Redox-active inverse crowns for small molecule activation
Johannes Maurer, Lukas Klerner, Jonathan Mai, Hannah Stecher, Stefan Thum, Michael Morasch, Jens Langer, Sjoerd Harder
Abstract
Abstract Cyclic crown ethers bind metal cations to form host–guest complexes. Lesser-known inverse crowns are rings of metal cations that encapsulate anionic entities, enabling multiple deprotonation reactions, often with unusual selectivity. Self-assembly of a cycle of metal cations around the multiply charged carbanion during the deprotonation reaction is the driving force for this reactivity. Here we report the synthesis of a pre-assembled inverse crown featuring Na + cations and a redox-active Mg 0 centre. Reduction of N 2 O followed by N 2 release and subsequent encapsulation of O 2 − demonstrates its reduce-and-capture functionality. Calculations reveal that this essentially barrier-free process involves a rare N 2 O 2 − dianion, embedded in the metalla-cycle. The inverse crown can adapt itself for binding larger anions like N 2 O 2 2 − through a self-reorganization process involving ring expansion. The redox-active inverse crown combines the advantages of a strong reducing agent with anion stabilizing properties provided by the ring of metal cations, leading to high reactivity and selectivity.