A series of complexes of general formula [OsX<SUB>3</SUB>L<SUB>3</SUB>] and [OsCl<SUB>3</SUB>L<SUB>2</SUB>L'] where X is a chloride or bromide and L and L' are different tertiary phosphines or arsines have been synthesised. The X-ray diffraction crystal structures of the complexes, <I>mer</I>-[OsCl<SUB>3</SUB>(PMe<SUB>2</SUB>Ph)<SUB>3</SUB>], <I>mer</I>-[OsCl<SUB>3</SUB>(PEt<SUB>2</SUB>Ph)<SUB>3</SUB>], <I>mer</I>-[OsBr<SUB>3</SUB>(PPr<SUP>n</SUP><SUB>3</SUB>)<SUB>3</SUB>], <I>mer</I>-[OsCl<SUB>3</SUB>(AsME<SUB>2</SUB>Ph)<SUB>3</SUB>], <I>mer</I>-[OsCl<SUB>3</SUB>(PPr<SUP>n</SUP><SUB>2</SUB>)<SUB>2</SUB>(AsPr<SUP>n</SUP><SUB>3</SUB>)], <I>mer</I>-[OsCl<SUB>3</SUB>(PPr<SUP>n</SUP><SUB>2</SUB>)<SUB>2</SUB>(PEtPh<SUB>2</SUB>)] and <I>mer</I>-[OsCl<SUB>3</SUB>(P(OMe)<SUB>2</SUB>Ph)<SUB>2</SUB>(AsPr<SUP>n</SUP><SUB>3</SUB>)] show them to have slightly distorted octahedral metal environments with the <I>trans</I> influence of the Group 15 ligands evident. The <I>mer</I> complexes have been studied electrochemically and all show two one-electron processes; an oxidation and a reduction process. Both couples involve the osmium metal centre. The one electron reduction step is rapidly followed by a chemical reaction resulting in the formation of an electroactive daughter product of general formula [OsCl<SUB>2</SUB>L<SUB>3</SUB>Y] where Y is a neutral coordinating ligand. The chemical reaction has been studied by kinetic and spectrochemical methods. The redox potentials of the <I>mer</I> species gives a good linear correlation with Tolmans electronic parameter for the tertiary phosphine. The electronic spectra of the compounds have been recorded and the peaks assigned to specific electronic transitions <I>via </I>the use of Extended Huckel Molecular Orbital Calculations. Electrochemical elucidation of these systems has shown that the redox potentials of the complexes are predominantly dependent on one ligand, namely the phosphine/arsine <I>trans</I> to the halide. The <I>fac</I> isomers also show two metal based one-electron couples at very different potentials from the analogous <I>mer </I>isomers. The reduction also produces an electroactive daughter product. The oxidation results in the isomerisation of the <I>fac</I> isomer to that of the <I>mer</I> isomer. The kinetic parameters of the reaction have been measured, and a mechanism is proposed for the isomerisation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660462 |
| Date | January 1997 |
| Creators | Payne, Nicholas N. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15608 |
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