Ligand-based electronic effects on the electrocatalytic hydrogen production by thiosemicarbazone nickel complexes.

This work reports on the synthesis and characterization of a series of mononuclear thiosemicarbazone nickel complexes that display significant catalytic activity for hydrogen production in DMF using trifluoroacetic acid as the proton source. The ligand framework was chemically modified by varying the electron-donating abilities of the para substituents on the phenyl rings, which was expected to impact the capability of the resulting complexes to reduce protons into hydrogen. Over the four nickel complexes that were obtained, the one with the thiomethyl substituent, NiSCH3, was found to overtake the catalytic performances of the parent complex NiOCH3 featuring lower overpotential values and similar maximum turnover frequencies. These results confirm the electronic effects of the ligand on HER when using thiosemicarbazone nickel complexes and support that chemical modifications can tune the catalytic performances of such systems.

Hydrogen Evolution Reactions Catalyzed by a Bis(thiosemicarbazone) Cobalt Complex: An Experimental and Theoretical Study.

The synthesis and characterization of a dinuclear bis(thiosemicarbazone) cobalt complex [Co2 L2 (NCS)2 ] is reported. This complex exhibits significant catalytic activity for hydrogen production in DMF by using triethylammonium (Et3 NHBF4 ) as the proton source. Cyclic voltammetry data allowed a maximum turnover frequency of 130 s-1 for 1 m proton concentration to be determined. The catalytic nature of the process and the production of dihydrogen were confirmed by gas analysis during controlled potential electrolysis experiments. Quantum chemical calculations show that the complex displays a ligand-assisted metal-centered reactivity and supports a catalytic mechanism involving ligand-based reduction and protonation steps followed by metal-centered processes.

2,6-Bis(bromo-meth-yl)pyridine.

In the title mol-ecule, C7H7Br2N, the C-Br vectors of the bromo-methyl groups extend to opposite sides of the pyridine ring and are oriented nearly perpendicular to its plane. In the crystal, the mol-ecules related by a c-glide-plane operation are arranged into stacks along the c axis, with centroid-centroid distances between neighboring aromatic rings of 3.778 (2) Å. A short Br⋯Br contact of 3.6025 (11) Šis observed within a pair of inversion-related mol-ecules.