Organometallic reactions involve transformations at metal-carbon bonds and play a central role in catalysis, organic synthesis, and industrial processes. These reactions are governed by the interplay of metal-ligand bonding, oxidation state changes, and coordination geometry. Below is a summary of key reaction types:
Definition: Exchange of one ligand for another at a metal center.
Mechanisms:
*Associative (ASN2-like):* Incoming ligand binds first (common in 16e- complexes).
*Dissociative (D/SN1-like):* Leaving group departs first (typical for 18e- complexes).
Importance: Fundamental step in catalytic cycles.
Definition: Cleavage of an X–Y bond (e.g., H–H, C–X) by a metal, increasing its oxidation state by +2.
Mechanisms:
Concerted (3-center transition state).
SN2-like (nucleophilic attack).
Radical pathways.
Applications: C–H activation, cross-coupling.
Definition: Coupling of two ligands to form a new bond (X–Y), reducing the metal’s oxidation state by –2.
Key Points:
Requires cis arrangement of ligands.
Reverse of oxidative addition.
Role in Catalysis: Forms C–C/C–X bonds (e.g., in Pd-catalyzed couplings).
Definition: Insertion of an unsaturated ligand (CO, alkene) into an adjacent M–X bond (X = H, alkyl).
Examples:
CO insertion → acyl complexes (hydroformylation).
Olefin insertion → chain growth (polymerization).
Stereochemistry: Retention at chiral centers.
Definition: Elimination of a β-hydrogen from a metal alkyl to form a metal hydride and alkene.
Requirements:
Syn-coplanar M–Cα and Cβ–H bonds.
Vacant coordination site.
Applications: Alkene formation, catalyst regeneration.
Concept: Metal coordination activates ligands (e.g., CO, alkenes) toward nucleophiles.
Examples:
Aldehyde synthesis from metal-CO complexes.
Wacker oxidation (nucleophilic attack on coordinated ethylene).