Redox Series of Cyclometalated Nickel Complexes [Ni((R)Ph(R′)bpy)Br]+/0/–/2– (H–(R)Ph(R′)bpy = Substituted 6‑Phenyl-2,2′-bipyridine)
journal contributionposted on 14.09.2018, 13:21 by Aaron Sandleben, Nicolas Vogt, Gerald Hörner, Axel Klein
New organonickel complexes [Ni((R)Ph(R′)bpy)Br] carrying various substituted derivatives of the tridentate –C∧N∧N ligand 6-(phenyl-2-ide)-2,2′-bipyridine (−Phbpy) were synthesized from the precursor [Ni(COD)2] (COD = 1,5-cyclooctadiene) and the protoligands (ligand precursors) Br–(R)Ph(R′)bpy. Several synthetic routes for the protoligands were studied and compared. All new compounds have been analyzed and spectroscopically characterized. From several complexes crystal and molecular structures were obtained from XRD experiments. UV–vis absorption spectroscopy and detailed electrochemical measurements reveal the impact of the various substituents on the electronic structure of the complexes. Quantum chemical DFT calculations illustrate the composition of highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) and support the assignment of the single-electron reduction and oxidation products as bpy-localized ligand radical species and transient nickel(III) intermediates, respectively.