Nature utilizes multimetallic sites in metalloenzymes to enable multielectron chemical transformations at ambient conditions and low overpotentials. One such example of multimetallic cooperativity can be found in the C-cluster of Ni-carbon monoxide dehydrogenase (CODH), which interconverts CO and CO2. Toward a potential functional model of the C-cluster, a family of Ni-Fe bimetallic complexes was synthesized that contain direct metal-metal bonding interactions. The complexes were characterized by X-ray crystallography, various spectroscopies (NMR, EPR, UV-vis, Mössbauer), and theoretical calculations. The Ni-Fe bimetallic system has a reversible Fe(III)/Fe(II) redox couple at -2.10 V (vs Fc+/Fc). The Fe-based "redox switch"can turn on CO2 reactivity at the Ni(0) center by leveraging the Ni→Fe dative interaction to attenuate the Ni(0) electron density. The reduced Ni(0)Fe(II) species mediated the formal two-electron reduction of CO2 to CO, providing a Ni-CO adduct and CO32- as products. During the reaction, an intermediate was observed that is proposed to be a Ni-CO2 species.
Bibliographical noteFunding Information:
The authors thank Prof. John Lipscomb for access to the EPR spectrometer, J.T. Moore and Michael Dorantes for collecting EPR spectra, Bernd Mienert and Dr. Peter Solheid for collecting the Mössbauer spectra, and Dr. Victor G. Young, Jr. for assistance with X-ray crystallography. J.R.P. was supported by the National Science Foundation (NSF) Graduate Research Fellowship Program. The synthetic work was supported by NSF (CHE-1800110). X-ray diffraction experiments were performed using a crystal diffractometer purchased through a grant from NSF (MRI-1229400) and the University of Minnesota. The computational work was supported by NSF (CHE-1746186). The computational resources were provided by the Minnesota Supercomputing Institute (MSI) at the University of Minnesota.
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