Summary of the Mechanisms for Reductive Elimination

As with oxidative addition, we find several mechanisms for reductive elimination. The most common, and the one we will invoke for all the catalytic cycles discussed at the end of this chapter, is a concerted elimination. However, radical mechanisms and those involving bridging structures are possible. In all cases, the loss of a ligand or the use of electron withdrawing ligands facilitates the reactions due to the formal reduction at the metal center. 

The Sandmeyer reaction is usually covered in introductory organic chemistry in a chapter on electrophilic aromatic substitution, along with diazonium ion chemistry and the formation of diazo dyes. The Sandmeyer reaction involves the substitution on an aryl diazonium compound with Cu(l) salts, as shown to the right. The mechanism of these transformations is sketchy, but now that we know 

Let s examine the possibilities with CuCI. In HCl (typically present under the reaction conditions), cuprous chloride is in equilibrium with dichlorocuprate ion (CuCU ). This electron rich anion can transfer an electron to the dia-zonium ion (step 1), which then eliminates N2, generating phenyl radical (step 2). At this point, the mechanism is not 

There is an entire class of eliminations that occur at metal centers where a group or atom from the ligand migrates to the metal while at the same time an unsaturated system is produced (Eq. 12,34). These reactions are reminiscent of elimination reactions in organic chemistry that were covered in Chapter 11. 

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