Highly Selective and Efficient Electrocatalytic Semihydrogenation of Diphenylacetylene to Z-Stilbene Using Pt-Pd Alloy Cathode Catalyst

Abstract

The electrical energy can be provided from renewable energy source such as solar and wind, thus making the electrocatalytic hydrogenation process is expected one of important technology to reduce carbon dioxide emission in organic synthesis industry. The selective hydrogenation of alkynes to Z-alkenes is highly important for the construction of numerous valuable compounds, such as bioactive molecules, natural products, flavors, and industrial materials. Although a number of methods for the stereoselective synthesis of Z-alkenes have been developed so far, the Lindlar catalytic semihydrogeneation of alkynes is a long-standing synthetic transformation and still remains the favored system. HoweveTo develop more environmentally benign and efficient semihydrogenation systems, we have demonstrated electrocatalytic hydrogenation of diphenylacetylene (DPA) in a proton exchange membrane (PEM) reactor. 1 In our system, the oxidation of water was employed as an anodic process (Figure 1 (a)).Especially, in this work, we have investigated systematically influences of catalyst materials such as Pt, Pd, and PtPd alloy for a PEM reactor on the product selectivity for Z-stilbene and partial current density for Z-stilbene formation in the hydrogenation of diphenylacetylene. As a result, PtPd alloy with a composition of Pt1Pd99 was found to be a most suitable catalyst material in order to achieve both high partial current density for Z-stilbene formation and high Z-stilbene selectivity (Figures 1 (b) and (c)). As shown in Figure 1 (b), it was also found that the partial current density for Z-stilbene is much improved by the addition of a small amount of Pt which has the high hydrogenation activity. Moreover, the synergy of Pt electrocatalysis for the formation of adsorbed hydrogen species (Had) (H+ + e− → Had) and Pd catalysis for hydrogenation of DPA (2Had + DPA → Z-stilbene) might be required in order to achieve the high stereoselective formation of Z-stilbene. Acknowledgement This work was support by JST CREST Grant No. JPMJCR18R1, Japan. The authors gratefully acknowledge for ISHIFUKU Metal Industry corporation the generous gift for cathode catalysts. References 1) A. Fukazawa, J. Minoshima, K. Tanaka, Y. Hashimoto, Y. Kobori, Y. Sato, M. Atobe, ACS Sustain. Chem. Eng. 2019, 7, 11050–11055. Figure 1