Syntheses and Redox Properties of Carboxylate-Ligated Hexanuclear Ce(IV) Clusters and Their Photoinduced Homolysis of the Ce(IV)-Ligand Covalent Bond.

Oxo- and hydroxo-bridged hexanuclear Ce(IV) clusters surrounded by 12 carboxylate ligands, CeO(OH)(OCR)(L) (R = 2,6-Me-4-MeOCH (), 2,6-Me-4-BuCH (), 2,4,6-MeCH (), 2,6-MeCH (), 2,6-Me-4-FCH (), 2,6-Me-4-ClCH (), 9-anthracenyl (), and CHBu (), L = HO or RCOH), were synthesized by treating Ce(OBu) with the corresponding carboxylic acids (2-3 equiv.) in acetone or toluene, and the molecular structures of and were clarified by X-ray diffraction studies. UV-vis analyses of the clusters showed broad absorption corresponding to the ligand-to-metal charge transfer (LMCT) in the ultraviolet A (315-400 nm) to blue light region; density functional theory (DFT) studies of the simplified Ce(IV) and related Zr(IV) clusters, MO(OH)(OCR) (M = Ce, Zr, R = Ph, Me), revealed that the low-lying vacant 4f-orbitals of the Ce(IV) were responsible for absorption in the ultraviolet A to blue light region. Irradiation of blue LED light to under an argon atmosphere resulted in the formation of 7-methylisobenzofuran-1(3)-one (), which involved the following four steps: photoinduced homolysis of the Ce(IV)-OCOR bond, intramolecular hydrogen atom transfer to generate the corresponding benzyl radical, oxidation to the benzyl cation, and intramolecular cyclization. Cyclic voltammetry of cerium clusters having 2,6-dimethyl-4-substituted arylcarboxylate ligands showed electrochemically irreversible redox waves in the range of -0.79 to -0.38 V ( [CpFe]/CpFe for ). The one-electron-reduced Ce(III)Ce(IV) clusters were isolated by reducing with CpCo to give [CpCo][CeO(OH)(OCR)(thf)] (); cluster was the first structurally determined hexanuclear cerium cluster containing a [CeO(OH)] core.