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)(2)NC(RN)(2)]Ce[N(SiMe3)(2)](2) (R = Pr-i, 1-Pr-i; 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-Pr-i, and 1-Cy with lifetimes of 24, 67, and 61 ns, respectively. Time-dependent density functional theory (TD-DFT) studies on 1 and 1-Pr-i revealed the (2)A(1) excited states corresponded to singly occupied 5d(z2) orbitals. The strongly reducing metalloradical character of 1, 1-Pr-i, and 1-Cy in their (2)A(1) excited states afforded photochemical halogen atom abstraction reactions from sp(3) and sp(2) 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.