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Hydrogen atom donors and cooperative ligands stemming from oxyallyl frameworks – HALIGO

Hydrogene donors and cooperative ligands based on oxyallyl frameworks

Oxyallyl radical cations are a new class of stable paramagnetic molecular bricks.

Oxyallyl radicals: new paramagnetic molecular bricks

Whereas oxyallyl radicals have been considered as non-isolable oddities for long, our recent results (Angew. Chem. Int. Ed., 2013, 52, 7014) show that they can be, in fact, highly stable. This project intends to capitalize on this paradigm shift, to find simples synthetic routes towards these molecules, to study, and then to apply, their unusual reactivity.

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We already showed that the stability of oxyallyl radical cations was electronic in nature. While rationalizing this unusual stability, we showed that (amino)(carboxy)radicals could be designed. Before our work, such capto-dative stabilized C-radicals were disregarded as non-isolable oddities. They constitute a new unforeseen family of paramagnetic molecular bricks.

Simple synthetic methods (unpublished results) allow to consider a vast variety of structures, for application in organic synthesis and homogeneous catalysis.

1.«The quest for observation and isolation of oxyallyl derivatives»
Organic Chemistry Frontiers, 2015, vol. 2, p 1536–1545.
(Themed collection « emerging investigators »)

2.«Air-persistent Monomeric (Amino)(carboxy) Radicals Derived from CAACs»
Journal of the American Chemical Society, 2015, vol. 137, p 7519–7525

The discovery and development of stable versions of elusive intermediates, such as radicals or carbenes, have deeply impacted modern chemistry. These compounds are not only academic landmarks, which introduce unprecedented concepts and understandings of fundamental issues, but they also set the stage for the development of new practical applications. Herein, we want to consider oxyallyls, which are postulated intermediates in several reactions (1-3 dipolar cycloadditions, Favorskii rearrangement, Nazarov-type cyclizations, etc). Oxyallyls are non-Kekulé molecules: their neutral pi-system cannot be assigned to a classical Kekulé-type structure, but only to zwitterionic or diradical resonance forms, despite having an even number of electrons. They have been considered as non-observable species because their ring closure into the corresponding cyclopropanone usually occurs with a negligible activation barrier. However this traditional belief has been recently challenged by the recent report of oxyallyls derivatives, which are stabilized by strong pi-donor substituents. We intend to capitalize on this paradigm shift and explore further viable designs for oxyallyl derivatives, including their O-protonated forms (oxyallyl cations) and the corresponding radical cations (which can be perfectly air-stable!).
Our preliminary results demonstrate that oxyallyl frameworks have hydrogen atom transfer capabilities and can be used as multi-electron redox platforms. Thus, stable versions of oxyallyls and their derivatives are more than chemical oddities: they have potential for paving the way to fruitful concepts with original applications. In addition to the synthesis and study of organic derivatives, the implementation of oxyallyl patterns in complexes of transition metals will also be considered, with the aim of offering new original opportunities in the field of cooperative catalysis.

Project coordinator

Monsieur David MARTIN (Département de Chimie Moléculaire de l'Université Joseph Fourrier)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

DCM Département de Chimie Moléculaire de l'Université Joseph Fourrier

Help of the ANR 205,221 euros
Beginning and duration of the scientific project: September 2014 - 48 Months

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