A Density Functional Theory Approach to Migratory Insertion of Carbon Monoxide

A Static and Dynamic Density Functional Theory Study of Methanol Carbonylation

Minserk Cheong, Rochus Schmid and Tom Ziegler

Department of Chemistry, University of Calgary, 2500 University Drive, N.W., Calgary, Alberta, Canada T2N 1N4

Quantum mechanical calculations based on density functional theory (DFT) were carried out in order to investigate the reaction mechanism for the carbonylation of methanol to acetic acid by [M(CO)₂I₂]^- (M = Rh,Ir). The study included the initial oxidative addition of CH3I to [M(CO)₂I₂]^- :

[M(CO)₂I₂]^- + CH3I Æ [M(CO)2I3(CH3)]- (1),

as well as the migratory insertion of CO into the M-CH3 bond:

[M(CO)2I3(CH3)]- Æ [M(CO)I3(COCH3)]- (2) .

Considerations were also given to migratory insertion processes where the I--ligand trans to methyl was replaced by another ligand L ( where L= MeOH, MeC(O)OH, CO, P(OMe)₃ and SnI₃^- ) or an empty coordination site. The calculated free energies of activation and heat of reactions are in good agreement with the experimental data. A full analysis is provided of how ligands trans and cis to the migrating methyl group influence the barrier of migratory insertion.