The work described in this thesis concerns the synthesis of actinide complexes and their reactivity towards small unsaturated molecules. Complexes bearing tetraphenoxide, borohydride and boroxide ligands have been evaluated. Additionally, work towards the synthesis of heterobimetallic uranium transition metal complexes and their applications in catalysis is discussed. Chapter one reviews important organoactinide complexes reported in the literature which effect chemical transformations on small unsaturated substrates. Actinide complexes supported by aryloxide or borohydride ligands are reviewed, along with actinide complexes in which metal p-arene interactions are present. Chapter two reports the synthesis and characterisation of a set of tetraphenol ligands, in addition to a number of attempted synthetic routes to tetraphenol ligands with alternate substitution. The chemistry of those tetradentate aryloxide ligands is introduced with bimetallic uranium(IV) and thorium(IV) complexes using different An(IV) and U(III) precursors. Chapter three reports the synthesis and characterisation of monometallic uranium and thorium complexes using a tetraphenol ligand. The varying chemistry between the two similar An(IV) ions, where the uranium complexes exist as a mixture of oligomers and the thorium complexes remain as well defined mononuclear complexes, is discussed within. A range of base adducts of mononuclear actinide complexes are reported, including a thorium trimethylsilylazide complex, a rare example of a metal organoazide. Chapter four describes the synthesis of homoleptic boroxide and heteroleptic borohydride complexes of uranium(III). The reactivities of these complexes with small unsaturated molecules are assessed, including the reaction of a low coordinate uranium(III) boroxide complex towards CO2 to provide a dinuclear uranium carbonate bridged complex. Chapter five introduces work towards heterobimetallic uranium transition metal complexes carried out in the Arnold group. The application of these complexes towards ring opening polymerisation chemistry is discussed in addition to investigations into the incorporation of transition metals into uranium(IV) complexes. Chapter Six presents the detailed experimental methods used to carry out this research.

Thorium(IV) and uranium(IV) coordination complexes have been studied for the last 60 years. They have shown interesting reactivity that is often divergent from that of transition metal complexes, and that also provides an insight into some unanticipated differences between thorium(IV) and uranium(IV). An introduction to thorium(IV) and uranium(IV) organometallic chemistry supported by carbocyclic and N-donor ligands is given in Chapter One. The reactivity of actinide alkyl, amide and alkynyl complexes towards small molecules is discussed and select examples provided. The redox chemistry of thorium and uranium is also introduced. Chapter Two describes the alkylation and amination chemistry of uranium(IV) and thorium(IV) trans-calix[2]benzene[2]pyrrolide ((L)2-) complexes, [(L)AnCl2], yielding new actinide(IV) complexes of the type [M(L-2H)An(R)] (M = Li or K, R = Me, CH2SiMe3, CH2Ph, N(SiMe3)2), where (L)2- undergoes further deprotonation to (L-2H)4-. Additionally, the lability of the [M(L-2H)An(R)] “ate”-complexes towards M+ ion exchange is addressed. Further, the selective ligand reprotonation of (L-2H)4- to (L)2- using HSiR'3 (R' = Me, iPr) and [Et3NH][BPh4] yielding [(L)An(C≡CSiR'3)2] and [(L)An(R)][BPh4] respectively, is explained. The reactivity of these complexes towards amines, silanes, alkenes, tin hydrides, silicone grease, tBuNC, H2, CO, CO2 or CS2 is described. Crystallographic characterisation shows that [(L)Th(N(SiMe3)2)][BPh4] contains an unusual example of a thorium(IV) bis-arene coordination mode. The reactivity of [(L)Th(C≡CSiMe3)2] towards a number of substrates including alkenes, [Ni(COD)2], [Pt(norbornene)3], P4, CO2 or H2 is also discussed. Activation of CO2 by [(L)Th(C≡CSiMe3)2] at 80 °C results in (L)2- functionalisation and abstraction to yield a new tricyclic organic molecule with the general formula LCO. The addition of [Ni(COD)2] to [(L)Th(C≡CSiMe3)2] and PR''3 (R'' = phenyl, cyclohexyl) yields heterobimetallic complexes [(L)Th(C≡CSiMe3)2·Ni(PR''3)]; these products display both dipyrrolic and bis-arene coordination. The changes in ligand coordination mode are discussed alongside DFT computational analyses that have been carried out by collaborators. The substitution reactions of [(L)AnCl2] with NaBH4 to form actinide(IV) borohydride complexes [(L)An(BH4)2] and subsequent attempted abstractions of BH3 from [(L)Th(BH4)2] are presented. Conclusions are provided at the end of the chapter. Chapter Three focusses on the oxidation chemistry of uranium(IV) within the (L)2- and (L-2H)4- ligand framework, prompted by the isolation of a uranium(V) complex [Li[(L)UO2]·LiI] from the oxidation of the uranium(IV) complex [Li(L-2H)U(Me)]. Conclusions are provided at the end of the chapter. Experimental methods and characterising data are given in Chapter Four.

<p>Metal alkyls have a variety of uses including important intermediates in a variety of  processes. In this research, a thorium bis-alkyl species was fully characterized and explored for its potential reactivity, specifically for the formation of thorium bis-amide complexes. A series of three thorium bis-amide complexes was synthesized and characterized in this work. Additionally, several pathways have been attempted to synthesize an actinide alkylidene within this project including the use of a homoleptic tetrabenzyl complex, the use of diazoalkanes through the loss of dinitrogen, deprotonation of alkyls, and reducing a metallacycle complex. However, many of these did not result in products that suggest that an alkylidene was formed. These reactions ranged from being thermally unstable, decomposing, not reacting, or forming multiple products and being unable to discern one major product.<br> </p>