In this thesis five iron phthalocyanines (FePc’s), four of which having different electron withdrawing or electron donating substituents, were evaluated as 0₂ reduction reaction (ORR) catalysts. The experimental approach simulated a PEM fuel cell environment using both ex-situ electrochemical techniques and in situ fuel cell testing. The kinetic ORR parameters for the FePc species each adsorbed on a pyrolytic graphite WE were evaluated at four temperatures (20, 40, 60, 80°C) in a novel half cell using cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. Kinetic ORR parameters included the overall ORR electron transfer number, reaction rate constants, cathodic Tafel slopes, electron transfer numbers in the rate determining step, and electron transfer co-efficients. An increase in temperature from 60°C to 80°C showed a decrease in the overall electron transfer number observed for all four substituted FePc species. A mechanism was also proposed based on the experimental results. The RDE results were confirmed using a rotating ring disk electrode (RRDE). From these RRDE results, the fraction of H₂0₂ produced (XH₂₀₂) at the disk during the ORR was calculated. These XH₂₀₂ values agreed with the overall ORR electron transfer numbers from the RDE results obtained under the same conditions. lron(Il) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25 — hexadecachioro 29H,31H-phthalocyanine (FePcCI₁₆)was down selected for further investigation as the most stable and active substituted FePc species for the ORR. Both FePcCl₁₆ and the unsubstituted FePc, were supported on carbon and made into catalyst inks for carbon fibre paper (CFP) electrode testing, and then evaluated using CV in the N₂ purged, followed by the air saturated, electrolytes, respectively. Finally, MEA’s for fuel cell testing were made using FePc species catalyst ink cathodes, and commercial Pt/C anodes. The MEA’s were tested using custom designed and built fuel cell hardware. Open circuit voltages, polarization curves, and power curves were recorded. Initial results indicated the FePcCI₁₆ MEA’s showed superior stability, higher open circuit voltages, as well as better polarization and power curves when compared to the unsubstituted FePc species. It was found that FePc species with strongly electron withdrawing substituents, such as FePcCl₁₆ showed the highest stability and greatest ORR activity. FePc species, including pyrolized FeNx/C analogues, show much promise as alternatives to Pt in PEMFC’s, as well as dye sensitized solar cells (DSSC’s).

In this thesis five iron phthalocyanines (FePc’s), four of which having different electron withdrawing or electron donating substituents, were evaluated as 0₂ reduction reaction (ORR) catalysts. The experimental approach simulated a PEM fuel cell environment using both ex-situ electrochemical techniques and in situ fuel cell testing. The kinetic ORR parameters for the FePc species each adsorbed on a pyrolytic graphite WE were evaluated at four temperatures (20, 40, 60, 80°C) in a novel half cell using cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. Kinetic ORR parameters included the overall ORR electron transfer number, reaction rate constants, cathodic Tafel slopes, electron transfer numbers in the rate determining step, and electron transfer co-efficients. An increase in temperature from 60°C to 80°C showed a decrease in the overall electron transfer number observed for all four substituted FePc species. A mechanism was also proposed based on the experimental results. The RDE results were confirmed using a rotating ring disk electrode (RRDE). From these RRDE results, the fraction of H₂0₂ produced (XH₂₀₂) at the disk during the ORR was calculated. These XH₂₀₂ values agreed with the overall ORR electron transfer numbers from the RDE results obtained under the same conditions. lron(Il) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25 — hexadecachioro 29H,31H-phthalocyanine (FePcCI₁₆)was down selected for further investigation as the most stable and active substituted FePc species for the ORR. Both FePcCl₁₆ and the unsubstituted FePc, were supported on carbon and made into catalyst inks for carbon fibre paper (CFP) electrode testing, and then evaluated using CV in the N₂ purged, followed by the air saturated, electrolytes, respectively. Finally, MEA’s for fuel cell testing were made using FePc species catalyst ink cathodes, and commercial Pt/C anodes. The MEA’s were tested using custom designed and built fuel cell hardware. Open circuit voltages, polarization curves, and power curves were recorded. Initial results indicated the FePcCI₁₆ MEA’s showed superior stability, higher open circuit voltages, as well as better polarization and power curves when compared to the unsubstituted FePc species. It was found that FePc species with strongly electron withdrawing substituents, such as FePcCl₁₆ showed the highest stability and greatest ORR activity. FePc species, including pyrolized FeNx/C analogues, show much promise as alternatives to Pt in PEMFC’s, as well as dye sensitized solar cells (DSSC’s).

