Structural effects upon the durability of hydrogenase-inspired hydrogen-producing electrocatalysts: Variations in the (mu-edt) [Fe-2(CO)(6)] system

Three variations of the common [FeFe]-Hydrogenase active site mimic mu-(SCH2CH2S)-Fe-2(CO)(6), 1, have been studied: mu-(SCH(CH3)CH2S)-Fe-2(CO)(6), 2; mu-(SCH(CH3)CH(CH3)S)-Fe-2(CO)(6), 3; and mu-(SCH2CH(CH2OH)S)-Fe-2(CO)(6), 4. The electrochemistry of these four species is compared, indicating that 3 displays greater durability upon electrochemical cycling. This enhanced stability is ascribed to steric blockage of decomposition routes, rather than any change to the Fe2S2 butterfly structure. Electrocatalysis using a weak acid (4-tert-butylphenol, pK(a) = 27.5 in acetonitrile) is observed for each catalyst with similar overpotential. The enhanced stability of the reduction products of 3 leads to a modest increase of the apparent catalytic rate. Compound 4 was tested for an enhancement of the rate of the acid deprotonation step; compound 4 failed to behave in such a manner, providing no improvement in electrochemical catalysis compared to the parent compound.