Oxo and peroxo ligand transfer reactions involving methylrhenium trioxide

مرکز و کتابخانه مطالعات اسلامی به زبان های اروپایی

منو

" Oxo and peroxo ligand transfer reactions involving methylrhenium trioxide "
M. M. Abu-Omar J. H. Espenson

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112834
Doc. No	:	TLpq304306825
Main Entry	:	J. H. Espenson
	:	M. M. Abu-Omar
Title & Author	:	Oxo and peroxo ligand transfer reactions involving methylrhenium trioxide\ M. M. Abu-OmarJ. H. Espenson
College	:	Iowa State University
Date	:	1996
student score	:	1996
Degree	:	Ph.D.
Page No	:	151
Abstract	:	Methylrhenium dioxide (MDO), prepared in aqueous solution from the reaction of methylrhenium trioxide (MTO) and hypophosphorous acid, reacts with oxo donor compounds by oxygen-atom abstraction at record-high rates. These include inorganic oxoanions (e.g. ClO{4\sp-}), organic oxo substrates (e.g. sulfoxides), and few metal oxides (e.g. VO The mechanism of oxygen-atom transfer from oxygen donors (X=O) to MDO involves nucleophilic attack of the substrate at the oxophilic rhenium forming an adduct prior to oxo transfer. The kinetic data have been related to some extent to the element-oxygen force constants. MTO reacts with hydrogen peroxide to form the catalytically active species usd\rm CH\sb3ReO\sb2(\eta\sp2\rm O\sb2),usd A, and usd\rm CH\sb3ReO(\eta\sp2\rm O\sb2)\sb2(H\sb2O),usd B. The catalytic reactions of these rhenium peroxides with a large family of phosphines have been investigated. Systematic changes in the substituents on phosphorous were made to vary the nucleophilicity and cone angle of the phosphine. The kinetic data support a mechanism that allows nucleophilic attack of the substrate at the rhenium peroxides. MTO also catalyzes the oxidation of usd\betausd-diketones by usd\rm H\sb2O\sb2usd to give cleavage products, carboxylic acids. The kinetics of the initial oxidation which features epoxidation of the enol form, the majority species, have been investigated for a group of cyclic usd\betausd-diketones. Its rate responds to substituents in the "normal" manner: electron-donating groups accelerate the reaction. In contrast, the subsequent oxidation steps controlled by O-insertion into a C-C bond involve A and B as nucleophiles rather than their "normal" electrophilic behavior. In the absence of a substrate, the MTO-usd\rm H\sb2O\sb2usd catalyst undergoes decomposition to afford methanol and perrhenate. The deactivation kinetics feature complex dependences on hydrogen peroxide and pH. The catalyst is most stable at high acid and peroxide concentrations. Methanol and perrhenate are formed from the action of HO{2\sp-} on MTO; the mechanism of deactivation involves methyl migration to a peroxo bound oxygen. The diperoxo complex, B, on the other hand, is stable towards decomposition to methanol and perrhenate; instead it evolves molecular oxygen and regenerates the starting MTO.
Subject	:	Chemistry
	:	Pure sciences