MONONUCLEAR AND DINUCLEAR ZINC-COMPLEXES OF XDK, H(2)XDK=M-XYLENEDIAMINE BIS(KEMP TRIACID IMIDE), AND THEIR REACTION WITH PHOSPHATE-ESTERS

The reaction of Zn(NO3)(2) . 6H(2)O with H(2)XDK and NaOH afforded the mononuclear zinc complex, [Zn(XDK)-(H2O] (1), in good yield. Treatment with pyridine converted complex 1 to [Zn(XDK)(py)(2)]. H2O (2 . H2O), which was characterized by X-ray crystallography (2 . CHCl3: monoclinic, P2(1)/c, a 12.324(4) Angstrom, b = 14.902(3) Angstrom c = 24.674(5) Angstrom, beta = 102.86(3)degrees, V = 4418(2) Angstrom(3), Z = 4, and R = 0.088 and R(w) = 0.089 for 3833 independent reflections having I > 3 sigma(I)). Complex 2 has two Zn-O and two Zn-N bonds at average distances of 2.04 and 2.07 Angstrom, respectively, contributed by a distorted XDK and two pyridine ligands. There is also a longer interaction to a third oxygen atom of the XDK ligand, Zn-O = 2.39 Angstrom. Recrystallization of 2 . H2O from a methanol/pyridine mixed solvent gave {Zn(eta(1)-carboxylato)(2)(py)(2)} (2'), which was isolated and structurally characterized (2'. CH3OH: monoclinic, P2(1)/n, a 12.257(2) Angstrom, b = 16.448(2) Angstrom, c = 20.432(3) Angstrom, beta = 103.46(1)degrees, V = 4006.0(9) Angstrom(3), Z = 4, and R = 0.048 and R(w) = 0.054 for 4140 independent reflections with I > 3 sigma(I)). Complex 1 readily reacted with Zn(NO3)(2) . 6H(2)O to give the dizinc complex, [Zn-2(XDK)(NO3)(2)(CH3OH)(H2O)(2)] (3), and a similar reaction in the presence of pyridine gave [Zn-2(XDK)(py)(2)(NO3)(2)]. 2H(2)O (4 . 2H(2)O). Complex 4 was characterized by X-ray crystallography (4 . CH(2)Cl(2)Et(2)O: monoclinic, P2(1)/n, a = 17.938(3) (A)ngstrom, b = 21.232(4) Angstrom, c = 15.436(3) Angstrom, beta = 112.48(1)degrees, V = 5432(2) Angstrom(3), Z = 4, and R = 0.072 and R(w) = 0.082 for 3590 independent reflections with I > 3 sigma(I)). The Zn ... Zn separation is 3.739(2) Angstrom, and both zinc atoms adopt a tetrahedral geometry. When complex 1 was treated with Zn(acac)(2) .2H2O, the asymmetrical dinuclear zinc complex, [Zn-2(XDK)(acac)(2)(CH3-OH)(2)]. H2O (5 . H2O), was obtained in good yield. An X-ray crystallographic analysis revealed a dizinc structure bridged by XDK and acac ligands; one zinc atom has trigonal bipyramidal geometry, and the other, octahedral geometry. The Zn ... Zn interatomic distance is 3.463(1) Angstrom (5: monoclinic, P2(1)/c, a = 17.629(3) Angstrom, b = 12.373(1) Angstrom, c 21.731(4) Angstrom, beta = 90.11(2)degrees, V = 4740(1) Angstrom(3), Z = 4, and R = 0.049 and R(w) = 0.054 for 5137 independent reflections with I > 3 sigma(I)). Reaction of complex 3 with phosphate ester salts NaC{RO)(2)PO2}, R = Ph or p-NO2-Ph, yielded the phosphate-bridged dinuclear zinc complexes, [Zn-2(XDK){mu-(RO)(2)PO2}(CH3OH)(2)](NO3) (6a, R = Ph; 6b, R = p-NO(2)Ph), which were further transformed into [Zn-2(XDK)mu-{RO)(2)PO2}(py)(2)(NO3) (7a, R = Ph; 7b, R = p-NO(2)Ph) by treatment with pyridine. These phosphate ester-bridged dizinc compounds are structural models for postulated intermediates in the mechanism proposed for phosphate ester hydrolysis by Escherichia coli alkaline phosphatase and DNA polymerase I, both of which contain a pair of zinc atoms in their active sites.