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 ‐ t Bu‐calix[4](OMe) 2 (OH) 2 in toluene gave the new cerium(IV) calix[4]arene complex { p ‐ t Bu‐calix[4](OMe) 2 (O) 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 ‐ t Bu‐calix[4](OMe) 2 (O) 2 }Ce(acac) 2 ( 3 ). The bromination reaction of 3 gave the bisbrominated complex { p ‐ t Bu‐calix[4](OMe) 2 (O) 2 }Ce(Br‐acac) 2 ( 4 ). 1 H 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 X‐ray 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 ox in these complexes are detected. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)