Lithium magnesiate complexes

In this section, the surprisingly diverse structural chemistry of recently published lithium magnesiate complexes, containing carbon- and/or nitrogen-based anions, will be surveyed. Since 2007, several different structural motifs have been reported. In this section, these will be summarized according to the ligand sets within the lithium magnesiate framework. 

Fig. 8 Common Weiss motifs - lower-order (top left) [36], higher-order (top right) [37] and solvent-separated higher-order (bottom) [38] lithium magnesiate complexes...

Structure of the Reagent. Distinct properties of isopropylmagnesium chloride-lithium chloride complex are a result of its monomeric magnesiate-like structure, which differs from usually oligomeric organomagnesium species. This feature increases solubility and reactivity of this complex in comparison to isopropylmagnesium chloride. 

Sato and coworkers fonnd that site-selective iodine-magnesinm exchange reactions of 1,4-diiodo-l,3-alkadienes were attained only by nsing the organomagnesinm ate complex, lithium dibutylisopropyhnagnesate (Scheme 9). The magnesiated iodoalkadienes were transformed into polysnbstitnted styrenes and phenols. 

Magnesium amides can form a wide range of mixed metal amido complexes with alkali metal ions (M2[Mg(NH2)4]) (M = K, Rb or Cs).These contain tetrahedral Mg-centered [Mg(NH2)4] ions connected in three-dimensional networks by coordination of the amido groups to the group 1 metal ions. The most common hetero metal is lithium and lithium amido magnesiates are readily accessible by the addition of a lithium amide to a magnesium amide. 

The examples discussed thus far are classed as contacted ion pairs, as both distinct metals are contained within the same molecule. Since 2007, one example of a solvent-separated lithium tris(aryl) magnesiate (ie, the complex exists as distinct cationic and anionic moieties) has been reported. [Li (THF)4] [Mg(mesityl)3] , 5 (where mesityl is 2,4,6-trimethylphenyl) resembles many other trialkyl/aryl Hthium magnesiates and consists of a tetrahedraUy disposed tetra-THF-solvated lithium cation and a trigonal planar magnesium tris(aryl) anion (Fig. 5). ... 

It is yet an open question whether ate complexes simply represent a storage form of their constituents and thus ultimately mirror alkyllithium chemistiy or deploy a reactivity pattern of their own. Magnesiates are for sure infinitely more nucleophilic than any ordinary Grignard reagent. This "turbo effect" is also a characteristic of heteromagnesiates, in particular of the adducts composed of a diorganomagnesium and lithium chloride. 

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