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  • Title: Versatile scorpionates and new developments in the denticity changes of NNCp hybrid scorpionate/cyclopentadienyl ligands in Sc and Y compounds: from kappa1-Neta5-Cp to kappa2-NNeta5-Cp.
    Author: Otero A, Fernández-Baeza J, Lara-Sánchez A, Antiñolo A, Tejeda J, Martínez-Caballero E, Márquez-Segovia I, López-Solera I, Sánchez-Barba LF, Alonso-Moreno C.
    Journal: Inorg Chem; 2008 Jun 02; 47(11):4996-5005. PubMed ID: 18447332.
    Abstract:
    Reaction of hybrid scorpionate/cyclopentadienyl ligands in the form of the lithium derivatives [Li(bpzcp)(THF)] [bpzcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl], [Li(bpztcp)(THF)] [bpztcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl], and the in situ-generated "Li(bpzpcp)" [bpzpcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-phenylethylcyclopentadienyl] with MCl3(THF)3 afforded the group 3 halide compounds [MCl2(bpzcp)(THF)] (M=Sc, 1; Y, 2), [MCl2(bpztcp)(THF)] (M=Sc, 3; Y, 4), and [MCl2(bpzpcp)(THF)] (M=Sc, 5; Y, 6). The H2O adduct of 4, [YCl2(bpztcp)(H2O)] (7), was formed when a solution of 4 was allowed to stand at room temperature in the presence of moisture. Complexes 1-7 adopt a pseudo-octahedral structure with heteroscorpionate ligands kappa2-NNeta5-Cp coordinated to the metal through the cyclopentadienyl group and two imino nitrogens of pyrazole rings. The alkyl heteroscorpionate scandium and yttrium complexes recently reported by our group, [M(CH2SiMe3)2(bpzcp)], react with 2,6-dimethylphenol and 3,5-dimethylphenol to give the bis(aryloxide) derivatives [M(OAr)2(bpzcp)] (M=Sc, OAr=2,6-dimethylphenoxide, 8; M=Y, OAr=2,6-dimethylphenoxide, 9; M=Y, OAr=3,5-dimethylphenoxide, 10). Complex 9 underwent an interesting hydrolysis process to give the tetranuclear complex [{Y(bpzcp)}(micro-OH)2(micro3-OH){Y(OAr)2}]2 (11). Variable-temperature 1H NMR experiments on 9 and 10 revealed a rapid fluxional exchange between coordinated and noncoordinated pyrazolyl rings, producing interconversion between the two enantiomers in which the scorpionate ligand can be coordinated in a kappa1-Neta5-Cp form. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 2, 7, and 11 were also established. Complexes 1 and 2 are active olefin polymerization catalysts after activation with methylaluminoxane. These compounds gave atactic polystyrenes with narrow molecular weight distribution (Mn/Mw 1.26-1.91) and with low molecular weights.
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