DISPLACEMENT OF LIGANDS IN [PTBR2(EN)] (EN = ETHYLENEDIAMINE) BY BETA-MERCAPTOAMINE AND GAMMA-MERCAPTOAMINE

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 beta-mercaptoamine the product is cyclo-[{Pt(mu-SCH2CH2NMe2-N,mu-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 gamma-mercaptoamines, three crystalline products have been obtained, of formulae [(en)Pt(mu-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 beta- and gamma-mercaptoamines results in total displacement of ethylenediamine from the starting material by the beta-mercaptoamine, but substitution of only bromine by the gamma-mercaptoamines.