Ruthenium(II) complexes of phosphorus-based mixed-donor ligands as catalysts for the hydrogenation of levulinic acid to γ-valerolactone
- Authors: Amenuvor, Gershon
- Date: 2018
- Subjects: Ruthenium compounds , Ruthenium catalysts , Catalysts
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/278727 , uj:29916
- Description: Ph.D. (Chemistry) , Abstract: Several phosphorus containing ligand complexes of ruthenium(II) were synthesised and investigated as catalysts for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). The outcomes of these studies are reported in this thesis and summarized as per the chapter studies. Pyrazolylphosphite and pyrazolylphosphinite ruthenium(II) complexes (1-8) were prepared according to literature procedure. Complexes 1-8 were used as pre-catalysts for solvent-free conversion of LA to GVL by molecular hydrogenation and formic acid-mediated hydrogenation. The catalyst precursors were found to be more efficient when the source of hydrogen was molecular hydrogen as compared to formic acid. In situ NMR studies of reactions involving formic acid as a hydrogen source indicated that the initial step in the reaction involves the decomposition of formic acid to CO2 and H2. Recyclability studies showed that the catalyst can be used up to three times without significant loss of activity and selectivity. However, mercury poisoning experiments revealed that a cocktail of active species (both homogeneous and heterogeneous) were responsible for the hydrogenation reactions. Compounds 4-(diphenylphosphino)benzoic acid (L1), 3-(diphenylphosphino)-propanoic acid (L2) were reacted with [Ru(p-cymene)Cl2]2 in equimolar amounts to obtain the new complexes 9 and 10 respectively. Compounds 9 and 10 were further reacted with Zn(OAc)2 in 2:1 mole ratio to form hetero-hexanuclear complexes (11 and 12) containing four ruthenium and two zinc centres. Complexes 11 and 12 were formed through coordination of ruthenium to a phosphine, while the phosphines’...
- Full Text:
- Authors: Amenuvor, Gershon
- Date: 2018
- Subjects: Ruthenium compounds , Ruthenium catalysts , Catalysts
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/278727 , uj:29916
- Description: Ph.D. (Chemistry) , Abstract: Several phosphorus containing ligand complexes of ruthenium(II) were synthesised and investigated as catalysts for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). The outcomes of these studies are reported in this thesis and summarized as per the chapter studies. Pyrazolylphosphite and pyrazolylphosphinite ruthenium(II) complexes (1-8) were prepared according to literature procedure. Complexes 1-8 were used as pre-catalysts for solvent-free conversion of LA to GVL by molecular hydrogenation and formic acid-mediated hydrogenation. The catalyst precursors were found to be more efficient when the source of hydrogen was molecular hydrogen as compared to formic acid. In situ NMR studies of reactions involving formic acid as a hydrogen source indicated that the initial step in the reaction involves the decomposition of formic acid to CO2 and H2. Recyclability studies showed that the catalyst can be used up to three times without significant loss of activity and selectivity. However, mercury poisoning experiments revealed that a cocktail of active species (both homogeneous and heterogeneous) were responsible for the hydrogenation reactions. Compounds 4-(diphenylphosphino)benzoic acid (L1), 3-(diphenylphosphino)-propanoic acid (L2) were reacted with [Ru(p-cymene)Cl2]2 in equimolar amounts to obtain the new complexes 9 and 10 respectively. Compounds 9 and 10 were further reacted with Zn(OAc)2 in 2:1 mole ratio to form hetero-hexanuclear complexes (11 and 12) containing four ruthenium and two zinc centres. Complexes 11 and 12 were formed through coordination of ruthenium to a phosphine, while the phosphines’...
- Full Text:
The in-situ fabrication of high-performance metal-polymernanocomposites, within electro-catalysts, for the detection of dopamine and iodine respectively
- Authors: Brink, Raugmé
- Date: 2018
- Subjects: Nanocomposites (Materials) , Catalysts , Dopamine
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/292769 , uj:31821
- Description: M.Sc. (Chemistry) , Abstract: Dopamine (DA) as a well-known neurotransmitters (NT), is a chemical messenger involved in the renal, hormonal, cardiovascular and central nervous system and enables neuronal communication. Dopamine forms part of some crucial metabolic and physiological processes within the body. Various diseases and disorders such as Parkinson’s Disease and Schizophrenia may stem from its imbalance [1, 2]. Certain analytes such as iodide, as an essential micronutrient, may also be indicative of the physiological health of a person. Its imbalance within the physiological system may either cause Goiter or act as a Goitrogen. It has been seen to affect 656 million people worldwide [1, 3]. The development of rapid and sensitive methods for the detection of these electroactive biomolecules and analytes, are important for both clinical and numerous non-clinical applications. The aim of the study was to synthesize metal enriched polymers as electro-catalysts for the efficient and sensitive detection of electroactive analytes. Electro-analytical chemistry has served as an alternative branch for the study of some physiological systems. These electrochemical sensors are attractive due to their high sensitivity, good controllability, rapid response rate and real-time detection [1]. Functional composite materials with unique physical and chemical properties have provided significant benefits for biological detection. Metallic nanoparticles contribute interesting qualities to materials, with respect to their unique electronic and electrocatalytic properties. It is dependent on their size and morphology. The detective potential, sensitivity and selectivity of Ag (0)-2ADPA and Cu(I)-PANI towards dopamine and iodide in an electrochemical based system was investigated during this study.
- Full Text:
- Authors: Brink, Raugmé
- Date: 2018
- Subjects: Nanocomposites (Materials) , Catalysts , Dopamine
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/292769 , uj:31821
- Description: M.Sc. (Chemistry) , Abstract: Dopamine (DA) as a well-known neurotransmitters (NT), is a chemical messenger involved in the renal, hormonal, cardiovascular and central nervous system and enables neuronal communication. Dopamine forms part of some crucial metabolic and physiological processes within the body. Various diseases and disorders such as Parkinson’s Disease and Schizophrenia may stem from its imbalance [1, 2]. Certain analytes such as iodide, as an essential micronutrient, may also be indicative of the physiological health of a person. Its imbalance within the physiological system may either cause Goiter or act as a Goitrogen. It has been seen to affect 656 million people worldwide [1, 3]. The development of rapid and sensitive methods for the detection of these electroactive biomolecules and analytes, are important for both clinical and numerous non-clinical applications. The aim of the study was to synthesize metal enriched polymers as electro-catalysts for the efficient and sensitive detection of electroactive analytes. Electro-analytical chemistry has served as an alternative branch for the study of some physiological systems. These electrochemical sensors are attractive due to their high sensitivity, good controllability, rapid response rate and real-time detection [1]. Functional composite materials with unique physical and chemical properties have provided significant benefits for biological detection. Metallic nanoparticles contribute interesting qualities to materials, with respect to their unique electronic and electrocatalytic properties. It is dependent on their size and morphology. The detective potential, sensitivity and selectivity of Ag (0)-2ADPA and Cu(I)-PANI towards dopamine and iodide in an electrochemical based system was investigated during this study.
- Full Text:
'n Studie oor die aktiwiteit van 'n seolietkatalisator met betrekking tot die isomerisasie van hekseen
- Authors: Coetzee, Johannes Hendrik
- Date: 2015-10-22
- Subjects: Catalysts , Zeolites , Isomerization , Butyric acid
- Type: Thesis
- Identifier: uj:14415 , http://hdl.handle.net/10210/14897
- Description: M.Sc. (Chemistry) , At Sasol the zeolite catalyst HZ-1 is used to isomerize short-chain hydrocarbons. In this reaction unwanted organic acids are also formed. This investigation has as focal point the interaction between one of these acids, n-butyric acid, and the catalyst. This experimental study consisted of kinetic experiments with a continuous reactor as well as a pulse reactor. In addition to this, temperature programmed desorption was used ...
