Concerning the Properties of Silenes

The silicon-carbon double bond has attracted the attention of theoretical chemists who have now performed a large number of high quality calculations on various properties of siienes. It is gratifying to observe that there is close agreement between experiment and calculation in most properties investigated, as summarized below. 

The tt Bond Strength of Siienes and Their Singlet-Triplet Energy Levels 

A large number of calculations have been done to determine the vibrational frequencies of some simple silenes. The parent silene and its deuterated analogs have been investigated (4,9,188) as well as 1,1-dimethylsilene, its deuterated derivatives (38,181), and 1,1-dichlorosilene (4). For the undeuterated compounds a Si=C stretching vibration of approximately 1000 cm-1 was calculated. Deuteration usually results in a decrease of this value. 

An interesting conclusion that Apeloig and Kami have made, based on additional calculations, is that the effects of substituents on the Si=C bond length are approximately additive. Thus, they are able to predict the 

Apeloig and Kami (13) have also studied the effects of substituents on the reactivity of silenes by the frontier molecular orbital (FMO) approach. They have concluded that, concerning electronic factors, the polarity of the carbon-silicon double bond, and thus the coefficients of the frontier orbitals, play a more important role than the energies of these orbitals in controlling the reactivity of silenes. 

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