# What is an easy way to reduce a boronic acid to borane?

I have a selection of boronic acids that I want to reduce to borane forms. Some of the boronic acids in question are phenylboronic acid (C6H5B(OH)2), tolylboronic acid (C7H7B(OH)2), and p-phenylenediborinic acid (C6H4(B(OH)2)2). I want to convert them into phenylborane (C6H5BH2), tolylborane (C7H7BH2), and p-phenylenediborane (C6H4(BH2)2).

I think I can do this by dissolving the boronic acid in ether and adding Lithium Aluminum Hydride (LAH). Giving a reaction that looks something like:

However, I am afraid that, given how aggressive a reducing agent LAH is I might get something like:

So I guess I have two questions:

• Will LAH attack the boron-carbon bond shown in the second reaction diagram?
• Can the reduction of the boronic acid be accomplished via a less aggressive reducing agent, perhaps Sodium BoroHydride?

Just a note: I am well aware that the boranes produced will be oxygen sensitive, either converting back to boric acid on exposure to oxygen, or catching fire.

• There are quite a lot of reducing agents out there. $\ce{DIBAL-H}$ is one of them. $\ce{Sn + HCl}$ is yet another. So is $\ce{NaBH4}$. So many out there. – Pritt Balagopal May 15 '17 at 15:11
• I know there are a lot out there, but are they strong enough to reduce boronic acids? As I said in one of my questions: Can the reduction be accomplished with something less aggressive than LAH, like NaBH4. – James Matta May 15 '17 at 15:22
• @PrittBalagopal Just because reducing agents exist doesn't mean they will be able to affect a particular transformation – orthocresol May 15 '17 at 19:05