woelen - 7-5-2007 at 06:14
I received a very old (but never opened and still sealed) bottle of dimethylamine-borane complex, (CH3)2HN:BH3. This is a 100g bottle.
This material contains a borane group, which is bound to the nitrogen, using the lone-pair of electrons of the nitrogen to share with the empty space
on the boron atom.
I expected this compound to be an extremely reactive chemical, with such a borane-group in it.
When I opened up the bottle, I was greeted with an intense smell, resembling old piss and/or bad fish (dimethylamine), so the dimethylamine part still
is there 
. But I have some doubts about the borane part.
If I add the solid to some water, then nothing happens. The solid simply dissolves and I obtain a clear solution, with the smell of dimethylamine.
When I add acid to this solution, then still hardly anything happens. I expected a violent reaction with formation of lots of hydrogen or even
diborane, but I obtain only faint bubbling of hydrogen. After some time, and also with some shaking, more hydrogen is formed, and the hydrogen-air
mixture in the tube can be ignited, giving a loud whistling noise.
I dissolved some of the material in 1 M HNO3, and that results in slow formation of hydrogen. This solution reduces dichromate, but only slowly. It
takes a minute or so to go from the orange to a green/blue solution. When I add a silver nitrate solution to the solution, then silver metal is formed
quickly. Copper metal and nickel are not reduced.
A basic solution of dimethylamine borane has a strong smell of piss, but it does not reduce chromate.
When I add a solution of this dimethylamine-borane to a solution of copper sulfate, then a light blue precipitate (Cu(OH)2 I think) is formed, but no
reduction of copper (II), not even to copper (I) 
. Only when solid sodium hydroxide
is added, the blue precipitate is reduced to metallic spongy copper.
So, I wonder, is this material still good, or did it loose most of its reducing properties? Also, if it is good, then how vigorous a reductor should
it be? I expected a very vigorous reductor, but it is slow and surprisingly weak.
[Edited on 7-5-07 by woelen]
Eclectic - 7-5-2007 at 06:48
It's supposed to be good for electroless copper plating, such as through holes in printed circuit boards. Try it with an ammonium hydroxide solution
of copper hydroxide or carbonate?
stoichiometric_steve - 7-5-2007 at 10:47
the amine boranes are quite stable...not as vigorous in reaction as the BH3*THF adducts for instance.
turd - 7-5-2007 at 11:59
Stability of BH3<-L:
PF3 < CO < Et2O < Me2O < Me2S < C5H5N < NMe3 < H-
(cf. HSAB-theory)
There's review articles about this.