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 C_3v and C_2v 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 5d_z² 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.