Electrochemical Behavior of Ni(II) Complexes with N2S2 and N6 Ligands as Potential Catalysts in Hydrogen Evolution Reaction

In this work, two Ni(II) complexes with the tetradentate ligand N2S2 (pdto=1,8-bis(2-pyridyl)-3,6-dithioctane,) and the hexa-dentate ligand N6 (bdahp= 2,9-bis-(2',5'-diazahexanyl)-1,10-phenan-throline) were prepared in order to explore its electrochemical behavior, that indicate their potential use as molecular catalysts for the hydrogen evolution reaction. The Ni(II)-pdto complex presented two consecutive one electron transfer [Ni(II)-(pdto)] + 1e- [Ni(I)-(pdto)] and [Ni(I)-(pdto)] + 1 e- - Ni(0) + pdto. On the other hand the Ni(II)-bdahp complex presented the electrochemical reduction Ni(II)-(bdahp) + 1e- Ni(I)-(bdahp) followed by a coupled chemical reaction in an ECi mechanism, where a de-coordination of the diiminic moiety of the bdahp ligand was proposed. It was demonstrated that the pdto ligand promotes reduction over Ni(II) at less negative reduction potential in comparison when the ligand bdahp is presented.