Heterodinuclear Zinc(II)−Iron(III) Complexes and Dinuclear Zinc Complexes as Models for Zinc-Containing Phosphatases

Abstract

Five new dinuclear model complexes for zinc-containing phosphatases with dinucleating ligands have been prepared and characterized by single-crystal X-ray crystallography. The heterodinuclear, μ-alkoxo-bridged zinc(II)−iron(III) complexes 1−3 contain the symmetric ligands N,N,N′,N′-tetrakis[2-(5,6-dimethyl)benzimidazolylmethyl]-1,3-diamino-2propanol (Htdmbpo) and N,N,N′,N′-tetrakis{2-[N′′-(2hydroxyethyl)]benzimidazolylmethyl}-1,3-diamino-2-propanol (Hthebpo), and the asymmetric ligand N,N-bis[2-(4,5-dimethyl)benzimidazolylmethyl]-N′,N′-bis(2-pyridylmethyl)-1,3-diamino-2-propanol (Hbdmbbppo), respectively. X-ray crystallography revealed that the zinc center exhibits a trigonal-bipyramidal coordination, while the octahedral coordination sphere of the iron center is completed by a solvent molecule. In contrast, the zinc complexes 4 and 5, which also have (alkoxo)(cacodylato)dimetal cores with the dinucleating ligands used in 1 and 3, exhibit both metal centers in a trigonal-bipyramidal environment. Additionally, the solution speciation of the zinc(II) complexes formed with Htdmbpo and Hbdmbbppo were determined and the activity of the in situ prepared zinc complexes towards the transesterification of the RNA model substrate 2-(hydroxypropyl)-4-nitrophenyl phosphate (hpnp) was investigated. The dinuclear [Zn2LH−1(OH)]2+ complex of both ligands efficiently promotes the transesterification. The kinetic data indicated a higher activity for the complex of the asymmetric ligand Hbdmbbppo, as a result of its stronger substrate binding ability. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)