Addition of polysubstituted alkenes, aromatic alkynes, and dienes to a metal-stabilized thiyl radical via carbon–sulfur bond formation: Electrochemical, chemical, and computational investigations

The addition of polysubstituted alkenes, alkynes, and dienes to the metal-stabilized thiyl radical complex [Ru-1]+ was evaluated by electrochemical, chemical, and computational methods. The [Ru-1]+ radical complex was generated by two successive one-electron oxidations of the metal thiolate precursor PPN[Ru(DPPBT)3], PPN[Ru-1]−, (PPN = bis(triphenylphosphine)iminium; DPPBT = diphenylphosphinebenzenethiolato). Rate constants were experimentally determined by cyclic voltammetric methods over multiple scan rates using [Ru-1]− solutions containing unsaturated substrates. Rate constants for polysubstituted alkenes range from 1.1 × 101 to 8.8 × 102 M−1 s−1, which are at 3–5 orders of magnitude slower than their monosubstituted counterparts. Rate constants are slower for substituted alkynes varying from 2.3 × 102 to 1.2 × 104 M−1 s−1, which are ∼100 times slower than the corresponding alkenes. Selected complexes were spectroscopically characterized following synthesis by chemical oxidation methods. Addition of asymmetrically substituted alkenes and alkynes yield [Ru-1·substrate]+ products as a mixture of isomers, which were assigned based on 31P NMR and density functional theory calculations (B3LYP/LANL2DZ + 6–31 g). The solid state structure of [Ru-1·cyclohexene]PF6 was determined by single crystal X-ray diffraction.