Synthesis of Asymmetric Variants in a Dinucleating Ligand Family and Application for Dinuclear Copper(II) Complexes

We developed a dinucleating ligand system with two identical tetradentate coordination compartments and varying terminal donors. Here, we report the synthesis of two differently asymmetric dinucleating ligands: the ligand selma (= 4,7,10-trimethyl-1,1,10-tris(2-pyridylmethyl)-1,4,7,10-tetraazadecane) with one N-3- and one N-4- and the ligand susan(H2Me2) (= 4,7-dimethyl-1,1-bis(6-methylpyridine-2-yl-methyl)-10,10-bis(2-pyridylmethyl)-1,4,7,10-tetraazadecane) with two different N-4-coordination compartments. The initial synthesis of the ligand selma based on extending dipicolylamine with 2-(methylamino)ethyl units in repeated reductive aminations. Synthesis of 1-trifluoroacetyl-4,7-dimethyl-1,4,7,10-tetraazadecane allowed the synthesis of both ligands selma and susan(H2Me2). To study the influence of the terminal donors, the Cu-II chloride complexes of selma and susanH(2)Me(2) and the two symmetric susan and susan(6) (Me) were synthesized. The introduction of the 6-methyl substituents on the pyridines increases the bond lengths, reduces the electron donation, and shifts the reduction potentials anodically. The large 6-methyl substituents enforce a meridional coordination of the dipicolylamine subunits, while it is mainly facial without the 6-methyl substituents. Analysis of the solid-state structures and the d-d transitions in solution demonstrate a flat potential energy surface for the 5-coordinate polyhedra. Analysis of d-d transitions and reduction potentials indicate that the properties of the (CuCuII)-Cu-II complexes are additive for but cooperative for selma reflecting the difference of these asymmetric dinucleating ligands. [GRAPHICS] .