Date of Award
Doctor of Philosophy
James H. Espenson
The chemistry of chromium-oxygen compounds has been investigated. The previously-characterized superoxochromium(III) ion, CrO[superscript]2+, was found to catalyze the autoxidation of the hydroxymethylchromium ion, CrCH[subscript]2OH[superscript]2+ to Cr[superscript]2+ and HCHO. In the absence of O[subscript]2 the reaction is much faster than in its presence, and is autocatalytic. The inorganic product of the aerobic reaction is the novel hydroperoxochromium ion, CrO[subscript]2H[superscript]2+, containing peroxide in the rare end-bound configuration. Reaction of CrO[subscript]2[superscript]2+, CrO[subscript]2Cr[superscript]4+ or TlOH[superscript]2+ with Cr[superscript]2+ yields the aquachromium(IV) ion, CrO[superscript]2+. This species has not previously been observed directly, although it has been invoked as an intermediate in many chromium redox mechanisms. In the presence of O[subscript]2, the CrO[superscript]2+ catalytically converts PPh[subscript]3 to O=PPh[subscript]3 by oxo transfer. The CrO[superscript]2+ oxidizes a variety of organic substrates, such as alcohols, aldehydes, carboxylates and ethers by a two-electron, hydride transfer mechanism. Contrary to literature predictions, alkyl radicals are not produced except in a few unusual cases. The reaction of CrO[superscript]2+ with Cr[superscript]2+ does not yield the species identified in the literature as the CrOCr[superscript]4+ ion. The latter is in fact mischaracterized as an oxo species. Evidence for its true nature as a bimetallic semiquinone radical complex, CrQCr[superscript]5+, is presented.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Susannah Lesley Scott
Scott, Susannah Lesley, "Reactions of some chromium-oxygen complexes containing superoxo, hydroperoxo, oxo, and [mu]-peroxo ligands " (1991). Retrospective Theses and Dissertations. 9682.