GreatOxidative addition is one of the fundamental steps in organometallic and inorganic chemistry.
Oxidative Addition
Definition
Oxidative addition is a reaction in which a metal center increases its oxidation state and coordination number by adding fragments of a molecule that breaks apart. Essentially, the metal inserts itself into a bond (often X–Y), forming two new metal–ligand bonds.
Key Features
- Increase in Oxidation State
- The metal formally loses electrons to the newly attached ligands.
- For example, a metal in oxidation state +2 may become +4.
- Increase in Coordination Number
- Since the metal binds to two new groups, its number of attached ligands increases.
- Common Bonds Involved
- Hydrogen–hydrogen (H–H)
- Carbon–halogen (C–X)
- Hydrogen–halogen (H–X)
- Carbon–hydrogen (C–H)
Conditions Favoring Oxidative Addition
- Low oxidation state metals (electron-rich, often d⁸ or d¹⁰) are most reactive.
- Soft metals (like Pd, Pt, Rh, Ir) are especially good at this.
- Ligands that donate electron density (phosphines, carbenes) make the metal more willing to undergo oxidative addition.
Why It Matters
- It is a key step in catalytic cycles, especially in organometallic catalysis.
- Crucial in processes like:
- Cross-coupling reactions (Suzuki, Heck, Negishi, etc.)
- Hydrogenation and hydroformylation
- C–H activation chemistry
- In biology, related processes occur in metalloenzymes (e.g., activation of H₂ by hydrogenases).
In simple words: Oxidative addition is when a metal complex grabs a molecule, breaks its bond, and attaches both parts to itself — ending up more oxidized and more crowded.