Net Oxidative Addition of H2 to {MII}2+ (M = Pd, Pt) by Heterolysis and Protic Rebound

Electrophilic transition metal complexes like {M^II(EtXantphos)₂}²⁺ (M^II = Pd^II, Pt^II) heterolyze H₂ into a hydride-associated electrophile {H–M^II(EtXantphos)₂}⁺ and a proton, which typically associates to an added base (or basic ligand). For {H–M^II(EtXantphos)₂}⁺, the metal can be the most basic site in the system, which results in a product that is indistinguishable from oxidative addition {(H)₂M^IV(EtXantphos)₂}²⁺. By considering the kinetics and thermodynamics of each elementary step – initial heterolysis, followed by a subsequent return of the heterolyzed proton – we suggest that oxidative addition products may be underrepresented tautomers in heterolytic pathways. The gained understanding was used to characterize the first (di)hydride of Pd^IV, generated by formal oxidative addition of H₂ to Pd^II.