posted on 2025-01-15, 08:31authored byHoang-Long Pham, Xinxin Jiang, Qiaolin Yan, Yat-Ming So, Wan Chan, Herman H. Y. Sung, Ian D. Williams, Wa-Hung Leung
The
protonolysis and redox reactivity of a Ce(IV) carbonate complex
supported by the Kläui tripodal ligand [(η5-C5H5)Co{P(O)(OEt)2}3]− (LOEt–) have been
studied. Whereas treatment of [Ce(LOEt)2(CO3)] (1) with RCO2H afforded [Ce(LOEt)2(RCO2)2] (R = Me (2), Ph (3), 2-NO2C6H3 (4)), the reaction of 1 with PhCH2CO2H resulted in formation of a
mixture of Ce(IV) (5) and Ce(III) (6) carboxylate
species. In benzene in the dark, 5 was slowly converted
into 6 via Ce(IV)-O(carboxylate) homolysis. Recrystallization
of a mixture of 5 and 6 from hexane led
to isolation of yellow crystals of 6 that were identified
as [Ce(LOEt)2(PhCH2CO2)]. Treatment of 1 with sulfamic acid, trifluoroacetamide,
and trifluoromethanesulfonamide gave [Ce(LOEt)2(SO3NH)2] (7), [Ce(LOEt)2(CF3CONH)2] (8),
and [Ce(LOEt)2(CF3SO2NH)2] (9), respectively. The crystal structures of 2, 4, and 6–8 have been determined.
H atom transfer (HAT) of 2,6-di-tert-butylphenol
and 9,10-dihydroanthracene (DHA) with 1 afforded 3,3′,5,5′-tetra-tert-butyldiphenoquinone and anthracene, respectively. The
oxidation of DHA with 1 under air yielded anthracene
and anthraquinone. While 1 is stable in acetonitrile,
it is readily reduced to a Ce(III) species in tetrahydrofuran. In
air, 1 reacted with tetrahydrofuran to produce tetrahydrofuran
hydroperoxide that can reduce the Ce(IV) carbonate rapidly. Upon irradiation
with blue LED light, the Ce(IV)-LOEt carboxylate complexes
underwent facile decarboxylation via Ce–O homolysis. 1 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 1 under air afforded benzyl alcohol and benzaldehyde in 10 and 90%
yield, respectively.