The original purpose of this work was to investigate the catalytic properties of a series of Rh₂(CO)₄(P-P)₂ complexes (where P-P = ditertiary phosphines of the type PR₂(CH₂)nPR₂, R = alkyl or aryl) for hydroformylation. The preparation of Rh₂(CO)₄(P-P)₂ involves the synthesis of Rh(P-P)₂Cl, followed by reaction with NaBH₄ to give RhH(P-P)₂, which when treated with CO in benzene yields Rh₂(CO)₄(P-P)₂, as reported in the literature. The dimer, Rh₂(CO)₄(dpp)₂, where dpp = PPh₂(CH₂)₃PPh₂, was prepared and examined for its interaction with H₂, and H₂/CO, in order to test its capabilities for catalytic homogeneous hydroformylation. The interaction of Rh₂(CO)₄(dpp)₂ (49) with H₂, and the reaction of CO with RhH(dpp)₂ (52) to yield 49, are summarized as follows: [Formula Omitted] All the species shown, except 59, have been detected by ¹H and ³¹P{¹H} NMR spectroscopy. Formation of the monomeric hydride, 50, from 49, occurs at high [dpp]. The reaction of Rh₂(CO)₄(dpp)₂ and 6 equivalents dpp with synthesis gas (H₂ : CO = 1 : 1) gives initially 50 and R₂(CO)₄(dpp)₂ reforms after 30 minutes of interaction. This is consistent with the previous finding of low turnover rate for hydroformylation of 1-hexene using as catalyst the co-ordinatively saturated Rh₂(CO)₄(dpp)₂. Treatment of 52 in toluene with ~1 atm CO, followed by treatment with ~1 atm H₂, sets up the following equilibria (where dpp* = monodentate dpp): [Formula Omitted] The homogeneous hydrogenation of 1-hexene at 31° C, - 1 atm H₂, catalyzed by "the RhH(dpp)₂/CO/H₂ system" in toluene is ascribed to the formation of an unidentified "RhH" from 50 and/or 51. The H₂-uptake curve displayed an initial ("inductive") period required for the generation of an active species "RhH", a second period of maximum rate, and a final slowing down period. The mechanism suggested for homogeneous hydrogenation of 1-hexene catalyzed by the "RhH(dpp)₂/CO/H₂ system" is presented as follows: [Formula Omitted] The corresponding rate law for the maximum rate, consistent with the kinetic data, is given by: [Formula Omitted] where ["Rh"]t is total concentration of the active "RhH" catalyst. At high [1-hexene], where k₃[1-hexene] >> k₋₃ + k₄[H₂], the rate law is simplified to: Rate = k₄[H₂],["RhH"]t where ["RhH"]t ~ total rhodium concentration in solution. The values of k₃ and k₄ at 31° C were found to be 0.42 M⁻¹ s⁻¹ and 20 M⁻¹ s⁻¹ respectively. The Rh(dcpe)₂ ⁺X⁻ complexes (X = CI, BF₄, PF₆; dcpe PCy₂(CH₂)₂PCy₂) were prepared and found to have no reactions with NaBH₄ or LiAlH₄. Consequently, the dcpe carbonyl dimer could not be prepared. The Rh(p = p)₂ ⁺Cl⁻ complex, where p = p = PPh₂C₂H₂PPh₂, was isolated and characterized; its reaction with NaBH₄ was incomplete, partially generating RhH(p=p)₂. Treatment of the mixture with CO gave partially Rh(CO)(p=p)₂ ⁺Cl⁻ and another uncharacterized carbonyl complex. A single crystal X-ray structure determination of Rh(dcpe)₂ ⁺Cl⁻ showed that the geometry around Rh is distorted square planar. Also, the extremely air-sensitive species [RhCl(dcpe)• solv]n (solv = THF or 0.1 C₆H₆) and RhCl(dcpe)(CH₂Cl₂)•C₆H₆ were isolated. The interaction of Rh(dcpe)₂ ⁺Cl⁻ with small gas molecules was studied in order to test its potential as a catalyst. There is interaction between Rh(dcpe)₂ ⁺Cl⁻ and HCI, Cl₂, and CO, in CH₂C1₂. The reaction with HCI to give cis-RhHCl(dcpe)₂ ⁺Cl⁻ is extremely rapid. The use of stopped-flow kinetics and UV-VIS spectrophotometric techniques at 25° C gave an equilibrium constant of 4.2 x 10⁷ M⁻¹ for the reaction. The forward reaction was first-order in both [Rh(dcpe)₂ ⁺Cl⁻] and [HCI], indicating a concerted oxidative addition reaction. The RhHCl(dcpe)₂⁺ species reacts further with HCI to give RhHCl₂(dcpe) and the diphosphonium salt, dcpe(HCl)₂. The Rh(dcpe)₂ ⁺Cl⁻ complex reacts with Cl₂ to give RhCl₂(dcpe)₂ ⁺Cl⁻, which was also obtained by prolonged treatment of RhHCl(dcpe)₂ ⁺Cl⁻ with CDCl₃ The reaction of Rh(dcpe)₂ ⁺Cl⁻ with CO to give Rh(CO)(dcpe)₂ ⁺Cl⁻ yielded k on and k off values of 2.2 x 10⁻² M⁻¹ s⁻¹ and 5.02 x 10⁻⁴ s⁻¹ respectively at 25° C. The Rh(dcpe)₂ ⁺Cl⁻, complex was inactive as a catalyst for decarbonylation of benzaldehyde, or hydrogenation of 1-hexene. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Ph.D. (Chemistry) / Rhodium-catalyzed hydroformylation is one of the most important industrial processes for the production of linear and branch aldehydes. Aldehydes serve as intermediates in the production of various fine chemicals. Rh-based homogeneous catalysts for aldehydes production have demonstrated high yields and selectivity. Catalyst separation and recovery of expensive Rh-metal from reaction mixtures is a challenge to this process. With increasing industrial demand for highly selective processes, homogeneous catalysis could well be extensively employed if catalyst recovery from products and recyclability could be accomplished more efficiently and economically. The above problems justify the investigation of immobilized (heterogenized) catalysts by both academia and industry. This would solve the separation problem by making it possible to separate the catalyst from the reaction medium with simple filtration techniques and to regenerate the catalyst for reuse. Moreover, the ease of recovery of catalyst from products and reusability can minimize the impact of the process on the environment. Immobilization of metal complexes on solid supports is an effective approach to overcome the limitations of homogeneous catalysis. Support materials such as Mobil Composite Material (MCM-41) and Santa Barbara Amorphous type material (SBA-15) are attractive candidates for immobilizing metal complexes because of their high surface area, adjustable pore sizes, large pore volumes and high surface silanol groups. In the present work, mesoporous silica supports, MCM-41 and SBA-15 were synthesized. Rhodium(I) complex species, trans-aquacarbonyl bis(triphenylphosphine) [Rh(CO)(OH2)(PPh3)2]OTf and trans-aquacarbonyl bis{tris-(m-sulfonphenyl)-phosphine} [Rh(CO)(OH2)(TPPTS)2]OTf were synthesized as catalyst precursors and anchored onto the mesoporous MCM-41 and SBA-15 framework structure via an electrostatic method to form immobilized (heterogenized) catalysts. The support and catalyst were characterized using a range of solid-state techniques. Results showed that the structural integrity of the catalyst supports was maintained after immobilization. Results also revealed a strong interaction between rhodium complex species and the inner walls of the ordered mesoporous materials, thus leading to the formation of stable heterogenized catalysts. In addition, immobilized catalysts constrained the pores, thus leading to a confinement effect, which enhanced activity and regioselectivity in the hydroformylation process. Selected immobilized catalysts were...

