AbstractMolecular oxygen as a ligand in transition metal complexes is of interest for biochemistry, and for inorganic and organometallic chemistry. Several examples of O2complexes, as well as the kinetics and mechanism of their formation are presented. The influence of other ligands on the activation of O2is discussed on the basis of a MO description of the electronic structure of the oxygen molecule and of the bonding within the metal‐oxygen complexes. Reactions of coordinated oxygen are describe