Aqueous redox flow batteries with organic active materials offer an environmentally benign, tunable, and safe route to large-scale energy storage. Development has been limited to a small palette of organics that are aqueous soluble and tend to display the necessary redox reversibility within the water stability window. We show how molecular engineering of fluorenone enables the alcohol electro-oxidation needed for reversible ketone hydrogenation and dehydrogenation at room temperature without the use of a catalyst. Flow batteries based on these fluorenone derivative anolytes operate efficiently and exhibit stable long-term cycling at ambient and mildly increased temperatures in a nondemanding environment. These results expand the palette to include reversible ketone to alcohol conversion but also suggest the potential for identifying other atypical organic redox couple candidates.
Aqueous organic redox flow batteries are a promising technology for large-scale energy storage. The stability of the redox active organic molecules is increasingly being recognized as one of the major...
A phosphinite-based dinickel pincer complex, {2,3,5,6-( i Pr2PO)4C6}Ni2Cl2, is synthesized by heating a mixture of 1,2,4,5-tetrahydroxybenzene, i Pr2PCl, NiCl2, and Et3N at 150 °C in a microwave reactor or refluxing 1,2,4,5-( i Pr2PO)4C6H2 with NiCl2 and Et3N at 175–250 °C in a flask. Substitution of chlorides by hydrides (from LiAlH4 or LiEt3BH) and methyl groups (from MeLi) generates {2,3,5,6-( i Pr2PO)4C6}Ni2H2 and {2,3,5,6-( i Pr2PO)4C6}Ni2Me2, respectively. Protonation of the methyl complex with HCO2H gives {2,3,5,6-( i Pr2PO)4C6}Ni2(OCHO)2. Spectroscopic and crystallographic data of these Janus POCOP pincer complexes are compared to those of the analogous mononuclear complexes {2,6-( i Pr2PO)2C6H3}NiX (X = Cl, H, Me, and OCHO). The hydride complex {2,3,5,6-( i Pr2PO)4C6}Ni2H2 reacts with phenylacetylene and CO2 to give insertion products. It also catalyzes the reduction of CO2 with catecholborane (HBcat) to yield CH3OBcat and catBOBcat with a turnover frequency of 7.5 min–1. The stoichiometric and catalytic activities of {2,3,5,6-( i Pr2PO)4C6}Ni2H2 are compared to those of {2,6-( i Pr2PO)2C6H3}NiH.
A nickel hydride complex, {2,6-( i Pr2PO)2C6H3}NiH, has been shown to catalyze the coupling of RCHO and R′OH to yield RCO2R′ and RCH2OH, where the aldehyde also acts as a hydrogen acceptor and the alcohol also serves as the solvent. Functional groups tolerated by this catalytic system include CF3, NO2, Cl, Br, NHCOMe, and NMe2, whereas phenol-containing compounds are not viable substrates or solvents. The dehydrogenative coupling reaction can alternatively be catalyzed by an air-stable nickel chloride complex, {2,6-( i Pr2PO)2C6H3}NiCl, in conjunction with NaOMe. Acids in unpurified aldehydes react with the hydride to form nickel carboxylate complexes, which are catalytically inactive. Water, if present in a significant quantity, decreases the catalytic efficiency by forming {2,6-( i Pr2PO)2C6H3}NiOH, which causes catalyst degradation. On the other hand, in the presence of a drying agent, {2,6-( i Pr2PO)2C6H3}NiOH generated in situ from {2,6-( i Pr2PO)2C6H3}NiCl and NaOH can be converted to an alkoxide species, becoming catalytically competent. The proposed catalytic mechanism features aldehyde insertion into the nickel hydride as well as into a nickel alkoxide intermediate, both of which have been experimentally observed. Several mechanistically relevant nickel species including {2,6-( i Pr2PO)2C6H3}NiOC(O)Ph, {2,6-( i Pr2PO)2C6H3}NiOPh, and {2,6-( i Pr2PO)2C6H3}NiOPh·HOPh have been independently synthesized, crystallographically characterized, and tested for the catalytic reaction. While phenol-containing molecules cannot be used as substrates or solvents, both {2,6-( i Pr2PO)2C6H3}NiOPh and {2,6-( i Pr2PO)2C6H3}NiOPh·HOPh are efficient in catalyzing the dehydrogenative coupling of PhCHO with EtOH.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.