In this thesis five iron phthalocyanines (FePc’s), four of which having different electron withdrawing or electron donating substituents, were evaluated as 0₂ reduction reaction (ORR) catalysts. The experimental approach simulated a PEM fuel cell environment using both ex-situ electrochemical techniques and in situ fuel cell testing. The kinetic ORR parameters for the FePc species each adsorbed on a pyrolytic graphite WE were evaluated at four temperatures (20, 40, 60, 80°C) in a novel half cell using cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. Kinetic ORR parameters included the overall ORR electron transfer number, reaction rate constants, cathodic Tafel slopes, electron transfer numbers in the rate determining step, and electron transfer co-efficients. An increase in temperature from 60°C to 80°C showed a decrease in the overall electron transfer number observed for all four substituted FePc species. A mechanism was also proposed based on the experimental results. The RDE results were confirmed using a rotating ring disk electrode (RRDE). From these RRDE results, the fraction of H₂0₂ produced (XH₂₀₂) at the disk during the ORR was calculated. These XH₂₀₂ values agreed with the overall ORR electron transfer numbers from the RDE results obtained under the same conditions. lron(Il) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25 — hexadecachioro 29H,31H-phthalocyanine (FePcCI₁₆)was down selected for further investigation as the most stable and active substituted FePc species for the ORR. Both FePcCl₁₆ and the unsubstituted FePc, were supported on carbon and made into catalyst inks for carbon fibre paper (CFP) electrode testing, and then evaluated using CV in the N₂ purged, followed by the air saturated, electrolytes, respectively. Finally, MEA’s for fuel cell testing were made using FePc species catalyst ink cathodes, and commercial Pt/C anodes. The MEA’s were tested using custom designed and built fuel cell hardware. Open circuit voltages, polarization curves, and power curves were recorded. Initial results indicated the FePcCI₁₆ MEA’s showed superior stability, higher open circuit voltages, as well as better polarization and power curves when compared to the unsubstituted FePc species. It was found that FePc species with strongly electron withdrawing substituents, such as FePcCl₁₆ showed the highest stability and greatest ORR activity. FePc species, including pyrolized FeNx/C analogues, show much promise as alternatives to Pt in PEMFC’s, as well as dye sensitized solar cells (DSSC’s). / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Substituent effects in eta5-cyclopentadienyl (Cp) transition metal complexes have been intensely studied since the discovery of the first such complex, ferrocene. Modifications of the Cp ligand framework effect changes in the physical properties and chemical reactivity of the coordinated transition metal. This concept is useful when applied to catalysis mediated by Cp complexes, because the performance of the catalyst can be markedly improved using well-chosen ligand substituents. Studies of electronic substituent effects ideally employ a wide range of electron-donating and electron-withdrawing groups. Unfortunately, most of the available electron-withdrawing groups suffer from problems with Cp ligand synthesis, Cp anion stability, and electron-withdrawing group stability under catalytic conditions. This dissertation shows that the pentafluorophenyl (C6F5) substituent is highly electron-withdrawing but avoids all of these problems. Several new C6F5-substituted cyclopentadienes are prepared by the reaction of sodium cyclopentadienide and hexafluorobenzene (C6F6) under varying conditions. Corresponding C6F5-substituted cyclopentadienyl ligands (sodium salts) are obtained upon deprotonating the dienes with NaH. Complexes of Mn(I), Re(I), Fe(II), Co(II), Zr(IV) are synthesized by reacting these ligands with transition metal halides. The acidities of several C6F5- and C5F4N-substituted cyclopentadienes and indenes are measured using 19F NMR spectroscopy. The electron-withdrawing fluorinated aryl groups have a substantial acidifying effect. The identity and number of substituents (C6F5, C5F4N, CH3, and t-Bu), the position of the substituents on the cyclopentadiene, and the intramolecular (vicinal) steric effects also influence acidity. The electron-withdrawing ability of the C6F5 group is also characterized by infrared spectroscopic analysis of substituted CpM(CO)3 (M = Mn(I) and Re(I)) and electrochemical analysis of substituted ferrocenes. X-ray crystal structures of several C6F5-substituted Cp complexes reveal interesting structural motifs, including pi-stacking of the C6F5 substituents, Cp-M bond elongation, and CO-C6F5 interactions. In addition, dynamic Cp-C6F5 and Cp-M rotational barriers are measured by variable temperature NMR spectroscopy. Finally, ethylene polymerizations and ethylene/1-hexene copolymerizations are conducted using C6F5- and C6H5-substituted zirconocene dichlorides as catalysts. Contrary to findings published elsewhere, this study shows that substituent electronic effects induce substantial changes in comonomer incorporation. / Ph. D.

