| This dissertation employs the complex, bis(triphenylphosphoranylidene)ammonium(tris-(2-diphenylphosphinothia-phenolato)ruthenium(II)), [PPN][Ru(DPPBT)3] (1), to investigate ligand-versus metal-centered reactivity in alkylation, oxygenation, and redox reactions. Complex 1 reacts with dichloromethane, under ambient conditions, to generate tris-(2-diphenylphosphinothia-phenolato)ruthenium(III), [Ru(DPPBT) 3] compound 3, which contains a methylene bridge between cis sulfurs. Since dichloromethane is a weak electrophile, nucleophilic attack of thiolates to generate thioethers demonstrates the electron rich character of the sulfurs. Complex 1 can also be oxygenated with molecular oxygen, in which case modification of two sulfurs to sulfenate moieties occurs, Ru(RSO2)2. FTIR displays stretching frequencies at 802 cm-1, 1022 cm-1, 1110 cm-1 consistent with the presence of RSO2-, while the cyclic voltammogram shows a single reversible oxidation at +477 mV. Stoichiometric oxygenation with hydrogen peroxide failed to produce either sulfonate Ru(RSO 3-) or sulfinato Ru(RSO-) products. The cyclic voltammogram of 1 shows two reversible events at -345 mV and +455 mV. Spectroelectrochemical investigation of the oxidation event at -345 mV indicates a reversible, one-electron process. The electrochemically generated product (2) was identified as the Ru(III) analogue of 1 via chemical synthesis and ESIMS analysis. Further one electron oxidation in acetonitrile at +455 mV yields a short-lived intermediate with an absorbance at 850 nm, which is observable only at low temperature. Ligand-centered oxidation to produce a thiyl radical is proposed. The rate of the radical decay, measured via chronoamperometry, is ∼10-3 s -1 and concentration independent producing a yellow solution with a new reversible oxidation potential at +800 mV. The product, 7, can be further oxidized by one electron to an EPR active (S = ½) compound, 8, but it cannot be reduced. Based on spectroscopic investigations and a first order rate constant, intramolecular disulfide formation is proposed. The electrochemical oxidation of 2 in acetone also produces a thiyl radical intermediate. However, in this case further decay results in a new carbon-sulfur bond, 9. Structural characterization reveals an alkylation of the sulfur via acetone. The cyclic voltammogram of 9 shows a single reversible event at +468 mV, consistent with the modification of a single thiolate. Similar reactivity is observed with 2-butanone and acetophenone, but not with 3-pentanone or methyl acetonate. A mechanistic pathway for thiyl radical reactivity with ketone is proposed. |
