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 in the intermolecular
hydroamination reactions with 1-octene.