Abstract not available.

The structure, thermochemistry, isomerization and dissociation of the CH2BH2 and CH3BH radicals, cations and anions have been explored with a wide range of ab initio levels of computational theory and their formation has been probed by tandem mass spectrometry and RRKM kinetic theory. Calculations predict that CH2B H2&ceilr0;+ is not an equilibrium structure on the potential energy surface. The CH3B H&ceilr0;+ was characterized by its collision-induced dissociation mass spectrum and neutralization-reionization (NR) mass spectrometry was used to generate the CH3B H&ceilr0;• radical. While both CH2B H2&ceilr0;• and CH3B H&ceilr0;• are stable with respect to isomerization and dissociation, a relatively low barrier to the 1,2-hydrogen shift means that pure CH3B H&ceilr0;• can only be made cold, and so the above NR experiment likely produces a mixture of neutrals, of which only CH3B H&ceilr0;• can be reionized. Vertical electron attachment to CH3B H&ceilr0;• is endothermic which means the CH3B H&ceilr0;- anion is unlikely to be made from the cation or radical. In addition, the anion lies in a shallow well of only 48 kJ mol-1 and will undergo fast isomerization to CH2B H2&ceilr0;- below the dissociation limit. The B(N(CH3)2)3 radical cation and dication structures and dissociation products have been investigated by high level ab initio calculations and experimentally characterized by tandem mass spectrometry. The KER was measured for the metastable dissociation products of the B(N(CH 3)2)3 dication. There were four observed dissociation channels, two involving neutral losses and two involving charge separations. The neutral loss channels successfully compete with the charge separations, the dominant process actually being neutral loss of H2. The KER for the four metastable dissociations were determined to be T0.5(141++) = 368 +/- 18 meV, T0.5(127++) = 144 +/- 12 meV, Th (99+) = 2365 +/- 156 meV, Th(44+) = 2046 +/- 279 meV, and Th(128+) = 1942 +/- 332 meV.

Treatment of ruthenium chloride complexes RuCl2(PPh 3)3 1a or RuHCl(PPh3)3 1b with monodentate aryloxides in non-alcohol solvents affords pi-bound aryloxide derivatives with the general formula Ru(eta5-ArO)( o-C6H4PPh2)(PPh3) 2 9 or RuX(eta5-ArO)(PPh3) 2 (X = H (3a) or Cl (11b)). In the presence of alcohols, hydridocarbonyl complexes with the general formula RuXY(CO)(PPh 3)3 (X = H, Y = H 2a; X = H, Y = Cl 2b ) are generated by hydride abstraction and decarbonylation of formaldehyde. Treatment of 1a with one equivalent of aryloxide in the presence of isopropanol liberates the phenol and acetone, affording clean 1b in quantitative yields. Treatment of 3a with ethereal HCl gives [RuH(eta 6-ArOH)(PPh3)2]Cl 12a. Arresting sigma → pi isomerization was attempted using a P,O-chelate ligand ((+/-)-2-(diphenylphosphino)-2'-hydroxy-1,1 '-binaphthyl (binop; 29). The entropy gain was not favourable enough to prevent isomerization. The binop ligand in the product, RuCl2(binop)(PPh3) 31, is sigma-bound via the phosphorus donor, and n-bound via the 'phenoxide' ring, as indicated by detailed spectroscopic and MALDI-mass spectrometric analysis. Reaction of RuHCl(PPh3)3 1b with 3-chloro-3-methyl-1-butyne effects transformation into the alkylidene complex RuCl2(=CHCH=CMe 2)(PPh3)2 34. RuHCl(PPh3) 3 1b is commercially available or obtained via quantitative reaction of RuCl2(PPh3)3 1a with alkali aryloxides, as described above. Phosphine exchange between 34 and PCy3 is rapid at room temperature, affording RuCl 2(=CHCH=CMe2)(PCy3)2 37. Complex 34 is stable indefinitely in the solid state at room temperature under N2, but dimerizes slowly in solution to give RuCl(PPh3)2(mu-Cl)3Ru(=CHCH=CMe2)(PPh 3)2 36. A side-product arising from use of excess 3chloro-3-methyl-1-butyne in the synthesis of 34 was identified as a Ru(IV) carbyne complex RuCl3(≡CCH=CMe2)(PPh 3)2 35. t,t-Benzaldehyde azine 40 is formed as a byproduct in the synthesis of phenyldiazomethane 39. Azine 40 coordinates to ruthenium at room temperature, generating Ru 2Cl4(dppb)2(t,t-benzaldehyde azine) 52. At 50°C, a novel N-N activation reaction yields Ru2Cl4(dppb)2(NCPh) 43 and Ru 2Cl4(dppb)2(HN = CHPh) 44 in a 1:1 ratio. The structure of 43 was confirmed by X-ray analysis. A systematic investigation into ROMP of 2,3-dicarboalkoxynorbornadienes 53--55 and 2,3-diphenylamidonorbornadiene 56 via molybdenum biphenolate catalysts 49 showed that polymer tacticity was dependent on biphenolate and monomer substituents. Thermal analysis of the polymers by DSC, TGA and IR experiments showed that polymers prepared from 2,3-dicarboalkoxynorbornadiene monomers underwent C = C degradation even at 80°C. In contrast, the bulky amide polymer was stable up to 275°C. All of the polymers decompose above 300°C. Investigations of the tertiary structure of the polymers indicated no helicity in solution: though high crystallinity in the solid state could result from helicity, the extreme mechanical sensitivity of the samples precluded confirmation by wide-angle X-ray diffraction.

