Synthesis and catalytic activity of group 5 metal amides with chiral biaryldiamine-based ligands

A new series of group 5 metal amides have been prepared from the reaction between V(NMe2)(4) or M(NMe2)(5) (M = Nb, Ta) and chiral ligands, (R)-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (1H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (2H(2)), (R)-6,6'-dimethyl-2,2'-bis(mesitoylamino)-1,1'-biphenyl (3H(2)), (R)-2,2'-bis(mesitylenesulfonylamino)-6,6'-dimethyl-1,1'-biphenyl (4H(2)), (R)-2,2'-bis(diphenylthiophosphoramino)-1,1'-binaphthyl (5H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (6H(2)), (R)-2,2'-bis[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (7H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-1,1'-binaphthyl (8H(2)), (S)-2-(mesitoylamino)-2'-(dimethylamino)-1,1'-binaphthyl (9H), and (R)-2-(mesitoylamino)-2'-(dimethylamino)-6,6'- dimethyl-1,1'-biphenyl (10H), which are derived from (R) or (S)-2,2'-diamino-1,1'-binaphthyl, and (R)-2,2'-diamino-6,6'-dimethyl-1,1'-biphenyl, respectively. Treatment of V(NMe2)(4) or M(NMe2)(5) (M = Nb, Ta) with 1 equiv of C-2-symmetric amidate ligands 1H(2), 2H(2), 3H(2), 4H(2), and 5H(2), or Schiff base ligands 6H(2), 7H(2) and 8H(2) at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the vanadium amides (1)V(NMe2)(2) (11), (2)V(NMe2)(2) (14), (3)V(NMe2)(2) (17), (5)V(NMe2)(2) (22), (6)V(NMe2)(2) (23) and (7)V(NMe2)(2) (24), and niobium amides (1) Nb(NMe2)(3) (12), (2)Nb(NMe2)(3) (15), (3)Nb(NMe2)(3) (18), (4)Nb(NMe2)(3) (20) and [2-(3-Me3C-2-O-C6H3CHN)-2'-(N)-C20H12][2-(Me2N)(2)CH-6-CMe3-C6H3O] NbNMe2 center dot C7H8 (25 center dot C7H8), and tantalum amides (1)Ta(NMe2)(3) (13), (2)Ta(NMe2)(3) (16), (3)Ta(NMe2)(3) (19) and (4)Ta(NMe2)(3) (21) respectively, in good yields. Reaction of V(NMe2)(4) or M(NMe2)(5) (M = Nb, Ta)with 2 equiv of C-1-symmetric amidate ligands 9H or 10H at room temperature gives, after recrystallization from a toluene or n-hexane solution, the chiral bis-ligated vanadium amides (9)(2)V(NMe2)(2)center dot 3C(7)H(8) (27 center dot 3C(7)H(8))and (10)V(NMe2)(2) (28), and chiral bis-ligated metallaaziridine complexes (10)(2)M(NMe2)(eta(2)-CH2NMe)(M = Nb (29), Ta (30))respectively, in good yields. The niobium and tantalum amidate complexes are stable in a toluene solution at or below 160 degrees C, while the vanadium amidate complexes degrade via diemthylamino group elimination at this temperature. For example, heating the complex (2)V(NMe2)(2) (14)in toluene at 160 degrees C for four days leads to the isolation of the complex [(2)V](2)(mu-NMe2)(2) (26)in 58% yield. These new complexes have been characterized by various spectroscopic techniques, and elemental analses. The solid-state structures of complexes 12, 13, and 15-30 have further been confirmed by X-ray diffraction analyses. The vanadium amides are active chiral catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to good yields with good ee values (up to 80%), and the tantalum amides are outstanding chiral catalysts for the hydroaminoalkylation, giving chiral secondary amines in good yields with excellent ee values (up to 93%).