This thesis describes the synthetic, structural and reactivity studies of η- cycloheptatrienyl-molybdenum and -tungsten chemistry. Chapter 1 presents an overview of the chemistry of η-cycloheptatrienyl derivatives of transition metals, in particular group 6 metals. The functional group properties of the η-cycloheptatrienyl ligand are also discussed. Chapter 2 describes the synthesis of [Mo(η-C<sub>7</sub>H<sub>7</sub>)(η<sup>5</sup>-C<sub>7</sub>H<sub>9</sub>)] from Mocl<sub>5</sub> or [MoCl<sub>4</sub>(thf)<sub>2</sub>], which provides a convenient route to η-cycloheptatrienyl-molybdenum compounds, such as [Mo(η-C<sub>7</sub>H<sub>7</sub>)LX<sub>2</sub>] and [Mo(η-C<sub>7</sub>H<sub>7</sub>)L<sub>2</sub>X], where L = tertiary phosphines or acetonitrile and X = halogen, [NBu<sub>4</sub>] [Mo(η-C<sub>7</sub>H<sub>7</sub>)I<sub>3</sub>], [Mo(η-C<sub>7</sub>H<sub>7</sub>)(η- C<sub>5</sub>H<sub>4</sub>R)] (R = H or Me) and [Mo(η-C<sub>7</sub>H<sub>7</sub>)(η<sup>5</sup>-C<sub>9</sub>H<sub>7</sub>)]. The X-ray crystal structures of [Mo(η-C<sub>7</sub>H<sub>7</sub>)(MeCN)I<sub>2</sub>], [NBu<sub>4</sub>][Mo(η-C<sub>7</sub>H<sub>7</sub>))I<sub>3</sub>] and [Mo(η-C<sub>7</sub>H<sub>7</sub>)(η-C<sub>5</sub>H<sub>4</sub>Me)] are presented. The compound [Mo(η-C<sub>7</sub>H<sub>7</sub>))(MeCN)I<sub>2</sub>], mixed with Me<sub>3</sub>SiCH<sub>2</sub>MgCl, is a catalyst for ring-opening polymerisation of norbornene giving trans polymer exclusively. The electron-transfer complexes [Mo(η-C<sub>7</sub>H<sub>7</sub>)(η-C<sub>5</sub>H<sub>4</sub>Me)][tcne] and {[Mo(η-C<sub>7</sub>H<sub>7</sub>))(η- C<sub>5</sub>H<sub>5</sub>}<sub>2</sub>[tcnq]} and the intercalation compound {ZrS<sub>2</sub>[Mo(η-C<sub>7</sub>H<sub>7</sub>)(η-C<sub>5</sub>H<sub>4</sub>Me)]o.22} are also described. An extension of these synthetic pathways to tungsten is described in chapter 3. Reduction of WCl<sub>6</sub> with sodium amalgam in the presence of cycloheptatriene gives [W(η- C<sub>7</sub>H<sub>7</sub>)(η<sup>5</sup>-C<sub>7</sub>H<sub>9</sub>)], which is a precursor to the compounds [W(η-C<sub>7</sub>H<sub>7</sub>)(MeCN)I<sub>2</sub>], [W(η- C<sub>7</sub>H<sub>7</sub>)(PMe<sub>3</sub>)X<sub>2</sub>] (X = Br or I), [W(η-C<sub>7</sub>H<sub>7</sub>)(dmpe)I], [W(η-C<sub>7</sub>H<sub>7</sub>)(η-C<sub>5</sub>H<sub>4</sub>R)] (R = H or Me) and [Mo(η-C<sub>7</sub>H<sub>7</sub>)(η<sup>5</sup>-C<sub>9</sub>H<sub>7</sub>)]. The [W(η-C<sub>7</sub>H<sub>7</sub>)(MeCN)I<sub>2</sub>] / Me<sub>3</sub>SiCH<sub>2</sub>MgCI system is an active catalyst for ring opening polymerisation of norbomene. The electronic structures of [W(η-C<sub>7</sub>H<sub>7</sub>)(η-C<sub>5</sub>H<sub>4</sub>R)] (R= H or Me) are discussed on the basis of their He I and He II photoelectron spectra. The