Bifunctional phosphines : synthesis and evaluation in catalysis
- Authors: Shaw, Megan Lorraine
- Date: 2012-09-10
- Subjects: Phosphorus compounds - Synthesis , Catalysis , Ligands , Transition metal catalysts
- Type: Thesis
- Identifier: uj:9860 , http://hdl.handle.net/10210/7261
- Description: M.Sc. , This study focused on the synthesis and evaluation of phosphine ligands with multiple functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic systems were synthesised, as were ligands incorporating a boron atom in an intramolecular Lewis acid-Lewis base interaction with the phosphorus atom. A malonate moiety was readily incorporated into a phosphorus starting material, and derivatives were obtained by reduction of the ester groups. The polar diol products were reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic catalysis. Wittig chemistry was employed to introduce alkenes of varying electronic nature into a phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction making use of diboron reagents was used to introduce a boron functionality into the resulting a, n-unsaturated ester phosphine I igands. All of the ligands produced were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and the hydroformylation reaction. The polar and water soluble ligands all showed comparable or improved yields to the standard benchmark triphenylphosphine ligand in organic, biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands of the ligands rather than by electronic considerations. It was also found that the boron containing ligands showed an enhanced activity in comparison to the boron free unsaturated and saturated ester ligands. This enhancement was directly ascribable to the Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands which where shown to influence transition metal-catalysed reactions based specifically on the functionality present.
- Full Text:
- Authors: Shaw, Megan Lorraine
- Date: 2012-09-10
- Subjects: Phosphorus compounds - Synthesis , Catalysis , Ligands , Transition metal catalysts
- Type: Thesis
- Identifier: uj:9860 , http://hdl.handle.net/10210/7261
- Description: M.Sc. , This study focused on the synthesis and evaluation of phosphine ligands with multiple functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic systems were synthesised, as were ligands incorporating a boron atom in an intramolecular Lewis acid-Lewis base interaction with the phosphorus atom. A malonate moiety was readily incorporated into a phosphorus starting material, and derivatives were obtained by reduction of the ester groups. The polar diol products were reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic catalysis. Wittig chemistry was employed to introduce alkenes of varying electronic nature into a phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction making use of diboron reagents was used to introduce a boron functionality into the resulting a, n-unsaturated ester phosphine I igands. All of the ligands produced were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and the hydroformylation reaction. The polar and water soluble ligands all showed comparable or improved yields to the standard benchmark triphenylphosphine ligand in organic, biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands of the ligands rather than by electronic considerations. It was also found that the boron containing ligands showed an enhanced activity in comparison to the boron free unsaturated and saturated ester ligands. This enhancement was directly ascribable to the Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands which where shown to influence transition metal-catalysed reactions based specifically on the functionality present.
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Mechanistic study on tertiary phosphine complexes of ruthenium as olefin metathesis catalysts.
