This section will describe organometallic reactions that involve modification of unsaturated ligands. 14.2.1: Introduction to Insertion 14.2.2: CO Insertions (Alkyl Migration) 14.2.3: Migratory Insertion-1,2-Insertions Insertions of π systems into M-X bonds establish two new σ bonds in one step, in a stereocontrolled manner. As we saw in the last post, however, we should take care to distinguish these fully intramolecular migratory insertions from intermolecular attack of a nucleophile or electrophile on a coordinated π-system ligand. The reverse reaction of migratory insertion, β-elimination, is not the same as the reverse of nucleophilic or electrophilic attack on a coordinated π system. 14.2.4: β-Elimination Reactions In organic chemistry class, one learns that elimination reactions involve the cleavage of a σ bond and formation of a π bond. A nucleophilic pair of electrons (either from another bond or a lone pair) heads into a new π bond as a leaving group departs. This process is called β-elimination because the bond β to the nucleophilic pair of electrons breaks. Transition metal complexes can participate in their own version of β-elimination, and metal alkyl complexes famously do so. 14.2.5: Abstraction and Addition