C1-Symmetric Rare-Earth-Metal Aminodiolate Complexes for Intra- and Intermolecular Asymmetric Hydroamination of Alkenes

A series of novel C-1-symmetric aminodiolate rare-earth-metal complexes have been prepared via arene elimination from [Ln(o-C6H4CH2NMe2)(3)] (Ln = Y, Lu) and the corresponding aminodiol proligand. The NOBIN-derived aminodiolate ligands feature sterically demanding triphenylsilyl and methyldiphenylsilyl ortho substituents on the naphtholate moiety and substituents of varying steric demand ranging from tert-butyl to tris(3,5-xylyl)silyl on the phenolate moiety. Complexes with a triphenylsilyl substituent on the naphtholate moiety displayed good catalytic activity in the hydroamination/cyclization of aminoalkenes, while complexes with a methyldiphenylsilyl substituent exhibited somewhat lower reactivity. The highest enantioselectivities for five- and six-membered-ring formation were observed utilizing complex 9c-Lu (R-1 = Ph, R-2 = Me, R-3 = SiPh3) in the cyclization of (2,2-diphenylpent-4-enyl)amine (92% ee, N-t = 200 h(-1) at 25 degrees C) and (2,2-diphenylhex-5-enyl)amine (73% ee, N-t = 20 h(-1) at 25 degrees C). The complexes can be applied in asymmetric intermolecular hydroaminations of 1-heptene and 4-phenyl-1-butene with benzylamine with enantioselectivities of up to 40% ee using complex 9b-Y (R-1 = Ph, R-2 = Me, R-3 = SiPh2Me). Here the higher catalytic activities are achieved with catalysts having a methyldiphenylsilyl substituent on the naphtholate moiety. Lanthanum aminodiolate catalysts generated in situ from [La{CH(C6H5)NMe2}(3)] did not exhibit improved catalytic activity in the intermolecular hydroamination in comparison to the corresponding yttrium and lutetium catalysts. The overall catalytic activities of the aminodiolate complexes are somewhat diminished in comparison to previously studied binaphtholate complexes due to the presence of the additional amine donor site in the ligand framework.