- Authors: Oosthuizen, Sharon
- Date: 2008-05-15T13:28:00Z
- Subjects: Phosphine , Alkenes , Chemical kinetics , Reactivity (Chemistry) , Metathesis (Chemistry) , Ruthenium , Transition metal catalysts , Complex compounds synthesis
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/374346 , uj:1717 , http://hdl.handle.net/10210/405
- Description: Ruthenium carbene complexes, with the general structure, [LL’Ru=CHR], are commonly known as Grubbs type catalysts, named after the discoverer of these metathesis catalysts. The discovery was quite revolutionary, since the catalysts proved to be easy to handle, tolerant towards various functional groups and more stable with regard to air and water than previous transition metal catalysts. Another important advantage was that all types of olefin metathesis reactions could be initiated without the help of co-catalysts or promoters. Today Grubbs type catalysts find wide application in especially organic and synthetic chemistry. A well-known example is the SHOP-process which produces long chain -olefins, while other important applications include the synthesis of macro-cyclic and cyclic olefins. The current study involved experimental and theoretical work to investigate various aspects comprising synthetic procedures, reactivity, kinetics, geometry and electronic properties of the complexes. Results are discussed briefly in the following paragraphs. The first aim of the project was to synthesise a Grubbs type catalyst. Initial efforts were focused on the preparation of a first generation catalyst through various methods. This included modifying the reported method for the synthesis of [(PPh3)2Cl2Ru=CH-CH=CMe2] to yield [(PPh2Cy)2Cl2Ru=CHCH= CMe2] instead; a phosphine exchange reaction with the complex [(PPh3)2Cl2Ru=CH-CH=CMe2] and free phosphine PPh2Cy; and utilising the analogue arsine ligand, AsPh3, to synthesise [(AsPh3)2Cl2Ru=CHCH=CMe2]; but unfortunately no success was achieved. However, it was possible to synthesise a novel second generation Grubbs type catalyst, [(IMesH2)(PPh2Cy)Cl2Ru=CHPh], through the phosphine exchange reaction of [(IMesH2)(NC5H5)2Cl2Ru=CHPh] and PPh2Cy. The new complex was tested in kinetic reaction studies and phosphine exchange reactions. Results showed that [(IMesH2)(PPh2Cy)Cl2Ru=CHPh] was catalytically active for the ring closing metathesis of commercial diethyl diallylmalonate. The reaction was first order with regard to the olefin, contrary to the second order kinetic results reported for similar reactions catalysed by first generation Grubbs catalysts. The phosphine exchange reactions were very successful and a rate constant could be determined. The rate constant was independent of the free phosphine concentration and activation parameters had relatively large, positive values; results indicative of a dissociative mechanism. These findings are in correlation with literature reports. A kinetic investigation was done on the catalyst-olefin coordination involving the functionalized olefins vinyl acetate, allyl acetate and allyl cyanide; and the first generation Grubbs catalyst, [(PCy3)2Cl2Ru=CHPh]. A two-step rate law, similar to an interchange mechanism, was determined. Phobcat, [(PhobCy)2Cl2Ru=CHPh], is modified first generation Grubbs type catalyst with rigid bicyclic phosphine rings which was recently developed by the Sasol Homogeneous Metathesis Group. In the current study Phobcat was compared to Grubbs1-PCy3 in the cross metathesis reaction of 1-octene. Results showed that Phobcat was up to 60% more active and had a 5 hour longer lifetime than Grubbs 1-PCy3. Theoretical studies were done on the three functionalized olefins of the earlier experimental study to gain fundamental understanding of steric and electronic influences on these catalyst-olefin systems. Without exception, coordination via the heteroatom of the olefin was significantly more favourable than coordination via the double bond functionality. This result indicates that metathesis of these olefins is highly unlikely, since the stable heteroatom coordination will suppress the parallel Ru=C/C=C interaction which is compulsory for the metathesis reaction. Orbital studies highlighted the difference between coordination of acetate and cyanide, but no trend of an electronic nature could be recognised. , Prof. A. Roodt
