Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV) amides with chiral biphenyldiamine-based ligands

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe2)(4) (M = Ti, Zr) and C-2-symmetric ligands, (R)-2,2'-bis(pyridin-2-ylmethylamino)-6,6'-dimethyl-1,1'-biphenyl (2H(2)), (R)-2,2'-bis(pyrrol-2-ylmethyleneamino)-6,6'-dimethyl-1,1'-biphenyl (3H(2)), (R)-2,2'-bis(diphenylphosphinoylamino)-6,6'-dimethyl-1,1'-biphenyl (4H(2)), (R)-2,2'-bis(methanesulphonylamino)-6,6'-dimethyl-1,1'-biphenyl (5H(2)), (R)-2,2'-bis(p-toluenesulphonylamino)-6,6'-dimethyl-1,1'-biphenyl (6H(2)), and C-1-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-2'-(dimethylamino)-6,6'-dimethyl-1,1'-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-2'-(dimethylamino)-6,6'-dimethyl-1,1'-biphenyl (8H), which are derived from (R)-2,2'-diamino-6,6'-dimethyl-1,1'-biphenyl. Treatment of M(NMe2)(4) with 1 equiv. of N-4-ligand, 2H(2) or 3H(2) gives, after recrystallization from an n-hexane solution, the chiral zirconium amides (2) Zr(NMe2)(2) (9), (3) Zr(NMe2)(2) (11), and titanium amide (3) Ti(NMe2)(2) (10), respectively, in good yields. Reaction of Zr(NMe2)(4) with 1 equiv of diphenylphosphoramide 4H(2) affords the chiral zirconium amide (4) Zr(NMe2)(2) (12) in 85% yield. Under similar reaction conditions, treatment of Ti(NMe2)(4) with 1 equiv. of sulphonylamide ligand, 5H(2) or 6H(2) gives, after recrystallization from a toluene solution, the chiral titanium amides (5) Ti(NMe2)(2)center dot 0.5C(7)H(8) (13.0.5C(7)H(8)) and (6) Ti(NMe2)(2) (15), respectively, in good yields, while reaction of Zr(NMe2)(4) with 1 equiv. of 5H(2) or 6H(2) gives the bis-ligated complexes, (5)(2)Zr (14) and (6)(2)Zr (16). Treatment of M(NMe2)(4) with 2 equiv. of diphenylthiophosphoramide ligand 7H or N-3-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chiral zirconium amides (7)(2)Zr(NMe2)(2) (17) and (8)(2)Zr(NMe2)(2) (19), and bis-ligated chiral titanium amide (8)(2)Ti(NMe2)(2) (18), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and 17-19 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 moderate ee values, while the titanium amides are not. (C) 2009 Elsevier B.V. All rights reserved.