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

Abstract

Luminescent Ce­(III) complexes, Ce­[N­(SiMe₃)₂]₃ (<b>1</b>) and [(Me₃Si)₂NC­(RN)₂]­Ce­[N­(SiMe₃)₂]₂ (R = ^<i>i</i>Pr, <b>1-</b>^{<i><b>i</b></i>}<b>Pr</b>; R = Cy, <b>1-Cy</b>), with <i>C</i>_3<i>v</i> and <i>C</i>_2<i>v</i> solution symmetries display absorptive 4f → 5d electronic transitions in the visible region. Emission bands are observed at 553, 518, and 523 nm for <b>1</b>, <b>1-</b>^{<i><b>i</b></i>}<b>Pr</b>, and <b>1-Cy</b> with lifetimes of 24, 67, and 61 ns, respectively. Time-dependent density functional theory (TD-DFT) studies on <b>1</b> and <b>1-</b>^{<i><b>i</b></i>}<b>Pr</b> revealed the ²A₁ excited states corresponded to singly occupied 5d_<i>z</i>² orbitals. The strongly reducing metalloradical character of <b>1</b>, <b>1-</b>^{<i><b>i</b></i>}<b>Pr</b>, and <b>1-Cy</b> 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