Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references.

Ionic liquid/scCO₂ biphasic systems have been studied as a possible solution to the main problems concerning homogeneous catalysis reactions such as, the product/catalyst separation, the catalyst retention in the reaction medium and the use of organic solvents. The hydroformylation of long chain alkenes (1-octene) has been carried out as a continuous flow reaction using [OctMIM]Tf₂N (OctMIM = 1-octyl-3-methylimidazolium, Tf = CF₃SO₂) as the reaction solvent and scCO₂as the mobile phase to extract the products. The performance of the rhodium complexes formed with the ionic ligands [PentMIM][TPPTS] (1-pentyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) and [OctMIM][TPPTS] (1-octyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) is described under different sets of experimental conditions. Continuous flow hydroformylation of 1-octene was also carried out using a SILP (Supported Ionic Liquid Phase) catalyst formed with the TPPTS-based ionic ligands named above. The SILP system described in this work has the peculiarity of introducing the “without gases” approach: syn gas was synthesised in situ by the decomposition of formaldehyde. The performance of both systems is compared in the end. The extension of the continuous flow ionic liquid/scCO₂ biphasic system is shown with the optimisation of the silver-catalysed heterocyclisation of furans. A comparison is carried out with a previously developed and optimised continuous flow heterogeneous system.

Thesis (M.S.)--Mississippi State University. Department of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2008. / Additional advisors: Houston Byrd, Chris Lawson, Sadanandan Velu, Charles Watkins. Description based on contents viewed Feb. 9, 2009; title from PDF t.p. Includes bibliographical references.

The objective of the research described in the first part of this thesis involves the application of carbon monoxide and transition metals in key steps of a synthetic route to lavendamycin, an antic cancer compound, and its analogues. Lavendamycin is a pentacyclic compound that possesses a quinoline-5,8-quinone AB ring linked to a b- carboline CED ring. The development of general routes to the synthetic equivalents of the lavendamycin AB quinoline system together with a linker atom, quinoline -2- carboxaldehydes, as well as to the lavendamycin DE indole ring system, namely tryptophan derivatives, was addressed. The Pictet-Spengler cyclisation approach towards lavendamycin involves the reaction between quinoline-2-carboxaldehyde and tryptophan methyl ester to furnish the pentacyclic precursor of the methyl ester of lavendamycin. This synthetic approach requires the availability of quinoline-2-carboxaldehydes, previously prepared by the oxidation of 2-methylquinolines with toxic selenium dioxide. A general strategy towards the synthesis of the AB ring moiety utilising a pre-formed ring system such as commercially available 8-hydroxyquinoline has been successfully developed. It involved the high pressure palladium catalysed formylation of 2-bromo or other suitable 2-substituted quinoline derivatives under syngas (1:1 CO:H2). The preparation of the required 2-substituted quinoline derivative involved the methylation of the 8-hydroxylgroup followed by N-oxidation and then a rearrangement step. In both the Pictet-Spengler and Bischler-Napieralski synthetic approaches to lavendamycin, the CDE ring moiety is introduced using tryptophan methyl ester as building block. The application of this approach to the synthesis of lavendamycin analogues with a substituted D-ring required the availability of substituted tryptophan methyl esters. A general strategy towards the tryptophan derivatives starting with a Wittig reaction between a suitable 2-nitrobenzaldehyde precursor and 1,3-dioxolan-2- yl-methyltriphenylphosphonium bromide, followed by a two-stage, one -pot rhodium catalysed hydroformylation/reduction reaction, has been successfully developed. This methodology yielded ten different possible tryptophan precursors in moderate to good yields. The second part of the research described in this thesis included the identification of factors effecting the rate and regioselectivity of palladium catalysed methoxycarbonylation of a-olefins. The results showed that fast reactions under polar conditions give mainly linear esters. However, reactions under less polar conditions are slower, yielding mainly branched esters. Detailed analysis of the results suggest the operation of a so-called “cationic” mechanism (involving cationic palladium intermediates) in the formation of mainly linear esters, but the operation of a so-called “neutral” mechanism (involving neutral palladium intermediates) in the formation of mainly branched esters. The nature of the phosphine ligands was found to play a significant, but secondary role in determining regioselectivity of methoxycarbonylation. Another objective was the optimisation of the palladium catalysed hydroformylation of a-olefins. An evaluation of the efficiency of the palladium catalysed hydroformylation process required a comparison with the hydroformylation processes based on cobalt and rhodium. Variation of ligands (diphosphines of the type R2P(CH2)nPR2), solvents, acids, etc. had a dramatic effect on the products and the rate of the reaction. In the presence of trifluoroacetic acid 1-pentene is converted to C-6 aldehydes, while in the presence of trifluoromethanesulfonic acid 1-pentene is converted to C-11 ketones. Corresponding results were obtained with 1-octene as substrate. The palladium catalysts were found to also effect isomerisation of the a- olefin into internal olefins, but isomerisation was not a rate limiting process with respect to the hydroformylation reaction. Palladium catalysed isomerisation reactions occurred at a slower rate than the corresponding cobalt catalysed isomerisation process. However, with rhodium no isomerisation occurred. The comparison between cobalt, rhodium and palladium showed that rhodium is the best catalyst for the hydroformylation of a-olefins. The pressures and temperatures required for this process are much lower than that required for palladium and cobalt. The ligand used is triphenylphosphine, which is relatively inexpensive and non-toxic,in contrast with the more expensive ligands required for the cobalt and palladium hydroformylation processes. The use of palladium opens up the unique possibility of converting a-olefins into “dimeric” ketones, which show promise as precursors for the new class of geminidetergents. / Prof. C.W. Holzapfel

