title: Rare-earth metal diisopropylamide-catalyzed intramolecular hydroamination.
abstract: Rare-earth metal diisopropylamide complexes LiLn(NiPr2)4(THF) (Ln = Sc, Y, La), [LiY(NiPr2)4]n, NaLn(NiPr2)4(THF) (Ln = Sc, Y), Sc(NiPr2)3(THF) and Ce(NiPr2)4were screened as catalysts for the intramolecular hydroamination/cyclization (IHC) of 1-amino-2,2-dimethyl-4-pentene, 1-amino-2,2-diphenyl-4-pentene, and 1-amino-2,2-diphenyl-5-hexene at ambient and moderately increased temperature of 60 °C in C6D6. The lithium ate complexes displayed the most efficient precatalysts with high conversion rates at 60 °C for the phenyl-substituted substrates and Ln = Y and La, affording turnover frequencies Ntas high as 164 h-1. The catalytic activity could be increased by employing THF-free complex [LiY(NiPr2)4]n(Nt= 45.8 h-1at 26 °C; 34.1 h-1for LiY(NiPr2)4(THF)). In situ generation of putative LiY(NiPr2)4(THF) from YCl3(THF)3.3and four equivalents of LiNiPr2(LDA) in C6D6generated a catalyst revealing Ntcomparable to pre-isolated crystallized LiY(NiPr2)4(THF) but yielding even higher substrate conversion. The IHC reactions were also examined for rare-earth metal bis(trimethylsilyl)amide catalysts Ln[N(SiMe3)2]3(Ln = Sc, Y, La) as well as for LDA using the same reaction conditions, revealing overall superior activity of the silylamide derivatives but poor performance of LDA compared to the rare-earth metal diisopropylamide complexes LiLn(NiPr2)4(THF). Cyclization of 1-amino-2,2-diphenyl-5-hexene to the 6-membered heterocycle 2-methyl-4,4-diphenylpiperidine by lanthanum derivative LiLa(NiPr2)4(THF) was accompanied by a competitive isomerization reaction affording max. 20% of 1-amino-2,2-diphenyl-4-hexene after 2 h at 60 °C. Crystalline tetravalent Ce(NiPr2)4showed a better IHC performance than crystalline trivalent Sc(NiPr2)3(THF) as preliminary examined for 1-amino-2,2-diphenyl-4-pentene at 26 °C (Nt= 5.6 and 0.9 h-1, respectively), but cyclization came to a halt after 2 h, probably due to decomposition of the catalyst.
authors.affiliation: Institut für Anorganische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany. reiner.anwander@uni-tuebingen.de.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Spallek
authors.affiliation: Institut für Anorganische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany. reiner.anwander@uni-tuebingen.de.
authors.forename: Reiner
authors.initials: R
authors.lastname: Anwander