Establishing Structure–Activity Relationships in Photocatalytic Systems by Using Nickel Bis(dithiolene) Complexes as Proton Reduction Catalysts

Herein, we present an artificial photocatalytic system for H 2 evolution based on a series of proton reduction catalysts, namely [Ni{S 2 C 2 (Ph) 2 } 2 ] ( 1 ), [Ni{S 2 C 2 (Ph) 2 } 2 ](NEt 4 ) ( 1 – ), [Ni{S 2 C 2 (Ph)(Ph–OCH 3 ‐4)} 2 ] ( 2 ), [Ni{S 2 C 2 (Ph)(Ph–OCH 3 ‐4)} 2 ](NEt 4 ) ( 2 – ), [Ni{S 2 C 2 (Ph–OCH 3 ‐4) 2 } 2 ] ( 3 ) and [Ni{S 2 C 2 (Ph–OCH 3 ‐4) 2 } 2 ](NEt 4 ) ( 3 – ), [Ni(mnt) 2 ] (NBu 4 ) ( 4 – ), [Ni(mnt)(S 2 C 2 (Ph) 2 )](NBu 4 ) ( 5 – ). These complexes are different of both in charge and the substituents on dithiolene ligand and represent a group of active catalysts for the reduction of protons with high TONs. A series of Re I complexes, [ReBr(CO) 3 (bpy)], [ReCl(CO) 3 (bpy)], [Re(NCS)(CO 3 )(bpy)], [ReBr(CO) 3 (amphen)] and [ReBr(CO) 3 (pq)] were used as photosensitizers, in combination with triethanolamine as a sacrificial electron donor and acetic acid as a proton source. The differences of the ligands in the electron donating properties and reactivity are discussed in the light of the experimental data. We also present the physicochemical characterization of a previously reported heteroleptic monoanionic complex ( 5 – ), by UV/Vis spectroscopy, FTIR spectroscopy, cyclic voltammetry and single‐crystal X‐ray diffraction studies.