Cobalt comparison with iridium

Cobalt and iridium complexes can also function as hydroformylation catalysts, but of course the cobalt catalysts are much better known.t The reduced activity of Co and Ir compared to Rh has been attributed to the greater stability of their 18-electron complexes to ligand dissociatioii. The Co and Ir systems do provide some interesting comparisons with Rh, both in the behavior of the catalytic systems and in the identification of catalytic intermediates. 

The long time scale of most kinetic experiments on iridium substitution kinetics may be presumed to be the reason for the continuity paucity of references in comparison with rhodium(III) and, especially, cobalt(III). There are a few references to substitution at low-spin df" iridium(III), and two references to qualitative kinetic observations on the almost equally inert (P iridium(IV). 

Comparison of Rhodium with Cobalt and Iridium Catalysts... 

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