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

Abstract

A series of novel C 1 -symmetric aminodiolate rare-earth-metal complexes have been prepared via arene elimination from [Ln(o-C 6 H 4 CH 2 NMe 2 ) 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 fiveand six-membered-ring formation were observed utilizing complex 9c-Lu (R 1 = Ph, R 2 = Me, R 3 = SiPh 3 ) in the cyclization of (2,2-diphenylpent-4-enyl)amine (92% ee, N t = 200 h −1 at 25 °C) and (2,2-diphenylhex-5enyl)amine (73% ee, N t = 20 h −1 at 25 °C). The complexes can be applied in asymmetric intermolecular hydroaminations of 1heptene 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 = SiPh 2 Me). 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(C 6 H 5 )NMe 2 } 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.

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2013

“…Lanthanum aminodiolate catalysts generated in situ from La[CH(C 6 H 5 )NMe 2 ] 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 were found to be somewhat diminished in comparison to previously studied binaphtholate complexes due to the presence of the additional amine donor site in the ligand framework [31].…”

Rare Earth Pincer Complexes: Synthesis, Reaction Chemistry, and Catalysis

“…Hence, less bulky ancillaries were required. Finally, it should be noted that these catalysts were less active than previously reported bidentate binaphtholate complexes [153]. by Chen and colleagues as catalysts for intramolecular hydroamination.…”

Recent developments in enantioselective lanthanide-catalyzed transformations

“…The highest enantioselectivity achieved to date is 95% ee, and was obtained by using sterically hindered yttrium binaphtholate complexes [76]. Recently, several other examples have been reported, such as that reported by Hultzsch and Reznichenko, dealing with asymmetric lutetium-catalyzed intramolecular hydroamination of aminoalkenes 130a-e into the corresponding cyclic chiral amines 131a-e (Scheme 44) [77]. The reaction was promoted by novel C 1 -symmetric aminodiolate lutetium complexes in situ generated from 1.4 to 2 mol% of the corresponding chiral ligands 132 or 133, and the same quantity of [Lu(o-C 6 H 4 CH 2 NMe 2 ) 3 ] as precatalyst.…”

“…The ring-opening of racemic substituted N-acylaziridines 150a-f with TMSN 3 was also studied in the Scheme 46. Yttrium and lutetium-catalyzed intramolecular hydroamination of alkenes [77].…”