Cerium-quinone redox couples put under scrutiny.

Homoleptic cerous complexes Ce[N(SiMe)], [Ce{OSi(OBu)}] and [Ce{OSiPr}] were employed as thermally robust, weakly nucleophilic precursors to assess their reactivity towards 1,4-quinones in non-aqueous solution. The strongly oxidizing quinones 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or tetrachloro-1,4-benzoquinone (ClBQ) readily form hydroquinolato-bridged ceric complexes of the composition [(CeL)(μ-OCR)]. Less oxidising quinones like 2,5-di--butyl-1,4-benzoquinone (BuBQ) tend to engage in redox equilibria with the ceric hydroquinolato-bridged form being stable only in the solid state.

Effect of Substituents of Cerium Pyrazolates and Pyrrolates on Carbon Dioxide Activation.

Homoleptic ceric pyrazolates (pz) Ce(RR'pz) (R = R' = Bu; R = R' = Ph; R = Bu, R' = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe)] with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO insertion was found to increase in the order of Bupz < Phpz < BuMepz < Mepz.

Carbonyl group and carbon dioxide activation by rare-earth-metal complexes.

The rare-earth elements (Ln = Sc, Y, La-Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.

Cerium Pyrazolates Grafted onto Mesoporous Silica SBA-15: Reversible CO Uptake and Catalytic Cycloaddition of Epoxides and Carbon Dioxide.

The activation and catalytic conversion of CO is a current topic relating to molecular chemistry and materials science alike. As a transdisciplinary field of research, surface organometallic chemistry (SOMC) might be applicable to perform synergistically, thus striking a new path in sustainable chemistry. Both ceric and cerous rare-earth-metal pyrazolates, which were recently shown to reversibly insert CO and to promote the catalytic cycloaddition of epoxides and carbon dioxide, were grafted onto large-pore mesoporous silica SBA-15, thermally pretreated at 500 °C.

Emergence of a New [NNN] Pincer Ligand via Si-H Bond Activation and β-Hydride Abstraction at Tetravalent Cerium.

The cerium(IV) pyrazolate complexes [Ce(Me pz) ] and [Ce(Me pz) (thf)] initiate β-hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl-substituted silylamido ligand, namely [Ce(Me pz) (bpsa)] (bpsa=bis((3,5-dimethylpyrazol-1-yl)dimethylsilyl)amido; Me pz =3,5-dimethylpyrazolato), along with some cerium(III) species. Remarkably, the nucleophilic attack of the pyrazolyl at the silicon atom and concomitant Si-H-bond cleavage is restricted to the tetravalent cerium oxidation state and appears to proceed via the formation of a transient cerium(IV) hydride, which engages in immediate redox chemistry. When [Ce(Me pz) ] is treated with [Li{N(SiMe ) }], that is, in the absence of the SiH functionality, any redox chemistry did not occur.