Carbanions arsenic-stabilized

Whereas alkali metal phosphinomethanides have been well studied and a large number of complexes have been structurally characterized, there are apparently no reports of alkali metal complexes with arsenic-stabilized carbanions. 

It has been pointed out previously that silylation of ylides leads to stabilized products and that this is only one example of the very general phenomenon of carbanion stabilization through silicon (34, 61, 72). This effect was also found for arsenic ylides (34, 73), and is the basis for the preparation of other compounds of this series. The influence of silicon is by no means solely an electronic effect. In many cases, where alkylsilyl substituents are introduced, a steric effect may well dominate, which may reduce lattice energies for salts in transylidation reactions, preventing intermolecular contacts in decomposition processes, and rendering the formation of salt adducts unfavorable. This steric effect is reduced to a minimum, but not eliminated, if simple SiH3 groups are employed (61). Even then, however, a pronounced silicon effect is found, which must be based on electronic influences (49, 60, 61). 

Extremely efficient stabilization can be observed for dipolar ions if the atoms or groups of atoms bearing the opposite charges are in the close vicinity. Such is the case with ylides, dipolar ions in which the carbanionic center is stabilized by the positive charge located on a neighboring multiple-electron atom such as phosphorus, sulfur, arsenic, etc. (onium centers). Typical ylides are represented in the structures 37 and 38 ... 

CARBANIONS STABILIZED BY ARSENIC, GERMANIUM, TIN, ANTIMONY, LEAD AND BISMUTH 203... 

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