Synthesis of Group 4 Metal Amides with New Chiral Biaryldiamine-Based Ligands and Their Use as Catalysts for Asymmetric Hydroamination/Cyclization

Abstract

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe2)4 (M = Ti, Zr) and chiral ligands, (S)-2-(pyrrol-2-ylmethyleneamino)-2′-(dimethylamino)-1,1′-binaphthyl (4H), (R)-2-(pyridin-2-ylmethylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (6H), (S)-2-(diphenylphosphinoylamino)-2′-(dimethylamino)-1,1′-binaphthyl (7H), (R)-2-(diphenylphosphinoylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (8H), (S)-2-(mesitoylamino)-2′-(dimethylamino)-1,1′-binaphthyl (9H), (R)-2-(mesitoylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (10H), and (R)-5,5′6,6′7,7′8,8′-octahydro-2-(mesitoylamino)-2′-(dimethylamino)-1,1′-binaphthyl (11H), which are derived from (S)-2-amino-2′-(dimethylamino)-1,1′-binaphthyl (1), (R)-2-amino-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (2), or (R)-5,5′6,6′7,7′8,8′-octahydro-2-amino-2′-(dimethylamino)-1,1′-binaphthyl (3). Reaction of M(NMe2)4 with 2 equiv of 4H or 6H gives, after recrystallization from an n-hexane solution, the monoligated chiral titanium amides (4)Ti(NMe2)3 (12), (6)Ti(NMe2)3 (13), and zirconium amide (6)Zr(NMe2)3 (14), respectively, in good yields. Under similar reaction conditions, treatment of Zr(NMe2)4 with 2 equiv of diphenylphosphoramide 7H or 8H affords, after recrystallization from a toluene solution, the bis-ligated chiral zirconium amides (7)2Zr(NMe2)2·2C7H8 (15·2C7H8) and (8)2Zr(NMe2)2 (16), respectively, in good yields. Reaction of M(NMe2)4 (M = Ti, Zr) with 2 equiv of mesitoylamide 9H, 10H, or 11H also gives, after recrystallization from a toluene or n-hexane solution, the bis-ligated chiral titanium amides (9)2Ti(NMe2)2·2.75C7H8 (17·2.75C7H8) and (10)2Ti(NMe2)2 (19) and zirconium amides (9)2Zr(NMe2)2·C7H8 (18·C7H8), (10)2Zr(NMe2)2 (20), and (11)2Zr(NMe2)2 (21), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of compounds 1, 2, 9H, and 12−20 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to excellent yields with good ee values, while the titanium amides are not.