Isomerization of trans-[Ru(PTA)4Cl2] to cis-[Ru(PTA)4Cl2] in water and organic solvent: revisiting the chemistry of [Ru(PTA)4Cl2].

trans-[Ru(PTA)4Cl2] (trans-1), (PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane) has been isolated and structurally characterized by X-ray crystallography. The structure reveals ruthenium in a slightly distorted-octahedral environment bound to two axial chlorides and four equatorial PTA ligands. In organic solvents, trans-1 undergoes a relatively clean isomerization to cis-1. In aqueous environments, trans-1 undergoes a more complicated transformation involving isomerization, protonation, and ligand substitution affording cis-1 and a series of structurally related molecules. From these results, we conclude that the synthesis of [Ru(PTA)4Cl2] (1) affords trans-1, not cis-1, as earlier reports suggest. The water-soluble hydride cis-[Ru(PTA)4H2] (2) has also been synthesized from the reaction of trans-[Ru(PTA)4Cl2] with excess sodium formate. Compound 2 is stable in deoxygenated water and undergoes H/D exchange with D2O (t1/2 approximately equal to 120 min, at 25 degrees C). The solid-state structures of both trans-1 and 2 are described.