Ligand migration reactions

The first reaction we will discuss is the ligand migration reaction, or, as it is sometimes called, the insertion reaction. This well defined elementary reaction is a step in many important reactions of organometallics, including several catalytic processes of industrial importance. For a general review see Basolo and Pearson 36), or Schrauzer 37). 

Fig. 12. Detailed MO representation of the naechanism of the ligand migration reaction. Electrons move from filled bonding orbital between M and L to empty anti-bonding orbital between M and olefin. Filled orbitals shaded...

It is not necessary to have a transition metal complex to have the ligand migration reaction. An example is the hydroboration reaction, which probably proceeds by the following sequence. 

Insertion or ligand migration reactions show a much greater sensitivity to solvent. The reaction ... 

This is the reverse of insertion in which the B-hydrogen of an alkyl group migrates to the metal atom and further strengthens the description of the elimination reaction as a ligand migration reaction. a-Elimination is also possible but is much less understood. 

The exchange reaction between deuterium of [MDL ] and the ortho hydrogen in triarylphosphines also occurs through oxidative addition. The exchange between [MHL ] and C2D4 takes place when the ligand migration reaction is possible ... 

Both primary ami secondary insertions are encountered in the cis ligand migration reactions. One is favored over the other to an extent that depends cm electronic factors (the particular transitiem metal, the nature of ligands) and cm reactiem conditions (temperature, solvent, etc.). Where electronic factors do not wholly Hreclude one cd the possible insertions, sterk factors can also play a role. 

Closely related heterobimetallic Fe-Pd and Fe-Pt complexes that are bridged by the PR2 group instead of bidentate phosphine chelates were also reported by Braunstein. " It is interesting to note that novel intramolecular metal-to-metal silyl ligand migration reaction on these phosphido-bridged Fe-Pt complexes can be effected by the... 

Many reactions of organolithium or organomagnesium compounds depend upon the migration of the alkyl or aryl group from the metal on to the adjacent ligand. Such reactions are not clearly within the scope of this chapter as the reactions are organometallic in nature and the mechanisms... 

This reaction might also be imagined to proceed by adsorption of C2H4 followed by ligand migration (an associative surface reaction). 

It should be noted that the carbene ligand migrated from W to a position bridging the Pt—Pt bond during the course of reaction (21). On the basis... 

R. B. King, and M. S. Saran, Metal Complexes with Terminal Dicyanomethylenecar-bene Ligands formed by Chlorine Migration Reactions, J. Chem. Soc., Chem. Comm. 1972, 1053-1053. 

---