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Formic acid is unique among liquid organic hydrogen carriers (LOHCs), because its dehydrogenation is highly entropically driven. This enables the evolution of high-pressure hydrogen at mild temperatures that is difficult to achieve with other LOHCs, conceptually by releasing the “spring” of energy stored entropically in the liquid carrier. Applications calling for hydrogen-on-demand, such as vehicle filling, require pressurized H 2 . Hydrogen compression dominates the cost for such applications, yet there are very few reports of selective, catalytic dehydrogenation of formic acid at elevated pressure. Herein, we show that homogenous catalysts with various ligand frameworks, including Noyori-type tridentate (PNP, SNS, SNP, SNPO), bidentate chelates (pyridyl)NHC, (pyridyl)phosphine, (pyridyl)sulfonamide, and their metallic precursors, are suitable catalysts for the dehydrogenation of neat formic acid under self-pressurizing conditions. Quite surprisingly, we discovered that their structural differences can be related to performance differences in their respective structural families, with some tolerant or intolerant of pressure and others that are significantly advantaged by pressurized conditions. We further find important roles for H 2 and CO in catalyst activation and speciation. In fact, for certain systems, CO behaves as a healing reagent when trapped in a pressurizing reactor system, enabling extended life from systems that would be otherwise deactivated.
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Pursuit of C–H Borylation Reactions with Non-Precious Heterobimetallic Catalysts: Hypothesis-Driven Variations on a Design Theme
This article presents a retrospective account of our group’s heterobinuclear (NHC)Cu-[MCO] catalyst design concept (NHC = N-heterocyclic carbene, [MCO] = metal carbonyl anion), the discovery of its application towards UV-light-induced dehydrogenative borylation of unactivated arenes, and the subsequent pursuit of thermal reaction conditions through structural modifications of the catalysts. The account highlights advantages of using a hypothesis-driven catalyst design approach that, while often fruitless with regard to the target transformation in this case, nonetheless vastly expanded the set of heterobinuclear catalysts available for other applications. In other words, curiosity-driven research conducted in a rational manner often provides valuable products with unanticipated applications, even if the primary objective is viewed to have failed. 1 Introduction to Heterobinuclear Catalysts for C–H Borylation 2 Pursuit of Thermal Borylation Conditions 3 Catalysts beyond Copper Carbenes 4 Conclusions
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- Award ID(s):
- 1664632
- PAR ID:
- 10142367
- Date Published:
- Journal Name:
- Synlett
- Volume:
- 31
- Issue:
- 02
- ISSN:
- 0936-5214
- Page Range / eLocation ID:
- 125 to 132
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1055/s-0039-1691504
