Switch in Catalyst State: Single Bifunctional Bi‐state Catalyst for Two Different Reactions

Disclosed here is a molecular switch which responds to acid‐base stimuli and serves as a bi‐state catalyst for two different reactions. The two states of the switch serve as a highly active and poorly active catalyst for two catalytic reactions (namely a hydrogenation and a dehydrogenative coupling) but in a complementary manner. The system was used in an assisted tandem catalysis set‐up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.     

C‐Propargylation Overrides O‐Propargylation in Reactions of Propargyl Chloride with Primary Alcohols: Rhodium‐Catalyzed Transfer Hydrogenation

The canonical S_N2 behavior displayed by alcohols and activated alkyl halides in basic media (O‐alkylation) is superseded by a pathway leading to carbinol C‐alkylation under the conditions of rhodium‐catalyzed transfer hydrogenation. Racemic and asymmetric propargylations are described.     

Cobalt Incorporated Graphitic Carbon Nitride as a Bifunctional Catalyst for Electrochemical Water-Splitting Reactions in Acidic Media

Non-noble metal-based bifunctional electrocatalysts may be a promising new resource for electrocatalytic water-splitting devices. In this work, transition metal (cobalt)-incorporated graphitic carbon nitride was synthesized and fabricated in electrodes for use as bifunctional catalysts. The optimum catalytic activity of this bifunctional material for the hydrogen evolution reaction (HER), which benefitted at a cobalt content of 10.6 wt%, was promoted by the highest surface area and conductivity. The activity achieved a minimum overpotential of ~85 mV at 10 mA/cm² and a Tafel slope of 44.2 mV/dec in an acidic electrolyte. These values of the HER were close to those of a benchmark catalyst (platinum on carbon paper electrode). Moreover, the kinetics evaluation at the optimum catalyst ensured the catalyst flows (Volmer–Heyrovsky mechanism), indicating that the adsorption step is rate-determining for the HER. The activity for the oxygen evolution reaction (OER) indicated an overpotential of ~530 mV at 10 mAcm⁻² and a Tafel slope of 193.3 mV/dec, which were slightly less or nearly the same as those of the benchmark catalyst. Stability tests using long-term potential cycles confirmed the high durability of the catalyst for both HER and OER. Moreover, the optimal bifunctional catalyst achieved a current density of 10 mAcm⁻² at a cell voltage of 1.84 V, which was slightly less than that of the benchmark catalyst (1.98 V). Thus, this research reveals that the present bifunctional, non-noble metallic electrocatalyst is adequate for use as a water-splitting technology in acidic media.     

Auto‐Tandem Catalysis: A Single Catalyst Activating Mechanistically Distinct Reactions in a Single Reactor

Domino reactions have received great attention as efficient synthetic methodologies for the construction of structurally complex molecules from simple materials in a single operation. Catalysts in domino reactions have also been well studied. In these reactions, a catalyst activates the substrate(s) only once, and the structure of the product is delineated at that time. Recently, the new concept of “tandem catalysis” in domino reactions, in which catalyst(s) sequentially activate more than two mechanistically distinct reactions, has been proposed. Tandem catalysis is categorized into three subclasses: orthogonal‐, auto‐, and assisted‐tandem catalyses. Auto‐tandem catalysis is defined as a process in which one catalyst promotes more than two fundamentally different reactions in a single reactor. An overview of recent and significant achievements in auto‐tandem catalysis is presented in this paper.