<p> 1,1-Bis(4-(trifluoromethyl)phenyl)germacyclobutane and 1,1-bis(3,5-bis(trifluoromethyl)phenyl)germacyclobutane have been prepared, and their photochemistry studied by steady state and nanosecond laser flash photolysis (NLFP) techniques. Photolysis of the two compounds in the presence of methanol leads to the formation of products resulting from reaction of the alcohol with two germanium-containing reactive intermediates, the germenes and germylenes.</p> <p> The reactivities of the two germenes with nucleophiles such as alcohols, carboxylic acids, and amines have been examined by NLFP techniques, and the results are compared to analogous data for 1,1-diphenylgermene and 1,1-diphenylsilene. Germene reactivity is shown to increase with increasing electron-withdrawing power of the substituents, consistent with a mechanism initiated by nucleophilic attack at germanium. The increased electrophilicity of the substituted 1,1-diarylgermenes results in kinetic behavior indistinguishable from that of 1,1-diphenylsilene, indicating that germenes and silenes form a mechanistic continuum in their reactions with nucleophiles.</p> / Thesis / Master of Science (MSc)

Betalaínas são pigmentos naturais derivados da L-tirosina encontrados em um número restrito de plantas e fungos. Sob o ponto de vista químico, betalaínas são iminas ou sais de imínio que se originam do acoplamento aldimínico entre o ácido betalâmico e aminas ou aminoácidos. Embora sejam conhecidas mais de 70 betalaínas naturais, os estudos sobre as relações entre a estrutura e as propriedades de betalaínas ainda são limitados. Esta Tese de Doutorado descreve a semissíntese e estudo da hidrólise e das propriedades fotofísicas e redox de três grupos de betalaínas não naturais: N-fenilbetalaínas (pBeets), N-metil-N-fenilbetalaínas (N-Me-pBeets) e N,N-difenilbetalaínas (dipBeets). O estudo de quatorze pBeets para substituidas sugere que a porção imina destes compostos está protonada em meio aquoso neutro e que substituintes atraentes de elétron na porção fenílica favorecem o deslocamento de carga do nitrogênio 2-piperideínico para a porção imínica. A constante de hidrólise aumenta linearmente com o aumento do valor de &#963;p de Hammett do substituinte, dado o aumento da eletrofilificade do carbono aldimínico. Por outro lado, pBeets com substituintes atraentes de elétron são mais fluorescentes. A adição de metila ou fenila ao nitrogênio da imina cria um ambiente hidrofóbico que compromete o ataque da água e diminui a constante de velocidade de hidrólise provocando, contudo, uma diminuição na fluorescência. Os resultados foram racionalizados empregando-se espectroscopia de ressonância magnética nuclear, espectrofotometria e voltametria cíclica. / Betalains are natural pigments derived from L-tyrosine that are found in a restricted number of plants and fungi. From the chemical point of view, betalains are imines or iminium salts that originate from the aldimine coupling between betalamic acid and amines or amino acids. Although more than 70 natural betalains are known, studies on structure-property relationships of betalains are still limited. This doctoral thesis describes the semi-synthesis and study of the hydrolysis as well as photophysical and redox properties of three groups of non-natural betalaines: N-phenylbetalaines (pBeets), N-methyl-N-phenylbetalines (N-Me-pBeets) and N,N-diphenylbetalaines (dipBeets). The study of fourteen substituted pBeets suggests that the imine portion of these compounds is protonated in neutral aqueous medium and that attractive electron substituents on the phenyl portion favor the displacement of 2-piperidene nitrogen charge to the imine portion. The hydrolysis constant increases linearly with the increase of the Hammett\'s &#963;p value of the substituent, given the increase in the electrophilicty of the aldimine carbon. On the other hand, pBeets with attractive electron substituents are more fluorescent. The addition of methyl or phenyl to the imine nitrogen creates a hydrophobic environment upon water attack and decreases the hydrolysis rate constant, however, causing a decrease in fluorescence. The results were rationalized using nuclear magnetic resonance spectroscopy, spectrophotometry and cyclic voltammetry.

