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

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.