Phosphato complexes of platinum(II): phosphorus-31 NMR and kinetics of formation and isomerization studies

Abstract

Ortho-, pyro-, and triphosphate anions form monodentate phosphato complexes with chloro(diethylenetriamine)platinum(II) chloride and various chelates with dichloro(ethylenediamine)platinum(II) in the pH range 2-11. Monodentate complexations largely proceed through the direct reaction with the PtCl(dien){sup +}. Phosphorus-31 NMR spectra reveal coordination chemical shifts of 3-6 ppM for the phosphorus atoms of the bound phosphate groups. Only the monodentate ({gamma}-triphosphato)platinum(II) complex was detected by {sup 31}P NMR spectroscopy, although this ligand is capable of coordinating through the {beta}-phosphate group as well. Phosphorus-phosphorus coupling constants for Pt(dien)(H{sub 2}P{sub 2}O{sub 7}) and Pt(dien)(H{sub 2}P{sub 3}O{sub 10}){sup {minus}} complexes were found to be in the range 19-23 Hz. Chelation to dichloro(ethylenediamine)platinum(II) by pyro- and triphosphate ligands is accomplished primarily through aquations of the platinum substrate. The triphosphate ligand forms both {beta},{gamma}- and {alpha}{gamma}-linkage isomers; the six-membered chelate ring ({beta},{gamma}-complex) formation dominates at lower pH (3-4), whereas the formation of the eight-membered chelate ring is favored in the pH range > 6. Coordinated phosphate groups exhibit 4-12 ppM coordination chemical shifts, and phosphorus-phosphorus coupling constants of 19-22 Hz were observed for the triphosphato chelates. Linkage isomerizations, {beta}{gamma} {yields} {alpha},{gamma} and {alpha},{gamma} {yields} {beta},{gamma}, for triphosphato complexes mainly proceed through an intramolecular mechanism. 36 refs., 4 figs., 6more » tabs.« less