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- Authors: Oosthuizen, Sharon
- Date: 2008-05-15T13:28:00Z
- Subjects: Phosphine , Alkenes , Chemical kinetics , Reactivity (Chemistry) , Metathesis (Chemistry) , Ruthenium , Transition metal catalysts , Complex compounds synthesis
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/374346 , uj:1717 , http://hdl.handle.net/10210/405
- Description: Ruthenium carbene complexes, with the general structure, [LL’Ru=CHR], are commonly known as Grubbs type catalysts, named after the discoverer of these metathesis catalysts. The discovery was quite revolutionary, since the catalysts proved to be easy to handle, tolerant towards various functional groups and more stable with regard to air and water than previous transition metal catalysts. Another important advantage was that all types of olefin metathesis reactions could be initiated without the help of co-catalysts or promoters. Today Grubbs type catalysts find wide application in especially organic and synthetic chemistry. A well-known example is the SHOP-process which produces long chain -olefins, while other important applications include the synthesis of macro-cyclic and cyclic olefins. The current study involved experimental and theoretical work to investigate various aspects comprising synthetic procedures, reactivity, kinetics, geometry and electronic properties of the complexes. Results are discussed briefly in the following paragraphs. The first aim of the project was to synthesise a Grubbs type catalyst. Initial efforts were focused on the preparation of a first generation catalyst through various methods. This included modifying the reported method for the synthesis of [(PPh3)2Cl2Ru=CH-CH=CMe2] to yield [(PPh2Cy)2Cl2Ru=CHCH= CMe2] instead; a phosphine exchange reaction with the complex [(PPh3)2Cl2Ru=CH-CH=CMe2] and free phosphine PPh2Cy; and utilising the analogue arsine ligand, AsPh3, to synthesise [(AsPh3)2Cl2Ru=CHCH=CMe2]; but unfortunately no success was achieved. However, it was possible to synthesise a novel second generation Grubbs type catalyst, [(IMesH2)(PPh2Cy)Cl2Ru=CHPh], through the phosphine exchange reaction of [(IMesH2)(NC5H5)2Cl2Ru=CHPh] and PPh2Cy. The new complex was tested in kinetic reaction studies and phosphine exchange reactions. Results showed that [(IMesH2)(PPh2Cy)Cl2Ru=CHPh] was catalytically active for the ring closing metathesis of commercial diethyl diallylmalonate. The reaction was first order with regard to the olefin, contrary to the second order kinetic results reported for similar reactions catalysed by first generation Grubbs catalysts. The phosphine exchange reactions were very successful and a rate constant could be determined. The rate constant was independent of the free phosphine concentration and activation parameters had relatively large, positive values; results indicative of a dissociative mechanism. These findings are in correlation with literature reports. A kinetic investigation was done on the catalyst-olefin coordination involving the functionalized olefins vinyl acetate, allyl acetate and allyl cyanide; and the first generation Grubbs catalyst, [(PCy3)2Cl2Ru=CHPh]. A two-step rate law, similar to an interchange mechanism, was determined. Phobcat, [(PhobCy)2Cl2Ru=CHPh], is modified first generation Grubbs type catalyst with rigid bicyclic phosphine rings which was recently developed by the Sasol Homogeneous Metathesis Group. In the current study Phobcat was compared to Grubbs1-PCy3 in the cross metathesis reaction of 1-octene. Results showed that Phobcat was up to 60% more active and had a 5 hour longer lifetime than Grubbs 1-PCy3. Theoretical studies were done on the three functionalized olefins of the earlier experimental study to gain fundamental understanding of steric and electronic influences on these catalyst-olefin systems. Without exception, coordination via the heteroatom of the olefin was significantly more favourable than coordination via the double bond functionality. This result indicates that metathesis of these olefins is highly unlikely, since the stable heteroatom coordination will suppress the parallel Ru=C/C=C interaction which is compulsory for the metathesis reaction. Orbital studies highlighted the difference between coordination of acetate and cyanide, but no trend of an electronic nature could be recognised. , Prof. A. Roodt
