Immobilization-Enabled Proton Reduction Catalysis by a Di-iron Hydrogenase Mimic

We have long been interested in the influence of surface immobilization on the electrochemical integrity of redox-active moieties [1–5]. Our studies have shown that, if the electroactive group itself is directly chemisorbed on (coordinated to) the electrode surface, profound alterations result in both the thermodynamics and kinetics of the electron transfer processes; the oxidative chemisorption of the iodide anion (to zerovalent iodine atoms) or the hydroquinone molecule (to benzoquinone) are prototypical examples. The changes are more subtle and less dramatic if the electroactive site is only a pendant moiety tethered to the surface via an anchor group; mercapto hydroquinone bound exclusively via the –SH group is a well-known specimen. We recently extended our investigations to include enzyme-inspired molecular electrocatalysts in which the multinuclear reactive site may require a certain entatic state to carry out its catalytic function; the anticipation is that the motion-restricted surface-tethered species would suffer diminished catalytic activity. The results are described in this brief communication.