Date on Master's Thesis/Doctoral Dissertation

5-2012

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Committee Chair

Grapperhaus, Craig

Author's Keywords

Metal-stabilized thiyl radicals; Oxidation reduction; Thiolates; Dienes; Alkenes; Alkynes

Subject

Radicals (Chemistry); Oxidation-reduction reaction; Alkenes--Oxidation

Abstract

The oxidation of metallothiolates is complicated by "non-innocence" or potential redox activity of sulfur to yield thiyl (RS•) radicals. In some instances, the one-electron oxidation of metal thiolates yields a product with the unpaired electron nearly equally delocalized between metal and sulfur such that, a specific site of oxidation cannot be defined. We refer to these complexes as metal-stabilized thiyl radicals. This dissertation explores reversible carbon-sulfur bond formation between metal-stabilized thiyl radicals and unsaturated hydrocarbons. Oxidation of the metal thiolate precursors [Ru(DPPBT)3]- Ru-l, and Re(DPPBT)3, Re-l, (DPPBT = diphenylphosphino-benzenethiolato), generates reactive species add with alkenes, alkynes, and dienes to yield metal-dithioether products. The electrochemical experiment reveals the addition of alkenes to [Ru-l]+ as an irreversible process. The oxidized intermediate [Re-l]+ binds alkenes reversibly with equilibrium binding constants that vary with complex charge. This dissertation employs the complex, [Ru-l]- to investigate metal-stabilized thiyl radical reactivity with alkenes, alkynes, and dienes. The successful works allow us to establish the scope and limits of these reactions. The rate constants of substrates are obtained through digital simulation of cyclic voltammograms at multiple scan rates. The electronic effects provide a measure of the relative reactivity of the substituted styrenes toward the metal-coordinated thiyl radicals, which yields a Hammett correlation (p = -0.7(1)) consistent with an electrophilic character for our thiyl radical complexes. Experimentally determined rate constants range from 4.6(5) x 107 M-1 S-l for electron-rich alkenes to 2.7(2) x 104 M-1 S-l for electron-poor alkenes. For cyclic alkenes, the rate of addition correlates with ring strain; knorbornene > kcyclopentene > kcyclohexene. The rate constant of alkyne addition are found to be approximately 100 times lower than alkenes as well-known. The dienes are obtained the addition rate in range between alkenes and alkynes. Crystalline samples of the ethylene addition products [Ru-l•C2H4]+ and [Re-l•C2H4]+ are obtained from preparative scale reactions using chemical oxidants. Chemical oxidation of [Ru-l]¨ in the presence of m-methylstyrene, pmethyl styrene, cyclohexene, and l-octyne yields the dithioether complexes [Ru-l• m-methylstyrenet]+, [Ru-l•p-methylstyrene]+, [Ru-l•cyclohexenet]+, and [Ru-l•octynet]+. All chemically synthesized complexes were fully characterized including 31P NMR and mass spectrometry.

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