Each cyclopentadiene anion ligand possess 2e⁻ pairs in all mettallocene 6e⁻ pairs from the cyclohexadienyl anion ligands occupy the 6 lowest energy orbitals and give M- Co bonding. The 8 is highest energy orbitals are ligand like s all are empty. The 5 orbitals at the centre are almost the metal like d-orbitals which are occupied by the e⁻ from the metal of those 2 at the lower which are strongly M-Co bonding. The 2 with high energy are anti-bonding and the centre is non- bonding.
The chemical properties of mettallocene depends on the ≠ of e⁻s present in these 5 orbitals. The e⁻ present in the anti-bonding orbitals which are responsible for the reactivity of mettallocene of the these mettallocene ferrocene is least reactive. The molecule has 18 valence e⁻ ( 12 from 2- (C₅H₅) and 6 from fe²⁺) where as 9 pairs of e⁻ occupy the bonding and non-bonding orbitals. There's no e⁻ occupy the bonding and non-bonding orbitals. There's no e⁻ in anti-bonding orbitals. Hence ferrocene is stable.
( Cobaltocene and Nickelocene species are more reactive than ferrocene because Cobaltocene (19 e⁻) one e⁻ in anti-bonding orbital and Nickelocene (20e⁻s) 2 e⁻s in the anti-bonding orbital. Valence (15e⁻) d³ r²⁺ 8 chromocene (16e⁻s) d⁴ Cr²⁺ and these are e⁻ efficient. They will add addition ligands that can contribute more electrons.
Example: (C₅H₅)₂ Mo react with H₂ to form dihydride molybdenocene.
It has 1se⁻ configuration 6e⁻ from each of Co ligand, 2e⁻ from each of cp ligand, 2e⁻ from each of 2 hydride ligand and 2e⁻s from Mo³⁺ to accommodate the H⁺ ligands the cp rings are bent away from their parallel positions.
