# Generation and Nitric Oxide Reactivity of a Cobalt(II) Superoxide Complex via Guanidine-Based Ligand Non-Innocence

## TL;DR

A new cobalt complex was created that activates oxygen and reacts with nitric oxide to nitrate its own ligand, thanks to a special guanidine-based ligand.

## Contribution

The study introduces a novel cobalt(II) complex with a redox-active guanidine-based ligand that enables O2 activation and NO reactivity without changing the cobalt oxidation state.

## Key findings

- A cobalt(II) complex forms a μ-hydroxo-bridged product via a superoxide intermediate without altering the cobalt oxidation state.
- The same reaction occurs with a zinc analogue, highlighting the ligand's role in O2 activation.
- The cobalt–superoxide intermediate reacts with nitric oxide to form a peroxynitrite intermediate that nitrates the ligand's phenyl groups.

## Abstract

A novel guanidine-based NNN pincer cobalt­(II) complex, Co1, was investigated for dioxygen (O2) activation.
Upon
reaction with O2 at room temperature, a μ-hydroxo-bridged
CoII–OH-CoII complex (Co2) was isolated as the final oxygenated product. In-depth spectroscopic
investigation revealed that the formation of Co2 occurs
via an intermediate superoxide species (Co1–O

2

•–
), by
taking advantage of the redox non-innocence behavior of the ligand
(3,3′-(pyridine-2,6-diyl)­bis­(1-methyl-N-phenylimidazolidin-2-imine)),
and therefore keeping the cobalt oxidation state unchanged at +2.
Interestingly, the zinc analogue, Zn1, was also shown
to yield a similar μ-hydroxo-bridged ZnII–OH-ZnII complex (Zn2) as the final product under the
same aerobic conditions, providing further confirmation of the ligand
influence on metal oxidation and spin states during O2 activation.
Further reactivity studies demonstrated that Co1–O

2

•–
reacts with nitric oxide (•NO) to form a CoII-peroxynitrite (Co1–O
NO2

–

) intermediate,
which performs an unprecedented intramolecular nitration of the phenyl
moieties of the ligand at the para position.