Silyl anions pyramidal inversion

A variety of other silyl anions has been studied. Hopkinson and Lien, using a dz basis set, found that the potentially conjugated NCSiH2, 0=CHSiHj and HC=CSiH2 anions314,352 are pyramidal at silicon and have substantial barriers to inversion (35.2, 19.9 and 34.3 kcalmol-1, respectively)314. This indicates that contributions... 

As a freely ionic, monomeric species, the silyl anion may undergo pyramidal inversion about the silicon center (equation 1). For the parent system H3Si , Nimlos and Ellison have obtained quantitative information about the inversion barrier from the photoelectron spectrum in the gas phase2. The photoelectron spectrum could be simulated by a model of the vibrational frequency as a linear oscillator perturbed by a Gaussian barrier. The out-of-plane angle (the deviation of one H from the plane defined by Si and the other two Hs) was found to be 32 2° and the barrier to inversion 9000 2000 cm 1 (26 6 kcal mol-1). This is the only experimental measurement to date of the barrier to inversion about trivalent, negative silicon. The anion was produced by reaction of silane (SiH4) with ammonia, and the photoelectron spectrum of the m/z 31 peak was then recorded. 

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