Self‐Assembly of Aminocyclopropenium Salts: En Route to Deltic Ionic Liquid Crystals

Litterscheidt, Juri; Bandar, Jeffrey S.; Ebert, Max; Forschner, Robert; Bader, Korinna; Lambert, Tristan H.; Frey, Wolfgang; Bühlmeyer, Andrea; Brändle, Marcus; Schulz, Finn

doi:10.1002/ange.202000824

Cited by 2 publications

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References 72 publications

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“…From substitution of alcohols to enantioselective Brønsted base catalysis to electrophotocatalysis, the smallest of the aromatic rings has proven to be a versatile and advantageous engine for discovery. Not discussed here is the fact that we have also utilized cyclopropeniums for applications outside of method development, including for the synthesis of polymers 73 useful for applications ranging from transfection 74 to energy storage 75 in collaboration with Prof. Luis Campos (Columbia University), as ionic liquid crystals with Prof. Sabine Laschat (University of Stuttgart), 76,77 and for lactide polymerization with Prof. Robert Waymouth (Stanford University). 78 We expect that the versatile cyclopropenium ion will continue to provide new and unexpected discoveries, both in catalysis and beyond.…”

Section: Discussionmentioning

confidence: 99%

Cyclopropenium Ions in Catalysis

Wilson

Lambert

2022

Acc. Chem. Res.

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Conspectus Cyclopropenium ions are the smallest class of aromatic compounds, satisfying Hückel’s rules of aromaticity with two π electrons within a three-membered ring. First prepared by Breslow in 1957, cyclopropenium ions have been found to possess extraordinary stability despite being both cationic and highly strained. In the 65 years since their first preparation, cyclopropenium ions have been the subject of innumerable studies concerning their synthesis, physical properties, and reactivity. However, prior to our work, the reactivity of these unique carbocations had not been exploited for reaction promotion or catalysis. Over the past 13 years, we have been exploring aromatic ions as unique and versatile building blocks for the development of catalysts for organic chemistry. A major portion of this work has been focused on leveraging the remarkable properties of the smallest of the aromatic ionscyclopropeniumsas a design element in the invention of highly reactive catalysts. Indeed, because of its unique profile of hydrolytic stability, compact geometry, and relatively easy oxidizability, the cyclopropenium ring has proven to be a highly advantageous construction module for catalyst invention. In this Account, we describe some of our work using cyclopropenium ions as a key element in the design of novel catalysts. First, we discuss our early work aimed at promoting dehydrative reactions, starting with Appel-type chlorodehydrations of alcohols and carboxylic acids, cyclic ether formations, and Beckmann rearrangements and culminating in the realization of catalytic chlorodehydrations of alcohols and a catalytic Mitsunobu-type reaction. Next, we describe the development of cyclopropenimines as strong, neutral organic Brønsted bases and, in particular, the use of chiral cyclopropenimines for enantioselective Brønsted catalysis. We also describe the development of higher-order cyclopropenimine superbases. The use of tris(amino)cyclopropenium (TAC) ions as a novel class of phase-transfer catalysts is discussed for the reaction of epoxides with carbon dioxide. Next, we describe the formation of a cyclopropenone radical cation that has a portion of its spin density on the oxygen atom, leading to some peculiar metal ligand behavior. Finally, we discuss recent work that employs TAC electrophotocatalysts for oxidation reactions. The key intermediate for this chemistry is a TAC radical dication, which as an open-shell photocatalyst has remarkably strong excited-state oxidizing power. We describe the application of this strategy to transformations ranging from the oxidative functionalization of unactivated arenes to the regioselective derivatization of ethers, C–H aminations, vicinal C–H diaminations, and finally aryl olefin dioxygenations. Collectively, these catalytic platforms demonstrate the utility of charged aromatic rings, and cyclopropenium ions in particular, to enable unique advances in catalysis.

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Section: Discussionmentioning

confidence: 99%

Cyclopropenium Ions in Catalysis

Wilson

Lambert

2022

Acc. Chem. Res.

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Current Topics in Ionic Liquid Crystals

et al. 2021

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Ionic liquid crystals (ILCs), that is, ionic liquids exhibiting mesomorphism, liquid crystalline phases, and anisotropic properties, have received intense attention in the past years. Among others, this is due to their special properties arising from the combination of properties stemming from ionic liquids and from liquid crystalline arrangements. Besides interesting fundamental aspects, ILCs have been claimed to have tremendous application potential that again arises from the combination of properties and architectures that are not accessible otherwise, or at least not accessible easily by other strategies. The current review highlights recent developments in ILC research, starting with some key fundamental aspects. Further subjects covered include the synthesis and variations of modern ILCs, including the specific tuning of their mesomorphic behavior. The review concludes with reflections on some applications that may be within reach for ILCs and finally highlights a few key challenges that must be overcome prior and during true commercialization of ILCs.

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Self‐Assembly of Aminocyclopropenium Salts: En Route to Deltic Ionic Liquid Crystals

Cited by 2 publications

References 72 publications

Cyclopropenium Ions in Catalysis

Cyclopropenium Ions in Catalysis

Current Topics in Ionic Liquid Crystals

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