Nickel(II) bis(acetylacetonate)

Nickel(II) bis(acetylacetonate) is a chemical compound with the formula Ni(C₅H₇O₂)₂. It is a coordination complex of nickel with acetylacetonate (acac), a negatively charged bidentate ligand formed by deprotonation of acetylacetone (2,4-pentanedione). This compound is of interest both in the field of coordination chemistry and for its applications in catalysis, particularly in processes involving olefin polymerization and alkene oxidation.

Structure and Properties

Nickel(II) bis(acetylacetonate) is characterized by a square planar geometry around the nickel center, typical for d⁸ metal ions such as nickel(II). The nickel atom is coordinated by two oxygen atoms from each acetylacetonate ligand. The ligands are arranged in a planar, chelating manner, which stabilizes the metal center and contributes to the compound's overall stability.

The compound is usually encountered as a green solid, which is soluble in organic solvents such as chloroform, ethanol, and diethyl ether. Its solubility in these solvents makes it useful in organic synthesis and catalytic processes that require a homogeneous catalyst.

Synthesis

Nickel(II) bis(acetylacetonate) can be synthesized by reacting nickel(II) salts, such as nickel(II) chloride, with acetylacetone in the presence of a base. The base, typically a tertiary amine like triethylamine, deprotonates the acetylacetone, forming the acac ligand, which then coordinates to the nickel ion. The reaction typically yields the nickel complex as a green precipitate:

NiCl₂ + 2 C₅H₈O₂ + 2 NEt₃ → Ni(C₅H₇O₂)₂ + 2 NEt₃HCl

Applications

Nickel(II) bis(acetylacetonate) serves as a versatile catalyst in organic synthesis. It is particularly effective in the polymerization of olefins, where it can act as a catalyst for both the oligomerization and polymerization of ethylene and other alkenes. Additionally, it has been employed in the oxidation of alkenes to ketones, an important reaction in the synthesis of fine chemicals and pharmaceutical intermediates.

Safety and Handling

As with many nickel compounds, nickel(II) bis(acetylacetonate) is considered to be potentially hazardous. It can cause allergic skin reactions and is suspected of causing cancer. Proper personal protective equipment, including gloves and eye protection, should be used when handling this compound. Additionally, operations involving this compound should be conducted in a well-ventilated area or under a fume hood to minimize exposure to dust or vapors.

See Also

• Coordination complex
• Catalysis
• Acetylacetone
• Olefin polymerization