Nickelocene

Nickelocene, Ni(C5H5)2, is an organometallic compound classified as a metallocene. It consists of a nickel atom sandwiched between two cyclopentadienyl rings bound in η5 fashion, forming a stable, symmetric two-ligand structure. Nickelocene is the nickel analogue of ferrocene and is a widely studied example in metallocene chemistry.

Structure and bonding: The molecule features two Cp rings bound parallel to each other with the nickel center in the middle. The Cp rings can adopt staggered arrangements in the solid state; Ni–Cp contacts are typical of η5-Cp coordination. The compound is best described as a two-ligand sandwich complex.

Synthesis: Nickelocene is prepared under inert atmosphere by reaction of a nickel(II) salt with cyclopentadienide sources, such as sodium cyclopentadienide (NaCp). The reaction mixture is worked up and the product is isolated by purification techniques under exclusion of air.

Properties and handling: Nickelocene is typically moisture- and air-sensitive and decomposes upon exposure to air. It is soluble in nonpolar organic solvents and is used as a reagent and precursor in organometallic synthesis.

Applications: As a representative metallocene, nickelocene serves as a model system for bonding in organometallic chemistry and as a precursor to other nickel complexes and catalysts. See also related metallocenes such as ferrocene and more broadly the class of organonickel compounds.