- Full Text:
- Authors: Coetzee, Johannes Hendrik
- Date: 2015-10-22
- Subjects: Catalysts , Zeolites , Isomerization , Butyric acid
- Type: Thesis
- Identifier: uj:14415 , http://hdl.handle.net/10210/14897
- Description: M.Sc. (Chemistry) , At Sasol the zeolite catalyst HZ-1 is used to isomerize short-chain hydrocarbons. In this reaction unwanted organic acids are also formed. This investigation has as focal point the interaction between one of these acids, n-butyric acid, and the catalyst. This experimental study consisted of kinetic experiments with a continuous reactor as well as a pulse reactor. In addition to this, temperature programmed desorption was used ...
- Full Text:
A structural study of palladium complexes containing hemilabile ligands
- Authors: Thompson, Catharine
- Date: 2012-09-06
- Subjects: Palladium compounds , Chemical reactions , Ligands , Catalysis , Catalysts
- Type: Thesis
- Identifier: uj:9678 , http://hdl.handle.net/10210/7092
- Description: D.Phil. , Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.
- Full Text:
- Authors: Thompson, Catharine
- Date: 2012-09-06
- Subjects: Palladium compounds , Chemical reactions , Ligands , Catalysis , Catalysts
- Type: Thesis
- Identifier: uj:9678 , http://hdl.handle.net/10210/7092
- Description: D.Phil. , Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.
- Full Text:
'n Studie oor kraking en hidrokraking met wolfram houdende katalisatore
- Authors: Vermaire, Dirk Cornelis
- Date: 2014-11-25
- Subjects: Tungsten compounds , Catalysts , Hydraulic fracturing
- Type: Thesis
- Identifier: uj:13109 , http://hdl.handle.net/10210/13084
- Description: D.Sc. , Please refer to full text to view abstract
- Full Text:
- Authors: Vermaire, Dirk Cornelis
- Date: 2014-11-25
- Subjects: Tungsten compounds , Catalysts , Hydraulic fracturing
- Type: Thesis
- Identifier: uj:13109 , http://hdl.handle.net/10210/13084
- Description: D.Sc. , Please refer to full text to view abstract
- Full Text:
Bydrae tot die studie van metatesereaksies van onversadigde silane met Re207-katalisatore op draers
- Authors: Louw, Sonet
- Date: 2015-10-21
- Subjects: Catalysts
- Type: Thesis
- Identifier: uj:14385 , http://hdl.handle.net/10210/14867
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
- Authors: Louw, Sonet
- Date: 2015-10-21
- Subjects: Catalysts
- Type: Thesis
- Identifier: uj:14385 , http://hdl.handle.net/10210/14867
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
Aluminium triflate as a Lewis acid catalyst in some epoxide and aromatic transformations
- Authors: Lawton, Michelle Claire
- Date: 2012-03-14
- Subjects: Lewis acids , Aluminum , Alcoholysis , Epoxy compounds , Catalysts , Aromatic compounds , Substitution reactions
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/368554 , uj:2163 , http://hdl.handle.net/10210/4536
- Description: M.Sc. , Lewis acids play an important role in catalysis; they are associated with mild conditions, high selectivities and unique reactivities. Traditional Lewis acids such as AlCb and BF3 successfully catalyse such well known reactions as the Friedel-Crafts acylation reaction, Aldol condensation reactions and many more. These catalysts, however, must be used in a stoichiometric amount and are destroyed during the aqueous workup procedures. Lately, there has been a lot of interest in the role of metal triflate as Lewis acid catalysts. They were found to be effective in a wide range of reactions when used in catalytic amounts. They were also found to be recyclable and reusable without the loss of activity. Most of this research has been centred around the lanthanide triflates as well as scandium, bismuth and yttrium triflates. Very little research has been done using aluminium triflate and this triflate forms the focus ofthis study. The work contained in this dissertation demonstrates that Al(OTf)3 is an efficient catalyst for the ring opening of a variety of epoxides by alcohols when present in only ppm amounts. These reactions provided products in very high yields and selectivities. Simple acyclic and cyclic epoxides readily underwent ring opening reactions with a range of alcohols, typically providing the monoglycol ethers as single compounds (from the cyclic epoxides) or as mixtures of the two possible glycol monoethers (from the acyclic epoxides). In the case of styrene oxide, essentially a single compound was isolated. In contrast, the glycidyl ethers required slightly higher catalyst loadings before similar rates and conversions to product were observed. Additionally, an interesting selectivity was observed in the orientation of the attack of the alcohol onto the epoxide, which appeared to be chelation controlled. Similarly, the Al(OTf)3 also catalysed the aminolysis of a variety of epoxides. These reactions proceeded smoothly with catalytic amounts of the triflate present, and served to nicely highlight the role that steric and electronic factors played in these reactions. A preliminary study was carried out into the efficacy of Al(OTf)3 as a catalyst for Friedel-Crafts acylation and aromatic nitration reactions. From these studies it is evident that the Al(OTf)3 is indeed an effective catalyst for these reactions when present in substoichiometric levels and further studies will be carried out in this area in the future.
- Full Text:
- Authors: Lawton, Michelle Claire
- Date: 2012-03-14
- Subjects: Lewis acids , Aluminum , Alcoholysis , Epoxy compounds , Catalysts , Aromatic compounds , Substitution reactions
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/368554 , uj:2163 , http://hdl.handle.net/10210/4536
- Description: M.Sc. , Lewis acids play an important role in catalysis; they are associated with mild conditions, high selectivities and unique reactivities. Traditional Lewis acids such as AlCb and BF3 successfully catalyse such well known reactions as the Friedel-Crafts acylation reaction, Aldol condensation reactions and many more. These catalysts, however, must be used in a stoichiometric amount and are destroyed during the aqueous workup procedures. Lately, there has been a lot of interest in the role of metal triflate as Lewis acid catalysts. They were found to be effective in a wide range of reactions when used in catalytic amounts. They were also found to be recyclable and reusable without the loss of activity. Most of this research has been centred around the lanthanide triflates as well as scandium, bismuth and yttrium triflates. Very little research has been done using aluminium triflate and this triflate forms the focus ofthis study. The work contained in this dissertation demonstrates that Al(OTf)3 is an efficient catalyst for the ring opening of a variety of epoxides by alcohols when present in only ppm amounts. These reactions provided products in very high yields and selectivities. Simple acyclic and cyclic epoxides readily underwent ring opening reactions with a range of alcohols, typically providing the monoglycol ethers as single compounds (from the cyclic epoxides) or as mixtures of the two possible glycol monoethers (from the acyclic epoxides). In the case of styrene oxide, essentially a single compound was isolated. In contrast, the glycidyl ethers required slightly higher catalyst loadings before similar rates and conversions to product were observed. Additionally, an interesting selectivity was observed in the orientation of the attack of the alcohol onto the epoxide, which appeared to be chelation controlled. Similarly, the Al(OTf)3 also catalysed the aminolysis of a variety of epoxides. These reactions proceeded smoothly with catalytic amounts of the triflate present, and served to nicely highlight the role that steric and electronic factors played in these reactions. A preliminary study was carried out into the efficacy of Al(OTf)3 as a catalyst for Friedel-Crafts acylation and aromatic nitration reactions. From these studies it is evident that the Al(OTf)3 is indeed an effective catalyst for these reactions when present in substoichiometric levels and further studies will be carried out in this area in the future.
- Full Text:
Metal triflates as alternative catalytic promoters to Brønsted acids in carbonylation chemistry
- Authors: Bredenkamp, Tyler
- Date: 2014-07-15
- Subjects: Metal carbonyls , Catalysts , Acids
- Type: Thesis
- Identifier: uj:11653 , http://hdl.handle.net/10210/11376
- Description: Ph.D. (Chemistry) , The thesis presented here is focussed on the methoxycarbonylation reaction. The reaction requires a catalyst (most of often palladium), a co-catalyst (typically Brønsted acids), ligand, methanol and carbon monoxide to afford esters that find use in both industrial and medical application. The focus given here in this thesis is specifically targeted to the co-catalyst. When the Brønsted acid co-catalyst is changed, two variables in the reaction are altered, namely the acid strength and the weakly coordinating counter anion arising from the acid. The work presented in this thesis provides results for which only one variable is changed, that being the counter anion and as such the role of the counter anion could be determined...
