Bis(cyclooctadiene)nickel(0)

Bis(cyclooctadiene)nickel(0) is the organonickel compound with the formula Ni(C8H12)2, also written Ni(cod)2. It is a diamagnetic coordination complex featuring tetrahedral nickel(0) bound to the alkene groups in two 1,5-cyclooctadiene ligands. This highly air-sensitive yellow solid is a common source of Ni(0) in chemical synthesis.

Preparation and properties
The complex is prepared by reduction of anhydrous nickel(II) acetylacetonate in the presence of the diolefin:
 * Ni(acac)2 +  2 cod  +  2 AlEt3  →  Ni(cod)2  +  2 acacAlEt2  +  C2H6  +  C2H4

Ni(cod)2 is moderately soluble in several organic solvents.

If exposed to air, the solid oxidizes in a few minutes to nickel(II) oxide. As a result, this compound is generally handled in a glovebox.

Reactions
The reactivity of Ni(cod)2 has been extensively examined. One or both 1,5-cyclooctadiene ligands are readily displaced by phosphines, phosphites, bipyridine, and isocyanides.

Oxidation gives the highly reactive monocation, which can be isolated when using weakly coordinating anions:
 * Ni(cod)2 + Ag[Al(OCH(CF3)2)4]  ->  [Ni(cod)2][Al(OCH(CF3)2)4]  + Ag

Of its many catalytic reactions, Ni(cod)2 in the presence of phosphine ligands catalyzes the demethoxylation of anisoles by hydrosilanes:
 * 2 C6H5OCH3 + [(CH3)2HSi]2O  ->  2 C6H6  +  [(CH3)2(CH3O)Si]2O