Arene activation and functionalisation by reducing complexes of uranium and iron

Abstract

The primary focus of the work described herein concerns the synthesis of uranium complexes and their reactivity towards small-molecules i.e. simple unsaturated kinetically inert compounds. Chapter 4 investigates the reactivity of beta-diketiminate ligated low valent iron complexes. The unifying theme of this thesis is that of arene activation, however, dinitrogen activation is also a recurring topic.

Chapter one reviews important organoactinide and relevant organolanthanide complexes reported in the literature to date. Focus is placed upon complexes of uranium which possess a ligand derived from C6 aromatics with the family of inverse arene sandwich (IAS) complexes thoroughly reviewed and attention paid to both structural and reactivity profiles. Dinitrogen complexes of both actinides and lanthanides are reviewed with comments on the degree to which particular metal fragments impart activation on the N2 derived fragment. The reactivity of organouranium complexes with carbon oxygenates (CO and CO2) is also summarised.

Chapter 2 reports studies on the synthesis of U(III) complexes and their reactivity with small molecules, specifically that of homoleptic U(III) aryloxide complexes with C6 arenes. In particular, the arene activation chemistry of U(ODipp)3, previously thought to have no reactivity with small molecules, is described. Here its reactivity with arenes is described and compared to related examples of uranium mediated arene activation previously in the Arnold group as well as in the wider literature.

Chapter three describes the synthesis and uranium-chelation of tetraphenolate ligands with para-terphenyl derived backbones of general form (–OAr)2C-(p-terphenyl)-C(ArO–)2 and denoted “terTP” ligands. Building on previous work conducted within the Arnold group on related tetraphenolate ligands a number of uranium adducts are described and the binding modes compared to related complexes previously described in the literature. The ligand syntheses are adaptable, facilitating systematic variations in ligand structure and substitution.

Chapter four describes research conducted over the period of three months within the research group or Prof. Patrick Holland at Yale University. The introduction supplements the N2 activation chemistry discussed in chapter one shifting focus away from electropositive f-element dinitrogen complexes and focusing on the fixation of N2 by well-defined complexes of molybdenum and iron. Complementary to the other work described in this thesis, the research discussed here focuses upon the arene and N2 reactivity of low valent beta-diketiminate complexes of iron. The work describes the sequential activation of both arenes and dinitrogen which, upon treatment with a silylating reagent, results in the formation of silylanilines and silylamines. The process described is found to generate N(SiMe3)3 catalytically whilst, at present, the aniline forming pathway remains substoichiometric due to low yielding intermediate reaction steps. Evidence is presented however, that demonstrates that the catalytic formation of anilines from arenes and N2 is a viable transformation.

Chapter five presents experimental details employed whilst carrying out this research.