The hydroformylation of olefins is one of the most important homogeneously catalyzed processes in industry to produce bulk chemicals. Despite the high catalytic activities and selectivity’s using rhodium-based homogeneous hydroformylation catalysts, catalyst recovery and recycling from the reaction mixture remain a challenging topic on a process level. Therefore, technical solutions involving alternate approaches with heterogeneous catalysts for the conversion of olefins into aldehydes have been considered and research activities have addressed the synthesis and development of heterogeneous rhodium-based hydroformylation catalysts. Different strategies were pursued by different groups of authors, such as the deposition of molecular rhodium complexes, metallic rhodium nanoparticles and single-atom catalysts on a solid support as well as rhodium complexes present in supported liquids. An overview of the recent developments made in the area of the heterogenization of homogeneous rhodium catalysts and their application in the hydroformylation of short-chain olefins is given. A special focus is laid on the mechanistic understanding of the heterogeneously catalyzed reactions at a molecular level in order to provide a guide for the future design of rhodium-based heterogeneous hydroformylation catalysts.

The purpose of this research was to characterize the rhodium exchanged NaX and NaY zeolites as propylene hydroformylation catalysts. Catalytic activity was measured in a differential bed reactor. Flow in situ infrared spectroscopy was used to probe the coordination chemistry of the zeolite modified rhodium carbonyls. The catalytic activity of rhodium zeolites at atmospheric pressure and between 100-150ºC was measured. The rate of n-butyraldehyde production was approximately 5x10⁻³ moles/g-Rh hr at 150°C. Regioselectivity was dependent upon pretreatment. Precarbonylation with carbon monoxide, drying with air, and heating with N₂ prior to hydroformylation conditions produced a straight to branched isomer ratio (n/i) of 1.9-2.3. Partial reduction with 10% H₂ in N₂ at 127°C lowered n/i to 1.3. Hydrogenation to propane was 3-10 times faster than the hydroformylation rate at 150°C. Catalytic activity was sensitive to cation exchange conditions. Rhodium form, pH, temperature, and salt concentration altered catalyst behavior. Only RhCl₃•3H₂O preparations on NaY zeolite produced above 80ºC, a pH above 4, and a salt concentration of 0.1N NaCl were required in order to produce an active hydroformylation catalyst. Ammine complexes did not activate under any circumstances. It was found that the degree of hydration controlled the formation of rhodium carbonyls. On NaY, the hydrated rhodium zeolite reacted with CO at 120ºC to form Rh₆(CO)₁₆. By drying the zeolite in air at 190ºC, two rhodium dicarbonyls, Rh(CO)₂(O_z)₂-NaY and Rh(CO)₂(O_z)(H₂O)-NaY, were formed. The rhodium carbonyls were reacted with n-hexyl diphenylphosphine to determine rhodium locations. Rh(CO)₂(O_z)₂-NaY was located at the surface while the other two species were located within the zeolite cages. One dicarbonyl species, Rh(CO)₂(O_z)₂-NaX, was observed on NaX. It was determined by reactions with phosphines that this species resides in the zeolite cages. Reaction intermediates identified by FTIR under hydroformylation conditions suggested that the heterogeneous catalyst proceeds through a mechanism similar to that occurring in solution. Heterogeneous reaction orders also agreed with those reported for homogeneous hydroformylations. Addition of dimethylphenylphosphine (DMP) to the rhodium zeolites significantly increased regioselectivity. Rates were slightly less than those from the unmodified rhodium carbonyls. However, the phosphine modified rhodium zeolites deactivated within 16 hours. Continuous exposure to DMP decreased the rate of deactivation. / Ph. D.

Supported Ni and Rh catalysts were developed for the reforming of two greenhouse gases, methane and carbon dioxide to syngas (a mixture of hydrogen and carbon monoxide). This is an endothermic, equilibrium limited reaction. To overcome the thermodynamic limitations, a commercially available porous membrane (Vycor glass) was used in a combined reactor-separator configuration. This was to selectively remove one or more of the products from the reaction chamber, and consequently shift the equilibrium to the right. However, the separation mechanism in this membrane involved Knudsen diffusion, which provided only partial separations. Consequently, there was some transport of reactants across the membrane and this led to only marginal improvements in performance. To overcome this limitation, a new membrane was developed by modifying the Vycor substrate by the chemical vapor deposition of a silica precursor. This new membrane, termed Nanosil, provided high selectivity to hydrogen at permeabilities comparable to the support material. Application of this membrane in the combined reactor-separator unit provided higher conversions than that obtained using the Vycor membrane. / Ph. D.

