Natural Science Forum / Chemistry / Organic Synthesis / September 2006

That will depend on what reaction you're trying to do--i.e., what do you
mean by "activity".  Will partially-oxidized boranes like H2B(OH).THF or
HB(OH)2.THF do the reaction (i.e., be active), or will only BH3.THF do it?

Here's what I would try, in order of decreasing simplicity (depending on the
cost/availability of broadband NMR time:

1)  11B NMR of the solution, neat or diluted (neat may overcome the dynamic
range of your NMR, but if not, it doesn't introduce the complications of
possible reactive solvent impurities like O2.  Gated decoupling for NOE
suppression so you can quantitate the BH3.THF present (and maybe look for
other BH or BH2 species by either known chemical shifts or B-H coupling
patterns).

2)  Use a related reaction, with a simple, inexpensive model substrate, then
assay the product by GC, GC/MS, NMR, etc. for the expected product.

Eric Lucas

Oops, to add to my other post....

If you dilute the solution to run NMR (for example, to provide D as a lock),
make sure to use an unreactive solvent like C6D6--obviously don't use CDCl3.

Also, the following is from the Aldrich website.  This measures all 3
B-Hs--do all three B-Hs react in the reaction for which you want to use the
BH3.THF?  Do all remaining B-Hs in partially-hydrolyzed BH3.THF react in
your reaction?

http://www.sigmaaldrich.com/aldrich/bulletin/al_techbull_al123.pdf

Google is your friend.

Eric Lucas