16 - Organomagnesium Compounds in the Synthesis of Other Organometallic Compounds

Abstract

This chapter discusses the application of organomagnesium compounds in the synthesis of other organometallic compounds. The reaction of an organomagnesium compound with a derivative, usually the halide of a less electropositive metal, is a very important general method for the synthesis of organometallic compounds. In many cases either an organomagnesium compound or the corresponding organolithium compound gives equally satisfactory results. In general, organomagnesium compounds are less reactive than organolithium compounds, but they are also less basic and poorer single electron reducing agents, and so less prone to side reactions arising from these properties. In cases where the organomagnesium compounds themselves are too “hard”, organozinc or organoaluminum compounds may be preferable. Occasionally the presence of the halide in a Grignard reagent may cause complications, but these can be avoided by the use of the corresponding dialkylmagnesium compound. Organomagnesium compounds show a lesser tendency than organolithium compounds to form the cationic part of ‘ate complexes. Indeed, even with aluminum the complexes are probably better regarded as mixed aggregates, for example Mg2AI2(CH3)8 and the volatile complexes [(n-C4H9)2MgAI(OR)3]2. It should be noted that magnesium can also participate in the “anionic” part of ‘ate complexes.