The equimolar reaction between 1,9-bis(N,N-dimethylaminomethyl)-5,5 '-diphenyldipyrromethane, H(2)L1 or 1,9-bis(3,5-dimethylpyrazolylmethyl)-5,5 '-diethyldipyrromethane, H(2)L2 and [NiCl2(DME)] in the presence of KH yielded the neutral mononuclear nickel(II) complexes [Ni(L1)-kappa N-4,N,N,N], 1 and [Ni(L2)-kappa N-4,N,N,N], 2, respectively. Their X-ray structures revealed the formation of triple chelation by the ligand in both structures with quite different nickel(ii)-surrounded square planar geometries owing to the steric difference between -NMe2 and 3,5-dimethylpyrazolyl groups. While the -NMe2 group substituted ligand L1 afforded nickel complex 1 with a plane of symmetry, 3,5-dimethylpyrazole substituted L2 rendered helical chirality in the structure of complex 2. Both the enantiomers (Delta and Lambda) of complex 2 were observed in the crystal lattice. Their solution state behaviors were consistent with the solid-state structures as monitored by H-1 NMR spectroscopy. Both the enantiomers of complex 2 were present in a dynamic equilibrium in solution and studied by variable temperature H-1 NMR spectroscopy. Similar to the chiral complex, the corresponding ligand H(2)L2 also exhibited chirality as shown by its crystal structure and the two ligand enantiomers participated in a very fast dynamic interconversion, which became slower upon metalation.
