Osmium migratory insertion reactions

The osmium hydroxycarbene complex 18 is formed in an acid-assisted migratory-insertion reaction of OsClEt(CO)2(PPh3)2. This alkyl compound results from reaction of the ethylene adduct 19 with one equivalent of acid 46). 

The rate of migratory insertion see Migratory Insertion) reactions is usually lower for osmium complexes than for analogous ruthenium or iron complexes. In comparing CO insertion see CO Insertion) into M-C bonds, the rate of insertion depends on metal according to Ru > Fe Os or Fe > Ru Os, depending on the ligand set. ... 

Electrophilic attack at carbyne complexes may ultimately place the electrophile on either the metal or the (former) carbyne carbon, the two possibilities being related in principle by a-elimination/migratory insertion processes (Figure 5.39). The reactions of the osmium carbyne complex are suggestive of an analogy with alkynes. Each of these reactions (hydro-halogenation, chlorination, chalcogen addition, metal complexation see below) have parallels in the chemistry of alkynes. 

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