Magnesium organometallic compounds

From a synthetic point of view, direct alkylation of lithium and magnesium organometallic compounds has largely been supplanted by transition-metal-catalyzed processes. We will discuss these reactions in Chapter 8 of Part B. 

Alkane elimination is readily used for lithium and magnesium organometallic compounds... 

Markl, Lieb and Merz have described the carbanionic addition of lithium or magnesium organometallic compounds to the P atom of 2.4.6-triphenyl-X -phos-phorins, which form deep red s ts 143. These can be alkylated either at the P atom to form X -phosphorins 144 or at C—2 to yield 1,2-dihydro-X -phosphorins 145. Acylation with benzoylchloride affords the 1,4-dihydro-X -phosphorin derivatives 146. Addition of acids or water leads to the synthetically important intermediates 147 which can be reconverted to the X -phosphorin-salts 143 by 2 N NaOH. 

Unlike the caustic oxides and hydroxides of group 1A metals, magnesium hydroxide, Mg(OH)2, formed by the reaction of air and water with magnesium organometallic compounds, is a relatively benign substance that is used as a food additive and ingredient of milk of magnesia. 

Benzyne can also be generated from o-dihaloaromatics. Reaction of lithium amalgam or magnesium results in formation of a transient organometallic compound that decomposes with elimination of lithium halide. l-Bromo-2-fluorobenzene is the usual starting material in this procedure. 

After a vigorous initial activity, whereby new fluorinated organometallic compounds were first synthesized, much of the research effort has decreased Some activity has been concerned with the reactions of perfluoroaromatic magnesium compounds... 

Grignard reagents are a very important class of organometallic compounds. For their preparation an alkyl halide or aryl halide 5 is reacted with magnesium metal. The formation of the organometallic species takes place at the metal surface by transfer of an electron from magnesium to a halide molecule, an alkyl or aryl radical species 6 respectively is formed. Whether the intermediate radical species stays adsorbed at the metal surface (the A-modelf, or desorbs into solution (the D-model), still is in debate ... 

Many metals occur in crude oils. Some of the more abundant are sodium, calcium, magnesium, aluminium, iron, vanadium, and nickel. They are present either as inorganic salts, such as sodium and magnesium chlorides, or in the form of organometallic compounds, such as those of nickel and vanadium (as in porphyrins). Calcium and magnesium can form salts or soaps with carboxylic acids. These compounds act as emulsifiers, and their presence is undesirable. 

D. A. Shirley, The Synthesis of Ketones from Acidhalides and Organometallic Compounds of Magnesium, Zinc and Cadmium, Organic Rcaktions, Vol. VIII, 28 (1954). 

It occurs with the alkyls, aryls or acetylides of metals more electropositive than magnesium, but including Grignard reagents, and is often carried out by adding a solution of the organometallic compound in an inert solvent to a large excess of powdered, solid C02 it is a particularly useful method for the preparation of acetylenic acids. The Kolbe-Schmidt reaction (p. 291) is another example of carbanion carbonation. 

The carbonates, sulfates, nitrates, and phosphates of the group IA and IIA metals are important materials in inorganic chemistry. Some of the most important compounds of the group IA and IIA elements are organometallic compounds, particularly for lithium, sodium, and magnesium, and Chapter 12 will be devoted to this area of chemistry. 

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