Magnesium, bonding

What effect does the solvent have on the structure, charges and reactivity of Grignards Compare geometries, atomic charges and electrostatic potential maps of the diethyl ether complex to that of methylmagnesium chloride itself. How does solvent-magnesium bond formation affect the reactivity of the methyl group Explain. 

We saw in Section 17.5 that treatment of an aldehyde or ketone with a Grignard reagent, RMgX, yields an alcohol by nucleophilic addition of a carbon anion, or carbanion. A carbon-magnesium bond is strongly polarized, so a Grignard reagent reacts for all practical purposes as R - +MgX. 

The molecular geometry of 3 comprises a central magnesium atom pairwise linked via four two-electron three-center bonded methyl groups to the two dimethylaluminium units. The four carbon-to-magnesium bonds (2.20, 2.22, 2.19 and 2.22 A) are slightly elongated compared to the C-Mg distances observed in linear bis(neopentyl)magnesium... 

The only data omitted in this analysis are those for vinyl- (determined in THF) and cyclopentadienylmagnesium bromide. Including the data point for cyclopentadienyl in the analysis worsens the correlation. This may be caused by a difference in carbon bonding to the magnesium for cyclopentadienide compared to the other carbon-magnesium bonds. This bonding will be mentioned in a later section on magnesium sandwich compounds. 

Organomagnesium compounds undergo fast intermolecular carbon-magnesium bond exchange in solution. One such process in THF solution, (equation 14) was studied by NMR line-shape analysis ... 

Schlenk intermediates and the addition path have been made so far. However, our results seem to provide simple and realistic pathways. The Grignard addition occurs in a dimeric dichlorine-bridged form. A vicinal-magnesium bonding alkyl and C=0 interaction causes C—C bond formation via a four-center interaction as shown in Scheme 20 (polar mechanism). When the interaction is improbable owing to the steric effect, the Mg—0=C bond formation precedes the C—C bond formation and the Mg—C bond is ruptured (SET). 

Electrophilic functional groups in ortho-position to the carbon-magnesium bond allow two sequential alkylations. Starting from ort/io-iodobenzyl chloride 104, the benzannulated heterocycles 105 and 106 are obtained after the reaction with appropriate electrophiles (Scheme 8) . ... 

The reactivity of the 1,1 -diorganometallics (61) has been extensively investigated by Knochel and co-workers.9293 Since the reactivity of a carbon-lithium or a carbon-magnesium bond is considerably different from that of a carbon-zinc bond, a selective reaction of (61) with two different electrophiles is often possible. The general reaction pathways are summarized in Scheme 33. The addition of allylic zinc... 

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