Coordination 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. 

C. Diorganozinc Compounds Containing Intramolecularly Coordinating Substituents... 

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. 

In [2,6-bis(methoxymethyl)phenyl]2Mg (38), the intramolecularly coordinating substituents force the complex into a distorted octahedral coordination mode. The complex is solvent free its central magnesium atom is... 

It has been well established that the configurational stability of the tin centers in trioiganotin halides, which is usually very low, is enhanced to a considerable extent when intramolecularly coordinating substituents are present (123). The presence of a C,N-chelating ligand allows a detailed study concerning the fluxional processes that may be operative in solution. The two basic processes are (i) Sn—N dissociation/association and (ii) inversion of configuration of the tin center see Fig. 13. 

Cyclization of an organolithium tethered to a suitably positioned carbon-carbon jt-bond is a thermodynamically favorable process that proceeds in a totally regioselective exo-fashion with a high degree of stereocontrol via a transition state in which the lithium atom is intramolecularly coordinated with the remote rc-bond.9 The stereochemical outcome of the cyclization of a substituted 5-hexenyllithium follows from the preference of the substituent to occupy a pseudoequatorial position in the chair-like transition state depicted below.7... 

Compounds such as phenylacetate esters and phenylethyl ethers, which have oxygen substituents that can serve as directing groups, show high ortho. para ratios under these conditions.12 These reactions are believed to involve coordination of the N02+ at the substituent oxygen, followed by intramolecular transfer. 

The choice of tridentate amine has a critical impact on the coordination mode of the ambidentate nitrite ligand, N02.499,500 Complexes with substituted tri- and tetraamines have shown that bulky substituents may prevent the formation of the -N02 bridged polymeric complexes, and the intramolecular hydrogen network may stabilize N coordination of nitrite. 

According to the 29Si NMR spectral data (vide infra), the silicon center of 36 is assumed to be pentacoordinated due to its intramolecular interaction with both terminal amino groups attached to the substituents. This kind of two-fold coordination of the nucleophilic side arm of the 2-(dimethylaminomethyl)phenyl substituent to... 

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