Kinetics of the methylation of a platinum(II) diimine dithiolate complex

•Reaction with methyl iodide results in methylation of a thiolate ligand of a platinum(II) complex.•Kinetics parameters are consistent with an SN2 mechanism.•The structure of a sulfinate adduct was determined.•Self-quenching parameters are reported for one complex.

Pt(dbbpy)(bdt) and Pt(tmphen)(bdt) (dbbpy = 4,4′-di-t-butyl-2,2′-bipyridine; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline; bdt2− = 1,2-benzenedithiolate) are reported. Pt(dbbpy)(bdt) reacts with one equivalent of methyl iodide to give the S-methylated product, [Pt(dbbpy)(CH3bdt)]I. The reaction follows second order kinetics with a rate constant of 1.3 × 10−2 M−1 s−1 at 311 K. The accumulated data are consistent with direct nucleophilic attack by the coordinated bdt2− ligand sulfur atom on the carbon atom of the methyl iodide. Variable-temperature experiments yield an Arrhenius activation energy of 51 ± 3 kJ/mol. Activated complex reaction theory yields an enthalpy and entropy of activation of 48 ± 2 kJ/mol and −125 ± 7 J/(mol K), respectively, consistent with an SN2 reaction mechanism. The structure of the monosulfinate adduct, Pt(dbbpy)(bdtO2), also is reported. The fluid-solution luminescence of Pt(tmphen)(bdt) is concentration dependent and characterized by a 1591 ± 41 ns lifetime and 2.6 ± 0.2% quantum yield at infinite dilution. The observed chemical reactivity and self-quenching behavior have important implications for the design of photochemical devices based on the platinum(II) diimine dithiolate chromophore.

Graphical abstractA platinum(II) diimine dithiolate complex was found to react with one equivalent of methyl iodide to give the S-methylated product. Kinetic parameters are consistent with an SN2 reaction mechanism. The structure of a comparatively rare sulfinate adduct is reported. The fluid-solution luminescence lifetime and quantum yield of a third compound are concentration dependent, consistent with excited-state self-quenching.Figure optionsDownload full-size imageDownload as PowerPoint slide