Catalyst‐Free Transfer Hydrogenation from Amine‐Borane Small Oligomers

Abstract

AbstractAmine‐borane dimers and oligomers with varied steric and electronic profiles were prepared via capping agent‐controlled AA/BB polycondensations. They were used for transfer hydrogenations to aldehydes, ketones, imines as well as electron‐poor alkene/alkyne moieties. The amine‐borane Lewis‐paired oligomers and the congested bis(amine‐borane)s provided the highest yields. This was likely helped by facilitated dissociation (oligomers) or H‐bond assistance. In the case of the oligomers, the second equivalent of H2 present was also engaged in the reaction. Solid‐state NMR characterization provides evidence that the boron‐containing materials obtained after transfer dehydrogenation are highly similar to those obtained from thermal dehydrogenation. The oligomers bridge the gap between simple amine‐borane molecular reductants and the poly‐amine‐boranes and provide a full picture of the reactivity changes at the different scales.