Synthesis of Amidolanthanides with New Chiral Biaryl-Based NNO Ligands and Their Use as Catalysts for Enantioselective Hydroamination/Cyclization

Abstract

A new series of amidolanthanides have been prepared from the reactions between Ln[N(SiMe3)2]3 and the chiral NNO ligands, (S)-2-(pyrrol-2-ylmethyleneamino)-2'-hydroxy-6,6'-dimethyl-1,1'-biphenyl (2H2) and (S)-5,5',6,6',7,7',8,8'-octahydro-2-(pyrrol-2-ylmethyleneamino)-2'-hydroxy-1,1'-binaphthyl (3H2), which are synthesized from the condensation of pyrrole-2-carboxaldehyde with 1 equiv of (S)-2-amino-2'-hydroxy-6,6'-dimethyl-1,1'-biphenyl or (S)-5,5',6,6',7,7',8,8'-octahydro-2-amino-2'-hydroxy-1,1'-binaphthyl, in the presence of molecular sieves at 70 degrees C, respectively. Treatment of 2H2 with 1 equiv of Ln[N(SiMe3)2]3 (Ln=Sm, Yb) in toluene under reflux, followed by recrystallization from a toluene solution, gives the dimeric amido complexes, {2-SmN(SiMe3)2}2.0.5C7H8 (6.0.5C7H8) and {2-YbN(SiMe3)2} 2.1.5C7H8(8.1.5C7H8), in good yields. While under similar reaction conditions, the reaction of 2H2 with 1 equiv of Y[N(SiMe3)2]3 leads to the isolation of a mixture of {2-YN(SiMe3)2}2 (7a) and {(2)2Y}Y[N(SiMe3)2]2(7b) in 82% total yield; the reaction of 3H2 with 1 equiv of Ln[N(SiMe3)2]3 (Ln=Y, Yb) gives the trinuclear complexes, {(3)2Ln}2LnN(SiMe3) 2.1.5C7H8 (Ln=Y(9.1.5C7H8), Yb(10.1.5C7H8)), in good yields. All compounds have been characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of compounds 2H2 and 6- 10 have been further confirmed by X-ray diffraction analyses. Complexes 6- 9 are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good yields with moderate ee values.