Catalysts and mechanisms

Hydrogenase enzymes catalyse the reversible reduction of protons to H2. In collaboration with Reiner Lomoth, Sascha Ott and Gustav Berggren, we investigate the catalytic cycle of synthetic Fe2-complexes inspired by the active site of FeFe-hydrogenases. 

We use time-resolved IR spectroscopy for FeFe-hydrogenase active site mimics, to follow kinetics of individual ET and PT steps and detect intermediates of the catalytic cycle. By comparison with DFT calculated spectra we can determine their structures, which in many cases are not known. In one study, we showed every step and intermediate of a complete catalytic cycle of [Fe2(Cl2bdt)(CO)6], for the first time for any proton reduction catalyst, and directly monitored the final turn-over step. We also studied the azadithiolate (adt) complex [Fe2(adt)(CO)6] that has been proposed to work via facilitated proton shuttling from adt-H+ to the reduced metal center. This would be in analogy with the proposed function of the enzyme, and an important example of a popular catalyst design principle with a putative proton shuttle in the second coordination sphere. However, by direct time-resolved IR spectroscopy monitoring we could show that proton shuttling does not happen on a time scale relevant for catalysis. We instead suggested other effects behind the catalytic improvement of the adt complex relative to the propyldithiolate analogue.

Direct Spectroscopic Detection of Key Intermediates and the Turnover Process in Catalytic H2 Formation by a Biomimetic Diiron Catalyst
Shihuai Wang, Sonja Pullen, Valentin Weippert, Tianfei Liu, Sascha Ott, Reiner Lomoth* and Leif Hammarström*.
Chem. Eur. J. 2019, 25, 11135-11140.

Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H2 formation with FeFe hydrogenase model complexes
Alexander Aster, Shihuai Wang, Mohammad Mirmohades, Charlène Esmieu, Gustav Berggren, Leif Hammarström and Reiner Lomoth*
Chem. Sci. (2019) 10, 5582-5588.