- Full Text:
- Authors: Bredenkamp, Tyler
- Date: 2014-07-15
- Subjects: Metal carbonyls , Catalysts , Acids
- Type: Thesis
- Identifier: uj:11653 , http://hdl.handle.net/10210/11376
- Description: Ph.D. (Chemistry) , The thesis presented here is focussed on the methoxycarbonylation reaction. The reaction requires a catalyst (most of often palladium), a co-catalyst (typically Brønsted acids), ligand, methanol and carbon monoxide to afford esters that find use in both industrial and medical application. The focus given here in this thesis is specifically targeted to the co-catalyst. When the Brønsted acid co-catalyst is changed, two variables in the reaction are altered, namely the acid strength and the weakly coordinating counter anion arising from the acid. The work presented in this thesis provides results for which only one variable is changed, that being the counter anion and as such the role of the counter anion could be determined...
- Full Text:
Divalent iron, cobalt, nickel and palladium complexes of 1H-pyrazol-1-yl-imine and 1H-pyrazol-1-yl-ethanol ligands: coordination chemistry and evaluation as ethylene oligomerization catalysts
- Authors: Ainooson, Michael Kojo
- Date: 2011-05-16T08:07:20Z
- Subjects: Ligands , Ethylene , Catalysts , Coordination compounds synthesis , Transition metals synthesis
- Type: Thesis
- Identifier: uj:7079 , http://hdl.handle.net/10210/3641
- Description: M.Sc. , This dissertation deals with the syntheses of tridentate (O^N^N) coordination ligands [{2,4-di-tert-butyl-6-[(2-(3,5-RR-pyrazol-1-yl-ethylimino)-methyl] phenol}, R = H (L1), Me(L2), Ph(L3), t-Bu(L4)], which was reacted initially with MX2 (M = Fe, Co, Ni; X = Cl, Br). The ligands L1-L4 were also modified by functionalizing the phenol group in this ligand group to an ethoxy in L5 and L6 (L5 = [(3,5-di-tert-butyl-2-ethoxy-benzylidene)-[2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-amine, L6 = [(3,5-di-tert-butyl-2-ethoxy-benzylidene)-[2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-amine)], or into a phenoxy in L7 (L7 = (3,5-di-tert-butyl-2-phenoxy-benzylidene-(2-pyrazol-1-yl-ethyl)-amine)). Another ligand L8 (L8 = [4-(4-tert-butyl-benzylidene)-[2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-amine], which was devoid of the phenoxy group was also synthesized. These modified ligands were also reacted with MX2 or PdCl(COD)Me to form bidentate (N^N) chelating complexes. Further modification of the ligand L1-L4, to replace the phenoxy pyrazolylimine unit with a source of oxygen donor other than a phenoxy led to the use of already known ligands L9, L10 (L9 = 2-(3,5-dimethyl-pyrazol-1-yl)-ethanol, L10 = 2-(3,5-di-tert-butyl-pyrazol-1yl)-ethanol and L11, where in L11, the alcohol moiety is replaced by an electron withdrawing chloro group, L11 = 1-(2-chloroethyl)-3,5-di-methyl-pyrazole). These ligands were also reacted with MX2 (M = Fe, Co, Ni, Pd; X = Cl, Br) to form complexes. The synthesized complexes were characterized by a combination of IR and NMR spectroscopy, mass spectrometry, microanalysis and in selected cases single crystal X-ray crystallography.
- Full Text:
- Authors: Ainooson, Michael Kojo
- Date: 2011-05-16T08:07:20Z
- Subjects: Ligands , Ethylene , Catalysts , Coordination compounds synthesis , Transition metals synthesis
- Type: Thesis
- Identifier: uj:7079 , http://hdl.handle.net/10210/3641
- Description: M.Sc. , This dissertation deals with the syntheses of tridentate (O^N^N) coordination ligands [{2,4-di-tert-butyl-6-[(2-(3,5-RR-pyrazol-1-yl-ethylimino)-methyl] phenol}, R = H (L1), Me(L2), Ph(L3), t-Bu(L4)], which was reacted initially with MX2 (M = Fe, Co, Ni; X = Cl, Br). The ligands L1-L4 were also modified by functionalizing the phenol group in this ligand group to an ethoxy in L5 and L6 (L5 = [(3,5-di-tert-butyl-2-ethoxy-benzylidene)-[2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-amine, L6 = [(3,5-di-tert-butyl-2-ethoxy-benzylidene)-[2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-amine)], or into a phenoxy in L7 (L7 = (3,5-di-tert-butyl-2-phenoxy-benzylidene-(2-pyrazol-1-yl-ethyl)-amine)). Another ligand L8 (L8 = [4-(4-tert-butyl-benzylidene)-[2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-amine], which was devoid of the phenoxy group was also synthesized. These modified ligands were also reacted with MX2 or PdCl(COD)Me to form bidentate (N^N) chelating complexes. Further modification of the ligand L1-L4, to replace the phenoxy pyrazolylimine unit with a source of oxygen donor other than a phenoxy led to the use of already known ligands L9, L10 (L9 = 2-(3,5-dimethyl-pyrazol-1-yl)-ethanol, L10 = 2-(3,5-di-tert-butyl-pyrazol-1yl)-ethanol and L11, where in L11, the alcohol moiety is replaced by an electron withdrawing chloro group, L11 = 1-(2-chloroethyl)-3,5-di-methyl-pyrazole). These ligands were also reacted with MX2 (M = Fe, Co, Ni, Pd; X = Cl, Br) to form complexes. The synthesized complexes were characterized by a combination of IR and NMR spectroscopy, mass spectrometry, microanalysis and in selected cases single crystal X-ray crystallography.
- Full Text:
Metal triflate catalysed organic transformations
- Authors: Lawton, Michelle Claire
- Date: 2010-10-28T08:11:00Z
- Subjects: Organic compounds synthesis , Catalysts , Lewis acids , Metal triflate , Trifluoromethanesulfonate
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/388178 , uj:6946 , http://hdl.handle.net/10210/3456
- Description: Ph.D. , The research described in this thesis was directed at advancing the application of metal triflates, Al(OTf)3 in particular, in organic synthesis, on the one hand and to contribute to the understanding of the underlying basis for their catalytic activity. The study was undertaken against the background and on the bases of a detailed literature study of metal triflates, their chemical and catalytic properties and applications thereof. Amongst others, it deals with the possible role of metal-bound water that give rise to Brønsted type acidity and that this induced Brønsted acidity may be responsible for the catalytic activity that is observed. The study was prompted by the realisation that Al(OTf)3 was largely neglected as a potential reusable catalyst. This is in marked contrast to the attention paid to other metal triflates, the rare earth metals in particular. Earlier work in this laboratory has shown that Al(OTf)3 is stable in water from which it can be recovered easily for reuse. In addition it showed promise as a Lewis acid catalyst and is relatively soluble in several organic solvents. New applications for the use of Al(OTf)3 have now been demonstrated. These include the efficient formation of acetals from aldehydes and ketones. The conversions can be carried out in an alcohol/orthoester mixture or preferably in neat orthoester. Other metal triflates, notably Sc(OTf)3 and In(OTf)3, are useful alternative catalysts. Al(OTf)3 can be easily recycled without loss of activity. This methodology also can be applied to aldehydes and ketones containing TBDMS groups without effecting deprotection of the ethers. In view of the sensitivity of the TBDMS groups to hydrolysis in the presence of triflic acid the results suggest little hydrolysis (or alcoholysis) of the metal triflates in the protic solvents used, which would generate trifluoromethanesulfonic acid as a consequence of such metal based hydrolysis. Al(OTf)3 was also found to be a good catalyst for the formation of THP ethers. It proved to be excellent for Friedel Crafts reactions using alkynes as substrates. Al(OTf)3 together with other triflates offers a mild alternative to the more traditional water sensitive Lewis acids, e.g. BF3, AlCl3 and TiCl4, which are difficult to recover and require the use of extremely dry solvents.
