An integrated approach to the design of potential rutheniun-based metathesis catalysts is described, in which closely defined synthetic forays provide the focus and rationale for detailed computational and mechanistic studies. The ground-state geometry of a 1st-generation Grubbs catalyst has been explored at the molecular mechanics, semi-empirical and DFT levels, and the resulting structures have been shown to compare favourably with literature data and with the structure of a known crystalline analogue. The DMol³ DFT code has also been shown to represent accurately both the geometry of the corresponding co-ordinatively unsaturated monophosphine derivative, and the ligand dissociation energy associated with its formation. A DFT free-energy profile of the degenerate metathesis of ethylene has been generated, using a truncated model of the 1st-generation Grubbs catalyst, permitting location, for the first time, of the three expected transition states and providing new information regarding the rate-determining step. DFT methods have been used to facilitate the design of a tridentate camphor-derived ligand for use in the construction of a novel Grubbs-type catalyst. The phosphine ligand dissociation energy of the putative catalyst and the ethylene metathesis energy profile of a truncated model have also been studies at the DFT level. The attempted synthesis of the proposed ligand proceeded via a novel 8-bromocamphoric anhydride intermediate and afforded several unexpected and novel products, including a cisfused γ-Iactone, and a bromo camphoric acid derivative. Single crystal X-ray analysis of the latter reveals a chiral, polymeric H-bonded packing arrangement, rendering it suitable for chiral inclusion studies. Computational methods, including the GAUSSIAN-based GIAO NMR prediction technique, were used to support the structural characterisation of the novel camphor derivatives. DFT-Ievel computational analysis of the C-8- and C-9 bromination of camphor has afforded theoretical insights which permit the reconciliation of two earlier empirical explanations regarding the regioselectivity of these transformations; moreover, the theoretical results suggest that a third, previously disregarded factor, plays a significant role. A coset analysis, in conjunction with DFT-Ievel energy profiling, has also been used to resolve conflicting opinions regarding the origin of the major byproduct. Computed electronic parameters (CEP's) have been calculated for the anionic ligands involved in a series of 2nd-generation Grubbs-Hoveyda-type catalysts, and used to explain some apparently anomalous trends in catalyst activity. A linear relationship between ligand CEP's and selected ¹H NMR chemical shifts has also been demonstrated and used to identify a transient ruthenium complex in solution. The ability of the malonate di-anion to bind to ruthenium in a bidentate manner has been explored and demonstrated, under suitable conditions. DFT methods have been used to design and assess the ruthenium-chelating potential of a novel tridentate malonate derivative. A synthetic pathway to this ligand has been designed and several novel heterocyclic intermediates have been isolated and characterised. An NMR-based kinetic study of the Grubbs-catalysed self-metathesis of l-octene has been completed, and the effects of temperature, concentration and solvent variations on the kinetic parameters have been studied. Application of the Guggenheim method and a simplified mechanistic model has permitted the accurate calculation of pseudorate constants for the initiation and, for the first time, the propagation phase of the reaction. Theoretical studies of this reaction at the DFT and molecular mechanics levels have been shown to support previous assumptions regarding the selectivity and temperature-dependence of metallacycle formation.

Computational techniques were employed to investigate pathways that would improve the properties and characteristics of transition metal (i.e., ruthenium) catalysts, and to explore their mechanisms. The studied catalytic pathways are particularly relevant to catalytic hydroarylation of olefins. These processes involved the +2 to +3 oxidation of ruthenium and its effect on ruthenium-carbon bond strengths, carbon-hydrogen bond activation by 1,2-addition/reductive elimination pathways appropriate to catalytic hydrogen/deuterium exchange, and the possible intermediacy of highly coordinatively unsaturated (e.g., 14-electron) ruthenium complexes in catalysis. The calculations indicate a significant decrease in the Ru-CH3 homolytic bond dissociation enthalpy for the oxidation of TpRu(CO)(NCMe)(Me) to its RuIII cation through both reactant destabilization and product stabilization. This oxidation can thus lead to the olefin polymerization observed by Gunnoe and coworkers, since weak RuIII-C bonds would afford quick access to alkyl radical species. Calculations support the experimental proposal of a mechanism for catalytic hydrogen/deuterium exchange by a RuII-OH catalyst. Furthermore, calculational investigations reveal a probable pathway for the activation of C-H bonds that involves phosphine loss, 1,2-addition to the Ru-OH bond and then reversal of these steps with deuterium to incorporate it into the substrate. The presented results offer the indication for the net addition of aromatic C-H bonds across a RuII-OH bond in a process that although thermodynamically unfavorable is kinetically accessible. Calculations support experimental proposals as to the possibility of binding of weakly coordinating ligands such as dinitrogen, methylene chloride and fluorobenzene to the "14-electron" complex [(PCP)Ru(CO)]+ in preference to the formation of agostic Ru-H-C interactions. Reactions of [(PCP)Ru(CO)(1-ClCH2Cl)][BAr'4] with N2CHPh or phenylacetylene yielded conversions that are exothermic to both terminal carbenes and vinylidenes, respectively, and then bridging isomers of these by C-C bond formation resulting from insertion into the Ru-Cipso bond of the phenyl ring of PCP. The QM/MM and DFT calculations on full complexes [(PCP)(CO)Ru=(C)0,1=CHPh]+ and on small models [(PCP')(CO)Ru=(C)0,1=CH2]+, respectively, offered data supportive of the thermodynamic feasibility of the suggested experimental mechanisms and their proposed intermediates.