The thesis comprises four main chapters on chemical reactions and kinetics of some of the processes involved in the global mercury cycle. In the first chapter, the UVA irradiation of aqueous acidic mercuric chloride in the presence of large excess of Fe(III) organic diacid complexes results in partial reduction of the mercuric ion to elemental mercury. The pseudo-first-order rate constant (k) for photoreduction reaction is pH-dependent. Similar results were obtained using visible irradiation although the rates were ca. 10 times slower. The mechanism of photoreduction is inferred to involve reaction of Hg(II) with a secondary photoproduct, the strongly reducing radical anion CO 2-•. No other previous reports have suggested the involvement of this radical in mercury reduction. In the presence of dissolved oxygen, competition for CO2-• between Hg(II) and O2 reduces the rate and efficiency of mercuric ion reduction. The O2-•/HO2 products do not reduce Hg(II). On the contrary, their disproportionation leads to the formation of H2O2 which causes a slow reoxidation of Hg(0). In the second chapter, the reaction rate of UVA photoreduction of Hg(II) ions by fulvic and humic acids was found to have higher values in the pH range of 5 to 6 which is relevant to most aquatic environments, within this pH range, speciation calculations show that most of Hg(II) will bind to DOC. The effects of environmentally relevant parameters such as Hg(II)/HS ratio, and chloride concentration were investigated and the likely mechanism identified. The interaction of DOC with Hg species is not only limited to photoreactions but also the complexation reaction affects the bioavailability and speciation of Hg. This was the topic of the last two chapters. The kinetic stability of Hg-HS and McHg-HS complexes was characterized by different combined techniques; the competitive ligand exchange method (CLEM) combined with inductively coupled plasma-mass spectrometer (CLEM-ICP-MS) and the tangential flow ultrafiltration (TFUF) combined to CLEM-ICP-MS. The Hg-HS complexes can be described by at least two kinetically distinguished components; the more inert (slow) with a dissociation rate constant in the order of 10-5 s -1, and a labile component with a dissociation rate constant in the order of 10-3 s-1, protons (H+) was found to compete with Hg2+ for the strong binding sites, Hg/HS concentration ratio also was an important parameter, when [Hg 2+] was high then the strong binding sites was saturated and the excess Hg bound to the weak sites. (Abstract shortened by UMI.)

