Synthesis, structure, and properties of isopropylidenemalonatoplatinum(IV) complexes

Abstract

Diamineplatinum(II) complexes of the isopropylidenemalonate(ipm) ligand A(2)Pt(OOC)(2) C=C(CH3)(2) (A = NH3 or NH2CH3) have been prepared and oxidized by an aqueous solution of H2O2 to obtain dihydroxoplatinum (IV) complexes, cis,cis,trans-A(2)Pt((OOC)(2)C=C(CH3)(2))(OH)(2). Subsequent reaction of these dihydroxoplatinum(IV) complexes with carboxylic anhydrides in CH2Cl leads to the dicarboxylatoplatinum(IV) complexes, cis,cis,trans-A(2)Pt((OOC)(2)C=C(CH3)(2))(OCOR)(2) (R = CH3, CF3, C2H5 and n-C3H7). One of the platinum(II) complexes (NH3)(2)Pt(OOC)(2)C=C(CH3)(2) (1) and its corresponding diacetatoplatinum(IV) complex, cis,cis,trans-(NH3)(2)Pt((OOC)(2)C=C(CH3)(2))(OCOCH3)(2) (5), have been characterized by X-ray crystallograpic analysis. The average Pt-N and Pt-O bond lengths of the complex 5 are similar to those of complex 1. In the complex 5, however, the boat conformation of the chelated dicarboxylate ring is less bent than that of complex 1. When an aqueous solution of the title Pt-IV complexes was exposed to 1 equiv. of ascorbic acid in pH 7 buffer solution at room temperature, all the Pt-IV complexes were reduced to the corresponding Pt-II complexes with variable rates. We have examined the disappearance of the Pt-IV complexes, in aqueous HCl solution at 37 degrees C. At 0.01 N HCl concentration, neligible decomposition occurs over a 72 h period. (C) 1997 Elsevier Science Ltd.