(Invited) Delivering Electrons and Protons to the Substrate in Molecularly-Based Reductive Electrocatalysis

Abstract

To steer away from fossil fuels the primary sourcing for goods and chemicals, combining renewable electricity with sustainable feedstocks in an electrochemical strategy is a formidable synthetic opportunity. In that frame, we investigate how molecular electrocatalysis can foster electrosynthetic conversions, in particular for organics reductions.[1] Here, we will disclose that alkyne semihydrogenation, an important synthetic manifold, can be selectively electrocatalyzed by a simple molecular catalyst [Ni(bpy)3]2+, based on the earth-abundant metal nickel.[ 2 ] Our combined electrochemical, synthetic and computational investigations support that the catalytic cycle proceeds via the protonation of a nickelacyclopropene species and bypasses the need to generate a competent hydride.[3] As a proof-of-concept for molecular electrocatalytic alkyne semihydrogenation, this work opens a platform to develop original electrochemical routes for the hydrogenation/-functionalization of organics and small molecules.We will also discuss the use of Pickering emulsion that separates organic substrates and aqueous electrolytes in different phases for electrocatalytic hydrogenation at the interface. We developed a hybrid design based on carbon nanotube-supported Pd nanoparticles that places at the interface and acts both as emulsion stabilizer and electrocatalyst. The system electrohydrogenates styrene into ethylbenzene with high faradaic efficiency (95.0%) and Pd specific current density (–148.1 mA·cm–2). Our system combines good solubility of the substrates, high conductivity, facile product isolation and applies to the transformation of various alkenes. This strategy may thus provide original solutions to the ECH of substrates having low water-solubility.[4] References [1] N. Kaeffer, W. Leitner, JACS Au, 2022, 2, 1266.[2] M.-Y. Lee, C. Kahl, N. Kaeffer, W. Leitner, JACS Au, 2022, 2, 573.[3] G. Durin, M.-Y. Lee, T. Weyhermüller, N. Kaeffer, W. Leitner, ChemRxiv, 10.26434/chemrxiv-2023-whtfd.[4] C. Han, J. Zenner, J. Johny, N. Kaeffer, A. Bordet, W. Leitner, Nat. Catal., 2022 , 5, 1110.