Nickel carbonyl is the organonickel compound with the formula Ni(CO)4. This colorless liquid is theprincipal carbonyl of nickel. It is an intermediate in the Mond process for the purification of nickel and a reagentin organometallic chemistry. Nickel carbonyl is one of the most toxic substances encountered in nickel chemistry.

Reactions in which Ni(CO)4 works as catalyst

1. Carbonylation of alkenes and alkynes i.e. Hydrocarboxylation: carboxylic acids are the products

Alkynes also give hydrocarboxylation reaction. Product of the reaction is an alpha-beta unsaturated acid

Hydroxy carboxylation takes place at triple bond when compound has double as well as triple bonds

2. Carbonylation of Organic halides Allyl halides undergo carbonylation in the presence of Ni(CO)4 to give Beta-gamma unsaturated

carboxylic acids, pi-allyl nickel complex is the intermediate in this reaction. When alcohols are used, esters are the products

Nickel carbonyl promotes the combination and carbonylation of allyl halides and alkynes

If carbonylation reaction is carried out in an aprotic solvent the product is cyclopentenone derivativeformed by intramolecular insertion of the terminal double bond into acyl-nickel bond

Anionic Carbonyl Nickel as reagent in Organic Synthesis

Tetracarbonyl Nickel can be reduced by sodium alkoxide in THF to Nickel carbonyl anion which isgood nucleophile and displaces halide anion from vinyl, aryl and alkyl halides to form metal-carbonsigma bonds.

Halides are converted into esters

Anionic carbamoyl nickel complexes can be formed by reaction of nickel carbonyl with amines andlithium amides.

The complex derived from lithium dimethylamide has been used to convert vinyl, allyl, aryl and benzylhalides into corresponding carboxylic dimethyl amides and acyl halides into related alpha-oxo amides

Organolithium reagents convert Nickel tetracarbonyl into lithiumacylnickelates. It has found numeroussynthetic applications.