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Synthesis, Structural Characterization, and Reactivity of Organolanthanides Derived from a New Chiral Ligand, (R)-Bis(pyrrol-2-ylmethyleneamino)-1,1‘-binaphthyl

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posted on 02.04.2020, 17:21 by Li Xiang, Qiuwen Wang, Haibin Song, Guofu Zi
Condensation of (R)-2,2‘-diamino-1,1‘-binaphthyl with 2 equiv of pyrrole-2-carboxaldehyde in toluene in the presence of molecular sieves at 70 °C gives (R)-bis(pyrrol-2-ylmethyleneamino)-1,1‘-binaphthyl (1H2) in 85% yield. Deprotonation of 1H2 with NaH in DME, followed by reaction with YCl3 in DME gives the complex 1-YCl(dme) (2) in 75% yield. A salt metathesis reaction between 2 and (Me3Si)2NNa in a mixed solvent of THF and toluene (1:1) gives the organoyttrium amide 1-Y[N(SiMe3)2](thf)·C7H8 (4) in 70% yield. Alternatively, the organolanthanide amides may also be prepared by silylamine elimination. For example, treatment of 1H2 with 1 equiv of Ln[N(SiMe3)2]3 in toluene at reflux gives, after recrystallization from a mixed toluene and THF solution, organolanthanide amides 1-Ln[N(SiMe3)2](thf)·(C7H8)n (n = 1, Ln = Sm (3); n = 1, Ln = Y (4); n = 0, Ln = Yb (5)) in good yields. Reaction of 4 with one equiv of Me3N·HCl or excess of Me3Al leads to formation of 1-YCl(dme) (2) and 1-Y(μ-Me)2AlMe2 (6), respectively. Treatment of 5 with excess of 1H2 in toluene at reflux gives, after recrystallization from a benzene solution, the dinuclear complex {(1)3Yb2}3·2C7H8·2C6H6 (7) in 65% yield. All compounds have been characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of compounds 24 and 7 have been further established by single X-ray diffraction analyses. Organolanthanide amides 35 are active catalysts for asymmetric hydroamination/cyclization of aminoalkenes and polymerization of MMA, affording cyclic amines in good yields with moderate ee values and syn-rich poly(MMA)s, respectively.