Synthesis, structure, and reactivity of cerium(IV) calix[4]arene complexes

The equimolar reaction of Ce(hfac)(4) (1) (hfac = 1,1,1,5,5,5-hexafluoropentanedionato) with p-tBu-calix[4](OMe)(2)(OH)(2) in toluene gave the new cerium(IV) calix[4]arene complex (p-tBu-calix[4](OMe)2(0)2)Ce(hfaC)2 (2). The single-crystal X-ray structure shows the cone geometry of the calixarene ligand with the methoxy groups coordinated to the cerium; it shows slightly longer cerium-oxygen (acetylacetonate ligand) bond lengths than the corresponding bonds in the analogous nonfluorinated complex (p-tBu-calix[4](OMe)(2)-(O)(2)}Ce(acac)(2) (3). The bromination reaction of 3 gave the bisbrominated complex {p-tBu-calix[4](OMe)(2)(O)(2)}Ce(Br-acac)(2) (4). H-1 NMR spectroscopic studies and a single-crystal X-ray structure of 4 revealed that the bromination took place in the 3-position of the acac ligand. Furthermore, the first Xray photoelectron spectroscopy (XPS) evaluation of the Ce oxidation state in cerium calix[4]arene complexes 2 and 3 is presented, and X-ray induced changes of Ce x in these complexes are detected. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)