The reaction of [K(thf)0.33][Co(η4-cod)2] (E; cod = 1,5-cyclooctadiene) with 0.5 equiv of MgCl2 led to the isolation of the magnesium dicobalt complex Mg[Co(η4-cod)2]2 (1). Complex 1 forms a tight ionic complex in the solid state and in toluene solution due to electrostatic interactions between the Mg2+ cation and the [Co(η4-cod)2]− anions. The complex is a successful precatalyst for the hydrogenation of sterically challenging tri- and tetra-substituted alkenes, surpassing the catalytic capabilities of related alkali metal and β-diketiminate magnesium complexes.