Synthesis, structure, and reactivity of bis(N,N′-bis(2-hydroxybenzylidene)-2-hydroxyphenylmethanediaminato)zirconium(IV), a Schiff base complex with 6,4,6-membered chelate rings


The title complex Zr(dshpm)2 has been successfully prepared by heating a 1:2 mole ratio of Zr(OBun)4 and the free ligand in absolute ethanol. It is mononuclear and eight-coordinate in the solid state with a dodecahedral coordination sphere. The two O,N,N,O donor atom quadridentate Schiff base ligands each form 6,4,6-membered chelate rings. As expected, the change in a chelate ring sizes from 6,5,6- to 6,4,6- resulted in significantly more labile complex, as indicated by TLC and NMR of heated solutions and its subsequent chemical reactions. The 0.010 Å shorter average ZrN bond distance was not anticipated, and appears to result from the zirconium atom's preference that the oxygen atoms occupy certain locations. Preparations of two heteroleptic complexes from the title complex were undertaken to evaluate potential of the title compound as a synthon. A new fluorine-substituted homoleptic Schiff base Zr complex was also prepared, for comparison purposes. Despite the reasonable stability of Zr(dshpm)2 in air, the decomposition of labilized Hdshpm(2-) ligand on silica gel and in heated solution interfered with the purifications of the desired heteroleptic products.

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