The synthesis of dendritic ligands supported on silica gel and polymers, and their use in the rhodium catalyzed hydroformylation reaction is presented in this thesis. In building a softer, more organic moiety on the surface of a heterogeneous support, the potential of uniting the advantages of heterogeneous catalysis with that of homogeneous systems is explored. The synthesis of polyamidoamine (PAMAM) dendrimers anchored on silica, via the iterative additions of methylacrylate and ethylenediamine to aminopropyl silica, is carried out. A series of C4, C6 and C12 diamines were also used to construct PAMAM dendrimers with longer diamine linkers. Phosphanylation of the various PAMAM dendrimers on silica was accomplished and the supported bis-(diphenylphosphanylmethylated) ligands were complexed to rhodium. The heterogeneous complexes were found to be effective catalysts for the hydroformylation of various aryl olefins and vinyl esters, showing good to excellent regio-selectivity for the branched aldehydes. Aliphatic olefins were also easily converted into the corresponding aldehydes, however, only a slight excess of the linear product was observed. Rhodium complexes of bis-(diphenylphosphanylmethylated) pseudopeptide based ligands immobilized on resin were prepared and studied in the hydroformylation of various olefins. The effect of relocating the metal centers from the periphery to the interior of the dendrimer was also examined. The recyclability of the aforementioned heterogeneous catalysts was investigated, however, leaching of the metal from the support and the accompanying loss of activity is observed. The synthesis of PAMAM and polyarylether ligand supported on PEG was attempted. The preparation of a soluble triphenylphosphite supported on PEG was also attempted and the crude system was evaluated as a recyclable ligand for the hydroformylation of 1-octene. Preliminary investigations into the activity of the zwitterionic (eta6-C6H5BPh 3)-Rh+(1,5-cyclooctadiene) complex with phosphite under mild hydroformylation conditions resulted in a surprising regioselective outcome where the industrially more important linear aldehyde of 1-octene was favoured with high selectivity.

This thesis describes the synthesis and characterization of various polyamidoamine (PAMAM) dendrimer moieties supported on amorphous mesoporous and periodic mesoporous silica supports. The surface characteristics of the supports are investigated using various methods and found to be intricately involved in the success of the dendrimer synthesis. The dendrimers are phophinomethylated and complexed with either palladium or rhodium and used as catalysts for carbonylation reactions. The palladium complexed C6-PAMAM dendrimers supported on aminopropyl silica gel are recyclable catalysts for the hydroesterification of olefins and turnover numbers (TON) of up to 1200 are possible. C2-PAMAM dendrimers supported on LPMCM-41 and Davisil are complexed with rhodium and used as catalysts for the hydroformylation reaction of olefins. These catalysts show how the pore geometry influences the activity and recyclability of the catalysts. The dendrimer-rhodium complexes supported on LPMCM-41 exhibit very high activity and a TOF of up to 1800 h-1 are observed for the hydroformylaton of 1-octene. These catalysts can be recycled effectively by simple filtration. A negative dendrimer effect is observed with the higher generations exhibiting lower activity than the lower generations. The dendrimer-rhodium complexes supported on Davisil also exhibit very high activity and a TOF of up to 1700 h-1 are observed for the hydroformylation of 1-octene. The activity of these catalysts are less dependent on the generation than the LPMCM-41 dendrimers, and excellent activity is observed up to the third generation for the hydroformylation reaction of 1-octene.

The density functional package DeFT is used for systems with a large number of charge distributions, and the bottleneck of the computation is the evaluation of two-electron integrals. Previously, it scaled quadratically with system size. A particular strategy, called the continuous fast multipole method, has been implemented in DeFT and combined with traditional methods for evaluating the two-electron integrals. The result is a code which scales linearly with system size and is able to treat larger systems. The Continuous Fast Multipole Method (CFMM) uses the divide-and-conquer strategy to approximate the pairwise potentials between continuous charge distributions. Pairwise potentials are computed using the direct method if they are within a defined distance of one another; and are approximated by a multipolar expansion if they are not. The algorithm involves successive subdivisions of the simulation space until the desired precision is reached, which reduces the number of pairwise potentials evaluated. For large systems, this algorithm scales linearly with the number of charge distributions. Enzyme-catalyzed phosphoryl transfer reactions have many applications in biological systems. It has been shown in previous investigations that phosphoryl transfer in enzymes proceeds via a pentacoordinate phosphorus intermediate. Few theoretical investigations have been conducted on this class of enzymes due to the large number of atoms treated quantum mechanically. In this investigation, models of the pentacoordinate phosphorus intermediate are investigated with density functional methods. Comparison of the results of calculations using the VSXC functional with experiment and perturbation theory are employed to validate its use in investigations of phosphoryl transfer reactions.

