Magnesium-halogen bonds

The structures of only a very few heteroleptic monoorganomagnesium compounds with a magnesium-heteroatom bond with heteroatoms other than halogen, oxygen or nitrogen have been determined. 

II. PREPARATION OF MAGNESIUM ENOLATES A. Reductive Metal Insertion into Carbon-Halogen Bonds... 

Processes (b) and (c) are limited by diffusion and heat removal. The activation energies of these processes are low. Process (a) involves common chemical reactions and is improbable at low temperatures ( 80 K). Indeed, as already mentioned, only the most active organic halides with weakened carbon-halogen bonds react with magnesium immediately in the course of condensation. Therefore, only the aggregation and stabilization processes are actually important. Let us consider them in the light of quantum-chemical calculations. 

The reaction scheme is easy enough to draw, but what is the mechanism Overall it involves an insertion of magnesium into the new carbon-halogen bond. There is also a change in oxidation state of the magnesium, from Mg(0) to Mg(II). The reaction is therefore known as an oxidative insertion or oxidative addition, and is a general process for many metals such as Mg, Li (which we meet shortly), Cu, and Zn. 

Ab initio calculations by David [92] on the insertion of an isolated magnesium atom into the carbon halogen bond of fluoromethane and chloromethane included calculations of transition state energies, geometries, and vibrational frequencies. Both systems exhibited similar geometries for the transition state with C, symmetry (Scheme 34). 

Since magnesium becomes bonded to the same carbon that previously held halogen, the alkyl group remains intact during the preparation of the reagent. Thus /1-propyl chloride yields H-propylmagnesium chloride, and isopropyl chloride yields isopropylmagnesium chloride. 

Davis, S. R. Ab initio study of the insertion reaction of magnesium into the carbon-halogen bond of fluoro- and chloromethane. J. Am. 

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