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
Fischer-Tropsch process[edit]
- 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]
Oxidative addition[edit]
Reductive elimination[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]
Cossee-Arlman mechanism[edit]
Alkene metathesis[edit]
Specific applications[edit]
- Ring-opening metathesis polymerisation of cyclic olefins
- Ring-closing metathesis