Electrocatalytic Proton Reduction by Dimeric Nickel Complex of a Sterically Demanding Pincer-type NS₂ Aminobis(thiophenolate) Ligand

Basic methanolysis of a sterically hindered aminobis­(<i>S</i>-arylthiocarbamate) affords a novel aminobis­(thiophenolate) pincer-type ligand NS₂^2–; the in situ generated dianion reacts cleanly with Ni²⁺ and Zn²⁺ resulting in dimeric complexes with bridging thiophenolate ligands, as determined spectroscopically and by X-ray crystallography. The <i>C</i>₂-symmetric [Ni­(NS₂)]₂ dimer (<b>1</b>) has a square planar coordination geometry around the Ni²⁺ ions, while the [Zn­(NS₂)]₂ analogue (<b>2</b>) is characterized by a distorted tetrahedral geometry around each independent Zn²⁺ ion. Addition of the neutral monodentate donor L = 2,6-xylylisocyanide to [Ni­(NS₂)]₂ affords the monomeric complex [LNi­(NS₂)] (<b>3</b>), which is characterized in the solid state by a square planar geometry with the isocyanide donor trans to the tertiary amine of NS₂. The pincer NS₂ ligand provides redox plasticity to <b>1</b>, manifested in the accessibility of the putative Ni⁺Ni⁺ and Ni³⁺Ni³⁺ dimeric complexes, based on comparative cyclic voltammetry studies with <b>2</b> and <b>3</b>. The redox properties of <b>1</b> endow it with hydrogenase-type activity, as evidenced in the electrocatalytic reduction of protons in a mixed aqueous/organic phase, as well as the oxidation of hydrides from NaBH­(OAc)₃. Both <b>1</b> and <b>3</b> are resilient under protic and oxidative conditions, as evidenced in reactivity tests monitored by UV–vis spectroscopy

Enhanced Electrochemical Hydrogenation of Benzaldehyde to Benzyl Alcohol on Pd@Ni-MOF by Modifying the Adsorption Configuration

Electrocatalytic hydrogenation (ECH) approaches under ambient temperature and pressure offer significant potential advantages over thermal hydrogenation processes but require highly active and efficient hydrogenation electrocatalysts. The performance of such hydrogenation electrocatalysts strongly depends not only on the active phase but also on the architecture and surface chemistry of the support material. Herein, Pd nanoparticles supported on a nickel metal–organic framework (MOF), Ni-MOF-74, are prepared, and their activity toward the ECH of benzaldehyde (BZH) in a 3 M acetate (pH 5.2) aqueous electrolyte is explored. An outstanding ECH rate up to 283 μmol cm–2 h–1 with a Faradaic efficiency (FE) of 76% is reached. Besides, higher FEs of up to 96% are achieved using a step-function voltage. Materials Studio and density functional theory calculations show these outstanding performances to be associated with the Ni-MOF support that promotes H-bond formation, facilitates water desorption, and induces favorable tilted BZH adsorption on the surface of the Pd nanoparticles. In this configuration, BZH is bonded to the Pd surface by the carbonyl group rather than through the aromatic ring, thus reducing the energy barriers of the elemental reaction steps and increasing the overall reaction efficiency