intercalation of [W(η-C<sub>7</sub>H<sub>7</sub>)(η-C<sub>5</sub>H<sub>4</sub>Me)] into ZrS<suv>2</sub> is also described. The magnetic properties of the 17-electron compounds [Mo(η-C<sub>7</sub>H<sub>7</sub>)(MeCN)I<sub>2</sub>], [Mo(η-C<sub>7</sub>H<sub>7</sub>)(PMe<sub>3</sub>)I<sub>2</sub>], [W(η-C<sub>7</sub>H<sub>7</sub>)(MeCN)I<sub>2</sub>], [W(η-C<sub>7</sub>H<sub>7</sub>)(PMe<sub>3</sub>)I<sub>2</sub>] and [W(η-C<sub>7</sub>H<sub>7</sub>) (PMe<sub>3</sub>)I<sub>2</sub>] are discussed in chapter 4. They behave as one-dimensional antiferromagnets which was suggested by magnetic model fittings and the crystal structure of [Mo(η-C<sub>7</sub>H<sub>7</sub>)(MeCN)I<sub>2</sub>]. Chapter 5 comprises of two parts. The first part describes a new series of binuclear thiolato-bridged molybdenum complexes [(η-C<sub>7</sub>H<sub>3</sub>R¹<sub>4</sub>)Mo(μ-SR²)<sub>3</sub> Mo- (η-C<sub>7</sub>H<sub>3</sub>R¹<sub>4</sub>)][BF<sub>4</sub>] (R¹ = H or Me; R² = Et, Pr, Bu, Ph or CH<sub>2</sub>Ph). Dynamic NMR studies reveal that all of these complexes (except for R² = Ph) are fluxional due to inversion at the pyramidal sulfur centre. Cyclic voltammetric studies show that they undergo two reversible one-electron reductions. Second part of this chapter describes the new bridging-imido compound [(η-C<sub>7</sub>H<sub>7</sub>)Mo(μ-NAr)<sub>2</sub>Mo(η-C<sub>7</sub>H<sub>7</sub>)] (Ar = 2,6- diisopropylphenyl). Chapter 6 discusses the η-l,2,4,6-tetramethylcycloheptatrienyl-molybdenum system. The new η-tetramethylcycloheptatriene molybdenum compounds [M'(η-C<sub>7</sub>H<sub>4</sub>Me<sub>4</sub>- 1,3,5,7)],[M'(η-C<sub>7</sub>H<sub>4</sub>Me<sub>4</sub>-l,2,4,6)] and [M'(η-C<sub>7</sub>H<sub>4</sub>Me<sub>4</sub>-l,3,4,6)], M' = Mo(CO)<sub>3</sub>, and new η-tetramethylcycloheptatrienyl-molybdenum compounds [M"(CO)<sub>3</sub>]+, [M"(CO)<sub>2</sub>C1], [M"(dmpe)Cl], [M"(η-C<sub>6</sub>H<sub>5</sub>Me)]+ and [M"(acac)(PPh<sub>3</sub>)], M" = Mo(η- CC<sub>7</sub>H<sub>3</sub>Me<sub>4</sub>-1,2,4,6), and [Mo(η<sup>3</sup>-C<sub>7</sub>H<sub>3</sub>Me<sub>4</sub>-l,2,4,6)(dmpe)(CO)<sub>2</sub>Cl] are described. Chapter 7 gives the experimental details for the work described in preceeding chapters. Appendix A presents characterising data for all the new compounds and previously unreported data for known compounds. Crystallographic details for the X-ray structure determinations and X-ray powder diffraction data are listed in Appendix B and C respectively.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:334196 |
| Date | January 1993 |
| Creators | Ng, Kee-Pui Dennis |
| Contributors | Green, M. L. H. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:b41ab51d-7f86-4989-8b34-3d3e06627c9c |
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