Alkyne 1,1‐Hydroboration to a Reactive Frustrated P/B‐H Lewis Pair

Abstract

The Mes2P‐C≡C‐SiMe3 alkyne reacts with the borane H2B‐Fmes by means of a rare 1,1‐hydroboration reaction to give an unsaturated C2‐bridged frustrated P/B‐H Lewis pair. Most of its reactions are determined by the presence of the B‐H functionality at the FLP function and the activated connecting carbon‐carbon double bond. It reduces carbon monoxide to the formyl stage. With nitriles it reacts in an extraordinary way: it undergoes a reaction sequence that eventually results in the formation of a P‐substituted dihydro‐1,2‐azaborole derivative. Several similar examples were found. In one case a P‐ylide was isolated that was related to an intermediate of the reaction sequence. It subsequently opened in an alternative way to give an alkenyl borane product.