Story of Hydroboration: Experimentally Generated Mechanistic Insights

Reductionof various unsaturated organic substrates viahydroborationrepresents one of the most commonly used procedures. Nevertheless,controversial information about the mechanistic insights regardingthis particular transformation still exists in the literature. Inthis work, we show that three-coordinate mono-aminoboranes do notact as effective hydroboration reagents as recently reported unlessthese boron-containing species are able to form four-coordinate analogueseither through dimerization or addition of a base. Furthermore, wealso demonstrate that imine-BH3 adduct(s) and mono-aminoboranes do not represent key intermediates during Me2S-BH3 catalyzed hydroboration of imines using HBpin as recentlyreported. In fact, we believe that in both of these reported studies,the Clark mechanism is mainly, if not solely, responsible for theobserved/examined hydroboration reactions.

Automated summary

In this work, it is shown that three-coordinate mono-aminoboranes are not efficient hydroboration reagents unless they can form four-coordinate analogues. It is also demonstrated that imine-BH3 adduct(s) and mono-aminoboranes are not key intermediates in the Me2S-BH3 catalyzed hydroboration of imines. Instead, the Clark mechanism is believed to be mainly responsible for the observed hydroboration reactions in both of these reported studies.