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Late transition metal organometallic porphyrin complexes as catalysts for the activation of organic and biological substrates
The porphyrin ligand provides a stable, adjustable environment for a wide variety of metal ions. Two distinct porphyrin systems were studied; core-modified rhodium and iridium porphyrins (Chapter 1-2) and water-soluble β-fluorinated rhodium porphyrins (Chapters 3-5). Both porphyrin systems were used in the development of tunable complexes for catalytic transition metal mediated organic and biological reactions. Our initial hypothesis was that this weakly basic ligand environment could be used to access new pathways for catalytic oxidation reactions of alkanes, oxidants for biological substrates, and as catalysts to generate or purify gases for use in fuel cells. Rhodium(III) and iridum(III) derivatives of 5,10,15,20-tetraphenyl-21-thiaporphrin [STPP] and 5,10,15,20-tetramesityl-21-thiaporphyrin [STMP] were synthesized for use as alkane functionalization catalysts (Chapter 1). Rhodium complexes of 5,10,15,20-tetraphenyl-21-oxaporphrin [OTPP] and 5,10,15,20-tetramesityl-21-oxaporphyrin [OTMP] were synthesized to provide a more porphyrin-like coordination geometry, as described in Chapter 2. The syntheses and characterization data for water-soluble β-fluorinated porphyrins is reported in Chapter 3. The oxidation of nicotinamide cofactors catalyzed by rhodium derivatives of water soluble porphyrins under aerobic conditions is discussed in Chapter 4. The water-soluble β-fluorinated metalloporphyrins described in Chapter 4 were used to catalyze the oxidation of formic acid or its by-product (carbon monoxide) to generate pure hydrogen fuel cell streams (Chapter 5). Up to 18,000 turnovers were calculated for the decomposition of formic acid at ninety degrees Celsius with rhodium(III) 5,10,15,20-tetrakis(3-sulfonato-2,b-difluorophenyl)2,3,7,8,12,13,17,18-octafluoroporphyrin (RhTSF16TPP). The oxidation of carbon monoxide catalyzed by these water-soluble complexes showed the greatest rate with RhTSF16TPP (140 M-1s-1) in 100 mM sodium hydroxide solution at room temperature. With the addition of redox mediators (phosphomolybdic acid or indigo carmine) this reaction was catalytic under anaerobic conditions. Addition of halides (Cl-, Br-, I-) increased the rate of reduction of RhTSF16TPP at neutral pH to rates competitive with the reaction in 100 mM NaOH. These complexes apparent lack of reactivity with hydrogen makes them good candidates as catalysts for the selective oxidation of carbon monoxide in hydrogen fuel streams. ^
Biffinger, Justin C, "Late transition metal organometallic porphyrin complexes as catalysts for the activation of organic and biological substrates" (2005). ETD collection for University of Nebraska - Lincoln. AAI3194106.