Speaker
Description
Catalysis is a fascinating opportunity for chemists to unbolt new reaction pathways in mild conditions. Among promising fields of catalysis, photoredox catalysts have shown good reactivity. However, mostly-used photocatalysts are still mainly based on precious metals such as iridium and ruthenium. Efforts to develop more abundant metals photoactive complexes brought some examples using iron, copper, and chromium complexes as photocatalysts. However, they remain only mildly reductive. Among other abundant metals, cerium is an interesting candidate: as abundant as cobalt (66.5 ppm) and cheaper, its comprehensive photochemical behaviour has been recently highlighted both as a powerful Single-Electron Transfer (SET) reagent in +III oxidation state,1,2 and as a Hydrogen Atom Transfer (HAT) reagent in +IV oxidation state, even capable of activating light alkanes (including methane).3,4
Nevertheless, the widespread use of CeCl3 as the photocatalyst hampers the progress in cerium photocatalysis. Indeed, its low solubility in apolar solvents significantly narrows the scope of possible reactions in mild conditions, and non-tunable redox potential complicates using this species in a multicatalytic system. Moreover, the mechanism of HAT reactions of cerium is still discussed, mainly the nature of the HAT agent. This is particularly due to the high coordination number of lanthanide complexes, which renders the intermediates more difficult to ascertain.
To overcome those issues, we synthesized a highly soluble cerium complex: Ce(N(CH2CH2NSiiPr3)3) CeTRENTIPS, which displays SET reactivity with aryl and alkyl halides (Cl, Br, I) under +III oxidation state. Having a single open apical coordination position, CeIIITRENTIPS can be easily oxidized in corresponding CeIV mono-halides.
