Hydrogenolysis: the only way that early transition metals with d0 counts can
activate H2. Lanthanides and actinides also typically use hydrogenolysis. As
with oxidative addition, the metal center needs to have an empty orbital to bind
the H2 and an anionic ligand (e.g., alkyl, halide) that can be protonated off. No
change in oxidation state of the metal.