated Hydrogenation Process

The selective hydrogenation of nitroarenes to N-arylhydroxylamines is an important synthetic process in the chemical industry. It is commonly accomplished by using heterogeneous catalytic systems that contain inhibitors, such as DMSO. Herein, DMAP has been identified as a unique additive for increasing hydrogenation activity and product selectivity (up to >99%) under mild conditions in the Pt/C-catalyzed process. Continuous-flow technology has been explored as an efficient approach toward achieving the selective hydrogenation of nitroarenes to N-arylhydroxylamines. The present flow protocol was applied for a vast substrate scope and was found to be compatible with a wide range of functional groups, such as electron-donating groups, carbonyl, and various halogens. Further studies were attempted to show that the improvement in the catalytic activity and selectivity benefited from the dual functions of DMAP; namely, the heterolytic H2 cleavage and competitive adsorption.

Aqueous phase semihydrogenation of alkynes over Ni–Fe bimetallic catalysts

Bimetallic Ni–Fe catalysts (Ni/Fe, 1 : 1, 1 : 3, and 3 : 1) are synthesized and explored for their catalytic activity in semihydrogenation of internal alkynes using H₂ gas in water–ethanol solution.