Synthesis, Characterization, and HER Activity of Pendant Diamine Derivatives of NiATSM

Abstract

A pair of bis‐thiosemicarbazonato‐Ni(II) complexes with pendant polyamines, (N,N′‐(dimethylethylenediaminothiosemi‐carbazonato)‐4‐(methylthiosemi‐carbazonato)butane‐2,3‐diimine)‐nickel(II) (1) and (N,N′‐bis(dimethylethyl‐enediaminothiosemi‐carbazonato)butane‐2,3‐diimine)‐nickel(II) (3), have been synthesized. Methylation at the terminal amines yields the cationic derivatives 2 and 4. All complexes are fully characterized by spectroscopic, electrochemical, and single‐crystal X‐ray diffraction methods. Single crystal X‐ray diffraction studies on all four Ni(II) complexes confirm a square planar Ni(II) framework with no significant changes in the coordination environment as a function of the pendant groups. Spectroscopic studies are consistent with a similar electronic structure in all complexes. However, electrochemical investigations reveal significant cathodic shifts in the Ni(II)L/Ni(II)L·– and Ni(II)L·–/Ni(I)L·2– reduction potentials of the methylated vs. non‐methylated species. The HER activity of all four nickel complexes were evaluated in acetonitrile with glacial acetic acid. The 3 complex was shown to have the highest activity with a TOF of 6.3 × 103 s‐1, an overpotential of 0.56 V, and faradaic efficiency of 100 %.

Copper bis(thiosemicarbazone) Complexes with Pendent Polyamines: Effects of Proton Relays and Charged Moieties on Electrocatalytic HER

“…Selected bond distances and angles are summarized in Table 2. Overall, complexes Cu‐1–Cu 4 display the same general coordination environment as their nickel analogs with similar bond angles around the metal center and slightly longer (∼0.1 Å) metal‐ligand bond distances [14] …”

“…All reactions were performed open to air and under ambient conditions unless otherwise indicated. The ligands H 2 L 1 and H 2 L 2 were prepared as previously described [14] …”

“…The effect of through‐space interactions on electrocatalysis has also been evaluated through the introduction of a secondary coordination sphere [9,10,12,13] . Ligands with bulky groups, fixed charge sites, and hydrogen‐bonding proton relay pendents are of growing interest as they may play an important role in generating and stabilizing reactive intermediates during catalysis [9,14] . For example, incorporation of charged groups in the second coordination sphere, as part of the ligand framework or as appended groups, have been shown to reduce the reduction potential of the complex via through‐space interactions [11,14] …”

“…[9,10,12,13] Ligands with bulky groups, fixed charge sites, and hydrogen-bonding proton relay pendents are of growing interest as they may play an important role in generating and stabilizing reactive intermediates during catalysis. [9,14] For example, incorporation of charged groups in the second coordination sphere, as part of the ligand framework or as appended groups, have been shown to reduce the reduction potential of the complex via through-space interactions. [11,14] Several bis(thiosemicarbazone) (BTSC) metal complexes, including derivatives of diacetyl-bis(N-methyl-3-thiosemicarbazone) (H 2 ATSM), have been evaluated as hydrogen evolution reaction (HER) electrocatalysts.…”

Recent advances in the mechanisms of the hydrogen evolution reaction by non-innocent sulfur-coordinating metal complexes

“…Recently, the group of Grapperhaus presented the nickel complexes 71-74 bearing pendant amines on the thiosemicarbazone ligand framework 181 centered reduction at −2.31 V. In the presence of an acid, metal centered reduction shifts anodically, indicating an ECEC reaction pathway. Based on the relative catalytic efficiencies of complexes 71-74 and the observation that the overpotentials of the catalysts increase, when the scan rate is increased, the authors proposed that metal center reduction is coupled with Scheme 33 (a) Her catalysts carrying pyrazine substituents on their thiosemicarbazone ligands.…”