Standard Organometallic Reaction Types

1. Standard Organometallic Reaction Types • Ligand dissociation/association • Insertion/elimination • Oxidative addition/reductive elimination • s-bond metathesis • Isomerization • Nucleophilic or electrophilic attack at metal • Nucleophilic or electrophilic attack at ligand Reaction Types

2. Less Common Reaction Types • Hapticity changes • Single-electron oxidation/reduction • Bond homolysis • Electrocyclic reactions Reaction Types

3. What else is there? • Most organometallic reactions can be written in terms of series of these standard reactions. • Whether they really go like that is not always certain. • When looking for an acceptable mechanism, try to restrict yourself to the "standard steps". Reaction Types

4. Ligand dissociation/association • Electron count changes by -/+ 2 • No change in oxidation state • Dissociation easiest if ligand stable on its own (CO, olefin, phosphine, Cl-, ...) • Steric factors important Reaction Types

5. Insertion/elimination • Migratory insertion! • The ligands involved must be cis. • Electron count changes by -/+ 2 • No change in oxidation state • Olefins: 1,2-insertion, b-elimination • CO, RNC: 1,1-insertion, a-elimination Reaction Types

6. Oxidative addition/reductive elimination • Electron count changes by +/- 2(assuming the reactant was not yet coordinated) • Oxidation state changes by +/- 2 • Mechanism may be complicated Reaction Types

7. s-bond metathesis • Requires an empty site • Electron count does not change • Oxidation state does not change • Can often be viewed as an acid-base reaction Reaction Types

8. Isomerization • Movement of ligands around the metal • No change in electron count, oxidation state • Common for 3- and 5-coordinate species,less usual for 4-coordinate complexes,hardly ever for 6-coordinate octahedral complexes Reaction Types

9. Nucleophilic or electrophilic attack at metal • Nucleophilic: • requires an empty site • is basically ligand association • Electrophilic: • requires a metal-centered lone pair • no change in electron count • usually +2 in oxidation state Reaction Types

10. Nucleophilic or electrophilic attack at ligand • Nucleophilic: • requires an electron-poor ligand atom(acidic proton, coordinated C=X bond) • Electrophilic: • requires a ligand-centered electron pair(usually a lone pair, ligand p-bond, or M-C s-bond) • often reduces electron count by 2 Reaction Types

11. Hapticity changes • Often indenyl, dienes; sometimes for Cp • Changes electron count • Does not change oxidation state • Is usually a way for a systemto "make room" for another reactionor to avoid counts above 18-e Reaction Types

12. Single-electron oxidation/reduction • Changes both electron countand oxidation state by 1 • Usually by an added oxidant/reductantor electrochemically • Oxidized and reduced species typically differ widely in reactivity Reaction Types

13. Bond homolysis • Requires a weak M-C bond • Typically for: • heavier main-group metals • first-row transition metals in high oxidation states Reaction Types

14. Electrocyclic reactions • Can often be written as insertionsor oxidative additions • Most common for complexes bearing two coordinated alkenes or alkynesand in olefin metathesis • Usually change both electron count and oxidation state Reaction Types