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Nitrogen-donor nickel and palladium complexes as olefin transformation catalysts
- Authors: Ojwach, Stephen Otieno
- Date: 2009-04-30T10:05:35Z
- Subjects: Alkenes , Transition metal catalysts , Transition metal compounds , Nickel compounds , Palladium compounds , Complex compounds synthesis
- Type: Thesis
- Identifier: uj:8340 , http://hdl.handle.net/10210/2466
- Description: Ph.D. , Compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L2) were prepared by phase transfer alkylation of 2,6-bis(bromomethyl)pyridine with two mole equivalents of the appropriate pyrazole. Ligands L1 and L2 reacted with either [PdCl2(NCMe)2] or [PdClMe(COD)] to form mononuclear palladium complexes [(PdCl2(L1)] (1), [(PdClMe(L1)] (2), [(PdCl2(L2)] (3), [(PdClMe(L2)] (4). All new compounds prepared were characterised by a combination of 1H NMR, 13C NMR spectroscopy and microanalyses. The coordination of L2 in a bidentate fashion through the pyridine nitrogen atom and one pyrazolyl nitrogen atom has been confirmed by single crystal X-ray crystallography of complex 3. Reactions of 1, 2 and 3 with the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation of the stable tridentate cationic species [(PdCl(L1)]BAr4 (5), [(PdMe(L1)]BAr4 (6) and [(PdCl(L2)]BAr4 (7) respectively. Tridentate coordination of L1 and L2 in the cationic complexes has also been confirmed by single X-ray crystallography of complexes 5 and 6. The analogous carbonyl linker cationic species, [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction from [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] with NaBAr4, were however less stable. While cationic complexes 5-7 showed indefinite stability in solution, 9 and 10 had t1/2 of 14 and 2 days respectively. Attempts to crystallise 1 and 3 from the mother liquor resulted in the isolation of the salts [PdCl(L1)]2[Pd2Cl6] (11) and [PdCl(L2)]2[Pd2Cl6] (12). Although when complexes 1-4 xviii were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerisation or polymerisation were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerised and polymerised phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) were prepared by phase transfer alkylation of 2-picolylchloride hydrochloride with one mole equivalent of the appropriate pyrazole. Compounds 2-(3,5-bis-trifluoromethyl-pyrazol-1-ylmethyl)-6-(3,5-dimethyl-pyrazol-1-ylmethyl)-pyridine (L5) and 2-(3,5-dimethyl-pyrazol-1-ylmethyl)-6-phenoxymethyl-pyridine (L6) were isolated in good yields by reacting (2-chloromethyl-6-3,5-dimethylpyrazol-1-ylmethyl)pyridine with an equivalent amount of potassium salt of 3,5-bis(trifluoromethyl)pyrazolate and potassium phenolate respectively. L3-L6 react with either [Pd(NCMe)2Cl2] or [PdClMe(COD)] to give mononuclear palladium complexes 13-18 of the general formulae [PdCl2(L)] or [PdClMe(L)] where L = is the bidentate ligands L3, L4, L5 and L6 respectively. Single crystal X-ray crystallography of complexes 13, 15 and 16 has been used to confirm the solid state geometry of the complexes. In attempts to generate active olefin oligomerisation catalysts, the chloromethyl Pd(II) complexes 14 and 16 were reacted with the halide abstractor NaBAr4 in the presence of stabilising solvents (i.e Et2O or NCMe) but no catalytic activities were observed. Decomposition was evident as observed from the deposition of palladium black in experiments using Et2O. In experiments where NCMe was used as the stabilising solvent, the formation of cationic species stabilised by NCMe was evident from 1H NMR analyses. Reaction of complex 14 with NaBAr4 on a preparative scale in a mixture of CH2Cl2 and NCMe solvent gave the cationic complex [[PdMeNCMe(L3)]BAr4 (19) in good yields. Complex 17 reacted with NABAr4 to give tridentate cationic species [[PdMe(L5)]BAr4 (20) which is inactive towards