RESUMEN
Several novel routes for the immobilization of modified Cu(salicylaldimine) complexes on commercially available silica are described. New pulse electron paramagnetic resonance (EPR) and electron-nuclear double resonance sequences, which provide more detailed information than that available previously, in combination with continuous wave EPR, allow a definitive assignment of the geometry at the copper center in the immobilized Cu(salicylaldimine). Immobilization of the modified Cu(salicylaldimine) on silica was followed in situ by monitoring the intensity of the characteristic free- and metal-coordinated imine bands as a function of time using attenuated total reflectance IR spectroscopy. On the basis of these studies, the outcome of the Schiff base condensation of Cu-bis(salicylaldehyde) with gamma-aminopropyl-modified silica gel is shown to provide immobilized trans-O(2)N(2)- and O(3)N-coordinated immobilized Cu(salicylaldimine)-type compounds. In addition, trans-O(2)N(2)- or O(3)N-coordinated copper centers are selectively prepared on silica by controlling the aminopropyl modifier loading, thus opening a route to compounds not available by conventional synthesis. The O(3)N-coordinated Cu(salicylaldimine)-type compound on silica was investigated as a precursor for the synthesis of a tethered chiral Cu(salicylaldimine) via reaction of the coordinated carbonyl group with (R)-(+)-alpha-methylbenzylamine. Supported Cu(salicylaldimine) was also prepared via the immobilization of the appropriate silylethoxy-modified homogeneous precursor on silica gel. Precursors and silica-supported Cu(salicylaldimine) materials have been fully characterized. Comparisons are drawn with related Cu(salicylaldimine) immobilized in silica aerogels.
RESUMEN
Tetrameric [{(C(5)Me(5))MF(3)}(4)] (M = Zr, Hf) react smoothly with Me(3)SiCl in CH(2)Cl(2) at room temperature to give [{(C(5)Me(5))ZrF(2)Cl}(4)] (1) and [{(C(5)Me(5))HfF(2)Cl}(4)] (2), respectively, in high yield. Treatment of [{(C(5)Me(5))MF(3)}(4)] (M = Zr, Hf) with Me(2)AlCl in toluene gives mixtures of 1 and [(C(5)Me(5))(4)Zr(4)(&mgr;-F)(2)(&mgr;-F(2))(2)(&mgr;-Cl)(2)Cl(4)] (3), and 2 and [(C(5)Me(5))(4)Hf(4)(&mgr;-F)(2)(&mgr;-F(2))(2)(&mgr;-Cl)(2)Cl(4)] (4), respectively, in an approximately 1:1 molar ratio. Metallocene type complexes [(C(5)Me(4)Et)(2)ZrCl(2)] and [(C(5)Me(5))(2)HfCl(2)] react with 1 equiv of Me(3)SnF to give [(C(5)Me(4)Et)(2)ZrClF] (5) and [(C(5)Me(5))(2)HfClF] (6), respectively. The complexes 1-6 were characterized by spectroscopic methods ((1)H and (19)F NMR and mass spectroscopy). The solid state structures of 1, 3, and 5 were determined by single-crystal X-ray diffraction analyses.
