Oxidizing Cerium(IV) Alkoxide Complexes Supported by the Kläui Ligand [Co(η5-C5H5){P(O)(OEt)2}3]-: Synthesis, Structure, and Redox Reactivity.

Tetravalent cerium alkoxide complexes supported by the Kläui tripodal ligand [Co(η5-C5H5){P(O)(OEt)2}3]- (LOEt-) have been synthesized, and their nucleophilic and redox reactivity have been studied. Treatment of the Ce(IV) oxo complex [CeIV(LOEt)2(O)(H2O)]·MeCONH2 (1) with iPrOH or reaction of [CeIV(LOEt)2Cl2] (2) with Ag2O in iPrOH afforded the Ce(IV) dialkoxide complex [CeIV(LOEt)2(OiPr)2] (3-iPr). The methoxide and ethoxide analogues [CeIV(LOEt)2(OR)2] (R = Me (3-Me), Et (3-Et)) have been prepared similarly from 2 and Ag2O 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 [CeIV(LOEt)2(OiPr)Cl] (4). Treatment of 3-iPr with HX and methyl triflate (MeOTf) afforded [Ce(LOEt)2X2] (X- = Cl-, NO3-, PhO-) and [CeIV(LOEt)2(OTf)2], respectively, whereas treatment with excess CO2 in hexane led to isolation of the Ce(IV) carbonate [CeIV(LOEt)2(CO3)]. 3-iPr reacted with water in hexane to give a Ce(III) complex and a Ce(IV) species, presumably the reported tetranuclear oxo cluster [CeIV4(LOEt)4(O)5(OH)2]. The Ce(IV) alkoxide complexes are capable of oxidizing substituted phenols, possibly via a proton-coupled electron transfer pathway. Treatment of 3-iPr with ArOH afforded the Ce(III) aryloxide complexes [CeIII(LOEt)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, [CeIII(LOEt)2(tBu4C12H4O2H)] (7) (tBu4C12H4O2H2 = 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.

A Combined Experimental and Theoretical Study of the Versatile Reactivity of an Oxocerium(IV) Complex: Concerted Versus Reductive Addition.

A combined experimental and theoretical investigation on the cerium(IV) oxo complex [(LOEt )2 Ce(=O)(H2 O)]⋅MeC(O)NH2 (1; LOEt - =[Co(η5 -C5 H5 ){P(O)(OEt)2 }3 ]- ) demonstrates that the intermediate spin-state nature of the ground state of the cerium complex is responsible for the versatility of its reactivity towards small molecules such as CO, CO2 , SO2 , and NO. CASSCF calculations together with magnetic susceptibility measurements indicate that the ground state of the cerium complex is of multiconfigurational character and comprised of 74 % of CeIV and 26 % of CeIII . The latter is found to be responsible for its reductive addition behavior towards CO, SO2 , and NO. This is the first report to date on the influence of the multiconfigurational ground state on the reactivity of a metal-oxo complex.

Reactions of cerium complexes with transition metal nitrides: synthesis and structure of heterometallic cerium complexes containing bridging catecholate ligands.

In an attempt to synthesize heterometallic cerium nitrido complexes, we studied the reactions of cerium complexes supported by the Kläui tripodal ligand [Co(η5-C5H5){PO(OEt)2}3]- (LOEt-) with transition-metal nitrides. Whereas no reactions were found between Ce-LOEt complexes and [RuVI(LOEt)(N)Cl2] (2), treatment of the Ce(iv) oxo complex [CeIV(LOEt)2(O)(H2O)]·MeCONH2 (1) with 2 resulted in reduction of both the Ce(iv) and Ru(vi) complexes, and formation of a heterometallic Ce(iii)/Ru(iii) complex with a bridging deprotonated acetamide ligand, [(LOEt)2(H2O)CeIII{µ-O,N-MeC(O)NH}RuIII(LOEt)Cl2] (4), along with a minor product, [CeIII(LOEt)2(NO3)]. Ce(iv)-LOEt complexes such as [CeIV(LOEt)2Cl2] (3) can oxidize [ReV(LOEt)(N)(PPh3)Cl] to give the Re(vi) nitride [ReVI(LOEt)(N)(PPh3)Cl]+. Chloride abstraction of 3 by TlPF6 followed by reaction with [PPh4]2[MnV(N)(CN)4] afforded a diamagnetic red solid that is tentatively formulated as a heterometallic Ce(iv)/Mn(v) complex, [Ce(LOEt)2(H2O){Mn(N)(CN)4}] (5). Reactions of 3 with [nBu4N][MVI(N)(cat)2] (cat2- = catecholate(2-)) afforded the Ce(iii)/M(vi) complexes [(LOEt)2CeIII{(µ-cat)2MVI(N)}] [M = Ru (6), Os (7)], in which the Ce(iii) and M(vi) centers are bridged by two oxygen atoms of the two catecholate ligands. Similarly, the catecholate-bridged Ce(iii)/Re(v) complex [(LOEt)2CeIII{(µ-cat)2ReV(O)}] (8) was prepared from 3 and [Me4N][ReV(O)(cat)2]. In CH2Cl2, 8 was air-oxidized to the Ce(iii)/Re(vii) complex [CeIII(LOEt)2(H2O)2][cis-{ReVII(O)2(cat)2}] (9) with a cis-dioxo-Re(vii) counter-anion. The crystal structures of 4, 6, and 9 have been determined.