- Full Text:
- Authors: Lawton, Michelle Claire
- Date: 2010-10-28T08:11:00Z
- Subjects: Organic compounds synthesis , Catalysts , Lewis acids , Metal triflate , Trifluoromethanesulfonate
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/388178 , uj:6946 , http://hdl.handle.net/10210/3456
- Description: Ph.D. , The research described in this thesis was directed at advancing the application of metal triflates, Al(OTf)3 in particular, in organic synthesis, on the one hand and to contribute to the understanding of the underlying basis for their catalytic activity. The study was undertaken against the background and on the bases of a detailed literature study of metal triflates, their chemical and catalytic properties and applications thereof. Amongst others, it deals with the possible role of metal-bound water that give rise to Brønsted type acidity and that this induced Brønsted acidity may be responsible for the catalytic activity that is observed. The study was prompted by the realisation that Al(OTf)3 was largely neglected as a potential reusable catalyst. This is in marked contrast to the attention paid to other metal triflates, the rare earth metals in particular. Earlier work in this laboratory has shown that Al(OTf)3 is stable in water from which it can be recovered easily for reuse. In addition it showed promise as a Lewis acid catalyst and is relatively soluble in several organic solvents. New applications for the use of Al(OTf)3 have now been demonstrated. These include the efficient formation of acetals from aldehydes and ketones. The conversions can be carried out in an alcohol/orthoester mixture or preferably in neat orthoester. Other metal triflates, notably Sc(OTf)3 and In(OTf)3, are useful alternative catalysts. Al(OTf)3 can be easily recycled without loss of activity. This methodology also can be applied to aldehydes and ketones containing TBDMS groups without effecting deprotection of the ethers. In view of the sensitivity of the TBDMS groups to hydrolysis in the presence of triflic acid the results suggest little hydrolysis (or alcoholysis) of the metal triflates in the protic solvents used, which would generate trifluoromethanesulfonic acid as a consequence of such metal based hydrolysis. Al(OTf)3 was also found to be a good catalyst for the formation of THP ethers. It proved to be excellent for Friedel Crafts reactions using alkynes as substrates. Al(OTf)3 together with other triflates offers a mild alternative to the more traditional water sensitive Lewis acids, e.g. BF3, AlCl3 and TiCl4, which are difficult to recover and require the use of extremely dry solvents.
- Full Text:
Towards modification of Grubbs 1st and 2nd generation metathesis catalysts: synthesis of ruthenium building blocks
- Authors: Chonco, Zandile Hlengiwe
- Date: 2010-04-12T10:22:23Z
- Subjects: Metathesis (Chemistry) , Ruthenium compounds synthesis , Ligands , Catalysts
- Type: Thesis
- Identifier: uj:6772 , http://hdl.handle.net/10210/3182
- Description: M.Sc. , In this study, the pyrazolyl-based ligands were synthesised and used in the synthesise of new ruthenium pyrazolyl-based complexes. The ruthenium pyrazolyl-based complex 2.4 was tested as a catalyst for the self-metathesis reaction of 1-octene. The N^N ligands: 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 4-(3,5- dimethylpyrazol-1-ylmethyl)pyridine (L2) were prepared from the reaction of 2- picolyl chloride (for L1) and 4-(bromomethyl)pyridine (for L2) with 3,5- dimethylpyrazole. Reactions of L1 and L2 with [RuCl2(PPh3)3] and [RuCl3·3H2O] produced [2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine) dichlorotriphenylphosphine]ruthenium (2.1) and bis[4-(3,5-dimethylpyrazol-1- ylmethyl)pyridine-trichloride]ruthenium (2.3), respectively. The N^O ligands: 2- (3,5-dimethylpyrazol-1-yl)ethanol (L3), 2-(3,5-diphenylpyrazol-1-yl)ethanol (L4), were prepared from the reaction of 2-hydroxyethylhydrazine (for L3) and dibenzoylmethane (for L4) with 2-hydroxyethylhydrazine. Reaction of L3 with (3-phenylindenylidene)dichlorobis-(triphenylphosphine)ruthenium produced [3-phenylindenylidene-(3,5-dimethylpyrazol-1-yl)-ethanolate chlorotriphenylphosphine]ruthenium (2.4). Ligands, 2-(3,5-dimethylpyrazol-1-ylmethyl)-phenol (L5) and bis(3,5- dimethylpyrazol-1-yl)acetic acid (L6), were prepared from the reaction of o-(α- bromo-methyl) phenyl methanesulfonate (for L5) and dibromoacetic acid (for L6) with 3,5-dimethylpyrazole. Reaction of L6 with [RuCl2(PPh3)3] produced bis-[(3,5-dimethylpyrazol-1-yl)-acetic-acid-chloro(bistriphenylphosphine)] ruthenium (2.6). The C^N ligands: 1-[2-(3,5,-dimethylpyrazol-1-yl)-ethyl]-3- methyl-3H-imidazol-1-ium bromide (L7) and 1-[2-(3,5,-dimethylpyrazol-1-yl)- ethyl]-3-methyl-3H-imidazol-1-ium bromide (L8) were prepared from the reaction of 1-(2-bromoethyl)-3,5-dimethyl-1H-pyrazole (for L7) and 1-(2- bromoethyl)-1H-pyrazole (for L8) with 1-methylimidazole. Reactions of L7 and L8 with silver(I) oxide (Ag2O) produced 3,5-dimethyl-1-[2-(3-methyl-2,3- dihydro-imidazol-1-yl)-ethyl-1H-pyrazole]silver bromide (2.7) and 1-[2-(3- methyl-2,3-dihydro-imidazol-1-yl)-ethyl-1H-pyrazole]silver bromide (2.8), respectively. Reactions of silver complexes (2.7) and (2.8), respectively, with [RuCl2(PPh3)3] produced 3,5-dimethyl-1-[2-(3-methyl-2,3-dihydro-imidazol-1- yl)-ethyl-1H-pyrazole-dichloro(triphenylphosphine)]ruthenium (2.9) and 1-[2- (3-methyl-2,3-dihydro-imidazol-1-yl)-ethyl-1H-pyrazoledichloro (triphenylphosphine)]ruthenium (2.10). The synthesised complexes were obtained in moderate to low yields and were characterised by 1H, 13C{1H}, 31P{1H} NMR, IR spectroscopy, mass spectrometry, elemental analyses and ligand L5 was also characterised by X-ray crystallography. Complex 2.4 was screened for self-metathesis reaction of 1-octene. Initial run from 30-90 oC showed no activity for 1-octene metathesis below 105 oC. At 105 oC small amounts of 7-tetradecene was obtained, indicating that metathesis reaction occurs at very high temperatures (105 oC). Thermal stability test of complex 2.4, showed that rearrangement in the proposed structure of complex 2.4 occurs after heating at 90 oC for 16 h, this was evident by the 31P{1H} NMR spectrum of complex 2.4 obtained as a singlet at 28.9 ppm (after being heated), (complex 2.4 appears at 30.0 ppm before heating). From the 31P{1H} NMR study, it could be proposed, that the pyrazole arm of the ligand dissociates thus influencing the environment of the phosphorus (of the triphenylphosphine), and therefore a shift in the peaks is observed.
