Oxidizing Cerium(IV) Alkoxide Complexes Supported by the Kläui Ligand [Co(η-CH){P(O)(OEt)}]: Synthesis, Structure, and Redox Reactivity.

Tetravalent cerium alkoxide complexes supported by the Kläui tripodal ligand [Co(η-CH){P(O)(OEt)}] (L) have been synthesized, and their nucleophilic and redox reactivity have been studied. Treatment of the Ce(IV) oxo complex [Ce(L)(O)(HO)]·MeCONH () with PrOH or reaction of [Ce(L)Cl] () with AgO in PrOH afforded the Ce(IV) dialkoxide complex [Ce(L)(OPr)] (). The methoxide and ethoxide analogues [Ce(L)(OR)] (R = Me (), Et ()) have been prepared similarly from and AgO in ROH. Reaction of with an equimolar amount of yielded a new Ce(IV) complex that was formulated as the chloro-alkoxide complex [Ce(L)(OPr)Cl] (). Treatment of with HX and methyl triflate (MeOTf) afforded [Ce(L)X] (X = Cl, NO, PhO) and [Ce(L)(OTf)], respectively, whereas treatment with excess CO in hexane led to isolation of the Ce(IV) carbonate [Ce(L)(CO)]. reacted with water in hexane to give a Ce(III) complex and a Ce(IV) species, presumably the reported tetranuclear oxo cluster [Ce(L)(O)(OH)]. The Ce(IV) alkoxide complexes are capable of oxidizing substituted phenols, possibly via a proton-coupled electron transfer pathway. Treatment of with ArOH afforded the Ce(III) aryloxide complexes [Ce(L)(OAr)] (Ar = 2,4,6-tri--butylphenyl (), 2,6-diphenylphenyl ()). On the other hand, a Ce(III) complex containing a monodeprotonated 2,2'-biphenol ligand, [Ce(L)(BuCHOH)] () (BuCHOH = 4,4',6,6'-tetra--butyl-2,2'-biphenol), was isolated from the reaction of with 2,4-di--butylphenol. The crystal structures of complexes , , , and - have been determined.