Derek Barton and coworkers demonstrated that triarylbismuth(V) complexes readily undergo reductive elimination to generate functionalized arenes. We are interested in understanding this aryl transfer chemistry to develop a practical synthesis of derivatized arenes. To make such reactions atom economical, it is critical to understand the factors that govern selectivity in reductive eliminations from Bi(V). In this presentation, we will provide data on the regioselectivity of reduction elimination of functionalized arenes from Ar4BiX compounds, which we used to elucidate the relative importance of steric and electronic effects on the selectivity of aryl transfer. Triarylbismuth(III) compounds were oxidized to the corresponding Ar3Bi(V)F2 complexes, which were further elaborated to form more than 50 distinct Ar3Ar’BiX complexes. Upon heating, these compounds underwent reductive elimination to afford Ar’-X with varying regioselectivities. Importantly, the impact of ortho substituents on Ar’ was profound, and very high selectivities were observed for elimination of 2- or 2,6-substituted arenes. Computational modeling and X-ray crystal structure determination data showed substituents in the ortho position force an equatorial aryl group into the appropriate reactive conformation (orthogonal to the axial Bi-X bond), thereby enhancing the rate of aryl transfer for substituted arenes. The electronic effects of substituents on spectator aryl groups were also studied and, in line with what was observed by Barton, were shown to be modest, whereas steric effects exhibit profound influence on the rate and regioselectivity of reductive elimination from tetraarylbismuth(V) compounds. This study provides clues to the design and optimization of ligand systems for selective aryl transfer chemistry from bismuth(V) complexes.

Regioselective reductive elimination from Bismuth(V) compounds for aryl transfer to nucleophiles

ACS Fall 2021

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