- Full Text:
- Authors: Chonco, Zandile Hlengiwe
- Date: 2010-04-12T10:22:23Z
- Subjects: Metathesis (Chemistry) , Ruthenium compounds synthesis , Ligands , Catalysts
- Type: Thesis
- Identifier: uj:6772 , http://hdl.handle.net/10210/3182
- Description: M.Sc. , In this study, the pyrazolyl-based ligands were synthesised and used in the synthesise of new ruthenium pyrazolyl-based complexes. The ruthenium pyrazolyl-based complex 2.4 was tested as a catalyst for the self-metathesis reaction of 1-octene. The N^N ligands: 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 4-(3,5- dimethylpyrazol-1-ylmethyl)pyridine (L2) were prepared from the reaction of 2- picolyl chloride (for L1) and 4-(bromomethyl)pyridine (for L2) with 3,5- dimethylpyrazole. Reactions of L1 and L2 with [RuCl2(PPh3)3] and [RuCl3·3H2O] produced [2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine) dichlorotriphenylphosphine]ruthenium (2.1) and bis[4-(3,5-dimethylpyrazol-1- ylmethyl)pyridine-trichloride]ruthenium (2.3), respectively. The N^O ligands: 2- (3,5-dimethylpyrazol-1-yl)ethanol (L3), 2-(3,5-diphenylpyrazol-1-yl)ethanol (L4), were prepared from the reaction of 2-hydroxyethylhydrazine (for L3) and dibenzoylmethane (for L4) with 2-hydroxyethylhydrazine. Reaction of L3 with (3-phenylindenylidene)dichlorobis-(triphenylphosphine)ruthenium produced [3-phenylindenylidene-(3,5-dimethylpyrazol-1-yl)-ethanolate chlorotriphenylphosphine]ruthenium (2.4). Ligands, 2-(3,5-dimethylpyrazol-1-ylmethyl)-phenol (L5) and bis(3,5- dimethylpyrazol-1-yl)acetic acid (L6), were prepared from the reaction of o-(α- bromo-methyl) phenyl methanesulfonate (for L5) and dibromoacetic acid (for L6) with 3,5-dimethylpyrazole. Reaction of L6 with [RuCl2(PPh3)3] produced bis-[(3,5-dimethylpyrazol-1-yl)-acetic-acid-chloro(bistriphenylphosphine)] ruthenium (2.6). The C^N ligands: 1-[2-(3,5,-dimethylpyrazol-1-yl)-ethyl]-3- methyl-3H-imidazol-1-ium bromide (L7) and 1-[2-(3,5,-dimethylpyrazol-1-yl)- ethyl]-3-methyl-3H-imidazol-1-ium bromide (L8) were prepared from the reaction of 1-(2-bromoethyl)-3,5-dimethyl-1H-pyrazole (for L7) and 1-(2- bromoethyl)-1H-pyrazole (for L8) with 1-methylimidazole. Reactions of L7 and L8 with silver(I) oxide (Ag2O) produced 3,5-dimethyl-1-[2-(3-methyl-2,3- dihydro-imidazol-1-yl)-ethyl-1H-pyrazole]silver bromide (2.7) and 1-[2-(3- methyl-2,3-dihydro-imidazol-1-yl)-ethyl-1H-pyrazole]silver bromide (2.8), respectively. Reactions of silver complexes (2.7) and (2.8), respectively, with [RuCl2(PPh3)3] produced 3,5-dimethyl-1-[2-(3-methyl-2,3-dihydro-imidazol-1- yl)-ethyl-1H-pyrazole-dichloro(triphenylphosphine)]ruthenium (2.9) and 1-[2- (3-methyl-2,3-dihydro-imidazol-1-yl)-ethyl-1H-pyrazoledichloro (triphenylphosphine)]ruthenium (2.10). The synthesised complexes were obtained in moderate to low yields and were characterised by 1H, 13C{1H}, 31P{1H} NMR, IR spectroscopy, mass spectrometry, elemental analyses and ligand L5 was also characterised by X-ray crystallography. Complex 2.4 was screened for self-metathesis reaction of 1-octene. Initial run from 30-90 oC showed no activity for 1-octene metathesis below 105 oC. At 105 oC small amounts of 7-tetradecene was obtained, indicating that metathesis reaction occurs at very high temperatures (105 oC). Thermal stability test of complex 2.4, showed that rearrangement in the proposed structure of complex 2.4 occurs after heating at 90 oC for 16 h, this was evident by the 31P{1H} NMR spectrum of complex 2.4 obtained as a singlet at 28.9 ppm (after being heated), (complex 2.4 appears at 30.0 ppm before heating). From the 31P{1H} NMR study, it could be proposed, that the pyrazole arm of the ligand dissociates thus influencing the environment of the phosphorus (of the triphenylphosphine), and therefore a shift in the peaks is observed.
- Full Text:
Knoevenagel and Heck catalytic studies with Metal Organic Frameworks (MOFs)
- Authors: Burgoyne, Andrew R.
- Date: 2013-07-24
- Subjects: Metal Organic Frameworks , Knoevenagel Condensation Reaction , Mizoroki-Heck Reaction , Porous materials , Chemical reactions , Heck reaction , Catalysts , Catalysts - Synthesis
- Type: Thesis
- Identifier: uj:7678 , http://hdl.handle.net/10210/8545
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
- Authors: Burgoyne, Andrew R.
- Date: 2013-07-24
- Subjects: Metal Organic Frameworks , Knoevenagel Condensation Reaction , Mizoroki-Heck Reaction , Porous materials , Chemical reactions , Heck reaction , Catalysts , Catalysts - Synthesis
- Type: Thesis
- Identifier: uj:7678 , http://hdl.handle.net/10210/8545
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
Applications of metal triflates and assisted acids as catalysts for organic transformations
- Authors: Sibiya, Mike Sbonelo
- Date: 2012-11-05
- Subjects: Metal triflates , Organic compounds , Catalysts , Lewis acids , Organic reaction mechanisms , Organic chemistry
- Type: Thesis
- Identifier: uj:7340 , http://hdl.handle.net/10210/8089
- Description: Ph.D. , The research contained in this thesis was aimed at the applications of Lewis acids (metal triflate salts in particular) and Brønsted acids as catalysts for various organic synthesis reactions. The ultimate objective was to prepare combinations of the Lewis and Brønsted acids to form assisted acids. The assisted acids yield to the formation of highly acidic assisted acids which exhibit high activity as compared to the individual Lewis and Brønsted acids. A detailed literature study was undertaken, with emphasis on the applications of metal triflate salts as catalysts for various organic reactions and the applications of assisted acids. The study was motivated by the fact that metal triflate Lewis acids are thermally stable, non corrosive and water tolerant catalysts, hence can be used industrially to replace the corrosive, moisture sensitive acids as catalysts. However, metal triflates have not yet been recognised and utilised in the chemical industry. On the other hand, the active Brønsted acids such as triflic acid, H2SO4 etc. are corrosive, which restricts the type of construction material to hastelloy. However, the assisted acids composed of less corrosive Brønsted acids and metal triflate Lewis acid is desirable to address the corrosion and safety challenges. The metal triflate salts and Brønsted acids were evaluated as catalysts for etherification reactions of alcohols and olefins, Friedel-Crafts alkylation reactions phenolic substrates with isobutylene. The study showed that some dependence of the charge density to the activity, i.e. metal triflate salts such as Al(OTf)3, Zr(OTf)4 and Sc(OTf)3 with relatively high charge density were more effective in catalysing the reactions than those with relatively smaller charge density such as lanthanides, which were virtually active. The activity of Brønsted acids showed a clear dependence on the acid strength pKa, with H3PO4 giving the least activity. The assisted acids formed via a combination of metal triflate salts with mineral Brønsted acids showed a significant enhancement of the reaction rates as compared to the individual acids. This set of new combined acids was proven to be excellent catalysts for the etherification reactions, Friedel-Crafts alkylation reactions and also for the synthesis of biologically active compounds called chromans. The assisted acids as well as Al(OTf)3, and Zr(OTf)4 could be recycled at least four times without significant loss of activity. The study also showed that assisted acids could be recycled for both etherification and Friedel-Crafts reactions.