This thesis describes some research in gas-phase ion chemistry, using mass spectrometry techniques combined with theoretical calculations. Metastable ion and collision-induced dissociation mass spectra, kinetic energy release and isotopic labelling were used to characterize and identify precursor and fragment ions and to predict reasonable reaction mechanisms which were then further elucidated by calculations. MP2, B3-LYP and G3 levels of theory were employed to obtain the structures corresponding to energy minima and transition states and thus to obtain a complete potential energy surface for each system. A major focus of this work was to investigate the unimolecular reactions of some ion-molecule complexes, especially the isomerizations that take place within them and then to discover the mechanisms by which such reactions take place. Particular attention was devoted to ion-molecule complexes that comprise ketones (including aldehydes), enols and distonic ions of alcohols. The first two systems studied were acetaldehyde associated with the distonic methanol cation (•CH2OH2 +), [CH3CHO/H+O(H)CH2 •], and with its conventional isomer (CH3OH +•), [CH3CHO/+•HOCH3]. The isomerization barrier for ionized acetaldehyde to rearrange to its enol isomer, vinyl alcohol CH2CHOH+•, was lowered significantly (by 133 kJ/mol) by its association with •CH 2OH2+. This reaction resulted from a H +/H• transfer mechanism, involving a transition state of low energy requirement. In contrast, the CH3OH +• ion did not facilitate the rearrangement of acetaldehyde to its enol ion. Similar observations were obtained for ion-molecule complexes of acetone and methanol, [(CH3)2C=O/H+O(H)CH 2•] and [(CH3)2C=O/ +•HOCH3]. One metastable ion dissociation of the latter involved the loss of a methyl radical, producing a new [C3H 7O2]+ isomer, [CH3C+···(H)OCH 3], whose structure was assigned by calculations. A water molecule is one of the smallest species that have been used as a catalyst within an ion-molecule complex, thus the gas-phase reactions of the ion [CH3CHO/H2O]+• were also investigated in this thesis. The metastable ion (MI) mass spectrum revealed that this ion-molecule complex decomposed spontaneously by the losses of H 2O, CO and •CH3. Hydrogen-bridged water complexes were found to be the major products of the losses of CO and •CH3. The CO loss produced the [•CH 3···H3O+] ion and involved a backside displacement mechanism. The product ions arising from • CH3 loss (via two different reaction channels) were assigned by theory to be the isomers, [OC···H3O +] and [CO···H3O+], and their 298 K enthalpy values, calculated at the G3 level of theory are Delta fH[OC···H3O+] = 420 kJ/mol and DeltafH[CO···H3O+ ] = 448 kJ/mol. (Abstract shortened by UMI.)

This work examined several cermet materials as possible anode materials for solid oxide fuel cell (SOFC) systems operating in multiple fuel environments. In particular, these materials consisted of two phase M-YSZ (M = Ni, Cu or Co, YSZ = yttria stabilized zirconia) cermets synthesized via the gel-precipitation method. Relations between synthesis conditions and cermet structure/performance dominated the first section of this work. SOFC anode performance was correlated back to original synthesis conditions, whereby dM/dYSZ was controlled via the production of a crystalline intermediate. Electrochemical characterization of Ni- and Co-YSZ anodes in H2 and H2S/H2 fuels was performed and each arc observed in the impedance curves was ascribed to a specific process. The high- and mid-frequency arcs were related to transport and charge transfer processes respectively. Non-traditional relationships between inverse Tafel (Lefat) slopes and temperature were observed. This resulted in a change in charge transfer coefficients with respect to temperature. By evaluating this dependence, a charge transfer coefficient of 1.5 for hydrogen oxidation on Ni-, Co- and NiS-anodes was determined. CoS-anodes resulted in a charge transfer coefficient of 0.2. NiS- and CoS-anodes were stable in sour gas environments and selective towards the electrochemical oxidation of H2 over H2S as suggested by open circuit voltage and mass spectrometry. Cell performances of and CoS-anodes in sour gas environments were stable over a 6 day period and showed no signs of deterioration. However, H 2S was required in the fuel stream to maintain optimal performance of these anodes. Once H2S was removed, the CoS-anodes reverted to Co-YSZ. For CoS-based anodes, optimum cell performance was maintained at a H2S content >1v/v%. Investigations of bimetallic NiCu- and NiCo-anodes were also performed. The addition of Cu to Ni-based anodes resulted in larger metal particle sizes and decreased anode activity for hydrogen oxidation. Small additions of Co to Ni-based anodes showed a marked improvement in hydrogen oxidation activity. The bimetallic anodes were also tested in H2S/CH4 mixtures and showed good activity for all anodes tested over a 15 hour period.

No description available.