Redox-active ligands

Article By:

Heyduk, Alan F. Department of Chemistry, University of California, Irvine, California.

Cameron, Lindsay Department of Chemistry, University of California, Irvine, California.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.576480

A special class of ligand that can access multiple oxidation states. Redox reactions are a fundamental type of chemical reaction that is critical to the bond-making and bond-breaking events that drive nearly all chemical transformations. In nature, many reactions that are crucial to life are multielectron redox reactions. For example, sunlight is stored in chemical bonds by photosynthesis, which splits water into O₂ and H₂ as NADPH (nicotinamide adenine dinucleotide phosphate) via a four-electron process. The reverse process, respiration, uses O₂ and four electrons to synthesize ATP as an energy source in cells. Nitrogen fixation (ammonia synthesis), CH bond functionalization, and CO₂ reduction are all multielectron redox reactions carried out in biology, and each of these processes is facilitated by enzymes that contain first-row transition metals such as Mn, Fe, Co, Ni, Cu, and Zn. Because these metals typically react by one-electron pathways, nature often includes redox-active cofactors to help expand their reactivity to allow multielectron processes to occur. In synthetic inorganic chemistry, redox-active ligands can be used to achieve the same goal and afford multielectron reactivity at a metal ion that is prone to one-electron redox reactions. See also: Adenosine triphosphate (ATP); Biological oxidation; Enzyme; Nicotinamide adenine dinucleotide (NAD); Nitrogen fixation reactions; Oxidation-reduction; Photosynthesis; Plant respiration; Transition elements

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