Types of organomagnesium compound

Magnesium can form one or two covalent bonds to carbon. In the former case, the other valency is available to form bonds to a variety of other groups. (For a discussion of coordination to Mg(n), see Section 2.1.2.) Some of the resulting types of organomagnesium(n) compounds are listed in Table 2.1. Of these compounds, only the chlorides, bromides and iodides, and to a lesser extent the dialkylmagnesium compounds, are widely used in synthesis, and almost all the examples described in this book involve these classes. (Some of the others may be important as intermediates in certain reactions see, for example. Section 6.1.) Accounts of the chemistry of the other classes of compounds may be found in General Ref. [D] and in Refs [1] and [2] other references are given in Table 2.1. 

In addition to the types of compounds listed in Table 2.1, cyclopentadienyl compounds and ate complexes should be noted.  

Di(cyclopentadienyl)magnesium (magnesocene) is easily prepared (see p. 48) and is a valuable starting material for the preparation of cyclopentadienyl derivatives of other metals (see Chapter 15). 

Nature of X Common name Chemical Abstracts name  

NR R Alkylmagnesium dialkylamide Alkyl(dialkylamino)magnesium or alky](A, A- dialkylaminato)magnesium 

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The stereochemistry of addition of organomagnesium compounds to ketones is governed by similar factors to those influencing their addition to aldehydes (see Section 6.1.1). For addition of achiral organomagnesium compounds to a-chiral ketones, steric approach control is commonly observed, but chelation control may also operate [63, 64], It is noteworthy that a pioneering asymmetric synthesis — one of the first which could be regarded as virtually stereospecific, was of this type [65] ... 

Understanding of chemical bonding is needed to understand which bond types are possible and to draw relations to the physical behavior of organomagnesium compounds. Comparison with other main group metals, especially lithium, is of interest. 

The variation in solvents that are available for synthesis with the aid of organomagnesium compounds is rather limited most of the research in this field is done in ethereal solvents, such as diethyl ether, di-n-butyl ether, tetrahydrofuran, furan, anisole, and 1,2-dimethoxyethane. Some amines, such as triethylamine, dimethylaniline, and a few others of that type, have also been applied. 

While a still-growing number of the heteroleptic derivatives [(Ar)CaX(solv) ] was reported during the last decade, the chemistry of the related homoleptic diarylcalcium derivatives is still underdeveloped and only a few well-characterized examples are known. In ethereal solutions these two types of species are connected by an equilibrium resembling the Schlenk equilibrium of organomagnesium compounds. A simplified version is shown in Scheme 8, indicating that the diorganyl species should be accessible if the appropriate conditions are found to shift the equilibrium to the right. 

Grignard reagent (Section 14.4) An organomagnesium compound of the type RMgX formed by the reaction of magnesium with an alkyl or aryl halide. 

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