In many catalytic systems, the catalytic performance of a metal supported catalyst would be affected by the size and shape of the metals, and this phenomena is called structure sensitivity. Generally, the structure sensitivity effect is considered being led by a combination of geometric property change and electronic property change of the surface metals. The particle size variation is an effective way to change the surface structure of the supported metal catalyst, leading to different fractions of the active sites exposing on the support that would take effect on catalyzing the reaction. In this project, a series of Ir/MgAl₂O₄ catalysts with different particle sizes that less than 2nm were utilized for ethane and n-butane hydrogenolysis reactions to study the structure sensitivity effect as well as the potential reaction mechanism. The results show that the activity on the catalysts with nanoparticles and mostly single atoms is evidently higher than that with the subnanometer clusters in both reactions, but the selectivity to the target product of ethane is not quite dependent on the particle size in the n-butane hydrogenolysis. After the fundamental analysis, it is proposed that the reaction mechanism of alkanes hydrogenolysis on the single atom catalysts including single active sites is probably distinctive from that generally accepted on the large particles containing multiple active sites from literature. For n-butane hydrogenolysis, the parallel reaction pathway of central C-C bond cleavage is dominant at low temperature or in the low conversion range. As the temperature going up or the conversion increasing at a certain temperature, the parallel reaction pathway of terminal C-C bond cleavage becomes more and more competitive. The series reaction pathway of hydrogenolysis on propane intermediate would always take place, but the level would be drastically enhanced when the conversion keeps increasing in the very high range. The C-C bond cleavage on the ethane product would not easily happen unless the conversion is close to 100%. / M. S. / Shale gas is natural gas trapped in shale rocks. Among all the countries that have abundant shale gas reserves, the US, benefited from advanced extraction technology, has the largest production of it. What’s more, the production rate will keep increasing at least for the coming 20 years, and shale gas will eventually become the largest source for natural gas. After extraction, there is a series of treatments shale gas has to go through before it can be utilized, catalytic reaction of alkanes (molecules found in most fuels) is one of these essential procedures. Although they are among the most important compositions of shale gas, different types of alkanes are difficult to separate and purify through traditional methods like condensation. To overcome this obstacle, this thesis focuses on exploring efficient catalysts to convert the n-butane (a straight chain alkane with 4 carbon atoms) to ethane (alkane with 2 carbon atoms). Two reactions are involved: n-butane hydrogenolysis and ethane hydrogenolysis. Catalysts are some specific materials that can accelerate certain chemical reactions. The catalysts discussed in this thesis are tiny metal (iridium) particles attached to the support material (magnesium aluminate). In this study, the performance of these catalysts with different particle sizes were tested for the above mentioned hydrogenolysis reactions. The results show that changing the particle size of the catalysts considerably affects the rate of these catalytic reactions. The fundamentals of the catalytic system presented in this work can also help the researchers to rationally design the catalysts aiming at higher efficiency and lower cost in the future work.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

This thesis describes the synthesis, characterisation and coordination chemistry of a variety of fluorinated ß-diketonate ligands (I) and carboxylate ligands (II), the catalytic activity of the resultant metal complexes for oxidation and C-C bond forming reactions, and an evaluation of fluorous methodologies for catalyst/product separation. (Fig. 3706) Chapter 1 introduces the concept and application of fluorous methodologies, including fluorous biphase catalysis and fluorous reverse phase silica gel (FRPSG), as alternative approaches to product/catalyst separation in homogeneous catalysis. Chapter 2 describes the synthesis and characterisation, in some cases by X-ray diffraction, of the fluorinated ß-diketonate ligands and an evaluation of the influence of the perfluoroalkyl groups on the coordination of these ligands to a variety of transition metals including copper, nickel, palladium and zinc. Chapter 3 outlines attempts to sue fluorous nickel ß-diketonate complexes for the oxidation of sulfides. The results indicate that a metal catalyst is not necessary for oxidation in this system although the veracity of catalyst separation using FRPSG was established. This chapter also describes the investigation of a fluorous molybdenum ß-diketonate complex for the oxidation of alkenes, although the extreme moisture senstiviity of the complex negated any attempts at recovery and recycling. The scope of Lewis acid catalysed coupling of ß-diketones with cyanoformates and the ability to reuse and recycle the fluorinated ß-diketonate catalysts is described in chapter 4. Chapter 5 describes attempts to extend this efficient separation procedure to the C-C bond forming reactions of rhodium carboxylate dimers. Although catalysis was observed, catalyst/product separation using FRPSG was unsuccessful. Chapter 6 summarises all the experimental details and spectroscopic data, whilst a CD-rom includes all of the crystallographic data.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.