X-ray and NMR studies of trans-dihydroxo-platinum(IV) antitumor complexes

Products from oxidative-addition reactions of H2O2 with cis-diamineplatinum(II) complexes have been studied by NMR and X-ray crystallography. Reaction of H2O2 with cis-diamminemalonatoplatinum(II) gave one product which was shown by X-ray crystallography to be the trans-dihydroxoplatinum(IV) complex: trans-dihydroxo-cis-diamminemalonatoplatinum(IV) dihydrate, compound 1, triclinic, space group P1, a = 6.275, b = 8.801, c = 9.621 A, alpha = 106.73, beta = 107.17, gamma = 67.67 degrees. In contrast, reactions of H2O2 with the related 1,1-cyclobutanedicarboxylato and ethylmalonato-platinum(II) complexes gave two Pt(IV) products each with similar 195Pt chemical shifts (ca. 50 ppm apart) but different 1J(195Pt-14N) couplings of ca. 205 and 229 Hz. It is suggested that the different course of reaction for these complexes is related to destabilization of the boat conformation of the chelate ring in hydroxoplatinum(IV) complexes containing substituted malonates as shown by empirical energy calculations. The crystal structures of two other related Pt(IV) complexes are reported: cis-dichloro-trans-dihydroxo-cis-bis(methylamine)platinum(IV) tetrahydrate, compound 2, monoclinic, space group C2/c, a = 17.746, b = 7.460 and c = 9.248 A, beta = 94.33 degrees, and cis-dichloro-trans-dihydroxo-cis-bis(3-methoxy-n-propylamine)pl Platinum(IV), compound 3, triclinic, space group P1, a = 7.559, b = 8.407, c = 13.168 A, alpha = 105.57, beta = 105.50, gamma = 93.05 degrees. All coordination geometries were closely octahedral and there were extensive three-dimensional hydrogen-bonding networks in the crystals involving amine NH, OH, Cl, or carboxylate O, and lattice H2O.