ethylene oligomerisation or polymerisation reactions. The tridentate coordination of L5 in 20 has also been established by single crystal X-ray structure of 20. Catalysts generated from 18 and 19 catalysed ethylene polymerisation at high pressures to branched polyethylene; albeit with very low activity. The Choromethyl palladium complex 14 reacted with sulfur dioxide to form complex 21. The nature of the product has been established by 1H NMR, 13C NMR and mass spectrometry to be an insertion product of SO2 into the Pd-Me bond of 14. Compounds L1-L4 reacted with the nickel salts NiCl2 or NiBr2 in a 1:1 mole ratio to give the nickel complexes [NiCl2(L1)] (22), [NiBr2(L1)] (23), [NiCl2(L2)] (24), and [NiBr2(L2)] (25), [Ni2(μ2-Cl)2Cl2(L3)2] (26), [Ni2(μ2-Br)2Br2(L3)2] (27), [NiCl2(L4)] (29) and [NiBr2(L4)] (30) in good yields. Reaction of L3 with NiBr2 in a 2:1 mole gave the octahedral complex [NiBr2(L4)2] (28) in good yields. Complexes 22-30 were characterised by a combination micro-analyses, mass spectrometry and single crystal X-ray analyses for 27 and 30. No NMR data were acquired because of the paramagnetic nature of the complexes. When complexes 22-30 were activated with EtAlCl2, highly active olefin oligomerisation catalysts were formed. In the ethylene oligomeristion reactions, three oligomers: C11, C14 xx and C16 were identified as the major products. Selectivityof 40% towards α-olefins were generally obtained. In general catalysts that contain the bidentate ligands L3 and L4 were more active than those that contain the tridentate ligands L1 and L2. Dichloride complexes exhibited relatively higher catalytic activities than their dibromide analogues. Turn over numbers (TON) for oligomer formation showed high dependence on ethylene concentration. A Lineweaver-Burk analysis of reactions catalysed by 22 and 26 showed TON saturation of 28 393 kg oligomer/mol Ni.h and 19 000 kg oligomer/mol Ni.h respectively. Catalysts generated from complexes 22-30 also catalysed oligomerisation of the higher olefins, 1-pentene, 1-hexene and 1-heptene and displayed good catalytic activities. Only two products C12 and C15 were obtained in the 1-pentene oligomerisation reactions. The 1-hexene reactions also gave two products, C12 and C18, while 1-heptene oligomerisation reactions gave predominantly C14 oligomers. Five benzoazoles were used to prepare a series of palladium complexes that were invesitigated as Heck coupling catalysts. The compounds 2-pyridin-2-yl-1H-benzoimidazole (L7) and 2-pyridin-2-yl-benzothiazole (L8) were prepared following literature procedures. The new ligands 2-(4-tert-butylpyridin-2-yl)-benzooxazole (L9) and 2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L10) were prepared by ring closure of aminophenol and aminothiophenol with tert-butyl picolinic acid respectively. The ligand 6-tert-Butyl-2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L11) was prepared by intramolecular cyclisation under basic conditions is described. Reactions of L7-L11 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [PdClMe(L7)] (31), [PdClMe(L8)] (32), [PdCl2(L9)] (33), [PdMeCl(L9)] (34), [PdCl2(L10)] (5), [PdMeCl(L10)] (36) and [PdMeCl(L11)] (37) as xxi confirmed by mass spectrometry and micro-analyses. The palladium complexes 31-37 were efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions and showed good stability.
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- Authors: Ojwach, Stephen Otieno
- Date: 2009-04-30T10:05:35Z
- Subjects: Alkenes , Transition metal catalysts , Transition metal compounds , Nickel compounds , Palladium compounds , Complex compounds synthesis
- Type: Thesis
- Identifier: uj:8340 , http://hdl.handle.net/10210/2466
