The Shrinking World of Innocent Ligands: Conventionaland Non‐Conventional Redox‐Active Ligands

Abstract

AbstractThis essay for EurJIC's cluster issue on cooperative and redox non‐innocent ligands introduces the reader to redox‐active ligands, which range from the small archetypical NO+/•/– and O20/•–/2–systems via the classical 1,4‐dihetero‐1,3‐diene chelates (e.g. α‐diimine, dithiolene, or o‐quinone redox series) to π‐conjugated macrocycles. The increased attention paid recently to the redox activity of ligands in coordination chemistry has now prompted wider successful searches, resulting in the establishing of less‐conventional examples such as cyanide, carbon monoxide, thioethers, or acetylacetonate derivatives as non‐innocently behaving ligands. By considering situations with significantly covalent metal–ligand bonding, the cases of metal–oxo, metal–hydrido, and organometallic compounds will also be addressed, with a perspective on how pervasive non‐innocent ligand behavior is. The materials and reactivity potential of redox‐active ligands will be pointed out.