Tuning the Electronic and Molecular Structures of Bioinspired Heterodinuclear NiFe Catalyst for Enhanced Catalytic H Evolution.

With the aim of enhancing the HER activity of the previously described bioinspired [NiFe]-hydrogenase complex [LNiFeCp-(CO)] (, with L = 2,2'-(2,2'-bipyridine-6,6'-diyl)-bis-(1,1'-diphenylethanethiolate) and Cp = cyclopentadienyl), the electronic structure of the L site has been fine-tuned. In , the bipyridine (Bpy) unit was substituted with methoxy electron-donating groups, while in , the Bpy unit was replaced with the 1,10-phenanthroline backbone. These complexes were fully characterized, and their HER activity was investigated. A mechanistic study was conducted by using IR and EPR spectroscopies combined with density functional theory (DFT) calculations. Both complexes act as efficient electrocatalysts to produce H, following an ECEC mechanism, starting from the monoreduced species. exhibits the fastest kinetics among the series ( = 1.6 × 10 s), attributed to its higher Δp value for the protonation step of the two-electron reduced species, [ . In contrast, exhibits the lowest overpotential, with a cathodic shift of 150 mV. This improved performance is attributed to the fact that the phenanthroline backbone is more easily reduced with respect to a bipyridine unit.