Chapter 17. Catalytic Carbonylation

the chapter composition

1. the commercial formation of acetic acid and acetic anhydride
2. olefin hydroformylation
3. hydroamination
4. hydrocarbonylation and hydroesterification
5. carbonylation of epoxide and aziridines
6. carbonylation of organic halides
7. copolymerization of olefin and CO
8. Pauson-Khand Reaction

1. The industrial synthesis of acetic acid and acetic anhydride

acetic acid

• Monsanto's acetic acid process: [Rh(CO)₂I₂]^-
  The limitation of this process is the competitive degrade of catalyst to RhI₃ (less soluble) and [Rh(CO)₂I₃] (inactive). However, these could be rescued by water-gas shift reaction.
  The O.A. is promoted by nucleophilic attack.
• BP Cartiva's Process: [Ir(CO)₂I₂]^- and [Ru(CO)₄I₂] (promotor)
  Because the Ir belongs to third row T.M., the strong binding to ligands resulted in dramatical slow down of ligand exchange steps.
  The promoter could accelerate the ligand exchange steps, and adjust the concentration of iodine anion.

acetic anhydride

• Eastman Chemical's process: [Rh(CO)₂I₂]^-
  First coal-to-chemical facility

2. Hydroformylation of Olefin (oxo process)

linner/branched (l/b)ratio is important for this kind of reaction.

Cobalt catalyzed reaction

• HCo(CO)₄ system (from [Co(CO)₄]₂ and H₂)
  n/i = 3~4:1, the formation of alkynlcobalt complexes is reversible
• HCo(CO)₃(PR₃) system
  The usage of PR₃ ligand increase the bond strength of Co-CO, which resulted in higher n/i ratio. However, the overall yield of n-product didn't increase due to the side reactions.
  The internal alkene could be isomerized to terminal products.

HRh(PR₃)₂(CO)₂ system

has the moderate activity and high selectivity.
How to protect stereo-hindrance is the very problem to control the selectivity. The n/i ratio is related with the position of PR₃ ligands: diequitorial give higher ratio than equitorial-apical configuration.
By introducing highly polar group such as SO₃^-, the reaction could be performed in water phase.

• Bidentate ligands could affect the ratio by adjusting the natural biting angle of the ligands, which move the equilibrium of coordination configuration to diequitorial.
  The dentating PR₃ part with low electro-density prefers equitorial binding, vide versa.
• Challenges to achieve enantiomeric olefin hydroformylation:

1. substrate limitation
2. lack of binding mode
3. low reactivity
4. ligands are too far to project chirality
   Phosphine-Phosphite ligand, diazaphospholane have achieved the goal.

3. Cascade Process of catalytic carbonylation

hydroamination

= subsequent carbonylation of olefin and reductive amination

Hydrocarboxylation and Hydroesterification of alkene and alkyne

= nucleophilic attacking terminated catalytic cycle.
The hydroformylation of alkyne requires special ligand to assist the proton-transfer to alkyne, such as P(2-Pyridiyl)(Ph)₂.

carbonylation of epoxides, and aziridines

= lewis acid assisted ring-activation + carbonylation
usually the reaction processed with highly active lewis acids combined with catalysts for carbonylation: [(salen)Cr(THF)₂]⁺[Co(CO)₄]^-, or Al/Co combination.

carbonylation of organic halides

= C-X bond activation + carbonylation

Copolymerization of CO and olefin

the perfect alternation of CO and olefin is important for high quality polymers.
Pd²⁺ usually have better activity than Pd⁰.
Decrease the nucleophlicity of solvent could inhibit the termination of polymerization by nucleophlic attack.
The key to achieve perfect alternation of substrate is the energy gap of side reaction and sequence reaction.
The termination of polymerization is performed by chain-transfer and catalyst-decomposition.

• copolymerization of alpha-olefin
  2,1-insertion for styrene, and 1,2-insertion for propene.

Paul-Khand Reaction

= alkyne activation by [Co(CO)₄]₂ + olefin coordination + carbonylation