Advances in the organometallic and organoamidometallic chemistry of the lanthanoids and alkaline earths

Abstract

This thesis describes the organometallic and organoamidometallic chemistry of the lanthanoid (Ln) and alkaline earth (Ae) metals. Two main topics were covered during the course of the research project and these are: • coordination of C–F bonds in aryl rings to metals (M–FC(Ar)) and C–F activation of 2,3,5,6-tetrafluorophenylethane-1,2-diaminate (p-HC6F4N(CH2)2NR2)(1−) (LR; R = Me, Et) ligands (Fig. i) • the syntheses and characterisation of lanthanoid and organometallic complexes with bulky tetraphenylcyclopentadienyl and pentaphenylcyclopentadienyl ligands. Chapter Two describes the formation of lanthanoid complexes with LR ligands. These complexes display close Ln–FC(Ar) interactions and these were investigated as precursors to C–F activation. The chapter is split into two parts. The metals studied in Part A do not possess a readily accessible divalent state. A rare metal-organic cerium fluoride was isolated during the course of these studies. The metals studied in Part B do have a readily accessible divalent state. Interesting differences in behaviour were noted between europium and samarium. Mechanistic insights into C–F activation effected by lanthanoid metals were made. Chapter Three details the formation of magnesium and calcium complexes with LR ligands. These complexes display relatively strong Ae–F(C) binding, which is rare. Attempts to force some of these complexes to undergo C–F activation failed. The failure of these complexes to engage in C–F activation, in particular the calcium complex, has implications for the mechanism of C–F activation of the divalent lanthanoid analogues. Chapter Four outlines the syntheses and characterisation of divalent lanthanoid complexes with bulky tetraphenylcyclopentadienyl or pentaphenylcyclopentadienyl ligands. During one attempt to access a bis(tetraphenylcyclopentadienyl)ytterbium complex, the first crystallographically characterised divalent lanthanoid metal-organic fluoride was obtained. Rare divalent (polyarylcyclopentadienyl)lanthanoid sandwich complexes were synthesised, along with some divalent (polyarylcyclopentadienyl)lanthanoid halide complexes that defy facile rearrangement. Additionally, attempts were made to synthesise trivalent bis(tetraphenylcyclopentadienyl)lanthanoid halides as precursors for reduction. Chapter Five describes the reactions of tris(o-dimethylaminobenzyl)lanthanoid complexes with tetraphenylcyclopentadiene and pentaphenylcyclopentadiene. Interesting differences in behaviour were observed. These observations have raised queries about the nature of sterically-induced reduction and important progress was made in the understanding of this phenomenon. Chapter Six details the syntheses and characterisation of magnesium and calcium complexes with bulky tetraphenylcyclopentadienyl ligands. These complexes are the first crystallographically characterised alkaline earth metal complexes with these ligands. The first (cyclopentadienyl)calcium bromide complex was prepared by a redox-transmetallation/protolysis route using HgPhBr. Preliminary attempts were made to reduce some of these complexes.