Controlling E/Z Selectivity by Tuning the Coordination Sphere at Co in Mediated Tandem Electrocatalysis

In our previous study on hydride-free semi-hydrogenation using redox mediators and bidentate phosphine ligands on a Co co-catalyst, we learned important lessons by DFT in collaboration with the Gutierrez group: inner-sphere proton transfer due to acid coordination dictated the stereochemical outcome. In this work, Bryan and team take this coordination control in the opposite direction, favoring E-selectivity under hydride-free conditions by elegantly insulating the Co center with a triphosphine ligand and non-coordinating ammonium acid. We find that contact-ion pairing controls the inner-sphere proton transfer, and steric insulation favors subsequent outer-sphere proton transfer, yielding E-alkenes in high selectivity and yield. Check out the preprint here: https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010969/v1