Non-innocent ligand

The simplest case of a suspect ligand is NO..."[2] Conventionally, redox reactions of coordination complexes are assumed to be metal-centered.

Redox non-innocent behavior of ligands is illustrated by nickel bis(stilbenedithiolate) ([Ni(S2C2Ph2)2]z).

The charge-neutral complex (z =0), showing a partial singlet diradical character,[4] is therefore better described as a Ni2+ derivative of the radical anion S2C2Ph2•−.

The diamagnetism of this complex arises from anti-ferromagnetic coupling between the unpaired electrons of the two ligand radicals.

In the enzymes chloroperoxidase and cytochrome P450, the porphyrin ligand sustains oxidation during the catalytic cycle, notably in the formation of Compound I.

The catalytic cycle of galactose oxidase (GOase) illustrates the involvement of non-innocent ligands.

Anti-ferromagnetic coupling between the unpaired spins of the tyrosine radical ligand and the d9 CuII center gives rise to the diamagnetic ground state, consistent with synthetic models.

Oxygen rebound mechanism utilized by cytochrome P450 for conversion of hydrocarbons to alcohols via the action of "compound I", an iron(IV) oxide bound to a radical heme, which is non-innocent.