Linear magnesium compounds

Unlike Grignard reagents, crystal structures of dicoordinated organomagnesium compounds are known. These are formed when sterically hindered ligands cause excessive crowding in the environment around the Mg atom and prevent the coordination of any solvent molecules. The X-ray structure of bis[tris(trimethylsilyl)methyl]magnesium [Compound 19] indicates that the compound is linear (C—Mg—C=180°) and is centrosymmetric around the Mg atom [21]. 

The magnesium atom of compound 62a lies on a crystallographic inversion center, and consequently the substituents are in awft-configuration. The structure of 62b shows an eclipsed conformation and leads to steric repulsion between the dicyclopropy-Imethyl groups (Figure 36). As a consequence a slight deviation from linear structure is observed. 

Metal hydroxides in combination with various silicon-containing compounds have been used to reduce the amount of additive required to achieve a required level of flame retardancy in a variety of polymeric materials, including polyolefins.62-63 Systems that have been used contain a combination of reactive silicone polymers, a linear silicone fluid or gum, and a silicone resin, which is soluble in the fluid, in addition to a metal soap, in particular magnesium stearate. However, there is little insight given into how these formulations work. 

Condensation of carbonyl compounds. This magnesium phenolate catalyzes the self-condensation of linear aliphatie aldehydes. When the reaction is conducted in HMPT, 1,3-diol monoesters (3 and 4) are formed (equation I). When the reaction is conducted in benzene, 2,3-dialkylacrylaldehydes (5) are formed, also in high yield (equation II). Magnesium ions (MgBr and Mg ) are much more effective in these reactions than Li or Na . ... 

An isolated diorganylmagnesium molecule in the gas phase usually adopts a linear structure with a central i p-hybridized magnesium atom and two negatively charged ligands at opposite positions. In practice, this situation is very difficult to achieve only a few organomagnesium compounds can be transferred into the gas phase as thermal decomposition normally precedes vaporization. In a gas-phase electron diffraction study of dineo-pentylmagnesium (Section II), a linear molecule was indeed found. 

---