Displacement of ligands in [PtBr2(en)](en = ethylenediamine) by β- and γ-mercaptoamines

Abstract

The reactions of [PtBr₂(en)](en = ethylenediamine) with 2-(dimethylamino)ethanethiol, 3-dimethylaminopropane-1-thiol and 4-mercapto-1-methylpiperidine in alkaline aqueous solution give different types of complexes depending on the nature of the mercaptoamine. With the N-substituted β-mercaptoamine the product is cyclo-[{Pt(µ-SCH₂CH₂NMe₂-N,µ-S)Br}₃], consisting of discrete trimeric molecules with a central Pt₃S₃ ring. Each platinum atom is square-planar co-ordinated by a S₂NBr donor set; the aminothiolate ligands are simultaneously chelating, through S and N, and bridging, through S, while bromine is terminally bonded. With the two γ-mercaptoamines, three crystalline products have been obtained, of formulae [(en)Pt(µ-SR)₂Pt(en)]ⁿ⁺Br_n·xH₂O [R =(CH₂)₃NMe₂, n= 2, x= 0; R = C₅H₉NMe, n= 2, x= 6; R = C₅H₉NHMe, n= 4, x= 2]. The three cations differ chemically only in the nature of the thiolate substituent group R, and their core geometries are essentially identical, consisting of a central exactly planar Pt₂S₂ ring linked to two five-membered chelate Pt(en) rings. There is extensive hydrogen bonding in the hydrated complexes. The different chelating ability of the β- and γ-mercaptoamines results in total displacement of ethylenediamine from the starting material by the β-mercaptoamine, but substitution of only bromine by the γ-mercaptoamines.