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Carboxylate- and Phosphate Ester-Bridged Dimagnesium(II), Dizinc(II), and Dicalcium(II) Complexes. Models for Intermediates in Biological Phosphate Ester Hydrolysis

1996; American Chemical Society; Volume: 35; Issue: 26 Linguagem: Inglês

10.1021/ic960894h

1520-510X

Joanne W. Yun, Tomoaki Tanase, Stephen J. Lippard,

Chemical Synthesis and Characterization

Carboxylate-bridged dimagnesium(II) complexes were synthesized and characterized by employing the dinucleating ligand XDK, where H2XDK is m-xylylenediamine bis(Kemp's triacid imide). The reaction of 1 or 2 equiv of sodium diphenyl phosphate with [Mg2(XDK)(CH3OH)4(H2O)2(NO3)](NO3), 1(NO3), afforded [Mg2(XDK){μ-η2-(PhO)2PO2}(CH3OH)3(H2O)(NO3)]·3CH3OH (2·3CH3OH) and [Mg2(XDK){μ-η2-(PhO)2PO2}{η1-(PhO)2PO2}(CH3OH)3(H2O)]·CH3OH (3·CH3OH), respectively. These are the first structurally characterized phosphate ester-bridged dimagnesium(II) complexes. The reaction of 1 with 1 equiv of bis(4-nitrophenyl) hydrogen phosphate resulted in protonation of one of the carboxylate ligands and liberation of one magnesium(II) ion to give [Mg(HXDK)2(H2O)2] (4), an octahedral complex containing two short, low barrier intramolecular OH···O hydrogen bonds. The phosphate ester exchange rate of free and bound diphenyl phosphate in 3 in methanol solution was measured by variable-temperature 31P{1H} NMR spectroscopy and compared to that of structurally analogous dizinc(II), [Zn2(XDK){μ-η2-(PhO)2PO2}{η1-(PhO)2PO2}(CH3OH)2(H2O)] (5), and dicalcium(II), [Ca2(XDK){μ-η2-(PhO)2PO2}{η1-(PhO)2PO2}(CH3OH)3(H2O)]·CH3OH, (6·CH3OH), complexes. The synthesis and structural characterization of 6 is presented, along with a discussion of the differences between the carboxylate- and phosphate ester-bridged dimagnesium(II), dizinc(II), and dicalcium(II) centers. Crystallographic data are as follows. 1(NO3): monoclinic, P21/c, a = 11.240(3) Å, b = 13.019(2) Å, c = 30.208(7) Å, β = 99.11(1)°, V = 4365(2) Å3, Z = 4, R = 0.045, and Rw= 0.054 for 5021 independent reflections with I > 3σ(I). 2·3CH3OH: monoclinic, P21/c, a = 16.611(5) Å, b = 16.059(6) Å, c = 21.930(9) Å, β = 93.34(6)°, V = 5840(4) Å3, Z = 4, R = 0.069, and Rw = 0.085 for 3759 independent reflections with I > 2σ(I). 3.CH3OH: monoclinic, P21/n, a = 18.912(4) Å, b = 16.254(2) Å, c = 21.646(5) Å, β = 112.26(2)°, V = 6158(2) Å3, Z = 4, R = 0.060, and Rw = 0.072 for 5184 independent reflections with I > 3σ(I). 4: monoclinic, P21/n, a = 15.210(5) Å, b = 15.772(3) Å, c = 13.093(3) Å, β = 96.35(3)°, V = 3122(1) Å3, Z = 2, R = 0.069, and Rw = 0.070 for 1840 independent reflections with I > 2σ(I). 6.CH3OH: monoclinic, P21/n, a = 16.5471(3) Å, b = 24.3415(6) Å, c = 16.5865(3) Å, β = 104.2530(10)°, V = 6475.1(2) Å3, Z = 4, R = 0.053, and wR2 = 0.142 for 7858 independent reflections with I > 2σ(I).