Dinuclear metal phosphonates and -phosphates

The reaction of Cu(II) or Cd(II) salts with 2,4,6-iPr3C6H2PO3H2, 2,4,6-iPr3C6H2CH2PO3H2 or 2,6-iPr2C6H3OPO3H2 in the presence of strong chelating nitrogen ligands such as 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2-pyridylpyrazole (pypz) or 3,5-dimethyl pyrazole (dmpz) as the ancillary ligands afforded dinuclear copper or cadmium complexes [Cu2(2,4,6-iPr3C6H2PO3H)4(bpy)2] (4), [Cu2(2,6-iPr2C6H3OPO3H)2(bpy)2(OAc)2(CH3OH)2]·(CH3OH) (5), [Cd2(2,6-iPr2C6H3OPO3H)4 (bpy)2(CH3OH)2]·2(CH3OH) (6), [Cd2(2,6-iPr2C6H3OPO3H)4(phen)2] (7), [Cu2(2,6-iPr2C6H3OPO3H)2(PyPz)2(CH3OH)2] (8) and [Cu2(2,4,6-iPr3C6H2CH2PO3H)2(DMPz)2Cl2]·(CH3OH) (9) The molecular structures of 4–7 are grossly similar. The common structural features in these complexes are that the two metal centers are bridged by two bidentate [RPO2(OH)]− ligands generating a central eight-membered ring. Each of the metal centers also contains a chelating nitrogen ligand and a monodentate phosphonate or a phosphate ligand. In 5 and 6 other terminal ancillary ligands are also present. In compound 8, each of the two copper centers contains a monodentate [RPO2(OH)]− ligand along with a molecule of methanol. The two coppers are bridged by two monoanionic pyridylpyrazole ligands. The molecular structure of 9 is similar to that of 4–7. However, in 9 each of the two copper centers contain only terminal monodentate ligands in the form of two chlorides and a pyrazole. Magnetic studies on all of these copper complexes reveal an anti-ferromagnetic behavior at low temperatures. In addition, these complexes were found to be artificial nucleases and can convert supercoiled pBR322 DNA form I into nick form II in 1 min in the presence of an external oxidant through a hydrolytic and/or an oxidative pathway.