Metal ion directed template synthesis using 2-acetyl-1,3-indandione and ethylenediamine: steric and electronic restrictions

A Ni^II-directed template synthesis using 2-acetyl-1,3-indandione and ethylenediamine results in formation of octahedral Ni^II complex, whose crystal structure has been resolved using single crystal X-ray diffraction. The structure indicates that only exocyclic enolic oxygen atom of the triketone takes part in the condensation with ethylenediamine. Quantum chemical calculations reveal insights into the observed reactivity of an initial Ni^II complex of 2-acetyl-1,3-indandione with ethylenediamine and point out steric effects as the main restriction for a complete cyclization into a tetraaza macrocycle.