Diamine preparation for synthesis of a water soluble Ni(II) salen complex

A reliable and efficient synthesis of NiNi(II) salen complex useful in probing nucleic acid structure is described and illustrates a general approach for constructing cis diamines suitable for assembly into N2O2 Schiff base complexes. Two equivalents of an aryllithium reacted with 1,4-dimethylpiperazine-2,3-dione to form the symmetric α-dione. This material was then converted to its dioxime and reduced by TiCl4/NaBH4 to yield the meso-diamine. Condensation of the diamine and salicyladehyde, coordination of nickel and final methylation generated the desired water soluble and redox active complex.