Negative oxidation states of Si

According to *[List of oxidation states of the elements](https://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements)*, silicon has a possible oxidation state of $-4$.


[![Enter image description here](https://i.stack.imgur.com/xpktm.jpg)](https://i.stack.imgur.com/xpktm.jpg)


Now, I've been looking everywhere for a compound that contains Si(-IV), but I cannot find any definitive references. Perhaps one of the synthetic carbonyls of silicon has this OS? I've seen references to $\ce{[Mo(CO)\_4]^{-4}}$ and $\ce{[W(CO)\_4]^{-4}}$ in my research, but silicon never shows up.


I am also uncertain as to how these carbonyls come together, and whether or not they actually complex in the same way for metalloids as for the transition metals.




I am not sure if Silane ($\ce{SiH\_4}$) can really be considered. 


But there are [silicides](http://www.wikiwand.com/en/Silicide) which silicon forms with strongly electropositive metals. In these compounds, silicon has a negative oxidation state.


For [magnesium silicide](http://www.wikiwand.com/en/Magnesium_silicide) - $\ce{Mg\_2Si}$, the oxidation state of silicon would be -4.


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Silane can not be considered as one of these. This is mainly because the electronegativities of silicon and hydrogen are 1.8 and 2.1 respectively. 


$\ce{Si^{-4}}$ compounds include compounds of the form $\ce{SiM2}$ where $\ce{M}$ is a group 2 metal as $-4 + 2\cdot 2 = 0$. Examples of these include magnesium silicide $(\ce{Mg2Si})$, dicalcium silicide $(\ce{Ca2Si})$ and distrontium silicide $(\ce{Sr2Si})$!


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