REACTIONS OF THE CYCLIC PLATINUM(II) THIOLATE COMPLEX [PT(SCH2C(O)CH2)(PPH3)(2)] WITH ELECTROPHILES, AND THE SINGLE-CRYSTAL STRUCTURE OF [(PT[SCH2C(O)CH2](PPH3)2.HGBR2)(2)]

The cyclic thiolato complex [Pt{SCH2C(O)CH2(PPh3)2] 1 reacted with alkyl halides RX (Mel, EtBr or PhCH2Cl) giving the thioether complexes [Pt{RSCH2C(O)CH2}X(PPh3)] with the triphenylphosphine ligand trans to the thioether group. P-31-{H-1} NMR spectroscopy revealed that the alkylation reactions proceed through a cationic thioether intermediate of the type [Pt{RSCH2C(O)CH2}(PPh3)2]+X-, the rate of formation of which is highly dependent on the reactivity of the alkyl halide. Reaction of 1 with dimethyl sulfate rapidly produced an analogous intermediate which is rather stable in the presence of an excess of dimethyl sulfate as a result of the low nucleophilicity of the methyl sulfate anion. Proton NMR spectroscopy of the complexes [Pt{RSCH2C(O)CH2}X(PPh3)] is consistent with the presence of a rigid metallacycle in solution with the SMe group adopting an axial position. Complex 1 also forms sulfur-donor adducts with 'soft' metal centres such as Hg(II) and Ag(I). Adduct formation is readily monitored by the influence on the H-1 NMR shifts of the metallacyclic CH2 groups. A single-crystal X-ray diffraction study on the mercury(II) bromide adduct reveals the presence of a 1 :1 dimeric complex [{(SCH2C(O)CH2](PPh3)2.HgBr2}2]. The complex contains bridging thiolate ligands with a BrHg(mu-Br)2HgBr unit and distorted tetrahedrally co-ordinated mercury centres.