Structure intramolecularly coordinating substituents

It is rather surprising that only a few diorganomagnesium compounds have been reported in which intramolecular coordination of a heteroatom-containing substituent is present. The synthesis of (2-Me2NCH2C6H4)2Mg (67) was reported. It has been used in a study on the infiuence of the presence of potentially intramolecular coordinating substituents on Schlenk equilibria However, it has never been structurally characterized. 

The second structural motif, B (Figure 72), involves also a dimeric structure in which two alkoxy oxygen atoms bridge between two zinc atoms, but now an additional intramolecular coordinating substituent is present, resulting in the formation of four-coordinate zinc atoms. Most of these strucmral investigations are aimed at the elucidation of the mechanism of the enantioselective addition of organozinc compounds to aldehydes, a topic that will be discussed in Chapter 13. 

A comparable effect was also found, for example, in the case of substituted diphenylsilanes. The chemical shift of diphenylmethylchlorosilane was found to be 10.6 ppm. Introduction of a methoxymethyl substituent at the ortho position of the phenyl group was accompanied by a high-field shift of about 7 ppm leading to a chemical shift of 3.4 ppm by intramolecular coordination [2]. A decision whether the influence on the electronic structure of silicon is due to intramolecular ring formation (Scheme 3 B) or hyperconjugation (Scheme 3 C) cannot be made based on the present data. 

---