Synthesis and characterization of group 4 metal amides with new C-2-symmetric binaphthyldiamine-based ligands and their use as catalysts for asymmetric hydroamination/cyclization

摘要

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, (R)-2,2'-bis(p-toluenesulfonylamino)1,1'-binaphthyl (1H(2)), (R)-2,2'-bis(diphenylphosphinoylamino)1,1'-binaphthyl (2H(2)), (R)-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (3H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(pyrrol-2-ylmethyleneamino)-1, 1'-binaphthyl (4H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitoylamino)-1,1'-binaphthy l (5H(2)), and (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitylenesulfonylamino)-1,1' -binaphthyl (6H(2)), which are derived from (R)-2,2'-diamino-1,1'-binaphthyl. Reaction of M(NMe2) 4 with 1 equiv of arylsulfonylamides 1H(2) and 6H(2), diphenylphosphoramide 2H(2), mesitoylamides 3H(2) and 5H(2), or Schiff base ligand 4H(2) at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the chiral titanium amides (1) Ti(NMe2)(2)center dot 3C(6)H(6) (7 center dot 3C(6)H(6)), (4) Ti(NMe2)(2) (11), (5) Ti(NMe2)(2) (13) and (6) Ti(NMe2)(2) (15), and zirconium amides (1) Zr(NMe2)(2) (8), (2) Zr(NMe2)(2) (9), (3) Zr(NMe2)(2) (10), (4) Zr(NMe2)(2) (12), (5) Zr(NMe2)(2) (14) and (6) Zr(NMe2)(2)center dot C7H8 (16 center dot C7H8) respectively, in good yields. These amides are stable below 90 degrees C in toluene solution, but they degrade via ligand redistribution at a higher temperature. For example, treatment of (1) Zr(NMe2)(2) (8) or (5) Zr(NMe2)(2) (14) in refluxing toluene for three days leads to the isolation of the complexes (1) 2Zr center dot C7H8 (17 center dot C7H8) and (5) 2Zr center dot 3C(7)H(8) (18 center dot 3C(7)H(8)) respectively, in moderate yields. These new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 7-9, 11-13, and 15-18 have further been confirmed by X-ray diffraction analyses. The titanium amide 13 and all the zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to excellent yields with moderate to excellent ee values (up to 93%). Theoretical studies reveal the interaction between the carbon chain of the substrate and the sterically demanding ligand groups plays a key role in the stereodirection of the enantioselection during the Zr=N bond approaches to the C=C bond.