What is a metal-carbon bond?

A metal–carbon bond is a bond formed between a metal atom (often a transition metal) and a carbon atom from an organic group. It is the defining feature of organometallic compounds.

Types of Metal–Carbon Bonds

1. σ (sigma) bonds
   • The carbon atom donates a pair of electrons directly to the metal.
   • Example: In methyl lithium (CH₃Li), the C–Li bond is a σ bond.
   • Found in alkyl, aryl, and carbene complexes.
2. π (pi) bonds / π-complexes
   • The metal interacts with the π-electrons of an organic group (like alkenes, alkynes, or arenes).
   • Example: Zeise’s salt [PtCl₃(C₂H₄)]⁻ where Pt bonds with ethene.
   • Seen in complexes with alkenes, alkynes, or aromatic rings.
3. Synergic (backbonding) interactions
   • In some ligands like CO or alkenes, bonding is two-way:
     • The ligand donates electrons from C to the metal (σ donation).
     • The metal donates electrons back from its d-orbitals into the ligand’s π* orbitals (π backbonding).
   • Example: Metal carbonyls (Ni(CO)₄, Fe(CO)₅).

Importance of Metal–Carbon Bonds

• Defines organometallic chemistry – without a metal–C bond, a compound is not considered organometallic.
• Catalysis – central to many industrial and biological processes (hydrogenation, polymerization, cross-coupling, metathesis).
• Stability and reactivity – strength and type of bond affect how the complex behaves.
• Activation of molecules – allows transition metals to “hold” and transform organic molecules in reactions.

In simple terms:
A metal–carbon bond is the link between a metal and carbon in organometallic chemistry. It can be a direct σ bond (metal–alkyl, metal–aryl) or a π-type interaction (metal–alkene, metal–CO), and it’s the key to the special reactivity of organometallic compounds.