Osmium complexes as models for CO reduction intermediates

This thesis is concerned with the synthesis, and aspects of the chemistry, of carbon-donor complexes of osmium as organo-metallic models for CO reduction intermediates. In Chapter 1 some aspects of ligand reactivity of the carbon-donor ligands CO, CS, CSe, CTe and carbenes in transition metal complexes are reviewed. The reduction reactions of these ligands are emphasized. The preparation and structure of the osmium η2-formaldehyde complex Os(η2-CH2O)(CO)2(PPh3)2 is described in Chapter 2. This complex has proved to be a useful synthetic precursor for stable osmium formyl, hydroxymethyl, methoxymethyl and halomethyl (-CH2X, X = Cl, Br, I) complexes and some facets of the reactivity of these ligands have been investigated. A general synthetic route to neutral osmium formyl complexes Os(CHO)X(CO)2(PPh3)2(X = halide or alkyl) has been developed. The facile preparation of a stable example of an intermediate formed during decarbonylation of a simple aldehyde by a transition metal, the osmium monohapto-acetyl-hydrido complex Os(η1-C[O]CH3)H(CO)2(PPh3)2, has been demonstrated. A preliminary study of the reactions of the osmium iodomethyl complex Os(CH2I)I(CO)2(PPh3)2 is reported in Chapter 3. The typical reaction of this species is nucleophilic substitution; in many respects reactivity is analogous to an electrophilic methylidene complex. Reaction with a variety of nucleophiles [e.g. OR-, H-, EH- (E = S, Se, Te), NH2R and PR3] has been investigated and the ligand reactivity of some of these derivatives studied. A synthetic route to η2-CSeS and η2-CSe2 complexes of osmium without the use of molecular CSeS or CSe2 has been developed and the isolation of the geometrical isomers of the η2-CSeS complex Os(η2-CSeS)(CO)(CNR)(PPh3)2 (arising from η2-C,S or η2-C,Se coordination) has been achieved. The synthesis of a stable osmium hydrido-selenocarbonyl complex, OsHCl(CO)(CSe) (PPh3)2, has allowed the direct observation of hydride transfer from metal to CSe ligand. These latter results are discussed in Chapter 4.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemistry

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

1980

Author dc:creator

• Headford, Christine E. L.

Advisor dc:contributor.advisor

• Associate Professor W. R. Roper

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2292/1610

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/1610