Silyl anions, theoretical studies

Optimization of geometry for some silylenium cations was made (22,24). Such calculations predict that silylenium ions will adopt a planar structure in contrast to silyl anions, which are predicted to be pyramidal. It should be noted that theoretical studies also indicate a high ability of silicon to accommodate negative charge. The parent silyl anion H3Si was calculated to be more stable than its carbon analog by about 50 kcal/mol (24). This implies a remarkable affinity of silylenium ions toward electron-rich species. 

The use of the silyl anion derivative (CH30)n (CH3)3 Si Na+ [100] in the role of an active centre is as yet only possibility. The usefulness of theoretical studies of some centres of this kind, for example of those formed during phos-phazene polymerization (see Chap. 2, Sect. 1.1), should increase with time. 

In contrast to triorganosilyl anions, functionalized silyl anions have been studied less extensively. Functional groups reported so far are hydrogen, chlorine, amino, alkoxy, and carbonyl groups. In addition to these species, silacyclopentadienide anions are also described in this section. Theoretical studies on the effect of functional groups are described in Section... 

Antoniotti, P., Canepa, C., Tonachini, G. Theoretical studies on Wittig-type anionic migrations of alkyl, silyl and germyl groups. Trends in Organic Chemistry i095, 5, 189-201. 

---