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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Pd catalysed C-C bond forming and carbonylation
- Authors: Shaw, Megan Lorraine
- Date: 2012-05-03
- Subjects: Phosphine , Carbonyl compounds , Ligands (Biochemistry)
- Type: Thesis
- Identifier: uj:2250 , http://hdl.handle.net/10210/4689
- Description: M.Sc. , This study initially focused on the synthesis of a set of triaryl phosphine ligands, encompassing a broad range of electron withdrawing functionalities on the ortho-position of one of the aryl rings. These varying moieties were readily incorporated into diphenylphosphino benzaldehyde as starting material through both Wittig and Knoevenagel chemistry. The ligands produced were tested in the Pd-catalysed Suzuki reaction. The electronic as well as the steric nature of the alkene ligands largely dictated the activities observed: the more electron poor or the bulkier the ligand, the higher the activity observed in the Suzuki reaction. This is in contrast to much work in the literature stating that highly active Suzuki catalysts require a very electron rich system. At the same time, the literature indicates that co-ordinatively unsaturated Pd-complexes are also active catalysts. The activities observed were ascribed to the ability of these electron poor bulky phosphine alkene ligands to stabilise or promote the reductive elimination step of the Suzuki mechanism in preference to the oxidative addition step, which is the typical rate determining step. The study then investigated carbonylation reactions, specifically the methoxycarbonylation and hydrocarboxylation reactions, which are typically Brønsted acid co-catalysed. The alternative was the first time use of metal-triflate based Lewis acids as co-catalysts in these types of reactions. Thus, a systematic study was performed. It was found that metal trifluoromethane sulfonate (hereafter referred to as triflate) based Lewis acid co-catalysts outperformed the typical Brønsted acid co-catalysts by between one and a half to two and a half times on the rate of the methoxycarbonylation reaction, depending on the substrate used. The system was tested with Pd loadings in the region 2–0.03 mol%. A competing heat-induced styrene polymerisation reaction ultimately affected the results at such low Pd loadings. A low level kinetic analysis was performed indicating zero order kinetics on the alkene concentration of the reaction, with a fractional order dependence on the Lewis acid concentration. There was little to no effect on the linear/branched ratio of the product in response to the use of the Lewis acid. The nature of the metal within the metal triflate based co-catalyst also seemed to be critical to the reaction, with the 4+ based Zr and Hf ultimately providing the highest obtainable turn over frequencies, the 1+ and 2+ based metals providing no conversion, and reactivity in the presence of the 3+ metals depended on the specifics of the reaction. In addition to a great deal of work being performed on styrene and ethylene as substrates, reactions using phenylacetylene were also optimised. Here, it was found that the bidentate BINAP ligand and the literature preferred ligand, PyPPh2 afforded good catalyst activity. Both of these ligands offered much faster catalyst systems than PPh3 and various other bidentate ligands tested.
- Full Text:
- Authors: Shaw, Megan Lorraine
- Date: 2012-05-03
- Subjects: Phosphine , Carbonyl compounds , Ligands (Biochemistry)
- Type: Thesis
- Identifier: uj:2250 , http://hdl.handle.net/10210/4689
- Description: M.Sc. , This study initially focused on the synthesis of a set of triaryl phosphine ligands, encompassing a broad range of electron withdrawing functionalities on the ortho-position of one of the aryl rings. These varying moieties were readily incorporated into diphenylphosphino benzaldehyde as starting material through both Wittig and Knoevenagel chemistry. The ligands produced were tested in the Pd-catalysed Suzuki reaction. The electronic as well as the steric nature of the alkene ligands largely dictated the activities observed: the more electron poor or the bulkier the ligand, the higher the activity observed in the Suzuki reaction. This is in contrast to much work in the literature stating that highly active Suzuki catalysts require a very electron rich system. At the same time, the literature indicates that co-ordinatively unsaturated Pd-complexes are also active catalysts. The activities observed were ascribed to the ability of these electron poor bulky phosphine alkene ligands to stabilise or promote the reductive elimination step of the Suzuki mechanism in preference to the oxidative addition step, which is the typical rate determining step. The study then investigated carbonylation reactions, specifically the methoxycarbonylation and hydrocarboxylation reactions, which are typically Brønsted acid co-catalysed. The alternative was the first time use of metal-triflate based Lewis acids as co-catalysts in these types of reactions. Thus, a systematic study was performed. It was found that metal trifluoromethane sulfonate (hereafter referred to as triflate) based Lewis acid co-catalysts outperformed the typical Brønsted acid co-catalysts by between one and a half to two and a half times on the rate of the methoxycarbonylation reaction, depending on the substrate used. The system was tested with Pd loadings in the region 2–0.03 mol%. A competing heat-induced styrene polymerisation reaction ultimately affected the results at such low Pd loadings. A low level kinetic analysis was performed indicating zero order kinetics on the alkene concentration of the reaction, with a fractional order dependence on the Lewis acid concentration. There was little to no effect on the linear/branched ratio of the product in response to the use of the Lewis acid. The nature of the metal within the metal triflate based co-catalyst also seemed to be critical to the reaction, with the 4+ based Zr and Hf ultimately providing the highest obtainable turn over frequencies, the 1+ and 2+ based metals providing no conversion, and reactivity in the presence of the 3+ metals depended on the specifics of the reaction. In addition to a great deal of work being performed on styrene and ethylene as substrates, reactions using phenylacetylene were also optimised. Here, it was found that the bidentate BINAP ligand and the literature preferred ligand, PyPPh2 afforded good catalyst activity. Both of these ligands offered much faster catalyst systems than PPh3 and various other bidentate ligands tested.
- Full Text:
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