Reductive Elimination

Reductive elimination is the reverse of oxidative addition. The metal will gain electrons, reducing the oxidation state. The coordination number will increase as substituents are added. The two ligands being added must be cis to the metal center. If the ligands are trans, they will be rearranged through isomerization.

Reduction occurs when electrons are gained. In organic chemistry, this happens when there is a decrease in C-O, C-X, and C-N bonds, and an increase in C-H bonds.

Importance

• Reductive elimination can be used to form C-C and C-X bonds, which is extremely important in pharmaceuticals, green chemistry, and industry.
• Reductive Elimination is selective and reactions typically have a high yield. This is important to drug design and pharmaceutical companies that need high yields of their reactions to reduce costs. 
• It is an important step that is used in many reactions such as cross-coupling, C-H activation, carbonylation, and hydroformylation.

Mechanism

Factors that Affect Elimination

• Oxidation state - d⁸ and d¹⁰ metals such as Rh(III), Pt(IV), and Pd(II) favor elimination
• Ligand Effects - Bigger ligands will increase the rate of elimination. Electron-rich ligands weaken metal-substituent bonds to advance elimination.
• Sterics - Ligands must be cis. If trans, isomerization will need to occur.

Examples