- Full Text:
- Authors: Sibiya, Mike Sbonelo
- Date: 2012-11-05
- Subjects: Metal triflates , Organic compounds , Catalysts , Lewis acids , Organic reaction mechanisms , Organic chemistry
- Type: Thesis
- Identifier: uj:7340 , http://hdl.handle.net/10210/8089
- Description: Ph.D. , The research contained in this thesis was aimed at the applications of Lewis acids (metal triflate salts in particular) and Brønsted acids as catalysts for various organic synthesis reactions. The ultimate objective was to prepare combinations of the Lewis and Brønsted acids to form assisted acids. The assisted acids yield to the formation of highly acidic assisted acids which exhibit high activity as compared to the individual Lewis and Brønsted acids. A detailed literature study was undertaken, with emphasis on the applications of metal triflate salts as catalysts for various organic reactions and the applications of assisted acids. The study was motivated by the fact that metal triflate Lewis acids are thermally stable, non corrosive and water tolerant catalysts, hence can be used industrially to replace the corrosive, moisture sensitive acids as catalysts. However, metal triflates have not yet been recognised and utilised in the chemical industry. On the other hand, the active Brønsted acids such as triflic acid, H2SO4 etc. are corrosive, which restricts the type of construction material to hastelloy. However, the assisted acids composed of less corrosive Brønsted acids and metal triflate Lewis acid is desirable to address the corrosion and safety challenges. The metal triflate salts and Brønsted acids were evaluated as catalysts for etherification reactions of alcohols and olefins, Friedel-Crafts alkylation reactions phenolic substrates with isobutylene. The study showed that some dependence of the charge density to the activity, i.e. metal triflate salts such as Al(OTf)3, Zr(OTf)4 and Sc(OTf)3 with relatively high charge density were more effective in catalysing the reactions than those with relatively smaller charge density such as lanthanides, which were virtually active. The activity of Brønsted acids showed a clear dependence on the acid strength pKa, with H3PO4 giving the least activity. The assisted acids formed via a combination of metal triflate salts with mineral Brønsted acids showed a significant enhancement of the reaction rates as compared to the individual acids. This set of new combined acids was proven to be excellent catalysts for the etherification reactions, Friedel-Crafts alkylation reactions and also for the synthesis of biologically active compounds called chromans. The assisted acids as well as Al(OTf)3, and Zr(OTf)4 could be recycled at least four times without significant loss of activity. The study also showed that assisted acids could be recycled for both etherification and Friedel-Crafts reactions.
- Full Text:
Ligand influences on the Rh-catalysed hydroformylation reaction
- Kotze, Philippus Daniel Riekert
- Authors: Kotze, Philippus Daniel Riekert
- Date: 2009-05-07T07:22:27Z
- Subjects: Ligands , Hydroformylation , Catalysts
- Type: Thesis
- Identifier: uj:8359 , http://hdl.handle.net/10210/2500
- Description: M.Sc. , The main objective of the research described in this dissertation was to prepare a range of triaryl phosphine ligands having systematically changing stereo-electronic properties using Grignard reagents and P-Cl derivatives. These ligands were utilised in the Rh-catalysed hydroformylation reaction in order to determine the effects of stereo-electronic properties of these ligands on the outcome of the reaction. Initially, a first series of tri-aryl phosphine ligands having methyl or ethyl groups substituted on the ortho or para position of the phenyl rings was successfully synthesised. The stereoelectronic properties of these ligands were probed by determining the P=Se coupling constants of the Se-phosphine derivatives and the CO vibrational frequencies of the Vaskatype complexes of these ligands. It was shown that the substitution of alkyl groups on the phenyl rings of the phosphine ligands resulted in the formation of more electron-rich ligands. In the Rh-catalysed hydroformylation reaction a systematic decrease in the yields of aldehydes were observed as the basicity of the phosphine ligand increased. Inspired by the outcome of the first series, a second series of tri-aryl phosphine ligands having both methyl and fluoro groups variously substituted (ortho, meta and para positions) on the phenyl rings was successfully synthesised. It was observed that the group substituted on the ortho position electronically dominated over the group substituted in the meta and para position of the phenyl rings. Substitution of fluorine atoms on the ortho position and methyl on the para position of the phenyl rings resulted in the formation of less electron-rich phosphine ligands, while the opposite substitution pattern (p-F-o-Me) resulted in the formation of more electron-rich ligands. The former caused an increase in the yields of aldehydes obtained in the Rh-catalysed hydroformylation reaction compared to triphenylphosphine. viii A third series of tri-aryl phosphine ligands having trifluoromethyl groups substituted on the ortho, meta or para positions of the phenyl rings was successfully synthesised. It was observed that substitution of the trifluoromethyl groups on the meta and para positions of the phenyl rings resulted in the formation of less electron-rich phosphine ligands, while substitution on the ortho position resulted in the formation of more electron-rich ligands. The hydroformylation reaction with these ligands followed the same trend as with the first and second series of tri-aryl phosphine ligands. A series of tri-aryl phosphine-borane adducts of the first series of phosphine ligands was also successfully synthesised using BH3·THF. These ligands were employed in the Rh-catalysed hydroformylation reaction with the aim to determine whether in situ deprotection of the phosphine-borane adducts with CO was possible. The hydroformylation results with these adducts provided yields of aldehydes similar to those of the free phosphines. This suggested that deprotection had occurred to release the free phosphine which complexed to the Rh catalyst. This indicated that phosphine-borane complexes can be directly applied to carbonylation reactions eliminating the use of common deprotection methods and provides an opening for more research in this regard.
- Full Text:
- Authors: Kotze, Philippus Daniel Riekert
- Date: 2009-05-07T07:22:27Z
- Subjects: Ligands , Hydroformylation , Catalysts
- Type: Thesis
- Identifier: uj:8359 , http://hdl.handle.net/10210/2500
- Description: M.Sc. , The main objective of the research described in this dissertation was to prepare a range of triaryl phosphine ligands having systematically changing stereo-electronic properties using Grignard reagents and P-Cl derivatives. These ligands were utilised in the Rh-catalysed hydroformylation reaction in order to determine the effects of stereo-electronic properties of these ligands on the outcome of the reaction. Initially, a first series of tri-aryl phosphine ligands having methyl or ethyl groups substituted on the ortho or para position of the phenyl rings was successfully synthesised. The stereoelectronic properties of these ligands were probed by determining the P=Se coupling constants of the Se-phosphine derivatives and the CO vibrational frequencies of the Vaskatype complexes of these ligands. It was shown that the substitution of alkyl groups on the phenyl rings of the phosphine ligands resulted in the formation of more electron-rich ligands. In the Rh-catalysed hydroformylation reaction a systematic decrease in the yields of aldehydes were observed as the basicity of the phosphine ligand increased. Inspired by the outcome of the first series, a second series of tri-aryl phosphine ligands having both methyl and fluoro groups variously substituted (ortho, meta and para positions) on the phenyl rings was successfully synthesised. It was observed that the group substituted on the ortho position electronically dominated over the group substituted in the meta and para position of the phenyl rings. Substitution of fluorine atoms on the ortho position and methyl on the para position of the phenyl rings resulted in the formation of less electron-rich phosphine ligands, while the opposite substitution pattern (p-F-o-Me) resulted in the formation of more electron-rich ligands. The former caused an increase in the yields of aldehydes obtained in the Rh-catalysed hydroformylation reaction compared to triphenylphosphine. viii A third series of tri-aryl phosphine ligands having trifluoromethyl groups substituted on the ortho, meta or para positions of the phenyl rings was successfully synthesised. It was observed that substitution of the trifluoromethyl groups on the meta and para positions of the phenyl rings resulted in the formation of less electron-rich phosphine ligands, while substitution on the ortho position resulted in the formation of more electron-rich ligands. The hydroformylation reaction with these ligands followed the same trend as with the first and second series of tri-aryl phosphine ligands. A series of tri-aryl phosphine-borane adducts of the first series of phosphine ligands was also successfully synthesised using BH3·THF. These ligands were employed in the Rh-catalysed hydroformylation reaction with the aim to determine whether in situ deprotection of the phosphine-borane adducts with CO was possible. The hydroformylation results with these adducts provided yields of aldehydes similar to those of the free phosphines. This suggested that deprotection had occurred to release the free phosphine which complexed to the Rh catalyst. This indicated that phosphine-borane complexes can be directly applied to carbonylation reactions eliminating the use of common deprotection methods and provides an opening for more research in this regard.
