Alkyne 1,1-Hydroboration To A Reactive Frustrated P/B-H Lewis Pair

The Mes(2)P-C equivalent to C-SiMe3 alkyne reacts with the borane H2B-Fmes by means of a rare 1,1-hydroboration reaction to give an unsaturated C-2-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.