The insertion of 1,1-diphenylethylene into the Mg-Mg bond of two magnesium(I) dimers, [((Ar)Nacnac)Mg-](2) (Ar = C6H2Me3-2,4,6 (Mes); C6H3Et2-2,6 (Dep)), yielding 1,2-dimagnesioethane products, [{((Ar)Nacnac)Mg}(2)(mu-CH2CPh2)], is described. These reactions are readily reversible at room temperature and thus represent the first examples of room-temperature reversible redox processes for s-block metal complexes. The 1,2-dimagnesioethane products are highly activated magnesium alkyls and Show unprecedented, uncatalyted reactivity toward H-2, CO, and ethylene. Computational studies have investigated the mechanisms of all presented reaction types.