- Description: Ph.D. , Compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L2) were prepared by phase transfer alkylation of 2,6-bis(bromomethyl)pyridine with two mole equivalents of the appropriate pyrazole. Ligands L1 and L2 reacted with either [PdCl2(NCMe)2] or [PdClMe(COD)] to form mononuclear palladium complexes [(PdCl2(L1)] (1), [(PdClMe(L1)] (2), [(PdCl2(L2)] (3), [(PdClMe(L2)] (4). All new compounds prepared were characterised by a combination of 1H NMR, 13C NMR spectroscopy and microanalyses. The coordination of L2 in a bidentate fashion through the pyridine nitrogen atom and one pyrazolyl nitrogen atom has been confirmed by single crystal X-ray crystallography of complex 3. Reactions of 1, 2 and 3 with the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation of the stable tridentate cationic species [(PdCl(L1)]BAr4 (5), [(PdMe(L1)]BAr4 (6) and [(PdCl(L2)]BAr4 (7) respectively. Tridentate coordination of L1 and L2 in the cationic complexes has also been confirmed by single X-ray crystallography of complexes 5 and 6. The analogous carbonyl linker cationic species, [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction from [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] with NaBAr4, were however less stable. While cationic complexes 5-7 showed indefinite stability in solution, 9 and 10 had t1/2 of 14 and 2 days respectively. Attempts to crystallise 1 and 3 from the mother liquor resulted in the isolation of the salts [PdCl(L1)]2[Pd2Cl6] (11) and [PdCl(L2)]2[Pd2Cl6] (12). Although when complexes 1-4 xviii were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerisation or polymerisation were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerised and polymerised phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) were prepared by phase transfer alkylation of 2-picolylchloride hydrochloride with one mole equivalent of the appropriate pyrazole. Compounds 2-(3,5-bis-trifluoromethyl-pyrazol-1-ylmethyl)-6-(3,5-dimethyl-pyrazol-1-ylmethyl)-pyridine (L5) and 2-(3,5-dimethyl-pyrazol-1-ylmethyl)-6-phenoxymethyl-pyridine (L6) were isolated in good yields by reacting (2-chloromethyl-6-3,5-dimethylpyrazol-1-ylmethyl)pyridine with an equivalent amount of potassium salt of 3,5-bis(trifluoromethyl)pyrazolate and potassium phenolate respectively. L3-L6 react with either [Pd(NCMe)2Cl2] or [PdClMe(COD)] to give mononuclear palladium complexes 13-18 of the general formulae [PdCl2(L)] or [PdClMe(L)] where L = is the bidentate ligands L3, L4, L5 and L6 respectively. Single crystal X-ray crystallography of complexes 13, 15 and 16 has been used to confirm the solid state geometry of the complexes. In attempts to generate active olefin oligomerisation catalysts, the chloromethyl Pd(II) complexes 14 and 16 were reacted with the halide abstractor NaBAr4 in the presence of stabilising solvents (i.e Et2O or NCMe) but no catalytic activities were observed. Decomposition was evident as observed from the deposition of palladium black in experiments using Et2O. In experiments where NCMe was used as the stabilising solvent, the formation of cationic species stabilised by NCMe was evident from 1H NMR analyses. Reaction of complex 14 with NaBAr4 on a preparative scale in a mixture of CH2Cl2 and NCMe solvent gave the cationic complex [[PdMeNCMe(L3)]BAr4 (19) in good yields. Complex 17 reacted with NABAr4 to give tridentate cationic species [[PdMe(L5)]BAr4 (20) which is inactive towards ethylene oligomerisation or polymerisation reactions. The tridentate coordination of L5 in 20 has also been established by single crystal X-ray structure of 20. Catalysts generated from 18 and 19 catalysed ethylene polymerisation at high pressures to branched polyethylene; albeit with very low activity. The Choromethyl palladium complex 14 reacted with sulfur dioxide to form complex 21. The nature of the product has been established by 1H NMR, 13C NMR and mass spectrometry to be an insertion product of SO2 into the Pd-Me bond of 14. Compounds L1-L4 reacted with the nickel salts NiCl2 or NiBr2 in a 1:1 mole ratio to give the nickel complexes [NiCl2(L1)] (22), [NiBr2(L1)] (23), [NiCl2(L2)] (24), and [NiBr2(L2)] (25), [Ni2(μ2-Cl)2Cl2(L3)2] (26), [Ni2(μ2-Br)2Br2(L3)2] (27), [NiCl2(L4)] (29) and [NiBr2(L4)] (30) in good yields. Reaction of L3 with NiBr2 in a 2:1 mole gave the octahedral complex [NiBr2(L4)2] (28) in good yields. Complexes 22-30 were characterised by a combination micro-analyses, mass spectrometry and single crystal X-ray analyses for 27 and 30. No NMR data were acquired because of the paramagnetic nature of the complexes. When complexes 22-30 were activated with EtAlCl2, highly active olefin