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-<i>tert</i>-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-<i>tert</i>-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 (<b>1a)</b>, Ph (<b>1b</b>)). Neutral <b>1a</b> showed near-zero ethylene polymerization activity (1 atm, 20 and 80 °C), and in the presence of AlMe₃, <b>1a</b> converted to [(XN₂)­Y­{(μ-Me)₂AlMe₂}­(THF)] (<b>2</b>). Compound <b>2</b> is thermally robust, and transfer of the XN₂ ligand from yttrium to aluminum was not observed even at elevated temperatures. However, [(XN₂)­AlMe] (<b>3</b>) 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 <b>1a</b> proved to be highly active for both intra- and intermolecular hydroamination with various substrates, yielding Markovnikov products in the intermolecular hydroamination reactions with 1-octene