Silabenzyl cation

Over the last decade, the synthesis and characterization of trivalent silyl cations (silylium ions), including silatropy-lium ion 1 (Figure 1), have remained as a major challenge in organosilicon chemistry, and, therefore, was the subject of intensive studies. The earlier suggestion that silatropylium ion 1 is more stable than silabenzyl cation 2 and may... 

Recent theoretical results by Nicolaides and Radom , who employed isodesmic and isogyric reactions for an accurate determination of the heats of formation of both ions at the G2 level of theory, suggest that the silabenzyl cation 85 is more stable than the silatropylium ion 86 by approximately 40 kcalmol For the corresponding [C7,H7]+ surface, they found a reverse ordering, here the tropylium ion is 29 kcalmol more stable than the benzyl cation. These findings presumably reflect the well-documented inability of silicon to form 7r-bonds with significant strength. 

Electron impact ionization of phenylsilane has provided evidence for the silatropyhum (1) and silabenzyl (2) cations <92JA3573) the relative stabilities of the two cations have been determined by ab initio molecular orbital calculations <94JA9769>. The calculations indicated that (2) is more stable than (1) by 38 kJ mol , which is the contrary to the situation for the tropylium and benzyl cations. 

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