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.

A 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 as PowerPoint slide