The one-electron oxidation of metal thiolates results in an increased oxidation state of the metal ion or the formation of a sulfur-based, thiyl radical in limiting extremes. For complexes with highly covalent M-S bonds, the unpaired electron may be delocalized over the metal and the sulfur, yielding a metal-stabilized thiyl radical. Oxidation of the metal thiolate precursors [Ru(DPPBT)(3)](-), [Ru-1](-), and Re(DPPBT)(3), Re-1 (DPPBT = diphenylphosphinobenzenethiolate), generates metal-stabilized thiyl radicals that react with alkenes to yield dithioether-metal products. Alkene addition to [Ru-1](+) and [Re-1](+) is symmetry-allowed due to the meridional arrangement of the DPPBT chelates. Combined bulk electrolysis and cyclic voltammetry experiments reveal the addition of alkenes to [Ru-1](+) as an irreversible process with experimentally determined rate constants ranging from 4.6(5) × 10(7) M(-1) s(-1) for electron-rich alkenes to 2.7(2) × 10(4) M(-1) s(-1) for electron-poor alkenes. Rate constants for cyclic alkenes range from 4(2) × 10(7) to 2.9(3) × 10(3) M(-1) s(-1). Chemical oxidation of [Ru-1](-) by ferrocenium hexafluorophosphate (FcPF(6)) in the presence of m-methylstyrene or p-methylstyrene yields the dithioether complexes [Ru-1·m-methylstyrene](+) and [Ru-1·p-methylstyrene](+), respectively. Each complex was crystallized and the structure determined by single-crystal X-ray diffraction. (31)P NMR of the samples reveals a major and minor product, each displaying a second-order spectrum. The oxidized intermediate [Re-1](+) binds alkenes reversibly with equilibrium binding constants that vary with the complex charge from 1.9 × 10(-11) M(-1) for n = 0 to 4.0 M(-1) for n = +1 to 2.5 × 10(9) M(-1) for n = +2. The three binding regimes are separated by 240 mV. Crystalline samples of [Re-1·C(2)H(4)](2+) are obtained upon chemical oxidation of Re-1 with silver hexafluorophosphate (AgPF(6)) in the presence of ethylene. Strategies for the addition of alkenes to other metal-stabilized thiyl radicals are suggested.
The influence of oxidation state on the reversibility of carbon-sulfur bond forming reactions between ethylene and [Re(DPPBT)(3)](n+) (n = 0, +1, +2; DPPBT = 2-diphenylphosphinobenzenethiolate) has been investigated. For the neutral complex [Re(DPPBT)(3)], no reaction with ethylene is spectroscopically detectable consistent with the determined equilibrium constant, K(1), of (1.9 +/- 0.4) x 10(-11) M(-1). Oxidation by one electron to [Re(DPPBT)(3)](+) yields a stable complex that rapidly and reversibly binds ethylene with electrochemically determined constants of k(f) = (1.2 +/- 0.2) x 10(-1) M(-1) s(-1), k(r) = (3.0 +/- 0.4) x 10(-2) s(-1), and K(2) = 4.0 +/- 0.8 M(-1). C-S bond formation/cleavage can be regulated by ethylene concentration, and the system is stable to multiple cycles of nitrogen/ethylene purges. Further oxidation to the dication in the presence of ethylene by chemical or electrochemical methods stabilizes the C-S bond, K(3) = (2.5 +/- 0.9) x 10(9) M(-1), and the dithioether product has been characterized by X-ray crystallography. The large differences in K as a function of charge permit the controlled binding and release of ethylene as a function of applied potential.
The metal-stabilized thiyl radical complex [Ru(SP) + , {SP = 2-(diphenylphosphanyl)benzenethiolate} adds 1-octyne across the cis-sulfur sites to yield the S-alkylated dithiolene product + . The product complex exists as a pair of inseparable geometric isomers, which were char-
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