Synthesis, Structure, and Redox Reactivity of Ni Complexes Bearing a Redox and Acid–Base Non-innocent Ligand with NiII, NiIII, and NiIV Formal Oxidation States

• DOI: 10.1021/jacs.4c11751
• Publication Date: 2025-01-24T07:43:16Z
• Authors: Deepika G. Karmalkar; Hyeongtaek Lim; Mahesh Sundararajan; Yong-Min Lee; Mi Sook Seo; Dae Young Bae; Xiaoyan Lu; Britt Hedman; Keith O. Hodgson; Won-Suk Kim; Eunsung Lee; Edward I. Solomon; Shunichi Fukuzumi; Wonwoo Nam
• Keywords: Reactivity; Nickel compounds

A series of Ni complexes bearing a redox and acid-base noninnocent tetraamido macrocyclic ligand, H4-(TAML-4) {H4-(TAML-4) = 15,15-dimethyl-5,8,13,17-tetrahydro-5,8,13,17-tetraaza-dibenzo[a,g]cyclotridecene-6,7,14,16-tetraone}, with formal oxidation states NiII, NiIII, NiIV were synthesized characterized structurally spectroscopically. The X-ray crystallographic analysis the revealed square planar geometry, [Ni(TAML-4)] complex state was to be [NiIII(TAML-4•+)] NiIII ion one-electron oxidized TAML-4 TAML-4•+. radical cation TAML-4•+, supported by absorption spectroscopy density functional theory calculations. reversible interconversions between [NiII(TAML-4)]2- [NiIII(TAML-4)]- demonstrated in spectroelectrochemical measurements as well chemical reduction reactions. reactivities then investigated hydride transfer reactions using NADH analogs. Hydride from 9,10-dihydro-10-methylacridine (AcrH2) found proceed via electron (ET) AcrH2 no deuterium kinetic isotope effect (kH/kD 1.0(2)). In contrast, proceeded much more slowly concerted proton-coupled (PCET) process kH/kD 7.0(5). latter reaction, an proton transferred center respectively. mechanisms ET PCET ascribed different potentials complexes.