Synthesis and reactivity studies on oxo and sulphide compounds of the early transition metals

Abstract

This thesis describes studies directed towards the preparation of new oxo compounds of the early transition metals with a view to delineating some of the complex factors which govern their stability and reactivity. For a number of the types of compound studied, the work has also been extended to analogous sulphide systems in order to provide a contrast with another chalcogenide element and further aid an understanding of the bonding and reactivity of both of these elements in a transition metal enviroment. Chapter 1 highlights the areas of transition metal oxo chemistry of relevance to the general theme of the thesis. Chapter 2 describes the use of the commercially available reagents Me(_3)SiYR (R = alkyl, SiMe(_3); Y = O, S), for rapid, convenient, solution syntheses of transition metal oxohalide and sulphidohalide compounds of molybdenum, tungsten, niobium and tantalum. In addition, this methodology allows the preparation of mixed oxosulphidohalide materials and, in certain cases, intermediate alkoxo(siloxo) halide compounds have been isolated. Chapter 3 describes the synthesis, characterisation and reactivity of a series of mononuclear mono-oxo complexes of molybdenum and tungsten including M(O)(OAr)(_4) [M=W, Ar=2,6-Me(_2)C(_6)H(_3) (DMP), 2,4,6-Me(_3)C(_6)H(_2) (TMP), 2,6-Pr(^i)C(_6)H(_3) (DIPP); M=Mo, Ar=(DMP)], M(_2)(O)(_3)(DMP)(_6) and Mo(O)C1(_2)(DMP)(_2). Attempts to synthesise related mononuclear complexes containing the cis di-oxo moeity are also discussed. Chapter 4 describes the synthesis and reactivity of seven coordinate oxo and sulphidohalide derivatives of niobium and tantalum which exhibit the phenomenon of bond-stretch isomerism. Compounds prepared include Nb(O)Br(_3)(PMe(_3))(_3), Nb(S)X(_3)(PMe(_3))(_3) (X=C1, Br) and Ta(S)C1(_3)(PMe(_3))(_3). The latter three have been characterised by X-ray crystallography. Chapter 5 describes the synthesis and reactivity of half-sandwich oxo compounds of niobium and tantalum. Some of the derivatives prepared include[CpNbC1(_3)](_2)(µ(_2)-O), [CpTaC1(_3)](_2)(|µ(_2)-O) and [Cp*TaC1(_3)](_2)(µ(_2)O). The stability of [Cp*Ta(O)Cl(_2)](_2) has been investigated and the X-ray structure of the trinuclear decomposition product Cp*(_3)Ta(_3)O(_4)C1(_4) is described. Chapter 6 describes the use of alkali metal aryloxides as intercalating agents and the preparation of a series of novel intercalation compounds, of the type W(O)(_2)C1(_2)xM (M = Li, Na and K) which display the properties characteristic of tungsten bronzes. Chapter 7 gives experimental details for chapters 2 6.