Carbon-sulfur bond formation/cleavage reactions of metal-stabilized thiyl radicals by electrochemical and chemical methods.

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

Kagna Ouch Sampson, 1983-

University:University of Louisville

Department:Chemistry

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

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=2256&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

The oxidation of metallothiolates is complicated by "non-innocence" or potentialredox activity of sulfur to yield thiyl (RS•) radicals. In some instances, the one-electronoxidation of metal thiolates yields a product with the unpaired electron nearly equallydelocalized between metal and sulfur such that, a specific site of oxidation cannot bedefined. We refer to these complexes as metal-stabilized thiyl radicals. This dissertationexplores reversible carbon-sulfur bond formation between metal-stabilized thiyl radicalsand unsaturated hydrocarbons. Oxidation of the metal thiolate precursors [Ru(DPPBT)3]-Ru-l, and Re(DPPBT)3, Re-l, (DPPBT = diphenylphosphino-benzenethiolato), generatesreactive species add with alkenes, alkynes, and dienes to yield metal-dithioether products.The electrochemical experiment reveals the addition of alkenes to [Ru-l]+ as anirreversible process. The oxidized intermediate [Re-l]+ binds alkenes reversibly withequilibrium binding constants that vary with complex charge. This dissertation employsthe 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 ofthese reactions. The rate constants of substrates are obtained through digital simulation of cyclic voltammograms at multiple scan rates. The electronic effects provide a measure ofthe relative reactivity of the substituted styrenes toward the metal-coordinated thiylradicals, which yields a Hammett correlation (p = -0.7(1)) consistent with an electrophiliccharacter for our thiyl radical complexes. Experimentally determined rate constants rangefrom 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-pooralkenes. 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 usingchemical oxidants. Chemical oxidation of [Ru-l]¨ in the presence of m-methylstyrene, pmethylstyrene, 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.