Stabilisation of anions by silicon In my lecture notes it was stated that in $\ce{Me3SiCH2SMe}$, deprotonation with tBuLi generates an anion in between Si and S. I've been not able to find the $\mathrm pK_\mathrm a$ values (not listed in Reich nor Evans).  

Since Si is electropositive it should actively destabilise the anion, meaning that I'd expect to see terminal methyl group deprotonated. 

No additional detail about conditions was given, but since it was tBuLi I presume low temperature (kinetic deprotonation). 

Is there a reason why this deprotonation takes place? Are the $\mathrm pK_\mathrm a$ values relatively different?
3rd period heteroatoms can stabilize adjacent carbanions charges via hyperconjugation.



Consider ylides used for Corey,-Chaykovsky, Peterson, and Wittig olefinations. Granted those have formally positive sulfur, silicon, and phosphorus, but you will not see similar easy deprotonation with tetraalkylammonium for example.

The reactions of silicon-stabilized carbanions are described more fully in Clayden 1st ed., pp 1304–5 (this material seems to have been cut from the 2nd edition).