Capítulo de livro

General Considerations in the Application of Organomagnesium Compounds in Organic and Organometallic Synthesis

1995; Elsevier BV; Linguagem: Inglês

10.1016/b978-012730945-3.50004-9

Autores

B. J. Wakefield,

Tópico(s)

Chemical Synthesis and Analysis

Resumo

This chapter discusses the general considerations in the application of organomagnesium compounds in organic and organometallic synthesis. Magnesium can form one or two covalent bonds with carbon. It is convenient to formulate Grignard reagents simply as "RMgX;" the solutions obtained by the reaction of magnesium with an organic halogen compound usually contain an equilibrium mixture of a variety of species. The ratio of the species in solution varies with the organic group, the halogen, the solvent, the concentration and the temperature. A relatively simple example is "phenylmagnesium bromide." When this Grignard reagent is concentrated in diethyl ether, crystals of a monomeric dietherate are obtained, which has a simple structure. Dimethylmagnesium and diethylmagnesium are highly associated in solution, and precipitate/crystallize from diethyl ether as linear polymers. On the other hand, homologues are less highly associated in donor solvents. Some of the longer-chain alkyl derivatives are appreciably soluble in hydrocarbons; they are presumably associated, but little information on their constitution is available. In a Lewis-basic solvent such as diethyl ether, solvation of magnesium decreases its electrophilicity, but the polarization of the carbon–magnesium bond increases, thus increasing the carbanionic character of the organic ligand.

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