Mimicking the CO2‐Bound State of the [Ni,Fe]‐CO Dehydrogenase

Complexes, where a doubly reduced CO22– (carbonite) ligand is spanned between a nickel(II) centre and a transition metal(II) ion (TM = Fe, Co, Zn) have been accessed. In non‐coordinating solvents the carbonite ligand exhibits a flexible coordination behaviour as observed by NMR spectroscopy and supported by DFT calculations. In particular the [Ni‐CO2‐Fe] representative replicates the respective entity in an intermediate formed during CO2‐conversion by the enzyme [Ni,Fe]‐CODH in many ways (structure, spectroscopic properties, reactivity). Our investigations reveal that transition metal ions reduce the reduction potential of the carbonite unit but increase its tendency to undergo C‐O bond cleavage. This may explain the choice of an iron(II) ion as part of the active site.