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]

Abstract

The cyclic thiolato complex [[graphic omitted]H₂}(PPh₃)₂]1 reacted with alkyl halides RX (MeI, EtBr or PhCH₂Cl) giving the thioether complexes [[graphic omitted]H₂}X(PPh₃)] with the triphenylphosphine ligand trans to the thioether group. ³¹P-{¹H} NMR spectroscopy revealed that the alkylation reactions proceed through a cationic thioether intermediate of the type [[graphic omitted]H₂}(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 [[graphic omitted]H₂}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 ¹H 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 [{[graphic omitted]H₂](PPh₃)₂·HgBr₂}₂]. The complex contains bridging thiolate ligands with a BrHg(µ-Br)₂HgBr unit and distorted tetrahedrally co-ordinated mercury centres.