Story of Hydroboration: Experimentally Generated Mechanistic Insights

Abstract

Reduction of various unsaturated organic substrates via hydroboration represents one of the most commonly used procedures. Nevertheless, controversial information about the mechanistic insights regarding this particular transformation still exists in the literature. In this work, we show that three-coordinate mono-aminoboranes do not act as effective hydroboration reagents as recently reported unless these boron-containing species are able to form four-coordinate analogues either through dimerization or addition of a base. Furthermore, we also demonstrate that imine-BH3 adduct(s) and mono-amino boranes do not represent key intermediates during Me2S-BH3 catalyzed hydroboration of imines using HBpin as recently reported. In fact, we believe that in both of these reported studies, the Clark mechanism is mainly, if not solely, responsible for the observed/examined hydroboration reactions.

2-Anilidomethylpyridine-Derived Three-Coordinate Zinc Hydride: The Journey Unveils Anilide Backbone’s Reactive Nature

“…Hence, we refrain from making further comments on the mechanism. The present literature suggests that the carbonyl hydroboration is quite an easy process in terms of catalyst choices . Any Lewis acidic site can potentially catalyze the process, including the HBpin itself without the need of an external catalyst .…”

“…Thus, the mechanism does not necessarily proceed through a metal hydride intermediate. An anchoring mechanism has been proposed by many where the metal interacts with one of the oxygen atoms of HBpin, leading to more polarization of the B–H bond, which reacts with a carbonyl via a four-membered TS . We also plan to test 8 in other hydroelementation catalyses.…”