Iridium Reactivity in the Methanol Carbonylation Reaction

the migratory CO insertion reaction on the iridium center, which is the rate-determining step of the iridium catalytic cycle, is accelerated by T ligand dissociation. These results tend to rationalize the seminal and inspired observations of Forster at Monsanto Co. [25]. 

The reductive elimination step has undergone much less examination, with the majority of authors considering that the acyl species produces CH3COI and regenerates the active anionic [Irl2(CO)2] species. When a DFT study was carried out by Kinnunen and Laasonen [39], the Jac,cis-[Ir(COCH3)l3(CO)2] isomer was seen to be the dominant intermediate for the anionic route, whereas for the neutral pathway the mer,ds-[lr(COCHi)l2(CO)i] isomer allowed a faster reductive elimination reaction. 

it is worthy of note that dihydrogen, which is present in the medium via the WGS reaction, can also react in its own right with the iridium species 

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