- Full Text:
Role of catalysts in the reduction of iron oxides by solid carbon
- Authors: Szendrei, Thomas
- Date: 2014-02-17
- Subjects: Catalysts
- Type: Thesis
- Identifier: uj:4020 , http://hdl.handle.net/10210/9374
- Description: Ph.D. (Chemistry) , Please refer to full text to view abstract
- Full Text:
- Authors: Szendrei, Thomas
- Date: 2014-02-17
- Subjects: Catalysts
- Type: Thesis
- Identifier: uj:4020 , http://hdl.handle.net/10210/9374
- Description: Ph.D. (Chemistry) , Please refer to full text to view abstract
- Full Text:
Imidazolyl- and pyrazolyl-salicylaldimine transition metal complexes and their applications in olefin transformation reactions
- Authors: Yankey, Margaret
- Date: 2011-05-16T06:45:25Z
- Subjects: Salicylates , Transition metal complexes , Alkenes , Catalysts , Heck reaction , Ligands
- Type: Thesis
- Identifier: uj:7064 , http://hdl.handle.net/10210/3627
- Description: M.Sc. , This study deals with the synthesis of nitrogen-donor imidazolyl- and pyrazolyl-salicylaldimine compounds, their reactions with selected transition metals and applications as catalysts for Heck coupling reactions of aryl halides with butyl acrylate, ethylene polymerization reactions and reactions of higher α-olefins. Imidazole-based salicylaldimine compounds 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1) and 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L2) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 5-tert-butyl-2-hydroxybenzaldehyde respectively. The compounds were characterized by 1H, 13C{1H} NMR and IR spectroscopy; and high resolution mass spectrometry (HRMS). Compounds 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L3), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L4), 2,4-di-tert-butyl-6-[(2-pyrazol-1-yl-ethylimino)-methyl]-phenol (L5) and 2,4-di-tert-butyl-6-{[2-(3,5-diphenyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L6) were synthesized according to literature procedure. Reactions of L1-L3 with [PdCl2(MeCN)2] yielded complexes 2.1-2.3 respectively. Ligand L1 was also complexed with [FeCl2] and [CoCl2] to give complexes 2.4 and 2.5 respectively, while complexes 2.6-2.15 were synthesized by reactions of L1, L2 and L4-L6 with [VCl3] and [CrCl3(THF)3]; all in a ratio of 1:1. The palladium(II) complexes (2.1-2.3) were characterized by 1H, 13C{1H} NMR and IR spectroscopy, mass spectrometry and elemental analysis, while complexes 2.4-2.15 were characterized by IR spectroscopy, mass spectrometry and elemental analysis due to their paramagnetic nature. The structures of complexes 2.1 and 2.4 were confirmed by single crystal X-ray diffraction analysis. All the complexes formed were mononuclear.
- Full Text:
- Authors: Yankey, Margaret
- Date: 2011-05-16T06:45:25Z
- Subjects: Salicylates , Transition metal complexes , Alkenes , Catalysts , Heck reaction , Ligands
- Type: Thesis
- Identifier: uj:7064 , http://hdl.handle.net/10210/3627
- Description: M.Sc. , This study deals with the synthesis of nitrogen-donor imidazolyl- and pyrazolyl-salicylaldimine compounds, their reactions with selected transition metals and applications as catalysts for Heck coupling reactions of aryl halides with butyl acrylate, ethylene polymerization reactions and reactions of higher α-olefins. Imidazole-based salicylaldimine compounds 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1) and 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L2) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 5-tert-butyl-2-hydroxybenzaldehyde respectively. The compounds were characterized by 1H, 13C{1H} NMR and IR spectroscopy; and high resolution mass spectrometry (HRMS). Compounds 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L3), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L4), 2,4-di-tert-butyl-6-[(2-pyrazol-1-yl-ethylimino)-methyl]-phenol (L5) and 2,4-di-tert-butyl-6-{[2-(3,5-diphenyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L6) were synthesized according to literature procedure. Reactions of L1-L3 with [PdCl2(MeCN)2] yielded complexes 2.1-2.3 respectively. Ligand L1 was also complexed with [FeCl2] and [CoCl2] to give complexes 2.4 and 2.5 respectively, while complexes 2.6-2.15 were synthesized by reactions of L1, L2 and L4-L6 with [VCl3] and [CrCl3(THF)3]; all in a ratio of 1:1. The palladium(II) complexes (2.1-2.3) were characterized by 1H, 13C{1H} NMR and IR spectroscopy, mass spectrometry and elemental analysis, while complexes 2.4-2.15 were characterized by IR spectroscopy, mass spectrometry and elemental analysis due to their paramagnetic nature. The structures of complexes 2.1 and 2.4 were confirmed by single crystal X-ray diffraction analysis. All the complexes formed were mononuclear.
- Full Text:
Die reaktiwiteit van wolframhoudende katalisatore met behulp van kumeen as toetsreaktant
- Authors: Vermaire, Dirk Cornelis
- Date: 2015-03-02
- Subjects: Catalysts , Tungsten trioxide
- Type: Thesis
- Identifier: uj:13368 , http://hdl.handle.net/10210/13380
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
- Authors: Vermaire, Dirk Cornelis
- Date: 2015-03-02
- Subjects: Catalysts , Tungsten trioxide
- Type: Thesis
- Identifier: uj:13368 , http://hdl.handle.net/10210/13380
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
Phase-switchable ligands in transition metal-catalysed carbonylation reactions
- Mokhadinyana, Molise Stephen
- Authors: Mokhadinyana, Molise Stephen
- Date: 2012-08-15
- Subjects: Ligands , Catalysts , Amidines
- Type: Thesis
- Identifier: uj:9351 , http://hdl.handle.net/10210/5790
- Description: D.Phil. , Homogeneous catalysts can give very high activities and selectivities towards desired products; however, they suffer from the difficulties associated with separating the product from catalyst and reaction solvent. Only one two-phase catalyst recovery process has been commercialised in the form of the Rh-catalysed hydroformylation reaction where trisodium triphenylphosphinetrisulfonate is used as ligand. The present study intends to develop ligands that are mobile between two phases and not stationary in one phase, with the view to enhancing catalyst activity. To this end, substituted ligands that may readily protonate and deprotonate by the addition or removal of CO2 are sought, wherein the protonated form of the ligand is designed to be water soluble and the free-base organic soluble. The amidine functional group has been identified as possessing the appropriate pKa value for such proton cycling. With a vision to introduce structural diversity into the amidine functionality and study the effects of variation in the amidine structure on the effectiveness of catalyst switching, arylphosphines bearing acyclic and cyclic amidines were sought. Accordingly, triarylphosphine derivatives were synthesised from P-Cl derivatives, the intermediates of which were converted into their amidine analogues. Two areas were explored in this project, on the ligand synthesis side: 1. The synthesis of acyclic amidine functionalised phosphines from amino arylphosphines was achieved by condensation with excess dimethyl-acetamide dimethylacetal. The same modification was also successfully applied to Xantphos-type ligands with the aim to achieve high selectivity towards linear aldehyde in hydroformylation reaction while maintaining catalyst recycling. 2. The synthesis of cyclic amidine functionalised phosphines. This approach was found to be successful when making use of nitrile-containing phosphine derivatives. These were converted into their respective amidine analogues by making use of appropriate diamines and AlEt3. In so doing the synthesis has been abbreviated and the approach was shown to be applicable to mono-, di- and tri-substituted triarylphosphines. This method was also applied to Xantphos derivatives.Both of the methodologies described above provided a range of amidine functionalised ligands. Rhodium complexes of these newly synthesised ligands were found to be active catalysts in hydroformylation of 1-octene. Evaluation of catalyst recycling and re-use of such catalytic systems was carried out using aqueous biphasic separation with carbon dioxide induced phase switching. After phase separation and addition of fresh toluene, the complex can be transferred back into the organic phase by bubbling N2. These systems provide for the hydroformylation reaction of medium to long chain alkenes to be performed in purely organic solvents thereby retaining good reaction rates and selectivities, and only form two phase systems during recycling. Consequently, overcoming mass transport limitations experienced with aqueous biphasic systems.
