Manganese salts, transmetalation

Transmetallation of zinc organometallics with manganese(II) salts does not occur and cannot be used to produce functionalized organomanganese compounds. The reaction of unsaturated alkyl bromides furnishes, in the presence of a mixed metal-salt system composed of copper(I) chloride and manganese(Il) bromide [32], cyclization products in satisfactory yields (see Section 9.6.17 Scheme 9-55) [94]. 

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. 

The cyclohexasilane derivatives [(CO)2CpFe]—SisMen, [(CO)3PPh3Co]—SieMen, 1,3- or l,4-[(CO)2CpFe]2—SisMeio and l,4-[(CO)3PPh3Co]2-SieMem can be made quite similarly Manganese derivatives of cyclosilanes have also been prepared . An inverse salt elimination procedure, however, has to be applied in order to prevent extensive transmetallation reactions (equation 30). 

---