Group 14 elements silyl anions

The most fundamental issues of the structures of heavier group 14 element-centered anionic derivatives R3EM (R = alkyl, aryl, silyl E = Si, Ge, Sn, Pb M = alkali or alkaline earth metals) turned out to be the questions of their aggregation states (monomeric, dimeric, or oligomeric), nature of the E-M bond (covalent or ionic), and configuration of the anionic centers E (tetrahedral, pyramidal, or planar). The most important experimental techniques that are widely used to clarify these questions are NMR spectroscopy and X-ray diffraction analysis. 

In this chapter, we have tried to emphasize general aspects of main-group chemical bonding, with particular emphasis on periodic trends. The periodic table remains the most important classification tool in chemistry, and it is crucial to understand even subtle secondary periodicities if one is to make efficient use of the various elements for different chemical applications. The radial nodal structure of the valence orbitals has been pointed out to account for more of the known trends than most practitioners of chemistry are aware of. For example, the inversion barriers of phosphines or silyl anions, the dependence of the inert-pair effect on the electronegativity of the substituents, the stability of carbene- or carbyne-type species or of multiple bonds between heavy main-group elements are aU intricately linked to hybridization defects of s- and p-valence orbitals of disparate sizes. Even the question of hypervalency is closely connected to the effects of primogenic repulsion . 

The tricoordinate radicals of the heavier group 14 elements can be generated in one of the following ways (1) by the photolysis or thermolysis of the corresponding hydrides R3EH (E = heavier group 14 element) in the presence of the radical initiators, (2) by the y-irradiation of R4E or photolysis of RsE-Hg-ERs, or (3) by the thermolysis or photolysis of either R3E-ER3 or R3E-ER2-ER3 (4), (4) one-electron reduction of silicon cation (5), (5) one-electron oxidation of silyl anion (6), as well as by (6) one-electron reduction of alkylhalogenide (7). 

---