The ferrocene effect: enhanced electrocatalytic hydrogen production using meso-tetraferrocenyl porphyrin palladium(II) and copper(II) complexes.

Copper(ii) and palladium(ii) meso-tetraferrocenylporphyrins ( and ) were employed as catalysts for electrochemical proton reduction in DMF using trifluoroacetic acid (TFA) or triethylamine hydrochloride (TEAHCl) as acids. Gas analysis under electrocatalytic conditions at a glassy carbon working electrode confirmed the product as H2. showed catalytic behavior for both TFA and TEAHCl, whereas only TFA worked for . The performance of the two compounds for electrocatalytic hydrogen generation was compared to the analogous copper(ii) and palladium(ii) meso-tetraphenylporphyrins ( and ) under identical conditions. The presence of the ferrocence groups on the porphyrin favourably shift the overpotential to a less negative value by around 200 mV and increases the catalytic rate of hydrogen production in DMF/TFA by an order of magnitude to 6 × 10(3) s(-1). Moreover, while is fully inactive in a DMF/TEAHCl mixture, the ferrocene subunits activate the catalyst. Spectroelectrochemistry experiments and DFT calculations were consistent with a catalytic process proceeding via the phlorin anion.