# Oxidation states of boron

I have just been looking at https://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements and found that boron has a -5 oxidation state. I would like to know which boron compounds form this oxidation state.

As I remember I have read somewhere that $$\ce{Al3BC}$$ is konwn to have Boron in -5 oxidation state.