Trisilaallene

The first isolable trisilaallene compound was reported by Kira et al. in 2003, synthesized by reductive dehalogenation of tetrachlorosilane using potassium graphite.

Its remarkable stability is attributable to bulky substituents providing kinetic protection at the terminal silicon atoms.

[4][5] Although crystallographic analysis of the product was not successful, the formation of trisilaallene was confirmed by 1H-, 13C-, and 29Si-NMR spectroscopy, high-resolution mass spectrometry (HRMS), and reactivity study.

[1] While the bulky and electropositive silyl ( tBu2MeSi-) substituents widened the bond angle to 164.3º (calculated), no linear trisilaallene has been reported yet.

[6] The two planes that each terminal silicon atom and attached substituents lie on tend to be perpendicular to each other, which is analogous with allene.

The central silicon atom shows fluxional behavior in that its relative position varies with respect to the substituents planes, and the distribution of resultant isomers depends on the temperature.

[1][10] Larger alcohols such as isopropanol and tert-butanol did not react due to the steric congestion arising from the bulky substituents of trisilaallene.

In contrast, two methoxy groups were added to the central silicon atom of the silyl-substituted trisilaallene from the reaction with methanol.

[4] The resultant isomer, tetrakis(di-tert-butylmethylsilyl)cyclotrisilene, was calculated to be thermodynamically more stable than the parent trisilaallene compound by 10.5 kcal/mol.