Synthesis, structure and reactivity of new yttrium bis(dimethylsilyl)amido and bis(trimethylsilyl)methyl complexes of a tetradentate bis(phenoxide) ligand

The reactions of a bulky amino-methoxy bis(phenolate) ligand H2L with Y(CH2SiMe3)(3)(THF)(2) and Y[N(SiHMe2)(2)](3)(THF)(2) under mild condition leads to the selective formation of the thermally stable complexes [L]Y(CH2SiMe3)(THF) (1) and [L]Y[N(SiHMe2)(2)](THF) (2). The X-ray structures revealed very similar binding of the [ONOO] ligand core to the metal for both complexes, which feature an octahedral geometry involving coordination of the methoxy side-arm of the ligand and of a remaining THF molecule. H-1-NMR spectroscopy indicates that the solid state structure of 1 and 2 is retained in hydrocarbon solutions with THF coordinated to yttrium. Alkyl complex I showed no activity in ethylene polymerization, presumably due to the presence of coordinated THF. The amido complex 2 catalyzed sluggishly the polymerization of methyl methacrylate to give isotactic-rich PMMA but is very active for the ring-opening polymerization of c-caprolactone. (C) 2003 Elsevier B.V. All rights reserved.