# How to decide whether diborane undergoes symmetric or asymmetric cleavage?

How does one decide whether diborane undergoes symmetric or asymmetric cleavage, given the lewis base which attacks it. Is it possible to ascertain this theoretically?

Sterics is mentioned as the reason at some places, including some answers on this site. This reasoning does work when comparing between the cleavage products when ammonia and trialkyl amine are used as bases but does not explain the symmetric products when other bases like $$\ce{CO, PF3}$$ are used as bases as proposed in this unanswered question.

Therefore, is it really possible to determine the products just based on the lewis bases theoretically? If it is then what factors need to be accounted for?

• Does this answer your question? Why is diborane cleaved symmetrically by trimethylamine but unsymmetrically by ammonia? Aug 9 at 15:39
• Nope, I've already read that, but the reasoning behind "sterics" does not answer why CO,PF3 cleave it symmetrically. I've already mentioned that in my question. Infact that is why I posted this to clarify what are the other factors that are affecting this. Aug 9 at 16:18
• CO and PF3 are good pi acceptors, NH3 not so much. Might the appropriate combinations of relatively high energy B-H bonding orbitals take notice? Aug 9 at 21:13