Synthesis, structure, and catalytic activity of group 4 complexes with new chiral biaryl-based NO2 ligands

Article abstract of DOI:10.1016/j.jorganchem.2010.03.014

A new series of chiral bis-ligated group 4 complexes have been prepared from the reaction between M(NMe₂)₄ (M = Ti, Zr) and C₁-symmetric biaryl-based NO₂ ligands, (R)-2-(mesitoylamino)-2′-methoxy-1,1′-binaphthyl (1H), (R)-2-(mesitoylamino)-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl (2H), (S)-5,5′,6,6′,7,7′,8,8′-octahydro-2-(mesitoylamino)-2′-methoxy-1,1′-binaphthyl (3H), (R)-2-(3,5-di-tert-butyl-2-hydroxyphenylmethyleneamino)-2′-methoxy-1,1′-binaphthyl (4H), (R)-2-(3-tert-butyl-2-hydroxyphenylmethyleneamino)-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl (5H), which are derived from (R)-2-amino-2′-methoxy-1,1′-binaphthyl, (R)-2-amino-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl or (S)-5,5′,6,6′,7,7′,8,8′-octahydro-2-amino-2′-methoxy-1,1′-binaphthyl. Treatment of M(NMe₂)₄ with 2 equiv. of mesitoylamides 1H, 2H or 3H gives, after recrystallization from a toluene or n-hexane solution, the bis-ligated chiral titanium amides (1)₂Ti(NMe₂)₂ (6), (2)₂Ti(NMe₂)₂ (8), (3)₂Ti(NMe₂)₂ (10), and zirconium amides (1)₂Zr(NMe₂)₂ (7), (2)₂Zr(NMe₂)₂ (9), (3)₂Zr(NMe₂)₂ (11), respectively, in good yields. Under similar reaction conditions, treatment of M(NMe₂)₄ with 2 equiv. of Schiff base ligands 4H or 5H gives, after recrystallization from a toluene solution, the chiral bis-ligated titanium complex {(R)-2-[3,5-(Me₃C)₂-2-O-C₆H₂CH(NMe₂)N]-2′-(MeO)-1,1′-C₂₀H₁₂}₂Ti (12) and zirconium complex {(R)-2-[3-Me₃C-2-O-C₆H₃CH(NMe₂)N]-2′-(MeO)-1,1′-(6-Me-C₆H₃)₂}(5)ZrNMe₂ (13), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 1H, 6, 8, 9, 12 and 13 have further been confirmed by X-ray diffraction analyses. The titanium and zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to excellent yields with good ee values.