Di- and trimethylplatinum(IV) complexes with aspartate: some subtle effects of chelate ring size

The complex Na[PtMe(3)(asp-N,alpha O,beta O)] (H(2)asp = aspartic acid) was obtained as a solid from reaction of [PtMe(3)](2)(SO4). 4H(2)O with aspartate. In D2O, the interchange between this complex with aspartate tridentate and [PtMe(3)(D2O)(asp-N,alpha O)](-) was rapid on the NMR time-scale. Fac-[PtMe(2)Br(D2O)(3)](+) with D(2)asp at pD 2.5 gave the two isomers of [PtMe(2)Br(Dasp-N,alpha O) (D2O)] with the chelate ring trans to the methyl groups. With standing at pD 5-6, the two isomers of [PtMe(2)Br(asp-N,alpha O,beta O)](-) with N trans to methyl were formed, initially in similar proportions. With long standing, the isomer with N and beta-carboxylate trans to methyl predominated. When the pD was decreased to 3, this isomer was in equilibrium with a complex in which water replaced beta-carboxylate. UV irradiation of a solution containing the two isomers of [PtMe(2)Br(asp-N,alpha O,beta O)](-) with N trans to methyl caused formation of the isomer with N trans to bromide.