Silole anions

The silole and germole anions have been a topic of interest for quite some time, with initial theoretical studies of the silole anion dating back to 1983.198 The following narrative provides a brief glimpse into this area. 

Compounds containing the silicon-carbon double bond have been prepared (Scheme 85) and derivatives of silabenzene and germabenzene have been characterized (Section 1.20.13). Methyllithium and n -butyllithium will alkylate the silole (126) showing the ring silicon to be the site for nucleophilic attack. The reaction is quantitative and no silole anion (127) was detected (Scheme 205) (8lJOM(2l8)C2l). 

The search in recent years for silicon compounds with multiple bonds or cyclic n-systems has renewed interest in siloles (66)77 and their mono- and di-anions (48 and 49), and led to the successful isolation of stable silole anions coordinated to various metal counter ions (Li+, Na+, K+)10a-c 78 - 86 and as complexes with ruthenium (e.g. 6a and 6b)10d. 

TABLE 7. Experimental structural and magnetic properties of silole anions and dianions and conclusions regarding their degree of aromaticity... 

Silole anion Bond length (A) <5(29Si) (ppm) S(i3C) (ppm) Aromaticity Ref. 

TT-electron delocalization stabilizes planar strnctures, but other effects such as cr-skeleton strain may cause deviation from planarity, diminishing the degree of aromaticity ". Deviation from planarity is fonnd in many silicon compounds snch as hexasUabenzene and silole anions which, according to other criteria, are believed to be aromatic (see below). 

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