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Title: The chemistry of η-cycloheptatrienyl derivatives of molybdenum and tungsten
Author: Ng, Kee-Pui Dennis
ISNI:       0000 0001 3444 998X
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1993
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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-C7H7)(η5-C7H9)] from Mocl5 or [MoCl4(thf)2], which provides a convenient route to η-cycloheptatrienyl-molybdenum compounds, such as [Mo(η-C7H7)LX2] and [Mo(η-C7H7)L2X], where L = tertiary phosphines or acetonitrile and X = halogen, [NBu4] [Mo(η-C7H7)I3], [Mo(η-C7H7)(η- C5H4R)] (R = H or Me) and [Mo(η-C7H7)(η5-C9H7)]. The X-ray crystal structures of [Mo(η-C7H7)(MeCN)I2], [NBu4][Mo(η-C7H7))I3] and [Mo(η-C7H7)(η-C5H4Me)] are presented. The compound [Mo(η-C7H7))(MeCN)I2], mixed with Me3SiCH2MgCl, is a catalyst for ring-opening polymerisation of norbornene giving trans polymer exclusively. The electron-transfer complexes [Mo(η-C7H7)(η-C5H4Me)][tcne] and {[Mo(η-C7H7))(η- C5H5}2[tcnq]} and the intercalation compound {ZrS2[Mo(η-C7H7)(η-C5H4Me)]o.22} are also described. An extension of these synthetic pathways to tungsten is described in chapter 3. Reduction of WCl6 with sodium amalgam in the presence of cycloheptatriene gives [W(η- C7H7)(η5-C7H9)], which is a precursor to the compounds [W(η-C7H7)(MeCN)I2], [W(η- C7H7)(PMe3)X2] (X = Br or I), [W(η-C7H7)(dmpe)I], [W(η-C7H7)(η-C5H4R)] (R = H or Me) and [Mo(η-C7H7)(η5-C9H7)]. The [W(η-C7H7)(MeCN)I2] / Me3SiCH2MgCI system is an active catalyst for ring opening polymerisation of norbomene. The electronic structures of [W(η-C7H7)(η-C5H4R)] (R= H or Me) are discussed on the basis of their He I and He II photoelectron spectra. The intercalation of [W(η-C7H7)(η-C5H4Me)] into ZrS2 is also described. The magnetic properties of the 17-electron compounds [Mo(η-C7H7)(MeCN)I2], [Mo(η-C7H7)(PMe3)I2], [W(η-C7H7)(MeCN)I2], [W(η-C7H7)(PMe3)I2] and [W(η-C7H7) (PMe3)I2] 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-C7H7)(MeCN)I2]. Chapter 5 comprises of two parts. The first part describes a new series of binuclear thiolato-bridged molybdenum complexes [(η-C7H34)Mo(μ-SR²)3 Mo- (η-C7H34)][BF4] (R¹ = H or Me; R² = Et, Pr, Bu, Ph or CH2Ph). 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-C7H7)Mo(μ-NAr)2Mo(η-C7H7)] (Ar = 2,6- diisopropylphenyl). Chapter 6 discusses the η-l,2,4,6-tetramethylcycloheptatrienyl-molybdenum system. The new η-tetramethylcycloheptatriene molybdenum compounds [M'(η-C7H4Me4- 1,3,5,7)],[M'(η-C7H4Me4-l,2,4,6)] and [M'(η-C7H4Me4-l,3,4,6)], M' = Mo(CO)3, and new η-tetramethylcycloheptatrienyl-molybdenum compounds [M"(CO)3]+, [M"(CO)2C1], [M"(dmpe)Cl], [M"(η-C6H5Me)]+ and [M"(acac)(PPh3)], M" = Mo(η- CC7H3Me4-1,2,4,6), and [Mo(η3-C7H3Me4-l,2,4,6)(dmpe)(CO)2Cl] 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.
Supervisor: Green, M. L. H. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Transition metals ; Molybdenum compounds ; Tungsten compounds