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

Abstract

Complexes, where a doubly reduced CO₂ ^2- (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 instead of a s- or p-block-based Lewis acid as part of the active site.

Keywords: Bimetallic; CO2 activation; CODH; nickel β-diketiminate.