Tuning Organocerium Electrochemical Potentials by Extending Tris(cyclopentadienyl) Scaffolds with Terminal Halogenido, Siloxy, and Alkoxy Ligands

Treatment of cerous (Cp3Ce)-Ce-R(thf) (Cp-R = C5H4R; R = H, Me) with the halogenating reagents C2Cl6, TeBr4, and I-2 afforded the ceric halides (Cp3CeX)-Ce-R (X = CI, Br, I) in high yield. Subsequent salt metathesis with sodium alkoxides and siloxides led to a series of alkoxy and siloxy derivatives. Compounds (Cp3CeOR)-Ce-R' with R' = Me, Et, CH(2)tBu, iPr, tBu, SiMe3, SiEt3, Si(iPr)(3) SiPh3 (and Si(OtBu)(3)) have been isolated and characterized by H-1, C-13, and Si-29 NMR and DRIFT spectroscopy, magnetic measurements, X-ray structure analyses, cyclic voltammetry, and elemental analyses. The ceric complexes (Cp3CeX)-Ce-R and (Cp3CeOR)-Ce-R' are isostructural, featuring terminal ligands X and OR'. The magnetic measurements revealed temperature-independent paramagnetism (TIP), with positive magnetic susceptibilities in the range chi(0) (1.53-3.9) X 10(-4) emu/mol. Cyclic voltammetry indicated two types of redox processes: (a) chemical and electrochemical reversibility for halide and siloxide complexes and (b) EC- or ECE-type mechanisms for the alkoxides (chemical reversibility at high scan rates). In all cases formal potentials could be determined ranging from -0.583 V vs Fc/F+ for Cp3CeI to -1.259 V vs Fc/Fc(+) for (Cp3Ce)-Ce-Me(OEt). The electrochemical data revealed an increase in stabilization with respect to reduction of the cerium(IV) center in the series I < Br < Cl < siloxy < alkoxy ligand and a better stabilization with Cp-Me in comparison to Cp ligands by approximately 0.05-0.1 V. As a result, an improved stabilization of Ce(IV) was observed for more strongly electron donating ligands.

Automated summary

The study synthesized and characterized a series of cerium(IV) complexes with different ligands, revealing that the introduction of different ligands significantly affected the reduction stabilization of cerium(IV).