trans-Dichlorodiammineplatinum(II) is the trans isomer of the coordination complex with the formula trans-PtCl2(NH3)2, sometimes called transplatin.[1] It is a yellow solid with low solubility in water but good solubility in DMF. The existence of two isomers of PtCl2(NH3)2 led Alfred Werner to propose square planar molecular geometry.[2] It belongs to the molecular symmetry point group D2h.
The complex is prepared by treating [Pt(NH<sub>3</sub>)<sub>4</sub>]Cl2 with hydrochloric acid.[2]
Many of the reactions of this complex can be explained by the trans effect. It slowly hydrolyzes in aqueous solution to give the mixed aquo complex trans-[PtCl(H<sub>2</sub>O)(NH<sub>3</sub>)<sub>2</sub>]Cl. Similarly it reacts with thiourea (tu) to give colorless trans-[Pt(tu)<sub>2</sub>(NH<sub>3</sub>)<sub>2</sub>]Cl2. In contrast, the cis isomer gives [Pt(tu)<sub>4</sub>]Cl2. Oxidative addition of chlorine gives trans-PtCl4(NH3)2.
trans-Dichlorodiammineplatinum(II) has had far less impact on medicinal chemistry compared to its cis isomer, cisplatin, which is a major anticancer drug. Nonetheless, replacement of the ammonia with other ligands has led to highly active drugs that have attracted much attention.[3]