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Redox-active ligands for catalysis

These redox-active “metallo-ligands” are typically classic ligands where a redox-active organometallic endgroups, stable under two redox states, have been appended to the coordinating sites. Such species present usually several redox states with different electronic structures and their complexes with various metal centers might therefore exhibit also different properties. Depending on their design, redox chemistry might then be used to control their reactivity or to modulate a given photonic property of those molecular assemblies. We have currently focused our efforts to identify ligands allowing performing catalysis in a redox-switchable way.

Triarylphosphines-based metalloligands.

Four new triphenylphosphines ligands featuring peripheral electron-rich and redox-active “Fe(κ2-dppe)(η5-C5Me5)C≡C-” pendant substituents have been synthesized. These new triarylphosphine ligands perform comparably or better than triphenylphosphine when used as ligands in a Stille-type aryl-aryl cross-coupling reaction.

G. Grelaud, G. Argouarch, A. Tohmé, T. Roisnel, F. Paul New J. Chem. 2011, 35, 2740; DOI:10.1039/C1NJ20480G

Steric and electronic properties of these metallo-phosphines, which are stable and isolable under two redox-states, have been characterized. These new ligands open interesting perspectives for the realization of supramolecular assemblies featuring redox-switchable optical properties and reactivities.

A. Tohmé, G. Grelaud, G. Argouarch, T. Roisnel, A. Bondon, F. Paul Inorg. Chem. 2013, 52, 8993; DOI: 10.1021/ic4011828
A. Tohmé, H. Sahnoune, T. Roisnel, V. Dorcet, J.-F. Halet, F. Paul Organometallics 2014, 33, 3385; DOI: 10.1021/om500211e

Alkynylphosphines-based metalloligands.

New dimeric Fe(II) diphosphonium-bis-alkynyl complexes are formed quantitatively and reversibly by oxidation of the corresponding Fe(II) alkynylphosphine complexes. The structure of these new organometallic diphosphonium salts and their monomeric Fe(II) precursors have been established by X-ray studies. Remarkably, the P-P bond of the dimers appears to be quite labile and can be cleaved in a 2-electron reduction process to regenerate Fe(II) starting materials.

A. Tohmé, G. Grelaud, G. Argouarch, T. Roisnel, S. Labouille, D. Carmichael, F. Paul Angew. Chem. Int. Ed. 2013, 52, 4445; DOI: 10.1002/anie.201208682
A. Tohmé, C. T. Hagen, S. Essafi, A. Bondon,T. Roisnel, D. Carmichael, F. Paul Chem. Commun. 2015, 51, 1316; DOI: 10.1039/c4cc08993f.