Carbon-halogen bonds reductive metal insertion

II. REDUCTIVE METAL INSERTION INTO CARBON-HALOGEN BONDS... 

A. Reductive Metal Insertion into Carbon-Halogen Bonds. 438... 

In certain instances (Ir, Pt, Au), the carbon-transition-metal-mercury complexes are actually isolable. They also decompose in the manner indicated. When organomercury halides are employed in such reactions, similar oxidation-reduction processes occur, but evidence suggests that the transition metal inserts primarily into the mercury-halogen bond followed by loss of mercury " ... 

In the nickel(ll)-catalyzed NHK reaction, the first step is the reduction of Ni " to Ni that inserts into the halogen-carbon bond via an oxidative addition. The organonickel species transmetallates with Cr " to form the organochromium(lll) nucleophile, which then reacts with the carbonyl compound. To make the process environmentally benign, a chromium-catalyzed version was developed where a chlorosilane was used as an additive to silylate the chromium alkoxide species in order to release the metal salt from the product. The released Cr " is reduced to Cr " with manganese powder. 

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