Cp2Fe

Cp2Fe, also known as ferrocene, is an organometallic compound with the formula Fe(C5H5)2. It consists of a central iron atom sandwiched between two parallel cyclopentadienyl rings in an η5 coordination. The molecule is a classic example of a metallocene and is typically described as an 18-electron, Fe(II) complex. At room temperature the rings rotate rapidly about the Fe–Cp axis, making the molecule fluxional and giving rise to an average symmetry different from the instantaneous structure.

In terms of bonding, each cyclopentadienyl ring acts as a five-point, six-electron donor to iron, and together they stabilize iron in a formal +2 oxidation state. The compound is diamagnetic and exhibits the characteristic stability and inertness of well-known metallocenes. Ferrocene is soluble in nonpolar organic solvents and is relatively air-stable, attributes that contributed to its widespread use as a synthetic building block and as a standard reference material in electrochemistry.

Preparation of ferrocene typically involves the reaction of sodium cyclopentadienide with iron(II) salts (for example, iron(II) chloride) in an inert solvent such as THF, producing Fe(C5H5)2. Variants and derivatives of ferrocene are important in organometallic chemistry, serving as ligands, precursors to substituted metallocenes, and components in materials science and medicinal chemistry.

Historical significance and applications: ferrocene's discovery in the early 1950s and its subsequent structural elucidation sparked rapid growth in organometallic chemistry. The work led to the 1973 Nobel Prize in Chemistry awarded to Geoffrey Wilkinson and Ernst Otto Fischer for advances in organometallic compounds and metallocene chemistry.