Competing Suzuki and Stille cross coupling reactions were studied to elucidate the effect of phosphine ligands on chemodivergence in the transmetalation step of the catalytic cycle. Understanding the effect of ligands on the relative rates of transmetalation from boron vs. tin could enable the development of new cross coupling methodology with catalyst-controlled selectivity between multiple possible nucleophiles. During intermolecular competition reactions between boronic acids and tin reagents, aryl boronic acids were found to be much more reactive than aryl and vinyl tin reagents regardless of phosphine ligand. Conversely, electron-neutral aryl boronic acids were less reactive than alkynyl tin reagents under most conditions, but in some cases a phosphine-dependent reversal of selectivity was observed. Aryl boronic acids with electron withdrawing groups provided similar reactivity to alkynyl tin reagents. Novel reagents containing both boronic acid and tributyltin substituents were synthesized for use in intramolecular competition reactions.

Divergent transmetalation to palladium from boron vs. tin reagent

255th National Meeting (2018)

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