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. 


you can also reffer to this PDF page no. 139
PDF IN GERMAN