New scandium and titanium borylimido chemistry

Thesis

This Thesis reports the synthesis and reactivity of scandium and titanium borylimides. New, versatile synthetic routes to such complexes of these two metals were targeted, and their reactions with small, unsaturated compounds were explored, with a particular focus being the reactivity of alkynes with these systems.

Chapter One provides a background on Group 4 imido and hydrazido complexes. Group 4 alkoxyimides are also reviewed, as well as the developing field of rare earth imides. The Chapter focuses on the synthesis, structure, and stoichiometric and catalytic reactions of these complexes with unsaturated substrates, and ends with a description of the handful of known transition metal borylimides.

Chapter Two first describes the synthesis and structures of new titanium borylimido synthons prepared from Ti(NMe₂)₂Cl₂. From the borylimide Ti{NB(NAr'CH)₂}Cl₂(py)₃ are then formed five new compounds supported by a range of tridentate, nitrogen-based ligands.

Chapter Three describes the synthesis of half-sandwich titanium borylimides through tertbutylimide/borylamine exchange. A sandwich compound is also described, and the electronic structures of these complexes are analysed by DFT, QTAIM and NBO studies. Reactivity with heteroallenes, and exchange reactions with amines are also explored.

Chapter Four describes the reactivity of diamide-donor-supported titanium borylimides with terminal alkynes. The principal reaction outcomes are [2+2] cycloadditions and C–H bond activations, and an interesting C–F bond activation is also described. Kinetic studies of some reactions are presented, and will be supported by further DFT studies.

Chapter Five explores attempts to prepare the first rare earth borylimide. Kinetic and computational evidence is presented for the existence of a transient scandium borylimide which rapidly undergoes interesting sp, sp² and sp³ C–H bond activations.

Chapter Six presents full experimental procedures and characterising data for the new complexes reported.

Authors: Clough, B

• DOI: 10.5287/ora-xkb168jkj
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Scandium; Early transition metals; Titanium; Alkynes; Borylimides; Metal-nitrogen multiple bonds
• Subjects: Chemistry, Inorganic; Coordination chemistry; Organometallic chemistry