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-bpy-H]+) 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.