The purpose of this research was to directly compare the behavior of zeolites containing rhodium with that of homogeneous rhodium species as catalysts for liquid phase hydroformylation of 1-hexene in order to study the effects of zeolite immobilization. NaX zeolite was cation exchanged with several rhodium salts and used as hydroformylation catalysts at 50°C and 125°C in the presence of: triphenylphosphine (PPh₃), dimethylphenylphosphine (PMe₂Ph), and the poison for zeolite surface and solution rhodium: triphenylmethylmercaptan (Ph₃CSH). The results of these experiments were compared with those of several homogeneous catalysts under similar conditions. It was found that previously reported results of intrazeolitic activity with RhNaX at 50°C were probably incorrect, since, the addition of PMe₂Ph, Ph₃CSH, or both, virtually halted all reactivity of RhNax. The catalytic results at 125°C did not conclusively indicate the location of the active rhodium. Thus, intrazeolitic activity at 125°C may or may not have been observed, and needs further investigation. Reaction profiles were obtained for several of the catalyst systems, using an automatic sampling system. From these profiles, it was found that the addition of excess PMe₂Ph halted isomerization of 1-hexene to 2-hexenes for the zeolite-supported rhodium, and hindered, but did not stop isomerization for the homogeneous catalysts. Also, as expected, it was observed that the homogeneous catalysts reacted to completion faster than the heterogeneous catalyst. In addition, the effects of such treatments as preheating in air and precarbonylation of the heterogeneous catalysts were studied. Pretreatments had no effect upon the catalysis. Also, no activity was observed from the heterogeneous catalysts at 125°C unless phosphines were present. Finally, the hydrogenation of 1-hexene was studied. Heterogeneous and homogeneous rhodium catalysts showed hydrogenation activity which was accompanied by isomerization at 60°C and 125°C. / Master of Science

This thesis describes the catalysed addition of X-H bonds (X = S, O and N) to alkynes using a range of novel rhodium(I) and iridium(I) complexes containing hybrid bidentate phosphine-pyrazolyl, phosphine-imidazolyl and phosphine-N heterocyclic carbene (NHC) donor ligands. The synthesis of novel bidentate phosphine-pyrazolyl, phosphine-imidazolyl (P-N) and phosphine-NHC (PC) donor ligands and their cationic and neutral rhodium(I) and iridium(I) complexes [M(P N)(COD)]BPh4, [M(PC)(COD)]BPh4, [Ir(P-N)(CO)2]BPh4 and [M(P-N)(CO)Cl] were successfully performed. An unusual five coordinate iridium complex with phosphine-NHC ligands [Ir(PC)(COD)(CO)]BPh4 was also obtained. Seventeen single crystal X-ray structures of these new complexes were determined. A range of these novel rhodium and iridium complexes were effective as catalysts for the addition of thiophenol to a variety of alkynes. Iridium complexes were more effective than rhodium analogues. Cationic complexes were more effective than neutral complexes. Complexes with hybrid phosphine-nitrogen donor were more effective than complexes containing bidentate nitrogen donor ligands. An atom-economical, efficient method for the synthesis of cyclic acetals and bicyclic O,O-acetals was successfully developed based on the catalysed hydroalkoxylation. Readily prepared terminal and non-terminal alkyne diols were cyclised into bicyclic O,O-acetals in quantitative conversions in most cases. The efficiency of a range of rhodium and iridium complexes containing bidentate P-N and PC donor ligands as catalysts for the cyclisation of 4-pentyn-1-amine to 2-methyl-1-pyrroline varied significantly. The cationic iridium complexes with the bidentate phosphine-pyrazolyl ligands, [Ir(R2PyP)(COD)]BPh4 (2.39-2.42) were extremely efficient as catalysts for this transformation. Increasing the size of the substituent on or adjacent to the donor led to improvement in catalytic activity of the corresponding metal complexes. The mechanism of the catalysed hydroalkoxylation was proposed to proceed by the initial activation of the alkyne via ?? coordination to the metal centre. The ?? binding of both aliphatic and aromatic alkynes to [Ir(PyP)(CO)2]BPh4 (2.44) was observed by low temperature NMR and no reaction between 2.44 and alcohols was observed. In contrast, the facility in which thiol and amine oxidatively added to 2.44 led the proposal that in the hydrothiolation and hydroamination reaction, the catalytic cycle commences with the activation of the X-H bond (X = S, N) by an oxidative addition process.