Migration of the hydrocarbyl group

By using the dissymmetric diphosphine l-diphenylphosphino-2-tert-butyl-3-dicy-clohexylphosphinoprop-l-ene, van Leeuwen has demonstrated that the insertion of CO into Pd-Me proceeds via migration of the hydrocarbyl group to the CO ligand [24]. 

For the more general case, a coordinatively unsaturated intermediate of type A resulting from migration of the hydrocarbyl group may be stabilized in a number of ways . It has been pointed out that for CO insertion into the methyl-molybdenum bond of Me—Mo( -C5H5)(CO)3 [reaction (b)], which has been studied in tetrahydrofuran (THF) and in methyl-substituted THFs, the rate constant of the migratory step /ci significantly increases with the donicity of the solvent (the methyl-substituted THFs differ in donicity but have similar dielectric constants). 

Insertion of carbon monoxide and alkenes into metal-carbon bonds is one of the most important reaction steps in homogeneous catalysis. It has been found for insertion processes of platinum [16] that the relative positions of the hydrocarbyl group and the unsaturated fragment must be cis in the reacting complex [17], The second issue concerns the stereochemical course of the reaction, insertion versus migration as discussed in Chapter 2.2. 

Scheme 9 Examples for migration of hydride and hydrocarbyl groups from silicon to an N atom of the chelating ligand...

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