Reaction of platinum(II) diamine and triamine complexes with selenomethionine

We have reacted [Pt(dien)Cl]Cl, [Pt(en)(D2O)2]2+, and [Pt(Me4en)(D2O)2]2+ [Me4en = N,N,N′,N′-tetramethylethylenediamine] with selenomethionine (SeMet). When [Pt(dien)Cl]Cl is reacted with SeMet, [Pt(dien)(SeMet-Se)]2+ is formed; two Se–CH3 resonances are observed due to the different chiralities at the Se atom upon platination. In a reaction of [Pt(dien)Cl]Cl with an equimolar mixture of SeMet and Met, the SeMet product forms more quickly though a slow equilibrium with approximately equal amounts of both products is reached. [Pt(Me4en)(D2O)2]2+ reacts with SeMet to form [Pt(Me4en)(SeMet-Se)(D2O)]2+ initially but forms [Pt(Me4en)(SeMet-Se,N)]+ ultimately. One stereoisomer of the chelate, assigned to the R chirality at the Se atom, dominates within the first few minutes of reaction. [Pt(en)(D2O)2]2+ forms a variety of products depending on reaction stoichiometry; when one equivalent or less of SeMet is added, the dominant product is [Pt(en)(SeMet-Se,N)]+. In the presence of excess SeMet, [Pt(en)(SeMet-Se)2]2+ is the dominant initially, but displacement of the en ligand occurs leading to [Pt(SeMet-Se,N)2] as the eventual product. Displacement of the en ligand from [Pt(en)(SeMet-Se,N)]+ does not occur. In reactions of K2PtCl4 with two equivalents of SeMet, [Pt(SeMet-Se,N)2] is formed, and three sets of resonances are observed due to different chiralities at the Se atoms. Only the cis geometric isomers are observed by 1H and 195Pt NMR spectroscopy.