Luminescent Ce(III) Complexes as Stoichiometric and Catalytic Photoreductants for Halogen Atom Abstraction Reactions

Luminescent Ce­(III)
complexes, Ce­[N­(SiMe3)2]3 (1) and [(Me3Si)2NC­(RN)2]­Ce­[N­(SiMe3)2]2 (R = iPr, 1-iPr; R = Cy, 1-Cy), with C3v and C2v solution symmetries
display absorptive 4f → 5d electronic transitions in the visible
region. Emission bands are observed at 553, 518, and 523 nm for 1, 1-iPr, and 1-Cy with lifetimes of 24, 67,
and 61 ns, respectively. Time-dependent density functional theory
(TD-DFT) studies on 1 and 1-iPr revealed the 2A1 excited states corresponded to singly occupied 5dz2 orbitals. The strongly reducing
metalloradical character of 1, 1-iPr, and 1-Cy in their 2A1 excited states afforded photochemical
halogen atom abstraction reactions from sp3 and sp2 C–X (X = Cl, Br, I) bonds for the first time with
a lanthanide cation. The dehalogenation reactions could be turned
over with catalytic amounts of photosensitizers by coupling salt metathesis
and reduction to the photopromoted atom abstraction reactions.