N,N,N',N'-Tetramethylethylenediamine (TMED) reacts instantly with boron trifluoride ethyl etherate to give the highly insoluble product TMED•2BF3. This development made it of interest to synthesize and study the addition compounds of TMED with representative monoalkylboranes. TMED reacts readily with typical monoalkylboranes to form both the TMED-monoalkylborane TMED-BH2R and the corresponding bis adducts TMED•2BH2R. These are air stable and can be stored without apparent change for long periods of time. Boron trifluoride removes TMED from these adducts, rapidly and completely, precipitating TMED•2BF3. In this way the monoalkylboranes can be conveniently purified and stored as their stable adducts with TMED, with rapid convenient generation of the parent monoalkylborane as desired. © 1979, American Chemical Society. All rights reserved.