Fig. 1: Oxidative addition reactions.

a, IUPAC definition of formal oxidation states based on division of heteronuclear bonds and assignment of electrons based on Allen electronegativity. b, Continuum of redox outcomes for addition of H2 and Zn–Zn bonds to metal (and semi-metal) centres. c, Frontier molecular orbitals and the isoelectronic relationship between H2 and Cp*ZnZnCp*.