Functionalized Aminotroponiminate Zinc Complexes as Catalysts for the Intramolecular Hydroamination of Alkenes

Substituted aminotroponimines, {R-ATI(iPr)(2)}H (R = Br, l, PhN(2,) NO(2,) PhS, PhSc, PhTe, 3,5-(CF(3))(2)- C(6)H(3)S, PhS(O)), bearing different functional groups in the 5-position were prepared. Reaction of these compounds with ZnMe(2), in toluene at 0 degrees C delivered the corresponding methyl zinc complexes [{R-ATI(iPr)(2)}ZnMe] in high yields. The solid state structures of four selected examples were established via single-crystal X-ray diffraction analysis. In all compounds the zinc atoms are coordinated in a trigonal-planar fashion, All complexes were investigated as catalysts in the intramolecular hydroamination of non-activated alkenes. The attachment of electron-withdrawing groups in the 5-position such as nitro-or sulfoxide decreased the activity of the corresponding zinc catalysts. In contrast, donor substituents such as a thioether moiety at the backbone of the ligand increased the stability of the chelate and also rendered the zinc atom more reactive. On the other hand, the 5-brominated compound is very labile under the catalytic conditions used. In order to study the potential of an additional beneficial effect from the steric environment around the zinc atom on both reactivity and stability of the corresponding complexes, a prototypic ligand bearing a 5-phenylsullanyl substituent at the backbone and two cyclohexyl substituents at the nitrogen atoms, {PhS-ATI(Cy)(2)}H, and its corresponding zinc complex, [{PhS-ATI(Cy)(2)}ZnMe], were synthesized.