CO insertion into late transition metal alkyls

3 CO insertion into late transition metal alkyls 

Most known processes utilizing carbon monoxide are catalyzed by late transition metal complexes. This is due to the ease of oxidative addition of substrates such as organic halides to low valent transition metal complexes and reductive 

In the chemistry of group 8 and 9 metal complexes, consideration of octahedral complexes is required, whereas with group 10 metal complexes, particularly in Pd(II) complexes with tertiary phosphine ligands, the reactions proceed mostly under the constraint of square planar geometry with possible involvement of unstable five coordinate species. Thus mechanistic considerations of the reaction courses are somewhat simpler. 

The mechanism of the methyl migration to the adjacent CO ligand giving the T-shaped acetylpalladium species is in agreement with the result of theoretical calculation [3 lb,43]. 

Although the CO insertion proceeds by the alkyl migration mechanism, especially for the group 10 transition metal alkyls, the acyl complex may undergo the subsequent isomerization, depending on the nature of the ligand situated at the site trans to the acyl ligand. The presence of the rapid equilibrium makes the clear-cut determination of the mechanism a difficult matter. 

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