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Title: New cyclic, bicyclic and cage phosphines and fluorophosphines
Author: Garland, Michael Christopher
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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Abstract:
The preparation of the following new cyclic, bicyclic and cage phosphinites are reported and characterised by a combination of NMR spectroscopy, mass spectrometry and elemental analysis. l-methoxyphosphinane (2.8), l-methoxyphospholane (2.10), 5-methoxy- dibenzo[b,d]phosphole (2.12), I-methoxy-2,2,3,4,4-pentamethylphosphetane (2.14) (which has been previously reported), a-PhobPOMe (2.17), 1-(-)-menthoxyphosphinane (2.21), a-PhobP(-)- menthol (2.22), s-PhobP( - )-menthol (2.23), (S)-2,2' -bis(phosphinan-l-yloxy)-I, 1 ' -binaphthyl (2.24), (S)-2,2'-bis(s-phob-l-yloxy)-I,1 '-binaphthyl (2.25), CgPOR, R= OMe (2.29), OEt (2.30), oiPr- (2.31), 4-C6~OMe (2.32), 4-C6~Me (2.33), 4-C6~CI (2.35), 4-C6~CF3 (2.36), and 4-C6~CF 3 (2.37), The methoxy based phosphinites were treated with solutions of H20 in MeOH, while the cage phosphinites and the previously prepared compounds CgPOR where R = C6H5 (2.30), 2-C6~Me (2.34), 2,4,6-C6H2Me3 (2.35), 2,4-C6H3tBu2 (2.36), CH2CF3 (3.1), and CH2CH(CF3)2 (3.2) were treated with H20 in aq HCI and MeCN. The resulting hydrolysis reactions were followed by 31p NMR spectroscopy and the times to 50% hydrolysis (t50) compared. In general, the stability to hydrolysis was found to increase with increasing steric bulk, electronegativity of the substituents and as the phosphacycle C-P-C angle approaches 90°. Hydrolysis of (2.8) was carried out with 170 labelled water, with the results supporting the mechanism proceeding via nucleophilic attack of H20 at phosphorus. This was used to explain the increased stability of phosphinites as C-P-C angle approaches 90° by consideration of the relative energies of the individual trigonal bipyramidal intermediates. The synthesis of the fluorophosphines, CgPF (4.1), a-PhobPF (4.2), s-PhobPF (4.3) and tBu2PF (4.5) was achieved. All are shown to be completely stable to disproportionation, while stability to hydrolysis increased in the order (4.1) » (4.3) > (4.2) » (4.5). DFT calculations of disproportionation reactions are presented. These suggested that destabilisation of TBP intermediates is caused by ring strain in the fluorophosphines (4.1)-(4.3). This increases the energy of TBP intermediates and thus increases the stability of the bicyclic and cage fluorophosphines towards disproportionation. The electronic and steric properties of all novel compounds has been assessed by formation of the corresponding selenides, platinum(II) and rhodium(I) coordination complexes and comparison of the chemical shifts, coupling constants and carbonyl stretching frequencies. X- ray crystal structures for [PtCI2L2] where L = (2.8), (2.10), (2.12), (2.17), (2.29), (4.2) and (4.3), the oxides of (2.29), (2.30) and (2.31) and the free phosphinites (2.34), (2.39) and (2.40) are also reported. Rhodium complexes of the methoxyphosphinites and cage phosphinites and all fluorophosphines were tested as catalysts in the hydroformylation of l-hexene and/or l-heptene. The fluorophosphines were the most successful catalysts with (4.1) significantly outperforming PPh3. Variation of the amount of (2.35) used allowed the selective formation of either n- or iso- aldehyde. One equivalent of (2.35) led to a n:iso ratio of 1.3 while ten equivalents of (2.35) gave a n:iso ratio of 0.3. Due to the success of the fluorophosphines, their nickel complexes were also tested as catalysts in the hydrocyanation of 3-pentenenitrile. This was the first time that a fluorophosphine has been applied in catalysis and again (4.1) outperformed the other ligands, achieving comparable selectivities and activities to the commercially used P(O- Tolj; Finally the rhodium complexes of chiral phosphinites (2.21)-(2.25) were applied in asymmetric hydrogenation, although high conversions were obtained selectivities were low.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.573412  DOI: Not available
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