- Full Text:
- Authors: Mokhadinyana, Molise Stephen
- Date: 2012-08-15
- Subjects: Ligands , Catalysts , Amidines
- Type: Thesis
- Identifier: uj:9351 , http://hdl.handle.net/10210/5790
- Description: D.Phil. , Homogeneous catalysts can give very high activities and selectivities towards desired products; however, they suffer from the difficulties associated with separating the product from catalyst and reaction solvent. Only one two-phase catalyst recovery process has been commercialised in the form of the Rh-catalysed hydroformylation reaction where trisodium triphenylphosphinetrisulfonate is used as ligand. The present study intends to develop ligands that are mobile between two phases and not stationary in one phase, with the view to enhancing catalyst activity. To this end, substituted ligands that may readily protonate and deprotonate by the addition or removal of CO2 are sought, wherein the protonated form of the ligand is designed to be water soluble and the free-base organic soluble. The amidine functional group has been identified as possessing the appropriate pKa value for such proton cycling. With a vision to introduce structural diversity into the amidine functionality and study the effects of variation in the amidine structure on the effectiveness of catalyst switching, arylphosphines bearing acyclic and cyclic amidines were sought. Accordingly, triarylphosphine derivatives were synthesised from P-Cl derivatives, the intermediates of which were converted into their amidine analogues. Two areas were explored in this project, on the ligand synthesis side: 1. The synthesis of acyclic amidine functionalised phosphines from amino arylphosphines was achieved by condensation with excess dimethyl-acetamide dimethylacetal. The same modification was also successfully applied to Xantphos-type ligands with the aim to achieve high selectivity towards linear aldehyde in hydroformylation reaction while maintaining catalyst recycling. 2. The synthesis of cyclic amidine functionalised phosphines. This approach was found to be successful when making use of nitrile-containing phosphine derivatives. These were converted into their respective amidine analogues by making use of appropriate diamines and AlEt3. In so doing the synthesis has been abbreviated and the approach was shown to be applicable to mono-, di- and tri-substituted triarylphosphines. This method was also applied to Xantphos derivatives.Both of the methodologies described above provided a range of amidine functionalised ligands. Rhodium complexes of these newly synthesised ligands were found to be active catalysts in hydroformylation of 1-octene. Evaluation of catalyst recycling and re-use of such catalytic systems was carried out using aqueous biphasic separation with carbon dioxide induced phase switching. After phase separation and addition of fresh toluene, the complex can be transferred back into the organic phase by bubbling N2. These systems provide for the hydroformylation reaction of medium to long chain alkenes to be performed in purely organic solvents thereby retaining good reaction rates and selectivities, and only form two phase systems during recycling. Consequently, overcoming mass transport limitations experienced with aqueous biphasic systems.
- Full Text:
Hydrocracking of aromatic hydrocarbons over molybdenum based catalysts
- Foukaridis, George Nikiforos
- Authors: Foukaridis, George Nikiforos
- Date: 2014-05-19
- Subjects: Molybdenum , Catalysts , Catalysis
- Type: Thesis
- Identifier: uj:11108 , http://hdl.handle.net/10210/10696
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
- Authors: Foukaridis, George Nikiforos
- Date: 2014-05-19
- Subjects: Molybdenum , Catalysts , Catalysis
- Type: Thesis
- Identifier: uj:11108 , http://hdl.handle.net/10210/10696
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
- Full Text:
Aluminium triflate-mediated organic synthesis
- Authors: Cullen, Adam
- Date: 2012-08-20
- Subjects: Metal triflate , Organic compounds - Synthesis , Catalysts , Lewis acids
- Type: Thesis
- Identifier: uj:2736 , http://hdl.handle.net/10210/6177
- Description: Ph.D. , The work described in this thesis was directed at advancing the applications of Al(OTf)3, a metal triflate, in organic synthesis. Lewis acids play an important role in catalysis and catalyse reactions with high selectivities, unique reactivities under mild conditions. Metal triflates have become the Lewis acids of choice for acid catalysed organic transformations. A detailed literature study of metal triflates provided numerous examples of their use in organic transformations. Al(OTf)3 has been widely neglected as a Lewis acid which is contrasting to the attention the other metal triflates have received. Previous work in our laboratories had established Al(OTf)3 as an effective Lewis acid catalyst for the ring-opening of epoxides with simple alcohols and amines. The alcoholysis of epoxides provides a ready access to β-alkoxy alcohols. Whilst this reaction has been shown to occur with Al(OTf)3 as a catalyst, the established protocol calls for the use of the nucleophilic alcohol in an excess amount. Whilst this proves no problem when simple alcohols are employed as nucleophiles in the ring-opening reaction, it is a problem when more complex and expensive alcoholic nucleophiles are utilised. A modified procedure utilising Al(OTf)3 as a catalyst was developed which tolerates the use of only 1 equivalent of the nucleophilic alcohol for the ring opening reaction. The desymmetrisation of a meso-epoxide with chiral alcoholic nucleophiles was also investigated and the outcome of the diastereoselectivity of the reaction reported. The aminolysis of epoxides has been established utilising Al(OTf)3 as the Lewis acid catalyst. However, this has only been demonstrated for the ring opening of simple epoxides with simple amines. Piperazine derived β-amino alcohols with known biological activity were chosen as substrates with which to test the Al(OTf)3 catalysed aminolysis of epoxides in the synthesis of more complex β-amino alcohols. The various starting epoxides and amine nucleophiles were synthesised. During which a new approach towards the synthesis of - glycidyl amines was developed utilising a two step approach with the first step being catalysed by Al(OTf)3. It was also found that the optimal method for forming the β-amino alcohol bond was one in which the glycidyl motif was placed on the less basic heteroatom and ring opened by the more nucleophilic piperazine amine.
- Full Text:
- Authors: Cullen, Adam
- Date: 2012-08-20
- Subjects: Metal triflate , Organic compounds - Synthesis , Catalysts , Lewis acids
- Type: Thesis
- Identifier: uj:2736 , http://hdl.handle.net/10210/6177
- Description: Ph.D. , The work described in this thesis was directed at advancing the applications of Al(OTf)3, a metal triflate, in organic synthesis. Lewis acids play an important role in catalysis and catalyse reactions with high selectivities, unique reactivities under mild conditions. Metal triflates have become the Lewis acids of choice for acid catalysed organic transformations. A detailed literature study of metal triflates provided numerous examples of their use in organic transformations. Al(OTf)3 has been widely neglected as a Lewis acid which is contrasting to the attention the other metal triflates have received. Previous work in our laboratories had established Al(OTf)3 as an effective Lewis acid catalyst for the ring-opening of epoxides with simple alcohols and amines. The alcoholysis of epoxides provides a ready access to β-alkoxy alcohols. Whilst this reaction has been shown to occur with Al(OTf)3 as a catalyst, the established protocol calls for the use of the nucleophilic alcohol in an excess amount. Whilst this proves no problem when simple alcohols are employed as nucleophiles in the ring-opening reaction, it is a problem when more complex and expensive alcoholic nucleophiles are utilised. A modified procedure utilising Al(OTf)3 as a catalyst was developed which tolerates the use of only 1 equivalent of the nucleophilic alcohol for the ring opening reaction. The desymmetrisation of a meso-epoxide with chiral alcoholic nucleophiles was also investigated and the outcome of the diastereoselectivity of the reaction reported. The aminolysis of epoxides has been established utilising Al(OTf)3 as the Lewis acid catalyst. However, this has only been demonstrated for the ring opening of simple epoxides with simple amines. Piperazine derived β-amino alcohols with known biological activity were chosen as substrates with which to test the Al(OTf)3 catalysed aminolysis of epoxides in the synthesis of more complex β-amino alcohols. The various starting epoxides and amine nucleophiles were synthesised. During which a new approach towards the synthesis of - glycidyl amines was developed utilising a two step approach with the first step being catalysed by Al(OTf)3. It was also found that the optimal method for forming the β-amino alcohol bond was one in which the glycidyl motif was placed on the less basic heteroatom and ring opened by the more nucleophilic piperazine amine.
- Full Text: