title: Experimental and Theoretical Insight into Electrocatalytic Hydrogen Evolution with Nickel Bis(aryldithiolene) Complexes as Catalysts.
abstract: A series of neutral and monoanionic nickel dithiolene complexes with p-methoxyphenyl-substituted 1,2-dithiolene ligands have been prepared and characterized with physicochemical methods. Two of the complexes, the monoanion of the symmetric [Ni{S2C2(Ph-p-OCH3)2}2] (3(-)) with NBu4(+) as a counterion and the neutral asymmetric [Ni{S2C2(Ph)(Ph-p-OCH3)}2] (2), have been structurally characterized by single-crystal X-ray crystallography. All complexes have been employed as proton-reducing catalysts in N,N-dimethylformamide with trifluoroacetic acid as the proton source. The complexes are active catalysts with good faradaic yields, reaching 83% for 2 but relatively high overpotential requirements (0.91 and 1.55 V measured at the middle of the catalytic wave for two processes observed depending on the different routes of the mechanism). The similarity of the experimental data regardless of whether the neutral or anionic form of the complexes is used indicates that the neutral form acts as a precatalyst. On the basis of detailed density functional theory calculations, the proposed mechanism reveals two different main routes after protonation of the dianion of the catalyst in accordance with the experimental data, indicating the role of the concentration of the acid and the influence of the methoxy groups. Protonation at sulfur seems be more favorable than that at the metal, which is in marked contrast with the catalytic mechanism proposed for analogous cobalt dithiolene complexes.
authors.affiliation: Inorganic Chemistry Laboratory, Chemistry Department, National and Kapodistrian University of Athens , Panepistimiopolis, Zografou 157 71, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Zarkadoulas
authors.affiliation: DYNAMO/DYNAMOP, Institut de Biologie Structurale, UMR CNRS, Université Grenoble Alpes, CEA 5075, EPN Campus , 6 rue Jules Horowitz F-38000 Grenoble, France.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Field
authors.affiliation: Department of Chemistry, University of Cyprus , 1678 Nicosia, Cyprus.
authors.forename: Constantina
authors.initials: C
authors.lastname: Papatriantafyllopoulou
authors.affiliation: Laboratory of Chemistry and Biology of Metals, Université Grenoble Alpes, CNRS, CEA , 17 rue des Martyrs, F-38000 Grenoble, France.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Fize
authors.affiliation: Laboratory of Chemistry and Biology of Metals, Université Grenoble Alpes, CNRS, CEA , 17 rue des Martyrs, F-38000 Grenoble, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Artero
authors.affiliation: Inorganic Chemistry Laboratory, Chemistry Department, National and Kapodistrian University of Athens , Panepistimiopolis, Zografou 157 71, Greece.
authors.forename: Christiana A
authors.initials: CA
authors.lastname: Mitsopoulou