Yttrium and Aluminum Alkyl Complexes of a Rigid Bis-Anilido NON-Donor Ligand: Synthesis and Hydroamination Catalysis

The palladium-catalyzed coupling of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene (XBr2) with 2 equiv of 2,4,6-triisopropylaniline afforded the proligand 4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H2XN2), and reaction of H2XN2 with [Y(CH2SiMe2R)3(THF)2] (R = Me, Ph) produced the monoalkyl yttrium complexes [(XN2)Y(CH2SiMe2R)(THF)] (R = Me (1a), Ph (1b)). Neutral 1a showed near-zero ethylene polymerization activity (1 atm, 20 and 80 °C), and in the presence of AlMe3, 1a converted to [(XN2)Y{(μ-Me)2AlMe2}(THF)] (2). Compound 2 is thermally robust, and transfer of the XN2 ligand from yttrium to aluminum was not observed even at elevated temperatures. However, [(XN2)AlMe] (3) was accessible via the reaction of H2XN2 with AlMe3, demonstrating the ability of the wide-bite-angle XN2 ligand to coordinate to much smaller aluminum(III). Neutral 1a proved to be highly active for both intra- and intermolecular hydroamination with various substrates, yielding Markovnikov products i...

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