Metallasiloxanes containing Si-O-M functional groups (M main group metal, transition metal, or f-block element) have been envisaged as molecular analogues of zeolites due to their astonishing geometrical relationship. In recent years, the chemistry of metallasilsesquioxanes has been extensively covered. [2] Metallasilsesquioxanes of rare earth metals might be important as homogeneous analogues of silica-supported rare earth metal catalysts and rare earth silicates, which are potential materials for optoelectronics. Hence, this area of research is of considerable interest for several fields of chemistry, including catalysis and materials science. However, investigations on metallasilsesquioxanes of rare earth metals are often hampered by difficulties with crystallization and characterization of these compounds. Here we report the synthesis and structural investigation of the first Ce IV metallasilsesquioxane, a possible homogeneous model of Ce IV silicate oxidation catalysts, and a new synthetic route, which may provide access to other novel metallasilsesquioxane complexes.
Treatment of [Ce{N(SiMe 3 ) 2 } 3 ] with two equivalents of (c-C 6 H 11 ) 8 Si 8 O 11 (OH) 2 [3] in diethyl ether in the presence of an excess of pyridine exclusively afforded the diamagnetic complex [Ce{(c-C 6 H 11 ) 8 Si 8 O 13 } 2 (py) 3 ] (1). Compound 1 could also be prepared by direct reaction of anhydrous CeCl 3 with two equivalents of (c-C 6 H 11 ) 8 Si 8 O 11 (OH) 2 in THF/pyridine, albeit in somewhat lower yield (Scheme 1). Surprisingly, in both cases cerium was oxidized to the tetravalent oxidation state. The compound gave satisfactory C,H,N analyses and was fully characterized by IR and 1 H, 13 C, and 29 Si NMR spectra, as well as X-ray single-crystal diffraction.
The IR spectrum (KBr) of 1 exhibited characteristic pyridine bands at 1599 and 750 cm ร1 . 1 H NMR spectroscopy in [D 6 ]benzene gave a complex spectrum for a diamagnetic compound with broad multiplets between d 0.91 and 2.12 for the methine and methylene protons of the c-C 6 H 11 substituents. The spectrum also showed three characteristic signals attributable to pyridine. In the 13 C NMR spectrum the syringe. The flask was fitted with a condenser and refluxed under argon for 15 h. The reaction was monitored by thin-layer chromatography. After the solvent was evaporated, the product was purified directly on a silica gel column.