| Abstract |
A new series of group 5 metal amides have been prepared from the reaction between $V(NMe_{2})_{4}$ or $M(NMe_{2})_{5}$ (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 $V(NMe_{2})_{4}$ or $M(NMe_{2})_{5}$ (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 $(1)V(NMe_{2})_{2}$ (11), $(2)V(NMe_{2})_{2}$ (14), $(3)V(NMe_{2})_{2}$ (17), $(5)V(NMe_{2})_{2}$ (22), $(6)V(NMe_{2})_{2}$ (23) and $(7)V(NMe_{2})_{2}$ (24), and niobium amides $(1)Nb(NMe_{2})_{3}$ (12), $(2)Nb(NMe_{2})_{3}$ (15), $(3)Nb(NMe_{2})_{3}$ (18), $(4)Nb(NMe_{2})_{3}$ (20) and $[2-(3-Me_{3}C-2-O-C_{6}H_{3}CHN)-2′-(N)-C_{20}H_{12}][2-(Me_{2}N)_{2}CH-6-CMe_{3}-C_{6}H_{3}O]NbNMe_{2}·C_{7}H_{8}$ $(25·C_{7}H_{8}),$ and tantalum amides $(1)Ta(NMe_{2})_{3}$ (13), $(2)Ta(NMe_{2})_{3}$ (16), $(3)Ta(NMe_{2})_{3}$ (19) and $(4)Ta(NMe_{2})_{3}$ (21) respectively, in good yields. Reaction of $V(NMe_{2})_{4}$ or $M(NMe_{2})_{5}$ (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 $(9)_{2}V(NMe_{2})_{2}·3C_{7}H_{8}$ $(27·3C_{7}H_{8})$ and $(10)V(NMe_{2})_{2}$ (28), and chiral bis-ligated metallaaziridine complexes $(10)_{2}M(NMe_{2})(η^{2}-CH_{2}NMe)$ (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 °C, while the vanadium amidate complexes degrade viadiemthylamino group elimination at this temperature. For example, heating the complex $(2)V(NMe_{2})_{2}$ (14) in toluene at 160 °C for four days leads to the isolation of the complex $[(2)V]_{2}(μ-NMe_{2})_{2}$ (26) in 58% yield. These new complexes have been characterized by various spectroscopic techniques, and elemental analyses. 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%). |
