The separation of phobane isomers 9-H-9-phosphabicyclo[3.3.1]nonane (s-PhobPH)and 9- H-9-phosphabicyclo[4.2.1]nonane (a-PhobPH) was achieved either by selective protonation of the s-isomer or selective oxidation of the a-isomer. Two phobane precursors were synthesised, 9-chloro-9-phosphabicyclononane (PhobPCI) by literature methods and 9-bromo-9-phosphabicyclononane (PhobPBr) by slow addition ofBr2 to PhobPH. Both halophosphines were prepared as pure s isomer or sla mixtures and used in the synthesis of new phobane ligands. The 3 isomers 9-n-butyl-phosphabicyclo[3.3.1]nonane (s-PhobpnBu), 9-syn-n-butylphosphabicyclo[ 4.2.1 ]nonane (as-PhobpnBu) and 9-anti-n-butyl-phosphabicyclo[ 4.2.1] nonane (a7-PhobpnBu) were prepared selectively and their electronic properties were assessed from JPSe for PhobpnBu(=Se), JpPt for trans-[PtCb(PEt3)(PhobpnBu)] and Veo for trans-[RhCI(CO)(PhobpnBu)2]. The experimental data revealed the order of Cl-donation is a7 > s > as which was corroborated by DFT calculations. Competition experiments with complexes [Pt(CH3)(dppe)(PhobpnBu)]BP14 showed the order of affinity for Pt is also a7 > s > as. A series of phobane derivatives PhobPR where R = nBu, CH2CH2CF2CFs (fBu) , iBu, CH2Cy, sBu, tBu, neoPn, Ph, OMe and NHiPr was prepared by nucleophilic or electrophilic routes as pure s-isomers or sla mixtures. The selenides sla-PhobPR(=Se) (R = nBu, fBu, iBu, CH2Cy, sBu, tBu, neoPn, Ph, OMe, NHipr) were made from KSeCN and their J PSe determined. Reaction of [PtCb(NCtBu)2] with s-PhobPR gave the complexes ยท trans[ PtCb(s-PhobPR)2] (R = nBu, fBu, iBu, CH2Cy, tBu, neoPn, Ph) and eis-and trans-[PtCb(sPhobPR) 2] (R= sBu, OM e) mixtures. The complexes trans-[RhCI(CO)(s-PhobPR)2] (R = nBu, fBu, iBu, CH2Cy, sBu, tBu, neoPn, Ph, OMe, NHipr) were readily made from [RhCI(CO)2h and their Veo analysed. Variable temperature NMR studies on the complexes trans-[PtCb(s-PhobPR)2] (R = nBu, iBu, sBu, tBu) revealed restricted rotation about the MP bond. The activation energy for the M-P rotation was calculated and related to the bulk ofthe ligands, as supported by Molecular Mechanics calculations. Ligands s-, ar and as-PhobpnBu were tested for Rh-catalysed hydroformylation of 1- hexene. The activity of the catalysts was in the order as> s > a7, which is inversely related to the a-donor ability ofthe 3 isomers. Derivatives sla-PhobPR (R = nBu, fBu, iBu, CH2Cy, SBu) were tested for Co-catalysed hydroformylation which showed ligands with p-branched substituents give low alkane production. Derivatives sla-PhobPR (R = nBu, fBu, iBu, CH2Cy, sBu, tBu, neoPn, Ph, OMe, NHipr) were also tested for Rh-catalysed hydroformylation of 1- and trans-3-hexene. Hydroformylation of the terminal alkene showed conversions similar to that ofPPh3 except for R = Ph and OMe which gave lower activities. The selectivities obtained were poorer than for PPh3 with the exception of R = Ph and OMe where similar selectivities were achieved. Hydroformylation of the internal alkene showed the sla-PhobPR ligands form selective catalysts for internal alkenes with a small degree of isomerisation and conversions comparable to PPh3.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:658314 |
| Date | January 2009 |
| Creators | Carreira Mendez, Monica |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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