The hydroformylation of 1-octene with supported ionic liquid phase catalyst was demonstrated when using a system involving the substrate, reacting gases and products in CO₂ and N₂ flow over a fixed bed supported ionic liquid phase catalyst (silica gel and carbon aerogels as solid support respectively) at different system pressures. Yields, reaction rates, selectivities and rhodium leaching were all monitored. A pressure of CO₂ flow just below the critical point of the flowing mixture (106 bar at 100 °C if no 1-octene has been converted) was the best condition for the hydroformylation. It gave the highest acitivity (conversion to aldehyde up to 70 %), fastest reaction (TOF up to 575.3 h⁻¹) and best stable selectivity ( l:b ratio reaching 3.37 ). The utilization of scCO₂ as reaction media leads to remarkable stability of the catalyst. The supercritical or near critical (expanded liquid) system completely overcame the progressive decrease in activity of catalyst at 50, 75 bar with liquid phase transport and also showed much better results than when using other gas flows such as N₂ flow at 100 bar. In the high pressure scCO₂ phase, the concentration of 1-octene at the catalyst bed was reduced so that the conversion to aldehyde was reduced. The pore size and surface groups of the solid support should be suitable for the SILP catalyst consisting of metal complex, excess ligand and ionic liquid. Using microporous carbon aerogels as the supports, whether activated or not, gave disappointing results.

