consequently a three-centered ? complex is invoked, followed by intramolecular ligand bond cleavage of the ligand (probably by donation of electron pair into the sigma* orbital of the inter ligand bond) to form the oxidized complex. The resulting ligands will be mutually cis, although subsequent isomerization may occur.

This mechanism applies to the addition of homonuclear diatomic molecules such as H₂. Many C-H activation