A series of heteroleptic tris(cyclopentadienyl) CeIV complexes has been isolated and crystallographically characterized, revealing the broad accessibility of such organocerium(IV) compounds. The oxidation of complexes CpMe3 Ce(thf) and Cp'3 Ce(thf) (CpMe =C5 H4 Me, Cp'=C5 H4 SiMe3 ), bearing monosubstituted electron-poor cyclopentadienyl ligands, with 0.5 equivalents of 1,4-benzoquinone or C2 Cl6 gave the cerium(IV) hydroquinolate complexes CpMe3 Ce(OC6 H4 O)CeCpMe3 and Cp'3 Ce(OC6 H4 O)CeCp'3 , or the chloride complexes CpMe3 CeCl and Cp'3 CeCl, respectively; the iodide complex Cp'3 CeI was obtained from the reaction of Cp'3 Ce(thf) with elemental iodine. The behavior of Cp'3 CeCl in salt metathesis protocols employing alkali metal amides or alkyl, alkoxide, and aryloxide reagents was investigated, which gave rise to the robust and isolable cerium(IV) alkoxide Cp'3 Ce(OtBu). Trivalent [Cp'2 CeCl]2 was synthesized by AlMe4 →Cl exchange utilizing Cp'2 Ce(AlMe4 ) and AlMe2 Cl. The reactivity of [Cp'2 CeCl]2 towards the oxidants Ph3 CCl, C2 Cl6 , 1,4-benzoquinone, and I2 has been assessed, and has provided useful information on CeIII /CeIV redox deactivation pathways. In addition to X-ray structure analysis, all the complexes were characterized by NMR, DRIFT (diffuse reflectance IR Fourier transform), and UV/Vis spectroscopy as well as elemental analysis. The tetravalent compounds were further analyzed for their magnetic susceptibility by using Evans' method.
Keywords: X-ray diffraction; cerium; oxidation; salt metathesis.
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