Rare-earth metal diisopropylamide-catalyzed intramolecular hydroamination

Abstract

Rare-earth metal diisopropylamide complexes LiLn(NiPr)(THF) (Ln = Sc, Y, La), [LiY(NiPr)], NaLn(NiPr)(THF) (Ln = Sc, Y), Sc(NiPr)(THF) and Ce(NiPr) were 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 CD. 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 N as high as 164 h. The catalytic activity could be increased by employing THF-free complex [LiY(NiPr)] (N = 45.8 h at 26 °C; 34.1 h for LiY(NiPr)(THF)). In situ generation of putative LiY(NiPr)(THF) from YCl(THF) and four equivalents of LiNiPr (LDA) in CD generated a catalyst revealing N comparable to pre-isolated crystallized LiY(NiPr)(THF) but yielding even higher substrate conversion. The IHC reactions were also examined for rare-earth metal bis(trimethylsilyl)amide catalysts Ln[N(SiMe)] (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(NiPr)(THF). Cyclization of 1-amino-2,2-diphenyl-5-hexene to the 6-membered heterocycle 2-methyl-4,4-diphenylpiperidine by lanthanum derivative LiLa(NiPr)(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(NiPr) showed a better IHC performance than crystalline trivalent Sc(NiPr)(THF) as preliminary examined for 1-amino-2,2-diphenyl-4-pentene at 26 °C (N = 5.6 and 0.9 h, respectively), but cyclization came to a halt after 2 h, probably due to decomposition of the catalyst.

Rigid NON-donor pincer ligand complexes of lutetium and lanthanum: synthesis and hydroamination catalysis

“…1; R ¼ R 0 ¼ t Bu) catalysts 9 showed comparable activity, while the lanthanum analogue was nearly inactive. [19][20][21][22][23][24][25][26][27][28][29] As noted above, we previously described the synthesis and hydroamination activity of [(XN 2 )Y(CH 2 SiMe 3 )(THF)] (XN 2 ¼ 4,5-bis(2,4,6-triisopropylanilido)-2,7-di-tert-butyl-9,9dimethylxanthene; d in Fig. 1), 10 and in this work we report the synthesis of lutetium and lanthanum XN 2 complexes.…”

Rare-Earth-Metal-Complex-Catalyzed Hydroalkoxylation and Tandem Hydroalkoxylation/Cyclohydroamination of Isocyanates: Synthesis of Carbamates and Oxazolidinones

“…It should be noted that lanthanide catalysts have never been used in this reaction. As is known, the rare-earth-metal complexes could be utilized to promote the hydroalkoxylation of alkenes and alkynes and the hydroamination of alkenes because of their unique activity and selectivity. Herein, we report the first example of rare-earth-metal-complex-catalyzed intermolecular reactions of isocyanates with alcohols, as well as propargylic alcohols, offering an efficient and useful route for the synthesis of a series of N -alkyl and N -aryl carbamates and oxazolidinone derivatives in good-to-high yields.…”