◆ Ligand Dissociation and Substitution ◆ Oxidative Addition ◆ Reductive Elimination

1. (551p) Reactions involving gain or loss of ligands Ligand dissociation and substitution Oxidative addition Reductive elimination Nucleophilic displacement II. Reactions involving modification of ligands Insertion Carbonyl insertion (alkyl migration Hydride elimination Abstraction Organometallic REACTIONS ◆ Ligand Dissociation and Substitution◆ Oxidative Addition◆ Reductive Elimination 201001008 김승보

2. Classificationof Organometallic Reaction Is there an oxidation number changing on the metal?

3. Dissociative Mechanism (CO.) • Ni(CO)4 → Ni(CO)3 + CO(slow = rate limiting) • Ni(CO)3 + L → Ni(CO)3L (fast) • Ni(CO)4 + L → Ni(CO)3L + COoverall reaction rate is independent on concentration of L. • Rate = k1[Ni(CO)4]

4. Associative Mechanism- in the Ligand Substitution • Mo(CO)6 + L + (heat) → Mo(CO)5L + CO (L = phosphine) • Rate = k1[Mo(CO)6] + k2[Mo(CO)6][L] • Parallel pathwaysk1[Mo(CO)6] : DissociativeMo(CO)6 → Mo(CO)5 + CO (slow)Mo(CO)5 + L → Mo(CO)5L (fast)

5. Associative Mechanism - in the Ligand Substitution • Rate = k1[Mo(CO)6] + k2[Mo(CO)6][L] • k2[Mo(CO)6][L]: Associative Mo(CO)6 + L → [Mo(CO)6---L] (slow)[Mo(CO)6---L] → Mo(CO)5L + CO (fast)

6. Associative Mechanism • Most CO substitution reactions proceed primarily by a dissociative mechanism. • Associative Mechanism is more likely for large metals.involving highly nucleophilicligands. ≒ Association,etc. Substitution DissociationFirst +

7. Steric effects - Cone angle (553p) • θ : apex angle of a cone that encompasses the van der Waals radii of the outermost atoms of a ligand.

8. Ligand Cone Angles (554p) • Dissociation Rate increases with increasing Ligand bulk. 212

9. Cone Angle vs. Rate graph (554p)

10. OA and RE reaction • Both oxidation states and coordination number change.

11. Oxidative Addition • Lose electrons in d orbital (often 2e-) • The reaction is favored for metals that ▶ have low oxidation states ▶ electron-rich ▶ basic ▶ easily oxidized(basic metal : corrosive, easily oxidized. transition metals that located in relatively right side. Fe, Ni, Pb, Zn, etc.) • exception : [PtCl4]2− + Cl2 → [PtCl6]2− (high oxidation states)

12. Oxidative Addition • Requires vacant coordination site on metal. → common for 4, 5 coordination complex. • The most common substrates : R-X (alkyl halides), Ar-X (aryl halides), H-X.

17. Reductive Elimination • Reverse of an oxidative addition. • Two cisoidal anionic Ligands form bond, and leaves.