oligomerisation catalysts were formed. In the ethylene oligomeristion reactions, three oligomers: C11, C14 xx and C16 were identified as the major products. Selectivityof 40% towards α-olefins were generally obtained. In general catalysts that contain the bidentate ligands L3 and L4 were more active than those that contain the tridentate ligands L1 and L2. Dichloride complexes exhibited relatively higher catalytic activities than their dibromide analogues. Turn over numbers (TON) for oligomer formation showed high dependence on ethylene concentration. A Lineweaver-Burk analysis of reactions catalysed by 22 and 26 showed TON saturation of 28 393 kg oligomer/mol Ni.h and 19 000 kg oligomer/mol Ni.h respectively. Catalysts generated from complexes 22-30 also catalysed oligomerisation of the higher olefins, 1-pentene, 1-hexene and 1-heptene and displayed good catalytic activities. Only two products C12 and C15 were obtained in the 1-pentene oligomerisation reactions. The 1-hexene reactions also gave two products, C12 and C18, while 1-heptene oligomerisation reactions gave predominantly C14 oligomers. Five benzoazoles were used to prepare a series of palladium complexes that were invesitigated as Heck coupling catalysts. The compounds 2-pyridin-2-yl-1H-benzoimidazole (L7) and 2-pyridin-2-yl-benzothiazole (L8) were prepared following literature procedures. The new ligands 2-(4-tert-butylpyridin-2-yl)-benzooxazole (L9) and 2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L10) were prepared by ring closure of aminophenol and aminothiophenol with tert-butyl picolinic acid respectively. The ligand 6-tert-Butyl-2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L11) was prepared by intramolecular cyclisation under basic conditions is described. Reactions of L7-L11 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [PdClMe(L7)] (31), [PdClMe(L8)] (32), [PdCl2(L9)] (33), [PdMeCl(L9)] (34), [PdCl2(L10)] (5), [PdMeCl(L10)] (36) and [PdMeCl(L11)] (37) as xxi confirmed by mass spectrometry and micro-analyses. The palladium complexes 31-37 were efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions and showed good stability.
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Synthesis, characterisation and application of exfoliated graphite-metal oxides electrodes in the photo-electrochemical degradation of selected organic dyes pollutant in water
- Authors: Ama, Monday Onoyivwe
- Date: 2017
- Subjects: Transition metal oxides , Metallic oxides , Transition metal catalysts , Water - Electrolysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/266709 , uj:28283
- Description: Abstract: Exfoliated graphite was used as a suitable electrode material for electrochemical, photolysis and photoelectrochemical degradation of organic pollutants. The effect of four different photoactive nanomaterials (ZrO2, WO3, ZnO and TiO2,) on the degradation ability of exfoliated graphite was investigated separately We report the synthesis and application of novel exfoliated graphite–zirconium oxide EG-ZrO2 nanocomposite photoanode for the photoelectrochemical degradation of eosin yellowish dye in water. Zirconium oxide nanoparticle was synthesized by sol–gel, method and EG–ZrO2 nanocomposite was synthesized by wet solution method. Photoelectrochemical studies with the EG–ZrO2 nanocomposite showed a significant decrease in the initial dye concentration (20 ppm) compared with the bare exfoliated graphite (EG) and zirconium oxide (ZrO2) only. The results indicate that the ZrO2 nanoparticle in the EG–ZrO2 composite enhanced the degradation efficiency of the EG substrate. Thus, EG–ZrO2 composite can be used for the photoelectrochemical oxidation of organic pollutants, especially organic dyes. Tungsten-trioxide (WO3) nanoparticles was synthesized by sol-gel method. The exfoliated graphite / tungsten-trioxide (EG-WO3) was prepared by incorporating WO3 into EG by wet solution method. The materials were characterized using scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analysis (BET), Infrared (IR) spectroscopy and X-ray diffraction (XRD). The EG-WO3 was fabricated into a photoanode and applied for the photoelectrochemical degradation of eosin yellow and methylene blue dyes as model of organic pollutants in water. The process was carried out at a current density of 5 mA cm-2 with Na2SO4 as supporting electrolyte. A significant decrease in the dyes concentrations were obtained at the EG-WO3 electrode compared with the pristine EG electrode. This shows that the WO3 nanoparticles in the EG-WO3 composite enhanced the degradation of the eosin yellow and methylene blue dyes. Thus, the EG-WO3 electrode is applicable for the photoelectrochemical oxidation of organic pollutants, specifically synthetic dyes in water... , Ph.D. (Chemistry)
