[FeFe]‐Hydrogenase Mimics Bearing Germylene Ligands: Synthesis, Protonation, and Electrochemical Properties

This work shows that the presence of germylene ligands of marked basicity in [FeFe]‐hydrogenase mimics of the type [Fe 2 (µ‐S 2 X)(E) n (CO) 6–n ] (S 2 X = (SCH 2 ) 2 N( p ‐MeOC 6 H 4 ) ( adt ), (SCH 2 ) 2 CH 2 ( pdt ); E = amidinatogermylene; n = 1, 2; complexes 1 – 4 ), has a strong influence in the protonation and electrocatalytic behavior (proton reduction) of the mimics because these ancillary ligands appropriately increase the electron density of the [FeFe] core. Thus, electrochemical studies on 1 – 4 show cathodic shifts with respect to the all‐CO complexes [Fe 2 (µ‐S 2 X)(CO) 6 ]. By protonation with trifluoracetic acid (TFA), complexes 1 – 4 form stable cationic hydride‐bridged complexes at room temperature, which, in the case of the adt ‐bridged complexes, arise from the transfer of the N H proton from a transient N ‐protonated adt fragment to the [FeFe] core. Such a proton transfer process has now been spectroscopically detected by low temperature 1 H‐NMR. Electrocatalytic studies with TFA demonstrate hydrogen evolution reaction (HER) activity and high turnover frequencies, especially for the adt derivatives 1 and 2 .