Lanthanide and group 4 metal complexes with new chiral biaryl-based NNO-donor ligands

Abstract

A new series of lanthanide and group 4 metal complexes have been prepared from the reactions between Ln[N(SiMe₃)₂]₃ or M(NMe₂)₄ and chiral ligands, (R)-2-(pyrrol-2-ylmethyleneamino)-2′-methoxy-1,1′-binaphthyl (1H), (S)-5,5′,6,6′,7,7′,8,8′-octahydro-2-(pyrrol-2-ylmethyleneamino)-2′-methoxy-1,1′-binaphthyl (2H) and (R)-2-(pyrrol-2-ylmethyleneamino)-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl (3H). The steric effect of the ligand coupled with the size effect of the ions plays an important role in the formation of the lanthanide complexes. For example, treatment of 1H with 1 equiv of Ln[N(SiMe₃)₂]₃ (Ln = Y, Yb) in toluene gives the tris-ligated complexes, (1)₃Y·C₇H₈ (5·C₇H₈) and (1)₃Yb·2C₇H₈ (6·2C₇H₈) in good yields; reaction of 2H with 1 equiv of Sm[N(SiMe₃)₂]₃ also gives the tris-ligated product (2)₃Sm (7), while treatment of 2H with 1 equiv of Ln[N(SiMe₃)₂]₃ (Ln = Y, Yb) leads to the isolation of the bis-ligated organolanthanide amides (2)₂LnN(SiMe₃)₂·2C₆H₆ (Ln = Y (8·2C₆H₆), Yb (9·2C₆H₆)) in good yields. Reaction of 1H, 2H or 3H with 1 equiv of M(NMe₂)₄ gives, after recrystallization from a toluene or benzene solution, the chiral bis-ligated titanium amides (1)₂Ti(NMe₂)₂·0.75C₇H₈ (10·0.75C₇H₈), (2)₂Ti(NMe₂)₂ (12), (3)₂Ti(NMe₂)₂·C₆H₆ (14·C₆H₆), and zirconium amides (1)₂Zr(NMe₂)₂·C₇H₈ (11·C₇H₈), (2)₂Zr(NMe₂)₂ (13), (3)₂Zr(NMe₂)₂·C₆H₆ (15·C₆H₆), in good yields, respectively. Treatment of Zr(NMe₂)₄ with 1 equiv of (R)-2-(pyrrol-2-ylmethylamino)-2′-methoxy-1,1′-binaphthyl (4H₂), which was prepared from the reduction of 1H with an excess of NaBH₄ in a solvent mixture of MeOH and toluene (1 : 1) at 50 °C, gives the trinuclear complex [(R)-2-O-C₂₀H₁₂-2′-(NCH₂C₄H₃)]₂Zr₃(NMe₂)₆·2C₇H₈ (16·2C₇H₈) in 65% yield. Organolanthanide amides and zirconium amides are active catalysts for asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to good yields with moderate ee values, while the titanium amides are not. During the course of the catalytic reaction, 8 is decomposed leading to the isolation of (2)₃Y·C₇H₈ (17·C₇H₈) in 35% yield from a toluene solution. The organolanthanide amides are also active catalysts for ring-opening polymerization of rac-lactide, giving isotactic-rich polylactides. All compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 2H, 3H, 5–11, and 13–17 have further been confirmed by X-ray diffraction analyses.