- Full Text:
- Authors: Ama, Monday Onoyivwe
- Date: 2017
- Subjects: Transition metal oxides , Metallic oxides , Transition metal catalysts , Water - Electrolysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/266709 , uj:28283
- Description: Abstract: Exfoliated graphite was used as a suitable electrode material for electrochemical, photolysis and photoelectrochemical degradation of organic pollutants. The effect of four different photoactive nanomaterials (ZrO2, WO3, ZnO and TiO2,) on the degradation ability of exfoliated graphite was investigated separately We report the synthesis and application of novel exfoliated graphite–zirconium oxide EG-ZrO2 nanocomposite photoanode for the photoelectrochemical degradation of eosin yellowish dye in water. Zirconium oxide nanoparticle was synthesized by sol–gel, method and EG–ZrO2 nanocomposite was synthesized by wet solution method. Photoelectrochemical studies with the EG–ZrO2 nanocomposite showed a significant decrease in the initial dye concentration (20 ppm) compared with the bare exfoliated graphite (EG) and zirconium oxide (ZrO2) only. The results indicate that the ZrO2 nanoparticle in the EG–ZrO2 composite enhanced the degradation efficiency of the EG substrate. Thus, EG–ZrO2 composite can be used for the photoelectrochemical oxidation of organic pollutants, especially organic dyes. Tungsten-trioxide (WO3) nanoparticles was synthesized by sol-gel method. The exfoliated graphite / tungsten-trioxide (EG-WO3) was prepared by incorporating WO3 into EG by wet solution method. The materials were characterized using scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analysis (BET), Infrared (IR) spectroscopy and X-ray diffraction (XRD). The EG-WO3 was fabricated into a photoanode and applied for the photoelectrochemical degradation of eosin yellow and methylene blue dyes as model of organic pollutants in water. The process was carried out at a current density of 5 mA cm-2 with Na2SO4 as supporting electrolyte. A significant decrease in the dyes concentrations were obtained at the EG-WO3 electrode compared with the pristine EG electrode. This shows that the WO3 nanoparticles in the EG-WO3 composite enhanced the degradation of the eosin yellow and methylene blue dyes. Thus, the EG-WO3 electrode is applicable for the photoelectrochemical oxidation of organic pollutants, specifically synthetic dyes in water... , Ph.D. (Chemistry)
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Synthesis, characterization and application of Schiff base cobalt and zinc complexes as catalysts for CO2 and epoxide copolymerization reaction
- Authors: Lephoto, Mapudumo Lydia
- Date: 2013-07-24
- Subjects: Zinc compounds , Cobalt compounds , Transition metal catalysts , Copolymers , Polymerization , Epoxy compounds
- Type: Thesis
- Identifier: uj:7660 , http://hdl.handle.net/10210/8529
- Description: M.Sc. (Chemistry) , Pyrazolyl and imidazolyl-based compounds were used as ligands in the synthesis of cobalt(II) and zinc(II) complexes. These ligands were prepared using literature methods.
- Full Text:
- Authors: Lephoto, Mapudumo Lydia
- Date: 2013-07-24
- Subjects: Zinc compounds , Cobalt compounds , Transition metal catalysts , Copolymers , Polymerization , Epoxy compounds
- Type: Thesis
- Identifier: uj:7660 , http://hdl.handle.net/10210/8529
- Description: M.Sc. (Chemistry) , Pyrazolyl and imidazolyl-based compounds were used as ligands in the synthesis of cobalt(II) and zinc(II) complexes. These ligands were prepared using literature methods.
- Full Text:
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