The steric and electronic effects on the stability and reactivity of cerium(IV) aryloxide complexes supported by the Klaüi tripodal ligand [Co(η 5 -C 5 H 5 ){P(O)(OEt) 2 } 3 ] − (L OEt − ) have been investigated. A Ce(IV) oxo species (1) prepared in situ from [Ce(L OEt ) 2 Cl 2 ] and Ag 2 O has been used as a starting material for the synthesis of Ce(IV) aryloxide complexes. The reactions of 1 with aryl alcohols (ArOH) in hexane resulted in formation of three possible products:) has been synthesized by ligand exchange between 2-Cl 2,4 and [Ce IV (L OEt ) 2 Cl 2 ]. No obvious correlation was found between the Ce−O bond lengths [2.138(6)−2.215(3) Å]/Ce−O−C angles [138.6(3)−166.8( 3)°] and the substituents of the aryloxide ligands in 2-H, 2-Br 2,4 , 2-Br 3,5 , 2-Cl 2,4 , and 2-F 2,6 . Among the Ce(IV) bis(aryloxide) complexes synthesized, 2-F 2,6 was found to be most reactive with respect to Ce(IV/III) reduction. In hexane, 2-F 2,6 is capable of oxidizing 2,4,6-tri-tert-butylphenol (tbp) and 9,10-dihydroanthrancene, presumably via an H-atom abstraction pathway. Density functional theory calculations indicated that 2-F 2,6 has a triplet excited state lying 7.1 kcal mol −1 above the singlet ground state. The oxidation of tbp by 2-F 2,6 involves Ce−O aryl bond homolysis of the triplet excited state and H-atom transfer between the resulting 2,6-difluorophenoxyl radical and tbp. This work highlights the influence of the steric effect on the stability and reactivity of redox-active Ce(IV) aryloxide complexes.

No abstract

No abstract