Oxidative Coupling and Reductive Fragmentation

In oxidative coupling, Eq. 6.26, a metal couples two alkenes to give a metalacycle or two alkynes to give a metallole. Even CO and CN 

Alkynes undergo the reaction more easily than do alkenes unless activated by the substituents or by strain. C2F4 undergoes the reaction easily because F prefers the sp C-F of the product where the high electronegativity of F is better satisfied by the less electronegative sp carbon and repulsion between the F lone pairs and the C=C pi bond is relieved. 

Oxidative addition needs a metal that can undergo a 2e oxidation and a 2e (4e ionic model) change in electron count. 

Many mechanisms are seen (Table 6.3) concerted (Section 6.2), Sn2 (Section 6.3), radical (Section 6.4), and ionic (Section 6.5). Reductive elimination goes by the reverse of these mechanisms (Section 6.6). 

Sigma bond metathesis is an alternative pathway to oxidative addition followed by reductive elimination (Section 6.7). 

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