Organonickel(II) complexes containing aryl ligands with chiral pyrrolidinyl ring systems; syntheses and use as homogeneous catalysts for the Kharasch addition reaction

Abstract

AbstractNew chiral organonickel(II) complexes 3a‐d have been synthesized containing monoanionic terdentate ligands of the type 2,6‐bis[(1‐pyrrolidinyl)methyl]phenyl. Chirality is introducedmagnified imageat the nitrogen donor atoms, which are part of the pyrrolidinyl ring systems, by placing substituents on the 2 or 5 positions of the rings. The complexes have been characterized variously by 1H‐ and 13C‐NMR spectroscopy, UV/Vis spectroscopy and X‐ray crystallography.Crystals of 3b are monoclinic, space group P21, with a = 11.572(2), b = 11.804(2), c = 13.249(3) Å, β = 107.00(2)°, Z = 4, final R = 0.043 for 3043 observed reflections. Crystals of 3c are tetragonal, space group P412121, with a = b = 12.2957(14) Å, c = 26.418(3) Å, Z = 8, final R = 0.052 for 1479 observed reflections. Crystals of 3d are tetragonal, space group P412121, with a = b = 11.0869(5), c = 21.718(2) Å, Z = 4, final R = 0.046 for 1469 observed reflections.The catalytic ability of the nickel complexes in the addition reaction of polyhalogenated compounds with alkenes (Kharasch addition) is markedly influenced by the geometry around the nickel atom and only 3a and 3b prove to be effective catalysts. The highest enantiomeric excesses of 16‐17% obtained with 3b and L‐menthyl methacrylate in this catalytic reaction indicate that the C2 chiral fence produced by the Me‐substituted pyrrolidinyl rings is not very effective for the transfer of chiral information.