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

Abstract

Luminescent Ce(III) complexes, Ce[N(SiMe3)2]3 (1) and [(Me3Si)2NC(RN)2]Ce[N(SiMe3)2]2 (R = (i)Pr, 1-(i)Pr; 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-(i)Pr, and 1-Cy with lifetimes of 24, 67, and 61 ns, respectively. Time-dependent density functional theory (TD-DFT) studies on 1 and 1-(i)Pr revealed the (2)A1 excited states corresponded to singly occupied 5d(z(2)) orbitals. The strongly reducing metalloradical character of 1, 1-(i)Pr, and 1-Cy in their (2)A1 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.

Structure, Electronics and Reactivity of Ce(PNP) Complexes

“…10 mL) and storage of the filtrate at À25 8Cg ave orange blocks of 5.Y ield:1 95 mg, 82 %. 1 HNMR (400 MHz, C 6 D 6 , 25 8C): d = 46.3 (br), 34.9 (br), 27.8 (br), 19.4 (br), 17.7 (br), 14.6 (br), 5.2 (br), 0.3 (br), À3.9 (br), À6.6 (br), À10.5 (br), À13.1 (br), À16.6 ppm (br). Significant broadness of the resonance signals precluded the satisfactory measurement of their relative intensities.…”

“…The pentacoordinated Ce(1) ion is arranged centrally in the N(1)/N(2)/N(3) triangle with the NÀCeÀNa ngles ranging from 117.39(5)8 to 123.87(5)8.Asimilar environment of the cerium(III) ion was observed in [Ce{N(Si-Me 2 R) 2 } 3 ]( R = Me, tBu) [18] and[ Ce{(Me 3 Si) 2 NC(NiPr) 2 }{N(SiMe 3 ) 2 } 2 ] complexes. [19] The Ce(1)ÀN(2) bond is elongated compared to the Ce(1)ÀN(1,3) bonds (2.4706(16) versus 2.3628(16)/ 2.3715(16) ,T able 1). The Ce(1)ÀP(1,2) distances (3.1410(5) and 3.1899(5) )are slightly longer than those reported in literature for the Ce III complexes with P-donors (3.020(2)-3.152 (3) ).…”

Solvoluminescence of Cerium(III) Thiocyanate Complex

“…However, in contrast to the large number of reports for Ce III -dopeds olidstate phosphors, there are al imited number of reports for the luminescent molecular Ce III complexes. [6,7,18] They furtherd emonstrated that the emission quantum yield of tris(guanidinate) complexes correlates with the steric demand of the ligand backbone substituents in C 3 -symmetry. [5] Schelter and co-workersr eported that the Ce III complexes containing the disilazane and/org uanidine ligands showi ntense emissions with various colors from blue to yellow in toluene, whereast he Ce III complexes were handled under an inert atmosphere (N 2 ).…”

“…In contrast to the fact that the well-known Eu III and Tb III ions show their specifice mission colors basedo nt he parity-forbidden 4f-4ft ransitions, [2] the emission color of the Ce III ion is tunable from UV to red by changing the host materiali ni norganic crystals because the 5d orbital, which is sensitive to the surrounding environment, relatest ot he emissionf rom the Ce III ion; [3] for example, the Ce III ion doped in Y 3 Al 5 O 12 shows a yellow emission at 536 nm whereas Ce III ion doped in Li 2 SrSiO 4 shows ab lue emission at 442 nm. [3a] The molecular Ce III complexes,w hich can dissolve in organic solvents and sublime, have great potential in applicationsa s the emitter in organic light-emitting diodes (OLEDs) [4,5] and the photosensitizer in homogeneous photoredox catalysis [6,7] due to the characteristic emission features of the Ce III ion. [3a] The molecular Ce III complexes,w hich can dissolve in organic solvents and sublime, have great potential in applicationsa s the emitter in organic light-emitting diodes (OLEDs) [4,5] and the photosensitizer in homogeneous photoredox catalysis [6,7] due to the characteristic emission features of the Ce III ion.…”

“…[5,6,18] Figure 1b shows the emission spectral change excited at 330 nm. [5][6][7] By comparison of the amplitudes of the componentsa nd the molarf ractionso ft he excited species, which are calculated from Figure 2a nd the absorptionc oefficients of each Ce III complex (see the Supporting Information), the lifetime components of 9, 29-30, and The emission spectra of am ixture of Ce(OTf) 3 and nBu 4 NSCN (1:3 molar ratio) werem easured in several solvents at 298 K and it was found that some solvents changed the emission from blue to near UV or green (Figure 3a nd Table S1 in the Supporting Information). In addition, the formation of the cerium(III) thiocyanate complex was confirmed with IR and 13 CNMR spectra (Figures S1 and S2 in the Supporting Information).…”