Controlling Hydricity of Adsorbed Catalysts with Applied Electric Fields

We investigate the effects of applied electric fields on the reactivity of two iridium(III) half-sandwich complexes bonded to gold electrodes. Our theoretical results show that applied electric fields precisely and linearly control the aqueous effective hydricities of these catalysts. The field-dependent shifts in the hydricities of Cp*Ir-bipyridine ([Ir-bpyH]+) and Cp*Ir-phenylpyridine (Ir-ppy-H) are compared directly to those induced by chemical substitution, and they are found to be equivalent to a drastic change in substituent Hammett parameter without any chemical modification. Furthermore, we find that the Stark tuning rates of Ir-H vibrational modes are directly correlated with hydricity changes induced by the applied electric field, providing valuable spectroscopic probes of the actual electric field strength at the catalytic site and potential reactivity of the hydride. We anticipate that the reported findings should be particularly valuable for studies of non-Faradaic electrochemical control of catalytic reactivity at interfaces by applied external fields.