Based on the nature of metal-carbon bond, they are classified into two types:
1. σ-bonded organometallic compounds:
These are formed by main group (s- and p-block) elements non-metallic and metalloid elements and Zn, Cd, Hg through a normal 2 electron covalant bond. Examples are: R-Mg-X, (C2H5)2 Zn, (CH3)4 Sn, (CH3)4 Si,
2. π-bonded organometallic ompounds:
These are formed mainly by transition elements.
Example : ferrocene, dibenzene chromium
3. σ and π-bonded organometallic compounds (Metal carbonyls) :
Organometallic compound which contains only carbonyl ligands are homoleptic carbonyls [Fe(CO)5], [Ni(CO)4]
Bonding in metal carbonyls- M-C bonds in metal carbonyls have both σ and π character.
σ overlap- Donation of lone pair of electrons on carbon into vacant d orbitals on metal leading to formation of metal-carbon σ bond.
π overlap- Donation of electrons from a filled metal d orbital into vacant antibonding p orbital forming metal carbon π bond.
