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(NMe 2 ) 4 (M = Ti, Zr) and chiral ligands, ( S )-2-(pyrrol-2-ylmethyleneamino)-2′-(dimethylamino)-1,1′-binaphthyl ( 4 H), ( R )-2-(pyridin-2-ylmethylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl ( 6 H), ( S )-2-(diphenylphosphinoylamino)-2′-(dimethylamino)-1,1′-binaphthyl ( 7 H), ( R )-2-(diphenylphosphinoylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl ( 8 H), ( S )-2-(mesitoylamino)-2′-(dimethylamino)-1,1′-binaphthyl ( 9 H), ( R )-2-(mesitoylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl ( 10 H), and ( R )-5,5′6,6′7,7′8,8′-octahydro-2-(mesitoylamino)-2′-(dimethylamino)-1,1′-binaphthyl ( 11 H), 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(NMe 2 ) 4 with 2 equiv of 4 H or 6 H gives, after recrystallization from an n -hexane solution, the monoligated chiral titanium amides ( 4 )Ti(NMe 2 ) 3 ( 12 ), ( 6 )Ti(NMe 2 ) 3 ( 13 ), and zirconium amide ( 6 )Zr(NMe 2 ) 3 ( 14 ), respectively, in good yields. Under similar reaction conditions, treatment of Zr(NMe 2 ) 4 with 2 equiv of diphenylphosphoramide 7 H or 8 H affords, after recrystallization from a toluene solution, the bis-ligated chiral zirconium amides ( 7 ) 2 Zr(NMe 2 ) 2 ·2C 7 H 8 ( 15 ·2C 7 H 8 ) and ( 8 ) 2 Zr(NMe 2 ) 2 ( 16 ), respectively, in good yields. Reaction of M(NMe 2 ) 4 (M = Ti, Zr) with 2 equiv of mesitoylamide 9 H, 10 H, or 11 H also gives, after recrystallization from a toluene or n -hexane solution, the bis-ligated chiral titanium amides ( 9 ) 2 Ti(NMe 2 ) 2 ·2.75C 7 H 8 ( 17 ·2.75C 7 H 8 ) and ( 10 ) 2 Ti(NMe 2 ) 2 ( 19 ) and zirconium amides ( 9 ) 2 Zr(NMe 2 ) 2 ·C 7 H 8 ( 18 ·C 7 H 8 ), ( 10 ) 2 Zr(NMe 2 ) 2 ( 20 ), and ( 11 ) 2 Zr(NMe 2 ) 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, 9 H, 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.