Diborane is the correct chemical. You're looking at the manufacture of diborane, not the combustion of it. The combustion of diborane is very exothermic and is what the government wanted to use back in the 50s and 60s. The problems with it were:
1. Diborane extremely toxic--more than HCN (hydrogen cyanide--the stuff they use to kill inmates in the gas chamber).
2. It explodes on contact with oxygen and has wide lower and upper explosive limits in air, making it very dangerous to work with.
3. It is pyrophoric--meaning it bursts into flame on contact with moisture in the air.
4. When it burns, it leaves behind solid boic acid and other oxides of boron, which clog the rocket nozzle.
To affect complete combusion the military tried adding fluorine to diborane to oxidize it all the way so no solids were formed, but this did not work well, and the project was abandoned. For many years afterword, boranes of all types were easy to get as surplus, but are no longer easy to come by.
I did a lot of work with diborane as an undergrad and have seen the beautiful (and scary) green flame that comes from the combustion of diborane. It is the second most energetic fuel by weight (after hydrogen) and was sought to be exploited by the government because of this.
As for making it, I won't detail that here because of the dangers involved and also because you probably can't get the chemicals. If you can and you really need to make this stuff for legit research purposes, then you'll know where to look up how to make it (not that hard to do).
I do like the amatuer rocket and pyro scene, but diborane is not for the faint of heart. That stuff will take you out. We used to call it 'death chemistry' only half-jokingly.
For some great stories about the government's rocket program, look up a book called "The Green Flame". It's written by a guy who used to work in the chemical industry producing boranes in the 1950's and is an incredible read. I think it's OOP, but you might still be able to find it in certain places.
Let me know if you want some more info on the amatuer rocketry stuff.