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A. Catalysis of CO-PROX by water-soluble rhodium fluorinated porphyrins; B. Studies toward fluorination of electron rich aromatics by nucleophilic fluoride
Abstract
The rhodium(III) derivative of a water soluble, heavily fluorinated porphyrin is shown to catalyze the low temperature, low pressure selective oxidation of carbon monoxide in hydrogen gas streams for use in fuel cell applications. The catalytic activity is a direct result of the removal of electron density from the metal center. Selectivity for CO oxidation is a direct consequence of fluorination of the porphyrin periphery, since these substituents enhance the rate of the reaction and prevent the formation of Rh(II)-Rh(II) dimmers. Significantly, the dramatic increase in rhodium hydride acidity caused by fluorination precludes hydrogen activation and generation, thereby permitting preferential oxidation (PROX) of carbon monoxide in the presence of hydrogen. Addition of the redox mediator dye indigo carmine scavenges deleterious active oxygen species and hence permits air or dioxygen to be used as a terminal oxidant for this process. An improved arene fluorination methodology via the reductive elimination of diaryliodonium fluoride salts is applied to the synthesis of 2-fluoroestradiol, whose fluorine-18 analog is a radiotracer used in positron emission tomography (PET). The use of nonpolar solvents suppresses disproportionation and other deleterious reactions and leads to significant improvements in the fluorination yields. The method is conducive to the rapid synthesis of fluorine-18 labeled radiotracers using nucleophilic fluoride sources for PET applications. Attempts at accomplishing fluorination of an electron rich aromatic using nucleophilic fluoride via the reductive elimination of arylfluoropalladium(II) complexes are described.
Subject Area
Chemistry|Inorganic chemistry|Organic chemistry
Recommended Citation
Uppaluri, Shri Harsha, "A. Catalysis of CO-PROX by water-soluble rhodium fluorinated porphyrins; B. Studies toward fluorination of electron rich aromatics by nucleophilic fluoride" (2013). ETD collection for University of Nebraska-Lincoln. AAI3590991.
https://digitalcommons.unl.edu/dissertations/AAI3590991