Dinuclear Nickel Complexes in Five States of Oxidation Using a Redox-Active Ligand

Redox-active
nitrogen donor ligands have exhibited broad utility in stabilizing
transition metal complexes in unusual formal oxidation states and
enabling multielectron redox reactions. In this report, we extend
these principles to dinuclear complexes using a naphthyridine–diimine
(NDI) framework. Treatment of (i‑PrNDI) with Ni­(COD)2 (2.0 equiv) yields a Ni­(I)–Ni­(I)
complex in which the two metal centers form a single bond and the
(i‑PrNDI) ligand is doubly reduced.
A homologous series of (i‑PrNDI)­Ni2 complexes in five oxidation states were synthesized and structurally
characterized. Across this series, the ligand ranges from a neutral
state in the most oxidized member to a dianionic state in the most
reduced. The interplay between metal- and ligand-centered redox activity
is interrogated using a variety of experimental techniques in combination
with density functional theory models.