The reactivity of the cerium(IV) oxo complex [(L)Ce(═O)(HO)]·MeC(O)NH (1; L = [CoCp{P(O)(OEt)}], where Cp = η-CH) toward electrophiles and Brønsted acids has been investigated. The treatment of 1 with acetic anhydride afforded the diacetate complex [Ce(L)(OCMe)] (2). The reaction of 1 with B(CF) yielded [Ce(L)(MeCONH)][B(CF)(OH)] (3), in which the [B(CF)(OH)] anions are H-bonded to the O-bound acetamide ligands. The treatment of 1 with HCl and HNO afforded [Ce(L)Cl] and [Ce(L)(NO)], respectively. Protonation of 1 with triflic acid (HOTf) gave the diaqua complex [Ce(L)(HO)](OTf) (4), in which the triflate anions are H-bonded to the two aqua ligands. The treatment of 1 with phenol afforded the phenoxide complex [Ce(L)(OPh)] (5). The oxo-bridged bimetallic complex [(L)(MeCONH)Ce(O)NaL] (6) with the Ce-O and Na-O distances of 1.953(4) and 2.341(4) Å, respectively, was obtained from the reaction of 1 with [NaL]. Density functional theory calculations showed that the model complex [(L)Ce(MeCONH)(O)NaL] (6A; L = [CoCp{P(O)(OMe)}]) contains a polarized Ce═O multiple bond. The energy for dissociation of the {NaL} fragment from 6A in acetonitrile was calculated to be +33.7 kcal/mol, which is higher than that for dissociation of the H-bonded acetamide from [(L)Ce(═O)(HO)]·MeC(O)NH (1A) (calculated to be +17.4 kcal/mol). In hexanes containing trace water, complex 1 decomposed readily to a mixture of a tetranuclear cerium(IV) oxo cluster, [Ce(L)(μ-O)(μ-O)(μ-OH)] (7), and a cerium(III) complex, [Ce(L)(HO)][L] [8(L)], whereas the cerium/sodium oxo complex 6 is stable under the same conditions. The crystal structures of 3, 4·HO, 6, and 8(L) have been determined.

A tetranuclear Ce(IV) oxo cluster compound containing the Kläui tripodal ligand [Co(η(5) -C5 H5 ){P(O)(OEt)2 }3 ](-) (LOEt (-) ) has been synthesized and its reactions with H2 O2 , CO2 , NO, and Brønsted acids have been studied. The treatment of [Ce(LOEt )(NO3 )3 ] with Et4 NOH in acetonitrile afforded the tetranuclear Ce(IV) oxo cluster [Ce4 (LOEt )4 O7 H2 ] (1) containing an adamantane-like {Ce4 (μ2 -O)6 } core with a μ4 -oxo ligand at the center. The reaction of 1 with H2 O2 resulted in the formation of the peroxo cluster [Ce4 (LOEt )4 (μ4 -O)(μ2 -O2 )4 (μ2 -OH)2 ] (2). The treatment of 1 with CO2 and NO led to isolation of [Ce(LOEt )2 (CO3 )] and [Ce(LOEt )(NO3 )3 ], respectively. The protonation of 1 with HCl, ROH (R=2,4,6-trichlorophenyl), and Ph3 SiOH yielded [Ce(LOEt )Cl3 ] (3), [Ce(LOEt )(OR)3 ] (4), and [Ce(LOEt )(OSiPh3 )3 ] (5), respectively. The chloride ligands in 3 are labile and can be abstracted by silver(I) salts. The treatment of 3 with AgOTs (OTs(-) =tosylate) and Ag2 O afforded [Ce(LOEt )(OTs)3 ] (6) and 1, respectively. The electrochemistry of the Ce-LOEt complexes has been studied by using cyclic voltammetry. The crystal structures of complexes 1-5 have been determined.

Tetravalent cerium alkoxide complexes supported by the Klaüi tripodal ligand [Co(η 5 -C 5 H 5 ){P(O)(OEt) 2 } 3 ] − (L OEt − ) have been synthesized, and their nucleophilic and redox reactivity have been studied. Treatment of the Ce(IV) oxo complex [Ce IV (L OEt ) 2 (O)(H 2 O)]•MeCONH 2 (1) with i PrOH or reaction of [Ce IV (L OEt ) 2 Cl 2 ] (2) with Ag 2 O in i PrOH afforded the Ce(IV) dialkoxide complex [Ce IV (L OEt ) 2 (O i Pr) 2 ] (3-iPr). The methoxide and ethoxide analogues [Ce IV (L OEt ) 2 (OR) 2 ] (R = Me (3-Me), Et (3-Et)) have been prepared similarly from 2 and Ag 2 O in ROH. Reaction of 3-iPr with an equimolar amount of 2 yielded a new Ce(IV) complex that was formulated as the chloro-alkoxide complex [Ce IV (L OEt ) 2 (O i Pr)Cl] (4). Treatment of 3-iPr with HX and methyl triflate (MeOTf) afforded [Ce(L OEt ) 2 X 2 ] (X − = Cl − , NO 3 − , PhO − ) and [Ce IV (L OEt ) 2 (OTf) 2 ], respectively, whereas treatment with excess CO 2 in hexane led to isolation of the Ce(IV) carbonate [Ce IV (L OEt ) 2 (CO 3 )]. 3-iPr reacted with water in hexane to give a Ce(III) complex and a Ce(IV) species, presumably the reported tetranuclear oxo cluster [Ce IV 4 (L OEt ) 4 (O) 5 (OH) 2 ]. The Ce(IV) alkoxide complexes are capable of oxidizing substituted phenols, possibly via a protoncoupled electron transfer pathway. Treatment of 3-iPr with ArOH afforded the Ce(III) aryloxide complexes [Ce III (L OEt ) 2 (OAr)] (Ar = 2,4,6-tri-tert-butylphenyl (5), 2,6-diphenylphenyl ( 6)). On the other hand, a Ce(III) complex containing a monodeprotonated 2,2′-biphenol ligand, [Ce III (L OEt ) 2 ( t Bu 4 C 12 H 4 O 2 H)] (7) ( t Bu 4 C 12 H 4 O 2 H 2 = 4,4′,6,6′-tetra-tert-butyl-2,2′-biphenol), was isolated from the reaction of 3-iPr with 2,4-di-tert-butylphenol. The crystal structures of complexes 3-iPr, 3-Me, 3-Et, and 5−7 have been determined.