Betalaínas são pigmentos naturais derivados da L-tirosina encontrados em um número restrito de plantas e fungos. Sob o ponto de vista químico, betalaínas são iminas ou sais de imínio que se originam do acoplamento aldimínico entre o ácido betalâmico e aminas ou aminoácidos. Embora sejam conhecidas mais de 70 betalaínas naturais, os estudos sobre as relações entre a estrutura e as propriedades de betalaínas ainda são limitados. Esta Tese de Doutorado descreve a semissíntese e estudo da hidrólise e das propriedades fotofísicas e redox de três grupos de betalaínas não naturais: N-fenilbetalaínas (pBeets), N-metil-N-fenilbetalaínas (N-Me-pBeets) e N,N-difenilbetalaínas (dipBeets). O estudo de quatorze pBeets para substituidas sugere que a porção imina destes compostos está protonada em meio aquoso neutro e que substituintes atraentes de elétron na porção fenílica favorecem o deslocamento de carga do nitrogênio 2-piperideínico para a porção imínica. A constante de hidrólise aumenta linearmente com o aumento do valor de &#963;p de Hammett do substituinte, dado o aumento da eletrofilificade do carbono aldimínico. Por outro lado, pBeets com substituintes atraentes de elétron são mais fluorescentes. A adição de metila ou fenila ao nitrogênio da imina cria um ambiente hidrofóbico que compromete o ataque da água e diminui a constante de velocidade de hidrólise provocando, contudo, uma diminuição na fluorescência. Os resultados foram racionalizados empregando-se espectroscopia de ressonância magnética nuclear, espectrofotometria e voltametria cíclica. / Betalains are natural pigments derived from L-tyrosine that are found in a restricted number of plants and fungi. From the chemical point of view, betalains are imines or iminium salts that originate from the aldimine coupling between betalamic acid and amines or amino acids. Although more than 70 natural betalains are known, studies on structure-property relationships of betalains are still limited. This doctoral thesis describes the semi-synthesis and study of the hydrolysis as well as photophysical and redox properties of three groups of non-natural betalaines: N-phenylbetalaines (pBeets), N-methyl-N-phenylbetalines (N-Me-pBeets) and N,N-diphenylbetalaines (dipBeets). The study of fourteen substituted pBeets suggests that the imine portion of these compounds is protonated in neutral aqueous medium and that attractive electron substituents on the phenyl portion favor the displacement of 2-piperidene nitrogen charge to the imine portion. The hydrolysis constant increases linearly with the increase of the Hammett\'s &#963;p value of the substituent, given the increase in the electrophilicty of the aldimine carbon. On the other hand, pBeets with attractive electron substituents are more fluorescent. The addition of methyl or phenyl to the imine nitrogen creates a hydrophobic environment upon water attack and decreases the hydrolysis rate constant, however, causing a decrease in fluorescence. The results were rationalized using nuclear magnetic resonance spectroscopy, spectrophotometry and cyclic voltammetry.

Triazenes, compounds containing a diazoamino moiety (–N(1)=N(2)–N(3)<), are known for their reversible cis-trans isomerization character and hence, have the potential to be used in photoswitchable devices and photostorage media. However, little is known about their cis-trans isomerization mechanism. In this thesis, kinetic studies on the thermal cis-to-trans isomerization of N-(phenylazo)-substituted nitrogen heterocycles are presented. It is shown that the isomerization rate constant increases as the size and electron-donating character of the cyclic amine increases, as the electron-withdrawing character of the para substituent group on the phenyl ring increases, and as the polarity of the solvent increases. All these trends are interpreted in terms of a rotational isomerization mechanism involving a dipolar transition state. In addition, photolytic cleavage of the N(2)–N(3) bond of target substrates is shown to be affected as well by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, with the result that the photolysis yield increases as the isomerization rate decreases. Theoretical calculations on target substrates both in the gas phase and various solvents were also performed based on DFT-B3LYP/6-31+G* method. Overall, the cis-to-trans isomerization is predicted to take place through rotation around the N(1)=N(2) bond. Furthermore, the calculated energy barriers are found to be influenced by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, consistent with the effects obtained experimentally from the kinetic studies.

Triazenes, compounds containing a diazoamino moiety (–N(1)=N(2)–N(3)<), are known for their reversible cis-trans isomerization character and hence, have the potential to be used in photoswitchable devices and photostorage media. However, little is known about their cis-trans isomerization mechanism. In this thesis, kinetic studies on the thermal cis-to-trans isomerization of N-(phenylazo)-substituted nitrogen heterocycles are presented. It is shown that the isomerization rate constant increases as the size and electron-donating character of the cyclic amine increases, as the electron-withdrawing character of the para substituent group on the phenyl ring increases, and as the polarity of the solvent increases. All these trends are interpreted in terms of a rotational isomerization mechanism involving a dipolar transition state. In addition, photolytic cleavage of the N(2)–N(3) bond of target substrates is shown to be affected as well by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, with the result that the photolysis yield increases as the isomerization rate decreases. Theoretical calculations on target substrates both in the gas phase and various solvents were also performed based on DFT-B3LYP/6-31+G* method. Overall, the cis-to-trans isomerization is predicted to take place through rotation around the N(1)=N(2) bond. Furthermore, the calculated energy barriers are found to be influenced by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, consistent with the effects obtained experimentally from the kinetic studies.

Graduate / 0485