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Reference: Ng, Kee-Pui Dennis., (1993). The chemistry of [h]-cycloheptatrienyl derivatives of molybdenum and tungsten. DPhil. University of Oxford.Citable link to this page:


The chemistry of [h]-cycloheptatrienyl derivatives of molybdenum and tungsten

Abstract: 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-cycloheptatrienylderivatives of transition metals, in particular group 6 metals. The functional groupproperties 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-molybdenumcompounds, such as [Mo(η-C7H7)LX2] and [Mo(η-C7H7)L2X], where L = tertiaryphosphines 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)] arepresented. The compound [Mo(η-C7H7))(MeCN)I2], mixed with Me3SiCH2MgCl, is acatalyst 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} arealso 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 = Hor Me) and [Mo(η-C7H7)(η5-C9H7)]. The [W(η-C7H7)(MeCN)I2] / Me3SiCH2MgCIsystem is an active catalyst for ring opening polymerisation of norbomene. The electronicstructures of [W(η-C7H7)(η-C5H4R)] (R= H or Me) are discussed on the basis of their HeI and He II photoelectron spectra. The intercalation of [W(η-C7H7)(η-C5H4Me)] into ZrS2is 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-dimensionalantiferromagnets which was suggested by magnetic model fittings and the crystal structureof [Mo(η-C7H7)(MeCN)I2].Chapter 5 comprises of two parts. The first part describes a new series ofbinuclear thiolato-bridged molybdenum complexes [(η-C7H3R¹4)Mo(μ-SR²)3 Mo-(η-C7H3R¹4)][BF4] (R¹ = H or Me; R² = Et, Pr, Bu, Ph or CH2Ph). Dynamic NMRstudies reveal that all of these complexes (except for R² = Ph) are fluxional due toinversion at the pyramidal sulfur centre. Cyclic voltammetric studies show that theyundergo two reversible one-electron reductions. Second part of this chapter describes thenew 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-molybdenumsystem. 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 preceedingchapters. Appendix A presents characterising data for all the new compounds andpreviously unreported data for known compounds. Crystallographic details for the X-raystructure determinations and X-ray powder diffraction data are listed in Appendix B andC respectively.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:The digital copy of this thesis has been made available thanks to the generosity of Dr Leonard Polonsky


Green, M. L. H.More by this contributor



Prof. M. L. H. GreenMore by this contributor


 Bibliographic Details

Issue Date: 1993Identifiers

Urn: uuid:b41ab51d-7f86-4989-8b34-3d3e06627c9c

Source identifier: 603835839 Item Description

Type: Thesis;

Language: eng Subjects: Transition metals Molybdenum compounds Tungsten compounds Tiny URL: td:603835839


Autor: Ng, Kee-Pui Dennis. - institutionUniversity of Oxford facultyMathematical and Physical Sciences Division - - - - Contributors Gre



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