Mechanistic studies of the oxidations of hydrocarbons by manganese and ruthenium transition metal complexes

ResearchWorks/Manakin Repository

Search ResearchWorks


Advanced Search

Browse

My Account

Statistics

Related Information

Mechanistic studies of the oxidations of hydrocarbons by manganese and ruthenium transition metal complexes

Show full item record

Title: Mechanistic studies of the oxidations of hydrocarbons by manganese and ruthenium transition metal complexes
Author: Bryant, Jasmine R
Abstract: The oxidation of hydrocarbon C-H and O-H bonds can occur by a variety of mechanisms. These include stepwise processes such as initial electron or proton transfer, or concerted mechanisms such as hydride transfer or hydrogen-atom abstraction. Hydrocarbons containing weak C-H and O-H bonds are oxidized by Mn(hfacac)3 (hfacac = hexafluoroacetylacetonate) and [(bpy) 2(py)Ru=O]2+ (bpy = bipyridine and py = pyridine). Mn(hfacac) 3 is an easily prepared and reactive oxidant, forming stable solutions in benzene and methylene chloride. Based on an equilibrium established with tris(2,4-dibromophenyl)amine, a redox potential of 0.9 +/- 0.1 V vs. Cp2Fe+/° is calculated. Mn(hfacac)3 oxidizes 9,10-dihydroanthracene (DHA) cleanly to anthracene with a bimolecular rate constant of 6.8 x 10-4 M-1 s-1. Mn(hfacac)3 is also capable of oxidizing xanthene, 1,4-cyclohexadiene, 2,4-di-tert-butylphenol, toluene, and p-methoxytoluene. Product analyses and relative rates indicate that the more electron-rich substrates react by initial electron transfer to manganese. For the less electron-rich substrates, such as 1,4-cyclohexadiene, a mechanism of hydrogen atom abstraction is suggested.The oxidations of DHA, xanthene, and fluorene by [(bpy)2(py)Ru IVO]2+ give mixtures of products including oxygenated and non-oxygenated compounds. The products include those formed by organic radical dimerization, such as 9,9'-bixanthene, as well as by oxygen-atom transfer. The kinetics of these reactions and those of indene, cyclohexene, cumene, ethylbenzene, and toluene have been measured and display a clear correlation with substrate C-H bond dissociation energy. The kinetic isotope effect for the reaction of Ru=O2+ with DHA vs. DHA-d4 gives kH /kD ≥35. A mechanism of initial hydrogen-atom abstraction followed by competitive pathways of radical dimerization and trapping by the oxidant is indicated. The hydrogen-atom selfexchange rate for the transfer of H· between [(bpy)2(py)RuIIIOH] 2+ and [(bpy)2(py)RuIVO]2+ has also been measured (k'HSE = (7.6 +/- 0.4) x 104 M-1 s -1). When combined with an estimate for the DHA/HA· self-exchange rate in the Marcus cross relation, this value agrees well with the observed hydrogen-atom abstraction rate. The deuterium-atom self-exchange rate is also reported for the D· exchange between [(bpy)2(py)RuIIIOD]2+ and [(bpy)2(py)RuIVO]2+. The kinetic isotope effect for this self-exchange reaction is surprisingly near unity.
Description: Thesis (Ph. D.)--University of Washington, 2002
URI: http://hdl.handle.net/1773/8586

Files in this item

Files Size Format View
3072066.pdf 3.971Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record