Submitted in fulfillment of the requirements for the award of the Degree of Master of Applied Science in Chemistry, Durban University of Technology, Durban, South Africa, 2016. / The 𝛼-aminophosphonates (APs) and dihydropyrimidinones (DHPMs) exhibit a wide range of important biological activities. The great potential of these compounds in biological applications prompted an increased interest in the development of efficient synthetic methods for their preparation. A novel rhodium supported boron nitride (RhBNT) material was synthesized by simply mixing boron nitride in a solution of rhodium acetate, under inert atmosphere for 7 days followed by filtration; the yield was 95 %. It exhibited excellent catalytic properties for the synthesis of 13 novel APs and 5 DHPMs. Characterization of RhBNT was performed by several techniques: the crystalline nature of RhBNT and nano size was confirmed by SEM spectroscopy, EDX pattern for RhBNT showed signals for rhodium metal, the Brumnauer-Emmett-Teller (BET) analysis showed the specific surface area of RhBNT to be 28.12 m2/g, pore volume 0.23cm3/g and pore size of 199.8Aº thereby suggesting RhBNT as a potentially effective catalyst for organic reactions; the mesoporous nature of the material was established by a type- IV adsorption isotherm; the DSC-TGA Profile indicates that RhBNT has good thermal stability and can be used adequately for catalysis. The DSC curve showed evidence of a broad exothermic peak. The RhBNT was subsequently used in the Kabachnik-Fields and Biginelli reaction in order to assess its catalytic potential. Herein Vilsmeier-Haack reagent was used to synthesize 4-oxo-chromene-3-carbaldehyde and 4-oxo-4H-benzo[h]chromene-3- carbaldehyde from 2-hydroxyacetophenone and 1-hydroxy-2-acetonaphthone, respectively. These two carbaldehydes were subsequently used to synthesize thirteen novels APs and five DHMPs using RhBNT as the catalyst The antimicrobial activities of the synthesized compounds were assessed against Escherichia coli, Bacillus cereus, Micrococcus luteus, Staphylococcus aureus and Candida albicans using the disc diffusion method. It was found that none of the compounds inhibited growth of bacteria or fungus. The assessment of toxicity was evaluated by using the brine shrimp lethal test. It was found that six of the novel compounds exhibited more than 50% brine shrimp death and were considered toxic against Artemia sp. and hence unsuitable as a potential drug whilst four compounds were found to be less toxic, exhibiting a brine shrimp death of less than 50%. Molecular docking studies were carried out for 13 APs to estimate their binding interactions with HIV-1 reverse transcriptase. Four APs showed good potential for the inhibition of HIV-1 reverse transcriptase. / M

This thesis describes the synthesis of a number of hydroxy vinylsulphoxides and sulphones by a high pressure modification of the Baylis-Hillman reaction, together with their directed hydrogenation catalysed by rhodium catalysts. A detailed kinetic analysis of a number of the hydrogenation reactions carried out by numerical analysis is also presented. Chapter 1 serves as an introduction to directed hydrogenation and the chemistry of sulphur containing compounds. Chapter 2 details the synthesis of catalysts and substrates used in hydrogenation reactions. The use of high pressures to improve the performance of the Baylis-Hillman reaction is included. Chapter 3 details the products and the selectivity obtained in the hydrogenation of hydroxy vinylsulphoxides and sulphones. The kinetic resolution of 3-phenyl-2-(phenylsulphonyl)- propene-3-ol using a DiPAMP rhodium catalyst is described. Chapter 4 details the numerical analysis of the kinetics of the hydrogenation reactions of a number of hydroxy vinylsulphoxides and sulphones.

Thesis (Ph.D.) - University of St Andrews, November 2009.

Thesis (Ph.D.) - University of St Andrews, May 2008. / Restricted until 29th May 2010.

The aim of this study was to synthesise mono-phosphite complexes of type [Rh(OX)(CO){P(OY)3}], (where Y = the different phosphites that were used and OX = 8-hydroxyquinoline) and to do a kinetic study of iodine oxidative addition to these rhodium(I) square planar complexes in order to determine the rate constants and the reaction mechanism. Part of the characterization was X-ray crystallographic structure determinations which were done on two complexes, namely the [Rh(OX)(CO){P(O(2,4-t-BuPh))3}] and the [Rh(OX)(CO){ P(O(2,6-diMePh))3}]. From the characterization methods it can be said with certainty that the synthesis of the mono-phosphite rhodium(I) complexes was successfully achieved. Table 1 - Selected crystal data as obtained for the two Rh(I) crystal structures solved in this study. [Rh(OX)(CO){P(O(2,4-t- / Prof. A. Roodt

Fuel stocks today contain a large percentage of sulfur, nitrogen, and metals. To meet processing and environmental regulations, these components must be removed. Hydrodesulfurization reactions and the use of catalysts to enhance this process have been under extensive study in recent years. The main hydrodesulfurization catalyst used has been cobalt-molybdenum on an alumina support. This study investigated rhodium incorporated zeolites as catalysts for thiophene hydrodesulfurization reactions. The compounds RhCl₃ • 3H₂O, Rh₂(CO₂CH₃)₄, and Rh(PPh₃)₃Cl were adsorbed onto 13X and ZSM5 zeolites. Results of thiophene hydrodesulfurization over RhCl₃-13X and RhCl₃-ZSM5 were compared to those of commercial Co-Mo/Al₂O₃ to determine the most active catalyst under different experimental conditions. X-ray photoelectron spectroscopy, infrared spectroscopy, x-ray diffraction and microelectrophoresis were used to characterize the zeolites. Hydrodesulfurization reactions were carried out in a pulse microreactor/gas chromatograph system as a function of gas flow rate and reaction temperature. Reaction products were identified by mass spectrometry. RhCl₃-13X exhibited maximum thiophene conversion when presulfided with thiophene injections at 100°C, or with a 10 vol% H₂S/90 vol% H₂ gas mixture at 400°C. At a H₂S-sulfiding temperature of 250°C, the commercial Co-Mo/Al₂O₃ catalyst was most active. Over all catalysts, the only reaction products were hydrogen sulfide, butene and butane. The butene/butane product ratio increased with increasing temperature. On the basis of these results and XPS measurements, Rh(I) was identified as the active hydrodesulfurization species. / Master of Science