Synthesis, reactivity and magnetic properties of sterically bulky rare-earth and actinide metallocenes

Sterically bulky cyclopentadienyl ligands have seen extensive use in the fields of rare-earth and actinide organometallic chemistry, due to their ability to kinetically stabilise low-coordinate complexes of these elements. This property has been notably exploited in the development of dysprosium single-molecule magnets with desirable magnetic properties, including in the synthesis of [(Cp iPr5)Dy(Cp*)][B(C 6F 5) 4] by the Layfield group, which possesses a blocking temperature of 80 K. Bulky cyclopentadienyl ligands have also been shown to stabilise low-valent complexes of the rare-earth and actinide metals, including the series of divalent metallocenes [(Cp iPr5) 2M] (M = Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er) and the compound [(CpiPr5) 2U][K(crypt)], which features uranium in a formal oxidation state of +1 and is readily oxidised to U(II) and U(III) compounds. Thus, careful selection of appropriate cyclopentadienyl ligands can enable the formation of complexes with interesting magnetic and electronic properties, as well as reactivity.

This thesis describes the use of substituted cyclopentadienyl ligands, i.e., tri-tert-butylcyclopentadienyl, tetramethyl-tert-butylcyclopentadienyl and pentamethylcyclopentadienyl in the syntheses of novel dysprosium single-molecule magnets, divalent metallocenes which are capable of reducing dinitrogen, and metallocenium cations of uranium which exhibit apparent frustrated Lewis pair reactivity with phosphines. The findings presented herein illustrate the effectiveness of using sterically bulky cyclopentadienyl ligands to control the magnetic, structural, and electronic properties of rare-earth and actinide compounds, as well as produce compounds which can facilitate unusual types of reactivity.