Development of ligands with specific stereo- and electrochemical requirements in catalyst development is of imminent interest to synthetic chemists in academia and industry. The crucial aza-dithiolate linker in the active site of [FeFe]-H2ase has inspired the development of synthetic model complexes that feature built-in pendant bases. Several ligands, e.g. substituted phosphines and carbenes, have been utilized by the hydrogenase community to mimic the cyanides in the [FeFe]-H2ase enzyme active site. Utilization of ligands that serve as conventional σ-donors with pendant base features for H+ binding and delivery might be critical in the biomimetic catalyst development. Over the years, the Darensbourg group has synthesized several MN2S2 complexes (M = NiII, [(NO)Fe]II, [(NO)Co]II etc.). These complexes utilize cis-dithiolates to bind low valent metals, and they display hemi-lability and redox properties. Synthetic efforts have been made for the isolation and characterization of three hetero-trimetallics that employ metallodithiolate ligand binding to diiron scaffolds in three redox levels, viz., (µ-pdt)[FeI2(CO)6], (µ-pdt)[(CO)3FeI(Fe(NO))II(CO)L]+ and (µ-pdt)(µ-H)[L(CO)2FeIIFeII(CO)2L]+, to generate FeIFeI.MN2S2, FeI[Fe(NO)]II.MN2S2 and (µ-H)FeIIFeII.MN2S2 complexes. These complexes display efficient metallodithiolate binding to the diiron scaffold with one thiolate. This allows the free unbound thiolate to potentially serve as a built-in pendant base to direct proton binding, promoting electrocatalysis for the hydrogen evolution reaction (HER) in presence of acids. These complexes were characterized using IR, NMR, CV, and XRD techniques. Preliminary electrochemical results in the presence of trifluoroacitic acid showed an increase in the cathodic current response, indicating a possible Fe-H-...+H-S coupling mechanism. Further studies are being directed towards the isolation of proton-bound thiolates.

Metallodithiolate ligands as pendant base in [FeIFeI], [FeI[Fe(NO)]II] and [(µ-H)FeIIFeII] systems

255th National Meeting (2018)

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