Redox and Photochemical Reactivity of Cerium(IV) Carbonate and Carboxylate Complexes Supported by a Tripodal Oxygen Ligand.

The protonolysis and redox reactivity of a Ce(IV) carbonate complex supported by the Kläui tripodal ligand [(η-CH)Co{P(O)(OEt)}] (L) have been studied. Whereas treatment of [Ce(L)(CO)] () with RCOH afforded [Ce(L)(RCO)] ( = Me (), Ph (), 2-NOCH ()), the reaction of with PhCHCOH resulted in formation of a mixture of Ce(IV) () and Ce(III) () carboxylate species. In benzene in the dark, was slowly converted into via Ce(IV)-O(carboxylate) homolysis. Recrystallization of a mixture of and from hexane led to isolation of yellow crystals of that were identified as [Ce(L)(PhCHCO)]. Treatment of with sulfamic acid, trifluoroacetamide, and trifluoromethanesulfonamide gave [Ce(L)(SONH)] (), [Ce(L)(CFCONH)] (), and [Ce(L)(CFSONH)] (), respectively. The crystal structures of , , and have been determined. H atom transfer (HAT) of 2,6-di--butylphenol and 9,10-dihydroanthracene (DHA) with afforded 3,3',5,5'-tetra--butyldiphenoquinone and anthracene, respectively. The oxidation of DHA with under air yielded anthracene and anthraquinone. While is stable in acetonitrile, it is readily reduced to a Ce(III) species in tetrahydrofuran. In air, reacted with tetrahydrofuran to produce tetrahydrofuran hydroperoxide that can reduce the Ce(IV) carbonate rapidly. Upon irradiation with blue LED light, the Ce(IV)-L carboxylate complexes underwent facile decarboxylation via Ce-O homolysis. proved to be an efficient catalyst precursor for decarboxylative oxygenation of arylacetic acids. For example, irradiation of phenylacetic acid with blue LED light in the presence of 5 mol % of under air afforded benzyl alcohol and benzaldehyde in 10 and 90% yield, respectively.