User:Benjah-bmm27/degree/3/RBB
Organometallic Chemistry and Homogeneous Catalysis 1, RBB
[edit]Background
[edit]Historical use of transition metal catalysts
[edit]Sabatier-Senderens process
[edit]- CO + 3H2 → CH4 + H2O
- heterogeneous Ni catalyst
- Named for Jean-Baptiste Senderens and Paul Sabatier, who developed it in 1902
- Sabatier also famous for the closely-related Sabatier reaction
- CO + H2 → C1 - C30 alkanes and alkenes
- heterogeneous Co or Fe catalysts
Mechanistic aspects of homogeneous catalysis
[edit]Ligand effects
[edit]Electronic effects
[edit]Steric effects
[edit]Ligand association and dissociation
[edit]Migratory insertion and elimination
[edit]The catalytic cycle
[edit]Hydrogenation of alkenes
[edit]Lutetium hydride catalysis
[edit]- In 1985, Tobin J. Marks found that the organolutetium compound (Cp*2LuH)2 has a far higher turnover frequency (TOF) than transition metal catalysts
- J. Am. Chem. Soc. (1985) 107, 8111–8118.
| precatalyst | name | mol prod. / mol cat. |
|---|---|---|
| RhCl(PPh3)3 | Wilkinson's catalyst | 650 |
| [Rh(COD)(PPh3)2]+ | Osborn's catalyst | 4000 |
| [Ir(COD)(py)(PCy3)]+ | Crabtree's catalyst | 6500 |
| (Cp*2LuH)2 | ? | 120000 |
- Lu(III) is hard and very electropositive
- Does not undergo oxidative addition of H2 to form Lu(V)H2
- Lanthanide contraction makes it very hard to remove electrons from Lu(III)
- Impractical due to extreme air and moisture sensitivity...
- ...but it may be possible to get the same mechanism with titanocene catalysts
Alkene isomerisation
[edit]Alkene oxidation – the Wacker process
[edit]Alkene polymerisation
[edit]Heterogeneous catalysis
[edit]- Ziegler–Natta catalysts: TiClx / Al-R catalysis
- Phillips catalysts: CrOx on silica
Modern homogeneous catalysis
[edit]- Kaminsky catalysts: metallocene-based, e.g. zirconocenes
Co-catalyst: methylaluminoxane
[edit]Specific applications
[edit]- Ring-opening metathesis polymerisation of cyclic olefins
- Ring-closing metathesis