The Use of Molecular Design to Fine-tune the Redox Properties and Electronic Structure of Half-Sandwich Group 6 Metal Acetylide Complexes

Abstract

Chapter One introduces the chemistry of organometallic acetylide complexes, with a particular focus on complexes containing redox active half sandwich end-capping groups. Carbon chain complexes containing these auxiliaries are of particular interest for the development of molecular materials with: electronic, magnetic, luminescence and optical properties. An overview of the research undertaken in these areas and the spectroscopic analysis has been explored. Chapter Two describes the synthesis of the cycloheptatrienyl tungsten complexes: [W(C=CHR)(dppe)(η-C7H7)]+ and [W(C≡CR)(dppe)(η-C7H7)]. In common with the molybdenum counterparts, the structural and spectroscopic properties of these systems are controlled by the electronic structure of the W(dppe)(η-C7H7) auxiliary which has a frontier orbital with dz2 character. Chapter Three compares two series of cyclopentadienyl molybdenum alkynyl complexes, cis-[Mo(C≡CR)(CO)(dppe)Cp'] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp'] (Cp' = Cp or Cp*). The change in molecular geometry leads to enhanced alkynyl character in the HOMO of the cis derivatives when compared to the mainly metal-centred HOMO of the trans complexes. This work indicates the potential for a switchable redox response, via perturbation in electronic structure controlled by changes in molecular geometry. Chapter Four assesses the effect of elongation of the all-carbon chain on the redox chemistry and electronic structure. The synthesis, spectroscopy and electronic structure of the cycloheptatrienyl Group 6 metal complexes, [M{(C≡C)n-SiMe3)(L2)(η-C7H7)] (M = W, n = 2, L2 = bpy; M = Mo, n = 3, L2 = bpy or dppe) has been investigated. In the dppe series, chain extension serves to increase the carbon chain character of the HOMO. Chapter Five explores general conclusions derived from this thesis and the potential future work.

Date of Award	31 Dec 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mark Whiteley (Supervisor)