Structural and functional synthetic model of mono-iron hydrogenase featuring an anthracene scaffold

Mono-iron hydrogenase was the third type of hydrogenase discovered. Its Lewis acidic iron(II) centre promotes the heterolytic cleavage of the H-H bond and this non-redox H-2 activation distinguishes it from the well-studied dinuclear [FeFe] and [NiFe] hydrogenases. Cleavage of the H-H bond is followed by hydride transfer to the enzyme's organic substrate, H4MPT+, which serves as a CO2 'carrier' in methanogenic pathways. Here we report a scaffold-based synthetic approach by which to model mono-iron hydrogenase using an anthracene framework, which supports a biomimetic fac-C, N, S coordination motif to an iron(II) centre. This arrangement includes the biomimetic and organometallic Fe-C sigma bond, which enables bidirectional activity reminiscent of the native enzyme: the complex activates H-2 under mild conditions, and catalyses C-H hydride abstraction plus H-2 generation from a model substrate. Notably, neither H-2 activation nor C-H hydride abstraction was observed in the analogous complex with a pincer-type mer-C, N, S ligation, emphasizing the importance of the fac-C, N, S-iron(II) motif in promoting enzyme-like reactivity.