Chemical Mimicks

Based on structural information of the enzyme metal centers, the synthetic analogue strategy, as defined by Holm, allows defining the minimal structure required for a catalyst to achieve the biological function. The aim is both to better understand at the molecular level the catalytic mechanism of native hydrogenases and to develop new electrocatalysts to be used in fuel-cells for hydrogen uptake or in electrolytic/photosynthetic cells for hydrogen production. Significant synthetic achievements were achieved and the new biomimics of FeFe and NiFe hydrogenases show proton reduction activity: In our group, we focus on NiFe hydrogenase modelisation. We initially reported on the catalytic activity of a series of bio-inspired dinuclear nickel-ruthenium complexes in which various electron-rich organometallic ruthenium moieties were introduced as subrogates for the {Fe(CO)(CN)2} fragment. DFT calculations were carried out out on these systems in collaboration with the Modeling and Simulation group of Martin Field (IBS, Grenoble) and, coupled with electrochemical measurements, allowed a heterolytic mechanism for H2 evolution to be proposed. A bridging hydride derivative was identified as the active intermediate, with a structure similar to that of the Ni-C active state of NiFe hydrogenases (Figure 1). Recently, we prepared noble-metal free nickel-manganese and nickel-iron model compounds that also proved active for hydrogen evolution in non-aqueous solvents.

Figure 1: Top: Cristallographic structure of the active site of NiFe hydrogenase and the model complex [Ni(xbsms)FeCp(CO)]+. Bottom: Structure of the catalytically competent Ni-C state of NiFe hydrogenase and DFT-calculated structure of the key intermediate in heterolytic H2 evolution catalyzed by a Ni-Ru model compound.

Current research in this field is developed within the ANR-funded NiFe-Cat project, in collaboration with the group of Marius Réglier (BiosCiences, Aix-Marseille Université) and Martin Field (IBS, Grenoble). We aim at synthesizing novel dinuclear compounds displaying a distorded environment around the Ni center while keeping an organometallic iron moiety.

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