Grignard compounds directed

Benzyl chloride readily forms a Grignard compound by reaction with magnesium in ether with the concomitant formation of substantial coupling product, 1,2-diphenylethane [103-29-7]. Benzyl chloride is oxidized first to benzaldehyde [100-52-7] and then to benzoic acid. Nitric acid oxidizes directly to benzoic acid [65-85-0]. Reaction with ethylene oxide produces the benzyl chlorohydrin ether, CgH CH20CH2CH2Cl (18). Benzylphosphonic acid [10542-07-1] is formed from the reaction of benzyl chloride and triethyl phosphite followed by hydrolysis (19). 

The Grignard compounds do not react directly with the starting materials, and the results can only be explained by the formation of a silyl magnesium compound during the reaction. 

Fig. 16.11. Nickel-catalyzed arylation of Grignard compounds. The Grignard compound can be prepared via a substituent-directed peri-lithia-tion of a substituted naphthalene (see Section 5.3.1 for the analogous ortho-lithiation) and subsequent transmetalation with MgBr2 (for the method cf.

Of the other methods for preparing organosilicon compounds, the Grignard and direct methods have been selected for further consideration here. This is not to say that the Wurtz synthesis and the meta-thetical reactions of silicon tetrachloride with alkyls of zinc and mer-... 

The order of reactivity of organic halides is I > Br > Cl > F. Although organic iodides are the most reactive, they produce more Wurtz coupling products through the radical oxidative addition process. Thus, it is usually advisable to use the chlorides or bromides, except in the case of aromatic iodides and methyl iodide. 1-Alkenyl Grignard compounds are obtained by the direct reaction of magnesium and vinylic halides in THF [6], but the reaction is not completely stereospecific and the retention of the stereochemistry of haloalkenes varies from 60-90% [7]. The difficulty associated... 

In order to give the reader an extensive overview of the currenl stale of research concerning the sirttciure of Grignard compounds in solution, some methods of physical chemistry are described. In contrast to KXAI- S and LAXS, these methods do not provide direct structural information, i.e. for example ultra- and interatomic distances. In this context il is interesting to remember the different relations between physical data and structure. From the determination of energy levels with spectroscopic techniques, for example IR and NMR... 

Although crystal structure analyses cannot provide direct information about Grignard compounds in solution, they do provide ideas of which species possibly exist in solutions. In particular the LXAFS and LAXS investigations presented in Section 10.6 can only be verilied with crystal structures. Chapter 9 by K Bickelhaupt presents... 

The majority of the metallated hetero-aromatic compounds are obtained by direct metallation [1, 2, 5]. The hetero-atom effect (inductive, coordinative and polarizability influence) in most cases directs the metallation to the position a- to the hetero atom and gives rise to an easier deprotonation compared with that of benzene [1]. In some cases, bromine-lithium exchange offers the possibility of introducing the metal in a position that is not accessible by direct deprotonation. In incidental cases, Grignard compounds have been prepared from halogenated hetero aromates and magnesium. 

This rearrangement from isopropyl to n-propyl Grignard implies that any Grignard may be used to provide the intermediate subvalent titanium compound, and that addition of externally generated olefin would lead to the synthesis of organomagnesium compounds directly from olefins, without the intermediate formation of alkyl halide. 

Compared to the Grignard and direct processes, the addition method has the advantage of yielding one principal product rather than a mixture. The process is also economically attractive since olefins are low-cost materials and suitable Si—H containing compounds (trichlorosilane and methyldichlorosilane) are by-products of the direct process. The addition process is versatile but cannot, of course, be used to prepare methylchlorosilanes. It is particularly suitable for the production of silanes with organofunctional groups useful reactions of this type include the following ... 

---