Design, synthesis and characterization of a modular bridging ligand platform for bio-inspired hydrogen production

Synthesis and characterization of a novel type of ambident bridging ligands joining together the functional prerequisites for visible-light absorption, photoinduced electron transfer and catalytic proton reduction is presented. This class of compounds consists of a chromophoric 1,2-diimine-based π-acceptor site and a rigid polyaromatic dithiolate chelator. Due to the presence of a common conjugated linker moiety with an intrinsic two-electron redox reactivity and a suitable orbital coupling of the subunits, a favorable situation for vectorial multielectron transfer from attached electron donors to a catalytic acceptor site is provided. As an example for the application of this kind of bifunctional ligand systems, a [FeFe]-hydrogenase enzyme model compound is prepared and structurally characterized. Electrocatalytic hydrogen formation with this complex is demonstrated.
Graphical Abstract Highlights The catalytic acceleration of coupled two-electron / two-proton redox steps is a crucial functional feature for artificial photosynthesis and solar fuels research. For the first time, the building blocks for light absorption, multiple electron transfer and proton reduction have been successfully combined in a simple bio-inspired hydrogenase model system that can be readily further modified for solar photocatalytic applications.